ASME VIII-1 Figure UCS-66.3 (b)and curve selection

[YuJie_PV]

hi,all,

i encounter a problem regarding to determination of MDMT per UCS-66.
it's nozzle welded into shell. the nozzle and shell are evaluated based on their governing thickness, and UCS-66 curve respectively. i am clear with it, just how to deal with the tg1,tg2,tg3 in figure UCS-66.3(b). which curve shall be selected for their calculation of MDMT for the welds? for example, in case of tg1, select nozzle's or shell's curve?
i am just confused. the base metal's MDMT is already evaluated, why still need to consider the MDMT of weld? what's the consideration behind the requirement in the Code?

Thanks in advance

 

[Cobra17]

The lowest curve. If the shell is curve B and the nozzle is curve A, curve A is used. See the PTB-4 example problems, Example 3.4

 

[Geoff13]

If you have access to 2010 or earlier edition of the Code, Appendix L-9 had some worked through examples of the MDMT determinations. Reading your question I'm not sure if you are on the right track.

 

[YuJie_PV]

@Cobra17&Geoff13, thank you both for the replies.

i've already looked through Example 3.4 in PTB-4 and MDMT-related example in appendix L ASME VIII-1-2010, i think i figure out something.
just i disagree with Cobra17.
i understand it as that the subject material evaluated is specific to individual component, instead of any weld, which is just related to the governing thickness.

assume the lowest curve selected for particular weld as stated by cobra17, then which component should the calculated MDMT be assigned to? both?
if such logic applies, toughness of MOC is contagious from interior material to superior one by welding contact, it seems absurd.

@Geoff13, what do you think?

any comments appreciated.

 

[Geoff13]

Do you have a vessel, and you are trying to establish the MDMT that you can stamp on the nameplate. In my career I never had a customer ask this. Upon re-reading L-9 I see that's what they are doing, so I'm not sure I should have pointed at it.

Or has your customer specified an MDMT that they need, and you have to select materials, etc that meet this temperature? This is what I've always seen.

When Cobra17 replied they said "lowest curve", but then between A and B they picked A. Perhaps by lowest they meant alphabetically, not the position in Figure UCS-66. This interpretation would avoid the issue you pointed out.

 

[Cobra17]

I guess I should have said lowest alphabetically.

 

[YuJie_PV]

thanks Geoff, Cobra.

yes, i also follow the general practice that takes the MDMT in nameplate equal to the MDMT as design parameter.
i was reading the calculation sheet created by PVELITE, and wondering how is the MDMT of a component produced. that is why i raise the original question above.

 

[Geoff13]

I said the L-9 example established the MDMT for vessel with fixed materials.

To determine what materials will meet a customer specified MDMT here's a simple example. I picked the thicknesses and materials to demonstrate the method, not because they actually make sense for the rest of the Code.

 

[YuJie_PV]

@Geoff, thanks so much.
your example has clarified all my confusions.
Thanks so much.