Pigging is a concept in pipeline maintenance that involves the use of devices known as pigs, which clean pipelines and are capable of checking pipeline condition. This process is done without necessarily interfering with the flow of product in the pipe. Pigging is used in a number of different industries including oil & gas, lube oil, chemical plants and hygienic applications such as pharmaceutical or food. Selecting the right pig for a particular application requires extensive experience, something that Inline provides.
How Does Pigging Work
The primary purpose of pigging is to make sure that the pipe is clean and free from obstruction. The process is used to remove and possibly detect any build-ups within the pipe which can often lead to reduced performance, increased energy costs and cause corrosion which could lead to disastrous leaks and cracks in the pipe.
But how does pigging work? Here is a simple explanation:
The pigs are the maintenance devices that are used to clean and check if the pipes are in good condition and are inserted into the pipe using a pig trap. The pig trap or launcher is usually oversize to accommodate the tight fitting pig. A similar pig trap or receiver is located at the end of the pipe to retrieve the pig.
The pig is propelled through the pipeline: by the normal flow of existing product or can be driven by gas or liquid introduced specifically for that purpose. Pigs are usually cylindrical or spherical to aid movement and efficient cleaning.
Types of Pipeline Pigs
There are many different types of pipeline pig developed for many different applications.
The Foam Pig is the most basic type of pig and its purpose is to remove any debris or liquid from the pipeline.. Inline stocks a huge inventory of different types of foam pig. Bare Foam and coated pigs are used for general cleaning, batching and proving, especially after construction as they are extremely flexible; The Power Brush Pig® has brushes to remove stubborn material, typically corrosion deposits; The Foam Disc Pig is a flexible pig designed by Inline for the very efficient removal of liquids such as hydrotest water. Available in a large size range, foam pigs play an important role in the safe cleaning and proving of pipelines.
Mandrel Pigs usually consist of a metal body to which replaceable discs, cups and/or scraper brushes or gauging plates are bolted. Disc pigs such as the BD6 are ideal for liquids and wax removal. Cups are added where extra sealing or wear resistance is required and are particularly effective for accommodating pipes that are out of round. Inline’s ISTE pig consists of brushes, cups and discs and is very efficient at cleaning, liquids removal and especially the removal of black powder. Specially designed pencil brushes on Inline’s Pit Cleaning Pig® are designed to clean corrosion pitting and black powder removal.
Urethane Pigs – a more flexible pig such as the Uni-Cup Pig® is designed for cleaning, wax removal and liquids displacement, but are manufactured as a one-piece construction. All of Inline’s urethane products can be manufactured using Maxithane®, Inline’s proprietary long lasting, wear resistant formulation of polyurethane.
Important Considerations before Pipeline Pigging
In order to assess whether pigging is a viable option, there are a number of considerations that must be taken into account.. The following are some of the main pigging considerations that are commonly used by maintenance crews around the world:
What is to be achieved, the length of pipe and type of fittings to be negotiated and pressure and flow available will determine the type of pig and frequency it may be run.
Removing liquids such as water, oil, condensate or even product such as yoghurt from a line will require a high sealing pig like the Foam Disc Pig or VIPRS®. Removing wax could require more rigid discs, but with bypass to keep the wax moving ahead of the pig. Tight radius bends could require an all urethane pig like a Uni-Flex® or when frequent maintenance pigging is required perhaps replaceable discs or cups that the BD-6 has may be more economical.
Pipeline Design and Fittings The pig launcher and receiver are two important fittings in pipeline pigging. The launcher is used to introduce the pig into the pipe and the receiver collects it once the cleaning job is done. Safety closures prevent accidents happening by limiting access to the pipeline while it is under pressure to retrieve the pig and dust bags can be used to catch dust and debris removed by the pig.. Barred tees will prevent the pig inadvertently travelling into a branch line and long radius bends aid the progress of the pig.
Valve and Internal Obstructions: Pipes with varying internal diameters and valves could prove to be a challenge during pigging. In light of this, before any pigging starts, it is important to clearly establish if there are any internal features that might affect the pig’s progress. This will help maintenance crews use appropriate pigs and pigging methods.
How Is The Pig Movement Monitored?
A pig will often make a sound as it travels through a pipe and if it doesn’t a TX Transmitter can be installed into the pig. The pig can then be tracked through the pipe from above ground using an RX101 Receiver or a GeoAmp XT Geophone. Apache pigPro signalers are a reliable indicator that the pig has passed a certain point on the pipeline.
The Advantages of Using Pigging As a Pipeline Maintenance Practice
Pigging has a number of advantages compared to other pipeline maintenance options. The following are some of the advantages of using pigs in pipeline maintenance:
It’s a Cost Effective Option: Pigs can travel great distances through pipe with minimal input from operators, and clean while they travel. They can be fitted with loggers to record the position of various anomalies. Where regular maintenance is required, pigs can be run in a system and automatically launched and retrieved and even cleaned while inside the pipe.
Pigging Is Easier: Pigging simply involves launching a pig from one end of the pipe to another . The process often takes very little time and can be done quite easily. Regular maintenance crews can be trained in the operation of pigs and in establishing a pigging program tailored to their specific application.
Safer Option: Pigging is also one of the safest pipeline maintenance options. As long as the launchers and the receivers have good quality closures, the chances of accidents are considerably reduced. Training in the operation of pig traps and correct procedures is essential. Inline provides training in all aspects of pigging operations.
Summary – Pigging Best Practices
- Knowledge of the pipeline design and its fittings as well as the operational circumstances including the flow and pressures is necessary.
- The appropriate pig design is essential to achieve the required result and enable the pig to negotiate the pipeline efficiently
- The pigging process must be carried out by trained and experienced technicians.
- The pigging equipment must be good quality and in good condition