Multiple MDMT Cases - Nameplate Stamping
Multiple MDMT Cases - Nameplate Stamping
(OP)
Hello all,
Code: ASME VIII-1 (2013)
I am having a disagreement with our AI about the stamping of a nameplate for a pressure vessel where two MDMT cases have been specified. I would appreciate any opinions on the matter.
Customer specified design conditions:
MAWP: 150psi @ 200°F
MAEWP: FV @ 200°F
MDMT-Case 1: 20°F @ 150psi
MDMT-Case 2: -50°F @ 0psi
Per Footnote 10 and UG-20(b), multiple MDMT cases are allowed. So, along with the normal MAWP/MAEWP calculations, we have performed two low-temperature calculations at the conditions indicated above.
For the nameplate stamping, using our standard nameplate (only has one available line for MDMT), we would apply the following stamping:
MAWP: 150psi AT 200°F
MAEWP: FV AT 200°F
MDMT: 20°F/-50°F AT 150psi/0psi
Now, the concern that our AI has, is what happens at the intermediate temperatures (ex. 0°F). He has asked that we add an additional line of text to our nameplate along the lines of:
Is this interpretation not implied and standard understanding for a nameplate with the stamping I indicated above?
Extending this out to cases where you might have 3,4,5,... MDMTs, I shudder to think what additional text we would be asked to add on the nameplate.
Thanks for any opinions,
Marty
Code: ASME VIII-1 (2013)
I am having a disagreement with our AI about the stamping of a nameplate for a pressure vessel where two MDMT cases have been specified. I would appreciate any opinions on the matter.
Customer specified design conditions:
MAWP: 150psi @ 200°F
MAEWP: FV @ 200°F
MDMT-Case 1: 20°F @ 150psi
MDMT-Case 2: -50°F @ 0psi
Per Footnote 10 and UG-20(b), multiple MDMT cases are allowed. So, along with the normal MAWP/MAEWP calculations, we have performed two low-temperature calculations at the conditions indicated above.
For the nameplate stamping, using our standard nameplate (only has one available line for MDMT), we would apply the following stamping:
MAWP: 150psi AT 200°F
MAEWP: FV AT 200°F
MDMT: 20°F/-50°F AT 150psi/0psi
Now, the concern that our AI has, is what happens at the intermediate temperatures (ex. 0°F). He has asked that we add an additional line of text to our nameplate along the lines of:
Pressure not to exceed 0psi from -50°F To 20°F
Is this interpretation not implied and standard understanding for a nameplate with the stamping I indicated above?
Extending this out to cases where you might have 3,4,5,... MDMTs, I shudder to think what additional text we would be asked to add on the nameplate.
Thanks for any opinions,
Marty





RE: Multiple MDMT Cases - Nameplate Stamping
RE: Multiple MDMT Cases - Nameplate Stamping
I whole-heartedly agree that it should be the lowest bound. I'm more confused by the requirement to add an additional set of markings: Pressure not to exceed 0psi from -50°F To 20°F
Is the lower bound interpretation not typical? Would some plants assume a linear line of acceptable MDMT/MAWP ratings between two points?
RE: Multiple MDMT Cases - Nameplate Stamping
I agree that the phrase "Pressure not to exceed..." is redundant and unnecessary. On the other hand, it does make things crystal clear. If you are reluctant to include this, can you run it up the food chain at the AIA?