MDMT

[picasa]

How do you specify MDMT for a pressure vessel designed per ASME SEction VIII Div. 1? Is it per client input? Do you look up some chart or graph in ASME SEction VIII Div. 1 code? Do you refer to any other document? API 650 gives Figure 2-2 (Isothermal lines of lowest one-day mean temperature) for all of USA. Does ASME SEction VIII Div. 1 code have similar graph? Is specified MDMT same as lowest one-day mean temperature for the site location? If it is, over what period is the mean taken?

 

[CodeRef]

The majority of Section VIII Div 1 vessels have a typical MDMT of -20F. Paragraph UG-20(f)allows specific materials of specific thicknesses at specific temps exemption to -20F without the need for impact testing. Depending on the materials used and loadings involved, it will vary. Reference Section VIII Subsection C Requirements Pertaining to Classes of Materials for detailed information ( Parts UCS,UHA,UNF etc...)

 

[codeeng]

The MDMT must come from your Client. This could be derived from a number of sources including minimum ambient, service, or guaranteed warm-up.

 

[TomEun]

I agree with codeeng.

Additionally the client’s engineers (or representative) may consider the followings;

1. insulated or not ; i.e. -40 to -49F for skirt or saddles whilst -29F for shell & heads
2. normal temperature condition : i.e. -20 to + 32 F (or higher) for normally high temperature equipment whilst -40 (or less) to -29F for medium temperature (or lower) equipments

Thomas Eun
thomaseun@shaw.ca