Welding a small pressure test vessel...

China doesn't seem to have a problem making trillions with no QC program...

China doesn't have a problem with it's citizens being killed in relatively large numbers in mining and construction accidents, refinery or process piping failures, boiler explosions and hundreds of other ways that we in the U.S. consider completely unnaceptable from a moral standpoint, not to mention the toxic chemicals poured into the air/land/water from some of those incidents. But keep in mind they have some very strict QC programs in place for a lot of their product that's sold in the west when the west requires compliance. Look at the standards of quality and inspection required on a pipeline construction project in China, or Russia, or large sections of the world compared to one constructed in the U.S. Here, killing a dozen or so citizens in a pipeline failure, and pumping several thousands of gallons of pollutant into the groundwater is taken quite a bit differently than it is in many parts of the world. I'd rather not have the U.S. devolve into the China model for safety.

JTMcC.

Aren't those SIP scraps handy?

--Andy Asberry--

------Texas-----

Likely not for this one Pete -

But the group might be interested.

I have a plasma machine and it had been in and out of moisture in the lines. Not good for plasma.

I put two dryers in-line and it cleaned up. But I noticed I keep getting water in the tank (80-90$ RH here most of the time ) and I figured a little money was worth a rusted out tank and lots of bad cuts.

I would empty the tank when I could think of it - then one day I didn't get the valve as tight as I should. A slight (no sound) leak drives out of the bottom. It keeps the bottom dry or at least nothing comes out when opened up!

I noticed the tank turns on once in a while and I get the tank running to fill before I use it on the machine. There are two sets low and high - I like to start with the tank full to allow less pump on time. I pump faster than use anyway.

Martin

Mart> I'm not a certified welder in any way, shape or form. Mostly self taught

You might consider using a " Joy " test. Instead of pressurizing to do a leak test, immerse the item in water with some Joy ( or Dawn ) dishwashing detergent and pull a vacuum. It used to be called out on aerospace drawings as a leak test. The detergent is so you can see very small leaks that only generate a bubble every 5 minutes or so.

Dan

If that's more practical, then by all means. But if it's because of the safety angle then I'm sorry to hear it. Whenever these sort of things come up on Usenet, there's a always a flock of "better safe than sorry" posts. It's discouraging but tolerable when the project in question might involve the safety of the unsuspecting. But it's hard to take when the only person at risk is the one who's willing to take it. At the rate the scope of home projects is being limited by safety concerns, we're going to need licenses to sharpen our pocket knives before long. Your plan as you described it was certainly doable with reasonable skills and common sense. A conservative builder could test the thing to say, 5 times operating pressure. I expect that's a higher margin than was used for HF's paint pot, or countless portable air tanks etc. which everybody seems to have faith in.

Well, at least it'll be easy to tell if the test part leaked. :-)

Wayne

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

Yup, but I can't figure out what you think I used them for on this project. Maybe I forgot. ;-)

Wayne

snip

Good suggestion, and nice to see somebody thinking 'outside the box'.

Sometimes we go to great effort to implement an obvious solution when an alternate is simpler and safer and less work.

just my .02, YMMV

You're missing a lot here. To put it as simply as possible, this is a field where there are literaly hundreds of possible failure modes that will happily appear days or years after the vessel has passed a pressure test. A pressure test is one small portion of the overall picture and does not tell you you have a suitable vessel. There are dozens of red flags in the op's idea, number one being he has no way of knowing (and therefore duplicating) the original material specs, weld procedure, any pre/post heat treatment, ect. And, I can say with confidence that when you desire to build a vessel with flat plate, your engineering bill will turn straight up with many engineers not even willing to work it, and the thought of putting a fillet weld on the plate to pipe juncture would give your vessel engineer nightmares, you just can't design in a more wicked notch than that. I think thats a guaranteed fatigue failure down the road. This is the world of 100% weld penetration. Not an area hobby welders are going to excell. We could go on and on. Anyone who thinks this is a simple, solve it in the backyard type endeavor is showing how little they know about a very complex topic.

JTMcC.

How much do you think that 1/2", 8" diameter plate would really deflect from 150 PSI pressure?

Yes, No, and Maybe. I don't think anyone here would be worried if the pressure was going to be 1 psi. And no one would think it was trivial if the pressure was going to be 30 kpsi. I think that the stresses at 150 psi are going to be very low and fatigue is not going to be a problem. But I have not done any calculations. It would be interesting to build one and hydrostatic test it to destruction to see how much safety factor there is in the design.

Dan

I agree, excellent response.

"JTMcC" wrote

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

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

"Hundreds"? Would that be 20 fasteners holding the lid on, and 5 modes for each nut and bolt? Don't forget the washers. :-)

It was proposed to be overbuilt, and no mention was made of it being used for years. Nevertheless, I'd feel safer with it after ten years than I would with the average portable air tank. I bet you would too.

Lets cut to the chase - if it looked decent, and you knew it had been recently tested to several times its normal operating pressure, I very much doubt you'd be afraid to stand next to it pressurized. In fact, if you (or anyone) are willing to make a high enough wager, then I'll build it and we'll see if some of you may have been exaggerating the danger just a tad. Thinking ahead, I'm guessing you'll probably admit that it will work, but you just can't say for how long. I think that's a dodge considering that the project is so small it would be easy and quick to test it frequently if needed. Yeah yeah, it could test OK at

Wayne

with respect, YJDKWYDK

As to your attitudes regarding risk management they are your opinion and you have every right to express them, as do we. We leave it to the other contributors (and the lurkers, like Ernie who was smart enough to stand aside) to form their own opinions regarding which posters are to be regarded as credible.

As to your risk management attitudes (and your aircraft) I wish you good luck and happy landings, try not to take anyone with you.

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.

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.