Pressure Vessel vs Pipe 5

[shopper1732]

When does a Pressure Vessel become a Pipe and vice-versa?
Is there a minimum diameter for a Pressure Vessel?

 

[Ashereng]

John,

Yes. My solution is to not have a "air receiver" vessel. I want to replace the vessel with an "enlarged" air distribution header, made of pipe.

An air receiver basically takes the air from the dryer, holds it, acts as a "dampner" and holding volume to even out the air load requirements while maintaining pressure. I believe I can achieve the same with sufficiently large pipes.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[JohnGP]

As indicated above, I would agree. That sort of thing was considered for the project I'm presently on, but in the end I think it would have been more expensive to run large diameter pipe all over the place, rather than have receivers placed here and there. Plus the competition for space in the pipe racks is pretty fierce....

 

[moltenmetal]

Ashereng: just to add, local codes here catch compressed air piping above 3/4" size and define it as "pressure piping", whether or not it is associated with a registered pressure vessel as a receiver/storage tank. So you'd need to submit a design registration for a big pipe header and you'd have to fabricate it in accordance with the appropriate piping code: certified welders working under certified procedures, spot radiography, fittings with CRN#s etc. But if you keep the header below 6" diameter, you could avoid registering the thing as an ASME VIII vessel regardless of its ultimate volume.

 

[waskillywabbit]

Another fine example of overthinking and semantics. I think the line between the two is pretty clear...when is the last time somebody threatened to hit you in the head w/ a "pressure vessel".

Brian

 

[Ashereng]

Fair point.

When was the last time somebody threatened to hit you over the head w/a "300 ft length of 16" sched 40 pipe"?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[chicopee]

If you think about their respective purposes, you'll have your answer as to when a pipe becomes a vessel.

 

[Ashereng]

chicopee,

I don't understand your answer. Can you clarify, using my example?

If a pipe and a vessel both serve the same purpose, is it to piping or PV spec?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[chicopee]

well, a pipe is for the pupose of conveying material where as a tank can be either for storage or process. That in my view is the difference between piping and tank.

 

[Ashereng]

So, where is your opinion if a pipe is used for "storage" where a vessel is usually used, as in the case of an air receiver?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[alamin]

Interesting discussion thread.

I started to learn bits and pieces on Australian pressure vessel code (AS 1210) only recently. So excuse my limitation of knowledge on the topic at hand. However, having seen some examples in our plant, I think I can shed some light here with sufficient confidence.

I shall present two excerpts from AS 4343 (Hazard level) that will give you some pointer (if not definitive answer) to the topic under debate:

"Pressure piping is hazardous and, for simplicity, diameter is used in place of volume. The hazard level is made the same as for a pressure vessel with volume equal to that of a pipe length of 10 diameters."

"With a pressure vessel, the entire contents have the potential to be released instantaneously but with pressure piping it is only the volume close to the ends (at the pressure point) of a completely ruptured pipe which influences the immediate damage. In most cases, pressure would reduce and often the flow would be stopped through isolation being provided after the failure."

Due to the above reason, blanked (even if at one end only) pressure piping registered as a pressure vessel will have a lower hazard level than a pressure vessel (as we normally understand of it) of same volume. So, the bottom line is that intended design function and hazard level can dictate whether you will opt to register a blanked (with flanges) pipe segment as a pressure vessel.

For example, in the plant I am working I have seen 1.2m high pressure vessels (vapour condensers) made out of 450mm dia pipe section (ASTM A53 Gr. B, carbon steel) but registered as pressure vessels, because of their function and hazard level (mild-scale laden non-condensable odourous vapour condensed inside the vessel after being flashed off by the lake water spray injection; cleaned vapour is sucked out thru a nozzle on the top flange via a vacuum pump whereas scale laden lake water comes down (gravity flow) thru' the the bottom nozzle to a seal tank via 150mm dia piping.

Comments, most welcome.

Cheers,
Amin

 

[chicopee]

Well,lets take a look at a propane bulk storage facilty which we can all relate to. The piping between the bulk head incorporating the loading and unloading riser and the propane storage tank may become a storage facilty if the manual or emergency shut off valve under the tank is closed which is one reason why such piping is fitted with a hydrostatic valve. Because such piping is storing propane should we call it a storage vessel? The answer is no.