Pipe pressure rating

Hi all,

Ok, so I need to build a pressure vessel. It is basically a piece of steel tube, 100mm outside diameter and 40mm inside diameter. Everyone seems to use Barlow's formula which would mean this tube would yield at 36000psi.

I don't see how it can hold such a small amount of pressure, is there anyone out there who could plug this into a computer module. Pressure I'm wanting is nearer the 500,000psi mark for about a micro second or two, so it's just a peak but I'm not sure if it would stretch or break. I would say the average pressure would be around 100,000psi.

Hope anyone can help me, even if its an odd question.

Thanks,

Joe

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OK curiosity has got the better of me.

What on earth are you doing with that much pressure.? It's an awful lot even only for a fraction of a second.

A 22/250 rifle has a chamber pressure (depending on bullet choice and load) in the region of about 63,000 psi which will squirt said bullet out getting close to 4,000 fps if it's one of the lighter options.

How are you going to generate that much pressure.?

Nick from Curioustownsville.

My direct experience with containment vessels of that sort, years ago, showed that the UTS of the material,and

Barlows, is not the limiting parameter. It's called critical flaw size and has everything to do the size, shape and

orientation of the grain structure which must be correct for the material. And the material must exhibit exceptional

notch toughness.

That sort of containment vessel design is quite specialized. Make sure you have something very solid between

you and it if you proceed with the experiment.

Take care,

Pete

Joe,

If you want any meaningful help you need to give a lot more information.

I expect that somebody in a very secure place will be taking a close interest in this thread by now.

500K psi is nearly 10 times strength of steel? How is this going to work exactly?

Mark

I work with high pressure equipment - and I collaborate with people who work at really high pressures.

The design criteria for HP equipment are rather different from more typical vessels. The stresses vary a lot through the wall thickness of the pipe/vessel so the 'thin wall' approximations don't hold any more. See ASME VIII Division 3 for possible design approaches.

500 ksi - or around 34kbar is very high for a vessel, sounds more like a job for a diamond anvil press or such like.

100 ksi or 7kbar isn't too tricky at all. The numbers seem a bit vague. What steel?, how do you plan to seal it?

As already suggested, assume it will break catastrophically - the HSE has a very good guidance note (GS4) covering safety in pressure testing **LINK**

I suppose it is a little vague and not something for any of you to worry about, I assure you.

I like to keep within the law too, so it's not a weapon of any kind, I wish I could get the permission, but I highly doubt it.

Ok, so has anyone ever heard of the exploding wire? It's where a huge amount of power is dumped through a thin wire causing to explode, it creates huge pressure peaks in the air. Now submerge this underwater and you get huge pressures. Now the only thing I can get away with making in the UK is some kind of industrial equipment, like hydroforming or a press.

I have 8kJ of power to play with, approximately 400kA of peak current, 360MW peak power. A research paper using the same power input, 3.2GW peak power showed peak pressures of 7kbar for a microsecond and 100kbar for a nano second.

So I was going to make a steel press with a steel vanadium piston, enclose it in a steel ventilated box to contain any fractures and make a beast of a press. It was half one in the morning when I wrote the post. Peak pressure will be more around the 10kbar mark, and I guess for any reasonable amount of time it will be 1kbar. The vessel is not a perfect seal either as there will be a piston, clearance of about 0.02mm, and a small ventilation hole in the side to ventilate pressure. So I'm upping power as I measure the peak output pressure, I want around 1 or 2kbar to be the maximum.

I only wanted to know if there is some way to predict what pressures a tube would yield at so I could scale power up and still be within a margin of safety. Barlow's formula seems to only apply to thin tube and the only other calculation I got was from zeus which predicted 60,000psi (4kbar). So 1kbar peak, what I'm upping the power to, should hold.

For comparison, the pressure at the bottom of the Marianas Trench is about 15,000 psi.

As one of the three uses for this technology is detonating nuclear bombs this thread is making me a but nervous.

Perhaps you could be a bit more explicit about why you want to do this rather than why not?

Neil

Hi

Many many years ago I read an article where they, a lab in Russia IIRC,, were using a similar process to form stainless steel plates around a former. In this case they were making dental plates and having taken a mould of the person's palate they explosively formed the stainless before the mould disintegrated. I have no idea what pressures they were achieving or how long the pressure pulse lasted for.

Cheers

Martin

All very technical and interesting so far.

My own input would be stand well clear around a corner because this sucker is going to make one heck of a bang

The tube yields first at the inner wall (where stresses are highest).

This will be at pressure P = Qy. (K^2 -1)/K^2

Where Qy is the SHEAR yield stress of the material, and K is the ratio of outside to inside diameter of the cylinder. In high pressure design some bore yielding may be allowed. The Design Factor will be referenced against Plastic Collapse (Ballooning), or possibly even against Burst of the tube.

Most importantly, think about possible fatigue failure - becomes very common and can be very dramatic as harder steels are used. Choice of steel is very important

A couple of kbar is fairly run of the mill - one major type of plant for manufacturing Polyethylene operates at those sorts of pressures continuously. Fairly robust engineering, but not particularly exotic.

I guess people want to know why I'm doing this, well I have a 8kJ capacitor bank and a lathe, so why not. I guess some people don't have the same logic as me, but to me proving a theory, building something with a bang that's not illegal or generally just designing and fabricating something is fun.

I have even built a nuclear fusion reactor to fuse deuterium atoms into tritium and helium. It consisted of TIG welding, turning large pieces of stainless in the lathe and fabrication. In the end I get x-rays, neutrons, irradiated silver-108 or 110, tritium, helium, sounds horrific, but infact the radiation is so low that I would get more from a CRT TV. I do these projects for my own enjoyment rather than to be productive, I'm sure many model engineers like the process of design and building the thing probably more than the result.

Wow, I can babble on.

Anyway my website is

www.prometheanrifles.co.uk

All of the stuff on there is from what I research or build, it may not be 100% correct but I hope some of you might find bits interesting. It may be a week or so before I build this thing, but my application is hydraulic pressure observation, not a weapon.

Hi Martin, that's one of the things I want to achieve, hydroforming aswell as making nano particles and a press to crush things.

Thanks David for the input, this is a very similar equation to the Zeus book, I will probably be using mild steel for the main part, because it's cheap and easy to machine, plus it's a bit more elastic so shouldn't suffer fatigue as bad. It's all going to be enclosed, so if or when it fails it will be contained.

Edited By Joe Page 1 on 23/11/2015 15:02:58

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Something is not right here.!

So you have all that power and infrastructure available to you and don't have professional advice and a fully budgeted contract.

Boss - "Oh Joe that's a nice chunky tube contraption thingy you have made what are you going to do with it.?"

Joe - "Well I am going to connect it to our HV supply and make a nice big bang"

Boss - "Oh how very exciting.! Who has run all the figures and equations.?"

Joe - "Well they were done by a random crowd of really nice guys I was chatting to on the internet."

Boss - "Well thats OK then. Hook it up then and fire away Joe."

I am going to stick my neck out here and say that you are either an internet troll trying to get others to bite, simply a good ole fashioned terrorist or a saddo with too much time on his hands.

Nick

Edited By Nick_G on 23/11/2015 14:58:59

Wow, thanks Nick. Do you realise that this power comes from a capacitor bank half the size of a microwave. The power here is enough to power your kettle for 4 seconds, so it is all not that big and expensive. Why would I troll the internet on something like this? Why does this make me a terrorist?

And don't we all wish we had time on ours hands, I find it very sad that you live in a world where there is no spare time. Or maybe your just an internet troll trying to get a reaction out of me. People have different hobbies and interests, I like to research and build stuff out of the ordinary, I'm sure I will get more interest from this rather than the stuart 10V I'm building.

Edited By Joe Page 1 on 23/11/2015 15:19:46

I don't think Joe is either an internet troll or a terrorist.

He is just living in a different world probably turning a handle behind a curtain like the Wizard of Oz !

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Sussed. .......... Totally guilty.

If you are thus then I apologise totally. It's just that people playing 'games' here are not totally unknown. .......... I will stand corrected.

Out of curiosity (again) I bet that capacitor bank would make a wonderful instrument of torture. I want one. ...... Really I do.

Regards, Nick

Haha, no worries Nick, you got a reaction out of me anyway. Some reason everyone tells me that I'm living in a different world . I think I'm just a little eccentric.

It's unbelievably powerful, but so incredibly dangerous. China made it happen. I built it for a fusion project but the power was not high enough, so I'm trying to find a legal use for it. I will however destroy some fruit with it for your pleasure. I'm sure it would vaporise my finger if I touched the terminals, (sausage experiment?) not sure I would want to be tortured by it, but it would quartorise the wound (if that's how you spell it) Wanna buy it?