Reduction of Norsok Compact (L-005) Flange length from 75 mm to 55 mm by cutting 20 mm 2

[ASDcunha]

On a particular job, to provide clearance and avoid clash, it was required to reduce a 6" , 600# Norsok-L005 standard compact flange length from 75mm to 55mm by cutting 20 mm.
1)Is this allowed?
2) How does one validate that this design is acceptable. refer attached file for details.

 

[mrfailure]

Personally, I think this is the type of expedient "engineering" that asks for trouble and potential litigation down the line because you will be increasing stresses with the shortened flange, increasing the risk of service failure. This certainly needs sign-off and approval of an appropriate licensed design engineer, but I think cutting an existing flange is probably not acceptable in any circumstance and you would instead need a new part meeting Code requirements. You may need to literally go back to the drawing board to design the system that will fit the space.

 

[davefitz]

Lengthening the flange helps remove the weld line from the flange's larger bolt surface, which helps reduce the thermal stresses that occur at the weld line during startup/shutdown operations. Shortening the flange makes the thermal stresses much worse at the weld line, and high temperature applications will have to consider using extraordinary QC measures to ensure that there are no "stress raisers" within the weld to lead to a failure. The fatigue damage is worst for austenitic stainless steel flanges as the combination of yield stress, thermal conductivity and density is worse than for ferritic alloys, but some ferritic alloys have a weld "soft zone" that acts as a "metallurgical notch".Bottom line is , use the longest flange you can fit in the pipe while retaining the ability to inspect ( and repair) the weld root pass at the ID.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick