Post Forming Heat Treatment of NACT plates

[Raghuram Bathula]

Dear all

Can body share views on heat treat ment carried above tempering temperature for NACT plates? one of the case i have come across is stated below.

MOC: SA387 Gr11, Thickness 90mm, Delivery condition: Normalised+accelerated cooled+tempered (NACT)

Contract requirement: Cold formed D''end shall be normalised.

Since plate delivery condition is NACT, Mill certfies plate with 2NACT+3PWHT cycles on simulated coupons.

Fabricator will perform 2nd NACT (Fabricator assures that they do rapid quenching with water and tempering)  after cold forming (since normalising is mandatory irrespective % strain)

I am of the view that so far no mill has disclosed how will they perform NACT (complete cycle and cooling rates), thou Simulation is done at mill, in my opinion it is impossible to replicate the same NACT process at fab shop, and can't represent the simulation done at mill.

Also it is not known how mill perform accelerated cooling (by direct water quenching or water sprinklers or forced draft....?) one of the process photograph i have got on the web attached here with shows sprinklers .

[Welder's Helper]

Post forming heat treatment of NACT plates is normally advisable. I have gone through a special case during welding of one heat exchanger, heads of which are in A387 Gr.11 Cl. 2 (annealed) material. Specimens have been made after forming operation & heat treatment and tested for intended mechanical properties.

Better to consult the mill to get the information regarding temperature range where embrittlement may occur.
And I agree that you would not be finding the NACT operation details from the mill. However, spare NACT plates can be made available for preparation of test specimens; and normalizing can be made on the same by the fabricator after forming operation.

Thanks

 

Welder's Helper

 

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