PWHT Times & Temperatures for P6 Gr 1 (S41000) to P6 Gr 4 (CA6NM Class B)

[DonRoss]

Hello all,

I developed a P6 Gr 1 (S41000) to P6 Gr 4 (CA6NM Class B) WPS that require impacts as well as requirements for NACE and as such there are few details I require insight on.

Background:
In brief, we’re qualifying 1.5” Thk coupons to qualify thickness ranges of 5/8” to 8” thk and another, 0.24” thk to qualify 0.120” to 0.48” using E410NiMo/ER410NiMo-16 weld consumables. Impacts will only be performed on the 0.24” thk coupon to qualify thickness ranges of 0.120” to 8” as ASME Interpretation(s) IX-89-100R & IX-07-09 Permits.

ASME PWHT Temperature Requirements:
- According to ASME VIII Div 1, Table UHA-32, P6 Gr 1 specifies Normal Holding Temp of 1400°F min up to 2” for 1.25 hr, Over 2” to 8” for 2.25 hr for each additional inch over 2”.
- According to ASME VIII Div 1, Table UHT-56, P6 Gr 4 (SA-487 CA6NM) specifies Normal Holding Temps of 1050°F – 1150°F for 1.25 hr Min. for Nominal thickness >0.58”.
- According to SA-487, CA6NM Class B requires two PWHT cycles to meet NACE hardness of 255 BHN, 1st Temper of 1250°F +/-25°F and 2nd Temper of 1150°F +0°F/-25°F as FINAL.
- Heat up rates are according to UCS-56(d)-(1)(2)
- Cool Down Rates, according to UHT-56(c), UCS-56(d)-(5) need not apply.

ASME IX PWHT Time at Temperature Requirements:
- According to QW-407.2, The procedure qualification test shall be subjected to PWHT essentially equivalent to that encountered in the fabrication of production welds, including at least 80% of the aggregate
times at temperature(s). The PWHT total time(s) at temperature(s) may be applied in one heating cycle.
- PQR PWHT time at Temperature is based on qualification of 8” thk, total of 16 hours, less 20% of the total aggregate time, 12.8 hrs (13 Hrs).

>>> Insight required; shall the time at temp be qualified according to 8” thk material or shall it be according to 1.5” material thickness at 2 hrs (1.875 hrs)?

PWHT Requirements specified on the WPS are a combination of the two to meet both material requirements.
- 1st Temper at 1425°F +/-25°F for 1.25 hrs per inch for thicknesses less than 2”, 2.25 hrs per additional inch thickness.
- 2nd Temper at 1150°F +0°F/-50°F for 1.25 hrs per inch for thicknesses less than 2”, 2.25 hrs per additional inch thickness.

PWHT Requirements specified on the PQR are a combination of the two to meet both material requirements.
- 1st Temper at 1425°F +/-25°F for 13 hours
- Air Cool to below 77°F before 2nd Temper
- 2nd Temper [FINAL] at 1150°F +0°F/-50°F
- Air cool to ambient

*According to UHA-32(c), When Pressure Parts of Two Different P-Number Groups are joined by welding, the PWHT shall be that specified in either of Tables UHA-32 or UCS-56, with applicable notes, for the material requiring the higher Post weld Heat Treat Temperature.

>>> Insight required; CA6NM material is sensitive to high Postweld Heat Treat Temps and long PWHT Times, and as such, been found to harden the material making it difficult to meet NACE requirements of 255 BHN or (23 HRC), even after the 2nd Temper. Shall the temperatures follow the requirements of P6 Gr 1 or of P6 Gr 4 (CA6NM Class B), or shall it remain as I specified?

Thanks,

Don

 

[metengr]

Insight required; shall the time at temp be qualified according to 8” thk material or shall it be according to 1.5” material thickness at 2 hrs (1.875 hrs)?

Qualification shall be in accordance with production welding, meaning if you are welding 8" thick material, your PWHT will be applicable to 8" material, and the procedure will be qualified to 12.8 hours for impact testing.

Insight required; CA6NM material is sensitive to high Postweld Heat Treat Temps and long PWHT Times, and as such, been found to harden the material making it difficult to meet NACE requirements of 255 BHN or (23 HRC), even after the 2nd Temper. Shall the temperatures follow the requirements of P6 Gr 1 or of P6 Gr 4 (CA6NM Class B), or shall it remain as I specified?

As you stated the combined PWHT of both materials; initial temper at 1425 deg F for the 410 stainless steel followed by a second lower temperature temper for the CA 6NM at 1150 deg F.

 

[DonRoss]

Hi metengr,

I appreciate the response and verification. This is what I also understood and how I proceeded.

Thank You,

Don

 

[MitchFortier]

Metengr,

Are saying that although DonRoss is actually welding a 1.5" thick plate that he should still PWHT as if it were an 8" thick plate. Would this not invalidate his mechanicals? If DonRoss has results X for his 1.5" plate PHWT for 13 hours, what will be his mechanical properties be if he were to actually weld 8".

DonRoss,

What is the hold time identified in your WPS? What do you believe will be your maximum thickness you'll weld in production?

 

[metengr]

MitchFortier;
Yes, that is what I am saying above. The PWHT must simulate that used in production. Look at it another way, I can perform multiple PWHT cycles to simulate multiple repair cycles on only a 1.5" thick base material.

 

[DonRoss]

Mitch,

PWHT Requirements specified on the WPS are a combination of the two to meet both material requirements.
- 1st Temper at 1425°F +/-25°F for 1.25 hrs per inch for thicknesses less than 2”, 2.25 hrs per additional inch thickness.
- 2nd Temper at 1150°F +0°F/-50°F for 1.25 hrs per inch for thicknesses less than 2”, 2.25 hrs per additional inch thickness.

Qualifying S41000 to CA6NM will enable us to satisfy the requirements for welding 410 SS Pipe to CA6NM castings and if required, permit us to repair 410 SS forgings or CA6NM Castings using Low Carbon E(R)410NiMo materials. The procedure will be for both pipe fabrication welds and weld repair if required, for pump casings and or covers. Some covers alone are in excess of 6" thk, either made from forgings or castings. Therefore, having our PQR qualified to weld up to 8" thk is a requirement.