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PROCEDURE
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PROCEDURE
FOR
CORROSION COUPON & PROBE
UIC - QP - M - 018
APPROVALDescription N a m e Signature D a t e
Approved Steve Adrianto
Reviewed Hendro Basuki
Originator PIMS Team
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TABLE OF CONTENTS
1 PURPOSE
2 SCOPE
3 STANDARD AND REFERENCE
4 COUPON AND ER PROBE MONITORING
4.1LOCATION
4.2CORROSION COUPON
4.2.1 Exposure Period
4.2.2 Care and Handling
4.2.3 Data Evaluation
4.2.4 Corrosion Rate Classification4.3ER PROBE
4.3.1 ER Probe Reading
4.3.2 ER Probe Data Analysis
5 REPORTING
6 ATTACHMENTS
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1 PURPOSE
Internal corrosion monitoring is part of corrosion control and monitoringactivities. Result of internal corrosion device such as coupon and probe will be
evaluated to measure performance of corrosion control activities then determine
further mitigation program
This procedure provides a description methodology and data analysis for
corrosion measurement using corrosion coupon and ER probes for UNOCAL
Indonesia Company.
2 SCOPEThis procedure is applicable for all probes or coupon data that have been assigned
to monitor particular pipelines or other process facilities within Unocal Indonesia
Company.
3 STANDARD AND REFERENCEThis procedure shall refer to the following reference:
Corrosion Control in Petroleum Production, NACE Publication TCP-5.
NACE Standard Recommended Practice RP-0775-99, Item No. 21017:Preparation and Installation of Corrosion Coupons and Interpretation of Test
Data in Oil Production Practice.
Patton, Charles. C.: Applied Water Technology, First Edition SecondPrinting, Campbell Petroleum Series, 1991
UIC-QP-M-016, Procedure for Corrosion Probe Removal and Installation
4 COUPON AND ER PROBE MONITORINGCorrosion coupon and probe measurements are different than physical inspection.
This method only give indication of corrosion rates and not necessarily showing
actual corrosion rates in the system. Basically, the result of corrosion
measurement will reflect corrosion rate at the devices location under specificcondition at its location.
With general limitation of this method, this method always combined with othermethod such as chemical analysis.
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4.1 LOCATION
Location of coupon or probe installation can greatly affect the result since corrosion
rate along the pipeline/system does not always uniform. Multiple coupon locationsare an approach method to adequately monitor the various environments on thesystem since corrosive condition often different on various part of the system.
In multiphase systems, devices should be installed at the location that they will be
exposed to the water present, or they will not reflect corrosion in water wet area.
Figure 4.1 below give illustration of how coupon location give corrosion rate
indication on wet gas pipeline:
Condition 1.
Coupons at location A would indicate corrosion of little to none since they are
normally not wetted by water. Coupons at position B and C would show corrosionrate because of water build up and carry over. The numerical value of the corrosion
rate may not be the same, it depend on how much position B and C exposed to
water and water wet condition have been maintained.
Condition 2
The situation is almost similar where on position A, coupon would indicatecorrosion little to none while position B and C would indicate corrosion in the
system since it was always water wet.
In general, position C is the most preferred location since it always water wet whileB become next choice if not enough clearance for installation at C position.
Position A should only be used on water packed piping where the coupon
submergence is assured.
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4.2 CORROSION COUPON
Corrosion coupon is a small piece of metal that is inserted in the systems or
pipeline and allowed to corrode. The coupons then are carefully cleaned andweighed before and after exposing in a system. From the weight loss of couponsafter particular exposure period, the rate of corrosion can be determined.
Coupon come in many shapes and sizes, and there are many types of "coupon
station" (holders). One of the critical parts of corrosion rate evaluation from couponis its material selection. The coupon should have similar metallurgy with the
systems (pipe) in study.
4.2.1 Exposure PeriodExposure period will greatly affect the measured corrosion rate. If the exposure
time is too short, measured corrosion rate would higher than actual. Commonexposure period is a month and can be extended to longer exposure period if
corrosion rate under control.
4.2.2 Care and HandlingThe handling of coupon during installation and removal can affect the result. A
drop of sweat or sweaty hand prints can increase corrosion rate at that point. A
greasy thumb print can protect or partially protect an area of the coupon.
Once the coupon removed from the system, it should be prevented from further
corrosion by put it on sealed bag/envelope then process the coupon in laboratory
immediately.
The cleaned and weighed by laboratory, the coupon shall be kept and stored inprotective envelope or wrapping (the paper envelope come from manufacturer
with coupon). It may used in the future for coupon comparison or other
assessment.
4.2.3 Data Evaluation
Calculation of General Corrosion Rate
W x 22,270Corrosion rate (mpy) =
D x A x T
Where : W = weight loss, gram
D = metal density, gram/cubic centimeter (cm3)
A = coupon surface area, square inch (in2)
T = exposure time, days
mpy = mils per year, 1 mils =1/1,000inch
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Note:
carbon steel density = 7.86 gram/cubic centimeter (gr/cm
3
) Coupon surface area should refer to manufacture data, dependon its shape.
Calculation of Pitting Penetration Rate
depth of deepest pit (measure in mils) x 365 (days/ys)Pitting rate (mpy) =
Exposure time (days)
Note:
Pit depths may be measured with a depth gage or micrometer caliper with sharp
pointer probes. A microscope calibrated for depth measurement may be used also.
4.2.4 Corrosion Rate ClassificationQualitative guidelines for interpretation of measured corrosion and pitting ratesare shown on following table:
General Corrosion Rate Pitting RateCriteria
mpy mm/y mpy mm/y
Low 0.38
Note:
Refer to NACE Standard Recommended Practice RP-0775-99, Item No.21017: Preparation and Installation of Corrosion Coupons and
Interpretation of Test Data in Oil Production Practice.
mpy = mils per year, 1 mils = 1/1,000inch
mm/y = millimeters per year
4.3 ER PROBEER probe or electrical resistance probe is often called as electric coupon. It
determines metal loss by measuring the increase of resistance of a metal specimenas its cross sectional area is reduced by corrosion.
Several types of ER probe are available on the market to fit different situations. Theforms are wire or tubular with various wire diameter and wall tube thickness. The
thinner or smaller diameter would provide greater sensitivity but reduced its life
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time. Thicker wall tube or bigger diameter would have longer life time but reduced
its sensitivity.
4.3.1 ER Probe ReadingER probe can be read using its instrument at any time. Under controlled system,reading can be taken every 2 weeks up to a month. However, if reading result
indicate high corrosion rate, reading interval should be shorter.
Noise
Sometimes ER probe reading result show inconsistent results called as noise.
Noise is erratic reading the reading would be lower or higher than actual. It
may occur due temperature effect or instrument limitation. Avoid corrosion ratecalculation between two close readings to prevent data misinterpretations.
Iron Sulfide Bridging
When iron sulfide bridging occurred the reading would significantly drop. Iron
sulfide will shunt the sensor which cause the resistance is lower than actual. Themeasured/calculated corrosion rate would be lower than actual.
If the probe suffer iron sulfide bridging, it is recommended to change the probe
type to greater resistance probe such as cylindrical element (T20) or spiral
element. (S20).
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4.3.2 ER Probe Data Analysis
Corrosion Rate Calculation
Corrosion rate from ER probe reading result is calculated refer to following formula:
0.365(Reading Final Reading initial) x probe span in milsCorrosion rate (my)
Time in days
Where:
- Reading Final is the latest reading to be used in calculation,
- Reading initial is the first reading to be used in calculation
- Probe span is the measurement span or life of the probe measure element in mils
- Time in Days is the periods in days between the Reading Finaland Reading initial
The above equation is used for calculation in mpy (mils per year) when the probe
span is in mils and the time is in days. For the units of measure o thereparameters, alternate values for the constant, 0.365 should be substituted in the
above equation.
Units of Measure Substitute value of 0.365
Corrosion rate in millimeters per year (mm/) 0.00927
Corrosion rate (mpy), Time in hours 8.76
Corrosion rate (mm/y, Time in hours 0.223
SAMPLE of CALCULATION
A T10 CORROSOMETER probe, which has a span of 10 mils, is used in a
process application. On August 2nd
the probe had reading of 72 divisions andlater in the month of August 24
th the probe had reading of 95 divisions. The
corrosion rate calculation for this period is
0.365(95 72) x 10 mils
22 days= 3.82mpy
Note:
Although the above method is suitable for calculation of corrosion rate from two
readings, it is recommended to plot all of the probe readings over time on a
graph, an then calculate the slope of the graph over the time period of interest. Ifrates are calculated from data points that are too close together, the calculated
rates may be erratic compared to the underlying corrosion rates due to noise
associated with each individual reading.
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Data Interpretation
Following are example of typical data interpretation for corrosion probe
Probe type : W40
Probe span : 10Initial installation : 2-aug-00
Date Div Check Date Div Check
2-Aug-00 80 811 23-May-01 233 810
16-Aug-00 82 811 6-Jun-01 258 811
30-Aug-00 83 810 20-Jun-01 280 811
13-Sep-00 86 811 4-Jul-01 308 811
27-Sep-00 91 811 18-Jul-01 333 81111-Oct-00 90 815 1-Aug-01 358 811
25-Oct-00 92 811 15-Aug-01 350 816
8-Nov-00 90 819 29-Aug-01 408 811
22-Nov-00 96 811 12-Sep-01 433 811
6-Dec-00 98 810 26-Sep-01 458 811
20-Dec-00 108 811 10-Oct-01 483 811
3-Jan-01 118 820 24-Oct-01 508 813
17-Jan-01 128 811 7-Nov-01 200 811
31-Jan-01 138 807 21-Nov-01 206 815
14-Feb-01 148 811 5-Dec-01 212 811
28-Feb-01 158 811 19-Dec-01 218 819
14-Mar-01 190 809 2-Jan-02 224 811
28-Mar-01 178 811 16-Jan-02 230 817
11-Apr-01 188 809 30-Jan-02 236 811
25-Apr-01 198 811
9-May-01 208 811
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Corrosion Rate Calculation (please see graph below)
Slope = corrosion rate = 0.365 x (div x probe span) : ( days)
Slope 1 = 0.365 x (DIV2-Aug-00 DIV20 Dec-00 ) x 10 : [(2-Aug-00 20 Dec-00)]
0.365 x (108 80) x 10 : [140] = 0.73mpy
Slope 2 = 0.365 x (DIV9-may-01 DIV20 Dec-00 ) x 10 : [(9-may-01 20 Dec-00)]
0.365 x (208 108) x 10 : [ 140] = 2.60mpy
Slope 3 = 0.365 x (DIV10-oct-01 DIV9-may-01 ) x 10 : (3-jan-02 9-may-01 )
0.365 x (208 108) x 10 : [ 154] = 7.17mpy
Graph 1. ER Probe Reading Data Interpretation
5 REPORTING
MI & QA shall review the test result. Please record all the observation or reading
result into standard forms then submit the forms to MI & QA. A copy of
observation result shall be kept in field for reference and database.
Please refer to form attached for regular report of coupon and ER probe.
ERP Reading Result
0
100
200
300
400
500
600
23-Jun-00 1-Oct-00 9-Jan-01 19-Apr-01 28-Jul-01 5-Nov-01 13-Feb-02 24-May-02
Time
MetalLoss
(div)
Div
Possible iron sulfide bridging
slope 1
slope 3
slope 2
noise
noise
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6 ATTACHMENTS
The following attachments are forms for regular report of coupon and probe
UIC QP INS XXXA: Form No Coupon Installation/Removal Form
UIC QP INS XXXB: ER Probe reading
COUPON INSTALLATION/REMOVAL FORM
AREA:
Probe ID Coupon Coupon Coupon Initial
Holder Type Number Weight General Appearance
LengthDiameter
Coupon RemovalPipeline
Material DateRemoval
Date
Erosion
(Y/N)
Coupon Type Coupon Installation
Final
weight
No Field
A/F
Location
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PROBE READING RESULT
AREA :
FIELD :
PROBE ID :
PROBE TYPE :
NoReading
DateDiv Check Remarks