What is pipeline pigging?
What in the world is pigging? You may be picturing a nice sunny day out the in country. As you’re walking along a pipeline, you hear some faint, hollow oinks coming from inside the pipe. The oinks get louder and eventually pass by, and as you’re left staring the pipe in disbelief. Was there a pig inspecting that pipe?
Well, pigs do inspect pipes, but probably not the kind you’re thinking of now. PIGs are Pipeline Inspection Gauges, also called scrapers. Basic pigs perform maintenance on pipelines like simply cleaning the inside of the pipes while smart pigs can inspect pipes for integrity and problems. Pigs clean out pipes when buildup occurs and slows down movement inside, and prevent cracks or flaws from becoming disasters.
Image Credit: Wikipedia
Squeal: Why are they called pigs?
As we mentioned earlier, the official title for a PIG is “Pipeline Inspection Gauge” or sometimes “Pipeline Intervention Gadget”. However, these may back backronyms and there is another origin for the name. Early pigs were reportedly made with hay and barbed wire as well as leather. The resulting sound from pushing these pigs through the inside of the pipes is a noise that sounded like a squealing pig. There are reports that pigs still make still squeal due to the plastic on metal or metal on metal friction of them travelling down a pipe.
Ready for launch: How does a pig work?
They enter the pipeline through a pig trap (yes, that’s the real name). The trap includes a pig launcher and a pig receiver (yep, we’re launching pigs). Once inside, the pigs can travel with the fluid or be pulled by a cable or other device if needed. Either way, flow is not usually interrupted while the pig is in use. Shaped like a cylinder or sphere, they run through, scraping or inspecting the inside of the pipes.
Image Credit: Wikipedia
A variety of pigs: How many different types of pigs are there?
At first, pigs were just used for cleaning, but as technology advanced, pigs became more advanced as well. Utility pigs are used for simple cleaning of lines, removing substances like wax and other buildup inside the pipes. Lines also need to be pigged after construction to remove any leftover debris before the pipeline is actually put into use. Sealing pigs can remove liquid or serve as a barrier between different types of liquid inside a pipe.
Image Credit: Enbridge
Smart pigs gather data and inspect pipes. According to RigZone, “The type of information gathered by smart pigs includes the pipeline diameter, curvature, bends, temperature and pressure, as well as corrosion or metal loss.” They can use magnetic flux leakage (MFL) and ultrasonics (UT) to gather information about the pipe. MFL uses magnetic flux to determine if there are any leaks, imperfections, or problems in the pipelines. UT uses ultrasonic sounds to measure the thickness of the pipe by recording the time it takes the sounds to get back to the sensor.
Specialty pigs like plugs can stop a line so maintenance can be performed. Gel pigs are actually gelled liquids, and have some interesting uses “including product separation, debris removal, hydrotesting, dewatering and condensate removal, as well as removing a stuck pig”, according to RigZone. No one wants a pig stuck in their pipe!
Image Credit: STi Group
How often should we launch a pig?
A regular maintenance program with pigs keeps buildup to a minimum by keeping flow rates high, reducing equipment stresses, and spreading corrosion inhibitors. Depending on the pipelines and the product being moved through it, pigging can be needed several times per day or only once per year. Setting the schedule is important and best left to the pigging experts. According to Sheena Engledow, sales director of Pigs Unlimited International, “The biggest misconception would be that one pig and one run is all that is needed to do the job, and any pig will do the job.” So you must choose your pig wisely.
Pigs have environmental benefits. As mentioned above, they clean lines creating greater efficiency in the movement of product. Smart pigs inspect pipes and identify potential problems and disasters before they happen. Increased efficiency means less energy and better inspection of pipelines means safer for the environment due to less spilled chemicals. However, before pigging, clearing out a pipe meant flushing a cleaning agent through the pipe. This required solvent recovery and potential contamination of the next batch of product. Whether a solvent was used or the last product was simply flushed with the new one, downgrading the batch of product or simply dumping it was the common solution. Modern pigging systems are very precise, eliminating these problems and reducing waste.
Image Credit: EarthWorks
Flying pigs! How to safely launch and retrieve pigs
While a few systems use a “captive pig” where the pipeline is only checked occasionally to determine the condition of the pig, most systems use pigs that are loaded and removed after use, many being rented instead of purchased. In a normal system, pigs are loaded into a launcher and pressurized to launch the pig through kicker line into the pipeline. At the end of the run, the pig is removed at the receiver. However, sometimes there is a blockage, so many systems are designed to operate in either directions so the pig can be received at the launcher.
The barrel has to be depressurized before opening. If it isn’t fully depressurized, the pig can be ejected out of the barrel, very dangerous to people nearby. An incident in Arkansas saw a line opened while still pressurized, shooting a 150-pound pig 500 feet into a nearby house. This was an isolated incident, and proper safety precautions are followed to prevent flying pigs!
Check out the short video below of a pipeline pig being prepared for action!
It’s Fun Fact Friday, have a great weekend!
Disclaimer: No real pigs were required or even asked politely to enter any pipes. No pigs were harmed in the making of this blog post.
Pig with blue discs photo By Wilfra - Own work. Photo taken at and with kind permission by de:Nord-West-Oelleitung, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6214395