api 5000API 6A TEMPERATURE CLASS L: SERVICE -50ºF TO 180ºF (-46ºC TO 82ºC) 2,000 3,000 5,000 API 60K Alloy Steel Corrosive (CO2) & Sour (H 2S) NACE4 MR01-75 T26F F 2,000API has specified weld necks for many 6BX flanges, and not done so for many others, but API has provided the basis for determining the dimensions of a 6BX integral flange