Hot Tapping Dissimilar Materials. 2

[DeepuDivakaran]

Dear Experts,

We are planning for a hot tapping job with weldolet branch connection.Run pipe is API 5L and branch is A312 Gr TP 321. Electrode will be E309L. Line is Flare line. Size : 36" x 2". normal operating pressure is negligible,ie. 0.02 bar. Our plan is to purge the line with a min velocity of 1.5 m/s and max 10 m/s as it is gas line. As defined in client spec we have to maintain a min preheat of 65 deg C and max interpass temp of 250 deg C(FOR CS material). But here the case is dissimilar.

Experts please advice the preheat temp requirements for this case. Also what are the precautions I have to follow while hot tap welding the p8 to p1 joints.

 

[DVWE]

Preheat sounds appropriate, but you will want to limit the interpass temperature to 175 C for the stainless weld metal.

No other precautions...

 

[MickMc]

Why not have your material spec break downstream of the weldolet where I would imagine dissimilar weld is simpler?

 

[DeepuDivakaran]

Thanks,

We have successfully completed the mentioned welding.

But unfortunately I am going through a serious problem with other hot tap welding with split tee branch connection. Run pipe is 24" Sch 10 and branch is 10". Material A312 Gr 316L.Process is SMAW. Run pipe thickness is 6.15 mm during the recent UT measurement.Line is Flare line. we have done simulation test with split on 6" x 7.11 thickness pipe of same material. and the heat input calculated as Buttering layer 1 : 0.939 Kj/mm, Buttering 2 : 0.993, Root : 0.990 . when this value plotted on the Welding temperature of pipe wall chart the maximum wall temperature comes as 685 deg C, which is on the welding not permitted area of the graph.

My concern is whether there is possibility of burn through while we gone for welding in 24 " Sch 10 pipe.