hot tap split tee

[pipeliner3000]

following welding of a full encirclement split tee onto a live pipeline that will be used for a hot tap tie-in connection the tee is pressure tested. The hot tap supplier typically undertakes a leak test using nitrogen to prove the welds.

- is a leak test sufficient or should this be a strength test (hydrostatic test) to above the max operating pressure of the pipeline?
- The circumfrential welds joining the tee to the live pipeline are fillet welds. What NDT can be performed? (assuming no radiography) UT, MPI?

 

[LittleInch]

Before you actually cut the hole in the main pipe, you are quite limited in pressure you can apply to the hot tap tee and often this is no more than a few bar higher than the internal pressure otherwise you risk blowing a dent / hole in the inner pipe as it is not designed for external pressure in most circumstances. I would usually like to go for as high a pressure as I could get but it is dependant on guaranteeing a certain pressure in the pipe for the duration of the test.

This is why you need an experienced contractor and a good welding inspector present when the welding is being undertaken as it is not easy to test beforehand or do radiographic examinations.

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