Welding a small pressure test vessel...

On Sun, 13 May 2007 23:06:46 GMT, "JTMcC"
Great. I've generally enjoyed your posts, and can't remember ever disagreeing with you. I doubt I was alone in believing that reliably
capping some low pressure pipe was a piece of cake for you. So I was disappointed that you didn't offer any "this is how I'd probably do it" advice here, and a bit baffled that you haven't responded to direct questions about deflection and strength.

It's not a case of being "untrue". It's about spinning advice to the point of being needlessly discouraging to the OP and others who might have been willing to share their own experience. Despite all your posts to this thread, I still can't figure how you're able to reconcile "literally hundreds of failure modes" with your obvious lack of confidence that even one of those modes would manifest itself in testing that's well beyond the planned use of the subject item.

Well, not directly at least. But don't you think it would be fair to say that you did everything you could to scare him off the project? It's a bit ironic that a recent thread discussed how every welder is only as good as his last proven project, yet IIRC, three of you have pronounced the OP unfit without ever seeing his work.

Nobody said it did. My point was that one need not necessarily be an IA to successfully work on aircraft, just as one need not necessarily be an automotive engineer to successfully change wheel bearings, or need not necessarily be a pressure vessel designer to successfully build every type of pressure vessel. For example - imagine a reasonably competent farmer with a buzz box, capping off an 8" diameter, 12'' long, 1/2" wall pipe with 1/2" plate. One cap with a fitted and filled joint, the other with a heavy outside fillet. We'll further say that he was a bit lazy with the brushing and chipping between passes, that he left some undercut here and there, but had a minimum of 3/8" thickness at the thinnest part of the joints. Now we charge his work with water to 150 psi, and drag it behind a car for a while. I'd be willing to bet that it'll stay pressurized. How much would *you* wager that an ASME certified portable air tank would survive the same treatment? Can you not acknowledge any possibility that a home built version could be overbuilt to the point that it's not only acceptable for its application, but better in some ways than the factory model? How about the subject item with a steel lid, fixed fasteners, and a small view port, versus the commercial item with a full polycarbonate lid and hinged fasteners?

Yes, but everybody has their own idea of how far we should go in making others "aware", and too many can't see the downside of moving the safety line until *everybody* is on one side of it, no exceptions no matter what. We've met the enemy and he is us, and the cumulative effect is that we've already reached the point where store clerks wear unfastened back braces, and some folks are forced to pay professionals to pump their fuel. http://ask.yahoo.com/20040715.html . Much like what's happened in this thread, there are no doubt experts in NJ who cite flaming secretaries as proof positive that amateur fuel pumpers must be protected from themselves, even if their day job is driving a fuel tanker.

Respectfully, I'd like to trade your lame characterizations of my position, and your constant reminders that you're in the biz, for some answers to direct questions, and helpful comments on the best joint design, the fastest lid fastener scheme, the most secure gasket, the easiest view port arrangement, etc. How about it, do you have anything to offer?
Wayne
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wmbjk wrote:

FWIW the commercial version can be found here: http://www.gmcscuba.com as the 48300 and 48310 test chambers.
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Correct, hundreds. If you're interested I can point you in the correct direction to read more than any sane human would ever want to know about the topic. Those of you that seem to be packing all your eggs in the "pressure test" crate, are focusing all attention on a very small point in a very large field. I'll repeat one more time, he was given bad advise by unknowing people, that advise was tempered by people with real world, real life experience in the field. For someone who knows better to just walk on by without throwing in a comment is wrong. Period. Feel free to disagree with that.
JTMcC.

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A plate, fillet welded (or any partial pen weld) to a piece of pipe, by an hobby welder (or even by the best asme qualified welders I know, because it's still a plate fillet welded to a pipe), loaded, I would't be close to. That one particular design characteristic would do it for me. And I've made I don't know how many welds on loaded natural gas and gasoline pipelines over the years. I've also witnessed quite a few failures (after the fact ) under hydro. Anyone who has entertained themselfs and their children with one of those neat little deals that launch 2 liter soda bottles high into the air with a little bit of air pressure should have a tiny bit of intuitive understanding of how small metal pieces can be driven at medium to high velocity with relative low amounts of pressure.
JTMcC.

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On Sun, 13 May 2007 02:58:48 GMT, "JTMcC"

J.T., for God's sake the guy was talking about 150 psi.
If you've been doing this kind of work for any length of time, which I believe you have, I can't believe that you can't weld a piece of schedule 10, 8 inch pipe to a half inch plate and have it hold 150 psi.
Bruce in Bangkok (brucepaigeatgmaildotcom)
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Posted via a free Usenet account from http://www.teranews.com


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Right, 150 psi, I saw that part. The people who are high centered on the fact that they believe the material will hold the pressure and even an overpressure test are missing (my) point, they evidently think I'm missing theirs. But I'm aware of the 150 psi of pressure. My oxy acy hose will hold 150 psi (for a while), I'm pretty sure my garden hose would hold that much for a while. I think my kitchen faucet will hold that for a while. I've had my work (2500' of 18" line pipe) hydro'd to 1250 psi with nothing but a bead (root) and a fast hot pass. That pipe, as welded was not in any way fit for service, but it will hydro pretty high with very little weld. This was just to test the pipe for anomily repairs. I've got a bonehead understanding of what will hold what just from decades of observation. I've also seen systems on hydro for over 8 hours before letting go. Hydros are a funny and interesting thing. I'd have to think about it (and I'm not in the mood for that) but offhand I don't recall seeing any partial pen weld used in a pressure containment system ever, and I can't think of a fillet used for the same with the exception of socket fittings. I'm geared to the welding end of things and of course a partial pen fillet described just about does everything wrong. The mother of all notches on top of it all. You may be aware of all this, you may not care, but it's kind of interesting to me so I throw it out there. Like I said that's my take, take it or leave it.
Happy Mothers Day! JTMcC.

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JTMcC wrote:

In one your posts you mentioned that you could point a person to some info on pressure vessels and the stresses/dynamics/requirements. Without over loading me (I think you mentioned something about providing more informatiion than any human could want), do you have a favorite site(s) that explains the issues involved?
Thanks,
Peter
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I would also be interested. I pulled out the only book I have that has anything on pressure vessels, but it does not explain things clearly enough for me. The formula it gives for stress in a flat end gives 7200 psi for a 1/2 inch thick bottom on a 8 inch id tank with 150 psi pressure. But does not indicate if this is at the edge or center of the bottom.
Dan
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I don't really know of any one overview, such as a "pressure vessels for dummies" type thing (I'd have it if there was ; )), mainly because there is so much ground to cover. But here are some resources that have an awfull lot of information available to those interested. I'm not sure but I think the closest thing to an overview might be "Applying the ASME Codes Vol 2". I don't have the book, I'm just guessing here.
A) That and a lot of other information is available at the ASME website, www.ASME.org I don't think asme has anything that's free tho.
B) The National Board website, www.nationalboard.org also has tons of information available. Some of it is free, they have quite a few "technical articals" on the site that are pretty brief, but interesting. Both of those sites have a lot of books and publications at a cost.
C) There are many thousands of sometimes very interesting and enlightening posts on vessels, piping and related topics here: www.eng-tips.com The forums most on topic are: 1) Boiler and Pressure Vessel Engineering 2) Piping and Fluid Mechanics Engineering 3) Mechanical Engineering Other Topics 4) ASME (Mechanical) Code Issues
The forums that are related are: 1) Corrosion Engineering 2) Material Engineering Other Topics 3) Metal and Metalurgy Engineering
If I think of anything else that might be helpfull I'll post it but there is mucho info in the above three.
JTMcC.

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JTMcC wrote:

I'm sure some publisher will catch on to the vast untapped market of people interested in pressure vessels. I'm sure they could sell... dozens.

This is a great site. It also has a number of forums on subjects in which I am more normally interested.
Thanks,
Peter
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Matter of curiousity...
Suppose you had a blacksmith's forge, or a muffle furnace at say 1050C, and you forged a dome from a flat plate over a "mooring bollard" shaped object - going round and round with a hammer like you do for drawing copper to a bowl, until the ends of the plate had made it round 90deg at the furthermost point, normalised the plate a couple of times from 900C (that is, air-cooled it from 900degC) - then did a full-penetration butt weld - say 70deg included angle single-sided groove - between the end of the done and the end of the tube?
Would that get you anywhere in the right direction???
Richard Smith
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snip

BINGO, we have a winner, or at least somebody that is actually listening.
The only change that I would make is to just buy one from an industrial plumbing supply house. They are carefully engineered and CERTIFIED and manufactured under good production quality control. They come nicely finished in primer and with a prepared bevel edge that will just need a little work to clean up ready for welding. They are available in all standard sizes and are generally <$100. I don't know the price for 8" but I recently purchased a new regular priced 6" for $40.
There is also a way that a trained fitter can take the center cut from a branch opening and to weld it on the end of a pipe properly fish mouthed to fit. I once built several 12" dia x ~20' long air surge headers for an industrial mill using this technique. IIRC service pressure was 90 psi. The government boiler inspector said he couldn't pass it if I called it a surge tank but he could if I called it a header or a manifold! IMHO it is not as elegant or as strong as a proper cap but it does make a really elegant end closure for a pipe truck bumper.
I just cannot understand why people are still talking about PLATE. IMHO, It is a demonstration of monumental ignorance. TJDKWTDK
I leave it to you to figure out how to do the other end but the hint is 'flange'.
This doesn't solve the problem of how to PROPERLY make the CERTIFIED welds that will be required, but IMHO anybody qualified to make the weld AND ensure that it is properly CERTIFIED already knows what is required and where to go. If you need this kind of pressure vessel you should at least go talk to a shop that does LOTS of this work. They will know the codes and will do lots of the quality control that will enable them to CERTIFY it inexpensively. It is not always expensive to deal with pros, they can do it RIGHT and they need work too. IF you ask real nice, AND wear safety glasses, workboots and gloves, they might even let you watch. Bring your own mask and you may need a hardhat.
Just My Humble if Opinionated .02 YMMV
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wrote:

Because plate will be the cheapest solution, and if it's thick enough it will be as strong as a dome. The top is almost certainly going to be a plate regardless.

Humble? LOL Officious and pigheaded, but hardly humble.

Speak for yourself. Check this quote from pg 29 here http://www.powerengineering.ca/errata/PE2_%201_01_revised.pdf "Flat plates... are used extensively in boilers and pressure vessels. When a flat plate or cover is used as an end closure or head of a pressure vessel...". (calculations follow)
Is it your position that the ASME are demonstrating "monumental ignorance"?
Your points about the fish-mouth bottom and the availability of commercial flanges are well taken and much more useful than your insults and caps.
Wayne
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wmbjk wrote:

I'll note again that the commercial pressure test chamber with the flat plate base and flat plex top can be seen at: http://www.gmcscuba.com as items 48300 and 48310. Pictures and all...
I picked up the $40 HF 2.5 gal paint pot today. Haven't unpacked it yet, but it's a rather heavy box.
Pete C.
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Yesterday as I was working in the yard, I thought of how I might approach making a pressure test chanmber. And will post the idea here to see what more conservative people think.
I would go to the local scrap yard and look for a large steel argon or oxygen bottle. Even though it is out of hydro or even if it failed hydro, I suspect it would still be good for 150 psi. The local scrap yard has a band saw so would have them cut off the bottom and the top. A 12 inch by 12 inch granite floor tile would work for a surface plate and I don't think it would take long to get the cut surfaces flat to within 5 or 10 thousandths. Now the problem is to figure out the best way to secure the top piece to the bottom. I don't know what alloy is used for the compressed gas bottles. So I am not sure about welding lugs on. Anyone know what steel is used?
Dan
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snipped-for-privacy@krl.org wrote:

Why would you go with a piece of used cylinder of unknown composition and history when you could buy a piece of bran new, known grade pipe for not a lot more cost given the foot or so needed?
Pete C.
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Well for one thing I would not have to weld on a bottom plate.
Dan
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snipped-for-privacy@krl.org writes:

'nother thought - springs from last weekend visited the "HMS Belfast", a World War 2 era cruiser moored on the Thames in London opposite the Tower of London. It has "Yarrow" type (?) 3-drum water-tube boilers. And one of the lower drums was opened up to show the inside with the pipes coming in. And the way that could be done - if I remember rightly, it had an oval access plate on the inside, so that when there is no internal pressure and you push it inwards, by rotating it bit in space you can bring it out of the vessel narrowest-axis of panel to longest axis of opening - the classic boiler access plate.
So can you get "stock item" a tube dome end with an oval access panel built in, like you would use in the drum of a water-tube boiler?
Richard S.
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No welding required for the bottom. The pipe is likely to be welded and drawn. Gas cylinders are made from a billet and the top spun if I recall correctly. Someone here is likely to know what steel is used in making gas cylinders. It is probably some sort of alloy so would need to use a low hydrogen method of welding. TIG qualifies.
Dan
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snipped-for-privacy@krl.org wrote:

On that subject, there is an episode of "How It's Made" that shows the manufacture of steel compressed gas cylinders.
Pete C.
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