There are multiple stories in the industry of how they got to be called “pigs”, but the one that sounds the most plausible is that in the early 1900’s heavy crude oil pipelines experienced problems with paraffin buildup that restricted flow.  Some workers began fashioning leather balls bound with barbed wire and sending them through the line to clear the buildup.  As the cleaner negotiated the line, it made a squealing sound.  Also, when it was removed from the line and deposited on the ground (along with a healthy amount of oil), it looked like a pig in the mud.

The industry standard for optimum pig speed is approximately 3 to 5 feet per second.  Pigs can be used at lower and faster speeds, but each may experience inherent problems associated with perspective speeds.  For slower moving pigs (below 1 foot per second), it is possible that the pig will bypass (allowing the propellant to circumvent the pig) more than is being supplied to push the pig and the pig could become stuck.  For faster moving pigs (10 feet per second or faster), a different problem can be experienced.  The pig can actually shrink slightly and hydroplane over the product, thereby leaving a large amount of product left in the pipe after pigging.  For additional information, see Stuck Pig under Pigging Papers and Pigging Pressure Chart under Technical Papers in our Resources library.

No one can calculate exactly how much pressure is required to push a pig through a pipeline because there are so many different variables: pig diameter, type of pig, internal pipe diameter, type of product, the product’s viscosity, quantity and type of buildup, etc.  One slight change in any of these variables will change the pressure required. See our Pigging Pressure Chart under Technical Papers in our Resources library.

Because the outside diameter of a pig is larger than the internal diameter of the pipe, launchers and receivers are preferred for pigging operations.  Pigs can be manufactured to special diameters to facilitate hand-launching, but will not be as effective as standard-sized pigs.  Visit Technical Papers in our Resources library for Launching & Receiving Procedures.  There are also a few “field techniques” associated with pigging without launchers/receivers.  Please contact us to see which may suit your application best.

We have a specific Pigging Paper detailing various remedies for stuck pigs and we’re always here to assist you with any problems you may experience during pigging operations.  But if you’re asking this question because you’ve never pigged before, you’re anticipating a pig becoming stuck and want to know what to do, let us assure you that with proper pig selection and pigging procedures, stuck pigs are extremely rare.  Please contact us so we can help familiarize you with pigging techniques and pig selection to make your pigging experience a pleasant one.  For additional information, see Stuck Pig under Pigging Papers and Pigging Pressure Chart under Technical Papers in our Resources library.

The polyurethane foam and solid-cast urethane (for coating, solid-cast pigs and the cups & discs for steel pigs) actually perform very well for most chemical applications.  The reason for this is because of time.  Generally a pig is moving at 3 to 5 feet per second.  Therefore for every hundred feet of pipe, a pig is only being subjected to the chemical for 20 to 33 seconds.  Even an open-cell foam can withstand sulfuric acid for such a short period of time.  However for other applications, solid-cast pigs manufactured from rubber compounds (viton, neoprene, nitrile, epdm) can be used or equipping steel pigs with rubber-compound cups or discs.  Please contact us to determine which pig type will best suit your specific application.

Gauging plates are used for proving there are no deformations in the pipe, checking for ovality and pipe roundness, and checking for proper bend radius.  Gauging plates are generally manufactured from aluminum and are mounted to steel pigs for use. 

The outer diameter of gauging plates generally range between 90% to 92% of the pipe’s internal diameter.  As high as 95% of the pipe i.d. is sometimes used for special applications, but never more.  They generally are manufactured from aluminum (but steel can be used too) and have a 30- or 45-degree bevel on the face.  Sometimes they are slotted as well.  For thicknesses:  1/8” thickness is used for 2” to 4” pigs; 1/4” thickness is used for 6” to 24” pigs; 3/8” thickness is used for 30” and above.

Spring-loaded brushes easily win this contest because the tension of the spring keeps the brush in constant contact with the wall of the pipe even as the brush wears.  However, sometimes circular brushes are the only candidate.  Examples: 

• Small-diameter pigs – For 2” to 4”, the pigs are too small for spring-loaded brushes. Pig designs do exist for 6” to 14” pigs, but the overall length of the pig can be too long to negotiate a 1.5-D bend.
• Solid-cast pigs – Most designs cannot accommodate spring-loaded brushes
• Bidirectional pigs – Most springs are a cantilever type and attach to the pig at one end of the spring. If pigging direction is reversed, the springs could get caught while negotiating fittings (such as valves) and break.
• Tight-radius piping – Puts too much pressure on the spring while negotiating the tight bend and can break the springs.

Generally speaking, “yes” because for years there has been an industry standard for the bolting patterns for cups & discs.  However, in the last few years, some manufacturers have adopted bolting patterns for small-diameter pigs (6″ – 14″) where they used to just have a center hole.  Also, some companies have also changed bolt patterns for various sizes & various reasons.  Luckily, if our standard cups & discs are not compatible with your bolt patterns, we can modify our mold and pour parts to fit.

Pigs are generally designed for a one-time use, especially foam pigs.  However, after the initial pig run and upon a very thorough inspection of the pig (being sure to check pig diameter to ensure it is still larger than the internal diameter of the pipe; checking for cuts, tears, excessive abrasion along the sealing length or sealing elements; the overall structural condition of the pig; etc.), you feel that the pig can be used again, it is your choice.  But we would like to give this word of caution.  Given the overall cost of a pigging project (especially in new pipeline construction), the cost of one pig is very minimal — especially with foam pigs.  Is it worth running the risk of getting a pig stuck and having to spend a lot of time and money just to save a few dollars?