Pipeline internal surface cleaning
Types of cleaning works
All types of cleaning may be performed using cleaning pigs:
Cleaning after construction. Removal of debris from the pipeline and dents identification.
Pre-inspection cleaning. Assuring the best inspection results.
Routine cleaning. Corrosive buildups removal from product to minimize corrosion.
Cleaning per operating indications. Removal of auxiliary buildups creating bottlenecks, including removal of sand and clay, wax, etc. to maintain design flow rate.
|Paraffin||Sand and clay||Paraffin|
Cleaning pig is equipment very flexible in application, easily customized for specific tasks, polyurethane discs and cups with highest wearing capacity allow performing cleaning works in practically any medium.
Cleaning pigs used by NTC Neftegazdiagnostika proved themselves as having great inline cleaning efficiency. Cleaning pigs are designed so that optimum cleaning results are achieved at any pipeline conditions and circumstances, such as standard (R=3D) or narrow (R=1.5D) elbows, different types of debris, like heavy buildups, wax, scale, etc.
NTC Neftegazdiagnostika uses:
- Cast foam (urethane-foam) cleaning pigs — fig. 1
|fig.1 Cast foam pigs|
- Cup cleaning pigs
- Disc cleaning pigs
NTC Neftegazdiagnostika has 4 to 14 inch cleaning pigs available on one through bolt and 6 to 56 inch multiple-bolt pigs with 2 guides and 4 seal discs (fig. 2) or 2 cups instead of seal discs.
fig. 2 Multiple-bolt pig for long sections with discs and gauging plate
For long sections long distance pigs (fig.2) are recommended to be used. This pig type is equipped with 4 cups, 4 guiding discs and 4 seal discs.
Cleaning pigs with a pig tracking transmitter (fig.3) are available for the range of 4 to 12 inches as a transmitter-pig or cleaning pig coupled with a transmitter-pig; for 14 or more inches – with a removable transmitter installed using a crossover flange – more details are provided below. All cleaning pigs may be used for both underground (offshore) and aboveground pipelines. The transmitter allows tracking the pig movement route and will show the stuck pig location if required. The transmitter operating time is 175 – 250 hours.
Cleaning pigs selection
Pigs with discs ideally suit for pipeline drying and commissioning and for product metering as well as for general cleaning. Standard pig configuration is bi-directional and provides for high cleaning level.
Guiding discs are made of high strength low wear polyurethane. They provide for the pig alignment in the pipeline, bear the pig weight and clean dirt from pipeline walls.
Seal discs are bigger in size than guiding ones and are also made of high strength low wear polyurethane. Seal discs function is creating pressure drop, for that purpose they should fit truly against the pipeline walls. In addition seal discs remove accumulated dirt, dust, wax and debris from the pipeline.
Cup pigs are unidirectional. They ideally suit for use at low pressures. This type of pig is recommended to be run one of the first, especially in the situations when the pipeline was not cleaned for a long while, thus, it is not clear what volume of dirt accumulated inside. A risk of such pig sticking in the pipeline is minimum due to this pig low cleaning capacity and to the cup “bouncing” effect.
Cleaning pigs tooling
Depending on the pipeline contamination level cleaning pigs may be equipped with different tools, such as:
- Gauging plate (fig.2)
- Pig tracking transmitter
- Pressure valve
If required the above tools may be combined.
|fig. 3 Cleaning pig with a transmitter, brushes and magnets.|
Gauging plate contains raw data about any major bottlenecks in the pipeline and possibility of the following pigs unrestricted run through the pipeline. Normally the gauging plate is only used during the first and second pig runs.
Spider creates turbulence preventing dirt and wax accumulation in front of the pig.
The pig with brushes very effectively cleans hard buildups from pipeline walls.
The pig with magnets collects and removes from the pipeline metal debris, such as welding rods, braces, bolts, etc. High level of cleaning is reached due to use of powerful magnets.
Pig tracking transmitter
Cleaning pigs may be equipped with a transmitter to track them. Thick wall pipes, stainless steel pipes and even double wall pipes are no obstacle for the transmitter operation. The transmitter is used as a marker to locate the stuck pig or to identify exact time of pig passing the specified check point.
The transmitter sends out low frequency signals. These signals pass through the pipe wall and soil layer up to 8 meters deep and are detected by an electronic receiver EPD II within a radius of 10 m.
If due to the stuck pig pipeline pressure rises the valve opens and flow is restored.
Pig parts parameters
Pigs used for cleaning, gauging and product metering are made of materials per the below specification (it applies to a specific model/configuration):
- Material mainly consists of low wear polyurethan
- Shore hardness А : 85 +/- 5
- Mechanical properties are listed in table 1.
- Material mainly consists of low wear polyurethane. Shore hardness А : 65 +/- 5.
- Material mainly consists of low wear polyurethane. Shore hardness А : 85 +/- 5. Mechanical properties are listed in table 1.
Polyurethane mechanical properties
Guiding discs, cups
|Properties:||Measuring unit||Testing per standard||Value||Value|
|Shore hardness||Shore А||DIN 53 505||85(+/-5)*||65(+/-5)*|
|Density||g/cm3||DIN 53 479||1,247||1,242|
|Tensile strength||N/мм2||DIN 53 504||> 40||> 30|
|Ultimate elongation||%||DIN 53 504||> 450||>400|
|Elasticity||%||DIN 53 512||30||60|
|Fracture toughness||N/мм||DIN 53 515||> 40||> 20|
|Wear resistance||mm3||DIN 53 516||< 30||< 25|
|Compression set||%||DIN 53 517
20%, 20 °C, 72 hours
20%, 70 °C, 24 hours
|Temperature range||°C||от –40 до +70|
Spacing discs — polyurethane.
Gauging plates — aluminum alloy: AlMg3.
All pig metal parts (body, flanges, spider) are made of St. 37/St. 52 steel. Head bumper is made of metal or polyurethane.
- Ring brush: cold-drawn steel wire
- Spring type brush: cold-drawn steel wire, fixed on round springs
Permanent sintered ferromagnets enclosed in the stainless steel body.