A pig is a cleaning or inspection device for use in pipelines . Further tasks can be the clear separation between successive product batches or, depending on the consistency of the product, support of the transport itself. As a rule, operations should not be interrupted for this. This technology is used in gas, oil and product pipeline technology.
The pig fills the cross-section of the line and either simply wanders through the line with the product flow (mostly with oil) or has to be forced through the line by means of extra pressure (water or compressed air). As part of pigging technology, sluices built into the system (called "pig trap" in technical jargon) are required in addition to the pig, through which the pig is inserted into the lines and subjected to pressure from behind, but also after completing the intended test section, can be removed. There are two fundamentally different areas of application.
Areas of application
Pigging technology is a conveying method with which (mostly valuable) highly viscous liquids , pasty media, also powder and granulates are almost completely removed from piping systems by inserting an approximately spherical object, waisted in the middle, namely the pig , through the piping system with water or compressed air is pressed and pushes the medium to be expressed in front of it.
For larger diameter pipelines, especially for gas or oil, there are pigs for various service tasks . They each consist of a round plate roughly sealing the cross-section of the line (or completely with rubber sleeves) at both ends and a thinner middle section. The pig is tailored so that it can travel through curves in the line up to a certain radius.
The following variants and procedures are only examples:
- They are used for cleaning with attached brush rings .
- In rare cases, very different (oil) batches are also separated using simple pigs in pipelines, which are sent through the pipeline one after the other and should mix as little as possible.
- Pigs equipped with complex measuring technology are real robots . B. ultrasound or eddy current probes (then with Förster probes for an eddy current test ) measure the wall thickness and thus the corrosion status of the line. Stress cracks can also be detected using ultrasound or eddy currents; one then speaks of crack detection pigs . There are now ultrasonic pigs that can measure wall thickness and cracks at the same time. Since these have to carry a large number of measuring probes and a lot of electronics and power supply, they are built much longer, sometimes also coupled together like a train of several units. When it comes to the power supply, there are two alternatives: either carrying large and heavy batteries or using a pressure wheel and dynamo to draw energy from the movement. The latter, however, is very unsafe with crude oil because of its slipperiness and the slip of the dynamo wheel. In order to be able to assign the displays found after the measurement exactly to locations in the line , pig transmitters may be placed on the outside of the line at a certain distance , which are detected by the pig when passing. A verification round can result in a data volume of several hundred gigabytes, which is saved on flash memory in order to be read out afterwards.
If there is not a sufficiently large flow to gas consumers for the controlling pigging of a gas line, it can happen that gas is released at the destination of the pigging circuit, e.g. B. Natural gas must be flared.
- Bernd Skerra (Ed.): Manual pig technology. Vulkan-Verlag, Essen 2000, ISBN 3-8027-2178-0 .
- W. Krass, A. Kittel, A. Uhde (eds.): Pipeline technology, mineral oil pipelines (= TÜV handbooks. Vol. 3). TÜV Rheinland Verlag, Cologne 1979, ISBN 3-921059-32-1 .
- Dozens of emergency calls because of ten meter flames , orf.at, June 28, 2016, accessed June 28, 2016.