Calcs or no calcs

mgeorgiadis · **Joined:** Mon Jul 04, 2011 3:58 pm **Posts:** 13

Dear all
Can you advise when calcs are required and when no calcs are required. Is there a rule to know when it must be done?
Michael

Javed Nasir · **Posted:** Tue Sep 06, 2011 8:10 pm

Michael,

I completely not understand your intent.
Some Standard ASME pressure parts need not be calculated like flanges and flanged fittings of B16.5, valves of B16.34 etc. You have to select correct pressure-temperature rating/class of these components. You also need not to perform calculations for manufacturer's standard pressure parts if these are in compliance with UG-11.
Other than these situations, you have to perform calculations for each and every pressure and load bearing non-pressure part as far as Code minimum requirements are concerned.

mgeorgiadis · **Joined:** Mon Jul 04, 2011 3:58 pm **Posts:** 13

Nasir
Good evening! Thank you for your reply (again). My client said calcs not necessary for a particular vessel, but I want to know how to respond to him. If it is compulsory according to minimum requirements (not for standard parts like flanges), then I would like to know where to find the criteria to make the decision if the vessel is an extension of piping or indeed a pressure vessel. What classifies a vessel as a pressure vessel? Excuse me if this question appears very silly but I'm still new to pressure vessel design but not new to engineering.
From Michael

Javed Nasir · **Posted:** Wed Sep 07, 2011 6:35 am

Michael,

Whether the item is an extension of piping or it is indeed a pressure vessel, calculations are a must.
When we say, even for a B16.5 flange, that calculations are not required (in fact calculations have been performed not by you but by ASME Committee of B16.5). Same is the case of UG-11 parts.
I quite you another example, water column is a little vessel used in Boiler applications, it falls under Section I and B31.1 scope. we never perform calculations for it, we procure it from outside as a Standard Pressure Parts in compliance with PG-11 of Section I.

Dr. Koelbl · **Posted:** Thu Sep 08, 2011 11:48 am

Michael,

a vessel is subject to ASME Code when so specified and when within the limits of pargraph U-1.
Piping is used only for the transportation of fluids, pressure vessels for anything else.

UG-90 (b)(2) requires the Manufacturer to have a design calculation for every vessel.
Appendix 10 is also nice:

Quote:

10-5 DRAWINGS, DESIGN CALCULATIONS, AND SPECIFICATION CONTROL
The Manufacturer’s or Assembler’s Quality Control
System shall provide procedures which will ensure that
the latest applicable drawings, design calculations, specifications,
and instructions, required by the Code, as well as
authorized changes, are used for manufacture, examination,
inspection, and testing.

I have never been able to accept a vessel without a design calculation, and can not imagine to do so in the future.
Note that also piping requires design calculations according to the relevant piping code, e.g. B31.3.
DK

fayazam · **Joined:** Sun Sep 25, 2011 7:13 pm **Posts:** 2

Michael,

if there is internal pressure ranges 15psi to 3000psi then ASME section VIII Div 1 or 2 must be applicable. and it is considered as pressure vessel. So it is public safety requirement that vessel should be perfectly designed. So it is necessary to perform calculations.

FM

akonrad · **Posted:** Thu Sep 29, 2011 3:02 pm

Quote:

I have never been able to accept a vessel without a design calculation, and can not imagine to do so in the future.

Dirk, you know that guessing is a favourite engineering method in many reputable organisations...

Dr. Koelbl · **Posted:** Sun Oct 09, 2011 8:39 am

Konrad,

I am happy with GUESSING, when it is done properly. It should be appropriate, conservative and well documented.

Even in Section III: NQA-1 Req.t 3 says that "assumptions" and " assumptions that require verification during construction" shall be identified in calculations. This is one of my favourite questions as auditor. During Design Verification, the reviewer shall evaluate wheter or not the assumptions are appropriate and correct. How beautiful is this?

Okay, Sectin VIII is not on this level, and guessing is used in limited areas. Certainly guessing of a cylinder wall under internal pressure is not acceptable, UG-27 shall be applied. But when it comes to external nozzle loads guesing is always in play. When I remember all the drawings that specify "no external nozzle loads". Can you attach a piping spool to a nozzle without external loads?

DK

akonrad · **Posted:** Tue Oct 11, 2011 8:50 pm

Quote:

Can you attach a piping spool to a nozzle without external loads?

RCB 10-6: Heat exchangers are not intended to serve as anchor points for piping; therefore, for purposes of design, nozzle loads are assumed to be negligible, unless the purchaser specifically details such loads in his enquiry...

I always add to this: want this cheap? Get yourself a pipe hanger, they come cheaper than heat exchangers.

Calcs or no calcs

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