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Up Topic Welding Industry / Metallurgy / PWHT
- - By sreedhar Date 12-30-2017 06:57
hi friends,
the PWHT temperature for P92 is 760 C .
now my question is, if it was done for 800 C to complete the process quickly, what will happen regarding to its properties?
if it was done belo 760 C , what will occur to its mechanical properties and microstructure ?
Parent - - By 803056 (*****) Date 12-30-2017 21:22
That's why a PQR is required, to determine the mechanical properties for a specific PWHT procedure.

You can look in Section IX, assuming you are working to ASME requirements, to see the latitude permitted to the time and temperature.

Parent - - By sreedhar Date 01-02-2018 06:11
process according to PQR is one part.

my question is, if we have no sufficient time to complete project, we have to do PWHT quickly,
does we can increase temperature for higher level (i.e assume it will take 8hr at 720 C to PWHT, if we kept at 850 C for 6hr) what will happen with respect to mechanical properties and microstructure,
Parent - - By 803056 (*****) Date 01-02-2018 16:07 Edited 01-02-2018 16:12
720 degree C is below the lower temperature of transformation, so you are not transforming the BBC into FCC. Assuming you are working with a high strength low alloy steel or carbon steel, you are in the stress relief temperature range. However, 720 is playing fast and loose. There is a good chance you could exceed the transition temperature in certain locations. Bad news.

850 degrees C is well above the lower temperature of transition, so there will, at a minimum, be partial transformation of the BCC into FCC. Depending on the alloy system, it may be too low a temperature to achieve full transformation, so you are too low to normalize the steel. Again, not a good place to be.

It is very dependent on the specific alloy and chemistry of the steel (I assume you are working with steel) you are performing the PWHT on and the specific code you are working to. At the very least, you are going from a subcritical PWHT to a supercritical PWHT. That would require a new supporting PQR by many welding standards.

What is specified by the WPS and are you willing to requalify the WPS to demonstrate the required mechanical properties are achieved at the higher temperature. If you are already pressed for time, I doubt you have time to requalify the WPS.

The two hour different in PWHT is a minor time constrain in comparison to the time it took to set up and weld and the cost and time expended to repalce the weld if it doesn't work. Pennies versus dollars.

Parent - - By skulkarni Date 01-29-2018 11:10
P92 is similar to P91 with 0.5 Mo and 1.7 W. It is martensitic stainless steel. So preheat must be around 200°C interpass to be not more than 370°C. Regarding post weld treatment. It is better to See phase diagram of 0.1 C -10 Cr steel . U can see above 800°C so deletrious intermetallic forms which impair the impact toughness. So PWHT should be done at 760°C
Parent - By Anandhperumal Date 05-21-2018 10:22
In PWHT,Rate of heating and Rate of cooling, and during welding preheating & Interpass temperature are very important.if WPS is not followed for the above parameters Hardness will be high which is not advisable
Parent - By CL Vaidya Date 09-05-2018 10:54
Yes Kulkarniji.
But the PWHT temperature for Gr 91 ,92 differs with Tempering temp.during manufacturing.The PWHT temp.always preferred below tempering temp.
- By H.K.R (*) Date 02-26-2019 11:19
dear all

which code mentioned the PWHT for alloy steel ?
and stainless steel does need for PWHT?
i will be very thankful for helping.
Up Topic Welding Industry / Metallurgy / PWHT

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