nace rp 0575-2001 standard recommended practice internal cathodic protection systems in...

bNACE" NACE Standard RP0575-2001 Item No. 21015

T H E C O R R O S I O N S O C I E T Y

Standard Recommended Practice

Internal Cathodic Protection Systems in Oil-Treating Vessels

This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone, whether he has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. Nothing contained in this NACE International standard is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This standard represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. NACE International assumes no responsibility for the interpretation or use of this standard by other parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies which preclude the issuance of interpretations by individual volunteers.

Users of this NACE International standard are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard. Users of this NACE International standard are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard.

CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication. The user is cautioned to obtain the latest edition. Purchasers of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International Membership Services Department, 1440 South Creek Drive, Houston, Texas 77080-4906 (telephone + I 281/228-6200).

Reaffirmed 2001-09-20 Approved October 1975

Revised March 1995 NACE International

1440 South Creek Drive Houston, TX 77084-4906

+ I 281/228-6200

ISBN 1-57590-1 35-8 O 2001, NACE International

COPYRIGHT NACE InternationalLicensed by Information Handling ServicesCOPYRIGHT NACE InternationalLicensed by Information Handling Services

RP0575-2001

Foreword

This standard recommended practice is a general guide for the application of effective cathodic protection to all oil-treating vessels. This standard covers design criteria, the selection and installation of applicable systems, and the operation, monitoring, and maintenance of installed systems. There are many design variations in existing oil-treating vessels, with new designs being introduced continually. The preparation of a recommended practice for the cathodic protection of each individual vessel design is not practical. Therefore, this standard is not specific with respect to one or more vessel designs. It is intended for use by corrosion engineers involved in oil and gas production, especially those concerned with surface facilities. Nothing contained in this standard is intended to conflict with applicable codes, including OSHA"' regulations.

This standard was originally prepared in 1975 by Task Group T-IE-6, a component of Unit Committee T-1E on Cathodic Protection of Oilfield Equipment, and revised in 1995 by Task Group T-I E-I 1. It was reaffirmed in 2001 by Specific Technology Group (STG) 35 on Pipelines, Tanks, and Well Casings. This STG is composed of corrosion consultants, corrosion engineers from oil- and gas-producing companies, representatives from manufacturers, and others concerned with internal corrosion control in oil-treating vessels.

I In NACE standards, the terms shall, must, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shall I and must are used to state mandatory requirements. Should is used to state something considered

II good and is recommended but is not mandatory. optional.

May is used to state something considered II (I) Occupational Safety and Health Administration (OSHA), 200 Constitution Ave. NW, Washington, DC 20210

NACE International I


RP0575-2001

1. 2. 3. 4. 5. 6. 7. 8. 9.

NACE International Stand a rd

Recommended Practice

Internal Cathodic Protection Systems in Oil-Treating Vessels

Contents

General .......................................................................................................................... 1 Definitions ...................................................................................................................... 1 Determination of Need for Cathodic Protection ............................................................. 2

2 Anode Installation 4 Reference Electrode Entrance ...................................................................................... 5 Criteria for Protection .................................................................................................... 5 Monitoring, Records, and Maintenance ........................................................................ 5 Safety ............................................................................................................................ 6

Design and Selection of Cathodic Protection System

References .......................................................................................................................... 6

.. II NACE International


RP0575-2001

Section 1: General

1 .I This standard presents recommended practices for the 1.3 Effective petformance of the cathodic protection cathodic protection of internal sutfaces of oil-treating system requires operation within the limits of the design, vessels, heat exchangers, or the water side of process monitoring of the system, and maintenance to replace vessels. damaged and consumed parts.

1.2 The provisions of this standard should be applied 1.4 Cathodic protection is not effective when applied to under the direction of a corrosion engineer. The term steel surfaces in the oil or gas phase because of the “corrosion engineer,” as used in this standard, refers to a absence of an electrolyte. Coatings and/or chemical person who, by reason of knowledge of the physical inhibitors should be used to control corrosion on the steel sciences and the principles of engineering and sutfaces in the oil and gas phase. mathematics, acquired by professional education and related practical experience, is qualified to engage in the practice of corrosion control in oil-treating vessels.

Section 2: Definitions

Anode: The electrode of an electrochemical cell at which oxidation occurs. Electrons flow away from the anode in the external circuit. Corrosion usually occurs and metal ions enter the solution at the anode.

Cathode: The electrode of an electrochemical cell at which reduction is the principal reaction. Electrons flow toward the cathode in the external circuit.

Cathodic Protection: A technique to reduce the corrosion of a metal sutface by making that sutface the cathode of an electrochemical cell.

Coating: A liquid, liquefiable, or mastic composition that, after application to a sutface, is converted into a solid protective, decorative, or functional adherent film.

Corrosion: The deterioration of a material, usually a metal, that results from a reaction with its environment.

Corrosion Engineer: A person, who by reason of knowledge of the physical sciences and the principles of engineering and mathematics, acquired by professional education and related practical experience, is qualified to engage in the practice of corrosion control.

Current Density: The current to or from a unit area of an electrode sutface.

Driving Potential: Difference in potential between the anode and the steel structure.

Electrode: A conductor used to establish contact with an electrolyte and through which current is transferred to or from an electrolyte.

electrolyte refers to the water, including the chemicals contained therein, adjacent to and in contact with a submerged metal surface.

Galvanic Anode: A metal that provides sacrificial protection to another metal that is more noble when electrically coupled in an electrolyte. This type of anode is the electron source in one type of cathodic protection.

Holiday: A discontinuity in a protective coating that exposes unprotected surface to the environment.

Impressed Current: An electric current supplied by a device employing a power source that is external to the electrode system. (An example is direct current for cathodic protection.)

Passivation: A reduction of the anodic reaction rate of an electrode involved in corrosion.

Polarization: The change from the open-circuit potential as a result of current across the electrode/electrolyte interface.

Reference Electrode: An electrode whose open-circuit potential is constant under similar conditions of measurement, which is used for measuring the relative potentials of other electrodes.

Salt Bridge: A salt solution used with a reference electrode to bridge a gap in an electrical circuit to obtain potential data with a reference electrode.

Steel-to-Water Potential: The potential difference between a steel vessel sutface and a reference electrode immersed in the water with which the steel vessel sutface is in contact (sometimes referred to as cathodic solution potential).

Electrolyte: A chemical substance containing ions that migrate in an electric field. For the purpose of this standard,

NACE International 1


RP0575-2001

Section 3: Determination of Need for Cathodic Protection

3.1 General

3.1.1 Experience reveals that corrosion and metal loss is to be expected in any oil-treating vessel where any portion of the internal steel sutface is exposed to oilfield brines because of their aggressive corrosive nature. The need for cathodic protection is contingent on the severity of existing or anticipated corrosion and the extent to which it affects equipment operation. Consistent with the latter, cathodic protection should be installed when it will accomplish one or more of the following: remove or minimize unsafe conditions caused by failure, provide economical control over equipment failures and losses, and remove or minimize the possibility of vessel content loss because of leaks or vessel collapse.

3.1.2 Internal coatings may be used in conjunction with cathodic protection to protect oil-treating vessels. Internal coating reduces the sutface area of steel to be p rotected .

3.2 Corrosion Rates

3.2.1 The corrosiveness of a fluid stream is a function of the following:

3.2.1 . I Corrosion usually becomes more severe as the conductivity (dissolved solids content) of water (electrolyte) increases, but low-conductivity water can be corrosive.

3.2.1.2 Corrosion in produced oilfield brines usually increases as the partial pressure of acid- forming components, such as carbon dioxide (COZ) or hydrogen sulfide (HzS), increases.

3.2.1.3 Corrosion is accelerated by even trace amounts of oxygen.

3.2.1.4 Corrosion usually increases with increasing temperature unless scaling is increased.

3.2.1.5 Corrosion usually increases with increasing flow velocity and turbulence.

Section 4: Design and Selection of Cathodic Protection System

4.1 Basic Design Criteria

4.1.1 The design of a vessel’s cathodic protection system depends on the internal configuration of the vessel. Selection of the appropriate system depends on factors such as initial cost, maintenance, type and condition of coatings (if any), power availability and cost, and system life.

4.1.2 Vertical cylindrical vessels containing no baffles, compartments, firetubes, etc., are usually protected with anodes or strings of anodes suspended from the deck (roof) of the vessel. This design method offers two advantages over other designs: (1) better current distribution because anodes are parallel to the vessel walls, and (2) deteriorated or depleted anodes can be replaced without lowering the water level or draining the vessel.

4.1.3 Compartmented vessels or those containing baffles, firetubes, spreaders, etc., should have at least one anode installed in each compartment exposed to the corrosive fluid. If a vessel is not designed to accommodate a cathodic protection system that will provide effective protection throughout, it may be necessary to make modifications or redesign the vessel interior to provide access to areas needing cathodic protection by installing fittings in the vessel for

inserting anodes through the walls. An example of such modification is positioning of a spreader in a heater treater below the firetubes so there is sufficient clearance to install an anode between the firetube and spreader.

4.1.4 Correct location and position of anodes in vessels are essential for proper current distribution. Cathodic protection anodes should be placed such that their protective current can be distributed to all sutfaces exposed to the corrosive electrolyte. Each anode should be located as near to the center of the compartment or center of the electrolyte as practical.

4.1.5 Factors determining the number, weight, and shape of anodes required for cathodic protection of vessels are:

(a) area of bare water-immersed steel to be protected;

(b) current density required;

(c) anticipated current output of the anodes;

(d) vessel configuration; and

(e) desired life of the cathodic protection system.

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RP0575-2001

4.1.6 Current density requirements can range from 50 to 400 mAlm2 (5 to 40 mAlft2) of bare water-immersed steel. In the absence of specific current density data, 100 mAlm2 (IO mAlft2) is commonly used for design. However, vessels handling water containing depolarizers, such as H2S and oxygen, or operating at high temperatures and/or high flow rates, could require higher current densities to maintain protective potentials. Internal coating of vessels decreases the area of bare steel in contact with water and reduces the amount of current required for corrosion protection.

4.2 System Selection

4.2.1 Cathodic protection can be provided by impressed current systems or galvanic anode systems. Typical petformance data for commonly used impressed current and galvanic anodes are shown in Table 1. Prior to the application of either impressed current or galvanic anodes, it must be ensured that treated electrolytes are chemically compatible with the anode.

Table I-Typical Performance Data for Commonly Used Impressed Current and Galvanic Anodes

Type of Anode A-h/kg'A' A-h/lb'A'

Impressed Current Anodes

Linseed oil-impregnated graphite

High-silicon cast iron with chromium

13,000 to 15,000 (14,000)

18,000 to 24,000 (19,000)

6,000 to 7,000 (6,500)

8,000 to 11,000 (8,500)

Galvanic Anodes

Magnesium

Al um in u

1,000to 1,100 (1,000)

400 to 2,000 (1,300)

450 to 500 (450)

200 to 950 (600)

Zinc 700 to 800 (800) 300 to 350 (350)

(A) Values in parentheses are commonly used in design calculations.

treatment. Caution: The performance and efficiency of aluminum anodes vary with the alloy, and with certain alloys they vary with the heat

Note: Anode efficiencies vary widely, particularly for galvanic anodes. Factors influencing this include anode locations, position and sutface area, water composition and temperature, and selective electrochemical attack.

4.2.2 Impressed current systems have greater flexibility if high current demand is anticipated.

4.2.2.1 Impressed current systems can be used in any water, but are usually the most practical in high-resistivity waters where an appreciable amount of current is required to achieve protection.

4.2.2.2 Impressed current systems typically require more monitoring and maintenance than galvanic anodes.

4.2.2.3 Automatic potential rectifier systems decrease the likelihood of underprotection or the excessive use of power and coating disbondment resulting from overprotection (see Paragraph 4.3.2).

4.2.2.4 Impressed current anodes should be provided with individual lead wires to the rectifier for control and measurement of current output from each individual anode.

4.2.3 Galvanic anodes are commonly used when electrical power is not feasible to use or is not available and may be preferred for low-current-requirement installations, even if electrical power is available. The effects of the produced fluid chemistry on the petformance of a galvanic anode should be considered. The pH of produced fluids containing dissolved CO2 and/or H2S can be lowered to acidic levels that can attack zinc, aluminum, or magnesium. Large concentrations of H2S may also react with the anode to alter its petformance. The possibility of the presence of other impurities, such as amines, emulsions, or even small quantities of mercury, should be considered. Consideration should be given to effects of the various oilfield treating chemicals and workover fluids that may flow through the vessel being protected. Residual acids from stimulation treatments may cause severe attack on all galvanic anodes. The potential effects of demulsifiers, scale and corrosion inhibitors, drilling mud, and other material that might be added to production should be considered.

4.2.4 Galvanic anode materials most commonly used are aluminum, magnesium, and zinc alloys. The



RP0575-2001

5.1

5.2

composition, resistivity, and temperature of the electrolyte largely dictate which material is most suitable.

4.2.4.1 Aluminum alloys are commonly used in brines with resistivities below 1 O0 ohm-cm. Aluminum’s lower driving potential, compared with that of magnesium, leads to lower current output and longer life. Generally, more than one aluminum anode is required to provide current output equivalent to that of magnesium.

4.2.4.1.1 Consideration must be given to selection of the proper aluminum alloy (pure aluminum should not be used as an anode) to ensure adequate protection at optimum economy. The electrochemical properties (potential and current capacity) of aluminum anodes are dependent on the alloy, the electrolyte composition, and the electrolyte temperature. Temperatures above 49°C (120°F) can reduce the current capacity of aluminum anodes.

4.2.4.2 Magnesium alloys are commonly used in brines with resistivities above 1 O0 ohm-cm. Magnesium’s higher driving potential, compared with that of aluminum, leads to higher current output and shorter life. If magnesium anodes are used in low-resistivity electrolytes, current output should be controlled by resistors in the external circuits.

4.2.4.3 Zinc alloys are not commonly used in vessels because they may show a decrease in potential with increase in electrolyte temperature and may possibly become cathodic to steel at temperatures in the range of 54°C (1 30°F).

4.3 Internally Coated Vessels

4.3.1 Cathodic protection mitigates corrosion at coating holidays.

4.3.2 Excessive cathodic protection potentials may cause coating damage. Generally, at polarized potentials more negative than -1.05 to -1.10 V (copperkop pe r su Ifate reference e lectrode [CS E]), excessive hydrogen can be formed and cause coating damage.

Section 5: Anode Installation

Vertical Suspension

5.1.1 Anodes must be spaced to distribute current uniformly to the vessel walls and bottom, and at a depth that assures that some anodes are submerged regardless of water level. Either type of anode (galvanic or impressed current) can be installed in this manner.

5.1.2 Impressed current anodes must be suspended from a suitable hanger (deck mount), properly isolated to prevent grounding of the lead wire to the vessel.

5.1.3 Galvanic anodes should be electrically isolated where current monitoring is contemplated.

Internally Supported

5.2.1 Galvanic anodes may be placed on supports on the vessel floor and isolated from the vessel. Anode leads can be brought out through watertight connections welded in the clean-out plate and connected back to the vessel wall. Shunts and resistors may then be installed in the external anode leads to monitor or regulate anode performance.

5.2.2 Alternatively, galvanic anodes may be bolted or welded to brackets permanently affixed to the vessel surface. However, this type of installation does not

allow any method for monitoring the anode output or knowledge of anode consumption other than by visual inspection.

5.3 Vessel Wall Placement

5.3.1 Galvanic or impressed current anodes can be installed horizontally in compartmented vessels through mountings welded into the side of the vessel.

5.3.2 Anode heads for installation in nipples are most commonly made of a nonmetallic material designed to withstand the temperature and pressure within the vessel. The shield portion of the head must be of sufficient length to prevent anode grounding to the vessel or excessive current discharge close to the anode entrance port. In all cases, actual lengths of the nipple and the anode head, as well as the positioning of the nipple on the curved surfaces, must be related in design in order to prevent this undesired current discharge. Anode entrance ports should be installed during fabrication of vessels. Materials and welding procedures should be consistent with primary vessel design.

5.3.3 When steel anode mounting heads are considered, they must be properly designed to provide isolation between the anode mounting head and the vesse I.



RP0575-2001

Section 6: Reference Electrode Entrance

6.1 Methods

6.1.1 Entrance ports for insertion of reference electrodes should be installed in the vessel at the same time as the anode entrance ports.

6.1.2 In compartmented vessels, reference electrode ports must be installed as far from the anodes as possible in order to obtain potentials representative of the steel sutface. These ports are usually 2.5-cm (1-

in.) diameter connections welded into the vessel wall in each compartment and equipped with a 2.5-cm (I-in.) full-opening valve so that the reference electrode may be inserted into the vessel.

6.1.3 In vertical cylindrical vessels equipped with roof- type hatches, the reference electrode may be inserted through the hatches. If this is anticipated, the anodes should be installed at the maximum distance from the hatch.

7.1 Steel-to-Water Potential

Section 7: Criteria for Protection

7.1.1 The presence of a protective potential should be verified after the vessel is polarized. Polarization normally occurs within two weeks in bare vessels and within a few minutes in coated vessels.

7.1.2 The steel sutface is protected if the sutface is more negative than -0.85 V vs a CSE (-0.80 V vs a Ag/AgCI electrode). However, if the fluid contains sulfides/HnS, a protection potential of -0.95 V vs a CSE (-0.90 V vs a Ag/AgCI electrode) is required to achieve

7.2

protection. Polarization and protection of the vessel are generally assured if the potential immediately after switching the cathodic protection current off is equal to or more negative than these values.

Coupon Tests

7.2.1 Coupons may be installed to monitor the effectiveness of cathodic protection. Coupons must be electrically connected to the vessel wall. Coupon weight-loss measurements are used to determine the effectiveness of protection.

8.1 Monitoring

Section 8: Monitoring, Records, and Maintenance

8.1 . I Operating personnel should visually inspect sutfaces under cathodic protection whenever vessels are opened. In addition, thickness measurements of vessel walls should be taken to determine cathodic protection effectiveness.

8.1.2 Potential and/or anode current output surveys should be made monthly after initial installation of cathodic protection equipment until current requirements are established. After current requirements are established, quarterly surveys are usually adequate.

8.1.2.1 Care must be taken in placing the reference electrode into the treating vessel. For potential measurements, the electrode must be as far from the anodes as possible. In pressure vessels, the electrode is “inserted” (introduced into the vessel against existing vessel pressure) through a full-opening valve installed in the vessel for that purpose (see Paragraph 6.1.2). Reference electrodes manufactured to withstand pressure

and temperature can also be permanently installed.

8.1.2.2 Contamination of the reference electrode with oil or sediments such as iron sulfide must be avoided. A salt bridge may be used to prevent contamination of the reference electrode.’

8.1.2.3 Location of the reference cell near an anode may indicate a higher potential than elsewhere in the vessel.

8.1.2.4 Water levels lower than normal may result in higher potentials because of increased current density.

8.1.3 Galvanic anodes are sometimes installed without shunts. However, if the cathodic protection system cannot be monitored by potential measurements, shunts of known resistance (normally 0.01 ohm) should be installed. Current measurements can be obtained by measurement of the potential across the shunt of known resistance.



RP0575-2001

8.2

8.3

9.1

Records

8.2.1 Record keeping is vital to effective maintenance of cathodic protection systems (and thus continued protection of the vessels).

8.2.2 Monthly records should be kept for all impressed current anode installations. The records should show DC voltage and amperage readings for each anode.

8.2.3 Quarterly records should be kept for galvanic anode installations. The records should show current readings on galvanic anodes.

Maintenance

8.3.1 Malfunctions should be repaired promptly to ensure desired petformance. Corrosion damage can occur whenever the potentials are less negative than the values indicated in Paragraph 7.1.2.

8.3.2 Anodes must be replaced periodically as they are consumed. Zero current readings usually indicate deteriorated anodes, broken anode cables, malfunctioning rheostats, or loose connections in the circuit. Low current readings in galvanic systems may indicate similar problems.

8.3.3 Zero reported voltage or current readings may occur because of various malfunctions. A rectifier troubleshooting guide should be consulted when such malfunctions occur.

8.3.4 During maintenance of the vessel, visual examination of the vessel sutfaces should be conducted to verify the effectiveness of the cathodic protection system. Deterioration of the sutface of the vessel and/or interior welds indicates the need for relocation of the anodes, increasing quantity of anodes, or an appraisal of the cathodic protection system.

Section 9: Safety

Precautions must be taken to avoid sparks in the presence of flammable substances and explosive gas mixtures that may be present around oil-treating vessels.

9.2 The cable-to-anode connections in impressed current systems shall never be disconnected, nor shall the anode be removed, while the rectifier is in operation.

9.3 Usual precautions to prevent fire or explosion must be taken before a cathodic protection system can be installed or repaired in a vessel handling water mixed with oil or gas.

9.4 CAUTION: Usual precautions must be taken when monitoring or petforming maintenance on cathodic protection systems in vessels containing H2S. If the anodes in such vessels are to be removed for replacement or inspection, a mask approved for use in H2S environments must be worn. Additional information on the toxicity of H2S

can be obtained from the Manufacturing Chemists’ Association’s(’) “Chemical Safety Data Sheet SD-36,”’ and from Dangerous Properties of Industrial Materials3

9.5 The rectifier case, external AC disconnect switch box, and any related metallic equipment must be grounded.

9.6 Depending on the area classification, explosion-proof rectifiers and electrical devices may be required.

9.7 Special gaskets capable of withstanding high temperatures should be used to mount anodes in fired vessels, particularly if the gaskets are located near the fire tubes.

9.8 Equipment, wiring, enclosures, and installation of cathodic protection systems must comply with all applicable codes, including OSHA regulations.

References

1. NACE Publication 35201 (latest revision), “Report on the Application and Interpretation of Data from External Coupons Used in the Evaluation of Cathodically Protected Metallic Structures” (Houston, TX: NACE).

2. “Chemical Data Safety Sheet SD-36” (latest revision) (Washington, DC: Manufacturing Chemists’ Association).

3. N. Irving Sax, Dangerous Properties of Industrial Materials (New York, NY: Reinhold Book Corp., 1984).

(’) Manufacturing Chemists’ Association, 1825 Connecticut Ave. NW, Washington, DC 20009.

NACE International


NACE Standard RP0592-2001 Item No. 21057


Standard Recommended Practice

Application of a Coating System to Interior Surfaces of New and Used Rail Tank Cars in

Concentrated (90 to 98%) Sulfuric Acid Service



CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication. The user is cautioned to obtain the latest edition. Purchasers of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International Membership Services Department, 1440 South Creek Dr., Houston, Texas 77084-4906 (telephone + I [281]228-6200).

Reaffirmed 2001-09-12 Approved April 1992 NACE International

1440 South Creek Drive Houston, Texas 77084-4906

+ I 281/228-6200

ISBN 1-57590-1 32-3 02001, NACE International


RP0592-2001

Foreword

A large number of commercial 93% sulfuric acid (H2S04) shipments in the United States and Canada are made by rail in carbon-steel tank cars. Concentrated sulfuric acid is an oxidizing agent and a desiccant. The major problems in its handling and storage relate to its hygroscopic nature (absorption of atmospheric humidity), its exothermic reactivity with water on dilution, and velocity effects that erode the otherwise protective films of corrosion products.

Corrosion rates of approximately 0.25 mm/year (0.01 O in./year)’ have been measured in static storage tanks and tank cars that haul concentrated sulfuric acid. To cope with this uniform corrosion over a 40-year operation, 10 mm (0.4 in.) of extra wall thickness would be required on a tank car. The addition of this extra wall thickness would add substantially to the tank car’s weight and result in severe reductions in carrying capacity.

An even more serious problem is that uniform corrosion is invariably accompanied by severe localized corrosion in the top halves of tank cars. This localized corrosion, called hydrogen grooving, produces deep vertical grooves in localized bands that extend along the sides and across the heads of tank cars. Hydrogen grooves can progress through the steel far more rapidly than uniform corrosion, and can cause substantial damage after short periods of service. Extra wall thickness is not sufficient to cope with hydrogen grooving. Copper-bearing steels have also been used in order to improve resistance to sulfuric acid corrosion, but this has not been successful. Painting the exterior surfaces of the tank cars with a heat-reflecting color to keep the acid temperature as low as possible has reduced corrosion rates, but has not eliminated the problem. Anodic protection is another option that is sometimes considered.

Industry consensus points to internal coatings as a necessary protective measure for tank cars transporting concentrated sulfuric acid and/or to assure product purity. Many shippers of sulfuric acid apply a protective coating (usually a baked phenolic) to the interior surfaces of tank cars and specify a nominal steel corrosion allowance of 3.00 mm (0.125 in.) in the event of coating failure. The life expectancies of these coatings are highly dependent on the quality of application. For this reason, the proper application and inspection of interior coatings is very important to the maintenance of tank cars hauling sulfuric acid. This standard recommended practice provides guidelines for the high-quality application, surface preparation, inspection, and testing of coatings for the interior surfaces of rail tank cars handling shipments of concentrated sulfuric acid at ambient temperatures.

This NACE standard is intended for use by tank car owners, coating manufacturers, and coating applicators for the auditing of the facilities, equipment, and personnel that satisfy the requirements for tank car coating systems in this severe service. This standard was originally developed in 1992 by Task Group T-14C-1, a component of Unit Committee T-14C on Rail Equipment Corrosion. It was reaffirmed in 2001 following review by Task Group 061. This Task Group is administered by Specific Technology Group (STG) 43 on Land Transportation, and sponsored by STG 03 on Protective Coatings and Linings-Immersion Buried and STG 36 on Process Industry-Chemicals. It is issued by NACE under the auspices of STG 43.

In NACE standards, the terms shall, must, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shall and must are used to state mandatory requirements. The term should is used to state something good and is recommended but is not mandatory. The term may is used to state something considered optional.



RP0592-2001


Recommended Practice

Application of a Coating System to Interior Surfaces of New and Used Rail Tank Cars in Concentrated (90 to 98%) Sulfuric

Acid Service

Contents

1. General ........................................................................................................................... 1 2. Definitions ...................................................................................................................... 1 3. Areas of Responsibility .................................................................................................... 2

3 4

6. Coating System Materials .............................................................................................. 4 7. Coating Application ........................................................................................................ 4 8. Coating of Particular Parts and Attachments .................................................................. 5 9. Completed Coating System ............................................................................................ 5 I O . Inspection ...................................................................................................................... 5 11. Safety ............................................................................................................................ 6

6 7 e

Interior of Tank Cars for Concentrated Sulfuric Acid Service ......................................... 7 Appendix B: Dry Film Thickness Report ............................................................................. 9 Appendix C: Tank Car Coating System Inspection Report Form ..................................... 10

. . .

4. Surface Preparation for New Tank Cars 5. Surface Preparation for Used Tank Car

. .



RP0592-2001

Section 1: General

1 . I This standard describes a procedure for the application of a coating system to the interior sutfaces of new and used railroad steel tank cars used primarily in the transportation of concentrated (90 to 98%) sulfuric acid at ambient temperatures. The requirements for surface preparation, qualified inspection of the completed coating system, and testing by the use of adequate, readily available instruments are also covered in this standard.

1.2 For the purposes of this standard, the term concentrated sulfuric acid broadly refers to acid in the concentration range of 90 to 98%. Commercial sulfuric acid is usually handled at 93% concentration because its minimum freezing point is -34°C (-30°F). Sulfuric acid at 98% has the same high corrosiveness to carbon steel as 100% acid, and has a freezing point of approximately 7°C (45°F). All concentrations of sulfuric acid can contain impurities that can significantly alter its inherent corrosion characteristics.

1.3 In addition to adhering to the conditions set forth in this standard, tank cars hauling concentrated sulfuric acid must

comply with U.S. DOT"' and AAR"' specifications' pertaining to DOT 11 l-Al00-W2 tanks.

1.4 The minimum as-built wall thicknesses of metal sutfaces to be coated in accordance with this standard should be 11 .O mm (0.43 in.).

1.5 Liquid coatings used in this standard may be hazardous and therefore basic safety precautions regarding the handling and application of these coating materials and solvents should be used. Chapter 1 of NACE TPC Publication No. Z3 contains more detailed information. The material safety data sheet (MSDS) supplied by the coating manufacturer provides additional information relative to the coating and current government regulations.

1.6 This standard does not provide a full treatise on corrosion of steel by concentrated sulfuric acid; this is an extensive subject in its own right. Further information on this subject is published by NACE and other organizations.


Coating: A liquid, liquefiable, or mastic composition that, after application to a sutface, is converted into a solid readings for a coating. protective, decorative, or functional adherent film. For the purpose of this standard, any paint-type protective covering applied in one or more coats to the interior of the rail tank car to act as a barrier between the base metal and the commodity.

Measurement: An average of three or more film thickness

Pinhole: Coating defect characterized by a small pore-like flaw, which, when extended entirely through the coating, appears as a discontinuity. A pinhole in the finish coat may not appear as a discontinuity.

Contracting Authority: The person or firm that is responsible for the approval and purchase of a completed tank car coating system.

Contractor: The firm that is executing the coating work specified.

Discontinuity: A void, crack, thin spot, foreign inclusion, or contamination in a coating that significantly lowers its dielectric strength. It may also be identified as a holiday or pinhole.

Holiday: A discontinuity in a protective coating that exposes unprotected sutface to the environment.

Holiday Detector: A device that locates discontinuities in a coating applied to a conductive surface.

Quality Assurance: Comprises all those planned and systematic actions necessary to provide specified documentation and adequate confidence that the tank car coating system will petform satisfactorily in service.

Quality Control: Comprises those quality assurance actions related to the physical characteristics of the entire coating system's application as a means of providing compliance with specified requirements.

Reading: A single film-thickness gauge determination for a coating.

Shelf Life: The maximum length of time that a coating can be stored in a factory-sealed container, at a temperature range specified by the coating supplier, before application.

(I) U.S. Department of Transportation (DOT), 400 7th Street SW, Washington DC 20590. (') Association of American Railroads (AAR), 50 F Street NW, Washington DC 20001-1564



RP0592-2001

Tank Car Owner: The person or firm that owns the tank car. (The person or firm may also be the contracting authority.)

3.1

3.2

Section 3: Areas of Responsibility

Contracting Authority

3.1.1 An inspection of the contractor's facilities and equipment should be conducted before the coating project is sent out for bids.

3.1.2 A prejob conference shall be scheduled prior to beginning the coating work. The conference shall include representatives of the tank car owner, contracting authority, inspection agency, coating manufacturer, and contractor. The contractor shall include hidher quality control supervisor and responsible shop personnel directly involved in the coating application.

3.1.3 This standard shall be reviewed along with any other related specifications at the prejob conference. Any points of misunderstanding regarding applicable standards shall be clarified.

3.1.4 Inspection forms shall be approved by the contracting authority.

3.1.5 Quality assurance shall be the responsibility of the contracting authority.

3.1.6 If deemed essential to the proper sutface preparation of the tank car, the contractor shall be provided with information in writing about the last consignment carried in the tank car.

3.1.7 The contracting authority shall specify the type of coating, the color, the number of coats to be applied, and the minimum and maximum allowable film thickness for each coating.

Contractor

3.2.1 The quality control supervisor and responsible shop supervisory personnel directly involved in the coating application shall be present at the prejob conference scheduled by the contracting authority.

3.2.2 Quality control shall be the responsibility of the contractor.

3.2.3 Authorized shop personnel and representatives of the contracting authority shall have suitable access to all areas where work is in progress on subject tank cars.

3.2.4 Assurance shall be given by the contractor that the work is being petformed in compliance with all applicable regulations.

3.2.5 Subject to applicable regulations, the contractor is responsible for personnel safety in the handling, application, and disposal of the specified coatings. In accordance with OSHA'3' or the appropriate national regulatory agency, current MSDS for each component of a coating system to be applied shall be retained on file and made available to each person using the materials.

3.2.6 Current coating application instructions shall be retained at the application site.

3.2.7 The contractor shall forward the completed inspection forms to the contracting authority and retain a copy on file for a minimum of one year for each coating system installation.

3.2.8 The contractor shall inform both the contracting authority and the coating manufacturer when an application problem that affects the quality of the finished coating system arises.

3.2.9 If the contractor is inexperienced or unfamiliar with the specified coating system, then he/she shall obtain technical assistance from the coating man ufactu rer.

3.2.1 OThe contracting authority shall approve all metal repairs to the interior of tank cars prior to initiation of the repair. AAR/DOT requirements for such repairs must be met.

3.2.1 1 Essential facilities and equipment for application of a coating system to the interior of a tank car are described in Appendix A.

3.3 Coating Manufacturer

3.3.1 Technical assistance for application problems shall be provided if requested by the contracting authority and/or the contractor.

3.3.2 MSDS (consistent with current regulations) for each component of a coating system and current application instructions shall be sent to the contractor before the coating is applied.

(3) Occupational Safety and Health Administration (OSHA), 200 Constitution Ave NW, Washington DC 20210.



RP0592-2001

3.3.3 The coating manufacturer shall keep the contracting authority and the contractor apprised of any significant changes in the coatings, such as formulation, quality control, and supply.

3.3.4 Technically competent representatives of the coating manufacturer shall participate in the prejob conference if properly advised of it.

3.3.5 Containers of each component of the coating system shall display product identification and batch numbers as well as appropriate warning and hazard labels.

Section 4: Surface Preparation for New Tank Cars

4.1 Application of the coating shall not begin until the internal sutfaces of the tank car are prepared as required by Paragraphs 4.2 through 4.8.1.

4.2 The tank car interior sutfaces shall meet the following requirements:

4.2.1 All interior welds shall be continuous.

4.2.2 All interior welds shall be smooth but not necessarily flush; if necessary, grinding is the preferred method of correction. Sharp points, edges, burrs, and irregular sutfaces with less than 3.0 mm (0.13 in.) radius, or of a size that would intetfere with the application of a continuous coating, shall be r e ~ a i r e d ; ~ no filler other than weld metal shall be considered acceptable. AAR/DOT requirements must be met.

4.5.2 The blasting abrasive shall be angular, clean, dry, and of a suitable mesh size to produce a profile of 38 to 76 pm (1.5 to 3.0 mils) on the blasted sutface as measured by an appropriate visual comparator or replica film, such as that used in NACE Standard RP0287.' The blast profile shall appear uniform and continuous. Sutface profile of the tank shell shall be recorded on the inspection form. Because blasting dust could affect profile readings, all sutfaces shall be thoroughly cleaned prior to reading the blast profile.

4.5.2.1 Steel shot shall not be used as an abrasive.

4.6 Any slivers, plate laminations, cold lap welds, or mill defects in the plate revealed by the blasting operation shall be corrected and reblasted as necessary.

4.2.3 All weld slag, spatter, and flux shall be removed. 4.7 After the blasting is completed, the interior of the tank car shall be cleaned of all blast residues and foreign

4.3 Sutface contamination such as oil shall be removed materials. according to SSPC'4'-SP l5 or another effective cleaning method before blasting.

4.4 As determined in the prejob conference, all components that will not be coated, including manway covers, outlet valves, and vents, shall be removed or protected prior to blasting.

4.5 Sutfaces shall be prepared for coating by dry abrasive blasting to a white metal blast finish in accordance with NACE No. l/SSPC-SP 5.6

4.5.1 The compressed air used for blasting shall be free of water and oil. 4.8

4.7.1 Compressed air blowdown of steel surfaces is not an effective means of complete dust removal and could be a source of sutface contamination.

4.7.2 A more efficient cleaning method is the use of a fine bristled brush or broom followed by vacuum cleaning. Brushes and brooms should be cleaned and/or replaced frequently.

4.7.3 Magnets can effectively remove steel grit particles not removed by other methods.

If visible rust bloom occurs before the first coatina. then it shall be removed by reblasting to original specification.

4.5.1.1 The cleanliness of the air shall be determined by blasting without abrasive into a 4.8.1 The interior of the tank car shall be protected white cloth for 20 seconds. If oil or water appears from moisture from the time of blasting to the time of on the cloth, the trap and separators shall be coating application and the temperature of the steel blown down, along with any necessary corrective shall be a minimum of 3°C (5°F) above the dew point. action, until subsequent cloth tests show no oil or water contamination in accordance with ASTM'5' D 4285i7

(4) SSPC: The Society for Protective Coatings, 40 24th Street, 6th Floor, Pittsburgh, PA 15222-4643. (5) ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959.



RP0592-2001

Section 5: Surface Preparation for Used Tank Cars

5.1 Sutface preparation shall be completed as specified in Section 4, except for Paragraph 4.2.2.

5.2 Severe metal loss in the form of circumferential grooves on the upper half of the tank car may appear on tank cars that have been in sulfuric acid service. This phenomenon is referred to as hydrogen grooving, which in some cases may be so deep that extensive plate repair or replacement is necessary. Other forms of corrosion damage to the tank can also be present.

5.2.1 The grooves that exceed the minimum requirements specified by TC,@' the DOT, or AAR shall be repaired in accordance with TC, DOT, or AAR specifications. Before any repair work is conducted, the contracting authority must be notified in writing.

5.2.2 The contracting authority and contractor shall agree on the extent of grinding. Subject to the depth of the grooving or other conditions, these areas may be

ground to a sufficient degree of smoothness that allows coating to be applied with full coverage.

5.2.3 Following any welding and grinding, and before blasting, all tank shell sutfaces that show some degree of corrosion shall have the shell thickness ultrasonically measured and a report issued to the contracting authority.

5.2.4 The contracting authority shall approve the ultrasonic thickness report in writing before further sutface preparation and/or coating work is conducted.

5.3 A cleaning method approved by the contracting authority must be used to address the presence of invisible and/or soluble contaminants. These methods may include steaming for 24 hours, baking at metal temperatures above that of final coating cure, washing with high or ultrahigh- pressure water, or other procedures.

6.1

Section 6: Coating System Materials

The contracting authority shall specify the coating 6.2 Any materials used for thinning the coating shall be system to be applied to the interior of the tank car. recommended by the coating manufacturer.

Section 7: Coating Application

7.1 The coating application shall not proceed until the 7.5 Before or after spraying the first coat, all welds, temperature of the steel is 13 to 38°C (55 to 1 OO"F), and at grooves, pits, and other imperfections shall be scrub-striped least 3°C (5°F) above the dew point. at the discretion of the contracting authority.

7.2 At the time of coating application the blasted sutface must be in accordance with NACE No. l/SSPC-SP 5. The sutface shall be reblasted if rust bloom has formed between the time of blasting and the coating application.

7.3 The coating shall be applied in accordance with this standard and the latest information published by the coating manufacturer and as agreed upon at the prejob conference.

7.5.1 Scrub-striping is accomplished by moving the brush back and forth in a scrubbing motion to work the material into the imperfections of the weld.

7.5.2 The scrub-striping shall be petformed with a good-quality bristle brush using the specified coating that has been thinned according to the coating manufacturer's recommendations.

7.3.1 The contractor shall have current application 7.5.3 Bristles left on the sutface shall be removed instructions on the job site for the coating being according to the coating manufacturer's applied. recommendations. The cured coating shall be sanded

smooth and repaired.

7.6 Each coat shall be inspected visually for defects before the application of the next coat.

7.4 No coating that has exceeded the shelf-life limit recommended by the coating manufacturer shall be used.

(6 ) Transport Canada (TC), 222 Queen St., Ottawa, Ontario, Canada K I A 1G6.



RP0592-2001

7.6.1 Unacceptable defects, as determined in a prejob conference, shall be corrected prior to application of the next full coat and prior to the final cure.

7.7 The coating system shall be applied in multiple coats until the thickness specified by the contracting authority is achieved.

Section 8: Coating of Particular Parts and Attachments

8.1 Carbon-steel manway covers shall be coated. 8.3 Carbon-steel nozzle flange faces, manway nozzles, and stainless steel syphon pipe guide bracket shall be

8.2 Carbon-steel syphon pipes shall be coated as required coated as specified by the contracting authority. by the contracting authority.

Section 9: Completed Coating System

9.1 The finished coating shall be cured using a timehemperahre cycle that is recommended by the coating manufacturer and the contracting authority.

9.2 The minimum and maximum dry-film thicknesses of the finished coating system shall be in accordance with the contracting authority’s specifications or the coating manufacturer’s instructions as approved by the contracting authority.

9.3 The finished coating sutface shall be reasonably free of defects such as runs, sags, dirt, overspray, orange peel, and other sutface irregularities as defined at the prejob conference.

9.3.1 Prior to the final cure, all unacceptable defects, as defined in the prejob conference, shall be sanded as required and recoated to specified thickness.

9.4 A holiday test shall be conducted on the finished coating, both before and after final curing, as outlined in Paragraph 10.5 of this standard.

9.4.1 Holidays shall be repaired prior to final curing (as recommended by the coating manufacturer) by recoating, and the repaired coating areas shall be tested again for continuity.

9.4.2 The finished coating shall be tested for holidays after final curing; minute holidays that are not readily visible may be acceptable at a rate not to exceed 1 per 9 m2 (100 fi2) or at a rate determined at the prejob conference.

9.5 Repairs required for coating defects shall be completed by a method recommended by the coating manufacturer and the contractor. The repair method shall be approved by the contracting authority before a repair begins.

9.6 The coating system and identification, name of contractor, and the location and date of application shall be stenciled on the outside of the tank car in a location and manner specified by the AAR and the DOT.

9.7 A warning against mechanically damaging the coating system shall be stenciled on the tank car or as directed by the contracting authority.

Section IO: Inspection

10.1 Parts shall not be reinstalled until inspection work has 10.4.1 The dry-film thickness gauge shall be been completed. calibrated according to Section 2 of SSPC-PA 2.’

10.2 Ladders or scaffolding used for inspection shall be spark-free, well-designed, free of cracks or other defects that prevent safe usage, and well-padded to protect the finished coating sutface.

10.3 The contractor shall provide the proper explosion- proof lighting for inspection.

10.4 The contractor shall measure the thickness of the finished coating with a dry-film thickness gauge approved by the contracting authority.

10.4.2 A number of film-thickness readings as determined at the prejob conference shall be made in locations indicated on the dry-film inspection form in this standard (see Appendix B). If a reading is found to be outside the specified film thickness, a measurement shall be taken.

10.4.3 If a measurement is found to be outside the specified film-thickness range in a given area, the film thickness shall be measured over the adjacent areas to determine whether the average film thickness is within



RP0592-2001

specification. SSPC-PA 2 describes the area and film- thickness parameters to be considered in making such a determination.

10.5 The entire finished coating-system sutface shall be tested for holidays before and after final cure using a low- voltage (1 00-V maximum), wet-sponge holiday detector calibrated, if applicable, according to the manufacturer’s instructions.

10.5.1 Water used to wet the sponge shall be conductive (tap water). Distilled or deionized water shall not be used.

10.5.2 The sponge shall be wetted sufficiently to barely avoid dripping water while it is moved at a rate of 0.3 m/s (1 füs) over the coating. The sponge shall not be excessively squeezed free of water before use.

10.6 Coated sutfaces that have an amount of holidays that exceeds the allowable limit or that contain other unacceptable defects noted during the inspection shall be repaired according to Paragraphs 9.3.1 and 9.4.1 of this standard or as directed by the contracting authority.

10.7 Dry-film thickness measurements, holidays, and similar data required by the contracting authority shall be recorded on a coating system inspection report form similar to the form in Appendix C.

10.7.1 Completed inspection report forms shall be forwarded to the contracting authority.

10.7.2 Copies of the completed inspection report forms shall be kept on file by the contractor for one year after installation of a coating system in a tank car and shall be available for use by the contracting authority’s inspector during normal working hours.

Section 11: Safety

11.1 Prior to entering the tank car, the interior of the tank and the vapors inside must be checked to ensure that it is safe for entry.

11.2 Solvents, thinners, and other components of the coating system are government regulated; the contractor shall take proper precautions regarding the use and handling of coating materials, the health and welfare of personnel, and potential hazards.

11.3 The contractor is responsible for personnel safety in handling, application, environmental regulations, and disposal as it relates to the specified coatings. Relevant information should be obtained from sources such as the MSDS supplied by the coating manufacturer. Current MSDS for each component of the coating system to be applied shall be made available to the appropriate shop personnel and retained on file.

11.4 Detailed safety information for coatings application is found in Chapter 1 of NACE TPC 2.

Referen ces

1. C.P. Dillon, Materials Selector for Hazardous Chemicals, Volume 1, Concentrated Sulfuric Acid and Oleum, MT1‘7’ Publication No. MS-1. (St. Louis, MO: MTI, 1997).

2. AAR M-1002 (latest revision), “Specifications for Tank Cars,” Section C, Part III of the Manual of Standards and Recommended Practices (MSRP) (Washington, DC: AAR).

3. Coatings and Linings for Immersion Service, TPC 2, Revised Edition (Houston, TX: NACE, 1998), Chapter 1, “Safety.”

4. NACE Standard RP0178 (latest revision), “Fabrication Details, Sutface Finish Requirements, and Proper Design Considerations for Tanks and Vessels to Be Lined for Immersion Service” (Houston, TX: NACE).

5. SSPC-SP 1 (latest revision), “Solvent Cleaning” (Pittsburgh, PA: SSPC).

6. NACE No. l/SSPC-SP 5 (latest revision), “White Metal Blast Cleaning” (Houston, TX: NACE, and Pittsburgh, PA: SSPC).

7. ASTM D 4285 (latest revision), “Standard Test Method for Indicating Oil or Water in Compressed Air” (West Conshohocken, PA: ASTM).

8. NACE Standard RP0287 (latest revision), “Field Measurement of Surface Profile of Abrasive Blast Cleaned Steel Sutfaces Using a Replica Tape” (Houston, TX: NACE).

(7) Materials Technology Institute of the Chemical Process Industries (MTI), 1215 Fern Ridge Parkway, Suite 116, St. Louis, MO 63141-4401.



RP0592-2001

9. SSPC-PA 2 (latest revision), “Measurement of Dry Paint Thickness with Magnetic Gauges” (Pittsburgh, PA: SSPC).

Bibliography

NACE Standard RP0188 (latest revision). “Discontinuity of Concentrated Sulfuric Acid and Oleum at Ambient (Holiday) Testing of New Protective Coatings on Temperatures.” Houston, TX: NACE. Conductive Substrates.” Houston, TX: NACE.

NACE Standard RP0391 (latest revision). “Materials for NACE Standard RP0294 (latest revision). “Design, the Handling and Storage of Concentrated (90 to

Fabrication, and Inspection of Tanks for the Storage 100%) Sulfuric Acid at Ambient Temperatures.” Houston, TX: NACE.

A l .

A2.

APPENDIX A Essential Facilities and Equipment for Application of a Coating System to the Interior of Tank Cars for Concentrated Sulfuric Acid Service

General

A l . l The tank car coating shop shall comply with all applicable regulations, including those regulations on air quality, hazardous waste, and safety.

A1.2 The shop shall have adequate, explosion-proof lighting so that work can be done safely inside and outside of the tank car.

A l .3 Adequate respiratory protection shall be provided to personnel.

A1.4 The tank car shall be properly electrically grounded.

Clean I i ness

A2.1 The tank car coating shop shall be maintained at an acceptable degree of cleanliness so that coating applications are not hampered by dirt, dust, and other contaminants.

A2.2 The coating application area shall have concrete floors, or floors which are of a similar hard construction.

A2.3 The equipment used to apply the coating system materials shall be free of dirt, dust, sand, steel grit, old coating materials, and other foreign matter that can contaminate the coating system material.

A2.4 Workmen’s clothing, including footwear, shall be sufficiently clean to avoid contaminating the blast cleaned sutfaces and the completed coating system.

A2.5 Facilities and procedures shall be such that dirt, dust, sand, steel grit, and other foreign matter from the sutface preparation and blasting area shall not enter

the area where coating system materials are being applied.

A2.6 The compressed air supply shall be free of moisture, oil, grease, and other harmful foreign matter.

A2.7 Ladders shall be free of coating build-up and contaminants that can harm the coating system.

A3. Equipment

A3.1 The tank car coating shop shall have the necessary equipment to apply coating systems to tank cars and the equipment shall be in safe working order.

A3.2 The sutface preparation and blasting equipment shall be capable of preparing the sutface according to this standard.

A3.2.1 The abrasive that is used shall be capable of achieving the specified sutface profile.

A3.2.2 Abrasive removal equipment, such as fine bristled brushes and vacuum cleaners, shall be available.

A3.3 Adequate facilities or equipment shall be provided to prevent rust bloom on the blasted sutfaces when atmospheric conditions are likely to produce rust bloom before the coating can be applied.

A3.4 The compressed air supply shall be adequate to furnish compressed air at a minimum gauge pressure of 0.6 MPa (90 psi) at the blasting nozzles and to supply adequate compressed air for spray equipment.

A3.5 Spray equipment shall be capable of applying coating-system materials within a reasonable time and to the manufacturer’s specifications.



RP0592-2001

A3.6 Spare parts such as spray tips, blasting nozzles, etc., shall be in stock and on site.

A3.7 Abrasive paper, masking tape, clean-up thinner, and similar supplies shall be in stock.

A3.8 The tank car coating shop shall have equipment that can furnish sufficient hot, forced air free of contaminants to follow the coating manufacturer’s recommended curing schedules.

A4. Buildings

A4.1 The blast cleaning and coating application facilities shall be capable of protecting the tank car from inclement weather.

A4.2 A separate building or room shall be used for storing coating system materials where the temperature shall be kept at a maximum of 38°C (1 00°F).

A4.3 The building where coating applications are made shall be capable of keeping the metal temperature of the tank car at a minimum of 13°C (55°F).

A4.3.1 The preferred metal temperature is 21 to 27°C (70 to 80°F) when applying coating system materials.

A5. Test Equipment and Supplies

A5.1 The coating shop shall have adequate test equipment to ensure quality control of the coating application. The following test equipment shall be available in proper working order:

A5.1.1 Film thickness gauges

A5.1.1.1 Wet-film thickness gauges.

A5.1 .I .2 Nondestructive dry-film thickness gauges properly calibrated in accordance with SSPC-PA 2.

A5.1.2 A low-voltage (100-V maximum), wet- sponge holiday detector calibrated, if applicable, according to the manufacturer’s instructions.

A5.1.3 Replica tape or film and a spring micrometer (to measure tape or film).

A5.1.4 Humidity and temperature measuring equipment, including psychrometers and metal- sutface thermometers.



RP0592-2001

Car Number:

. 0 - A - -

- ' -

" A End

"A" -Ed

"A" @ " B

i ' I '

I . . I .

1 "B" End

Comments:



RP0592-2001

Final Metal Temperature ("C/"F) 1 st Coat

APPENDIX C: Tank Car Coating System Inspection Report Form

Time (hours)

CUSTOMER TANK CAR NO. CONTRACTOR

SHOP LOCATION COATING SYSTEM MATERIAL

COATING MANUFACTURER

APPLICATOR INSPECTOR CUSTOMER INSPECTOR

TANK CAR OWNER INSPECTION DATE

ABRAS IVE

TYPE NOZZLE SIZE SIZE

NOZZLE PRESSURE

BLAST PROFILE SPECIFIED PROFILE DEPTH

METHOD OF MEASUREMENT

DEPTH

Date/Time

Ambient Temperature

Relative Humidity

Dew Point

Metal Temperature ("C/" F)

ENVIRONMENTAL CONDITIONS AT THE TIME OF APPLICATION AND CURING:

CURING:

2nd Coat

3rd Coat

4th Coat

Final Cure



NACE Standard TM0294-2001 Item No. 21225


Standard Test Method

Testing of Embeddable Impressed Current Anodes for Use in Cathodic Protection of Atmospherically

Exposed Steel-Reinforced Concrete



CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication. The user is cautioned to obtain the latest edition. Purchasers of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International Membership Services Department, 1440 South Creek Dr., Houston, Texas 77084-4906 (telephone + I [281]228-6200).

Reaffirmed 2001-09-05 Approved March 1994

NACE International 1440 South Creek Drive

Houston, Texas 77084-4906 + I 281/228-6200

ISBN 1-57590-133-1 02001, NACE International


TM0294-2001

Foreword

This NACE International standard has been prepared to provide users and manufacturers of embeddable anodes with a test method for evaluating the anode material to an expected lifetime criterion. It is applicable to embeddable anode materials, such as titanium mesh, commonly used for cathodic protection of atmospherically exposed steel-reinforced concrete. The test is intended to evaluate whether an embeddable anode material complies with minimum required specifications of design life expectancy at rated current output. This test method is not applicable to surface- mounted anodes or conductive coating materials.

This NACE International test method was originally prepared in 1994 by Task Group T-3K-6 on Test Procedure for Anodes Used in Concrete, a component of Unit Committee T-3K on Corrosion and Other Deterioration Phenomena Associated with Concrete. It was reviewed by Task Group (TG) 045 on Anodes Test Procedures and reaffirmed in 2001 by Specific Technology Group (STG) O1 on Concrete and Rebar. TG 045 is administered by STG O1 and sponsored by STG 05 on Cathodic/Anodic Protection. This standard is issued by NACE International under the auspices of STG 01.

In NACE standards, the terms shall, must, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shall and must are used to state mandatory requirements. The term should is used to state something good and is recommended but is not mandatory. The term may is used to state something considered optional.



TM0294-2001


Test Method

Testing of Embeddable Impressed Current Anodes for Use in Cathodic Protection of Atmospherically Exposed SteeI-

Reinforced Concrete

Contents

1. General ........................................................................................................................... 1 2. Definitions ...................................................................................................................... 2 3. Solution Preparation ........................................................................................................ 2 4. Test Apparatus ................................................................................................................ 3 5. Test Proced

References .......................................................................................................................... 5 Figures Figure 1 : Test Cell with Luggin Probe Anode Potential Measurement Set-up .................. 3 Figure 2: Series Electrical Hook-Up for Duplicate Evaluations .......................................... 4 Tables Table 1 : Typical Results of Anode Life Testing 30 g/L NaCI Solution Table 2: Typical Results of Anode Life Testing 40 g/L NaOH Solutio Table 3: Typical Results of Anode Life Testing Simulated Pore Wat



TM0294-2001

Section 1: General

1.1 Accelerated testing of anodes for use in concrete is intended to provide an indication of an anode’s ability to petform satisfactorily for a specific number of years. Unfortunately, accelerated “life testing” cannot be conducted in concrete because testing at high current levels results in premature failure of the concrete as the test electrolyte. Accelerated life testing must therefore be conducted in an aqueous solution.

1.1.1 When using accelerated life tests, anodes shall be demonstrated to survive a minimum total charge density of 38,500 A-h/m2 (3,580 A-h/ft2) of actual anode sutface area. This is the amount of total charge density an anode is subjected to if operated at a current density of 110 mA/m2 (IO mA/ft2) of anode sutface for 40 years. If an anode is designed to operate at any other current density, the test should be modified to reflect the charge density equivalent to 40 years of operating life.

1.1.2 Under certain circumstances the user may require a greater total charge density than 38,500 A- h/m2 (3,580 A-h/ft2) of anode sutface, because of a longer life requirement than 40 years, or because of a higher operating current density. In these cases, the test may be extended or the charge density increased until the desired charge is met.

1.2 It is possible that a cathodic protection anode may be incorrectly powered cathodically during the initial system energization. This condition may not be noticed by merely observing the rectifier meters and can remain undetected until the depolarization test is petformed after several days of operation. It is also possible that an anode may be exposed to current reversal caused by an electrical short between the anode and the steel. In this case, the anode is subjected to cathodic current until the system is energized and tested, sometimes several months later. In view of these possibilities and the serious implications of damage to the anode, the ability of the anode to survive a brief current reversal must be ensured.

1.2.1 Assuming the anode is operated at a reversed current density of 110 mA/m2 (IO mA/ft2) of anode sutface for a period of one month, the anode experiences approximately 71 A-h/m2 (6.6 A-h/ft2) of cathodic charge density. It shall be tested to endure such a current reversal and then continue to provide an equivalent of at least 40 years, or 38,500 A-h/m2 (3,580 A-h/ft2) of anode surface, of protection.

1.3 The anodic portion of life testing shall be conducted over a period of at least 180 days.

1.4 Life testing shall be conducted using a constant- current, filtered DC power supply having a maximum ripple of 5%.

1.5 Accelerated life testing shall be conducted in duplicate in the following aqueous solutions:

1.5.1 30 g/L of sodium chloride in distilled or deionized water

1.5.1 . I Cathodic protection anodes are often used to protect bridge piers and pilings in seawater and therefore are exposed to this chloride environment. This solution tests the ability of anodes to tolerate the chlorine evolution reaction.

1.5.2 40 g/L of sodium hydroxide in distilled or deionized water

1.5.2.1 This solution, though at a higher pH than concrete, is conductive enough to nullify effects of solution changes. The solution also tests the ability of the anode to tolerate oxygen evolution, a reaction more favored at low current density and the low chloride contamination level experienced with fresh overlays.

1.5.3 Simulated pore water in sand

1.5.3.1 The electrolyte available to the anode in a cured concrete structure is pore water. This solution tests the ability of the anode to tolerate the actual concentrations of the pore water components and any possible synergistic effects imposed by these components. The use of fine sand to encompass the electrode, eliminating convective mixing, tests the ability of the anode to tolerate the situation most closely simulating its operation in cured concrete. The composition by mass of simulated pore water used shall be as fo I lows:

0.20% Ca(0H)z 3.20% KCI 1.00% KOH 2.45% NaOH 93.15% distilled or deionized water

1.6 Failure of the anode shall be determined by loss of the electrochemical activity as evidenced by an increase in anode potential as defined in Paragraph 5.2.



TM0294-2001


Luggin Probe: A small tube or capillary filled with Ripple: The alternating-current component in the output of electrolyte, terminating close to the metal sutface of an a direct-current power supply, arising within the power electrode under study, which is used to provide an ion- supply from incomplete filtering or from commutator action conducting path without diffusion between the electrode in a DC generator. under study and a reference electrode.

Section 3: Solution Preparation

3.1 30 g/L Sodium Chloride (NaCI) Solution 3.3 Simulated Pore Water in Sand

3.1.1 30.0 g of reagent grade NaCI shall be weighed and added to a 1 .O-L volumetric flask.

3.1.2 Approximately 500 mL of distilled or deionized water shall be added to the above, and the solution must be swirled in the flask until the NaCI crystals are totally dissolved.

3.1.3 The volumetric flask shall be filled to the 1.0-L mark with distilled or deionized water, and the solution must be thoroughly mixed.

3.2 40 g/L Sodium Hydroxide (NaOH) Solution

3.2.1 40.0 g of solid NaOH pellets shall be weighed as 100% NaOH and slowly added to a 1.0-L volumetric flask containing approximately 500 mL of distilled or deionized water. The solution must be swirled in the flask until the NaOH is totally dissolved. This reaction is exothermic and generates heat.

3.2.2 The volumetric flask shall be filled to just under the 1 .O-L mark with distilled or deionized water and the solution shall be allowed to cool to room temperature.

3.2.3 When the solution is cool, the volumetric flask shall be filled to the 1.0-L mark with distilled or deionized water and the solution shall be thoroughly mixed.

3.3.1 26.3 g of solid NaOH pellets shall be weighed out as 100% NaOH and slowly added to 1.0 L of distilled or deionized water in a flask. This reaction is exothermic and generates heat.

3.3.2 10.74 g of solid potassium hydroxide (KOH) pellets shall be weighed out as 100% KOH and slowly added to the solution. The solution must be swirled until all pellets are dissolved.

3.3.3 34.35 g of reagent grade potassium chloride (KCI) shall be weighed out and added to the solution. The solution shall be swirled until the crystals are dissolved.

3.3.4 2.15 g of reagent grade calcium hydroxide (Ca[OH]2) shall be weighed out and added to the solution. The solution shall be mixed with a magnetic stirrer until it has cooled.

3.3.5 Fine natural silica sand (40 to 50 mesh) shall be obtained in accordance with ASTM"' C 778.'

3.3.6 The test cell must first be filled with enough sand to cover the anode completely after the electrodes and Luggin probe are in place. The simulated pore water shall then be added to displace any air and fill the remainder of the cell.

3.3.7 Fresh sand and solution shall be used for the current-reversal test (Paragraph 5.5) and for the normal current test (Paragraph 5.9).

(')ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428



TM0294-2001

Section 4: Test Apparatus

4.1 Test Cell

4.1.1 The test cell shall be a tall-form glass 1.0-L beaker that is 18 cm (7.1 in.) high and 9 cm (4 in.) in diameter, fitted with a No. 15 rubber stopper at the top to hold the electrodes and reduce air contact. Glass beakers of other sizes may be used as long as electrodes remain immersed for the duration of the test. The gap between the anode and cathode shall be

approximately 50 mm (2 in.). The rubber stopper shall have a hole located midway between the electrodes that is fitted with an extension tube to vent gases away from the electrical connections. This hole may be used to locate the current-reverse supplemental anode and Luggin probe. There shall be an additional hole large enough to measure pH of the test solution. Figure 1 shows a typical Set-up for a test cell with Luggin probe for anode potential measurement.

Sot ur0 ted Calomel Electrode

Uec t rol ye Bridge

i\

I

Luggin Probe

Cothode

Figure 1 Test Cell with Luggin Probe Anode Potential Measurement Set-up

4.1.2 A sample of the anode having 20.0 om' (3.10 diameter x 8-in. long) titanium rod in two spots as in.') of anode sutface area shall be used. The anode shown in Figure 1. The titanium rod acts as the current sutface area shall be calculated by including all the carrier. For other types of anodes, an appropriate sutfaces that will be in contact with concrete when anode connection as recommended by the anode embedded. A titanium anode sample shall be welded manufacturer shall be made. The anode shall be to a 1.6-mm diameter x 200-mm long (0,063-in. connected to the positive lead of the power supply (the



TM0294-2001

@ a

negative lead during the current-reversal test) external to the cell using an insulated I-mm (0.04-in.) diameter (#I8 AWG"]) copper wire with a copper alligator clip.

4.1.3 The cathode shall be a 12.7-mm diameter x 200- mm long (0,500-in. diameter x 8-in. long) titanium rod Alternatively, relatively inert cathodes such as platinum or niobium may also be used. The cathode shall be fitted through the rubber stopper and extended to approximately 10 mm (0.4 in.) from the bottom of the cell. The cathode shall be connected to the negative lead of the power supply (not connected during the current-reversal test) external to the cell using an insulated I-mm (0.04-in.) diameter (#I 8 AWG) copper wire with a copper alligator clip.

Coostont Current o Power Supply 17.8 mA, 0-50 V

4.1.4 A supplemental anode is required for the current-reversal portion of the testing. This anode shall be identical to the one being life tested and shall be referred to as the current-reversal (CR) anode between the cathode rod and the anode to be life tested. During the current-reversal test, the CR anode shall be connected to the positive lead of the power supply external to the cell using an insulated I-mm (0.04-in.) diameter (#I8 AWG) copper wire with a copper alligator clip. The CR anode shall be removed from the cell during normal testing.

4.1.5 Figure 2 illustrates a typical Set-up for a series electrical hook-up for duplicate evaluations.

Toto1 Charge Measuring

- - - 30 glL NaCI 40 glL NaOH Simulated

Pore Water with Sand

Figure 2 Series Electrical Hook-Up for Duplicate Evaluations

4.2 Power Supply 4.3 Instrumentation

4.2.1 The power supply shall be a filtered DC power supply with a maximum ripple of 5% that is capable of supplying and maintaining a constant current of 17.8 mA I l % . This current is necessary to test 20 om' (3.1 in.') of anode for a total of 38,500 A-h/m' (3,580 A-h/ft') in 180 days.

4.3.1 A voltmeter shall be used to measure the voltage of each cell at the intervals specified in Section 5. The voltmeter shall have a high input impedance (IO M a or greater) and shall be capable of measuring cell voltage accurate to 11 %.

(') American Wire Gauge (AWG).



TM0294-2001

Section 5: Test Procedure

5.1 The cathode rod and anode to be life tested shall be installed in the rubber stopper so that the anodekathode gap is approximately 50 mm (2 in.).

5.2 The CR anode shall be installed midway between the cathode rod and the anode to be tested.

5.3 The test cell shall be filled with electrolyte solution to approximately the 900-mL mark, making sure that the anode sample is completely immersed. The solution shall not be stirred. The temperature of the solution shall be maintained at 20 f5"C (68 f9"F) throughout the test.

5.4 The electrolyte pH shall be recorded at the beginning of the test. The pH shall be measured periodically (approximately every 100 h) and recorded. The level of the solution in the cell shall be checked for evaporation losses at these time periods and distilled or deionized water shall be added as required to re-establish the 900-mL level.

5.5 The current-reversal test shall be conducted first. The negative lead from the power supply shall be attached to the anode to be life tested and the positive lead shall be attached to the CR anode.

5.6 The anode to be life tested shall be tested under reverse, or cathodic, polarity for 8 h at 17.8 mA. This results in a total charge density of 71 A-h/m2 (6.6 A-h/ft2) of anode sutface (or the equivalent of about one month of operation at an anode current density of 110 mA/m2 [IO m ~ / f t ~ ] ) .

5.7 During the current-reversal portion of the test, cell voltage and cell current shall be measured at 1 min, 1 h, and 8 h. The cell voltage measurements shall be obtained by attaching the leads from a voltmeter to the test electrode and the CR anode.

5.8 After completing the current-reversal test, the power supply leads shall be changed so that the positive lead is connected to the anode being life tested and the negative lead is connected to the cathode rod. The CR anode shall be removed from the cell. The Luggin probe shall be installed for anode potential measurements. The cells requiring sand must be completely emptied and refilled with fresh sand and test electrolyte in order to accomplish all tasks.

5.9 The test anode should then be operated under normal, or positive, polarity at 17.8 mA.

5.10 The following parameters shall be measured during the normal, or positive, polarity portion of the test:

5.10.1 Cell voltage and cell current shall be measured at 1 h, 24 h, 7 days, 14 days, 28 days, 42 days, 56 days, 70 days, 84 days, 98 days, 112 days, 126 days, 140 days, 154 days, 168 days, and 180 days.

5.10.2 Anode potential versus a stable saturated calomel electrode (SCE) or silver-silver chloride electrode shall be measured at the same intervals as the measurements taken in Paragraph 5.10.1. The anode potential measurements shall be obtained by attaching leads from a high-impedance voltmeter (1 O M a or greater) to the anode and to an SCE with a Luggin probe located 2 diameters (of the tip of the probe) away from the sutface of the anode.

5.11 The total quantity of charge passed during the test shall be measured accurate to f 1 %. The total charge at the end of the test shall confirm the minimum total charge density of 38,500 A-h/m2 (3,580 A-h/ft2), or greater if required by the user. If the anode has failed (see Paragraph 6.2), both measured and calculated charges shall be recorded.

Section 6: Acceptance Criterion

6.1 The anode material must be tested in the three 6.2 Anode failure is marked by a rapid escalation in both different electrolytes described in this standard and must cell voltage and anode potential. The time of failure should pass all three tests. be recorded when the anode potential increases by 4.0 V

above its initial value.

Section 7: Reporting Test Results

6.1 Test results shall be recorded in tabular form as shown in Tables 1, 2, and 3.



TM0294-2001

Table 1 Typical Results of Anode Life Testing

30 glL NaCI Solution (See Paragraph 3.1)

Test Time Cell Current Cell Voltage Anode Potential Solution (mA) (VI vs. SCE (V) PH

Reverse Current 1 min 17.8 1.91

I h 17.8 2.40

8.8 h 17.8 2.23

Normal Current I h 17.8 2.53 1.181 6.4

24 h 17.8 2.49 1.177 7.0

7 days 17.8 2.28 1.187 7.6

14 days 17.8 2.45 1.333 7.9

28 days 17.8 2.61 1.456 8.2

42 days 17.8 2.62 1.484 8.0

56 days 17.8 2.61 1.480 8.1

70 days 17.8 2.64 1.508 8.7

84 days

98 days

112 days

126 days

140 days

154 days

168 days

180 days

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

2.65

2.80

2.72

2.67

2.74

2.71

2.76

2.71

1.520

1.534

1.551

1.536

1.583

1.550

1.591

1.579

8.0

8.0

8.4

8.0

7.8

8.2

8.0

7.8



TM0294-2001


40 glL NaOH Solution (See Paragraph 3.2)



I h 17.8 1.66

8 h 17.8 1.64

Normal Current I h 17.8 1.91 0.577 12.9

24 h 17.8 1.91 0.585 13.0

7 days 17.8 1.94 0.606 13.0

14 days 17.8 1.93 0.605 12.9

28 days 17.8 1.95 0.594 12.8

42 days 17.8 1.95 0.617 13.1

56 days 17.8 1.93 0.610 13.0

70 days 17.8 1.96 0.625 13.0

84 days

98 days

112 days

126 days

140 days

154 days

168 days

180 days

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

1.96

1.94

1.99

1.97

2.03

2.00

2.05

2.02

0.620

0.602

0.633

0.629

0.650

0.645

0.663

0.656

12.5

13.0

12.8

12.6

13.2

12.8

12.7

12.0



TM0294-2001


Simulated Pore Water Solution (See Paragraph 3.3)



I h 17.8 1.74

8 h 17.8 1.70

Normal Current I h

24 h

7 days

14 days

28 days

42 days

56 days

70 days

84 days

98 days

112 days

126 days

140 days

154 days

168 days

180 days

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

17.8

1.90

1.90

1.93

1.91

1.93

1.93

1.92

1.94

1.93

1.80

1.92

1.92

2.02

1.98

2.01

1.98

0.540

0.553

0.566

0.562

0.566

0.572

0.565

0.578

0.575

0.567

0.585

0.577

0.602

0.588

0.604

0.596

12.9

12.9

13.0

13.0

13.1

13.1

13.1

13.0

12.6

13.0

13.0

12.9

13.2

13.0

13.3

12.3

Referen ces

1. for Standard Sand” (West Conshohocken, PA: ASTM).

ASTM C 778 (latest revision), “Standard Specification

8

ISBN 1-57590-133-1

NACE International


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