Inspecting, cleaning or changing the product in a pipeline would be exceedingly difficult without a device knows as a pipeline pig, especially if the task needs to be done without stopping the flow. Pipeline pigs are capsule shaped objects which travel through the pipeline to perform the specific function(s) for which they were created. Although pig types, sizes and functions are numerous and pipeline layout is integral when choosing the appropriate one, there are three basic designs:
- Polly Foam: These open-cell polyurethane foam types have the ability to negotiate short radius bends and ells, tees, miter bends, multi-dimensional piping and reduced port valves. These pigs come in various densities depending upon their application and agility requirements, and are often used for sealing and light abrasion removal.
- Unibody: These single-body cast-polyurethane pigs are quite popular and designed to be more “aggressive” than their Polly Foam counterparts. These pigs often have a multi-disc configuration and their uses include removing liquids, separating refined products, evacuating product, controlling paraffin buildup in crude oil lines and commissioning pipelines.
- Steel Mandrel: This variety is the most “aggressive” type of pig. The configuration of the steel body allows for multiple designs for multiple purposes, but there are three basic designs that are usually available: cleaning pigs, batch and gauging, and conical cup.
The three design varieties of pipeline pigs can be outfitted to perform various tasks from a simple cleaning all the way to complex data collection. The later variety, known as “smart pigs,” are highly sophisticated instruments that include electronics and sensors that collect various forms of data ranging from location and distance to pipe defects and deformations on their trip through the pipeline. With modern smart pigs the battery powered electronics are sealed within the pig and data is recorded on a solid state device similar to a flash drive since they often can’t communicate with the outside world due to pipeline materials and location.
Each type of pipeline pig, whether it is used for cleaning, inspection or product removal/separation, needs to have the capability of being inserted into the pipeline without stopping the flow of product. This is accomplished by inserting the pig into a “pig trap” which consists of a “pig launcher” or launching station and a “pig catcher” or receiving station. The launcher is an oversized section in the pipeline, reducing to the normal diameter. The pig is inserted into the launcher which is then closed and pressurized through a kicker line. The pressure-driven flow of the product in the pipeline is then used to push it down the pipeline, performing its function until it reaches the receiving trap where it is removed. In some unusual instances a pipeline will utilize what is known as a “captive pig” where the device remains in the pipeline which is only opened occasionally to check on the condition of the pig.
There are several hazards and risks involved in pigging operations such as exposure to high-pressure hydrocarbon gas or condensate (which can also ignite), the potential loss of containment through leaking flanges or open valves, and the physical exertion required to operate manual process valves or handle the pig itself. Some precautions to observe when performing pigging operations are:
- Always wear Personal Protective Equipment (PPE).
- Minimize exposure to the open launcher barrel.
- Never assume the launcher is depressurized since pressure can build up over time.
- Never attempt to open the barrel unless you are certain it is at atmospheric pressure.
- Use a trolley to assist in the insertion and removal of a pig when possible.
- Follow manual handling requirements to avoid injuries.
As a side note, there are two theories out there on where the device came to be known as a pig. The first of these claims that since the original pigs were made from straw wrapped in wire they made a sound like a pig squealing when traveling through the pipe. The second theory is that it is an acronym for “Pipeline Inspection Gauge” or “Pipeline Intervention Gadget.”