Welding of A 312TP 321H piping with Npur

By - Date 05-25-2000 11:12

We want to weld a One inch dia pipe of A 312TP 321H with ER 347 filler wire. Purging normally is done with Argon. However, in this particular case we would like to use Nitrogen for the back purging. Shielding will be with Argon only. Can pure nitrogen be used for welding of 321H pipe without causing any defects in the weld due to dissolved Nitrogen. ?The service temperature of the weld is 670 degC at a pressure of 450 psi and handles vaporized naphtha.

Any clarification will be highly appreciated.

Rajaram
Sr.Inspection Engineer
IOCL

By - Date 05-29-2000 02:03

Nitrogen purge is now more common as a shielding gas recently and I am not aware of a down side for its use if the Nitrogen does not tie up the material stabilizing elments during solidification.

One observation: 321H is stabilized with Ti a very strong stabilizing agent and has a min carbon content of 0.04 and you stated you were employing 347 filler which is stabilized with Nb /Cb and with out the H designation the elevated temperature strength may be a concern.

The allowable stresses per ASME Section II for base material are only stated for stainless material if the Carbon content is 0.04 min.

Just a word of caution.

Regards