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Re: [MW:8944] Backing gas

By Materials & Welding
Mr.Abdul,
 
Stainless steels are selcted for their corrosion resistance, and that is due to the presence of Cr2O3 passive film layer on the surface, When welded without purging gas the chromium around the weld joint will react with the atmospheric oxygen and then form heavy scales ofcourse it depends on the thickness of the process pipe wall thickness and the heat input that you apply.
 
some people may recommend to do IGC testing on the test samples done without purging, and for your surprise the results can also be acceptable, but it is not what we wanted.
 
If you concern is cost factor of purging the line with Argon, I would recommed to use nitrogen as purging / backing gas which is a cost effective way in these kind of situation.
 
In short any process pipe wall having thickness less than 6.3mm, there has to be backing gas when welding.
 
Regards,
 
Praveen
Muscat

--- On Fri, 12/24/10, abdul naveed <naveedhhi@gmail.com> wrote:

From: abdul naveed <naveedhhi@gmail.com>
Subject: [MW:8921] Backing gas
To: materials-welding@googlegroups.com
Date: Friday, December 24, 2010, 12:21 PM

Dear all ,

we are facing  problem for Stainless steel  bad support welding as per wps if wall thickness is less then 6.3 mm purging should be required but some of supports has been welded without purging

Material is A312-TP321 DN 150 SCH 10S

DO have any comments on this issue, for this problem actual purging is required or not

PLZ .write your comments

 

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