Pigging FAQ

Launchers and receivers provide the easiest form for launching and receiving pigs. The reason that launchers/receivers are preferred to launch/receive pigs is mainly due to the design of a pig. In order for a pig to perform properly, the outer diameter (o.d.) of the pig needs to be larger than the internal diameter (i.d.) of the pipe. Unfortunately, this “oversizing” (which as an industry standard is anywhere from 1% to 5%, with 2% being optimum) makes it very difficult — if not impossible — to manually insert a line-size pig into a line-size pipe.

Although pigs can be manufactured to any diameter to facilitate being directly loaded into the pipe by hand, a pig with an o.d. that is equal-to or smaller-than the i.d. of the pipe will permorm marginally at best. With this being said, there are “field techniques” available to assist in launching/receiving pigs without launchers/receivers. For more information on these techniques, please send us an inquiry.

Also, be sure to visit the “Pigging Papers” section of our website to download proper Launching and Receiving procedures.

The optimum speed for pigs is approximately 3 to 5 feet per second. Over the years this has proven to yield the best results for pigging operations. Pigs can be used at lower speeds (even as low as 1 foot per second) but it must be understood that the pig will experience a “stop & go” effect, which could allow the pig to become stuck.

If a pig is going slower than 1 foot per second, then it means that the propelling medium is slowly having to build up enough volume and pressure to overcome the frictional drag of the pig to move the pig. When it finally reaches this threshold, the pig lunges forward a short distance and the process is repeated. Even if no problems are encountered during the pig run, the pig’s performance will be very low whether the application is cleaning, batching, displacement, etc.

Because all pigs bypass (propellant circumventing the pig), it is possible in low-flow applications that the pig may allow more propellant to bypass the pig than is being supplied behind the pig. If this becomes the case, the pig will stop moving and be considered a “stuck” pig.

A different problem can be encountered if moving too fast. Anything above 10 feet per second can cause the pig to “hydroplane”. During this pigging phenomenon, the pig finds that it is physically easier to slightly shrink in its diameter and only push out a certain volume of the contents of the pipe, rather than remain full size and push out all. Although this is mainly found in foam pigs, it does not reside only with foam pigs. The same has been found in steel and solid-cast pigs.

To determine what volume of liquid or gas is needed to properly propel a pig at the recommended velocity, please be sure to visit the “Pigging Papers” section of our website and download the Pigging Pressures and Volume Chart.

Possible Causes and Solutions :
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.

The design of a spring-loaded brush is such that as the brush wears, the spring pushes the brush against the pipe wall for constant contact and pressure, because of tension on the spring. Although this is easily superior in design to circular and wrap-around brushes, sometimes other factors forbid or encumber the use of spring-loaded brushes. Some examples include: Small-diameter lines — It is impossible to have spring-loaded brushes on a 4″ pig. Tight-radius bends — These present a problem by putting too much pressure on the spring thereby over-stressing or breaking the spring. Bidirectional use — Most spring-loaded brushes are attached to the pig at one end. If moving in the opposite direction, the brush can snag during negotiating valves and other fittings resulting in spring breakage.
Possible Causes and Solutions :
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

Gauging plates, used in proving pipe roundness, bend radius and for determining if deformations exist in line, are smaller than the internal diameter of the pipe. Gauging plates can be manufactured to any diameter, but it is general practice for the diameter of the plate to be 90% to 92% of the internal diameter of the line. For special applications, the diameter can be up to 95%, but it should never be more.

The government has recently passed new regulations concerning pipeline risk assessment. They have declared that over the next seven years, ALL pipelines should be assessed. Although they are not mandating pigging, it will be required in order to properly assess the conditions of the pipelines. The mandate states that within the first 3-1/2 years, 50% of all pipelines must be assessed, with the remaining 50% being accomplished within the following 3-1/2 years. We assume, from past experience, that most companies will wait until the last minute, so two years from now should be phenomenal in sales. However, some companies are taking steps to begin with the assessment process.
As always, we will be keeping you up-to-date of any news.
YFor chemical-resistant applications, our standard urethane used in our foam pigs, solid-cast pigs, as well as the cups and discs for the spare components of our steel pigs, weather very well against most chemicals. However, for certain chemical another compound may be needed, such as neoprene, nitrile, epdm or viton. For such applications, we have very comprehensive chemical charts for proper selection. Unfortunately, these chemical charts are primarily used for o-ring selection, which is not the same application for pigging. O-rings are in constant with the chemical, whereas pigs moving through the line at three to five feet per second, are in contact with the chemical for a relatively short time. Furthermore, in some operations, it is only required that a pig be sent through the line one time. So, if a pig with neoprene cups can effectively pig the line, but cannot be used again, it served its purpose. Within the industry, this is referred to as “sacrificial pigging”. Some believe that viton is the best choice for any chemical application. It is true that viton´s chemical-resistance is very high, but its cost is also very high. Conversely, its wear-resistance is very low. Considering the parameters of an operation, even one that is routine in nature such as maintenance pigging, if the cost of a pig with viton cups is four to eight times the cost of a pig with neoprene cups, and the neoprene-cup pig only performs “half” as well as the pig with viton cups, the customer would be saving
No mathematician, scientist or engineer can answer this question. The reason for this is because there are too many variables, including pig type, the o.d. of the pig, product type, product viscosity, temperature, build-up quantity, etc. Charts are available in the “Pigging Papers” section of this website with general guidelines and approximate pressures and volumes needed to propel pigs.
Possible Causes and Solutions :
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.

Possible Causes and Solutions :
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.

Possible Causes and Solutions :
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.

Possible Causes and Solutions :
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.

Possible Causes and Solutions :
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.

Possible Causes and Solutions :
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.

Possible Causes and Solutions :
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.