Welding SA192 tubing

Date 08-20-2009 22:13 Edited 08-20-2009 22:20

If you are trying to use SA192 for temperatures over 750-800 F for prolonged periods of time, graphitization is definitely going to be a concern. You need to be looking at SA213-T11 or T22 if you are operating above 750 F. You can heat treat it to put the carbon back into solution, but that is a short term fix only.

By mnelson (*)

Date 08-24-2009 15:10

Unfortunately this SA192 tubing is in a forty plus year old reheater and replacement is years away. Our current issue is the weldability of the existing to new tubing during forced boiler outage repairs. Further compounding our problems are tube replacements with limited 360 access for welding. Window welds are typical.

You mention a short term fix, heat treat to put the carbon back into solution. Would you be suggesting an elevated preheat prior to welding?

Thanks for the input.

By lovely01 Date 08-24-2009 19:14

It is better to know the elevated preheat

By MBSims

Date 08-24-2009 19:22

The graphitization tends to be in the HAZ next to the welds. For your application, I would suggest moving the cut line away from the existing welds at least 1 inch, but preferably 6 inches just to be sure there are no welding issues. You can confirm the cut line location by having metallography performed on a sample of the old tube when it comes out. An elevated "preheat" would not be enough. You have to get above the lower transformation temperature, which is 1335 F typically for carbon steels.

By MBSims

Date 08-28-2009 00:31

I was in error - to put the carbon back into solution you have to go above the upper critical temperature, which is above 1700 F.

By MBSims

Date 08-28-2009 03:48

This should be helpful:

Attachment: InterpretingGraphitization.pdf (884k)