Welding P22 Chrome

Date 07-25-2007 19:53

We use GTAW & SMAW. ER90S-B3 and E9018-B3 for both of those material combinations.

Our procedure requires preheat to 400F and PWHT at 1275F - 1300F, if the material thickness exceeds 1/2".

Charles

By js55

Date 07-25-2007 20:19

Make sure you have a good furnace with adequate thermocouples on the dissimilars. CS has a lower transformation temperature of ~1340degF. And often specs or codes call for P22 to be cooked above 1300. Thats cutting it a little close.

By chall

Date 07-25-2007 21:00

We just went through this horror. We had 15 P5A headers with 30 P1 tubes each subjected to PWHT at 1340F (despite our written procedure which specified 1275 - 1300).

In order to clear the NCR we had to cut samples of each of the carbon steel materials welded to the P22 header and have them tensile tested after subjecting them to a "control" heat treatment at the same conditions our headers were subjected to (six different heats of P1 tube material). On the basis of obtaining tensile properties consistent with the MTR test results, we were able to accept the headers for use.

We cleared this through our AIA Code Services Manager. He explained that the lower transformation temperature of carbon steel varies with the actual chemisty. Since we were at the most widely accepted "approximate" lower transformation temperature published, our only recourse was to take a conservative approach and test all the different heats of carbon steel we had used to verify we did not adversely effect the mechnical properties due to PWHT at the temperature (and time at temp) we used.

How we got there is a mystery only god knows the answer to. Our sub explained that this had never happened before. I asked if they had a high temp alarm on the furnace and they replied "yes - but it is always set to max because they don't like hearing it" ??????

Anyway, we got out of it pretty well considering what it could have been.

Charles

By js55

Date 07-25-2007 21:32

charles,

Yeah, the transfomation is approximate.

By DP68

Date 07-26-2007 16:32

Thanks for the tips.

Well, my "Project Manager" agreed with the ER80S-B2. However, he will also be using that to weld the P22 to a standard A105 carbon steel flange. He seems to think it will be fine? He also offered the fact that he will not be doing any pre-heating. Um, opinions?

By DP68

Date 07-26-2007 16:37

OOPS.

I sent ER80S-B2 to the job by mistake, partly because I misread the number, and partly because I had some here in the warehouse, and just assumed it was left over from that same job a while back. Is this...ok?

By chall

Date 07-26-2007 16:45

The correct filler metal is what you have proven by PQR testing, and that which is specified on the WPS.

It sounds like you have neither.

My opinion is that you should qualify the P22 to P22 using preheat, ER90S-B3 (not 80S-B2 - since the chromium content is undermatched to the P22); and if the thickness exceeds 1/2", conduct PWHT.

For the P1 to P22 you may be able to get away with ER80S-B2, since the weld will be diluted with P22 & P1. Preheat is still required, and PWHT may be required depending on the thickness and code of construction.

If you are welding on P22, chances are the application is high temperature and pressure. To weld on such a system without having a qualified procedure is irresponsible (and could ultimately be criminal if a failure occurs as a result of your work). This has less to do with you and your company and more to do with the unfortunate people who will be working around the system while it is operating.

Charles

By DP68

Date 07-26-2007 16:51

Im on it. Thanks a lot.

By js55

Date 07-26-2007 18:33

B2 is fine on the dissimilar. In fact, I'v even heard of running carbon steel filler on the P22/P11 to CS dissimilars, though it seems to make most people nervous. I'm not sure why. Arguments to the contrary are welcome. It has advantages. Cost(of course), ease of welding (to a limited extent), and the fact that you will not get carbon migration across the fusion zone from the CS BM HAZ into the CS weld metal like you will with an alloy weld metal which essentially weakens the CS HAZ. Though, the weakening of the HAZ is seldom an issue since it holds up well under tensile conditions. And it seems as thouogh it holds up well under any creep conditions as well since there, at least to my knowledge seem sto be no reports of failures associated with this weldment combination.
But charles is absolutely right. You have to have a qualified procedure in place for all alloy combinations. You have to have preheat, and you have to have PWHT.