PWHT above the upper transformation Temperature

[xuanthien]

Dear Sir,

I don't know when we perform PWHT abobe the upper transformation Temperature. Normaly I see that PWHT at 500-600 Degree which below the lower transformation temperature.

 

[weldstan]

When required by design to provide greater uniformity of mechanical properties or to restore properties after an improperly performed PWHT. For example, if a P91 pipe spool and weld(s) therein was improperly heated above the lower critical temperature, the spool could be reheat treated by normalizing and tempering. The WPS would have to be qualified by a normalizing and tempering PWHT.

 

[sharmass]

Some times formed heads containing weld seam are normalised after forming or solution annealed (SS). In those situations you do go above upper transformation temp

 

[metengr]

A subcritical PWHT is typically used for most materials, and is qualified as such with a WPS. On occasion where re-heat treatment is desired to eliminate the weld heat affected zone in base materials or is required as weldstan mentioned, this operation can be performed. However, as a cautionary note, complete re-heat treatment may result in unwanted distortion.