Design MDMT Vs Rated MDMT 1

[daniel1978]

i wonder if any one can explain what is the differences between design MDMT and Rated MDMT? which one we use as base to determine if impact test is require for vessel or not?

 

[daniel1978]

I also need to know if my Design MDMT is warmer than my rated MDMT, what other option we could use to lower down MDMT?

 

[innovation2]

Ratings for individual components will need to be <= your design MDMT. Essentially you want all parts to be at or below your design MDMT.

Regarding how to lower you will need to review the code sections. It is a tricky subject which depends on many different factors.

How cold does your MDMT need to be? What type of material?

Your best bet to lower MDMT is to either use a material that is exempt to a cold temp like stainless steel (304, 316) or charpy impact test.

 

[metalonis]

daniel1978, please define what is meant by design MDMT and rated MDMT. Guess I just don't get why they would be different.

 

[TomBarsh]

I support innovation2's description.

The "design" MDMT is that specified by the vessel owner. The "rated" MDMT is that found from applying the rules of ASME Code. For example, VIII-1, Figure UCS-66.2 is the flowchart diagram showing the rules for determining the lowest (coldest) MDMT without requiring impact testing. The concept is analogous to pressure: there is a "design" pressure specified by the vessel owner, and there is the "rated" MAWP found by applying the rules of the Code to determine the maximum pressure that the component(s) can sustain. In both cases, pressure and MDMT, there will be a governing component...that with the lowest pressure rating for chamber MAWP and that with the highest (warmest) temperature rating for the chamber MDMT.