What is, and why do you use Deoxyaluminate?
Judging by the name of it, it is perfectly obvious to me why it is difficult to weld.
3.2
It is aluminum pigment with I don't know what kind of binder.
Was used by Stone and Webster and wasgood for 1 year exposure stored outdoors
I have never welded through it with P-91 Material, but I never had any trouble with it on other steels, and with several processes.
Deoxaluminate is a rust inhibitive, weld-thru coating. The deoxaluminate coatings I have seen in use are typically easy to remove by wire brushing or solvent cleaning (alcohol or acetone). Most WPS's I have seen require cleaning prior to welding using wire brushes or grinding wheels. So why would anyone want to weld over it, especially on a joint that requires RT?
That suposedly is the advantage - you don't have to clean this stuff off and the pigment acts as a deoxidizer -
I guess that just baffles me - if it is easy to brush off why not just remove it so it does not create any welding difficulties? Most welders I know would remove it anyway if the weld is going to be x-rayed.
P-91 is not your garden-variety carbon steel pipe. This material must be welded following a stringent regiment of precleaning, preheating, heat input, and post weld heat treatment. This material is creep resistant at high temperatures. Approaching the welding of P-91 as if it were SA-53 or SA-106 is a recipe for disaster.
Best regards – Al
How does this coating respond to pre-heat temperatures?
I could imagine it would be a bit messy.
3.2
Take A LOOK AT ANOTHER POST ABOUT DEOXALUMIINITE
Arthur,
we are using it on two power jobs on P91 material. Even though you can weld over it we do not weld over it, it must be cleaned off prior to welding. We have had some of the same problems with welders complaining about it. With P91 already having its weldabilty issues we have opted to make sure its cleaned off.
I would check to make sure the coating you are speaking about is weldable. Have you checked the manufactures data sheet to confirm it is weldable? The product we use is Bloxide weldable primer.
Jim
By 2009933
Date 11-19-2009 02:37
Edited 11-19-2009 11:24
I have been on many jobs where the coating refered to here is used, and when I was welding, would always clean it off as it would distort the puddle the same way using a flux coated SS wire would do. However, now that I have a say in what we use to coat our prepped tubes or pipe with, I suggest Steel Blue dye, which is typically used as layout dye, but works wonderfully as a rust inhibitor, and need not be reprepped before welding. Just to confirm this, we asked for MSDS and some information from the manufacturer, and according to Kryon, It completely vaporizes at just under 300 degrees F. Does anyone else here have experience using this?
