Pressure Vessel Under 15 psig in United States 1

[tmast2]

If a vessel is being operated under the 15 psig rating which keeps it from needing to be a stamped pressure vessel, what other codes or specifications does a manufacturer need to follow in the United States to be sure they design the vessel to cover them selves as well as make sure the vessel is safe?

 

[tmast2]

To give a little more information...
Multiple outlet reservoir for LN2 at atmospheric pressure.
Approximately 5-10 gallons.

 

[fegenbush]

It is still possible to design, construct, and hydrotest a vessel to ASME Section VIII standards without applying the ASME stamp. The documentation you keep could then be presented as evidence that you had done your engineering due diligence should a problem arise in the future.

Since the vessel is small, it may also be economical to construct two and proof test one to failure.

 

[weldstan]

UL.

 

[moltenmetal]

15 psig design pressure components are NON CODE, i.e. they are outside the scope of the codes. Specifying a hydrotest at 1.5x is still a good idea though. Presume that relief/venting for the N2 is already properly considered.

 

[davefitz]

Fegenbush is correct. The asme codes include material cert requirements, design rules, QC program and testing requirements ,welder qualifications, overpressure relief requirements, and stamping/ documentation . With the exception of stamping/ documentation aspect , a fault in any one of the other aspects can lead to a failure. However, how one can certify that one uses the ASME code for design and fabrication of a vessel and yet does not have the stamping/documentation is an open question.

"Whom the gods would destroy, they first make mad "

 

[fegenbush]

There are certain customers which either have dedicated quality personnel or contract out a shop (or field) inspection to ensure compliance with codes, standards, plans, and specifications. Depending on your relationship with your AI, they may be willing to perform such an inspection and sign a compliance report. Minus their jurisdiction or National Board commission number, of course.

 

[gr2vessels]

Any method of design which employs a significant safety factor to protect the operators and the owner from failure of the equipment is an acceptable engineering process. The easiest way is to follow an internationally recognized code/standard like ASME VIII, or Chinese, Russian, British PD5500, Australian AS 1210 standards which are accepted as relevant codes in USA. The key is the safety factor you employ, to ensure the safety of personnel and prevent loss of property. Also, it is the certification obtained after the review of a qualified body, like AI in USA and similar in the rest of the world.
Cheers,
gr2vessels

 

[GenB]

I disagree. an AI signing without proper endorsements has no value, and why will he/she do it and get exposed to liability. It may as well sign the proper doc. and be free of liability.
I also disagree with any one who says that"building to the Code" w/o final
stamping and certification is the same but it just short of data report and national board number. No, it is not the same, if the final Item has not been processed with the proper procedure and been intended to be stamped and certified has no value.
An ASME Code Shop does have a reputation and may get jobs that will not be stamped I agree. I make a lot of vessels for customers who wants to enjoy a cheaper vessel w/o stamping and certification. I must tell them that I will follow the ASME Cod ein the construction.
It's tricky too and note that my responsibility is greater if I do not stamp it.
think about it. I save the customer money, I get the Job on that basis but at the end I loose because my exposure is greater. The customer saves money and his/her exposure is greater. It's a game. Lets stamp most items please.
15 PSI. I have stamped 5 psi vessels by following the Code It shall be designed to 30 psi as a minimum.

 

[jte]

Well, there are multiple perspectives. I can see GenB's point of view of reduced liability for the shop. But from my perspective as an owner-user, I would generally counsel my folks to take the "design but do not stamp" approach due to reduced inspection and maintenance issues down the road. Simply put, if a thin spot or some other issue is discovered on the run, a short term repair such as a fillet welded lap patch can be applied to keep the unit up while maintaining the integrity of the equipment. Keep in mind that rapid, unplanned shutdowns and subsequent startups can be quite hazardous. The BP Texas City incident illustrates this point well.

I will take a bit of an issue with tmast2, specifically with the wording used in the original post:

If a vessel is being operated under the 15 psig rating which keeps it from needing to be a stamped pressure vessel...

What pressure a vessel is operated at is irrelevant. So is the PSV setting. What is relevant in making the "not exceeding 15 psi" call is the MAWP. So it would not be ok to take a piece of pressure equipment which is stamped for 16 psi and say that it does not need a U stamp [where the jurisdiction requires stamped vessels] simply because we put a PSV on it which is set for 14 psi and we operate it at 5 psi. It is ok to take the same equipment, put a 15 psi (or 14 psi if you want to be abundantly clear) MAWP on the nameplate, and then consider it exempt from stamping.

 

[moltenmetal]

A little caution here: there are plenty of containers which have relief pressures below 15 psig but which must be designed and fabricated to other codes- storage tanks for flammable materials come to mind. My response was specific to the OP's situation- a liquid nitrogen receiver.

As to the design and construction of devices below the scope of ASME VIII: it's the owner's call. Devices below the scope of the code on size (volume, diameter or both) but relieved above 15 psig are typically designed to either ASME VIII or B31.3 piping code, without stamping. Devices above the volume but operating below 15 psig get treated differently depending on size and what they contain, i.e. the hazards to be expected if the container were to fail.

There's an interesting thought experiment to consider when determining what code should apply to a device. Consider two large pressure vessels connected by a 24" pipe line. The pipe line is clearly B31.3 pipe, correct? Some might designate it a vessel in its own right, but really, it's pipe. Now assume there's a 2" reduction at either end of this 24" pipe, such that the lines connected to the large vessels are 2" at either end: most would still consider it to be pipe. Disconnect one end and replace with a blind flange- voila, it's a vessel. Connect one end to the atmosphere instead and it becomes non-code by virtue of relief below 15 psig. It's all a bit silly, don't you think? What really makes it a code vessel is its risk of harm on failure, relative to the risk of harm of failure of other components in the system: THAT is what merits the extra inspections and paperwork and rigour associated with designating something as a pressure vessel rather than as pipe.

 

[MJCronin]

An excellent discussion with good points made by many...

I have had experience with many "vessels" that were specified, designed and operated at less than 15 psig...

My suggestions:

- Please do not refer to them as "pressure vessels", you will run afowl of psychotic town, state and other regulatory people all to willing to accuse you of "getting away with something" and breaking the law ! ! . Call them "low pressure tanks" or something..... I realize that this is petty, but in the eyes of a government regulator, this can be a big idea !

- Be aware of the fabrication shops that have done this many times in the past. They are willing to provide all necessary testing, inspection and other documentation you will want to keep in your records. Consider the type of identification plate that you want to attach to your vessel and what it will say.

- I have found that the so-called "savings" amounts to very little when a vessel is fabricated to but not stamped to the ASME code. This usually amounts to only 3-5% of the total. Try to always get two cost quotes. One with the vessel designed to the actual max operating pressure (no stamp) and another at 15 psig (with a stamp).

Another consideration is the long term yearly "state fee" charged by some for the privledge of having a stamped pressure vessel on the plant site. Theoretically, the non-stamped "low pressure tank" should not have to pay this fee/tax.

MJCronin
Sr. Process Engineer

 

[jte]

Agreed, that this is a good discussion. If "pipe" or "vessel" was an easy question, it wouldn't come up as often. Clearly there is much gray area out there. That's why I am careful to point out my perspective - that of an owner-user. Since our perspectives on a given topic can greatly influence our commentary. As an example, a project engineer with say an Instrumentation background may look at the cost of procurement argument and determine that a 5% increase for a Code vessel is easily justified. However, that engineer has not paid the ongoing life-cycle costs of adding a vessel to the Inspection group to track and inspect on a frequency which is silly for that given service - simply because we chose to designate it as a vessel rather than a pipe. Never mind the difference in cost of field repairs.

My perspective is clearly biased towards the life-cycle cost - without compromising reliability and safety - of running a plant. Others will have different perspectives based on their own experinces, whether it be only dealing with greenfield projects, running fab shop work (even if they see the occasional repair job), or otherwise.

I recently was involved in the short term repair of a vessel which will be replaced within a few months. Simply put, the "proper" long term repair would have had an effective cost well above the replacement cost of this vessel. And this wasn't some little filter, it was somethig I'd classify as a medium sized vessel, replacement cost is six figures for the shop PO alone.

So, to each his own. Again, a good discussion, glad E-T is here to facilitate it.

 

[Ripz]

RAGAGEP