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Post by snark3 on Dec 22, 2019 13:28:06 GMT -8
I was at a LDS yesterday where the owner is vintage friendly. I had brought in an "oddball" tank I have to see if he had one kicking around he might be willing to sell. He had never seen the particular tank I brought in, but he did advise me not to look too hard because they changed the HYDRO process which has resulted in over 50% of the old steel tanks he sends out failing. Can anyone confirm this? I hate to have to get rid of my 72's.
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Post by cnotthoff on Dec 22, 2019 14:07:25 GMT -8
I've had a few steel tanks fail hydro in recent years, but most have passed.
There is a problem with newer high-pressure galvanized steel cylinders. The layer of zinc bonded to the outside of the steel would keep the cylinder from returning to its original dimension. This led to failures due to permanent expansion.
The hydro facility I use is familiar with the procedure to properly test these cylinders. I'm not completely sure of the process, but it consists of cycling the pressure during the test.
Good luck with your cylinders.
Good Dives,
Charlie
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Post by snark3 on Dec 22, 2019 14:30:58 GMT -8
The way he described it to me was they used to bring the pressure up some, then down then up to test pressure. That may be the cycling Charlie is referring to. The procedure they're using now, they just go directly to test pressure, which results in an over stretch, and a failure.
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Post by crabbyjim on Dec 22, 2019 15:05:36 GMT -8
What did he say, exactly?
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Post by snark3 on Dec 22, 2019 15:15:52 GMT -8
CJ- The way he phrased it was they used to bring the pressure up some lower it, then bring it up to tests pressure. Under the new rules they go direct to test pressure, which causes an "overstretch" and failure.
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Post by nikeajax on Dec 22, 2019 15:54:47 GMT -8
Hopefully Charlie can get the real skinny on this one for us: could this just be a Massachusetts thing Skip?
JB
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Post by crabbyjim on Dec 22, 2019 16:16:47 GMT -8
I’ll check tomorrow but Charlie, John and others who frequent this board know more than I do. My steel 38’s (1952) passed hydro last year.
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Post by cnotthoff on Dec 22, 2019 16:24:37 GMT -8
We are a small shop in a rural area, so don't do enough hydro's to make it profitable to have our own hydrostatic test equipment. I take our's to an Air Liquid operation. I've talked with the operators there about these procedures. All I can tell you is that they know more about it than I do.
We've seen the pictures and heard about the deaths and injuries that have occurred during scuba cylinder filling. When tanks fail, they get made into bells or used for target practice.
Merry Christmas
Good Dives,
Charlie
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Post by SeaRat on Dec 22, 2019 18:09:18 GMT -8
I know nothing about any "new" procedure for steel tanks. I'll ask the LDS when I go in next time, which should be in a week or two.
John
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Post by vance on Dec 22, 2019 18:13:13 GMT -8
Noooooo! Our steel tanks are good for a thousand years!!!
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