API 45K Carbon Steel Weld Neck Flange

Standard API Spec 6A, 6B welding neck steel flanges present some exciting fluid dynamic problems when connected to complete bore valves or flow lines. When bolted downstream onto flanges of full bore gear, these weld neck flanges present a restrictive shoulder inside the flow bore. Rapidly moving fluids will practical experience turbulence upon contacting this shoulder, premature failure of equipment may outcome. 

 

To stop erosion problems welding neck pipe flanges may have a particular entrance opening bevel, or they might have complete bores and particular weld necks which may or may not be compatible with industrial pipe sizes. API 6A will not specify full bore 6B welding neck flanges, so makers must utilize 60K yield strength material for these flanges as they would for complete bore integral pipe flanges. See illustrations below.