| Troubleshooting of various pigging problems can be very frustrating. This is because the problems encountered are not necessarily due to the pig as the client suggests. Although related, normally the real problem lies elsewhere.
Sometimes it requires a well-founded knowledge of how pigs perform under varying pigging conditions, (including a pig’s limitations), an understanding of pipeline fittings, equipment, and physics to successfully identify the true problem. Other times it takes a lot of luck.
Although there are many reasons for pigging problems, we find that misapplication (the incorrect pig selection for a particular function) is the most common, with improper pressures and volumes running a close second. Lack of operator training and understanding is usually to blame.
Unfortunately, some operators have had barely enough experience in pigging within a single application or single industry to assume all pigging operations are the same. Others have heard experienced-pipeliner tales that helped them form a misunderstanding of general pigging procedures. They then attempt to over-compensate for the misconception and usually result in causing the problem they were trying to avoid, or a completely different problem all together.
General rules regarding pigs include:
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Standard utility pigs, including foam pigs, steel pigs, and solid-cast pigs, bypass a small portion the propelling medium during the pig run. This bypass averages anywhere from 2% to 15%, depending on the type of pig. It is important to note that when a pig displaces liquids during a run, there will normally be a wetted surface left on the pipe wall. However, if the propelling medium is air or nitrogen, an evaporation or drying process may take place rather quickly. Sometimes it is reported that the pigs are bypassing or leaving large quantities, as much as 25%, of the product in the pipe after having made a displacement run. Once an understanding of how pigs work in a pipeline is achieved, it is apparent that this is an indication that the problem may lie in the mechanical portion of the system, such as piping configurations. |
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All pigs – regardless of style – are 1% to 5% oversize (i.e. larger than the internal pipe diameter). Often times, operators feel that if a pig fits in the pipe tightly, it is too large, but without the oversize it cannot do the job intended and a large amount of bypass will occur. |
Trouble-Shooting Guide
Following are many problems that have been experienced during usage of pigs, and recommended steps to take to solve the problem. Remember, pigs are not a difficult item to use once an understanding of how they work is gained. The key element is to ask questions (a lot of questions), and then apply reason, coupled with knowledge to arrive at a logical solution.
Please review the following examples to suit your current problem. If not found, click on the "Contact Us" link at the top of the web page, and tell us your specific problem in the "Additional Comments" box. We will answer you immediately.
Also, if you would like to offer any additional remedies to any of the following trouble-shooting tips, we would greatly appreciate it.
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Problem: Pig Does Not Leave The Launcher. |
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Possible Causes and Solutions: |
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Inadequate volume and pressure is being applied to pig.
Increase volume and pressure slowly, being sure to monitor pressure gauge for excessive pressure buildup.
Valves on launcher are not properly configured.
Shut down pigging operation. Reconfigure valves and resume pigging operation.
Source of propellant (pump, compressor, etc.) is not functioning properly.
Inspect propellant source and correct.
Pig is not properly sized and is bypassing propellant.
Verify by measuring diameter of pig. If smaller than internal diameter of pipe, replace pig with one that is properly sized.
Pig is behind launch line on launcher.
Push pig in front of launch line and properly seat it in the reducer portion of the launcher.
Pig is not seated properly in reducer portion of launcher.
Push pig until it properly seats in reducer portion of the launcher. A pig snubber, (device used to resist back pressure during launching procedure), may be needed.
Pig has defect and is allowing bypass.
Inspect pig for defects (tears, holes, out-of-round section, etc.) and replace with new pig, if necessary.
Improper launching sequence is allowing backpressure to unseat the pig in the reducer portion of the launcher.
Confirm and perform proper launching sequence. A pig snubber, (device used to resist back pressure during launching procedure), may be needed.
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Problem: Pig Does Not Enter The Receiver. |
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Possible Causes and Solutions: |
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A valve on a lateral line has is partially or completely open. Pig may have possibly entered side branch, or pig passed branch and product is flowing into it rather than pushing pig.
If flow is not being received at receiver, then pig possibly passed tee and did not try to enter. Ensure valves on all lateral lines are closed. Resume pigging operation. If flow is being received at receiver, then pig possibly tried to enter tee. If possible, try reversing flow from branch side of tee. Resume pigging operation. If unsuccessful, removal of the tee may be needed to extract pig.
The valve on the bypass line on the receiver is partially or completely closed.
Completely open valve on bypass line on the receiver.
Inadequate volume and pressure is being applied to pig.
Increase volume and pressure slowly, being sure to monitor pressure gauge for excessive pressure buildup.
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Problem: Pig Is Moving, But Has Bypass During Run. |
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Possible Causes and Solutions: |
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The outer diameter of the pig is smaller than the internal diameter of the pipe, and therefore does not create a proper seal. This may be due to an improperly sized pig, defects, excessive wear, damaged pig (from obstruction, such as large debris, partially closed valve, etc.), or trouble in negotiating a fitting, such as a tee or elbow.
Launch a swab through the line to re-establish seal. Upon retrieval, inspect pig for cause of problem. Replace with a new pig, properly sized pig, or better-suited pig. Also, inspect receiver for evidence of obstruction, and inspect piping and fittings.
Section of line has larger internal diameter.
Launch a swab that is large enough to accommodate the suspected larger internal diameter. If unsuccessful, launch a properly designed multi-diameter pig through the line.
Inadequate volume and pressure is being applied to pig.
Increase volume and pressure slowly, being sure to monitor pressure gauge for excessive pressure buildup.
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Problem: Pig Has Stopped In Line With No Flow Bypass. |
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Possible Causes and Solutions: |
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The pig is unable to negotiate a fitting, such as a tee, ell, valve, etc.
Increase volume and pressure slowly, being sure to monitor pressure gauge for excessive pressure buildup, or try reversing flow.
The valve on the bypass line on the receiver is partially or completely closed.
Completely open valve on bypass line on the receiver.
There is an obstruction in the pipeline.
Increase volume and pressure slowly, being sure to monitor pressure gauge for excessive pressure buildup, or try reversing flow, or try reversing flow.
Source of propellant (pump, compressor, etc.) is not functioning properly.
Inspect propellant source and correct.
Inadequate volume and pressure is being applied to pig.
Increase volume and pressure slowly, being sure to monitor pressure gauge for excessive pressure buildup.
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Problem: Pig Has Stopped In Line With Minimal Flow Bypass. |
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Possible Causes and Solutions: |
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The outer diameter of the pig is smaller than the internal diameter of the pipe, and therefore does not create a proper seal. This may be due to an improperly sized pig, defects, excessive wear, damaged pig (from obstruction, such as large debris, partially closed valve, etc.), or trouble in negotiating a fitting, such as a tee or elbow.
Launch a swab through the line to re-establish seal. Upon retrieval, inspect pig for cause of problem. Replace with a new pig, properly sized pig, or better-suited pig. Also, inspect receiver for evidence of obstruction, and inspect piping and fittings.
Section of line has slightly larger internal diameter.
Launch a swab that is large enough to accommodate the suspected larger internal diameter. If unsuccessful, launch a properly designed multi-diameter pig through the line.
Source of propellant (pump, compressor, etc.) is not functioning properly.
Inspect propellant source and correct.
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Problem: Pig Has Stopped In Line With Maximum Flow Bypass. |
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Possible Causes and Solutions: |
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The outer diameter of the pig is smaller than the internal diameter of the pipe, and therefore does not create a proper seal. This may be due to an improperly sized pig, defects, excessive wear, damaged pig (from obstruction, such as large debris, partially closed valve, etc.), or trouble in negotiating a fitting, such as a tee or elbow.
Launch a swab through the line to re-establish seal. Upon retrieval, inspect pig for cause of problem. Replace with a new pig, properly sized pig, or better-suited pig. Also, inspect receiver for evidence of obstruction, and inspect piping and fittings.
Section of line has larger internal diameter.
Launch a swab that is large enough to accommodate the suspected larger internal diameter. If unsuccessful, launch a properly designed multi-diameter pig through the line.
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Problem: Cannot Locate Pig, But All Operating Conditions Are Normal. |
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Possible Causes and Solutions: |
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Construction material of pig may not be compatible with product.
Test construction material sample with product. Make necessary changes if required.
Pig may never have launched.
Verify pig launched by looking inside launcher. If present, repeat launching procedures.
A valve on a lateral line has is partially or completely open. Pig may have possibly entered side branch.
Because all other operating conditions are normal, check downstream of tee branch for pig. On subsequent pig runs, ensure valves on all lateral lines are closed, and replace tee with pigging tee style.
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Problem: Product Left In The Line After Pig Is Received. |
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Possible Causes and Solutions: |
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A valve on a lateral line has is partially or completely open. Pig is not entering line, but after pig passage, product from lateral line is flowing into mainline.
Ensure valves on all lateral lines are closed. Launch another pig.
Even though all valves are closed on lateral lines, the space from tee to lateral line valve may be substantial. After pig passage, product from lateral line is flowing into mainline.
Launch another pig.
The outer diameter of the pig is smaller than the internal diameter of the pipe, and therefore does not create a proper seal. This may be due to an improperly sized pig, defects, excessive wear, damaged pig (from obstruction, such as large debris, partially closed valve, etc.), or trouble in negotiating a fitting, such as a tee or elbow. This is allowing product in front of the pig to work its way behind pig.
Upon retrieval, inspect pig for cause of problem. Replace with a new pig, properly sized pig, or better-suited pig. Also, inspect receiver for evidence of obstruction, and inspect piping and fittings.
The speed of the pig may be excessive, and allowing pig to hydroplane over product.
Calculate pig speed. Make appropriate corrections.
If dewatering line with air, the water vapor in propellant is condensing to a liquid.
Install a filter on compressor, or use nitrogen.
Pig may never have launched.
Verify pig launched by looking inside launcher. If present, repeat launching procedures.
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Problem: Excessive Pigging Pressure Is Experienced During Pig Run. |
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Possible Causes and Solutions: |
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Outer diameter of pig is larger than industry standard over-sizing, or construction materials of pig are too hard.
If pressures are not dangerous, continue pigging operation. On subsequent pig runs, reconsider pig diameter or density of construction material.
The product does not provide lubricity.
Depending on application and pig, a small amount of lubricating product can be added.
The valve on the bypass line on the receiver is partially or completely closed.
Completely open valve on bypass line on the receiver.
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Problem: Extremely Low Pigging Pressure Is Experienced During Pig Run. |
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Possible Causes and Solutions: |
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Outer diameter of pig is smaller than industry standard over-sizing, or construction materials of pig are too soft.
On subsequent pig runs, reconsider pig diameter or density of construction material.
The outer diameter of the pig is smaller than the internal diameter of the pipe, and therefore does not create a proper seal. This may be due to an improperly sized pig, defects, excessive wear, damaged pig (from obstruction, such as large debris, partially closed valve, etc.), or trouble in negotiating a fitting, such as a tee or elbow.
Launch a swab through the line to re-establish seal. Upon retrieval, inspect pig for cause of problem. Replace with a new pig, properly sized pig, or better-suited pig. Also, inspect receiver for evidence of obstruction, and inspect piping and fittings.
A leak exists in the pipe or fittings.
Inspect entire pipe length, all valves and fittings for leaks.
A valve on a lateral line has is partially or completely open. Pig may have possibly entered side branch, or pig passed branch and product is flowing into it rather than pushing pig.
If flow is not being received at receiver, then pig possibly passed tee and did not try to enter. Ensure valves on all lateral lines are closed. Resume pigging operation. If flow is being received at receiver, then pig possibly tried to enter tee. If possible, try reversing flow from branch side of tee. Resume pigging operation. If unsuccessful, removal of the tee may be needed to extract pig.
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