1-1/4 to 2-1/4 Chrome weld

Date 07-06-2003 19:43

My welders soon are going to be making a 1-1/4 to 2-1/4 chrome 6" sch. 160 weld. The reason for this weld is to repair a major crack that is over half the curcumfrence, we plan on gouging and grinding the whole weld out and re-welding the complete weld one half at a time "operations at tha plant won`t` let us remove the welded valves and equipment". It`s a high pressure steam line about 25 years old and the reason for failure are possibly creep cracking due to operations abuse for a long period of time of temp. around 900f. But any way the rod of choice , pre- heat and postweld heat treat will be critical to our success. My plan is to preheat at 300f, weld with ER90SB3 gtaw, needle purge with argon and post-weld heat treat at 1200f for one hour etc. I really want to be sure about my rod choice. Any suggestions or advice would be appreciated.

By pipewelder_1999 (****)

Date 07-06-2003 21:35

That is a typical filler metal for that application however I would use what is indicated on the applicable WPS that has been qualified by testing. I don't have a Section 1 or B31.1 available to check the PWHT temps so make sure you're in the right temp/time range for that material.

I have seen both Er90S-B3 and 80SB2(B3) used for this application. I performed a similar repair on a 10" Sch 160 line that was P22, or supposed to be. Later information revealed a pup piece that had been installed in the line that was A106.

This 1200PSI superheated steam line was cracked around 60% of the circumference. No one at the plant knew where the pipe had come from . HMMMM.

Be careful and follow an approved procedure. Make sure you know what you are welding to. If the pipe in the system has been subjected to severe conditions, it may be worth looking at a little closer.

Here are some things I remember

The pipe I welded on was very magnetic. We installed the strip heaters for PWHT prior to starting welding and when we got them up to temp the magnetism went down some but we had to wrap leads and degauss the pipe to keep the tig wire from sticking to the bevel.

The pipe had a lot of strain on it. When the joint was cut it travelled a couple of feet in two directions and nearly beheaded the fitter. The comealongs and chainfalls holding it vertically almost ripped the roof out of the boiler house. BE CAREFUL. If the pipe has creeped over that period of time, the spring cans and other supports may not be what you think they are.

Because of the above movement of the pipe, the best fitup we could get without cutting another joint required a gap of 3/4" on the bottom to 3/32" on the top. We were at a paper mill and cutting another joint didn't jive with the price of paper at the time. The weld RT'd fine but I wonder if its still in service . What a gap!

Anyway, I hope it works out and consult the code, a welding engineer and the owner if you have ANY doubts. In my opinion, if something failed in the first place without any hard evidence of a reason, its hard to make it any more resistant to failure by rewelding it without knowing what Really Needed to be corrected.

Have a nice day

Gerald Austin
http://www.weldinginspectionsvcs.com

By insp76

Date 07-08-2003 01:34

Well ,we did a PMI on the material and my procedure has the choice of rod I want and also the pre heat and post weld heat-treat procedure on it, that is a mandatory requirement per B31.3. The reason we are cutting out only one half of the pipe at a time is the problems I foresee in refitting that big boy "it`s only a 6" weld but it`s a reducer 6"x10" and on the other side of the valve we are welding to it`s a 14"x6" reducer",before we cut and bevel the cracked side, the line will be supported in all directions,there could be major stress on that line. The plant reliability engineer will get a boat sample out of the weld for testing to see if we can determine the cause of the crack. The PMI did reveal a low content of chrome, less than 1%, indicating possibly the wrong rod was used, 70-series maybe. So that`s why the choice of ER90SB3 was chossen over the lower chrome content ER80SB2. I was mainly concerned about the rod choice, I did hear mention from another inspector about using NICRO-3FE-1. Have you heard of useing this filler material on this type weld, I sure haven`t. By the way, the biggest gap I have welded for RT was 7/8" on bottom 1/4" on top 14"carbon pipe in a tight spot, left handed on one side and right handed on the other looking through the gap feeding the rod from the top quarter. I DON`T MISS THOSE DAYS.

By pipewelder_1999 (****)

Date 07-08-2003 03:50

I think theres a NiCrFe-3. Its inconel. I''ve used it to weld lugs on superheater panels and to weld inconel itself but not to join carbon or Chrome-Moly. I have heard it will join about anything together fine and I have done that in non-code applications.

I actually do miss those days. I'd rather weld than QC. But to stay busy I do both. You can say one thing about those big gaps, once you get that 1st bridge started it real easy to feed wire and look in the root. Mine was out in the open so ya got me on that one!

Have a nice day and don't weld up all the gravy :)

G Austin