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Pressure Vessel vs Pipe
5

Pressure Vessel vs Pipe

Pressure Vessel vs Pipe

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

RE: Pressure Vessel vs Pipe

Well, one way to define is the code that it's built to, if any.

Piping code = piping
PV code = PV
No code = call it what you want

While I am not aware of any real minimum dia. for a PV, vessels 6" dia and smaller are excluded from the scope of Sec VIII, Div 1, for example. Other codes may have different limits.

Also piping is primarily for transport of fluids, while PV's typically process them in some way, such as changing temps, separating, etc.

Hope this is helpful, no doubt somebody else can give you something more definitive.

Mike






RE: Pressure Vessel vs Pipe

Indeed as far as i know, the piping codes (at least the oens i am familiar with such as B31.3 & B31.4) have originated from ASME code and there is a close relation between them.

In any case heat exchangers, filters, scrubbers, and any equipment that is connected to a piping system with one or more objectives other than just transportation of fluids are PV's. Hence i agree with SnTMan.

RE: Pressure Vessel vs Pipe

(OP)
Thank you.
I am getting old.
I was trying to remember if it was 4" or 6" or what.
In this age of electronics, I do not have access to the section VIII or B31's except via computer.
It takes all day to search and I go blind mousing and screen-looking at damn PDF's
So, thanks again.

I did not complicate the question with reference to in-line (piping) devices such as static mixers, but my faulty memory says that they are exluded too.

RE: Pressure Vessel vs Pipe

shopper, I agree, there is NO substitute for a paper Code book. Much easier to flip back and forth, especially with the way they put three pages of figures in the middle of the paragraph you're trying to read. When I need to look at the (electronic) Code book, I just print that section. Eventually I'll have the whole thing.

Mike

RE: Pressure Vessel vs Pipe

a major benefit of the electronic codebook is that you don't lose all your templates/"pocket pals" in it winky smile

well..... plus you can search it easily too

RE: Pressure Vessel vs Pipe

arto, I don't seem to lose any less of them for having an e-book...

Mike

RE: Pressure Vessel vs Pipe

Pressure Vessels are defined in ASME Section VIII, Div 1 introduction....

"Pressure Vessels are containers for the containment of pressure either external or internal. The pressure may be obtained from an external source, or by the application of heat from a direct or indirect source, or any combination thereof..

This seems clear to me for pressure vessels - size has nothing to do with pressure vessels.

Piping is a pressure-retaining component that conveys fluids.

RE: Pressure Vessel vs Pipe

I think the line is blurry. Sometimes, a pipe can be a vessel and vice versa.

Here is another example: You can all decide.

I have a 50 scfm instrument air receiver. Most people would agree that it is a pressure vessel (100 psi).

I have a 16" pipe, schedule 40, of sufficient length to give me 50 scfm equivalent volume. Most people would agree that it is a pipe (100 psi).

I can use the two interchangeably, if I have to.

The air receiver falls under ASME Sect. VIII. The Pipe in my my case falls under CSA Z662.03.

It's a tough call.

My colleague and I still don't know what the right answer is.

"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?

RE: Pressure Vessel vs Pipe

Ashereng,

I agree that the line is blurry, but if an inline component is simply fabricated from standard pipe and piping components then it should be possible to design and fabricate to a piping code.

I have seen some pig launchers/receivers though designed to B31.3 and others to ASME VIII, so sometimes it seems to come down to personal choice.

Once one has to start rolling plate and pressing dished ends, then to my mind the component is definitely a pressure vessel.

In your case of the air receiver (I guess you meant 50 scf volume), there is no problem in using a piping system to provide a storage capacity above standard flow related sizing. I can't imagine even the most hardnosed AI insisting on the use of a PV code in such circumstances.

Just my thoughts,
John

RE: Pressure Vessel vs Pipe

3
ASME VIII and the over-arching Canadian pressure vessel document CSA B51 give definitions for what is a pressure vessel and what isn't.  Depending on the nature of the hazard represented by the fluid, the pressure and the diameter, the flowcharts given in B51 will tell you whether the component in question is a pressure vessel, a Category H fitting (for components to be fabricated and sold in multiples as discrete devices), or merely an enlargement in the pressure piping associated with other pressure vessels in the system.

Note also that there are provincial acts which exempt specific situations to ensure that devices such as domestic water heaters and water system expansion tanks are exempt.

The dividing line between vessels and pipe becomes gray as illustrated below:

Let's say we have a piece of 8" pipe connecting two large pressure vessels in a process plant.  That would generally be considered a piece of ASME B31.3 piping, even though it is greater than 6" ID and greater than 1.5 cubic feet in volume, and the relief pressure is above 15 psig.

Now let's say that the pipe has a reducer at each end to 4" linesize.  Still a piece of pipe, right?

Now let's say that it has reducers at either end to 1/2" NPT or a 1/2" flange, or a Swagelok connector for 1/4" OD tubing.  Is this still a piece of pipe?  Most people, presented with this piece of "pipe", would conclude it is an ASME VIII vessel, even though it is still no more than an assemblage of piping components.

Even though the codes don't state it in words, what they're concerned about is the volume of stored energy or hazardous material under pressure.  The principal enclosures with the largest stored volumes of materials are considered vessels and subject to the rules and codes as vessels, where the lines interconnecting these are considered pipe and subject to the rules and codes associated with pressure piping.

RE: Pressure Vessel vs Pipe

So moltenmetal,back to my example and John's. What is your opinion?

Is the air reciever pipe a pressure vessel or pipe?
Is the pig receiver/launcher pressure vessel or 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?

RE: Pressure Vessel vs Pipe

In reality it is up to the Regulatory body/agency or Jurisdiction or your insurer of the equipment to determine the applicable Code or Standard. If you happen to be in a location that does not regulate pressure vessels or you happen to be self insured, you decide.

If I was head of the Jurisdiction that regulates boilers and pressure vessels for your hypothetical situation, I would deem them pressure vessels.

RE: Pressure Vessel vs Pipe

metengr, I'm sorry, are you responding to my hypothetical situation?

"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?

RE: Pressure Vessel vs Pipe

Hypothetically, yes smile

RE: Pressure Vessel vs Pipe

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RE: Pressure Vessel vs Pipe

metengr,

Fair enough regarding the pig traps (depending on size I would tend to think of them as inline piping components though). There's no way however that I would consider a length of pipe in a system as being a pressure vessel, just because it had a larger diameter than one may think necessary to transport air from one location to another.

Regarding CSA B51, moltenmetal, I am totally not familiar with that document so cannot add anything there, but feel that if a piece of piping between a couple of vessels looks like a pipe, then it must be a pipe.

This in no way clarifies the blurriness that exists between what constitutes piping or pressure vessels in some cases (probably because my mind is just as blurred) - sorry shopper1732.

Cheers,
John

RE: Pressure Vessel vs Pipe

For those of you not from Canada, I apologize for the regional nature of my post- but these regulatory issues are ultimately subject to regional variations, so I can't comment beyond my knowledge.  Your rules may vary!

If the design were for use in Ontario and I was subject to the TSSA Act, the air receiver would be an ASME VIII vessel, whether you chose to make it from pipe or not.  It is the major source of hazard from stored energy in the associated system AND it would fall within the definition of an ASME vessel.  There is a specific exemption for small air receivers (to exempt the average shop air compressor tank) but I'm far too lazy to look it up.

Designation of mere line enlargements like pig launchers etc. is pretty much at the discretion of the owner.  As long as the components were designed and fabricated in accordance with either ASME VIII or B31.3, TSSA would probably be satisfied.



RE: Pressure Vessel vs Pipe

JohnGP,

My bad. The CSA came from me - I am currently working in Canada, and hence, the CSA requirement for my pipeline. However, in the US, pipeline would be covered by ASME would it not? In anycase, where to draw the line remains as fuzzy on both sides of the border.


moltenmetal,

The instrument air receiver (ASME pressure vessel kind) typically runs at abut, 120 psi, maybe 150 psi maximum depending on the compressors? This is hardly high pressure.

The instrument air (IA) header that runs around the plant (2" pipe) is at about 120 psi. I don't see the IA header piping posing any more of a stored energy hazard than the receiver. In fact, a receiver should present more of a hazard than the pipe?

By the way, I do agree with both you and metengr - it really comes down to the inspector. However, sometimes, they are wrong too! banghead

"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?

RE: Pressure Vessel vs Pipe

moltenmetal,

We may be crossing our wires to some extent - I was picturing Ashereng's scenario with the pipe of 50cuft volume as just a section of pipe of increased diameter within a system of air distribution pipework. To my mind designed in accordance with a piping code. I also agree that it is quite likely that a discrete "vessel" would be designed to a PV code (and required to be), even though it may be constructed from standard piping components. No problem. But the line between the two can become blurry as discussed above.

Ashereng, what happens in the US is just as big a mystery to me, but I suspect a similar situation applies - it really depends on how one's AI views the world. I'm sure the same fuzziness exists in all parts of the world.

Cheers,
John
 

RE: Pressure Vessel vs Pipe

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
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

RE: Pressure Vessel vs Pipe

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....

RE: Pressure Vessel vs Pipe

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.

RE: Pressure Vessel vs Pipe

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

RE: Pressure Vessel vs Pipe

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?

RE: Pressure Vessel vs Pipe

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

RE: Pressure Vessel vs Pipe

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?

RE: Pressure Vessel vs Pipe

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.

RE: Pressure Vessel vs Pipe

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?

RE: Pressure Vessel vs Pipe

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

RE: Pressure Vessel vs Pipe

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.

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