Pig-In-A-Poke OR Maybe a Bargain

[SurfLung]

- After all of this discussion, I simply HAVE to get these re-tested but I have not yet found a test facility that will confirm that they will do the test with the 90% System Check before the full pressure test. (I wish I lived next door to Time2Dive... I'd get the right hydro test and also live in Hawaii! )
- Captain... Yes, I watched the video and thanks for finding it for me. That certainly explains it. As for filling the tank before sending it in, that may have played a role. These tanks may have sat empty for years. I took the valves off before sending them for service so, they hadn't had any pressure for a long time before the test.
- Luis... Thanks for the references and explanations. I'm coming at this from the viewpoint of not knowing anything about hydro testing but learning fast. Its frustrating and discouraging to have the professionals who should know their business reply as they have. For example, my little USD Twin 38s are in much better condition inside and out than these Sportways 42s. They were full at 1800 psi when I bought them and I've been diving and refilling them all Summer without getting a fresh hydro. After hearing that guys comment about wrecking the threads, I'm very concerned about subjecting my beautiful 38s to an ignorant hydrotester.
- These Sportsways 42s were supposedly hydro tested to 5/3rds of the marked pressure (1880 psi)... That's 3,133 psi. That's WAY beyond what I'd ever fill them to. They didn't blow up. They simply gave a stretch characteristic that didn't meet a test spec. For a hydro tester to make out like these tanks are some great big danger after surviving such an over-pressure test... Its absurd.

[luis]

- These Sportsways 42s were supposedly hydro tested to 5/3rds of the marked pressure (1880 psi)... That's 3,133 psi. That's WAY beyond what I'd ever fill them to. They didn't blow up. They simply gave a stretch characteristic that didn't meet a test spec. For a hydro tester to make out like these tanks are some great big danger after surviving such an over-pressure test... Its absurd.

Your last statement is incorrect. It makes an assumption that is very incorrect. I apologize if my statement sounds harsh, but this is important.

The purpose of a hydro test is not to take a tank to a high pressure and see if it blows up. Not even close.

The primary purpose of the hydro test is to determine material condition: how brittle or how elastic the present condition of the material in the pressure cylinder.

If a steel cylinder has become brittle, it can easily hold the hydro pressure at one point, but in a few more pressure cycles it could fracture. The designed ductile material is also intended to crack and deform, but not fragment if a failure occurs. If the material properties have changed and the cylinder has become brittle it could (in theory and in reality) fragment (like a hand grenade).

A brittle steel cylinder can be very dangerous. Just to give you a visual picture, think of bending a metal coat hanger. It can take the load after a number of bends, but at some point it fails with relatively lower load.

The high strength materials used in the fabrication of pressure cylinders (both the steel and the aluminum types) can be subject to work hardening and/ or heat treatment in many different ways, both intentionally and by accident.


The test pressure is not at all an arbitrary high pressure; it is the low end of the design material yield point. I say low end because in reality it is not an exact stress point at which all the material yields. It is more like a region of stress values when the material starts to yield.

The amount of elastic deformation and (even as or more important) the amount of residual deformations is the critical data that will determine the status of the material properties.


One possible scenario that I can think of that could make some of the material in a cylinder brittle is if the cylinder was in a fire and it got quenched with water (by firefighting, sank in a burning boat, etc.)


Very few things can change material properties: basically heat and work hardening due to stress (and associated strain). But there is a number of ways that they could occur and the best way to test a cylinder is with a hydro.

Note: a hydro will not detect a number of other defects, for example if a crack has started (specially in aluminum cylinders), pits due to corrosion, rust, and a number of other surface defects.

[SurfLung]

- This afternoon I talked to the man who does the actual hydro testing for Brainerd School of Diving. I read off the galvanized tank procedure and asked if that's the way they do it. He replied, "We CAN do it that way."
- I've got the day off tomorrow and I'm going to run these tanks up to Brainerd for hydro testing. He said he could get them done while I wait. So, I should know one way or another if these tanks are any good by tomorrow night.

[SurfLung]

Passed by a WIDE Margin...

- The numbers don't lie. To fail, the stretch would have to be More than 10% of the 38.0 number in the chart above... It would have to be more than 3.8. But it was only .6!
- Theses tanks weren't even close to failing the hydro test.

- I had taken these tanks up to the Minnesota School of Diving in Brainerd, MN http://www.mndiving.com/home.html. The owner, Bill Matthies performed the hydro test personally, let me watch, and even explained the process to me. He said these 1/2" Straight Thread O-Ring tanks are pretty rare... He hadn't had any come in for testing in a long, long time. There's not much of a recess for the O-ring. In fact, the first attempt sprung a leak at the O-Ring and he had to use a different size to get a good seal.
- I told Bill the truth that these had failed at another facility. So, he quized me and also tried to discover why they failed by giving them an extra thorough visual examination. He suspects that maybe the other place had the same leaking problem... (Maybe a slower leak that they mistook for stretching?). Anyway, he said the internal rust was not severe... mainly just surface rust. Exteriors look great and he said these tanks are in excellent condition.
- Thank you... My Forum Friends... For encouraging me to get a second opinion!

[swimjim]

That's awesome Eben. I'm glad they made it!

Jim

[captain]

I had no doubt they would pass if it was done correctly.

[antique diver]

I am so glad that you didn't give up, and were able to save your cool cylinders. They will mean more to you for all you went through, and your experiences posted here will be invaluable to other forum members dealing with their vintage "tanks". Let it be a warning to all with galvanized cylinders to pick their hydro facilities with caution!

[couv]

Bravo to the cognizant gang of VDH. See my signature.

[eskimo3883]

Glad to see they got it right. I thought they were supposed to drill the tank or something similar if a tank fails hydro. Are you lucky they just painted them "failed" or is painting fail the norm?

Anyone in the SF bay area have a suggestion for vintage friendly hydros?

[SurfLung]

And Now Possibly a New Issue...

- After removing the orange paint and polishing these tanks, I was excited to assemble them back to the valve. That's when I discovered the two valve ends look like they were previously assembled with Form-A-Gasket rather than O-Rings. There's a remnant of teflon tape on the threads that hints at this not sealing very well.
- I wanted to check with the Forum before removing this stuff and finding a proper O-Ring to fit. This doesn't look like it has any chance of sealing properly. But if anyone has seen this type of seal from the Sportsways factory, I want to be careful about removing it. Basic Scuba indicates it should be an O-Ring.
- I'm imagining in the 50+ years since this valve was manufactured, somebody somewhere sometime couldn't find the right O-Rings at his local hardware. Or maybe it was a Scuba technician who just thought this was a better way?

[captain]

That just looks like a very old O ring that has taken a set and remained in the same shape it assumes when the manifold was assembled. It is probably hard as rock. They also look like they may have been the wrong size, too big a cross section. The ends should slip over the O rings by hand with out having to force them together. I got a Sportways manifold a few years ago that was recently rebuilt by someone who used too big an O ring that didn't allow the sections to be pulled into metal to metal contact. Nothing to save here, I have come across this many times in valves and regulators that haven't been serviced in 50+ years.

[Drado]

Have you informed the previous facility of the current status of your tanks?

[SurfLung]

- Thanks Captain. The old seal came off pretty easy and revealed a groove for the O-Ring. I found a perfect fit O-Ring and reassembled everything. Then, I filled the tanks up with a transfer whip... Stopping and listening for leaks every 500 psi. I topped them off at 2000 psi and all was well with all of the valve connections. I took them down to the lake and there were no leaks in the valve connections BUT, a tiny stream of bubbles from the one burst disk I had opened and closed once.
- So I let all the air out and installed brand new 2015 psi burst disks. My understanding is that you use a 2015 burst disk on a tank marked for 2015 psi? (I couldn't find one for 1880 psi). Well, this time when I filled the tanks, one of the Brand New burst disks let go at 1900 psi! Geez Loueez!
- Okay, so... I put the old burst disks back in with the new nylon gaskets and hex nuts. Refilled again to 2000 psi... Seems to have held pressure overnight but It was too late to check for leaks underwater.
(I've got to get all my other tanks refilled before I can do anymore transfer filling!)

[swimjim]

I think it's time you get one of these things.

[Bryan]

I think it's time you get one of these things.

What Jim said....Look around and I'll bet you find one cheaper than you thought. I have seen several on auction sites and Craigslist up your way that would be perfect for personal use......And there are plenty of knowledgeable guys here to help you keep it going.