Standard flanges are rated to -20° F MDMT as per UCS-66(c).

A colder MDMT rating may be obtained using the provisions of UCS-66(b)(1)(b). This paragraph allows the use of the coincident ratio defined in Figure UCS-66.1 for components such as flanges, flat covers, etc. For these components the coincident stress ratio is treated in terms of the ratio of the component's maximum pressure at design temperature to its maximum allowable pressure at the MDMT.

For standard flanges, COMPRESS takes the coincident ratio = (pressure chamber or nozzle MAWP) / (flange pressure rating at ambient temperature).

Note that for "body" flanges the MAWP of the pressure chamber is used in the above formula. For flanges on nozzles, the nozzle assembly's MAWP is used in the formula.

See www.codeware.com/support/faq/1279.html to learn more about nozzles manufactured as long weld neck flanges.