purging , why and how?

[Mikey D]

just need a little advice re purging stainless steel pipework ....

ocassionally i need to weld pipework usually about 40mm dia ,which carries milk . i guess i should really be purging with argon before tig welding ...

what is the purpose of the purging ? and how do you get the gas into the pipe to be welded and stop it escaping

thanks for any usefull advice and tips

 

[Drains]

You purge in an effort to keep the pipe clean and soot/oxide free, otherwise, as you cant internally clean the pipe back to clean steel, it loses its stainless properties. To stop the gas escaping make some sort of plug/membrane. To get the gas in.. a hole in plug/membrane etc.

It might be worth doing a search on UKWelder.com. Theres lots of info about stainless over there. If you can bear to walk into the lions den, ask on the forum.

Cheers
Si

 

[Mikey D]

cheers simon , i guess taping some polythene over the ends may do the job ,then fill with argon via the tig torch

regards mike

 

[Hitch]

The purpose is to keep the inside clean and free from oxidisation whilst welding. If done properly, the weld should look perfect inside and out.
Food grade pipework whould be purged.

If you rarely do it, you can usually get away with makeshift caps, something like a plastic cup taped over the ends is simple.
You can fill it with the torch, some welder have a purge mode, where it will just let gas out without an arc. Of if you have a spare bottle and reg, just use that with a piece of tape holding the hose in place.

If its a regualr thing, may be worth investing in some proper pipe bungs for purging

 

[malcolm]

The stuff inside stainless is fairly reactive. If you don't purge and you penetrate through you'll get something like the photo below on the reverse.

Some definate corrosion there, but it seemed concentrated on the surface. Not a problem for me as I had access to the reverse and it ground down well, but inside a pipe it might affect corrosion resistance.

I'd understood purging was normally done with a seperate argon supply under constant flow, though without one of those bear in mind argon is heavier than air - might be worth blocking one end off and having the pipe at an angle.

 

[rtbcomp]

The best way to plug a pipe is to get a rubber bung, drill a hole down the middle, penny washer each side and a nut & bolt through the middle. Insert the bung, tighten the nut and the washers squeeze the bung and seal the pipe.

You may need to weld the bolt head to the washer to stop it turning. Use a hollow bolt fitted with a tap to introduce or expel the gas.

Plumbers use bungs like this to seal & pressure test drains.

 

[DIY Welding]

Purging

There are quite a few products available for purging, you can get disolveable paper that you push in to the end of the pipe that fully disolves when in contact with water, you must have less than 1% Oxygen in the pipe before you can weld, most people buy a purge monitor if they are doing this job all the time, the best way is to put the argon into one end and keep the flow on , put a small hole in the other end of the sealed pipe

 

[Mikey D]

Thanks for all the advice guys ,most helpfull
we have rubber end caps that fit the pipe sizes we use ,so it will be straightforward to fit an argon supply hose to that ,would i be able to fit a tee piece and valve in the supply line to the tig welder to supply the purging gas ? i dont really want to have to get another bottle of gas and extra regulator


cheers mike

 

[DIY Welding]

Purging

Thats what most people do I have the y pieces in stock could make up a purging pipe to fit pm me for a price

 

[irondarren]

Mikey i have a Y piece connector, with valves in, I have used that in the past to split the flow from an argon bottle to two different machines, having the valves in allowed me to fine tune the flow so that each machine got the correct gas flow. Not sure if thats the one Diywelding has in mind, but it would most certainly work a treat