2 1/4 Cr/Mo P22 materials PWHT temp

[deepu78]

P22 Piping materials Tempering process carried out at typically 740degC. Whether PWHT holding temperature for P22 material can be above tempering temperature?

 

[ShabsRBI]

As per ASME Sec IX P22 material falls under P no. 5A and Gr. No. -1.
Looking ASME Sec VIII Div-II Table UCS, Normal holding temperature for PWHT is 675 Deg C with holding time as 1hr/inch with a minimum of 15 minutes.

 

[goutam_freelance]

As per B31.1 table 132.1.1-1, the holding temperature for P No 5A, Group 1 is 675-760 deg.

Again, as per clause 132.2 (a) the upper limit above (760 deg C) may be exceeded but it can not exceed the lower critical temperature, which is 805 deg C for P No 5A (ref 129.3.1-1).

 

[deepu78]

1. PWHT temp for P22 material -kept at 730+-15 deg C
- is this prevent prevent cracking of the weld
2.What is the optimum cooling rate after PWHT
3. Is post heat important for P22 welding

4."After welding, PWHT temperature is kept below the parent material tempering temperature by reasonable margin" Is this a correct statement.

 

[goutam_freelance]

1. PWHT is applied to increase toughness and to reduce the hardness. This improves ductility, especially in the HAZ. If there is high hardness, steel may be brittle, which may give rise to cracks due to thermal cycles or dynamic loads.

2.

132.5 PWHT Heating and Cooling Requirements

Above 600°F (315°C), the rate of heating and cooling
shall not exceed 600°F/hr (315°C/h) divided by one half
the maximum thickness of material in inches at
the weld, but in no case shall the rate exceed 600°F/hr
(315°C/h).

It is better to follow code requirements as these are the results of long experience. Adjustments within code requirements are to be made if the desired results(hardness etc.) are not achieved.

3. Yes, it is important, if not exempted by code.

4. Yes. Tempering temperature is equivalent to lower critical temperature A1.

 

[deepu78]

Regarding Point 4: Tempering temperature is equivalent to lower critical temperature A1

For SA 335 P22 -lower critical temperature mentioned is 805 deg C .
But in the material certificate tempering is done at 740 deg C

So can PWHT temperature be above 740 deg C?

 

[goutam_freelance]

Tempering temperature can be is slightly below A1.

As per code tempering temperature can be up to 805 degree C.

But it is not clear what are you looking at or what is your objective. Why do you want to increase the PWHT temperature?

 

[deepu78]

Our company procedure says PWHT shall meet 730+-15 deg C )for P-5A (2.25Cr-1Mo

Base Metal (P-No.)

Temperature °F / °C

Minimum Hold Time1 (hr)

P-5A (2.25Cr-1Mo)

1350 ± 25°F / 730 ± 15°C​

2​

Our fabricator procured this material and in their PWHT procedure has Holding temperature: 675°C (-0°C/+20°C)
So vendor saying typically, after welding PWHT temperature is kept below the parent material tempering temperature by reasonable margin. The requested PWHT temperature including tolerance allows this material tempering temperature to be exceeded.

My query is if the PWHT temp exceeds tempering temperature of 740 eg C but below 805 deg C which is the lower critical temperature,is there any concerns?

 

[goutam_freelance]

There should be no concern if PWHT temperature as well as heating and cooling rates are kept within the Code allowable range.

But please check the PWHT records (for temperature, cooling/heating) for checking conformity with the Code.

The lower critical temperature should not be reached as this may result in phase change within the base metal and/or the weld..

 

[deepu78]

Is there a TTT diagram for A335 P22 material?