Vessel, why, when or not? 5

[JLSeagull]

Sometimes people cheat. I have seen a few examples where it was obvious that an application was more than enlarged piece of pipe. For reasons not clear, project or mechanical engineers did not assign an equipment number, provide relief valves, etc. calling something a run of pipe – that everyone could clearly see was a vessel. They avoided ASME conformance. A few examples:
a starting air (perhaps start gas) accumulator for a Diesel emergency generator
seal oil accumulators for large gas compressors
some air accumulators for control valves (blowdown, etc.)

How do they get away with it? What rules make it a vessel?

Thanks for your input.

 

[JStephen]

"pressure containers which are integral parts or components of rotating or reciprocating mechanical devices, such as pumps, compressors, turbines, generators, engines, and hydraulic or pneumatic cylinders..." are exempted.

"pipe components, such as pipe, flanges, bolting, gaskets, valves, expansion joints, fittings, and the pressure containing parts of other components, such as strainers and devices which servce such purposes as mixing, separating, snubbing, distributing and metering or controlling flow" are exempted.

"a vessel for containing water under pressure, including those containing air the compression of which serves only as a cushion" within certain temperature/ pressure limits is exempted.

 

[metengr]

The statements above are excerpts from the Introduction of ASME Boiler and Pressure Vessel Code, Section VIII, Div 1 (unfired pressure vessels).

 

[gr2vessels]

JLSeagull,

The "cheating" people are not profesionals and those approving their work are administrators of the project. The examples you provided are classic pressure vessels, where the inlet/outlet nozzles are connected to other pressure systems. Between those inlet/outlet nozzles, the equipment is accumulating energy, which is the reason for existance of the pressure vessels code around the world. The ASME VIII code was generated to prevent the boilers and other pressure vessels killing their users. Remember, the casing of the pump must be hydrotested for pressure containment and comes with suitable rating. However, you cannot prevent people distorting the meaning of "pressure vessel" with their sight on the glitter of a copper coin.

Cheers,

gr2vessels

 

[JStephen]

Another issue that may enter in is whether the jurisdiction in question regulates pressure vessels in the first place. In Texas, they don't. So even if the object is clearly a pressure vessel, it doesn't have to be ASME stamped. (This may be kind of an indeterminate area still- seems like OSHA requires pressure vessels to be designed per ASME for workplaces.)

 

[LSThill]

TEAM MEMBERS & JStephen (Mechanical)

Is the State of Texas going to become a Pressure Vessel by jurisdiction in 2007; because of the new OSHA requires pressure vessels to be designed per ASME for workplaces.

 

[moltenmetal]

The intention of the ASME VIII rules is to ensure that the major energy storage volume in a system is a registered vessel.

A piece of 16" pipe connecting two large pressure vessels is a pipe, despite the fact that in volumetric, diameter and pressure terms it would be considered a pressure vessel if examined in isolation.

A piece of 1" pipe connecting two large pressure vessels, with a 16" enlargement in the middle of the line, is also still a piece of pressure piping- unless it contains some other means of pressurization distinct from that of the vessels it is connected to.

A piece of 1" pipe with a 16" enlargement in it connected only to valves, pumps etc.- is a vessel, provided it meets the ASME tests and is not exempted by local regs or covered by another statute (DOT etc.)

Note that pressure piping is still designed, fabricated, NDE'd etc. in accordance with an ASME code- in the case of chemical plant piping it's ASME B31.3. Just because it's not a registered vessel does not mean it's an unsafe assembly for the retention of pressure. The rules are simply different, proportional to the hazard that the device represents in the larger context.

Whether or not the system contains registered vessels, relief valves are required where they're required, and not required where the design so permits- i.e. in cases where another relief valve provides protection for two interconnected pieces of equipment not separated by unlocked valves etc.

 

[jte]

"pipe components, such as pipe, flanges, bolting, gaskets, valves, expansion joints, fittings, and the pressure containing parts of other components, such as strainers and devices which servce such purposes as mixing, separating, snubbing, distributing and metering or controlling flow" are exempted.

This part is sometimes reffered to by folks who think that if you build what would otherwise be a vessel out of only "piping components" such as pipe and piping end caps then it is excempt. As indicated in Interpretation VIII-1-04-47, this is not true. For example, you build a small KO drum with a 24" pipe shell and end caps but it is not excempt from the scope of VIII-1 on that basis.

A piece of 16" pipe connecting two large pressure vessels is a pipe, despite the fact that in volumetric, diameter and pressure terms it would be considered a pressure vessel if examined in isolation.

Provided that the intent of the pipe is to transport fluid between the vessels and it does not serve a processing function.

A piece of 1" pipe connecting two large pressure vessels, with a 16" enlargement in the middle of the line, is also still a piece of pressure piping- unless it contains some other means of pressurization distinct from that of the vessels it is connected to.

Again, provided that the 16" portion is there only to provide a transport function and is not intended for processing. Maybe one way to look at it is if a process engineer has to do much more design than a flow calculation then the 16" portion may well be a vessel. If the process engineer is determining things like residence time, then that 16" wide spot is most likely within the scope. I do not believe that the source of pressure is material here.

jt

 

[deanc]

How about a "moral duty"?

The ASME writes a proven safety code. Even if I was too cheap to get the itemed stamped I would at least design to the minimum requirement.

It would be hard to live with an unnessary death on my shoulders.When I am asked why someone should follow this standard,I respond by asking if they have any children.

Of course if money is your only goal,no nameplate will open the door for lots of fine and dedicated attorneys.

 

[metengr]

deanc;
Well said.

 

[moltenmetal]

To put your "moral" argument into place, you're making the presumption that a 16" diameter piece of pipe with caps on the end, connected by piping to a much larger source of stored energy and with no distinct source of pressurization, is somehow markedly less safe when designed and constructed in accordance with B31.3 than when designed and constructed in accordance with ASME VIII.

I don't agree with you. Nor do the majority of my colleagues and customers. I don't think we're especially immoral people!

Want to make this one a little greyer so that your judgment can be tested a little more accurately? Let's take that pipe enlargement down from 16" to 6" sch 40. Now the ID is just a hair greater than 6". Is THAT a vessel, or is it piping? What's magic about 6.000" versus 6.065".

This is an engineering judgment between two internationally recognized safety codes- it is not a "moral" issue.

As to whether the 16" "vessel" has a "processing intent"- that too is basically irrelevant to the selection of the design/fab code. Piping and vessels have the same ultimate design requirement: to safely contain a pressurized fluid against the loads and other factors that can be reasonably expected to be imposed by the service over a reasonable design life. What matters is if the "processing intent" in question imposes loads, corrosion, heat, other sources of pressurization etc. that the "piping" is not designed for, in which case there is a real reason to question the code selected.

What some folks are after is a slavish application of a set of clearly-defined perscriptive rules, such that engineering judgment never comes into it. If that were possible, there would of course be no need for professional engineers. That's where engineers prove their value: in producing designs which are not only safe and prudent, but economic as well.

It is possible for two engineers to make reasoned, defensible engineering judgments on a particular issue and to come to different conclusions. I respect your judgment in regard to the selection of what constitutes an ASME "vessel" and what doesn't, and trust it serves your employer and your clients well. I resent the implication that somehow my own judgment is "immoral" merely because it doesn't coincide with your own.

 

[metengr]

moltenmetal;
As someone who deals with ASME Codes and Standards and as a curious reader in the various fora, I don't believe deanc was trying to imply in his post that you or others are in any way taking the immoral route by trying to split hairs on which type of code, if any, is applicable. I read deanc's post as more of a general statement directed to companies run by bean counters that may not want to invest in the proper design of pressure retaining items (regardless of pipe or pressure vessel definitions).

I am of the opinion that B31 and ASME B&PV Codes are specific enough to provide the necessary requirements to assure long and safe operation of pressure retaining items.

 

[deanc]

moltenmetal:

You missed my point. metengr explains very well what I refer to.

The Code you use is based on application and jurisdiction....but are not all Codes safety focused?

Pick the best one and use it,if there is a problem over .065",I suspect that both may be satisfactory. The line must be drawn somewhere otherwise we go in circles.

I do not know you personally so I have no idea if one would consider you "moral" or not. I guess that depends on the Code you use?????

Best regards to all.

 

[JLSeagull]

I particularly liked the brief response provided by ASME Interpretation VIII-1-04-47.

Subject: Section VIII, Division 1 (2001 Edition, 2003 Addenda); U-1(c)(2)(e)
Date Issued: January 13, 2005
File: BC04-1115
Question: Is a pressure vessel intended for storage or processing of a fluid, built from piping components,
exempt from the scope of Section VIII, Division 1 per U-1(c)(2)(e), if none of the other exemptions listed
in U-1(c)(2) apply?

Reply: No.

 

[moltenmetal]

Sorry deanc and metengr: I'm a little touchy today. Re-reading your post I think I took your statement far too harshly! I do understand your points.

Choosing between design codes on an engineering basis is very different than choosing between a design code and NO design code based solely on money. That's not something we run into. But we DO run into people who have the ASME VIII box on their heads and can't see around it to the underlying design philosophy. They add unnecessary cost and schedule delay that somebody has to pay for, and that annoys me.

 

[VeryPicky]

Well, in my humble opinion, the quest for ruling on what is and what is not a pressure vessel should start at the local authority. The lack of legal description of the vessel by this authority would warrant code definition to be applied. Don't forget the code is becoming law if referred to by the legislature. Otherwise, it is just an expensive guideline, that has no teath.
Isthill was pointing in this direction, too.

As to the "cheating" issue, applying pressure vessel requirements to equipment that is not legally a pressure vessel seems a bit unnecessary (and expensive). That is the reason why those engineers get paid those extremely high salaries - they have to make a call on what is safe design for a particular piece of pipe with caps.


Putting Human Factor Back in Engineering

 

[JStephen]

VP- you might note that Texas, for example, has no vessel law- regulates boilers only.

 

[JLSeagull]

http://www.acusafe.com/Newsletter/Stories/0302NewsPart6PSI.htm

Does Isthill's OSHA comment trump JStephen's no Texas law comment? I would like to see the documentation about OSHA. Does the attached link tie section VIII into the OSHA 1910.119 PSM regulation? If so, why would Texas need a vessel law?

 

[VeryPicky]

JStephen your comment is duly noted. I don't think JLSeagull mentioned TX in his question. I apologize if I missed something.

Putting Human Factor Back in Engineering

 

[JLSeagull]

I am in Texas. Many but not all of my projects are in Texas. This issue was raised by a coworker. I don't actually know whether the plant is in Texas or not. He asked me because I am actually read some of the many codes that apply to the Instrumentation and Control Systems business.

However, if OSHA requires ASME section VIII design then it should not matter whether or not it is a local agency requirement. Right?