Are pipelines safe?
Yes , a properly designed and maintained pipeline is and extremely safe way of transporting hydrocarbon products such as oil and natural gas.
How do you get pigs in and out of pipes?
The pipeline is normally segmented into sections and a pig trap is fitted at the start and end of each section. The pig trap is similar to an air lock or a torpedo launch tube. It is isolated from the pipeline by a valve, so it can be depressurized to load the pig. Once loaded the trap door is closed and the trap is pressurized. With the main trap valve open, oil or gas flow can be directed behind the pig to push it into the pipeline. The reverse process applies at the other end of the line, when the pig is received.
Why are in-line inspection tools called "pigs”?
Surprisingly there is no definitive answer to this question. There are stories of the ancient Romans cleaning aqueducts using pig skins. There are also stories of pioneers using bundles of straw wrapped with barbed wire to clean out early oil pipes. The scraping of the wire in the pipe sounded like pigs squealing.
How are pigs propelled?
They are pushed through the line by the oil or gas product. Seals made of polyurethane , rubber or any other required material on the pig make it act like a piston in the pipeline.
How fast do pigs go?
Normally pigs travel through a pipeline at a walking to a running pace (0.5 to 4 m/s, 1 to 12 ft/s, or 0.7 to 8 mph). For faster flowing gas lines, the pig can be arranged to bypass some of the flow so that it does not hold back delivery.
How far do pigs go?
They are designed to travel up to 600 miles (1,000 km) in a single pass, but average pipeline sections are around 30 miles (50 km) long.
Do pigs (steel bodied) ever get stuck?
This might happen however very infrequently, this problem could be avoided by running poly foam cleaning pigs through the pipeline first, followed by a gauging pig fitted with a deformable aluminium plate machined to a specific diameter. If those pigs pass through the line without damage and correct pig is selected we consider the line as free.
What do you do when a pig gets stuck?
If a pig does get stuck it can sometimes be dislodged by increasing the pressure across it, either by raising the pressure behind it or reducing the pressure in front of it. Sometimes it can be freed by sending another rescue pig behind it to push it out, assuming the problem is damage to driving seals on the original pig. The final resort is to decommission the line and cut the pig out.
Can all pipelines be pigged?
Early pigs had a limited clearance to the pipewall. As a result, they could only tolerate limited bore variation and gentle bends. This is not the case today. Tools can now negotiate bends as tight as 1.5D bend radius and can pass dual diameter pipelines with selected type of pigs. The technology is currently available to develop solutions for most pipelines, although in some cases pipeline modifications are required.
Can pigs be used in plastic pipes?
Not at the moment. Most high pressure transmission pipelines are made of steel, and this will remain the case for the foreseeable future. Modern low pressure distribution lines are made from plastics.
Can pigs really detect stress corrosion cracking before the pipe fails?
Yes. The f.e. PII Pipeline Solutions UltraScan CD™ and Elastic Wave tools have been shown to detect stress corrosion cracking before it approaches failure level.
Do pigs damage the internal coatings of pipelines?
No. Although magnetic inspection pigs fitted with steel brushes may look like they would scrape internal coatings off a pipewall, they do not. The pig weight is spread over thousands of individual bristles, and as a result the point loadings are small. If required, special pigs such as the pin wheel pig can be designed to remove internal scale or damaged coatings.
Does the magnetization from pigs affect anything else for pipeline operation?
After inspection with a magnetic inspection pig, the pipeline is usually left in a state of low level magnetization. This can affect welding if a section has to be cut out and replaced. In this case, procedures are available to overcome the problem.
Do ultrasonic pigs need perfectly clean pipes for good results?
As with any inspection, the best results are obtained if the pipeline is clean. Ultrasonic inspection is a precise technique that can be affected more by dirt, debris and bubbles than a magnetic tool. A comprehensive range of cleaning tools are available to suit all inspection techniques, including ultrasonics.
Do pigs run away when they go down risers or hills?
Not normally. In an oil pipeline the pig is hydraulically locked in the incompressible liquid product and cannot run away. Even in gas pipelines, the force of drag against the pipewall on a magnetic pig is usually higher than the weight of the pig, so the pig may speed up but does not run away down the riser.
How do you prevent pigs from crashing into pipeline traps?
Because of its high drag, the pig needs a driving force behind it to keep it moving. Pig traps are designed with a branch tee to divert the product flow to the side before the pig touches the end of the pig trap. As a result, when it reaches this tee, the pig loses its drive and stops before it hits the trap door. It can then be maneuvered into position to be removed from the trap.
Can pigs miss defects?
All pigs are designed against a target inspection performance. The first step in the inspection process is to develop an inspection specification which, if achieved, means that no defect that could lead to pipeline failure remains undetected. Since there are many types of defects, including all forms of corrosion and cracking, there are also several types of pig with performance tuned for a particular type of defect. Provided the full range of pigs are available, all common types of defect can be detected before they grow sufficiently to cause a pipeline to fail.
Is it possible to have an all-in-one pig?
Although not yet developed, there is no technological reason why an all-in-one tool could not be produced. This would be an expensive development and would require more changes to the pipeline than conventional pigs, such as longer pig traps to accommodate the extra technology. In most cases, individual pipelines are susceptible only to a limited group of defects, and an all-in-one tool would be an expensive option.
What sizes of pig are available?
We offer mechanical pigs from 4” to 56” in (100 to 1400 mm) in diameter and Poly foam pigs from 1” to 100” ( 25 to 2500 mm)
What advantages do ultrasonic tools offer?
Ultrasonic wall thickness tools give a direct reading of pipewall thickness. This direct reading is not susceptible to vehicle settings or interpretation. As a result, corrosion growth comparisons from one run to the next can be exact. This makes the technique ideal for baseline surveys. Ultrasonic techniques also work well in thick wall pipe, and are the technique of choice in inspecting the very thick walls of nuclear reactor vessels. This makes them the best inspection technology for very heavy wall offshore pipelines. For the detection of cracks, ultrasonic techniques are the very best since ultrasound reflects even tight cracks and does not depend on metal loss to produce a signal. Ultrasonic tools are also very good at finding laminations.
What advantages do magnetic tools offer?
The magnetic flux leakage (MFL) technique is very robust. The action at a distance nature of magnetization means that the technique works even if dirt or debris are between the magnetic sensors and the pipewall. The technique is precise enough to allow high resolution inspection from many sensors. MFL inspection is rapid, with speeds as high as 15 ft/s (5 m/s).
How are pigs powered?
Pigs take their power from on-board battery packs (usually lithium cells). Before these high energy cells were available, we used on-board power generators to supplement rechargeable nickel cadmium batteries.
How much data do pigs collect?
The larger diameter pigs can collect more than 500 gigabytes of data. On-board data compression is used before the data is stored, usually on magnetic storage media, but also on solid state flash memory storage for high temperature applications.
Can pigs inspect flexible pipes?
Inspection pigs can pass through flexible pipes, but the complex construction of flexible pipe makes it difficult to inspect. Techniques have been developed, especially in Norway, for detecting breaks in the steel strain members and damage to the stainless steel liners. This is an area of development as usage of flexible pipes appears to be growing, especially as exploration moves to deeper waters. We do not offer inspection of flexible pipes at present.