Pipeline pig is a device used to perform various operations within a pipeline without stopping the flow of the product. These operations include cleaning, inspection, batching, and displacing liquids or gases. Pigs are typically inserted into a pig launcher and propelled through the pipeline by the flow of the product, with specialized features like cups, discs, brushes, or electronic sensors depending on their specific function. They are an essential tool for maintaining the integrity and efficiency of pipelines, ensuring safe and optimal transport of materials.
Pig Types
- Utility Pig (General Purpose) - A general-purpose device used in pipelines for routine maintenance and operational tasks. These pigs are typically made from materials like foam or solid polyurethane and are designed to perform basic functions such as cleaning (removing light debris or residue), dewatering (removing water from the line), drying, and batching (separating different products flowing consecutively through the pipeline). Their design prioritizes versatility and the ability to navigate various pipeline conditions, making them a common and cost-effective solution for everyday pipeline operations.
- Foam Pig - A versatile device used in pipelines for cleaning, batching, and drying. It's made from an open-cell polyurethane foam, which gives it a spongy, compressible nature. This flexibility allows the foam pig to navigate variations in pipe diameter, bends, and even some obstructions without getting stuck. They work by being propelled through the pipeline, typically by the product flowing through the pipe or by air pressure, and their design allows them to scrape and wipe the internal surface of the pipe, removing debris, liquids, or other unwanted materials. Different densities and coatings of foam can be used depending on the specific application, ranging from soft, low-density foam for light cleaning or drying to more abrasive, higher-density foams with external coatings for tougher cleaning tasks.
- Solid Cast Pig - A robust and durable pipeline pig designed for heavy-duty cleaning, batching, and product removal applications. Unlike foam pigs that are made from compressible foam, solid cast pigs are manufactured as a single, integral piece from specialized polyurethane elastomers, often in varying durometers (hardness) to suit specific pipeline conditions. This solid construction provides superior tear strength, abrasion resistance, and excellent sealing capabilities. Solid cast pigs typically feature cup-shaped or disc-shaped sealing elements, or a combination of both, which create a tight seal against the pipeline's internal wall. This design ensures highly effective cleaning and product separation.
- Spherical (Ball) Pig - A type of pipeline pig that is, as its name suggests, spherical in shape. Made from a durable, solid polyurethane elastomer, these pigs are highly flexible and conform to the internal shape of the pipeline. They are commonly used for a variety of tasks, including batching, liquid removal, and product separation. Spherical pigs are typically inflated with a liquid (like water) or gas (like air) to achieve the desired diameter and sealing force against the pipe wall. This adjustability allows them to create a tight seal, even in pipelines with varying internal diameters or significant ovality. Because they roll through the pipe, they can effectively push liquids, separate different product batches, and provide a light cleaning action by wiping the pipe's interior surface.
- Cleaning Pig - A specialized device engineered to remove debris, deposits, and foreign materials from the interior walls of a pipeline. Unlike general utility pigs, cleaning pigs are specifically designed for more aggressive scrubbing and scraping actions. They often feature components like brushes (wire, nylon, or stainless steel bristles) or scraper blades to dislodge and push out accumulated substances such as wax, scale, rust, and other unwanted buildups that can restrict flow or corrode the pipeline. By maintaining a clean internal surface, cleaning pigs help to optimize pipeline efficiency, prevent blockages, and ensure the integrity of the transportation system.
- Brush Pig - A cleaning device used to perform various maintenance tasks. Essentially a cylindrical device with brushes, scrapers, or other tools attached to its exterior, it's inserted into a pipeline and then propelled through it by the flow of the product (oil, gas, water, etc.) or by a pressurized fluid. The primary purpose of a brush pig is to clean the internal walls of the pipeline, removing accumulated debris, wax, scale, rust, and other deposits that can restrict flow, reduce efficiency, and potentially lead to corrosion. Besides cleaning, different types of pigs can be used for tasks like inspecting the pipeline for anomalies, batching different products, or dewatering pipelines after hydrostatic testing.
- Scraper (Line Scraper) Pig - A specialized device used to clean the internal walls and remove various accumulated deposits. It's typically a cylindrical tool with an exterior equipped with blades, brushes, or other scraping element. Propelled by the flow of the product within the pipeline (like crude oil, natural gas, or refined products) or by an external fluid under pressure, the scraper pig travels through the pipe. As it moves, its scraping components make direct contact with the pipe's interior surface, effectively dislodging and removing substances such as wax, scale, rust, debris, and other contaminants. This cleaning action helps to maintain the pipeline's efficiency by preventing blockages, optimizing flow rates, and reducing pressure drops. Beyond cleaning, scraper pigs can also be used for tasks like separating different products within a multi-product pipeline, or for preparing a pipeline for inspection or maintenance.
- Mandrel (Steel-bodied) Pig - A type of cleaning or utility pig, distinguished by its solid steel body or mandrel. This internal structure allows for the attachment of various external components, such as replaceable cups, discs, and brushes, which can be configured to suit specific pipeline maintenance needs. The key advantage of a mandrel pig lies in its modularity. As the external wear parts (cups, discs, brushes) wear down during operations, they can be easily replaced, effectively redressing the pig and extending its lifespan significantly. This makes mandrel pigs a cost-effective solution for long-term pipeline integrity management. They are commonly used for tasks like general cleaning, liquid displacement, product separation, and the removal of stubborn deposits like wax, scale, and black powder. Their sturdy construction and customizable elements also make them suitable for gauging pipelines to detect internal bore restrictions or deformations.
- Inspection (Smart/Intelligent) Pig - A sophisticated device equipped with advanced sensors and designed to gather detailed data about the internal condition of a pipeline. Unlike utility or cleaning pigs, their primary purpose is not to clean but to detect and assess various anomalies and defects within the pipe wall and structure. These pigs utilize technologies such as magnetic flux leakage (MFL) to identify metal loss due to corrosion or pitting, ultrasonic testing (UT) for precise wall thickness measurements, and caliper tools to detect and measure dents, ovalities, and other geometric deformations. The data collected by inspection pigs is crucial for pipeline operators to assess integrity, predict potential failures, and schedule timely repairs, thereby ensuring the safe and reliable operation of the pipeline.
- Magnetic Flux Leakage (MFL) Pig - A smart pig used for inspecting pipelines to detect and characterize flaws, primarily metal loss due to corrosion, pitting, or cracks. It works by magnetizing the pipe wall as it travels through the pipeline. Powerful onboard magnets create a strong magnetic field within the ferromagnetic material of the pipe. If there are any anomalies, such as areas where the metal has thinned due to corrosion or has a defect, the magnetic field is distorted and leaks out of the pipe wall. Highly sensitive sensors located on the MFL pig detect and measure these leakage fields. The data collected from these sensors is then analyzed by trained technicians to determine the location, type, and severity of the defects, providing crucial information for pipeline integrity management and maintenance planning. MFL pigs are particularly valuable because they can inspect pipelines while they are in operation, minimizing downtime.
- Ultrasonic Testing (UT) Pig - Used to measure the wall thickness and detect internal and external defects such as corrosion, cracks, laminations, and gouges. Unlike magnetic flux leakage (MFL) pigs which detect metal loss indirectly, UT pigs work by emitting high-frequency sound waves (ultrasound) from transducers mounted circumferentially around the pig's body. These sound waves travel through the pipe wall and are reflected back to the transducers. By precisely measuring the time it takes for the sound waves to travel through the pipe wall and return, the pig can directly calculate the wall thickness at thousands of points along the pipeline. Any variations in this travel time or distortions in the reflected signals indicate the presence and location of defects. UT pigs are particularly effective for quantitative measurement of metal loss, providing accurate sizing of anomalies, and are often used to verify or supplement data from other inspection methods like MFL. They are crucial for maintaining the integrity and safety of pipelines, especially those transporting hazardous materials.
- Caliper (Geometry/Deformation) Pig - A pig specifically designed to measure the internal diameter and detect deformations within a pipeline. It operates by having multiple mechanical arms or fingers that extend outwards and maintain contact with the inner wall of the pipe as the pig travels through it. Each arm is connected to sensors that precisely record its position relative to the pig's central axis. As the pig moves, any change in the pipeline's internal geometrys, uch as dents, ovalities, wrinkles, buckles, or other bore restrictions caused by external forces or manufacturing defects will cause these arms to move inwards or outwards. This movement is continuously recorded, allowing for a detailed profile of the pipeline's internal shape. The data collected is then analyzed to identify the exact location and severity of these geometric anomalies, which are crucial for ensuring pipeline integrity, preventing blockages, and facilitating the passage of other inline inspection tools.
- Internal Measurement Unit (IMU) Pig - A pig to precisely map the three-dimensional (3D) trajectory and geometry of a pipeline. It's crucial for understanding pipeline movement, bending strain, and accurate location mapping, especially in environments where GPS signals are unavailable, such as underwater or buried pipelines. The core of an IMU pig consists of accelerometers and gyroscopes, and sometimes magnetometers. As the pig travels through the pipeline, these sensors continuously measure its linear acceleration and angular velocity in all three dimensions. By integrating these measurements over time, the IMU can calculate the pig's position, velocity, and orientation. This data provides a highly accurate as-built map of the pipeline's path, identifying any subtle shifts, deformations, or changes in curvature caused by ground movement (geohazards), temperature fluctuations, or third-party interference. The information gathered by IMU pigs is invaluable for pipeline integrity management, enabling operators to predict potential issues, plan proactive maintenance, and ensure the safe and efficient operation of the pipeline. IMU data can also be combined with other inspection technologies, like MFL or UT, to provide a comprehensive picture of pipeline health.
- Special Purpose Pig - A pipeline pig designed for a specific, often unique, task beyond the general functions of cleaning, utility, or routine inspection. These pigs are developed to address particular operational challenges or to perform highly specialized activities within a pipeline. Their design and functionality are tailored to achieve precise outcomes for specific pipeline conditions or operational requirements.
- Gauge (Proving) Pig - A pig designed to verify the minimum internal diameter of a pipeline and detect any obstructions or deformations that could impede the passage of other, more sophisticated pigs (like smart pigs for inspection) or hinder product flow. It typically consists of a pig body fitted with one or more slotted metal plates, usually made of aluminum, which are slightly smaller than the pipeline's intended minimum internal diameter. As the gauge pig is propelled through the pipeline, if it encounters any restriction such as a dent, buckle, accumulated debris, or an improperly installed valve, the gauge plate will deform or bend at that specific point. After the pig is retrieved, the deformed plate provides clear evidence of the location and severity of the restriction. This information is crucial for ensuring that the pipeline is clear and ready for subsequent operations like cleaning, inspection, or the safe passage of larger in-line tools.
- Batching Pig - A pig primarily used to separate different products within a multi-product pipeline, or to separate product from a fluid used for maintenance activities like hydrostatic testing or dewatering. Unlike cleaning pigs, batching pigs are typically designed with multiple sealing cups or discs, often made of polyurethane, that create a tight seal against the pipe wall. This tight seal prevents the intermixing of the fluids on either side of the pig as it travels through the pipeline, ensuring product integrity and minimizing contamination. For example, a batching pig might be used to separate different grades of refined petroleum products (like gasoline from diesel) or to separate a liquid product from a slug of water introduced for cleaning or testing. By keeping the products distinct, batching pigs help to reduce product degradation, minimize the need for reprocessing, and optimize pipeline efficiency. They are a fundamental tool in the operation of multi-product pipeline.
- Dewatering Pig - A specialized type of pig primarily used to remove water or other liquids from a pipeline, typically after hydrostatic testing, cleaning, or a repair. The goal is to dry the pipeline interior to prevent corrosion, prepare it for gas service, or introduce a different product. These pigs are designed with multiple sealing cups or discs, often made from durable polyurethane, that create a very tight seal against the inner pipe wall. As the pig is propelled through the pipeline by air, nitrogen, or a subsequent product, it effectively pushes the water or liquid slug ahead of it, expelling it from the system. The multiple cups ensure a more thorough and efficient liquid removal compared to a single-cup design. Dewatering pigs are in commissioning new pipelines, recommissioning pipelines after maintenance, or whenever a pipeline needs to be completely free of residual liquids before being put into service or having a specific product introduced.
- Gel Pig - This is a unique type of cleaning or treatment pig consists of a highly viscous, often thixotropic (shear-thinning) liquid or semi-solid gel. Unlike traditional mechanical pigs made of solid materials, gel pigs are flexible and conform to the internal shape of the pipeline, making them ideal for pipelines with irregular internal diameters, sharp bends, or restricted access where conventional pigs might get stuck or cannot be easily launched/received. Gel pigs are pumped into the pipeline and propelled by the flowing product or an external fluid. As they move, their viscous nature and often sticky consistency allow them to adhere to and carry away debris, wax, scale, rust, and other contaminants. They can also be formulated with chemicals for specific treatments, such as corrosion inhibition, dewatering, or even removing stuck mechanical pigs. A significant advantage of gel pigs is their ability to be launched and received without the need for traditional pig traps in some cases, as they can be injected and extracted more easily. Furthermore, some gel pigs are designed to dissolve or break down in the pipeline's product or at certain temperatures, simplifying their removal.
- Bi-directional (bi-di) Pig - A type of pig specifically designed to be symmetrical, allowing it to be propelled and effectively perform its function when pressure is applied from either direction within a pipeline. This unique capability provides significant operational flexibility, as it eliminates the need to remove and re-launch the pig at the end of a run if the flow direction needs to be reversed or if the pig gets stuck and needs to be pushed back. These pigs typically feature multiple sealing cups or discs arranged symmetrically around a central body, ensuring a tight seal against the pipe wall regardless of the direction of travel. Bi-directional pigs are widely used for various tasks, including: hydrostatic testing, product separation, debris removal/cleaning, air or water displacement, and emergency recovery. Their versatility and ability to operate in both directions make them an indispensable tool for efficient pipeline operations and maintenance, especially in complex pipeline networks or situations with limited access points.
