Pipelines are a fundamental part of the oil and gas industry and they are by far the primary transportation method for crude oil, natural gas and even the refined product. However, building a pipeline network is a massive project and though most pipelines ultimately “pay for themselves” with the product they transport, they are still an expensive investment. It is essential for this investment to be well maintained and monitored. One of the most effective ways of doing that is with PIGs and the PIG launchers and receivers that facilitate them.
What Are PIG’s?
PIG’s are devices that are inserted into pipelines and used to clean, inspect, or maintain the pipeline as they pass through it. They may also be used to separate different batches or types of product within the pipeline. For effective movement through the pipeline they are usually cylindrical or spherical and may be bullet shaped.
PIG’s were traditionally used in the oil industry for large diameter pipelines. However, because of their useful qualities and the benefits they bring to pipelines, they have begun to be used in a very broad range of pipelines from small to large diameter. Nowadays they are also by no means found only in the oil and gas industry; they can be found in use at many plants and industrial sites and are effective just about anywhere a pipeline is in use. For example PIGs and PIG systems may be found in operation at plants and factories that process lubricating oils, toiletries, paints, a host of different chemicals, consumer cosmetics, and even foodstuffs.
Because the demands placed on PIGs are so diverse, the PIGs themselves may be made out of a wide variety of different materials. Often some type of steel is used and depending on requirements and budgetary concerns it could be stainless steel, duplex stainless steel, low-strength carbon steel, high-strength carbon steel. Again depending on how corrosive the materials the PIGs will be coming into contact with are, the PIGs may also be coated with corrosion-resistant materials or other specialty coatings. In addition to steel, PIGs may also be made out of polyurethane foam and other material types.
The earliest PIGs were likely made of straw and wrapped in wire to facilitate pipe cleaning. Conventional wisdom holds that it was from this early use that PIGs get their name since the squealing sounds they made as they passed through the pipes reminded people of the sounds a pig makes. The industry term PIG is likely a backronym and it is generally explained to mean ‘Pipeline Inspection Gauge;’ however, some people also use it to mean’ Pipeline Intervention Gadget.’
A special type of PIG called a “Smart PIG” puts a more high tech spin on things. This type of PIG has special electronics and sensors that allow it to not only clean and maintain the pipeline but to also gather additional information about the condition of the pipeline itself such as surface pitting, corrosion, cracks, or weld defects. This information is usually gathered using magnetic flux leakage (MFL) PIGS or PIGS equipped with electromagnetic acoustic transducers.
What are PIG Launchers and PIG Receivers?
In simplest terms the PIG launchers and PIG receivers are the sections of the pipeline which allow the PIG to enter and exit the pipeline. They are generally funnel, Y-shaped sections of the pipe which can be pressurized or depressurized and then safely opened to insert or remove PIGs. Most pigging systems use bidirectional launchers and receivers that can work in either direction. This is important to allow the PIG to be retrieved by the launcher if there is a blockage in the pipeline which prevents it from reaching the receiver.
PIG launchers and receivers come with safety valves and locking system to prevent accidents. They are also optimized to be suitable to the pressure and temperature requirements of the pipeline. Launchers and receivers may be horizontal or vertical depending on the needs of the pipeline.
Some launchers are designed to hold multiple PIGs at once and configured to launch them according to preset conditions. This is very useful because it allows much of the work to be done remotely. Additionally it prevents the launcher from having to be depressurized and repressurized again each time a single PIG is needed. It is the pressure from the flow of product that moves the PIGs through the pipeline. Thus one of the main roles of launchers and receivers is to safely interface between the low-pressure outside world and the high-pressure pipeline.
How Do PIG Launchers and Receivers Work?
The exact procedure for operating a PIG launcher or PIG receiver will vary somewhat depending on the particular pigging system being used. However, for the most part it will include the following steps:
Launcher:
- Pipeline operator should make sure that the isolation valve and kicker valve are closed.
- If the system is a liquid system then the drain valve and vent valve should then be opened to allow air to displace the liquid; if the system is a gas system then the vent should be opened so that the launcher reaches atmospheric pressure.
- After the PIG launcher is completely drained to 0 psi, with the vent and drain valves still open, the trap door should then be opened.
- The PIG should then be loaded with its nose in contact with the reducer.
- Closure seals and other sealing surfaces should be cleaned and lubricated as needed and then the trap door should be closed and secured.
- The drain valve is then closed and the trap is slowly filled by gradually opening the kicker valve.
- Once filling is complete the vent valve is closed so that the pressure will equalize across the isolation valve.
- The isolation valve is then opened and the PIG is ready for launching.
- Next the main valve is gradually closed, increasing the flow through the kicker and behind the PIG until finally the PIG leaves trap altogether and enters the pipeline itself.
- After the PIG leaves the launcher the mainline valve is fully opened and the isolation valve and kicker valve are closed.
Receiver:
- The receiver should be pressurized.
- The bypass valve should be fully opened.
- The isolation valve should be fully opened and the mainline valve partially closed.
- Once the PIG arrives the isolation and bypass valves should be closed.
- The drain valve and vent valve are then opened.
- Once the trap is fully depressurized to 0 psi the trap can be opened and the PIG removed.
- The closure seal and other sealing surfaces should be cleaned and lubricated as needed and the trap door should then be re-shut and secured.
- The receiver should then be repressurized and returned to its original condition.
These processes may differ somewhat on different systems and of course if the launcher will be launching multiple PIGs then they should all be loaded at the loading stage.
Why Are PIGs and PIG Launchers and Receivers Important?
There are four main benefits for using PIGs:
Separation – PIGs can be used to physically separate different products within a pipeline. Without PIGs the pipeline would need to either be flushed out between products, or a portion the second product would be contaminated with the first product. Both options would result in waste. With PIGs acting as separators, however, this problem is eliminated.
Cleaning and Maintenance – PIGs clean the pipeline by scraping away building up and debris and pushing it safely into the receiving trap. This improves the efficiency and flow of the pipeline and helps prevent corrosive damage to the pipes.
Inspection – Smart PIGs using technologies such as MFL and ultrasonics can inspect the pipeline for welding defects, cracks, pitting, and other problems. Caliper PIGs can also take estimates of the internal geometry of the pipeline.
Positioning and monitoring – Smart PIGs not only inspect and retain the data about the pipeline, they can also provide information about where the particular defect or trouble area of the pipeline is located. This prevents unnecessary digging up of healthy parts of the pipeline and if a problem isn’t severe enough to warrant replacing, it also allows the trouble section to be closely monitored and the PIG results to be compared across multiple time frames to track damage progression.
PIG launchers and PIG receivers are integral to the pipelines pigging system. Their safety valves, security locks, and ability to pressurize and depressurize provide a safe way for the PIGs to be loaded and removed without danger to the pipeline and equipment or human personnel. STI Group provides its customers with high quality, dependable PIG launchers and PIG receivers that can be used in standalone systems or as a skid mounted unit.
