Minimum Design Metal Temperature

The vessel is determined to be an uninsulated, horizontal, grade-level, cylindrical pressure vessel with a gas volume of 706 ft3 (20 m3). The vessel has a MAWP of 1,480 psig (102 bar) at 650°F (343°C) and a Minimum Design Metal Temperature (MDMT) of 40°F (4°C) since it is constructed of unnormalized steel material. Due to process conditions immediately prior to pressuring the vessel to 1,000 psig (69 bar), the vessel s metal temperature is approximately 30°F (-1°C). When the vessel is pressurized to 1,000 psig, it fails catastrophically. The distances to overpressure endpoints (1, 3, and 5 psig) are calculated as follows ... 

Fig. GR-2.1.2(b)B Reduction in Minimum Design Metal Temperature Without Impact Testing...

All pressure retaining steels applied at a specified minimum design metal temperature (2.11.4.5) below -30°C (-20°F) require a Charpy V-notch impact test of the base metal and the weld joint unless they are exempt in accordance with the requirements of paragraph UHA-51 in Section Vlll, Division 1 of the ASME Code. Impact test results shall meet the requirements of paragraph UG-84 of the Code. 

The purchaser shall specify the minimum design metal temperature used to establish impact test requirements. 

The purchaser shall specify the minimum design metal temperature the pump will be subjected to in service. This temperature shall be used to establish impact test requirements. Normally, this will be the lower of the minimum surrounding ambient temperature or minimum liquid pumping temperature. However, the purchaser may specify a minimum design metal temperature based on pump liquid properties, such as autorefrigeration at reduced pressures. 

To avoid brittle failures, materials of construction for low temperature service shall be suitable for the minimum design metal temperature in accordance with the codes and other requirements specified. The purchaser and the vendor shall agree on any special precautions necessary with regard to conditions that may occur during operation, maintenance, transportation, erection, commissioning and testing. 

Impact tests are not required when the Intersection of minimum design metal temperature (MDMT) and nominal material thickness lies on or above the applicable material curve in Figure UCS-66 however, impact testing is mandatory for the following ... 

Figure 2-54. Reduction in minimum design metal temperature without Impact testing.

Minimum Design Metal Temperature (MDMT) The MDMT is an ASME Code requirement and must be stamped on the nameplate, the lower of the following ... 

Bulk containers that have lost vapor pressure and have autoreffigerated may become colder than their minimum design metal temperature. Repressurization and a safe return to service requires special procedures. See CGA G-6.7 for further information and suggested procedures [10]. 

Other information pump type, required punip hydraulic horsepower, material of oonstritction, stress relief requirement, project pump specifications, pump position (vertical, horizontal, or inline), available utility such as cooling water, site conditions, pump location indoor or outdoor), minimum design metal temperature (MDMT), insulation requirement, steam out condition, etc. 

Others Project vessel specifications, site conditions, any hazardous nature of the process fluid in vessel, steam Out condition, minimum design metal temperature (MDMT), which is the minimum ambient temperature... 

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