Welding a small pressure test vessel...

Ignoramus6365 wrote:


Offhand, 1/2" grade 8 which I'm pretty sure are vastly stronger than necessary, but a convenient size. If I'm reading the specs correctly they're good for something like 21,000# tensile strength.
I expect the worst case tension would be equivalent to 1/3 of the total load or just under 9,200# based on the commercial units dimensions and test pressure. I don't believe there is a scenario that would apply worse loading since anything else would not be able to produce a seal to apply load at all.
Pete C.
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WOW! For someone who entered with,
I'm not a certified welder in any way, shape or form. Mostly self

you know an awful lot. If you're so sure of yourself, go ahead and build it. Why even stop here for advice?
Please keep us posted. (or have your next of kin post something)
Have you ever stayed at a Holiday Inn Express?
Steve
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On Fri, 11 May 2007 15:53:50 -0700, "Steve B"

I knew it was only a matter of time before somebody mentioned death or decapitation. :-) He said he was going to construct a small, low use, modest pressure, overbuilt test tank, not a submarine.

Nope. Yet I've built dozens of projects more difficult than what Pete proposed, including an entire airplane. It's depressingly obvious what would have happened if I'd come here for advice about any of them.
Wayne
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I agree. It's just that someone asks a question looking for a particular answer, and then disregarding or disrespecting whatever does not go along with the answer they're looking for.
Steve
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On Sat, 12 May 2007 14:32:34 -0700, "Steve B"

I'm suddenly reminded of contractors who advertise that they're happy to give free quotes, but get pissy if you don't automatically hire them.

I'm not sure where you could see any disrespect. He asked for comments on how to build something. Do you have anything to offer other than "don't do it"? IMO, all of the OP's posts emphasized that he'd be proceeding logically and responsibly. So I think the "you may die" type stuff is out of line. It seems that nothing less than "OK, I've given up the idea entirely" is going to satisfy the critics anyway. Which is sure to give pause to some who might have posted useful information about this or similar projects. :-(
BTW, have you thought about how many of the same "somebody's gonna' die" comments have been heard right before school boards shut down their shop classes? Why should parents risk their careless kids getting hurt around shop work if the consensus among adults with decades of experience, is that no reasonable amount of care or testing is sufficient to have even short-term confidence in something that's more than four times thicker than a similar $30 HF item?
Wayne
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Sure. The environment at some tire shops is complacent and haphazard even though tire seating doesn't provide any opportunity for prior testing. Workers in such situations are generally considered hapless victims, and society has deemed them worthy of protective regulation. BTW, I have 4 two-piece rims due for my attention. I use a home made slide hammer for busting them although it's obvious that most of the previous guys used a poorly aimed sledge instead. I fill them with a long hose from about 10' back and out of the line of fire. I don't even like walking by the damned things no matter how long they've been in service.
Anyway, I have a better analogy for you than tires - homebuilt aircraft. They're generally designated "experimental", as opposed to "CERTIFIED". ;-) Even if the builder starts with a kit, he is officially the manufacturer and therefore responsible for all design, construction, and ratings. He is assumed to have used some care in making his decisions. For example, it's generally his choice where he uses AN fasteners and where he substitutes butter bolts. The ship usually receives a single regulatory inspection before its maiden flight, and there's no way for that inspector to take the plane apart looking for every potential problem even if he was qualified to judge. The inspector will generally look for the obvious such as lock wire etc., but he's in no position to say if the spar can take 1G or 10, or if control surfaces were accurately balanced. All of that is expected to be accomplished and tested to the limits of his choosing by the manufacturer (AKA hobbyist), who generally gets the job done more by sheer determination than through any credentialed expertise. And yet it's undeniable that some pretty impressive ships come out of normal folk's backyards and basements. Mosey on over to Oshkosh if you want to see thousands of examples http://www.airventure.org /. Many of them are more advanced and better built than certified models. So you might try thinking of the OP's project in that light.
Wayne
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Here's another similar analogy: DIY submarines. I'm not saying that an airplane, a submarine, or a pressure vessel is beyond the abilities of a given do-it-yourselfer. I found a web site by an Austin, Texas couple who built an impressive submarine.
Nevertheless, we do these things at our peril. However, I lift my cup to the guy who does his homework, acquires the necessary skill, takes a deep breath, and plunges forward.
However, I personally would not undertake any of these projects, given my current skill level. Were I to want to do so, and inquire here, I would hope the advice would be: "You're ill advised to do this at your current skill level. But learn this and consider that. Then, if you still want to do it, go for it.
On the other hand, I would not consider it to be charitable or brotherly to simply say, "Go for it, dude!".
V
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I am not an experienced welder, but when I did my steel and stainless cert on 3/8" stock, I used a couple of different TIG machines both set at only about 120 amps. I made multiple passes and the process was slow, but both passed with no problems.
If the OP tapered the cylinder end so that he was certain to get full penetration and preheated the pieces, why wouldn't the machine he has suffice? I am not arguing here - just interested by your comment.
Peter
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I did not say impossible, I said impractical.
TIG has its place and IMHO is the most elegant of all the welding arts, and capable of making the best quality (and nicest appearance) welds on the greatest range if metals. I am sure that the OP's machine could easily be used for stick SMAW which would be my preference for heavier work, however the OP's honest appraisal of his training led me to suspect he probably lacked the required skill set.
No disrespect to the MIG guys but IMHO a TIG box equipped with both TIG and stick attachments is the best and most versatile welding system. My use of TIG has been limited to thinner materials and most commonly for SS, Aluminum and CrMo. Welding root passes with TIG does require additional setup in order to provide proper shielding gas to the back of the root. I suspect that a metallurgical or welding engineer would also specify additional pre and post weld heating and stress relieving which I suspect would be necessary due to the increased number of passes, and increased total heat input (time), but YMMV. IMHE, TIG is a lot slower and IMHO requires a high degree of (mostly left hand) skill.
Just my .02, YMMV
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You are not crazy to build it. But if it is going to be used by lots of other people I would over build it. How about using threaded rod and running the six bolts from the base to the top cap. No welding involved. Top cap and bottom identical.
Dan
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snipped-for-privacy@krl.org wrote:

A tie rod cylinder type design would be somewhat inconvenient in use. I'm thinking of a loosen knob and swing bolt out to side to open setup, similar to what you see on a trash pump where you need to be able to open and close conveniently to clear a clog. Some of the commercial units use a multi lug bayonet type locking setup on the lid, but I'm not really equipped to do that kind of machining on a piece this size.
Pete C.
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Depending on where you are located in the world it will be illegal for you to build it. Might not be a big deal if it's for your own use but if you sell it or put it in commercial use you'd be in legal trouble in many jurisdictions in the U.S.A.
JTMcC.
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I have to get in line behind JT. If ever there was a dimension where "code" welding is justified, it is pressure vessels.
V
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Vernon wrote:

Considering the operating pressure is in the same range as a normal shop compressor and not all of those have "code" tanks I'm not overly concerned on that front. I also don't plan to produce and sell them, it's a one or two off thing (one for me, one for a friend) though it will be used in a commercial environment.
Pete C.
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If you are in the U.S. they most certainly do.
JTMcC.
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JTMcC wrote:

Last time I looked, industrial suppliers like Grainger had both ASME code and non code tanks available.
Pete C.
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There are exemptions that allow some small air recievers (and a few other things) to be not considered an ASME vessel. Outside of those limited exemptions any envelope that contains 15 psi or more is legaly considered a pressure vessel. You mentioned in your original post the term pressure vessel. Depending on where you live, vessels may or may not be regulated. The number of places they aren't is diminishing due in part to the new treatment osha is giving vessels. If your jurisdiction does regulate vessels, the BPV Code carries the force of law and it's then illegal for you (without holding the required stamps and conforming to all other inspection, material tracking, and testing, ect. requirements) to build a vessel and expose the public to it. Vessel construction involves quite a lot more than just using materials that will calc out to the load. That's why the BPV code is so stinking huge and cost's over $10,000 in it's entirety. I have quite a few sections of the code, and I first started building vessels over 15 years ago. I'm no design expert but I am familiar with a FEW of the many, many considerations that go into vessel design. Vessel failure in the pressure range you mention can range from a simple hissing sound to catastrophic failure and there are quite a few cases of people being seriously injured or killed at pressures even lower than yours, loss of arms being the most common I've seen documented. The welding requirements in the BPV code are extensive and are there to compensate for a lot of different failure mechanisms, fatigue induced cracking, corrosion, built in notches, the list goes on for quite a bit. I haven't commented either way on what you intend to do but I have pointed out a few of the many factors those of us that have build vessels for a living (I don't anymore, I do still work in pressure piping) have to take into consideration. I consider it an endeavor well beyond anyone describing themselfs as you have. Not to mention the large amounts of liability insurance one has to carry to weld on either new construction or repair of any pressure containing device. I have no interest in argueing the point with you, build what you want but you no longer have the excuse if ignorance should your vessel cause damage in the future.
JTMcC.
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Amen, JT!
I was all in favor of Iggie building his trailer and emitting flatulence in the general direction of detractors and doomsday naysayers. That was because in a trailer, steel can reasonably be expected to YIELD befoe it fails.
With a pressure vessel it can reasonably be expected to EXPLODE before it fails.
I consider myself to be a moderately advanced and competent hobbyist welder. But that doesn't mean you'd want me welding in your nuke generating plant.
V
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By the way, Vernon, the trailer is quite well functioning, I recently used it to carry a 2,200 lb Bridgeport mill and it did not even budge. After about 50 miles, there was not a single trace of the mill ever having been transported.
Also, some concern was expressed that the drop axle's top was too close to the frame fo the trailer -- but even with the mill on the trailer, and some bumps on the way, the U-bolts never touched the frame.

I hope that you mean "soon after it fails".
i
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On Fri, 11 May 2007 09:03:43 -0500, Pete C. wrote:

Then don't you need some sort of approval for it?
--
Mike


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