Post-weld Stress Relief 1

[Xianglu]

Anyone has experince with post-weld stress relief for carbon steel piping welded to a casting part? What is the heating temperature? and holding time?
I would also appreciate if any references could be found.

Thanks in advance.

 

[metengr]

Yes. Could you please provide additional information regarding the chemical composition and dimensions of the casting, and the piping?

 

[Xianglu]

Thanks metengr.
Casting material, CS A216 WCB or A352 LCB. Pipes, A106 B, Sch 80, sizes range from 1" to 3". Casting weld joint wall thickness: 0.5", bore to pipe.
Welds: 1" and 1 1/2", SW, 3", BW.
There are two purposes to carry out stress relief, 1] reduce internal stress; and 2] ensure the final dimensional tolerance of the assembly.
If you need more info, please let me know.
Thanks again.
Henry Kong

 

[metengr]

Based on your information, the suggested stress relief is 1100 deg F for 30 minutes at this temperature. I would not perform local stress relief with resistance heating elements, use a furnace to provide uniform heat. I selected 1100 deg F to remain on the low end of the tempering temperature in the event you are using SA 352 LCB material (quenched or normalized and tempered).

To reduce the possibility of distortion from thermal gradients, place the welded component in a furnace that is at 600 deg F, and increase the temperature at increments of 450 deg F per hour until 1100 deg F is reached. Hold for 30 minutes, and ramp down at the same rate until 800 deg F is reached, cool in air.

 

[Xianglu]

Very much appreciate your valuable info, metengr.
Further more, since the casting had already been heat treated most probably quenched, prior to welding, does the PWHT affect casting's mechanical properties? If so, does the whole assembly need to be heat treated again?
Thanks again,
Henry

 

[metengr]

No. As long as you remain at or below the original tempering temperature (which is 1100 deg F minimum by specification) for post weld heat treatment, you should not effect the bulk properties of the casting. Most of these materials are typically tempered at 1150 deg F or higher.

 

[Xianglu]

Thank you so much metengr!

Henry Kong. PEng
Mechanical Engineer
QuestAir Technologies
kong@questairinc.com