What’s the Difference?
Pigging in Processing Applications, and Pigging in the Utility Industries.
Pipeline pigging is used in a wide variety of industries for a wide variety of products, and for a wide variety of different reasons. Since its inception, however, it has roughly split in to two branches: pigging systems for the process industries such as food, beverages, paint, cosmetics, personal care or household products, and those in the utility industries such as oil, water, waste and sometimes gas.
Although there is some overlap in the design, technology and objectives of each branch of pigging, there are also some major differences.
This article looks at the similarities and differences of pigging systems in the processing industries, (including sanitary or hygienic applications), and those used in utility applications.
Origins of Pigging
Pipeline pigging originated in the utility industries, in particular oil and water. The first ‘pigs’ were fairly crude contraptions made from bundles of cloth, rags or even straw held together with cord or wire. The purpose of these early pigs was pipeline cleaning: removing debris and deposits that had built up on the inside of the large diameter pipes.
Since then, pigging, product recovery and pipe cleaning technology has progressed a long way. Today, there’s a marked difference between pipeline pigging systems used in the utility industries and those used in liquid product processing.
Pipeline Size and Length
In the utility industries, the diameter and lengths of the pipelines (and hence the pigs) tend to be much larger than in liquid processing and manufacture. For example, transmission lines for oil and gas are often around 457 mm (about 18 inches) in diameter, and sometimes as large as 1219 mm (or 48 inches). Pipeline lengths in these industries are often cited in kilometres or miles, as opposed to feet or metres in the processing industries. In process applications, pipeline diameters and corresponding pig sizes typically range from just 25 mm (approximately 1 inch) to 203 mm (approximately 8 inches).
Objectives of Pigging
The key objectives of pigging, and so the design of the pigs, also tends to be different. In utility pigging, pigs are still used to clean the inside pipes. Cleaning pigs for utility applications usually include brushes and cleaning plates. However, they can also be used to inspect the condition of the inside of pipelines. These types of inspection pigs contain electronic inspection and sensing equipment, and can be highly sophisticated instruments. This has given rise to the terms ‘Smart Pigging’ and ‘Intelligent Pigging’.
There is a wide variety of reasons why organisations that process liquids deploy pigging systems. Key objectives for pigging systems in the process industries are usually a combination of increasing yields (and hence profits), reducing waste, improving green credentials, speeding up changeovers and reducing cleaning times. These benefits are usually achieved through product recovery.
Hygienic and Sanitary Pig Design
Although pipe cleaning is an integral function of modern sanitary or hygienic pipe pigging equipment, industrial process pigging systems are usually designed for product recovery more than pipe cleaning alone. In these systems, pigs for liquid processing tend to use interference fits to remove residual product that remains in pipelines after a particular process or product run. By recovering nearly all product inside the pipe, the pig is in effect cleaning it. However, instead of the product being removed from the inside of the pipe and disposed of, it’s perfectly useable so can be sold. So, while pipeline cleaning is part of the process, the key objective is usually product recovery.
Although not ‘intelligent’, pigs for industrial liquid processing are highly developed pieces of equipment and are nearly always detectable. For example, HPS pigs contain a flexible, magnetised silicon core. When in close proximity to a pig detector, an electronic signal is produced to enable semi or full pigging system automation and control. This flexible silicon core is a major advantage. Not only does it enable detection and hence PLC or software control, but because they contain no solid magnets, the pigs are extremely safe. They can also travel around pipe bends with no loss of performance. In addition, they are manufactured using food grade, FDA approved material, enabling their use in sanitary or hygienic environments.
Focus of Process Pigging
Every company is different. So while some businesses may focus on saving useable product from being flushed to waste, others may focus on saving water or improving process efficiency. The more valuable the product being processed, the more important product recovery becomes. However, on low-value products, the onus is often on reducing water consumption, using less cleaning fluids or speeding up processing and improving overall efficiency. Product recovery in process applications using pigging also has a positive environmental impact.
Similarities and Differences
There are some similarities and cross-over between utility and process pigging. For example, some types of oils and oil-based products are pigged using process pigging systems. Some process systems do use pigs purely for cleaning the insides of the pipe and not for product recovery. However, there are many differences between pigs and pigging systems used in industrial liquid processing applications and those used in the oil and utility industries, and this article has by no means covered them all. Safety procedures, pig detection, propellants, launching, receiving, storage, maintenance and many other factors vary considerably between the two.
In summary, pipeline pigging for large diameter pipes, such as those in the oil industry, is usually focused on pipeline cleaning and pipeline inspection. While cleaning is an integral part of process pipe pigging, the key objectives tend to be more focused on product recovery, increasing yields, improving efficiency and reducing waste. The design, application, and control systems are also significantly different.
Specialists in Product Recovery
HPS Product Recovery Solutions specialises in Pigging and Product Recovery Systems for the process industries, including food, alcoholic beverages, soft drinks, cosmetics, personal care, household goods, paints, coatings, varnishes and similar. With thousands of customer across the globe, HPS has improved the productivity, efficiency and profits of a massive range of organisations processing an extremely diverse range of liquids.
For more information about pigging solutions for your organisation, including troubleshooting systems that aren’t performing to your expectations as well as new pigging system design, then please get in touch.