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Staino Weld Fail

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Staino Weld Fail

Postby Coldman » Tue Aug 29, 2017 9:11 pm

About 18 months ago I designed a serpentine cooling coil for an industry colleague that was subsequently passed to to dedicated stainless shop for manufacture as it had over 800m (2600ft) of tube in it. 25mm x 1.6mm (1" x 1/16") 316L seamless tubing.
My colleague rang to say it sprung a leak at one weld joint and that he engaged a local welder to do the repair as he didn't want to bother me with such a small repair. I asked him to instruct the repair welder not to attempt to repair the weld but to cut a piece out and weld a new piece in so as to preserve the faulty weld for inspection as there are many welds in this coil and we need to know what we are up against.

I retrieved the cutout, here it is:

M1.jpg
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I sliced it in half with the bandsaw in vertical and prepared for macro inspection by polishing with 1200 grit wet & dry.

Taking Otto's advice on muriatic acid I used the following etchant I had on the shelf:
M3.jpg
M3.jpg (66.4 KiB) Viewed 357 times


Here are the macros:
M4.jpg
M4.jpg (79.34 KiB) Viewed 357 times

M5.jpg
M5.jpg (84.52 KiB) Viewed 357 times


Based on these what we see here I recon the chances of getting more leaks are high. The customer has told my colleague there better not be anymore leaks.
Don't know where this is going but my guess is it's not going to be pretty.
Flat out like a lizard drinkin'
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Re: Staino Weld Fail

Postby dave powelson » Tue Aug 29, 2017 9:37 pm

What was the criteria specified for these butt welds?

Full pen.?

Partial pen.?

Any WPS written by or furnished to the company doing the welding?

Any setup/test coupons required before production?

Any post weld inspection criteria?
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Re: Staino Weld Fail

Postby Coldman » Tue Aug 29, 2017 10:18 pm

My involvement ceased after design and took no part in the procurement process and installation so I can't answer most of the questions.
The design called for full penetration weld, purged with 100% argon. Pressure test to 3000kPa, and compliance with our pressure piping code AS4041. This code does not have any prequalified procedures so the there should have been a manufacturer's WPS in place for this project if it was to comply.
What actually went down is unknown to me but it would not look good for the manufacturer so far.
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Re: Staino Weld Fail

Postby Poland308 » Tue Aug 29, 2017 10:59 pm

If it's subject to the stresses of cycling temp change. As a cooling coil I'm sure it is. Then it would indeed need to be full pen. Or reasonably close to that. But from those macros I'd say your Spot on that the money they saved on the install will cost them lots more in the future.
I have more questions than answers

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Re: Staino Weld Fail

Postby noddybrian » Wed Aug 30, 2017 4:25 am

So redneck weld services have a depot in Oz ? - that's why we have'nt heard from cousin " Billy Bob " in a while then !
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Re: Staino Weld Fail

Postby Coldman » Wed Aug 30, 2017 7:49 am

Apparently


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Re: Staino Weld Fail

Postby Otto Nobedder » Wed Aug 30, 2017 9:46 pm

Scary stuff. We reworked about 250 welds like that in sch. 160 stainless, where the builder just butted and crowned them just like your macros. This was hydrogen gas service with a MAWP of 8800 psi :shock:

Crazy thing is, the client swore it was a 10% x-ray job, but couldn't find the documentation. I know not one weld on it was x-rayed, because not one weld in the system would have passed.

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Re: Staino Weld Fail

Postby noddybrian » Thu Aug 31, 2017 8:22 am

That sounds truly a disaster in the making - did this ever go into service in that condition & if so how did it not need to pass any kind of test ? over here even steam would need a 1.5 > 1 test / service pressure hydraulic test before being signed off as legal to use - I never dealt with hydrogen but assume the testing would be considerably more stringent especially due to the molecule size issues with micro porosity etc.
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Re: Staino Weld Fail

Postby Otto Nobedder » Thu Aug 31, 2017 6:05 pm

In this system, 10% overpressure is all that's required, as the test is pneumatic and the energies stored are immense. I don't know if that was initially done or not. The system was in service for at least 3 years without failure, but thermal cycling from ambient to -423F and back was going to produce a failure eventually.

Our repairs were 100% x-rayed. I was not directly involved in the repairs, but the unit came back later for a modification when it was discovered the engineers had used too large a pipe diameter in one circuit for the rated pressures, and I replaced all that piping, at 25% x-ray. (They only required 10%, but getting the NDT guys to the site was the expensive part, so we did the extra shots.) I then pressured the system with nitrogen to 9680 PSIG.

I work on potential bombs, so I work carefully.

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Re: Staino Weld Fail

Postby OzFlo » Thu Sep 07, 2017 2:49 am

"Staino".. Love your work Coldman! :D
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