Another "Leak hunt"

Sat Dec 21, 2013 8:25 am

The boss (Not my boss... the big boss) pretty much told me I was stupid... it can't happen...

Here it is:

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Sat Dec 21, 2013 8:30 am

He enjoyed the crow he was served.

This was an inner vessel leak on a vacuum-jacketed vessel. It was a small vesell without a built-in manway, so I had to make one.

Fat Bob · Sat Dec 21, 2013 8:56 am

Good for you Steve. Crow is best served COLD.

What do you mean it didn't have a built-in manway, you have to put a zipper in it?

Sat Dec 21, 2013 9:15 am

No, I actually had to cut my way in. 16" manway. I'm the only guy in the shop who could fit.

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Steve S

Sat Dec 21, 2013 9:24 am

The manway required a cofferdam, since it's a vacuum jacketed vessel, and I needed it to be under vacuum to find the leak.

It was a though exersize, to lay out the holes coaxially, so the cofferdam would fit both the inner and outer vessel, since both were compound curves with differing radii.

On the plus side, it only took me 16 hours to put my finger on the leak... The last I.V. leak was in the parent metal, not a weld, and took eight weeks to find.

Lord, grant me patience!

Steve S

Fat Bob · Sat Dec 21, 2013 10:30 am

8 Weeks!!! You have more patients than I.

Never really thought about having to have a cofferdam between vessels but it makes sense knowing what you work on.
I was just being a smart a$$ when I made the zipper comment.

Up to page 16 in General Shop Talk on the "topic move project".

TamJeff · Sat Dec 21, 2013 11:35 pm

I never considered that I might have ADD. But then I start looking at the troubleshooting phase of your projects and it gives me anxiety though the computer screen, thousands of miles away! You need a raise.

delraydella · Sun Dec 22, 2013 5:44 pm

Is that an ocean container that you're working on/in?

Mon Dec 23, 2013 8:33 pm

Good eye, Steve,

Yes, this is designed to carry liquid nitrogen to offshore platforms. It's the stantard size of a cargo container, and had built-in lift points and rigging to be "craned" on and off vessels and platforms.

It's a royal pain in the ass when a leak proves to be "internal", and I have to make a hole to get at it.

Steve S

Mon Dec 23, 2013 8:39 pm

TamJeff wrote:I never considered that I might have ADD. But then I start looking at the troubleshooting phase of your projects and it gives me anxiety though the computer screen, thousands of miles away! You need a raise.

It does take a great deal of patience, but it is, in the end, just a systematic testing of every possibility in order of likelyhood, beginning with penetrating welds (pipes and tubes that penetrate the vessel), moving to the welds that connect parts of the barrel and/or heads of the vessel (where this one was found) to the open parent metal the vessel is formed from.

The search has to be systematic, but is not particularly complicated.

DAMN TEDIOUS at times, though.

Steve s

Mon Dec 23, 2013 8:44 pm

Here's the root pass on the repair...

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in the inner vessel.

Mon Dec 23, 2013 8:58 pm

This crack was stop-drilled at 9/64", at 1/4" past each end, then sliced through. Ground with a 1/4" wheel face-on to about 75% depth, then sliced with a 1/16" cut-off wheel. I don't normally make a repair like this from one side, as there is mylar/tissue layers (approx. 200) on the backside, but the heat-sink properties of the dual-shield weld that cracked convinced me to make the attempt. The mylar on the backside prompted the "walk-the-cup" root, to limit the heat on the backside and avoid damage to the superinsulation.

The vessel, today, went through helium leak detection inside and out, as well as ASME restest pressurization. The latter meant pressuring it to 130% of MAWP while under full vacuum. MAWP is 45 PSIG, so 1.3X = 58.5 PSIG, plus full vacuum meaning an effective test pressure of 73.2 PSIA.

It's the equivalent of Hydro-testing, with fail mode determined by monitoring vacuum.

Steve S

MinnesotaDave · Sun Dec 29, 2013 8:12 am

Interesting job you have there Steve.

Sun Dec 29, 2013 6:42 pm

MinnesotaDave wrote:Interesting job you have there Steve.

Thank you. I think so, too.

I wandered for many years from job to job, going as far as the job would let me, and/or learning all the position had to offer, and finding something else that interested me. For almost 30 years, I averaged 12-14 months at a job before I was bored and wanted to learn something new.

I've been doing this more than three years, and haven't even seen the light at the end of this learning curve yet. I hope every welder finds work that is both challenging and satisfying.

Steve S

delraydella · Wed Jan 01, 2014 11:03 pm

How much do the containers cost versus the trailers? Is there a lower point where you would just scrap it if the leak was too bad?

Thu Jan 02, 2014 8:22 pm

Steve, I don't know what the price is for these offshore containers, but I'd think a tenth or less of the LHY trailers.

However, this was a warranty issue for our company, and their first ever on this style unit, so there was great interest in finding the problem. They've produced over 350 of these without a problem, so headquarters was very interested in what caused this one.

I'll have to add it up, but they usually value me at $65+/hr (minus my pay) when I'm working for clients (and I'm underpriced, but they make it up in "approved shop hours", like your car mechanic rapes you), yet they turned me loose on this for about 4 weeks or so. So it's what was lost in income plus what they paid me for all those hours.

Plus materials, and tied-up shop equipment.

It took a week to make the big boss believe me... He was in denial. Once he was convinced, he HAD to know how it failed. I admire that attitude.

Steve S

Thu Jan 02, 2014 9:05 pm

If you read the name of this topic quickly , its about a guy named Lee that you dont like very much.....lol.

Thu Jan 02, 2014 10:08 pm

weldin mike 27 wrote:If you read the name of this topic quickly , its about a guy named Lee that you dont like very much.....lol.

LOL! New Year's eve has passed... Put the beer down, and no one gets hurt...

Steve S

Thu Jan 02, 2014 11:52 pm

Ha...only getting warmed up for smashing the poms in the cricket and then Australia Day. Aussie Aussie Aussie.

Wed Jan 08, 2014 2:34 am

Hey,

Smashed the poms 5 nil in the Ashes tests, now bring on the One dayers, so we can smash em some more.

Mick

Wed Jan 08, 2014 7:35 pm

Had another leak hunt, a bit each of yesterday and today.

I think I set a record.

In four hours, I went from "here's the trailer" with no vacuum on it, to setting up the pump, setting up the mass-spec, pulling vacuum, and putting my finger on the leak.

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Steve S

Thu Jan 09, 2014 7:11 pm

That's what I get for bragging...

With that one fixed, I've now found an inner vessel leak in the same unit. (I should have suspected... These are always shipped to us with nitrogen under pressure in them, and this one had none.)

So now I'm back to crawling through another 16" manway. I'd have gone bigger, but this one is already there, built in.

As usual, I'll keep a photo journal, and share anything interesting or unusual.

Steve S

AKweldshop · Thu Jan 09, 2014 7:46 pm

sounds like fun

Braehill · Thu Jan 09, 2014 9:04 pm

Steve,

Even I can't guess the model of the trailer from that picture. But I'm quite sure who the customer is.

Len

Thu Jan 09, 2014 9:14 pm

Len,

The trailer's an all-steel Cryenco, in oxygen service. The back section of the outer barrel is SS. I expect the leak to be at the top front, where the "crash-bars" are welded to the ouside of the inner vessel. Likely right at the end of one of them. The history on this series says the trailer with the preceding serial number had the same problem.

And, yep, it's "that" shade of green.

Steve S