Maximum Temperature

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Division 2 requires that the design temperature “shall be based upon the actual metal temperature expected under operating conditions,” and should be determined from the maximum operating temperature in the same manner as described above for Division 1 vessels. The design temperature would normally be the maximum temperature permitted coincident with the design pressure, and […]

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Hydrotesting

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Hydrotesting a pressure vessel should never be performed at an ambient temperature below the minimum design metal temperature. The high stresses developed during a hydrotest would make the vessel especially vulnerable to failure by brittle fracture.

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Autorefrigeration

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The autorefrigeration temperature is defined as the temperature that the contents of a vessel would reach if the vessel is depressured to 40% of the MAWP (35% of MAWP for vessels built in 1999 and later). However, the autorefrigeration temperature need not always be used as the minimum design temperature. Autorefrigeration is not considered a […]

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Restricted Startup and Shutdown

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Most pressure vessels in locations with a mild winter climate will not require special materials selection or CV-impact testing to assure adequate resistance to brittle fracture at their operating pressure during startup and shutdown. The minimum design metal temperature for each component can be conveniently established by determining the minimum temperature permitted by the Code […]

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Startup and Shutdown at Ambient Temperature

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Pressure vessels that are installed at geographic locations with severe winter climates may be required to be at maximum operating pressure at low ambient temperatures during transient startup and/or shutdown conditions. The minimum design metal temperature for this situation should be the lowest ambient winter temperature that would be expected for a startup or shutdown […]

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Operation Below Ambient Temperature

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Pressure vessels that will be in continuous operation at temperatures below normal ambient temperatures are considered to be in “critical” service because of the risk of brittle fracture. The minimum design metal temperatures for these vessels are based on their normal minimum operating temperatures. The minimum design temperature will usually be designated at approximately 10°F […]

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Minimum Design Metal Temperature

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The minimum design metal temperature (MDMT) is defined in Division 1 as “the lowest (temperature) expected in service.” This temperature is essentially the same as the minimum pressurizing temperature (MPT) in Company terminology. For most vessels, the minimum design metal temperature is the lowest metal temperature permitted at the MAWP. The Company’s current practice is […]

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Establishing the Maximum Design Temperature

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The maximum design temperature is based on the normal maximum operating temperature obtained from the process design. The recommended practice is to add a margin of at least 25°F above the maximum operating temperature, to assure safe operation in the event of minor temperature excursions. Exothermic reactions or other process characteristics that may cause higher […]

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ASME Code, Section VIII, Division 1, Design Temperatures

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Many pressure vessels are designed to operate at high temperatures, but are usually required to be under pressure at ambient temperature during startup and/or shutdown conditions. A few vessels are required to operate at temperatures below ambient temperatures, and others can be subjected to “autorefrigeration” resulting from operational upsets or gas leaks. Both Divisions 1 […]

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External Pressure

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Most vessels are designed to contain positive internal pressure, but it is possible to develop a partial vacuum inside of the vessel during steam-out cleaning, when draining liquids, or during abnormal process conditions. Therefore, it is general practice to check all vessels that are designed for an internal pressure for their resistance to collapse under […]

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