[MW:17574] Pre heat requirements for tack welding in P91

[Binoy Soman]

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

 

 

[Lalu r p]

Dear Binoy 

When I was working in a power project in India as per Client's Requirement for P91 joints we used to keep the joints on external clamps and weld directly after the proper preheating and purging.for tubes as well as pipes we followed the same method.Direct tack welding was not allowed by the client.Correct me if i am wrong.

Thanks &Regards

LALU R.P

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[kannayeram gnanapandithan]

1.yes,but it is not good practice to tack weld on the job. if u take full welding immediately after tack weld it is ok, if it delay not advisable to tack weld and keep for longtime. 2.5minutes/mm holding time 

Pandithan

Welding Consultant

[Binoy Soman]

Sir,

Thanks for your response. Can you give any reference for “if it delay not advisable to tack weld and keep for longtime. 2.5minutes/mm holding time ”

 

S.Binoy