Inspection of non-piggable pipelines






INSPECTION OF NON-PIGGABLE PIPELINE

A piggable pipeline is a pipeline that is designed to allow a standard inspection tool to negotiate it, which requires basically a more or less constant bore, sufficiently long radius bends and traps to launch and receive the pigs.
Therefore, an un-piggable pipeline can be defined as not designed as described above. Non-piggable (Un-piggable) pipelines are built without launching/receiving facilities, consisting of varying diameters, mitred bends etc making normal pigging techniques impossible.

Any of the following methods could be used to inspect non-piggable (un-piggable) pipelines.
1.      Non-destructive evaluation
Non –destructive evaluation techniques that can be applied without inserting inspection tools into the pipeline. These methods can detect coating damage, external corrosion detection, and metal loss information.
a.       DC voltage gradient
b.      Current mapping
c.       Guided wave technology


Guided wave ultrasonic testing: Use to detect corrosion and other defects in the pipeline. A tool known as transducer ring is clamped around the pipe and transmits guided waves in both directions along the pipe. Reflected signals from defects and pipe features such as welds are received by the transducer ring and sent to the main unit. It detects internal and external metal loss.

2.      Modification of existing tools
Modify the pigging tool. Use a pig capable of negotiating different internal diameter.
3.      Pipeline modification
4.      Cable operated inspection
5.      Bi-directional inspection
Using extremely short Bi-directional inline inspection tools (various propulsion methods such as reverse flow can be used to bring the tool back to its entry point)
6.      Launch valve operation
Ball valve is used as launcher and receiver. Insert the In-line inspection (ILI) tool into the valve while the valve is closed and the door can be opened. After the door is closed, the valve is opened and the tool is launched with the flow. The next downstream ball valve has the same functionality and is used as a receiver. At one end of the ball valve a steel mesh is installed to stop the tool.
If only one ball valve is installed, it can be used as a launcher and pumped back into its entry point by reverse flow.

Launch valve operation method is applicable to pipelines without a launcher/receiver.
7.      Multi-diameter pig
Use dual diameter pig capable of negotiating different internal diameter

Note: To avoid the problem of non-piggable pipeline, it is advisable to use a constant internal diameter when designing a new pipeline.

Reference
Michael Beller, Tom Steinvoorte, Stefan Vages, ROSEN Group


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