Dear Sir: I would try and weld repair the 347SS gasket groove without prior thermal treatment. If excessive porosity occurs, you might try pre heating before welding. Hope this helps! David Hendrix The Hendrix Group Inc.

In response to the problem of de-gassing to remove hydrogen traces in materials subjected to hydrogen pressrues at high temperature, the most common problem occurs in low alloy steels (particularly heat exchanger tubes of low alloy steel material ( P3 or P5 grade materials) with grooves for strength welding. Grooved joints fail in high hydrogen service due to hydrogen related damage (it is called :high temperature hydrogen attack ). Fine cracks develop in the strength welded grooves at the HAZ areas as these areas are not properly stress relieved after original fabrication. At these hard zones, hydrogen penetrates and crack devlop in these exchangers in hydrogen service. Even though the tube sheet is covered with weld over-lay of SS 347 or Inconel alloys, the high hard HAZ low alloy steel tube fail due to high temperature hydrogen attack after prolonged use at high temperature of 330-380 degree centigrade. One way is to de-gas the low alloy steel portion before attempting repair welding. If repair welding is done without de-gassing then problems will further accelerate to other tubes as well. Normally, the SS 347 or Inconel weld over -lay is given to prevent this cracking problem. Simple repair welding with S.S 347 may not help you if your material used in such hydrogen service is low alloy steel of ASTM A 335 P3 or P5 grades. You have to do de-gassing the entire tube sheet and then only repai weld using either SS 347 or Inconel alloys to avoid dilution and also create problems of fine HAZ cracks due to high temperature hydrogen. Welding of such fine crevice / grooved strength welded tube to tube sheet joints has to be done in staggered ways and without much heat input at the joints to avoid future problem of high temperature hudrogen attack. Trust this information is helpful to you for yoru problem] Chakravarthi.V Srinivasan Tech Director Nishi Engineers Pvt Ltd Chennai 20 India March 26, 2004 If you need any clarification: please e-mail to: nishi@vsnl.com