Have a vessel to be revamped (Mtrl: P-4) -

CASE 1: Original case details: PWHT was done on the vessel in one heat at 650 Deg C for 90 min and simulation was provided on base metals for 650 Deg C @210 min. i.e., coverage of about 1.5 cycles. i.e., a simulation of 120 extra minutes to take care of future PWHT.

CASE 2: Revamp case details: Fabricator who is revamping the job is conducting local PWHT for revamped locations at temp of 665 +/-15 Deg C for 60 mins.

CORE ISSUE: There are locations where PWHT is required to be done twice in the revamp case, which means 120 min. of case 2 PWHT temperature. The problem that fabricator states is that since nominal temp now is 665 Deg C and not 650 Deg C thus the actual simulation time wrt new temp is 57 minutes only and not 120 minutes (calculated as per Larson Miller Parameter Formulae). I am not able to see through the logic of applying LMP theory in this scenario... calculation follows below for your review:

T1 Temp. in K 923
t1 Time in Hr. 2
T2 Temp. in K 938
t2 Time in Hr. ?

LMP = (T1 x (20+Logt1)
18737.85069

LMP = (T2 x (20+Logt2)
Hence
t2 =10^(LMP/T2-20)
0.947079986 Hrs
57 Minutes

content edited as above

content edited as above