Supplement or replace parts of ASME VIII Div. 1 calculations with Div. 2?

[julian89]

Hi guys,

I was wondering if it is permissible to supplement or replace calculations done in accordance with Div. 1 with Div. 2 (or visa-versa)? E.g., if a single part does not satisfy the requirements of Div. 1, is it possible to perform calculations for that specific component in accordance with Div 2 instead? For a specific example, I am currently working on recertification (client wants to increase working pressure) of an old (born 1960, originally designed after TEMA) heat exchanger, where one of the tubesheets does not meet the specs in Div 1, but is OK in acc. with Div. 2 (DBA).

EN 13445-3, for example, specifically states that this is permissible (replace or supplement DBF with DBA; cl. 5.4.1), however I can't find a similar statement in ASME VIII.

Cheers,

Julian

 

[TGS4]

You could try Code Case 2695. But your situation is much more complicated - involve your AI.

 

[SnTMan]

julian89, I am not at all familiar with Div. 2, but I'm curious. Why does the tubesheet pass under Div. 2, but not Div. 1? Is it due to higher Div. allowables by any chance, or are the rules different? You doing DBR or DBA?

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[julian89]

I'm doing DBA for this. For a summary of the differences, see this thread.

 

[TGS4]

If you're using DBA, then you need for follow U-2(g). The most important part of U-2(g) is that if there exists rules in Div 1, then you are obligated to follow those rules - no exception.

BTW, that thread is over 15 year old and refers to a version of Division 2 that is pre-re-write. I would consider that thread completely obsolete.

 

[SnTMan]

julian89, I agree w/ TGS4, if you are doing a new design you would be obligated to follow Div. 1. Your existing tubesheet most likely was designed per TEMA, as Sec VIII, Div 1 had no rules at that time as far as I know.

What do you mean by "recertification"?

Regards,

MIke

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[julian89]

My apologies, here is an updated one from 2015. Briefly, higher stresses are allowed but more NDT and more restrictions on materials.

The heat exchanger was indeed designed after TEMA as you point out. By "recertification" I should have said rerating (or uprating?) since the client wishes to increase the working pressure of the heat exhanger using ASME VIII.

 

[TGS4]

Most jurisdictions will not permit the type of uprating that you are discussing. In particular, the allowable stress basis is inherent in the steel effective the moment the vessel is "born" (i.e. the year and Code Edition/Addendum of the Code of Construction when the U-Stamp is applied), and is forever unchangeable. You could justify a different calculation method, such as those permitted in Code Case 2695, which replace the mandatory rules in Division 1, but if there are rules, then those must be followed, which excludes using DBA in many situations.

Especially for older heat exchangers (as SnTMan can attest) built to TEMA, the tubesheet thickness would never meet any current ASME rules without grossly altering the allowable stress basis. What you client wants may not be achievable.

 

[SnTMan]

TGS4, neither here nor there, but I have seen it go either way

julian89, I believe that even if Div. 2 calculations are permitted and used for Div. 1 vessels, one is still bound by Div. 1 allowables. If this is not correct, I am certain that it will be pointed out

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand