1 of 15

A Comparison of Refractory Lined Carbon Steel and Titanium EXW

Clad Pressure Vessels for Specific Operating Conditions

W. Bristowe, M. Pearson, and C. Stunguris

Hatch Ltd.

Oakville, Ontario, Canada

S. Gothard

W.E. Smith Engineering Ltd.

Coffs Harbour, New South Wales, Australia

ABSTRACT

Pressure vessels in hydrometallurgy and many chemical process industries

throughout the world require the use of specific lining systems to protect the parent

vessel materials from corrosion and/or abrasion. Typically, these lining systems are

required for processes that are corrosive and operate at elevated temperatures. Two

basic lining system types are: 1) refractory linings in conjunction with an

impervious corrosion resistant membrane, and 2) metal-clad vessels consisting of

titanium or other corrosion resistant metal bonded to a carbon steel shell.

Operating conditions play a key role in selecting the type of lining system to be

utilized for a specific application. Lining systems in turn have an impact on the

process vessel size, which ultimately affects the capital cost of the vessel. In

addition to the cost of the process vessel, the cost of each type of lining system must

be considered, as well as maintenance concerns, quality control, and delivery.

Operating conditions play a key role in the final selection of lining systems utilized

for specific projects based on initial capital cost, life-cycle maintenance costs, and

overall service life.

This paper examines the fundamentals of each lining system, their inherent

technical strengths and weaknesses, and presents relative cost comparisons for each

lining system as they apply to specific operating conditions and vessel sizes.

2 of 15

INTRODUCTION

Hydrometallurgical process engineers have successfully utilized both refractory

lined and alloy clad pressure vessels in many different process plants. Prime

examples where these types of vessels are used include high-pressure acid leach or

pressure oxidation facilities for the extraction of metals such as gold, copper, cobalt,

nickel, zinc, and uranium. In such facilities, the autoclaves, flash vessels, and slurry

heater vessels are candidates where these types of lining systems are utilized. This

paper focuses on metallurgical autoclave technologies; however, some of the

material is also relevant to other chemical processing industries that require the use

of lined or clad pressure vessels.

Typically, the processes utilised in such facilities operate at elevated temperatures

and pressures in very aggressive and corrosive environments that require a high

degree of corrosion resistance. Refractory lining systems have been used

successfully for many years in these environments. Refractory lining systems utilize

an impervious corrosion resistant membrane protected by a refractory layer that is

exposed to the process environment. The refractory is required to protect the

membrane from high temperatures and abrasion, since the membrane materials

themselves have generally poor thermal and abrasion resistance. Recently,

explosion-clad pressure vessels have gained significant use in high-pressure

autoclaves for the extraction of nickel and other metals. Clad vessels consist of a

corrosion resistant alloy, typically titanium, which has been explosion bonded to a

carbon steel shell. In this type of vessel, the titanium cladding material acts as the

corrosion barrier and is exposed directly to the process environment.

In many instances, the decision to utilize either a titanium clad vessel or a refractory

lined vessel must be made in the feasibility stage of a project, a difficult choice

considering the limited knowledge that exists at the outset of a new project. Both

types of lining systems have their own advantages and disadvantages. When it

comes time to build a demonstration plant or a commercial scale plant, economic

factors determine that decision in most instances. In such cases, all of the factors

such as installed capital cost, process risk, maintenance costs, and service life must

be considered to make that initial critical decision. This paper intends to highlight

specific operating conditions, in conjunction with the listed economic factors,

which may make one lining system more favourable than another for certain

conditions.

3 of 15

Refractory Lining Systems

The basis of a refractory lining system is the impervious corrosion membrane that is

applied to the carbon steel shell. Typical membranes that have been used

successfully in the past are homogeneously bonded lead, nickel alloy weld overlay,

acid resistant rubber membranes, vinyl ester membranes, as well as other

proprietary materials offered by companies specializing in refractory linings. A

refractory lining is required to protect the corrosion resistant membrane. Due to the

temperature limitations of the corrosion membrane, the main function of the

refractory is to thermally insulate the membrane from high process temperatures.

The second function of the refractory is to protect the membrane from abrasion due

to slurry flow induced by agitation (autoclaves), high velocity flash steam (heater

vessels) or high velocity slurry jets (flash vessels). Due to the fixed thermal

conductivity of a refractory materials and the temperature limited membrane,

additional refractory must be added as process temperatures increase in order to

maintain an acceptable membrane temperature.[1] This in turn requires a larger

vessel shell in order to maintain a desired process diameter or process volume. For

this reason, refractory lined vessels will always be larger and heavier than a titanium

clad vessel for the same working pressure, process diameter, and volume. Table 1

presents some of the advantages and disadvantages of refractory lined systems.

Table 1 – Refractory Lining Systems: Advantages and Disadvantages

Advantages Disadvantages

Good corrosion resistance in sulphuric acid environments

Higher maintenance costs associated with face course re-lines

Excellent abrasion resistance Requires larger vessel to accommodate thickness of refractory lining

Excellent resistance to oxidation and ignition (pyrophoricity)

Lower service temperature, due to stability limitations in lining thickness

Titanium Clad Lining Systems

Alloy clad lining systems utilize a layer of corrosion resistant material that is bonded

to a carbon steel parent material. Cladding materials can be titanium, tantalum,

specialty stainless steels or nickel alloys. The most common cladding material in

metallurgical processing plants is explosion bonded titanium which is utilized due

to it’s excellent corrosion resistant properties, ductility, and relatively low cost.[2]

Table 2 summarises some of the advantages and disadvantages of titanium clad

lining systems.

4 of 15

Table 2 – Titanium Clad Lining Systems: Advantages and Disadvantages

Advantages Disadvantages

Excellent corrosion resistance in oxidizing environments.

Potential for ignition in enriched oxygen environments (pyrophoricity).

Titanium can be in direct contact with

process media, resulting in smaller and lighter vessel.

Reduced abrasion resistance, especially to slurries of sulphide ores.

High temperature limitations – up to 315°C (600°F) permitted by ASME Code.

Susceptible to pitting and/or crevice corrosion in reducing environments.

Figure 1 indicates the relative unit costs of fabrication for carbon steel, lead lined

autoclaves and titanium clad carbon steel autoclaves as a function of total vessel

weight. All vessels are constructed of ASME SA-516 Gr. 70 normalised C-Mn-Si

steel. Fabrication unit costs for several sizes of flash vessels other refractory lined

vessels are also indicated for reference. The lower unit cost for these vessels can be

attributed to a simpler vessel design with fewer nozzles and smaller length to

diameter aspect ratios.

Relative Fabricated Unit Cost vs. Vessel Weight

0.0

0.5

1.0

1.5

2.0

2.5

0 100,000 200,000 300,000 400,000 500,000 600,000 700,000 800,000 900,000

Total Vessel Weight (kg)

Re

lati

ve

Fa

bri

ca

ted

Co

st

pe

r U

nit

We

igh

t

Ti EXW Clad A/C's

CS/Brick Lined A/C's

CS/Brick Lined Flash Vessels

CS/Brick Lined Other Vessels

Log. (Ti EXW Clad A/C's)

Power (CS/Brick Lined Flash Vessels)

Poly. (CS/Brick Lined A/C's)

Figure 1 – Relative Fabrication Unit Costs as a Function of Vessel Weight

5 of 15

The data points indicated in Figure 1 are derived from project data on actual vessels

that have been fabricated and placed into service, as well as firm and budget

quotations from vessel manufacturers. The relative fabricated unit costs presented

are Ex Works and include material, fabrication labour, consumables, non-

destructive examination, engineering, quality control, overhead and profit. Freight

costs are excluded so as remove regional disparities from the comparison. All costs

have been indexed to third quarter 2010 US Dollars, using the Marshall and Swift

Equipment Cost Index, and currency exchange rates at the time of order placement.

An expected trend in Figure 1 indicates that the fabricated unit cost of titanium

EXW clad vessels and carbon steel, brick lined flash vessels decreases as the vessels

get larger and heavier. This trend has been confirmed in conversations with vessel

manufacturers.

The reasons for this trend are as follows:

i) The fixed costs associated with the manufacture of a vessel such as

engineering, quality control, and overhead are distributed. Therefore, these

fixed costs will drive up the unit price of a smaller vessel, while in a larger

vessel these costs are distributed over more weight, resulting in a lower unit

cost.

ii) On larger vessels, the labour cost per kilogram of material is reduced since

automated welding machines provide more output on larger vessels and

heavier wall thicknesses.

iii) In addition to the fixed costs and larger output from automated machinery,

this trend is also affected by the fact that the percentage of costs associated

with additional material and fabrication for nozzles, clips, internals and

cladding becomes smaller as the vessels become larger.

The three factors affecting this trend hold true for the fabrication of titanium clad

vessels, refractory lined carbon steel flash vessels and solid alloy vessels, however

no such trend has been observed in the unit fabrication cost of refractory and lead

lined carbon steel autoclave vessels.

The absence of this trend in horizontal refractory lined vessels indicates that as

vessels get larger, the unit cost to fabricate a vessel decreases until a threshold is

reached which requires a step change in shell diameter and nozzle sizes (and vessel

cost) to accommodate additional refractory brick. In addition, as the diameter of the

vessel increases to accommodate another course of refractory brick, the shell

thickness and total weight of the vessel increase proportionally to the vessel

diameter.[1]

6 of 15

Design Conditions

Process conditions vary greatly from one process to another when it comes to the

design of metallurgical processing plants. The following table indicates some of the

typical process conditions and environments that can be found in some

metallurgical processing facilities currently in production or detailed engineering

design stages.

Table 3 – Process Conditions found in Metallurgical Processing Facilities

Operating Conditions*

Hydrometallurgical Process Temperature

°C

Pressure

kPa(g)

Typical Uses

High Pressure Acid Leach 250 – 275 4500 – 6300 Ni Laterite ore leaching

Bayer™ Alumina Process 260 – 280 7000 - 8000 High temperature caustic digestion

Total Sulphide Oxidation 200 – 235 2000 – 3500 Refractory gold sulphide

ore treatment

Acid Pressure Leaching 180 1730

Alkaline Carbonate Leach 120 350

Oxidative leaching of

uranium, rare earth ores

Freeport McMoRan Process 160 2000

CESL Process – Chloride assisted partial oxidation

130 – 155 1100 - 1275

Oxidative leaching of

chalcopyrite & Cu matte

Activox™ Process – Low Temp.

Oxidation 110 1000

Oxidative leaching of

Ni/Co concentrates

*Operating conditions do not necessarily reflect actual design conditions. Design conditions will be

higher than operating conditions.

Based on the operating conditions encountered in these metallurgical processing

plants, a matrix was developed to cover a range of operating temperatures and

pressures over a range of vessel sizes. From this matrix, vessel sizes and

corresponding wall thickness, mass, and surface areas etc. were calculated for a

typical six (6) compartment autoclave. Total capital costs were then estimated for

each vessel size.

7 of 15

Table 4 indicates the range of process conditions that formed the basis of the capital

cost comparison between titanium clad and refractory lined pressure vessels.

Table 4 – Process Conditions and Vessel Sizing Matrix*

Normal Operating Conditions

Normal Operating Temp. °C 150 175 200 225 250 275 300

Normal Non-condensable

Overpressure

kPa (abs) 350 350 350 350 350 350 350

Normal Operating Press. kPa (abs) 825 1242 1905 2900 4328 6299 8943

Maximum Operating Conditions

Maximum Operating Temp. °C 160 185 210 230 255 280 305

Max. Non-condensable

Overpressure

kPa (abs) 350 350 350 350 350 350 350

Maximum Operating Press. kPa (abs) 967 1473 2258 3148 4674 6770 9564

Design Conditions

Design Margin on MOP 10% 10% 10% 10% 10% 10% 10%

Design Temperature °C 164 189 215 235 261 286 312

Design Pressure – absolute kPa (abs) 1064 1621 2484 3463 5142 7447 10520

Design Pressure – gauge kPa (g) 963 1519 2383 3361 5041 7346 10419

ANSI Pressure Class 150 300 300 300 600 600 900

*Vessel process diameters range from 2.0 m thru 6.0 m in 0.5 m increments

Capital Cost Comparison

The costs included in the analysis for each vessel type are listed in Table 5. All unit

costs are derived from previous project data and are corrected to third quarter 2010

US Dollars using Marshall and Swift equipment cost indices.

Table 5 – Costs Included in Vessel Comparison

Refractory Lined Vessel Titanium Clad Vessel Solid Titanium Vessel

Vessel Fabrication Labour

Vessel Materials

Lead Membrane or Rubber Membrane

Refractory Lining

Vessel Fabrication Labour

Vessel Materials

Plate EXW Cladding

Exterior Thermal Insulation

Vessel Fabrication Labour

Vessel Materials

Exterior Thermal Insulation

8 of 15

Figure 2 shows the relative component costs for the fabrication of a 4.0 m process

diameter autoclave vessel. The trends indicated on this figure are fairly typical for

all of the other vessels included in the comparison matrix. One of the significant

trends revealed in the figure indicates that at low operating temperatures and

pressures, refractory lined vessels are slightly more economical than a similar sized

titanium clad vessel. In the figure, the lead lined vessels for 150°C and 175°C

conditions are lower in cost compared to the equivalent titanium Gr. 1 clad vessel.

Analyzing the data further reveals that the crossover point where titanium clad

vessels become more economical occurs when three (3) courses of refractory brick

would be required to thermally insulate the corrosion membrane.1 Where this

occurs, the additional labour for the installation of the third course of refractory

exceeds the incremental material and labour costs associated with the fabrication of

a titanium clad vessel.

0.0

1.0

2.0

3.0

4.0

Rela

tive

Co

mp

on

en

t C

ost

Fabrication Materials

Cladding / Membrane Insulation / Refractory

TITANIUM

CLAD

AUTOCLAVE

REFRACTORY

LINED

AUTOCLAVE

Design Temperature,°C

15

0

17

5

20

0

22

5

25

0

27

5

15

0

17

5

20

0

22

5

25

0

27

5

Figure 2 – Total Autoclave Cost as a Function of Vessel Operating Temperature

(4.0 m diameter vessel shown)

1 175°C is only a guideline that has been calculated with certain refractory brick conductivities,

membrane conductivities, convection and radiation coefficients. A detailed thermal calculation

should be performed to confirm the required brick thickness and corresponding courses of brick

required for a particular service.

9 of 15

An additional factor contributing to the higher overall cost of the refractory lined

vessel at higher operating conditions is that the vessel itself must be progressively

larger to accommodate the additional courses of refractory while maintaining the

same process volume. Although the unit cost of the carbon steel vessel is lower

than the unit cost to fabricate a titanium clad vessel, the carbon steel vessel ends up

being more expensive than the clad vessel due to the additional weight and

additional material required. Figures 3A & 3B illustrate the significant increase in

refractory lined vessel costs as the design temperature (and pressure) increase due to

additional refractory being required to protect the corrosion resistant membrane. At

high temperatures and pressures, the costs for a refractory lined vessel could be

50% - 60% higher than the cost of a titanium clad vessel with the same process

diameter.

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

0

2

4

6

8

10

12

14

16

18

Rel

ativ

e V

esse

l C

ost

Vessel Process Diameter, m

150°C

175°C

200°C

225°C

250°C

275°C

Figure 3A – Relative Ti Gr. 1 Clad Autoclave Cost vs. Process Diameter &

Operating Temperature

10 of 15

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

0

2

4

6

8

10

12

14

16

18R

elative

Vess

el C

ost

Vessel Process Diameter, m

150°C

175°C

200°C

225°C

250°C

275°C

Figure 3B – Relative Lead/Refractory Lined Autoclave Cost vs. Process Diameter &

Operating Temperature

While considering the low temperature and low-pressure applications, it should be

noted that a cost comparison was also made with solid titanium alloy constructed

vessels. This comparison revealed that at low operating temperatures and pressures

and corresponding vessel sizes, a solid titanium vessel would be more economical

than either a titanium-clad or refractory lined vessel. According to the calculations

for estimated capital costs, this trend holds true for solid alloy vessels up to a wall

thickness range of 20 – 25 mm. This trend confirms what vessel fabricators and

clad plate suppliers have indicated in past discussions and published documents by

Banker [2, 3]. Above this thickness, the additional titanium material costs required

to fabricate a solid vessel exceed the additional labour required to fabricate a clad

vessel, and clad construction becomes more economical. Some fabricators have

indicated that there is approximately 10% more labour involved in the fabrication

of a clad vessel as written by DeGaspari [4]. This additional labour is attributed to

the additional work associated with batten strap welding.

11 of 15

Other Cost Considerations

Cladding Thickness

All of the costs presented for titanium clad vessels assume that the vessel is clad

with 8 mm thick EXW titanium, as is common with autoclaves currently in use for

high-pressure acid leaching (HPAL) of nickel and cobalt. Other cladding thickness

such as 3 mm, 5 mm, and 6 mm are also available and commonly used and can

reduce the overall capital cost of the vessel. A cost comparison of 5 mm cladding

versus 8 mm cladding was performed to determine the sensitivity of overall vessel

capital cost with respect to cladding thickness. This analysis revealed that a

premium in the range of 1% to 3% of overall capital cost is paid for 8 mm cladding

over 5 mm cladding. As expected, this general trend indicated that the 3%

premium was noticed on the thinner walled, lighter vessels operating at lower

temperatures and pressures while the 1% premium exists for thicker walled, heavier

vessels operating at higher temperatures and pressures.

Alternative Materials of Construction

In refractory lining systems, specific process conditions (HCl, metal chlorides,

halides) may require more expensive brick alternatives. Also, lining materials such

as homogeneously bonded lead, rubber, and vinyl ester membranes vary

significantly in material and installation labour cost. For titanium clad materials,

different grades of titanium will be selected for particular services. Table 6 indicates

some of the alternative selections and relative cost premiums for each material.

Table 6 – Alternative Material Selections and Relative Cost Premiums

Relative Cost2

Titanium Clad Lining Systems Range Average

Ti Gr.1 EXW on SA-516 Gr. 70N 1.00 1.00

Ti Gr.7 EXW on SA-516 Gr. 70N 1.04 – 1.20 1.12

Ti Gr.11 EXW on SA-516 Gr. 70N 1.03 – 1.11 1.06

Ti Gr.17 EXW on SA-516 Gr. 70N 1.02 – 1.12 1.07

Membrane/Refractory Lining Systems Range Average

Lead/Fireclay Brick on SA-516 Gr. 70N 1.00 1.00

Bromobutyl Rubber/Fireclay Brick on SA-516 Gr. 70N 0.82 – 0.96 0.90

Vinyl Ester/Fireclay Brick on SA-516 Gr. 70N 0.77 – 0.94 0.87

Bromobutyl Rubber/Visil™ Brick on SA-516 Gr. 70N 0.90 – 1.00 0.96

Vinyl Ester/Visil™ Brick on SA-516 Gr. 70N 0.85 – 0.98 0.93 2 Relative costs are based on total estimated capital costs, and vary within the ranges specified

with vessel size, mass, and operating conditions.

12 of 15

Titanium Grade 1 material is shown as the base case for titanium clad vessels and is

suitable for many applications. The use of higher-grade alloys provides increased

crevice corrosion and pitting resistance that may be required for certain

applications.[3] Note that the relative costs of each material option are not constant

as shown by the ranges listed in the table. The range indicated in the table is the

relative cost over the range of different vessel sizes and operating conditions

considered herein. In general, the high value indicated occurs in the lower

temperature and pressure applications. This is attributed to the material cost

premiums being distributed over a lower initial cost, therefore the percentage

increase is greater.

The base case for refractory lined systems is a homogeneously bonded chemical

lead membrane with acid resistant fireclay brick. Other membrane options

included in the table are bromobutyl rubber and vinyl ester membrane. These

membrane options could potentially be combined with high silica grade refractory

such as Visil™ brick for use in high chloride environments. The range of relative

costs shown for these material combinations is attributed to the varying vessel sizes

and operating conditions.

It is very important for the materials engineer to understand all of the normal and

upset process conditions in order to select the proper materials of construction for a

specific process. Pilot plant testing of candidate materials is recommended when

new processes and process environments are encountered in the feasibility study

stage of a project. These initial decisions can have a significant effect on the

resulting capital cost of the vessels, and potential impact on project schedules.

Maintenance Issues and Quality Control

Both refractory and titanium clad lining systems both have the potential to provide

dependable and satisfactory service for the design life of most process facilities.

Acid resistant fireclay brick/lead lined Pachucca reactors have been used in 245°C

HPAL service at Moa Bay, Cuba since 1958. Titanium Gr. 1 EXW clad autoclaves

have been in 250°C HPAL service at Murrin Murrin (Minara Resources) in Western

Australia since 1999.[3] To ensure that maintenance issues are minimized it is

important that both types of lining systems are properly engineered and that suitable

fabrication techniques, quality control, and installation procedures are followed.

Refractory lining systems generally require routine inspections and maintenance

involving the cleaning and re-pointing of mortar joints on an annual basis. This

requirement varies with selected mortar (potassium silicate, litharge, furanic and

phenolic resin-based mortars) as well as actual process environments. Refractory

lining life is also limited by swelling and softening of brick in the vapour zone of

refractory sulphide pressure oxidation service, and generally requires a complete

13 of 15

face course reline every 5 – 7 years of operation. Due to these maintenance

requirements, refractory lining systems have higher associated maintenance costs.

Titanium clad lining systems are expected to have lower maintenance requirements

than refractory lined systems. However, this is only achievable with the selection of

suitable material grades for the process environment, proper vessel design, quality

assurance, and fabrication techniques. Titanium weld repair of clad vessels that

have been in service is challenging due to the environmental (cleanliness)

requirements for welding and purging.[5] If all of these factors are executed

properly, titanium clad linings are expected to provide equally long service life.

Delivery and Scheduling

Project schedule requirements should be considered in selection of a lining system

since they may limit the selection of specific lining systems. When selecting a

lining system, it is important to have a clear understanding of the material lead time,

fabrication and delivery associated with each system. A titanium clad vessel has a

longer material procurement time in receiving clad plate from suppliers, whereas a

lead lined vessel has a shorter time for material procurement, but a much longer

fabrication time due to the labour-intensive lead brazing process. Figure 4 shows

the relative fabrication, transport, and installation duration for titanium clad and

lead/refractory lined autoclave vessels.

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

Ti Flush

Batten

Ti Conv

Batten

Pb Lined

Brick Lining

Installation

Transport

Pb Lining

Vessel Fabrication

Figure 4 – Relative Schedule Duration for Ti Clad vs. Lead/Refractory Lined

Autoclave Vessels

14 of 15

A typical delivery period for a large titanium clad autoclave is in the range of 22 –

24 months. For a similar sized carbon steel, lead lined vessel, the delivery period is

estimated to be 28 months, plus 2 months to complete the brick lining on site for a

total of 30 months. Naturally, these delivery periods vary considerably and should

be confirmed for a specific project as they are dependant on vessel size, material

availability at the time of purchase, and vessel fabricator shop loading.

Conclusion

The selection of a specific lining system calls for sufficient knowledge of process

requirements related to vessel sizing, operating conditions and environments,

maintenance concerns, and fabrication and installation schedules. The relative cost

comparison presented reveals that refractory lining systems are cost effective at

lower operating temperatures and pressures over a range of vessel sizes. As process

temperatures increase, titanium clad vessels become significantly more economical.

Process environments that may require more expensive materials selection must be

evaluated on a case by case basis and have potential to significantly affect capital

costs. Maintenance requirements of refractory systems are generally higher,

although with proper material selection, design, fabrication and installation

procedures, maintenance issues can be reduced for both types of lining systems.

With a complete evaluation of operating conditions, materials selection,

maintenance, and schedule requirements, capital cost estimates can be generated

and suitable lining candidates can be selected.

15 of 15

REFERENCES

1. A. Koning and P. Lauzon, “Design Fundamentals for hydrometallurgy pressure

vessel refractory linings”, Proceedings of the International Conference on the

Use of Pressure Vessels for Metal Extraction and Recovery, 34th Annual

Hydrometallurgy Meeting of CIM, Banff, Canada, 2004, pgs. 617 - 638

2. J.G. Banker, Titanium Clad Autoclave Performance in Nickel Laterite

Hydrometallurgy, Clad Metal Products Inc., Boulder, Colorado, USA.

www.clad-metal.com

3. J.G. Banker, “Hydrometallurgical Applications of Titanium Clad Steel”, Reactive

Metals in Corrosive Applications, Sun River, Oregon, USA, 1999

4. J. DeGaspari, “Titanic Proportions”, Mechanical Engineering Magazine, March

2000.

5. W. Bristowe, A. Hanson, and M. Pearson, “Quality assurance programs for

fabrication of specialised vessels and exotic alloy piping”, Proceedings of the

International Conference on the Use of Pressure Vessels for Metal Extraction

and Recovery, 34th Annual Hydrometallurgy Meeting of CIM, Banff, Canada,

2004, pgs. 385 – 400.

ACKNOWLEDGEMENTS

The authors wish to acknowledge and thank the following people who provided

fabrication and material costs, design data, and technical support for the preparation

of this paper.

1. John G. Banker, President, CLAD Metal Products Inc., Boulder Colorado, USA.

2. R. Henson, Manager, Business Development, Uniti Titanium Ltd.

3. Julien Laermans, Commercial Manager, COEK Engineering N.V., Belgium.

4. Don Want, Engineering Manager, W.E. Smith Engineering Ltd., Coffs Harbour.

5. Paul Trotman, Manufacturing Manager, W.E. Smith Engineering Ltd., Coffs

Harbour.

A Comparison of Refractory Lined, Carbon Steel and Titanium EXW Clad Pressure Vessels for Specific Operating Conditions

S. GothardW.E. Smith Engineering Pty Ltd.

W. Bristowe, M. Pearson, C. StungurisHatch Ltd.

Introduction

Lead/Refractory Lined Autoclave

Ti Explosion Clad Autoclave

Typical Generic Membranes:• Homogeneously Bonded Lead• Panel Bonded Chemical Lead• Chlorobutyl Rubber• Bromobutyl RubberProprietary Membranes:• Derakane™ Vinyl Ester Resin• Pyroflex™ Bitumous Sheet

• Typical refractory lining system consists of an impervious membrane applied to a carbon steel shell.

• A refractory layer is applied to protect the corrosion membrane from high temperature and abrasion.

Bac

kgro

und Refractory Lining Systems

Refractory Lining Systems

Advantages• Good corrosion

resistance in sulphuric acid environments.

• Excellent abrasion resistance.

• Excellent resistance to oxidation and ignition (no pyrophoricity).

• Easy to replace damaged bricks and mortar.

Disadvantages• Requires larger vessel to

accommodate refractory.• Temperature limited by lining

stability and vessel diameter.• Refractory is susceptible to

structural damage due to rapid vessel depressurization.

• Increased maintenance costs associated with replacement of face course in 5 – 7 years.

• Refractory and mortar may be susceptible to degradation in vapor zone.

Bac

kgro

und

Metal Clad Lining Systems

• Corrosion resistant alloy is bonded to a carbon steel parent metal to protect the vessel pressure boundary.

• Preferred method of bonding is explosion cladding• Requires specialized fabrication techniques and batten

strap welding by experienced fabricators.

Bac

kgro

und

Typical Cladding Materials:• Titanium (Gr. 1, 7, 11, 17)• Zirconium• Tantalum• Ni alloy (Inconel™,

Hastelloy™)• Super austenitic stainless

steel (904L)

Titanium Clad Lining Systems

Advantages• Excellent corrosion

resistance in oxidizing environments.

• Upper temperature limit of 600°F (315°C).

• Titanium can be in direct contact with process media resulting in smaller and lighter vessels.

• Fewer limitations on transportation routes and types of transporters due to lighter vessel weight.

Disadvantages• Potential ignition in enriched

oxygen environments (pyrophoricity)

• Reduced abrasion resistance• Susceptible to pitting and/or

crevice corrosion in reducing environments.

• Susceptible to damage at free acid concentration > 10% w/w H2SO4

• Requires frequent de-scaling for corrosion inspection

• Repairs difficult to perform; require specialised welders.B

ackg

roun

d

Des

ign

Hydrometallurgical Process

Temp(°C)

PressurekPa(abs)

Typical Uses

High Pressure Acid Leach 250275

45006300

Ni Laterite ore treatment

Bayer™ Alumina Process 260280

70008000

High temperature caustic digestion

Total Sulphide Oxidation 200235

20003500

Refractory Au sulphides ore treatment

Acid Pressure Leaching 180 1730 Oxidative leaching of uranium & rare earth oreAlkaline Carbonate Leach 120 350

Freeport McMoran 160 2000 Oxidative leaching of chalcopyrite and Cu matte

CESL Process – Chloride Assisted Partial Oxidation

130155

11001275

Activox™ Process – Low Temp. Oxidation

110 1000 Oxidative leaching of Ni/Co concentrates

Operating Conditions

Des

ign

Design Conditions

Normal Operating ConditionsTemperature °C 150 175 200 225 250 275

Pressure kPa(abs) 825 1242 1905 2900 4328 6300

Maximum Operating ConditionsTemperature °C 160 185 210 230 255 280

Pressure kPa(abs) 934 1473 2258 3148 4674 6770

Design Conditions

Temperature °C 164 189 215 235 261 286

Pressure kPa(g) 963 1519 2383 3361 5041 7346

ANSI Class 150# 300# 300# 300# 600# 600#

Capital Cost Analysis

Refractory Lined Vessel

Titanium Clad Vessel

Solid Titanium Vessel

Fabrication Labour Fabrication Labour Fabrication LabourMaterials Cost Materials Cost Materials CostImpermeable

Membrane (Lead, Rubber, etc.)

EXW Cladding Exterior Thermal Insulation

Refractory Lining Exterior Thermal Insulation

All unit costs have been derived from previous project data and are corrected to Q3 2010 United States Currency using Marshall and Swift Indices.

Cos

ts

Cos

tsCapital Cost Analysis

• Equipment Data: has been retrieved from actual hydrometallurgical plants currently in service.

• Equipment Costs: based on firm and budget quotations from vessel fabricators.

• Material Costs: are based on supplier unit costs in for plate material at the time of writing.

• Vessel Fabrication: unit costs are back calculated on a fabricated weight basis.

• Membrane costs: based on previous project costs. Unit costs are back calculated on a per m2 basis.

• Refractory costs: based on previous project costs. Unit costs have been back calculated on a per m2

per course basis.

Relative Fabrication CostsC

osts

Relative Fabricated Unit Cost vs. Vessel Weight

0.0

0.5

1.0

1.5

2.0

2.5

0 100,000 200,000 300,000 400,000 500,000 600,000 700,000 800,000 900,000

Total Vessel Weight (kg)

Rel

ativ

e Fa

bric

ated

Cos

t per

Uni

t Wei

ght

Ti EXW Clad A/C'sCS/Brick Lined A/C'sCS/Brick Lined Flash VesselsCS/Brick Lined Other VesselsLog. (Ti EXW Clad A/C's)Power (CS/Brick Lined Flash Vessels)Poly. (CS/Brick Lined A/C's)

Relative Fabrication Costs

Vessel fabricated unit costs decrease as vessels get larger and heavier. This is due to the following:

• Fixed costs associated with manufacture (engineering, quality control, overhead) distributed over a larger vessel.

• The labor cost per unit weight of material is reduced on larger vessels since there is higher deposition rates from automated welding machines and higher quality of welds leading to less rework.

• Percentage of costs associated with additional material and fabrication of nozzles, clips, internals, etc. becomes smaller as vessels become larger.

Cos

ts

Component CostsC

osts

0.0

1.0

2.0

3.0

4.0

Rela

tive

Com

pone

nt C

ost

Fabrication MaterialsCladding / Membrane Insulation / Refractory

TITANIUM CLAD

REFRACTORY LINED

Design Temperature,° C

150

17

5

200

22

5

250

27

5

150

17

5

200

22

5

250

27

5

Ti Clad Vessel Relative Costs C

osts

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

02468

1012141618

Rela

tive

Ves

sel C

ost

Vessel Process Diameter, m

150° C175° C200° C225° C250° C275° C

Refractory Lined Vessel Costs

Cos

ts

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

02468

1012141618

Rela

tive

Ves

sel C

ost

Vessel Process Diameter, m

150° C175° C200° C225° C250° C275° C

Solid Titanium Alloy VesselsC

osts

Cost Comparison

70%

75%

80%

85%

90%

95%

100%

Ti FlushBatten

Ti ConvBatten

Pb Lined

Brick LiningVessel Ex Works

Autoclave cost difference based on same process volume.

Cos

ts

• Cladding Thickness• Specific Materials of Construction• Maintenance and Quality Control• Scheduling and Delivery

Cos

tsAdditional Considerations

Cladding Thickness

• All costs that have been presented use a cladding thickness of 8 mm.

• Sensitivity analysis was performed to compare 8 mm and 5 mm cladding over the range of vessels sizes presented.

• A premium of 1% to 3% of overall capital cost is paid for 8 mm cladding. This cost is mostly due to the additional material required.

• The 3% premium occurs on the thinner walled lighter vessels operating at lower temperatures and pressures while the 1% premium exists for the thicker walled heavier vessels.

Cos

ts

Materials of Construction

• Specific process environments may require ‘upgraded’ materials of construction to withstand certain corrosive environments.

• HCl, metal chlorides, and halides may require more expensive refractory materials.

• Selected membrane materials such as lead, rubber, and vinyl ester vary significantly in material and installation costs.

• More expensive high alloy grades of titanium may be required for crevice corrosion and pitting resistance in certain environments.C

osts

Material Relative Costs

Titanium Clad Lining SystemsRelative Cost

Range AverageTi Gr.1 on SA-516 Gr.70N CS 1.00 1.00Ti Gr.7 on SA-516 Gr.70N CS 1.20 - 1.04 1.12Ti Gr.11 on SA-516 Gr.70N CS 1.11 – 1.03 1.06Ti Gr.17 on SA-516 Gr.70N CS 1.12 – 1.02 1.07Refractory Lining SystemsLead / Acid Resistant Fireclay Brick 1.00 1.00Rubber / Acid Resistant Fireclay Brick 0.82 – 0.96 0.90Vinyl Ester / Acid Resistant FC Brick 0.77 – 0.94 0.87Rubber / VisilTM Brick 0.90 – 1.00 0.96Vinyl Ester / VisilTM Brick 0.85 – 0.98 0.93

Cos

ts

Maintenance & Quality Control

• Both refractory lined and titanium clad lining systems have the potential to provide dependable and satisfactory service for long periods of time.

• Both types of lining systems must be properly engineered and suitable fabrication techniques, quality control, and installation procedures followed.

• Refractory linings require routine inspections 12 –18 months apart for cleaning and re-pointing of mortar joints (varies with selected mortar & process environment).

• Titanium clad lining systems are expected to have lower maintenance requirements, however, this is only achievable with the proper selection of material grades, vessel design, QA, & fabrication techniques.

Qua

lity

Quality Control

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

ExperiencedFabricator

InexperiencedFabricator

Cost of VesselInspection

Qua

lity

Delivery and Schedule

• Titanium clad vessels have a longer lead time due to the time required for receiving clad plate.

• A typical delivery period for a large commercial scale titanium clad autoclave is 22 – 24 months.

• Delivery for a similar carbon steel, lead lined vessel is 28 months, plus 2 months for refractory lining on site for a total of 30 months.

Sch

edul

e

Delivery & Schedule

0.70

0.80

0.90

1.00

1.10

1.20

1.30

Ti FlushBatten

Ti ConvBatten

Pb Lined

Pb LiningVessel Fabrication

Autoclave delivery based on same process volume

Sch

edul

e

Project Schedule

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

Ti FlushBatten

Ti ConvBatten

Pb Lined

Brick LiningInstallationTransportPb LiningVessel Fabrication

Autoclave time to commissioning (1.00 = 90 weeks)

Sch

edul

e

Concluding Comments

• Selection of a specific lining system calls for sufficient knowledge of:– Process requirements related to vessel sizing– Operating conditions and environments– Materials selection– Maintenance concerns– Fabrication and installation schedules

• All of the above impact capital costs as well as long term maintenance costs.

• Refractory lined vessels appear to be more economical at lower temperatures over a range of vessel sizes.

• Titanium clad vessels become more economical at higher process temperatures (> 175°C).

Murray PearsonAutoclave Technology Group - Non-Ferrous

1075 North Service Road - Unit 21Oakville ON Canada L6M 2G2

Office: (905) 469-3401 Ext. 7340Mobile: (905) 484-3401

Email: mpearson@hatch.ca