Yup, I thought you,re right..Metallography examination shall be used for judgement if we need higher confidence level.
In API RP 582, we can use Hardness Test "12.6.2.5 Unless otherwise agreed between the manufacturer
and purchaser, the maximum allowable hardness for welds shall be:
a. P-1, P-3, and P-4 material-225 Brinell ".
Another problems are NDE after PWHT,I have never found about MPI after PWHT in ASME VIII div.2...but I always find it on actual...And in ASME VII-2, i just find statement "EXTENT RADIOGRAPHY"...(Table 7.2)..ha..ha..
In my experience, we use MPI 100% if the electrical is shutdown in the middle of PWHT..