High Temperature Purge Dam

[Mr168]

Is anyone aware of any soluble purge products that will withstand elevated temperatures, i.e 600°F minimum?

We have a closure weld at a nozzle that must be back-purged, and the nozzle is not of sufficient length such that we can get a paper purge in without burning up the dam. Being a closure weld, there is no access to remove any sort of inflatable bladder.

 

[btrueblood]

Teflon sheet? Or Polyimide sheet?

Past that, thin sheets of stainless steel or even aluminum foil. You may need an origami expert to help you get a reasonably shaped shield/dam through the nozzle outlet and back out again...

Or am I misreading what you are doing?

 

[metengr]

Mr168;
Why can't you use a small steel tube with backing gas applied to the weld root region through a window 180 degrees of where the welder is pulling the root? Seen it done many times in the field. Granted you will have a small region where backing gas will not be applied when you close the window. However, this is a small region and should not pose a problem.

 

[stanweld]

If the materials are stainless steel, flux coated TIG wires or Solar flux products could be used for the root pass. You could also consider qick freeze GMAW processes like Lincoln's STT in lieu of back purging.

 

[Mr168]

btrueblood: The problem would be removing the purge material when finished.

Met: That may in fact be our only option. Unfortunately, our material is P91.

 

[unclesyd]

I've used the method proposed by meteng many times with great success. A variation on this approach is to put your water soluble dams some distance from the weld zone and purge this area only as used with a direct purge at the weld zone.

Just remember that the majority of purge problems is too much flow on the gas side. It doesn't take much gas to purge a weld.

If your specifications will allow different approaches the links below will show a cross section of what's available and if nothing wlse keep them in mind for future purge problems.

You haven't mentioned the size or material, but maybe able to use a non-noble gas in the system.

What's available

http://www.arc-zone.com/index.php?main_page=index&cPat

Backing rings and consumable inserts

http://www.imperialweldringcorp.com/standard_weld_rings.htm

http://www.robvon.com/

Ceramic backing rings

http://www.cerbaco.com/index.html

variations on a theme

http://www.aquasolwelding.com/

 

[stanweld]

You might also consider using a gamma plug/hole to provide greater accesibility in employing metengr's recommendations or to pull out inflatable dams.

 

[MikeHalloran]

Fresh, soft white bread might take the temperature long enough to do the job.



Mike Halloran
Pembroke Pines, FL, USA

 

[Duwe6]

Please do not use "Solar Flux" for closure welds on pipe. The weld heat makes the flux flake off the upper portions of the weld. Welding on pipe is typically uphill, so viewing portions of root are limited to the bottom 2/3 of root, which will be good. Unviewable top third will be ruined, with massive "sugar" grossly oxidized material.

Try a teflon dam made in 4 pie-slices and secured with metal foil tape, as far from the weld as possible. May need 2 dams, one on each side of weld. Tie the segments together with wire, and attach a pull-wire to collapse the dam(s) and extract them. Take care not to melt the pull-wire.