LWN with appendix 2 MAP lower than MAWP

[Ehiman1]

Dear gents,
I have to check a long welding neck 2” #300 with corrosion allowance (3 mm) and external loads with ASME appendix 2, but doing so I found that MAP is lower than MAWP.
The required thickness is 20.3 mm and with LWN standard we have 20.7 mm.
I don’t understand how it is possible that MAP is lower than MAWP, someone could help me please?

 

[SnTMan]

Ehiman1, B16.5 flanges are known to often fail Apx 2 calculations due to the different methodologies.

You'll have to find another route.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[TGS4]

Why are you doing this? Use it because of the corrosion allowance or the external loads? How are you handling the external loads with Appendix 2?

 

[Ehiman1]

It is a client’s request when corrosion allowance is on the flange. I added an axial load and bending moment and calculated an equivalent pressure. Ah the same time they want I verify the rating and thickness of the flange against corrosion allowance

 

[r6155]

Ehiman1
Try with hand calculations.

Regards

 

[SnTMan]

It is very unusual that corrosion be applied to the flange thickness.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[TGS4]

Use UG-44(b) for the external loads and ignore the corrosion allowance. The use of Appendix 2 on standard flanges is inappropriate. That is not the purpose of Appendix 2.