Case

Everyday practice is yet often unlike theory

In Kampen, Enexis had to replace an old gas pipeline with the help of the contractor BAM.

This pipeline passed under a ditch and a large road and finished in a T-piece. This T-piece was also replaced by a 90° bend with a gate valve with steel welding ends DN150. In the curve a gas purge point with variable T-piece was placed. With this, Enexis now has the ability to blow clean the pipe section for the gate valve in order to carry out work on the pipe or to create a bypass. Behind the gate valve a high pressure connection was placed with a branch of 32 mm PE in order to provide a neighbouring company with gas.

In this project we see very clearly that practice is surely different to theory. First of all the gas pipeline broke and needed to be re-welded. At the location where the T-piece had to be removed, there were made some old welds many years ago, which no longer met the present standards. A new piece of pipeline had to be welded first and after that the gate valve and high pressure connection could be placed.

While digging maps were available on which it was indicated where the steel pipe was located, there was still some indistinctness about the diameter of the pipe. They also feared that a large water pipe was placed at the same location. Therefore, caution was required. After some research, a gas pipeline and water pipeline were found and both excavated. Now a gas purge point had to be installed in order to enable work on the pipeline in the future.

Before a welder is allowed to start welding a gas purge point on an 8 bar gas pipeline, a wall thickness test must be carried out (in this case by SGS). At the DN100 gas pipeline a wall thickness of 2.8 mm was measured. The instruction for a DN100 steel pipeline says that for welding under pressure the wall thickness must be no less than 3.4 mm. As a result, the pipeline had to be depressurized. This took place later in the day and then the gas purge point was placed.

Once again an example of the fact that practice is often different than theory. At the same time you see the importance of good asset management and the importance of good mapping of the pipe network with correct diameters and wall thicknesses.

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