How the two joints carry load

A weld neck flange uses a tapered hub and butt weld to transfer pressure, bending and thermal loads into the pipe. The geometry reduces abrupt stiffness change and makes volumetric examination of the butt weld possible where required.

A slip-on flange slides over the pipe and is normally attached with fillet welds. The joint is compact and alignment can be convenient, but stress concentration, crevice geometry and examination limitations can make it less attractive for severe cyclic service.

Pressure class does not make the joint equivalent

A Class 600 weld neck and Class 600 slip-on flange share a nominal class designation, but the completed joints do not have identical fatigue behaviour or welding details. Project piping classes frequently restrict flange types beyond the dimensional standard.

Check the design code, service category, owner specification and any restrictions for hazardous, hydrogen, buhar, thermal-cycle or vibration service.

Installation and inspection trade-offs

Selection questions for the RFQ

State flange type explicitly and provide pipe schedule, karşı karşıya, pressure class and material grade. Ask whether the joint will be shop or field welded, which NDE is required, and whether internal crevice geometry is acceptable for the service.

For a technical quotation, include design pressure and temperature, cyclic duty, fluid hazard and any owner flange-type restrictions.