Dear Experts,
Regarding the subject mentioned, kindly clarify my following doubts.
(a) Preheating required for P91 as per B 31.1 is 200°C (mini). Does it mean that this Pre heat shall be given for tacking also.
(b) PWHT holding time for P91 mentioned in B 31.1 is 1 hr/25 mm; minimum 30 minutes. Does it mean that if the thickness is 6/10/12.5 mm the holding time is 30 minutes & for 15 ,20,30,40 mm the holding time is 36 48,72,96 minutes respectively.
(c) I got some special heating curves for P 91 from our group. But Kindly explain about the reference /standard used for preparation of this heat curve ( eg- why the preheat maintenance is 4 hours & again free cooling).
S.Binoy
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