To determine time and temperature post weld heat treatment requirements, I would suggest following the post weld heat treatment guidelines outlined in the ASME Boiler and Pressure Vessel Code - Section I for Boilers (Table PW-39) or Section VIII, Div 1 for pressure vessels. The post weld heat treatment requirements associated with the B&PV Code are well established, and are conservative.
You could also use AWS D1.1 Structural Welding Code post weld heat treatment guidelines, as well.
Refer to ASME Sec VIII Div 1 UCS 56 for the Time and temperature data for Pressure vessel. UW 40 should give yo somemore useful infor as regards to the modality of PWHT
Further you may refer to ASME/ANSI B 31.3 for the same data for Piping.
Yes there exists a formula which acts as the basis of the Time Temp table. I had it noted down from one of the ASME but don't recollect from where i got it. I think it is in ANSI B 31.3.
It is not applicable for all material (I am afraid) it ofcourse applicable for CS material. Further you may refer to UCS 56 for the material for which lower temperature and higher soaking is permited. There is a small table given in UCS for tabulating the temperatures and soaking time.
By using this option (Higher soak at lower temp) (if you have not (Welding Engineer) planned) after commencement of fabrication, you may land up in PQR related troubles (Especially if the Vessel is in Sub zero service)
Not discouraging you, but giving you the pit falls. About 4 months back i remember there were discussion on this subject (Supporting PQR).
By proper planning (By welding engineer) this can be amicably settled.
Remained Residual Stress After PWHT [Reduction Rate]
0 psi [100%] after 2 hours @ 1400 F
1,200 psi [97%] after 1 hour @ 1400 F
3,000 psi [93%] after 4 hours @ 1300 F
3,500 psi [91%] after 2 hours @ 1300 F
4,700 psi [82%] after 1 hour @ 1300 F
3,000 psi [93%] after 16 hours @ 1200 F
4,000 psi [90%] after 12 hours @ 1200 F
5,000 psi [88%] after 8 hours @ 1200 F
5,800 psi [86%] after 4 hours @ 1200 F
6,200 psi [85%] after 2 hours @ 1200 F
7,200 psi [82%] after 1 hour @ 1200 F
7,000 psi [83%] after 8 hours @ 1100 F
7,700 psi [81%] after 4 hours @ 1100 F
8,000 psi [80%] after 2 hours @ 1100 F
9,000 psi [78%] after 1 hour @ 1100 F
8,000 psi [80%] after 8 hours @ 1000 F
9,900 psi [75%] after 4 hours @ 1000 F
10,800 psi [73%] after 2 hours @ 1000 F
12,000 psi [70%] after 1 hour @ 1000 F
The formula given by bmoorthy is so called Larson Miller tempering parameter. This is a simple formula for CS only. The draw back is it does not take into account the influence of heating and cooling cycle of the heat treatment. To make a provision for heating and cooling Holloma-Jaffe formula should be used. BTW Centigrade+273°C is Kelvin.
The formula given by bmoorthy is so called Larson Miller tempering parameter. This is a simple formula for CS only. The draw back is it does not take into account the influence of heating and cooling cycle of the heat treatment. To make a provision for heating and cooling Holloma-Jaffe formula should be used. BTW Centigrade+273°C is Kelvin.
Where:
HJ - Hollomon/Jaffe parameter
T - holding temperature [°C]
te - effective holding time [h]
th - correction in holding time for heating cycle [h]
tc - correction in holding time for cooling cycle [h]
h - heating rate [°C/h]
c - cooling rate [°C/h]
The formula was derived empirically and it seems to reflect better the effects of heating and cooling on tempering degree of metal than LM parameter. I used this formula to asess the remaining life of pressure vessels after multiple PWHT cycles. It was also used to set the parameters of PWHT simulation cycles.
