Minimum design metal temperature

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Minimum design metal temperature

Minimum design metal temperature (MDMT) is a design condition used for pressure vessels under the ASME Boiler and Pressure Vessels Code. Each vessel has its own MDMT stamped on the nameplate. In simple terms, the MDMT is the lowest temperature the vessel is designed to handle for the fluid and temperature range it will operate in.

MDMT must fit between two limits:

- CET (Critical Exposure Temperature): the lowest temperature the vessel will encounter in service, including normal operation, upsets, autorefrigeration, and ambient conditions. Sometimes it’s the lowest temperature at which significant stresses occur.
- (MDMT)_M: the minimum temperature allowed by the metallurgy of the vessel’s materials and thickness, accounting for low-temperature embrittlement and Charpy impact test requirements for each component.

Thus, (MDMT)_M ≤ MDMT ≤ CET.

The MDMT is chosen by the designer based on the fluid and operating range, but it must not be lower than the metallurgical limit or higher than the anticipated service temperature.

References: ASME Boiler and Pressure Vessels Code; Moss, Pressure Vessel Design Manual.