[Otto Nobedder]

Here we go again!

Microscopic leaks in a vacuum vessel, exposed in dye-penetrant.

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I skipped the pics of the grinding and prep, this time, and here's the finished product (last three passes not brushed).

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Here's a little context... These cracks were hidden under other structure and welds.

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Steve S

[Otto Nobedder]

Helium leak detection continues to fascinate me. There was no reason to suspect a leak in this vessel at all. It had been through the heat procedure (to drive moisture out), and had retained vacuum at 42 microns (0.0042 mm/HG) for two weeks, but we are now required to investigate all similar vessels due to the sheer number of leaks I've been finding.

This leak showed up at a "leak rate" of 2.5E-09 cc/second of helium at standard atmosphere. I did the math, and at that leak rate, it would take 12 years, eight months, and change, to leak one cubic centimeter of helium at standard atmospheric pressure.

Some days, I really like my job.

Steve S

[MinnesotaDave]

Steve S. - I am wondering under what circumstances a leak that small would be an issue?

It seems like it would be too small to cause problems? What is the reasoning please?

Btw, I checked your math and agree with your findings. I had to check it since it was an astonishingly small leak and I was curious if it was true - lol

[Otto Nobedder]

Steve S. - I am wondering under what circumstances a leak that small would be an issue?

It seems like it would be too small to cause problems? What is the reasoning please?

Btw, I checked your math and agree with your findings. I had to check it since it was an astonishingly small leak and I was curious if it was true - lol

LOL! Good on you for checking the math! It DOES sound odd talking about cubic nanometers of helium!

The point of repairing even something this small is because it always grows over time. Once the crack grows beyond the weld it started in, it can leak fast, eliminating the vacuum on the vessel. (Think HUGE thermos bottle, with very cold liquid inside.) A loss of vacuum on the road causes a boil-out of that liquid to gas, potentially dangerous depending on the liquid, and always expensive in the best of cases. A failure that threatened life and property would cost far more than making repairs as needed. Replacement cost on these vessels is about $2.5-$3 million with a two-year lead time, so repairs and PM are cost-effective.

Steve S

[MinnesotaDave]

Steve S. - I am wondering under what circumstances a leak that small would be an issue?

It seems like it would be too small to cause problems? What is the reasoning please?

Btw, I checked your math and agree with your findings. I had to check it since it was an astonishingly small leak and I was curious if it was true - lol

LOL! Good on you for checking the math! It DOES sound odd talking about cubic nanometers of helium!

The point of repairing even something this small is because it always grows over time. Once the crack grows beyond the weld it started in, it can leak fast, eliminating the vacuum on the vessel. (Think HUGE thermos bottle, with very cold liquid inside.) A loss of vacuum on the road causes a boil-out of that liquid to gas, potentially dangerous depending on the liquid, and always expensive in the best of cases. A failure that threatened life and property would cost far more than making repairs as needed. Replacement cost on these vessels is about $2.5-$3 million with a two-year lead time, so repairs and PM are cost-effective.

Steve S

I see - so a very necessary repair indeed!

Thanks for the tutorial Steve

[Braehill]

Steve,

Quit messin' around and get after it. My liquid sphere has been at or below target refill levels for two monthes now. Lets get that thing on the road. Just kidding, keep up the good work. I can appreciate what you do more than most people and enjoy seeing the pictures.

Len

[Otto Nobedder]

Movin' as fast as I can, Len!

I've finished that one, the safeties are in and being installed (got the four-safety modification), and once the repairs are painted and the vent side is back-pressured and snooped, we'll be releasing it.

Next task, I'm going inside an offshore liquid nitrogen vessel my company manufactured. It's the first confirmed leak in over 350 units produced. I've probed every pipe and penetration and found nothing (as I expected... the quality of workmanship actually stuns me), and expect to find the leak to be a flaw/inclusion in the metal the inner vessel was rolled from (which, unlike the welds, would not have been x-rayed).

I'm keeping a photographic record, and if the result proves interesting, I'll post some pics and info.

Steve S

[Braehill]

Cool!
Len

[jwmacawful]

this is an ongoing project. still welding lugs onto many,many and still more beds to prevent them from being used as battering rams or to facilitate suicide.they get bolted to the floor after welding.

[zank]

The usual.


Nathan S by Zanconato Custom Cycles, on Flickr


Nathan S by Zanconato Custom Cycles, on Flickr


Nathan S by Zanconato Custom Cycles, on Flickr

[Otto Nobedder]

As always, fine work, but this time, I see some of the jigs and fixtures. It helps me see the process. Thanks!

Steve S

[zank]

Thanks, Steve. There are some good shots of my coping setup and fixtures in the video I helped Jody with. I'll get a link.

Found it.

http://youtu.be/yT108iL-vMw

[Otto Nobedder]

Thanks, zank,

That was interesting. I'd seen that video, but had not really paid attention to the fixturing. I suppose my attention was drawn to the "sledgehammer" test.

Steve S

[Otto Nobedder]

Steve S. - I am wondering under what circumstances a leak that small would be an issue?

It seems like it would be too small to cause problems? What is the reasoning please?

Btw, I checked your math and agree with your findings. I had to check it since it was an astonishingly small leak and I was curious if it was true - lol

At some point, I intend to publish everything I've learned about this phenomenon, called "corrosion stress cracking", which is stainless-steel's version of rusting. One of the most insightful reports I've read was published by the Savannah River site (nuclear research facility).

Putting it all together will take a bit, though.

Steve S

[countryboy1127]

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I had to tig this weld on the inside of a flange today . this barrel came from the factory and the weld on the inside of the flange to the barrel had a small non fusion spot which caused hydraulic fluid to come out the bolt hole when pressured up. talk about a chore when all you have is a wp 17f aircooled torch running off a diesel ranger 250

[zank]

Merry Christmas by Zanconato Custom Cycles, on Flickr

[grinder]

Merry Christmas ! !

[zank]

A few more for some friends and family.


Ho ho ho by Zanconato Custom Cycles, on Flickr


Happy belated Hanukkah by Zanconato Custom Cycles, on Flickr


Merry Christmas by Zanconato Custom Cycles, on Flickr

[jwmacawful]

give a guy with some imagination a welding torch and the sky's the limit. when you're a welder life is good!!!

[Otto Nobedder]

Movin' as fast as I can, Len!

I've finished that one, the safeties are in and being installed (got the four-safety modification), and once the repairs are painted and the vent side is back-pressured and snooped, we'll be releasing it.

Next task, I'm going inside an offshore liquid nitrogen vessel my company manufactured. It's the first confirmed leak in over 350 units produced. I've probed every pipe and penetration and found nothing (as I expected... the quality of workmanship actually stuns me), and expect to find the leak to be a flaw/inclusion in the metal the inner vessel was rolled from (which, unlike the welds, would not have been x-rayed).

I'm keeping a photographic record, and if the result proves interesting, I'll post some pics and info.

Steve S

Len, I found and fixed that leak...

Once I entered the inner vessel, I had about 16 hours in putting my finger on it. That may sound like a lot, but the last inner-vessel leak I hunted took six weeks, an a LHY tanker (Wilkes-Barre unit). Turns out it was a small crack in a longitudinal weld in the barrel, that seemed to originate in a "worm-hole" porosity. That's speculation, though, since this is "after the fact" analysis.

I closed my impromptu manway to the inner vessel today, and will repair the superinsulation and close the outer vessel tomorrow.

I'll post up some pics in their own topic once I'm done.

Steve S

[Braehill]

@Steve,

I look forward to seeing the pictures.

So busy with my son's rehab I forget what the inside of my garage at home looks like. He's walking on his high dollar stick and should get to come home tomorrow, then out patient therapy for six more days. Christmas may come to our home after all.

Len

[Otto Nobedder]

@ Len,

That will make a good Christmas. Hoping for the best!

Steve

[countryboy1127]

Once you do one you get stuck with all of them . Apparently since the place that builds these barrels cant get the weld rite I get to fix all of them that we get

[weldin mike 27]

Hey,

Country boy: very nice work, tig where there has been oil can be a recipe for disaster, you did a fine job.

Zank, those are very cool, something for everyone.

Mick

[countryboy1127]

Thanks mike . It is a pain welding over machining oil especially when its trapped under non fused welds . I had a few problems with porosity on a couple of them but got it all sorted out