purge dams for tig welding

[coldcomfort]

looking for a material that will dissolve in hydraulic oil, that we can make a purge dam from - closure weld on a A312 316L hydraulic piping system, that we want to pressure test with oil .

 

[MikeMech]

How about starch based packing foam? It would dissolve in water, not sure about oil. A lot of packing peanuts are made of this, you could test it out.

Is it impractical to purge the whole system?

 

[unclesyd]

Like the post by MikeMech why can't you purge the whole system.

How big a system is it?

What size is the pipe?

One thing you might want to look into is use N2 as the back purge. We do this all time with very large SS systems.

 

[Kiwi2671]

coldcomfort,
Just type "rice paper purge dams" into google.
There are dozens of soluble paper dams available.
They all speak of dissolving in contact with water but you should be able to find out from manufacturer if they will dissolve in contact with oil,
Regards,
Kiwi

 

[unclesyd]

You might want to look at the consumable backup rings from Rovbon.

http://www.robvon.com/

Another possibility is use flux coated TIG wire. These wire very little if any residue using a feathered edge weld prep.

http://www.qwpinc.net/NEW/SS_flux_tigwire.pdf

 

[gtaw]

Will your system operate properly once the oil is contaminated with the material from which the soluble dams are made and other contaminates found on the interor surfaces of the pipe?

The water used to hydrotest the system is usually flushed to remove any soluble contaminates and suspendable solids once the initial hydrotest is completed. One of the contaminates is the material from which the soluble purge dams are made.

Do you anticipate replacing the contaminated oil with fresh oil once the system is hydrotested? If not, an inflatable bladder type purge dam may be a better alternative to the water soluble dams.





Best regards - Al

 

[coldcomfort]

Thanks everyone for the responses. I think we'll end up doing the pressure test with water, or maybe purging the entire system. Our QC guys won't accept consumable inserts or flux coated tig wire so those options are out. As a new system, we are required to flush the system with flushing oil before filling with lube/hydraulic oil; we were hoping to use the flushing oil for the pressure test as well, eliminating one fill/drain cycle.