Errors in Sampling/Monitoring in an Internal
Corrosion Program
NACE Eastern Area Conference
Lynsay Bensman
06 October 2009
Goals of Sampling/Monitoring
 Identify potentially corrosive species that may be present in a pipeline system
 Determine corrosion rate
 Determine effectiveness of mitigation
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Errors in Sampling/Monitoring
 Improper tests or equipment
 Choosing the incorrect location
 Poor timing
 Improper sampling techniques
 Improper sample preservation
 Misinterpreting results
 Missing sampling opportunities
 SAFETY
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Improper Tests or Equipment
 Using the wrong equipment for what you are actually trying to test
- Monitoring devices
 Using a kit that is not the proper range
 Using a kit that is expired or not properly working
- Check prior to going out in the field
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Monitoring Devices
 What are you trying to achieve?
 Do you need real time monitoring?
 Are you looking for pitting?
 Is erosion playing a role in the corrosion process?
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Incorrect Sampling/Monitoring Locations
 Representative or more severe than the corrosion in the system
 Not necessarily
- The easiest place
- The closest place
 Dilution effect
 How many locations is enough?
 Monitoring in conjunction with mitigation
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Monitoring Locations
 Coupons/probes on stick off the top of the pipeline are not exposed to liquids laying
alone the bottom of the line
 Coupons/probes off the bottom are not in the gas flow but allow liquids to collect if
present
 Coupons in flow should be as close to the bottom of the pipe as possible
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Poor Timing
 Liquid sample collection is not likely to yield optimum results
- Right after drip blowing or removal from separators
 At intervals that makes it difficult to interpret results
- Consideration for injection withdrawal cycles
- Consideration for chemical treatment
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Improper sampling techniques
 Waiting to perform field testing
 Performing analyses on samples that do not contain water
 Not following instructions
 Air
 Sample contamination
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Waiting to Perform Field Testing
 Reasons
- Weather
- Time
- Training
 Ramifications
- Some data is unreliable if not collected immediately
- Dissolved gases
- pH
- Bacteria culture testing
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Air
 Sample containers should be as full as possible to prevent reaction with air
 Solid samples can react with oxygen in air leading to misidentification
4FeS + 3O2
2Fe2O3 + 4S + heat
 Coupons that have been exposed to air should never be re-inserted
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Sample Contamination
 Liquid Samples
-
Should not re-use sample bottles
Grabbing a bottle that is just ‘lying around’
Not rinsing out test kit containers
Sampling from a common tank
Re-using bacteria inoculation syringes
 Pipe Samples
- External environment
 Coupons
-
Should never install a coupon if it has been dropped on the ground
Need to make sure wearing gloves when handling the coupon
Coupons should not be re-inserted if they have been removed from the system
Coupons should not be analyzed if they have been removed from the system and not
properly stored prior to analysis
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Bacteria Testing
 Perform immediately after sample collection or pipe exposure
- Prevent contamination
 Serial dilution media should match the salinity of the water present in the pipeline
 Should not expel any of the inoculation media
 Swabs need to be taken over consistent area size
 Proper labeling
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Gas Testing
 What are you actually testing?
 Need to purge sample container or testing container
 Some measurements are better performed on-site
 Storage containers for gas that may contain H2S
 What are on-line instruments monitoring
 Do you need to check for O2
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Improper Storage of Samples
 Samples need to be properly labeled (if further analysis is to be performed)
 Liquid samples should be stored in a cool environment until analyzed
 Bacteria inoculation vials should be stored at similar temperature to pipeline
operating temperature
Ok
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Misinterpreting Results
Garbage In = Garbage Out
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Misinterpreting Results
 How do operating conditions affect the results?
- Well work
- Change in flow direction
- Change in flow rate
 Iron counts
- Iron to Manganese ratios
- Correlation to corrosion
- Trending
 Bacteria
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Misinterpreting Results - Bacteria
 Planktonic
- Free floating
- Liquid sampling
 Sessile
- Attached to pipe wall
- Solids or swab sampling
 Correlation to MIC
- No known correlation between planktonic bacteria levels and the presence of MIC!!!
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Misinterpreting Results
 Do I have enough data to make a decision?
- Trending
 Do the data make sense?
- Is further investigation needed? (e.g., no liquids are recovered from drips but leaks are still
occurring in the system)
 Do the data support current monitoring/sampling and mitigation?
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Missing Sampling Opportunities
 After pigging operations
- Liquids
- Solids
- Swabs
 As pipe is being removed from system
- Liquids
- Solids
- Swabs
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SAFETY
 Safety is of primary importance!!!
 Sampling is always concern when collecting a sample from a live pipeline system
 Questions???
-
Is there potential for projectiles?
Are isolation valves shut?
Are there concerns for being sprayed with liquids?
Are there any pyrophoric materials present?
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Safeguarding life, property
and the environment
www.dnv.com
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