Challenge with CLASSES in ASME viii-2 Edition 2017 1

[Mm.Kaiser]

Hi,
As you know, in edition 2017 of asme viii-2, it has introduced the classes for vessels which made some challenges for me.
According to edition 2015 part5, I always perform FEA with S.F=2.4 and in E-P analysis, load factor 2.4. But in new edition, it seems that i have to consider my cases in CLASS1 which S.F=3 and load factor in E-P analysis=3.
These new criteria will make the thickness thicker although my special vessel parts and equipment according to previous version have been worked for more than 10 years without problem.
Please give me an advice.
thanks.

 

[Mm.Kaiser]

Thanks TGS4,
I do appreciate your regrads.

 

[marty007]

Mm.Kaiser,

If i do a FEA on a part with design factor 3.5 (AS you addressed in ASME PTB-4), so...
when do you use CLASS 2 with S.F=2.4 in your analysis?

You use Class 2 with S.F. = 2.4 when you are building an ASME VIII-2 Class 2 vessel. This means all aspects of the vessel (documentation / design / inspection / etc...) meet the requirements of VIII-2 Class 2. The vessel is then stamped with a U2 stamp and the MDR documents the vessel as VIII-2 Class 2.

I have checked lots of products from famous European manufacturers with FEA and most of them will fail if we use S.F=3.5. For example most of Piping Tees will fail with Div1 margin and they are using S.F=2.4.

Is this equipment being designed to ASME VIII-1 or a different code of construction? As DriveMeNuts states, other European codes use different design margins.

unfortunately it is Impossible for me to use S.F=3.5 because my products will not remain competitive with more material.

This is not an acceptable justification to violoate code rules. If they jump of a bridge are you also going to jump off a bridge? I also work at a fabrication shop, and occasionally I see designs from other ASME shops where I can spot clear code violations (repairs / replacements). This doesn't mean that I'm going to change our shop practice to do the same, instead I take it as an opportunity to educate our customer. I clearly explain why there is a problem with the previous design, how it violates the code, and how our shop will approach the fabrication detail differently. In most cases, the customer is very happy to have been educated on the matter, and is happy to have their equipment designed properly. For future equipment purchases, the customer is now confident that we know what we're doing, while second guessing the other fabricator, sending more work our way.

Cheers,
Marty

 

[Mm.Kaiser]

marty007,
I agree with you but the business is cruel!
The only way for me is using Class2 (according to successful experiences) and meet the requirements of it.
Note that Our projects have a consultant company who checked calculations and inspections. Also we perform NDT; heat treatment, radiography, hydrotest and all other examinations.
What else?
If you review ASME PTB-3 you will find out that it has uses S.F=2.4 for a simple vessel (which could easily calculate according to Div1). I prefer to follow this method instead of appendix 46
Please inform me for more steps that i have to consider related to viii-2-class2 if needed.
Thanks

 

[DriveMeNuts]

Making the use of Div 2 Class 2 to design your equipment and therefore take advantage of SF=2.4 is a valid choice.

However, perhaps you have failed to include the additional cost and time associated with design verification of a class 2 vessel. As I understand it, your won't be able to use your "consulting company" to verify the design calculations if they are not ASME accredited. You will have to find an engineer who is accredited by ASME to verify ASME Div 2 Class 2 calculations and who is willing to sign their life away by endorsing your design. With all of the additional insurances required to do this, I expect this will be expensive.

Perhaps after weighing up "all" the costs, Div 1 will remain the least expensive option.

"I agree with you but the business is cruel!"
This attitude of yours suggests that you are a cowboy, rather than an Engineer.
Your successful experiences are irrelevant. The only thing that matters in getting a U1 or U2 stamp is that the different verification procedures for each stamp are followed.

Have you considered that every other workshop in Asia wanting to U-Stamp a Pressure vessel has to follow the same rules as you and are going through the exact same dilemma, and that as a result you are not becoming less competitive? Your awareness seems short sighted.

 

[marty007]

The only way for me is using Class2 (according to successful experiences) and meet the requirements of it.
Note that Our projects have a consultant company who checked calculations and inspections. Also we perform NDT; heat treatment, radiography, hydrotest and all other examinations.
What else?

Simple, you must stamp and document the vessel as ASME VIII-2 Class 2.

 

[Mm.Kaiser]

Thanks Marty007.
And more thanks for DriveMeNuts although i am note completly agree with your interpretations and conceptions.
And still waiting for Tgs4 if any good news has come from Code Committee Meeting.
Regards