Hot Work Performing on Dish Head after Stress Relieving

[Quality2479]

Hello Everyone,

Name of Equipment - Thermal Oxidizer (Incinerator)

Design Code - ASME Sec.VIII Div.1

Note - NO PWHT & NO IMPACT

Type of Dish Head - Torispherical (6%)

Inside Diameter - 3964mm

Dish Head Thickness - Minimum-25mm, Nominal-30mm

Shell Thickness - 12mm

With reference to the above, According to Dish Head manufacturer and ASME Sec.VIII Div.1 UCS-79, the Dish head has to undergo Stress Relieving after Cold Forming. Dish Head consists of couple of Nozzles with RF pads and the Dish head is to be Welded to Shell 12mm Thick by making a butt joint and providing a 1:3 taper in Dish Head.

Question 1.
After Stress relieving whether any kind of Hot work (Welding/Cutting) is permitted since the welding/cutting activities to be performed.

Question 2.
Whether is it possible to perform Stress relieving after completing the Welding of Nozzles, RF pads on dish head and Butt Joint with Shell (No Stress Relieving after Cold forming) or If the Dish head is Stress Relieved once after Cold forming and no further Stress relieving would be required after performing cutting/welding.

Thanks

 

[metengr]

Question 1.
After Stress relieving whether any kind of Hot work (Welding/Cutting) is permitted since the welding/cutting activities to be performed.

Yes.

Question 2.
Whether is it possible to perform Stress relieving after completing the Welding of Nozzles, RF pads on dish head and Butt Joint with Shell (No Stress Relieving after Cold forming) or If the Dish head is Stress Relieved once after Cold forming and no further Stress relieving would be required after performing cutting/welding.

This is a fabrication process sequence question. The answer is that the formed head needs to be stress relieved from warm or cold forming. If this thermal treatment can be done after welding, yes, it can also be performed after forming and before welding (if no PWHT is required for welding).

 

[brkmech1234]

For the case 2 above, if the stress reklieving is done after welding the nozzels, you need to mention PHT in U stamp name plate.