Can someone throw light on the matter below :-
in one of the ammonia plants the client is asking for application of code case N-253 -
The issue is described below -

"ITB clause -
“Stress range reduction factor (f) for high temperature service shall be defined according to ASME Code Case N-253-12-Appendix B.”
Our defense ( not accepted by the client) :-
As per our understanding, Code Case N-253-12 (which is renamed N-253-13 as per latest edition) is part of ASME BPV (Boiler & Pressure Vessel Code or BPV code) and is applicable to internal piping of boiler & pressure vessels. External piping attached to boiler & pressure vessels is excluded.
Further attaching herewith (Attachment-3) extract from ASME B 31.3 showing the scope of ASME B 31.3. Fig. 300.1.1 indicates that piping covered by BPV code is excluded from scope of ASME B 31.3. Hence, for external piping of pressure vessels, we propose to use f=0.97 (for 25 years) as per the ASME B31.3 Para. 302.3.5 (1c).

Hence we opine that Code Case N-253-12 is not applicable for our plant.

Our interpretation of clauses from N-253-12 is that it addresses the creep failure issue. The initial creep temperatures for various materials are:-

a. Carbon Steel : 427 Deg C

b. Carbon +1/2 Moly : 454 Deg C.

c. 1-1/4 Cr + ½ Moly : 510 Deg C

d. 2 -1/4 Cr +1 Moly : 537 Deg C

e. SS : 565 Deg C

As per our piping specification, the materials are not exposed to temperatures above these values. From this aspect also, Code Case N-253-12 is not applicable to our plant.

"
Is our defense technically correct ?

The code is allowing the use of these materials as per attachment without any special treatment in analysis.
Regards,
Godbole