Welding problems with Hastelloy

[RanceRCannon]

Help! I have a sitution with welding on Hastelloy C-276 pipe. The pipe is 6inch diameter and std weight wall (1/4" wall). The welding process used is GTAW (filler ERNiCrMo-4) using 100% argon as purge. The pipe ends were capped off, Root openings are taped tight, purging (argon gas) thru the the bottom, venting out the top while the pipe was positioned horizontal. My purging process was to open the flow meter to its maximum (70cfh) for 10 minutes before welding the root. I started with the root opening weld at 2 oclock, with partial tape removal as not to lose the inert purge of the pipe. I am not sure if I have complete inert backing even after all these step were taken. The root appearance has rough look to it, low penetration, discoloration (dark, gray) with no rainbow color.
Do you have any advice?

[Mike Sherman]

Two things come to mind right away. 1) Are you welding too hot? Hastelloy will weld very similiar to Austenitic Stainless Steels. Welding will be sluggish and you will have shallow penetration. Use of proper joint design is important, trying to burn in the root pass will result in too high of heat input, giving you a rough interior weld profile. 2) Are you turning your purge gas pressure down after the initial purge? Sometimes if your pressure is too high you will create a swirling vortex inside the pipe and you will not get adequate purge coverage. You can even pull oxygen into the pipe if the circumstances are right.

[chip hayden]

Mike has suggested some excellent possibilities to your problem. however, you might try Damien_Kotecki@lincolnelectric.com.
if you are unfamiliar with him, he provides the corrosion resistant answers for we who are mere mortals.

[Mike Sherman]

Chip, I have Damien Kotecki coming out to our AWS chapter to lecture in November. He is very knowledgeable and an excellent resource.

[chip hayden]

Mike,
thanks, i wish you were a little closer. i'd press you for an invitation to that meeting.
regards,
chip

[Mike Sherman]

No invitation needed. AWS meetings are open to the public. And not only that, for $8.00 we'll feed you dinner.

[chip hayden]

Mike,
It's the distance thing. I've been a Boston section member for over 20 years, and even the 160 miles round trip to those meetings is usually not practical for me.

[JTMcCracken]

Is this a new problem? Have you made these welds in the past, using the procedure you described, with success? If anything I would try a purge at lower volumn for a longer period of time. Also, have you had this problem with only one argon bottle? Might try a different bottle. How long of a run of pipe are you purging?
The last time I worked in Richmond was the early 90's, in the Chevron refinery.

JTMcC.

[RanceRCannon]

Problem solved! First of all, thanks for your help, it all paid off. My solution; I increased the volume of backing purge gas. Before I was successful, the flow meter was set 40 CFH, changed that to a pressure regulator which I was able to increase the volume to 18psi. I replaced the regular small cup on my TIG torch, with a jumbo #10 cup. My torch purge was set at 40 CFH. That combination procuded a wetting action of the root pass. My inlet purge was placed at the bottom of my pipe spool and vented out the top. Welding was done at the 2:30 position, This weld was made in a rotating postitioner. What this did was eliminated any possible oxygen that remained and gave me a complete inert purged pipe spool. Also, I attached a home made diffuser, some stainless steel wool balled up (1-1/2" dia) and taped to end inlet hose. Also, while the pipe spool was ambient temperature the root pass went in more uniformly, than when pipe spool was hot after continous welding.