LMP Calc. Used to Determine UTS Reduction Between Two PWHT

[jweld81]

I have a current project to qualify ASTM A694, F65, Q&T to itself with PWHT in accordance with B31.3-2020 Ed. Min. UTS of this material is 77 ksi. The 1st qualification used base metal with a tempering temperature of 1000F. Therefore, PWHT was performed at 950F for 11 hrs. Filler metal used was E71T-12MJ and F7P8-EM14K. Tensiles broke at 89 & 89 ksi in the root and 80.5 & 81.0 ksi in the cap. All broke in the weld. It was determined that the root tensile had more SAW filler metal than FCAW filler metal. This qualification ended up failing impacts in HAZ per customer requirements.

Therefore, new material was sequestered from extra production material to re-do the qualification with a higher tempering temp. of 1100F. PWHT temperature is now set at 1050F for 2.75 hrs. minimum. The concern that I have is using the same filler metal with the higher PWHT may not meet tensiles, specifically in the cap weld as there is more undiluted filler metal in the center of this weld. I performed a Larson Miller parameter calculation with the anticipated ramp up and cool down rates to compare the previous PWHT to the new PWHT. The results are: 16.5 for 950F for 11 hrs. and 17.1 for 1050F for 2.75 hrs. There is going to be an anticipated reduction in tensile strength with the higher heat treatment based on this calculation. Approximately how much reduction can I anticipate? Is there a plot of stress vs. LMP for ASTM A694, F65?

Please note that a customer imposed NACE hardness test is required to be performed in addition to impact testing at -50F so I want to use the maximum PWHT temperature that will reduce hardness, restore adequate ductility and toughness to the weld joint and not degrade the mechanical properties of the base metal while maintaining adequate tensile strength. The qualification is intended to be welded with all stringers to help with maintaining the strength. There will be a preheat of 200F min. FCAW weld deposit is intended to be performed for the root with SAW for all remaining passes.

 

That's a lot to unpack.

Tensiles broke at 89 & 89 ksi in the root and 80.5 & 81.0 ksi in the cap. The higher base metal dilution (think carbon pickup) is a greater factor than the difference in weld process.

Keep in mind that CVN testing of weld HAZ (per ASME rules) is sketchy at best, because of the practical impossibility of capturing HAZ and HAZ only along the notch. Other zones on either side of the CGHAZ (presumed to have lowest impact toughness) are captured in the test. So while in principle HAZ properties are independent of weld metal composition, in reality the CVN tests are heavily compromised, for the reason just given.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[jweld81]

Thank you for your reply. I figured that there was more base metal dilution in root tensiles due to the smaller distance between each base metal test piece at this location. I understand the concerns with CVN testing in HAZ.

I found a plot for stress vs. LMP for a low carbon steel which was used to determine a rough estimate of tensile reduction with the higher PWHT. The result was below my comfort level, so I intend to weld the next qualification with E81T1-Ni1 & F8P8-ENi5-Ni5-H4. The customer was informed and they approved the use of these filler metals.

Thanks again for your reply.

 

[weldstan]

Did both weld metal and HAZ fail impacts? Your new choise of welding filler metals should assure the weld metal will meet -50F impact properties. Did you impact test a specimen from the base metal used in the procedure qualification?
If the base metal just meets the absorbed energy criteria, your chances of meeting them in the HAZ are not good.