Post Weld Heat Treatment - excessive soak time 1

[PeterIgg]

We have performed weld repairs on a valve body cast in ASTM A216 WCB. The client is accepting the weld repair but is querying the length of time that PWHT was held at temperature. The casting has a max wall thickness of 60 - 70 mm but the casting was held at 620°C for 6 hours. The client believes that this is detrimental to the life of the casting. The valve shall be used on a caustic slurry line.

This is outside of my metallurgical experience - can anyone shed any light as to why my client may think this way and is there any remedial action that can be taken?

 

[metengr]

Since this is a carbon steel casting and no impact qualification was performed there will be no significant affect on mechanical properties or reduction in service life for the longer hold time at the stated PWHT temperature.

A longer hold time for PWHT will decrease notch toughness and lower mechanical properties for low alloy steels, and this longer hold time should be factored in when qualifying a welding procedure for fabrication or repair welds.

 

[Christine74]

metengr,

"A longer hold time for PWHT will decrease notch toughness"

Wouldn't a longer PWHT improve notch toughness for low-alloy materials? I agree that it normally reduces ultimate tensile strength/yield strength.

-Christine

 

[metengr]

Christine74;
The effect of prolonged hold time during PWHT for certain low alloy steel weld metal deposits can result in temper embrittlement, where bulk mechanical properties are less affected but notch toughness is significantly reduced. This is why aggregate hold time is necessary for PWHT qualification.

 

[Christine74]

I see. Thanks metengr.