Section VIII Exclusion, But then what?

[tc7]

I have a 3000 psi MAWP air system in which we normally apply either ASME criteria or Mil-Std-278 criteria to all vessesls and piping design, construction or repairs. I need to install a new desiccant dryer. A vendor has told me that the pressure vessesls on their dryer are less than 6" I.D. and do not need to apply a Code stamp. I agreed with their statement but as an alternative I requested a set of design calculations and was told that the vessels are "spun" type tanks (carbon steel) and Code calculations don't apply but they will provide me with wall thickness information (presumably I can than do my own calculations!)

I am surprised that this vendor seems reluctant to show any calculations and am tempted to find another source of supply. I have two questions that I am asking for advice on:
1. Since the Section VIII excludes vessels under 6" I.D., what alternate design/fab/inspect criteria is appropriate?
2. Am I being unreasonable in requireing calcs for a simple dryer? What is your plant practice?

Thanks for sharing advice and experience.
Tom

 

[Scipio]

Personally, regardless of the code condition with 3000 psig of air I'd want to see how they arrived at their design thickness. If they don't have calculations to back it, I'd go somewhere else - that's a tremendous amount of stored energy. I have no idea what a 'spun' carbon steel tank is though, I've only heard that used with respect to fiberglass reinforced or carbon fibre construction.

Bear in mind just because code says the vessel in question doesn't have to be built under Section VIII, doesn't mean the equations can't be used anyway, so long as the material is applicable.

Depending on where you are there could be additional considerations, for instance with the vessel in question up here in Canada, no code stamp would be required, however it does require a Canadian Registration Number under CSA B51, which requires design pressure & thickness calculations be reviewed & approved by a provincial regulatory board.

 

[jte]

tc7-

I agree with both you and Scipio. Getting the vessel to Section VIII would be a good idea. There are other threads (thread292-47571, thread292-41922) in this forum which discuss whether a vessel which does not meet the scope of VIII-1 may be stamped. I'd feel better with the Code stamp, but its up to you to decide based on how much risk the vessel causes - if it's installed in the middle of a meeting room, the likelyhood of someone getting killed is higher than if its installed out in the middle of nowhere with a berm around it...

jt

 

[johnnymist2003]

I must confirm that I agree with the previous two replies also.

 

[deanc]

Any reputable company should be able to justify their work.
Perhaps they obtain them elsewhere.

 

[JamesBarlow]

I have only ever run into this once.

The situation was a vessel that had an ID of 6". This, as you pointed out, is an exclusion from Division 2. Our interpretation was that the exclusion only meant that you could not use Division 2 for the vessel. It was therefore a Division 3 vessel. This interpretation was also supported by our AIA. Management, of course, wanted to read the exclusion as being absolute for all of Section VIII and not stamp the vessel.

In the end the vessel was designed with Division 3 standards but was not stamped. This desicion was actually made by the customer. They had contacted their state boiler board and were told that the vessel did not need to be stamped because of the exclusion.

Since this event I have changed our company procedure to state that all vessels, regardless of customer or location, would be stamped to the appropriate code. This makes this much easier for everyone.

 

[tc7]

James and all-
That is interesting about Div 3, I'll have to review this very soon. I have been considering a system which employs DOT certified vessels certified to 5000 psig and will be delivered with a DOT stamp (or engraving). I feel this may be my safest and most economical alternative without resulting in a very costly special purchase.
Thanks for your reinforcing thoughts and replies.
TC7