QP-018, Quality Manual Procedure for Coupon and Probes Monitoring

8/12/2019 QP-018, Quality Manual Procedure for Coupon and Probes Monitoring

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UIC - QP - M -018

Rev : 0 Date: Nov 14, 04

Unocal Indonesia Co.

PROCEDURE

FOR

CORROSION COUPON

& PROBEPage 1 of 12

QP-018/SA

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

Documents

QP-018, Quality Manual Procedure for Coupon and Probes Monitoring