Design Text Pressure Vessel for Pressure Tests 8

[MarkCA]

I've been tasked with designing a pressure vessel that we can use to run pressure tests on our equipment. I've been looking for a text that covers this topic, but all the ones I've seen on Amazon seem to focus on Pressure Vessels and Boilers for Refineries. Are there any that are specific to this sort of testing vessel?

It's not the calculations for the stresses in the walls I'm concerned about so much, I can get those out of Rourk's; I'm more concerned about the little, but still important details. Designing the end caps properly to hold the pressure even after opening and closing the vessel multiple times, for instance.

With the size of the vessel and the amount of pressure (at least 20ksi) we'll be using and the inherent danger I need to get this right the first time.

 

[TGS4]

Where in the world are you? Depending on that, your answer may already be found in in local law. For most of the US and Canada, the law requires adherence to the ASME Boiler and Pressure Vessel Code, for pressure vessels that are within their scope. If you're talking about 20ksi internal pressure, that is significant, and would put you into the realm of ASME Section VIII, Division 3.

There are legal, insurance, and ethical implications here that are well beyond a textbook. Fabrication, inspection, materials, etc, in addition to the design/stress aspects are all considerations.

If you have no experience with this, please hire someone who does.

 

[dhengr]

Wow! A 20ksi internal pressure is indeed fairly significant, and might require a little extra attention to design and fabrication details. Me thinks... “been tasked with designing,” “20ksi internal pressure,” and “Rourk’s,” are synonymous with ‘don’t have the vaguest idea what to do with this problem.’ You really should talk more with your boss on this one, so you each know what the other does and doesn’t know on this topic and type of design and fabrication problem. What on earth are you testing? Vessel shape and dimensions? Volume used per test cycle? Number of loading and unloading cycles per day? Do you have a big enough tire pump to achieve those pressures?

I absolutely agree with TGS4. And, I don’t think you will find your answers on Amazon. This is truly a special problem, and you should get the help of someone with real experience.

 

[EngineerTex]

I would like to agree with TGS4 and dhengr and then up the ante. DO NOT CONSIDER DESIGNING THIS PRODUCT.

That being said, the design of this test vessel is going to be the least of your problems and the least expense. I work in a facility that routinely tests our products to 20,000 psi.

The testing is done in a bunker. The pressure vessel is underground, in this bunker, deep enough to be surrounded by thousands of tons of dirt. The access to the bunker is through a vertical shaft and the shaft has an access room at the surface made of concrete walls and a concrete ceiling. The walls are thick. Really thick. The roof (directly above the shaft) is even thicker - 3 feet of reinforced concrete.

The reinforced concrete doors are operated by enormous gearmotors and electronically controlled and monitored. Ridiculously meticulous security procedures and equipment has been implemented, including motion detectors inside the room to help ensure no person is inside the surface building when testing is performed.

That being said, I would now like to give you the good news. You do not have to design your vessel. You can rent it or buy it. Call around in Houston, TX, Edmonton, AB or Houma, LA to oilfield service equipment manufacturers and look for an API 6A riser spool used in well servicing operations. You can easily find a 13.625" ID riser spool flanged on each end and get it in most any length you need. These spools are offered in standard pressure ratings of 2ksi, 3ksi, 5ksi, 10ksi, 15ksi and 20ksi. I don't know what you're testing, but hopefully whatever it is, it will fit inside of a 13.625 ID. If it's smaller, you can find smaller-bore equipment. You can also readily find the normal accessories that you would need to assemble your test apparatus. Flanges, blind flanges, metal-to-metal seals for properly sealing these items, reducers, adapters, etc. And for connecting these items between your pressure vessel and your pump and instrumentation, Autoclave makes every manner of tubing, fitting and connector capable of up to 60ksi pressures.

After you have built your bunker and containment room, you still have huge tasks ahead of you including determining a way of removing all gases from your vessel, use only liquids that have been degassed for the testing, implement a testing procedure for the vessel itself - standard in my industry is full magnetic particle and ultrasonic or x-ray testing every three months of service (check with your manufacturer), find a big enough tire pump and then hide behind a D9 Caterpillar.

Again, I will make the statement as strongly as I possibly can -- do not try to design this product.

Engineering is not the science behind building. It is the science behind not building.

 

[SNORGY]

EngineerTex:

It sounds to me like you have a high pressure job with a lot of stress-related issues.

Regards,

SNORGY.

 

[berkshire]

Snorgy,
You just had to say that didn't you. []

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[MarkCA]

Alright, sorry for the delay. Holiday week and all that.

Anyhow, to broadly address the some of the questions/concerns:
I had thought that ASME BPV code applied to refineries and not to this sort of project. In retrospect, I don't know *why* I thought that, but there you are. At any rate, I'll call that the keystone mistake since everything else stems from that.

The reason we need that much pressure is for the hydrostatic testing of downhole tools. Which is something I (we) do know how to design. The tools I mean.

And no, I'll not be designing this. Now that I've corrected the location of my cranium with regards to the application of ASME BPV I'm not going to be trying to take that on. Having had experience in the past with ASME B31.3 (but with piping specs, not pressure vessels) and API Spec 7 I know what a daunting task it can be to learn the even the basics of industrial standards, much less the equally important details.

 

[gr2vessels]

MarkCA,
It is unclear your question of how to design the end cap for multiple opening and closing cycles;- you cannot open the removable end cap under pressure, because of depresurization consequences. Before opening the cap, you need to release completely the pressure from the vessel (obviously, after isolating the vessel from the source of pressure).
Typically, there are specialised manufacturers for so called 'Quick Opening Closures' who offer their proprietary design for pressures up to 6000 psi, but in cases they would provide custom design and fabrication for your particular vessel.
the vessel itself is no a big deal, any experienced pressure vessel engineer should be able to provide a correct design per applicable code. All you need to do is to ask the fabricator to provide full certification for the vessel, including appropriate ASME stamp. Lastly, you have to pay for all that expertise.
Simple, really.
cheers,
gr2vessels

 

[MarkCA]

When I said multiple opening and closings I meant that we would be opening the vessel, placing the test piece inside it, pressuring up and holding for, say, an hour, releasing pressure, opening the vessel and removing the piece, checking/testing it and then starting from the begining for, say, ten tests on a given tool. That would be a single test for one piece.

So we're going to need something that can be opened and closed over and over (unpressured) but that can still stand up to the 20ksi operating pressure when we're running the hydrostatic test on whichever tool we have in the vessel.

 

[EngineerTex]

You could also try something along the lines of what is commonly referred to as a "Grayloc Hub." Woodco makes them as well as a number of other manufacturers.

See API Specification 16A

And:

http://www.woodcousa.com/catalogs/clamp10.htm

Engineering is not the science behind building. It is the science behind not building.

 

[MarkCA]

We'll have to discuss that with the designer.

Though, just briefly looking at it, something like that could work, in theory. Maybe with a blind flange on one side (assuming it can withstand the pressure and stresses, of course) and the vessel on the other.

 

[MarkCA]

Actually, I take that part about the blind flange back. I don't think that would quite work the way I was thinking.

Anyhow, like I said, that's something we'll have to discuss with the designer.

 

[Cockroach]

I have a design for 30 ksi, usage of Modco Closures as entry to the vessel and Conax Buffalo ports for passage of wiring in and out the pressure containment envelope. You can follow CSA Z245.15 or other valving codes, Boiler Branch may have some literature.

You'll need a very thorough understanding of tri-axial stress analysis and material selection. I recommend that you have a Professional Engineer look at the design and acknowledge it once you have "roughed it out". I'm unsure of your dimensional requirements, but connections and weldaments will need a very high level of NDT with certification.

Good luck with it. I recommend placement in an underground bunker type arrangement.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[gr2vessels]

Mark,
You didn't mention the size of the vessel, perhaps is not a large diameter and you can make it safer than it looks at a first glimpse. I understand you are using water to pressurize the rig, so you can re-use the same water over and over again. The blind flange designed per ASME code is not out of question and you can use some bolting arrangement to speed-up the opening / closing operation. To depressurize the water inside the vessel will be a short squirt, then drain the vessel and open it.
Can you give us a feeling of the size to talk about?
Cheers,
gr2vessels

 

[MarkCA]

9-10 inch ID; at least a 6 ft interior length.

 

[racookpe1978]

Hmmmn.

Quick-opening, but needs to resist that much pressure?

Sounds like you could use an Army-surplus quarter-turn, interrupted-screw cannon-type breech.

Army: 105 mm cannon => 4 inch ID
150 mm => 6 inch ID, 8 inch cannon were also made.
Above that, you start getting into coastal artillery and battleship size units: 12 inch, 14 inch, 16 inch.

Expensive to build, but the concept is simple.

 

[MarkCA]

It doesn't have to be quick opening, per se, though that would certainly be welcome. Mainly it just needs to be durable enough to open and close repeatedly while withstanding the pressure.

 

[racookpe1978]

But think about your actual operating cycle: {i}When I said multiple opening and closings I meant that we would be opening the vessel, placing the test piece inside it, pressuring up and holding for, say, an hour, releasing pressure, opening the vessel and removing the piece, checking/testing it and then starting from the begining for, say, ten tests on a given tool. That would be a single test for one piece.[/i]

For a 20 - 30 bolts on a blind flange (depending on diameter and schedule of flange), you need a long time to torque the 20+ bolts back to spec: you need to firmly tighten all of them, then go to 30% torque, then 70%, then 100% torque. It's going to be an all-day affair to get just one test done - even if no bolt freezes, galls or fails and no flex gasket leaks.

Remember to replace the flex gasket each time.

The flange is going to be heavy enough you will need some rig to hold it up and swing it out of the way each time you move the flange.

 

[MarkCA]

The blind flange comment stemmed from the Grayloc Hub. If we end up with something like that, we'd be taking apart the Hub not removing the blind flange.

That's four bolts not a couple dozen.