An Overview of Pipeline Pigs used in Processing Industries.
Pigging works by using specialist projectiles (the ‘pigs’) to remove every last drop of useable liquid from within the inside of pipelines. Pigging is usually performed when liquids are changed over, processing has finished or the pipes are due to be cleaned. Typically, ‘every last drop’ means removing over 99% of the product left in the pipe.
A wide range of industries and processes use pigging-based product recovery systems. These industries are as diverse as food, drink, household goods, personal care, oils, paints, solvent production and many others. They generally share the common aim of using pigging to ensure that nearly all the liquid processed is used and not wasted. In other words, to recover product that would otherwise be flushed away or disposed of.
This article provides an overview of pipeline pigs used in processing industries. It covers what they do, what they are made of, how they work, and some interesting facts you might not have thought of.
Pigging System Components
There are many components in pigging-based product recovery systems. There are the pipelines of course, plus pig launchers, receivers, detectors, pig housing, propellant source, PLCs, control software, and various valves and fittings. And that’s just in a straightforward single-pig system. For more complex setups, such as tank drop-off pigging and double pig systems, there are more components and factors to consider.
Arguably though, the most important component of any type of pigging system are the actual pig (or pigs).
What Does a Pig Do?
Pipeline pigs are projectiles that the system propels through the pipeline. Propellants can be gas (depending on the application this is usually air, nitrogen or carbon dioxide), or a liquid such as water, or sometimes the next product in the process.
The pig has an interference fit which creates a strong seal with the inside of the pipe. This ensures no propellant or product bypass. So, as the pig travels along the pipe it forces all residual liquid out with it (or in front of it). This product is in perfectly useable condition so can be collected or sent to the next process.
Pig Construction and Shape
There are several types of process pig available. Generally, the simpler the shape, the more robust, reliable and effective the pig will be. Pigs that have complex external profiles, have fins, or elongated shapes, are more prone to getting stuck in pipes and more prone to damage; they may have pieces break off them, wear more quickly or become dented. To put this in perspective, HPS pigs, which have a relatively simple external profile, are so robust and long-lasting that they are guaranteed for 18 miles or 30 kilometres of pipeline travel. This is something way ahead of other pig types.
Additionally, the HPS pig is bi-directional, a design element that reduces the risk of injury to workers and potential contamination of the pig itself. By using a bi-directional pig the entire pigging process can be automated, speeding up the process even more.
Pig effectiveness comes down to a lot more than profile. However, HPS Pigs are solidly constructed and are shaped and designed from specialist materials. Their basic construction consists of a flexible, magnetised silicone core with a thick outer coating of FDA approved material. The precise outer material specification depends on the application, for example, food-grade pigs are different from those used with solvents.
Some types of pigs have a smooth finish, but the outside of HPS sanitary pigs has a special textured finish. This has been developed over a number of years to ensure the most efficient and highly effective product removal.
The design and construction ensures they can be used in sanitary, hygienic and other applications while recovering the maximum amount of product (up to 99.5%). The design also ensures they are detectable, can be steam cleaned, and are safe.
How Heavy is a Pig?
At first glance, HPS pipeline pigs may just look like lumps of plastic. However, one of the first things people notice when they pick up a pig (other than that it feels soft) is its weight. They’re heavier than expected because they’re made of silicone rubber with a flexible, magnetised silicone core. For example, the weight of a 4 inch (roughly 102 mm) pig, which is one of the most commonly used sizes, is about 1.4 kilogrammes, or just over 3 pounds. The largest commonly used pig in hygienic and sanitary applications from the HPS range is 8 inches long. It weighs around 14 kilogrammes, which is over 30 pounds.
Low-Pressure Propulsion
While they may seem heavy, weight is important to ensure optimum performance of the system. In contrast though, HPS pigs do not need high pressures to propel them. The actual pressure required depends on a variety of factors including the density of product, diameter of pipe and so on. However, the pressure required to propel HPS pigs is deliberately kept low. This reduces the use of propellants, lowering running costs saving resources.
Flexible Magnetic Core
In processing applications, pig tracking and pig detection is achieved through magnetisation. The majority of pigs used in processing applications contain solid magnets. The problem with pigs containing solid magnets, particularly in hygienic and sanitary applications, is if the pig gets damaged, overly worn or broken. In this case, the solid magnet, or parts of it, can become separated from the pig, break out and contaminate the line or product. This is why HPS pigs contain a flexible, silicone-based magnetic core. Not only does this minimise contamination risks (it doesn’t break or shatter), it also increases the robustness and reliability of the pigs and ensures they continue to be effective when travelling around pipeline bends.
What’s The Dot For?
HPS pigs have a round mark at one end. This mark has a specific purpose. We’ll leave you to guess what this purpose is! Why not contact us via one of our social media channels and tell us your best guess?
Unique Pig Design
Of course, there are other hygienic and sanitary pigs available from pig manufacturers other than HPS. However, the HPS pig design is unique. There’s really nothing like it. We believe it is the most effective, safest, robust and reliable pig, with the widest range of applications. We can retrofit our pigging systems on existing equipment, or build it into a new plant.
For more information about pigs and pigging systems, then please get in touch.