Re: [MW:18835] Post heating required for alloy steels after welding

Extract Regarding Post Heating from ASME B 31.1

 

131.6.1 After welding commences, the minimum preheat temperature shall be maintained until any required PWHT is performed on P-Nos. 3, 4, 5A, 5B, 6, and 15E, except when all of the following conditions are satisfied:

 

(B) For P-Nos. 3, 4, and 5A (with a chromium content of 3.0% maximum) materials, theweld is allowed to cool slowly to room temperature.

 

C) For P-No. 5B (with a chromium content greater than 3.0%), P-No. 6, and P-No. 15E materials, the weld is subjected to an adequate intermediate heat treatment with a controlled rate of cooling. The preheat temperature may be reduced to 200°F (93°C) (minimum) for the purpose of root examination without performing an intermediate heat treatment.

 

Extract Regarding Post Heating from ASME Sec I

PW-40.3.5 -

For materials greater than 1 in. (25mm) thick, after completing all welding, the repair area shall be heated to and maintained at a temperature of 450°F to 550°F (230°C to 290°C) for a minimum period of 4 hr.

Extract Regarding Post Heating from BS EN 1011-2

The occurrence of hydrogen cracking depends on a number of factors: composition of the steel, the welding procedure, welding consumables and the stress involved. If the

t8/5 time (cooling time from 800 °C to 500 °C) associated with welding is too short, excessive hardening can occur in the heat affected zone. When the hydrogen in the weld is above a critical level the hardened zone can crack spontaneously under the influence of residual stress after the weld has cooled to near ambient temperature. Welding conditions may be selected to avoid cracking by ensuring that the heat affected zone cools sufficiently slowly, by control of weld run dimensions in relation to metal thickness, and if necessary, by applying preheat and controlling interpass temperature. Procedures for avoiding hydrogen cracking, as well as selecting cooling times through the transformation temperature range to avoid hardened and susceptible microstructures, may involve controlling cooling in the lower temperature part of the thermal cycle, typically from 300 °C to 100 °C, thereby beneficially influencing the evolution of hydrogen from the welded joint. In particular, this can be achieved by the application of a post-heat on completion of welding which is typically a maintenance of the preheat temperature.

Regards

HIREN SEVAK

On Mon, Sep 30, 2013 at 9:42 AM, PK M <pkmqaqc@gmail.com> wrote:

Dear Experts,

Why post heating required for alloy steels after welding? I want to know that what is the procedure and acceptance of Post heating of alloy steel in piping specification like Section 31.3, 31.1 or Section VIII, API recommendation practices ?

 Thanks,

Pkm

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