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PWHT on materials

PWHT on materials

(OP)
Hello,

I need to conduct PWHT on a material S460 material and would like to know which type of material would handle better the PWHT:
- N (Normalized)
- QT (Quenched and tempered)
- TMCP (Thermo Mechanilly-Controlled Processing)

Which one would handle best the PWHT and which one will handle it worst? Thank you.

RE: PWHT on materials

What are welding to (another piece of the same metal alloy?)
How thick, and with what weld process?

Also, how large a final piece, and how do you plan to do the PWHT? (Whole part, in a furnace, local heating around just the joint?)

RE: PWHT on materials

(OP)
I am welding to F22 (ASTM A182). It would be FCAW and a 50 mm plate.

We plan to do a localized PWHT and the piece would be 2 m.

Thank you.

RE: PWHT on materials

A normalized heat treatment for the base material prior to welding. Your best option would be a subcritical PWHT where the welded component is placed in a furnace or done locally and heated to a temperature range of 700 deg C to 730 deg C for 1 hour per 25mm of thickness.

RE: PWHT on materials

1250 F + or -25F for 2 hrs min recommended.

RE: PWHT on materials

For a reliable statement concerning the PWHT of the above joint we must take into consideration the properties of both base metals:
  • S460 – European fine grain steel for Structure steel construction
  • ASTM A182 F22 Forged or rolled alloy steel pipe flanges, forged fittings, and valves and parts for high-temperature service
The PWHT recommendations above have only taken into account:
  • the property of F22 (typical PWHT requirements of ASME BPVC for P-No. 5A materials e.g. ASME VIII/1, table UCS-56-4).
  • and the typical ASME requirement (e.g. ASME UCS-56(c)) when pressure parts of two different P‐Number groups are joined by welding, the postweld heat treatment shall be that specified for the material requiring the higher postweld temperature
But these requirements work only if the members of the joint are ASME materials.
S460 is a fine grain steels acc. to a European standard and the ASME-PWHT-recommendations above will affect the mechanical properties of S460.
The similar steel to S460 for pressure vessels is P460 and is assigned to the base metal groups based on the heat treatment condition:
  • P460 N as well as S460 N is assigned to European Base metal group 1.3
  • P460 TM as well as S460 TM is assigned to European Base metal group 2.1
  • P460 QT as well as S460 QT is assigned to European Base metal group 3.1
The European equivalent to SA-182 F22 is EN 10222-2 11CrMo910 and is assigned to European Base metal group 5.2.
Table 10.1-1 of EN 13445-5 gives the PWHT requirements for pressure vessels (assume thickness=50 mm):
  • Base metal group 1.3: Holding Temperature 550-600. Holding time 45 minutes, but Pcrit 17.3
  • Base metal group 2.1: Holding Temperature 530-580. Holding time 45 minutes, but Pcrit 17.3
  • Base metal group 3.1: Holding Temperature 550-600. Holding time 100 minutes, but the maximum actual PWHT temperature shall be at least 30 °C below the minimum actual tempering temperature
  • Base metal group 5.2: Holding Temperature 660-720. Holding time 100 minutes, but Pcrit 19.2
In Addition note 2 of paragraph 10.1 pointed out:
Heat treatment as per Table 10.1-1 particularity in the upper range of holding temperature and/or holding time may unduly impair the physical properties (e.g. yield, tensile strength and toughness of the material) ….. This effect is explained and published as Hollomon-Jaffe Parameter P as given in Equation:
P = Ts (20 + lg t)/1000
where
Ts is the holding temperature, in Kelvin;
t is the holding time, in hours.
lg = log10
The above PWHT recommendations mean:
  • 700 to 730 ° C for 2 hour and leads to P= 19.75 to 20.36
  • 662 to 690 °C for 2 hour and leads to P= 18.98 to 19.54
That means all calculated Hollomon-Jaffe Parameter exceed significant the critical Hollomon-Jaffe Parameter of base metal group 1.3 and 2.1.
The holding temperatures of the above recommendation are not at least 30 °C below the minimum tempering temperature as required for base metal group 3.1.
In addition the minimum holding temperature of base metal group 5.2 is 60 to 80 °C above the maximum temperature for base metal groups 1.3, 2.1 or 3.1.
That means a redesign of the material combination is required to include a transition material (more than one transition material may be required) that overlaps the temperature ranges of both materials. Another possibility would be buttering of the F22 material (buttering works as a transition material).

Regards - Juergen

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