ASME IX PWHT Temperature Variation 1

[WeldGk]

What does ASME allow for temperature variation on approved WPS's? I do not see any variation in the code for this, it states that the temperature variation is an essential but as everyone is aware, furnaces fluctuate. Is there a set variation in ASME IX? I have heard that it is 25F but I do not see this in the code.

 

[metengr]

KimberleyS;
For some reason I don't track your post. What exactly are you asking regarding PWHT, the temperature range specified on the WPS versus the range qualified in the WPQR?

 

[WeldGk]

Does ASME IX specify a temperature variation? If my PQR states 1175 as the PWHT temperature, what variation is permitted on that.

 

[metengr]

Ok.
First off, I need you to carefully review ASME Section IX, QW-407.1. This is important because the following conditions apply regarding qualification of a new WPS based on a change in PWHT.

The first part of QW-407.1, paragraph (a) only applies to P-No 1 through P-No 11 base materials, excluding P-No 8 base materials because they do not require PWHT. If you read through (a) 1-5 you will notice that a specific PWHT temperature range is not specified for the WPS. This doesn't mean that you cannot specify a range, if you do, the range cannot fall below the minimum PWHT temperature specified by Code rules for a particular group of base materials, and the upper limit cannot exceed the lower critical transformation temperature.

If you have some other base material, which I doubt, paragraph (b) would apply in QW-407.1.

Normally, most WPS's that I have written and reviewed from contractors, provide a PWHT temperature minimum range of as little as 50 deg F above the minimum PWHT temeprature based on code rules for the specific P-No base material to as much as 125 deg F above the minimum PWHT temperature for paragraph (a) base materials mentioned above.

Keep in mind that the Code only requires a minimum PWHT temperature. This means that the PWHT temperature can range from minimum to just below the lower critical transformation temperature (except for certain materials where the Code specifies a PWHT range (min to max)). The reason for only specifying a minimum is to assure adequate tempering and stress reduction after welding, any temperature higher than the minimum PWHT temperature is a bonus regarding ductility, unless you exceed the lower critical transformation temperature.