How do I purge a SS pipe pls

[Noods]

Hi All

I've got my purge parts all set up can you please advise what I need to do to carry out the task..

I've already taped the ends up and placed an intake on one end, the other end I've put a couple of small holes it to expel air etc... How much argon do I add and for how long?

Many thanks

NöÔDs

 

[Tigman]

Show us a picture of the size of the job and the joint you are welding so we can tell you whats best way forward , is it tube ? butt weld ? need some more info Noods

 

[Noods]

Show us a picture of the size of the job and the joint you are welding so we can tell you whats best way forward , is it tube ? butt weld ? need some more info Noods

Ahhhh ... Me's at work mTe can't do pic at mo.. Pipe is marine grade 3mm stainless steel when complete will be a capital T shape.. Eg two pipes joined to make a T.. First joint will be an inside corner joint which is where the two pieces join.. The two more joints will be end caps which I'm guessing is a butt joint? These will cap off the ends... Was going to tack them first and then go back to purge and weld them up .. Taping off those I'm not working on at the time..

The two pipes to make the T shape are both 200mm long and 45mm wide..

Hope this helps.. X

 

[Tigman]

stick a picture up tomorrow !

 

[hotrodder]

1st rule of purging is to remember that argon is denser (heavier) than air i.e. whenever possible you want the argon inlet at a low point and, more importantly, the exit at a high point.

2nd rule is that (like welding gas flows) less is often more... high flow rates = turbulance = mixing argon with the air instead of displacing it

3rd rule is more of a guestimate in that without a spendy box of witchcraft to tell you the O2 content a good rule of thumb is to allow for a minimum of 6 complete changes of volume. Guestimate/roughly calculate the volume of what's being purged and then it's simple to work out how long it'll take to purge at 1 litre/min, 5 litres/min etc
In practice if what you're welding is small (like your T out of 200mm lengths of 45mm tube) it'll take a min or 3 to purge at very low flow rates... talking 2 l/min tops initially before turning it down to a trickle while welding. The purge is left running while welding to ensure that any leaks allow argon out rather than letting air in. You don't need, or want, too much flow because aside from wasting argon it can bite you when finishing the last weld i.e. the pressure can rise and blow the weldpool out

 

[Noods]

1st rule of purging is to remember that argon is denser (heavier) than air i.e. whenever possible you want the argon inlet at a low point and, more importantly, the exit at a high point.

2nd rule is that (like welding gas flows) less is often more... high flow rates = turbulance = mixing argon with the air instead of displacing it

3rd rule is more of a guestimate in that without a spendy box of witchcraft to tell you the O2 content a good rule of thumb is to allow for a minimum of 6 complete changes of volume. Guestimate/roughly calculate the volume of what's being purged and then it's simple to work out how long it'll take to purge at 1 litre/min, 5 litres/min etc
In practice if what you're welding is small (like your T out of 200mm lengths of 45mm tube) it'll take a min or 3 to purge at very low flow rates... talking 2 l/min tops initially before turning it down to a trickle while welding. The purge is left running while welding to ensure that any leaks allow argon out rather than letting air in. You don't need, or want, too much flow because aside from wasting argon it can bite you when finishing the last weld i.e. the pressure can rise and blow the weldpool out

Blimey! Nothing easy in tig is there... Must be easier to Get West Ham winning champs league.. X

 

[hotrodder]

Nah, it'll become easy once you've done it a few times...

The goal is to replace the air in the tubes with argon and it's not that different to filling a bucket with water from a hose... use a powerwasher and water goes everywhere. Same deal with purging, turn the argon flow up high and instead of slowly filling the tube it 'splashes' about mixing with the air instead of displacing it.

Your two 45mm dia x 200mm long tubes have a total volume of just under 0.25 litres. If you set the flow rate to 1 litre/min then after 1.5 mins in theory there'll have been 6 complete volume changes. At 5 litres/min you'll waste argon and the purge won't work any better, in fact it probably won't work as well. At 0.5 l/min it'll take 3mins and provided all the joints are taped up well it'll work at least as well
If you put the argon in at the top and have the vent at the bottom it won't work properly becasue argon is heavier than air. If the vent is at the top and all the joints are taped up then the argon will gradually displace the air and you're good to go. Once the purge is estabilished it doesn't matter if the part is moved about and the vent ends up at the bottom or whatever as you've already replaced the air with argon

If you turn the argon off then it'll leak out when you remove the tape to get at the welds. How well the joints fit obviously affect this. Assuming everything fits well and you're only removing the tape one joint at a time them the purge can be turned down to just a trickle
If there are big gaps (by accident or design) then you can't turn the purge down without letting air in until most of the job is done. Before finishing the last weld you need to remember to turn it down (or enlarge the vent hole) though as if there isn't room for the argon to escape the pressure will increase and it'll blow out the weldpool. This is where it gets a bit more complicated more experience is needed... getting the O2 content down to a few parts per million when purging large volumes and then maintaining it there while welding without wasting lots of argon or wasting lots of time estabilshing the purge

 

[Noods]

Nah, it'll become easy once you've done it a few times...

The goal is to replace the air in the tubes with argon and it's not that different to filling a bucket with water from a hose... use a powerwasher and water goes everywhere. Same deal with purging, turn the argon flow up high and instead of slowly filling the tube it 'splashes' about mixing with the air instead of displacing it.

Your two 45mm dia x 200mm long tubes have a total volume of just under 0.25 litres. If you set the flow rate to 1 litre/min then after 1.5 mins in theory there'll have been 6 complete volume changes. At 5 litres/min you'll waste argon and the purge won't work any better, in fact it probably won't work as well. At 0.5 l/min it'll take 3mins and provided all the joints are taped up well it'll work at least as well
If you put the argon in at the top and have the vent at the bottom it won't work properly becasue argon is heavier than air. If the vent is at the top and all the joints are taped up then the argon will gradually displace the air and you're good to go. Once the purge is estabilished it doesn't matter if the part is moved about and the vent ends up at the bottom or whatever as you've already replaced the air with argon

If you turn the argon off then it'll leak out when you remove the tape to get at the welds. How well the joints fit obviously affect this. Assuming everything fits well and you're only removing the tape one joint at a time them the purge can be turned down to just a trickle
If there are big gaps (by accident or design) then you can't turn the purge down without letting air in until most of the job is done. Before finishing the last weld you need to remember to turn it down (or enlarge the vent hole) though as if there isn't room for the argon to escape the pressure will increase and it'll blow out the weldpool. This is where it gets a bit more complicated more experience is needed... getting the O2 content down to a few parts per million when purging large volumes and then maintaining it there while welding without wasting lots of argon or wasting lots of time estabilshing the purge

Beautifully explained Muchly so.. Thank you x

 

[Tigman]

very well explained there hotrodder

 

[Richard.]

Yeah that is 1 hell of a post HR.
I didn't know purging flow rates could go down as low as 1/2lpm.
I usually trickle at 1-2lpm once air has been replaced 4 times over the part volume.
I didn't know it was a rule of 6 either so I'm going to change my purge habits slightly too.
Excellent reading and someone who's never purged SS before would easily follow that. One for a frame me thinks.

 

[Noods]

Nah, it'll become easy once you've done it a few times...

The goal is to replace the air in the tubes with argon and it's not that different to filling a bucket with water from a hose... use a powerwasher and water goes everywhere. Same deal with purging, turn the argon flow up high and instead of slowly filling the tube it 'splashes' about mixing with the air instead of displacing it.

Your two 45mm dia x 200mm long tubes have a total volume of just under 0.25 litres. If you set the flow rate to 1 litre/min then after 1.5 mins in theory there'll have been 6 complete volume changes. At 5 litres/min you'll waste argon and the purge won't work any better, in fact it probably won't work as well. At 0.5 l/min it'll take 3mins and provided all the joints are taped up well it'll work at least as well
If you put the argon in at the top and have the vent at the bottom it won't work properly becasue argon is heavier than air. If the vent is at the top and all the joints are taped up then the argon will gradually displace the air and you're good to go. Once the purge is estabilished it doesn't matter if the part is moved about and the vent ends up at the bottom or whatever as you've already replaced the air with argon

If you turn the argon off then it'll leak out when you remove the tape to get at the welds. How well the joints fit obviously affect this. Assuming everything fits well and you're only removing the tape one joint at a time them the purge can be turned down to just a trickle
If there are big gaps (by accident or design) then you can't turn the purge down without letting air in until most of the job is done. Before finishing the last weld you need to remember to turn it down (or enlarge the vent hole) though as if there isn't room for the argon to escape the pressure will increase and it'll blow out the weldpool. This is where it gets a bit more complicated more experience is needed... getting the O2 content down to a few parts per million when purging large volumes and then maintaining it there while welding without wasting lots of argon or wasting lots of time estabilshing the purge

That's so good ...it's a top shelfer if ever I've seen one... X

 

[hotrodder]

I didn't know it was a rule of 6 either so I'm going to change my purge habits slightly too.

The minimum number of volume changes is one of those things that often differs depending on source, IIRC i've seen as low as 4 and as high as 10 volume changes recommended. Minimum of 5 or 6 seem to be the numbers that come up more often, regardless of the target O2 level as many of these sources consider X volume changes a 'pre-purge' before getting out an O2 meter

I didn't know purging flow rates could go down as low as 1/2lpm

Probably wouldn't end well with a lot of stuff but when the purge volume is tiny and everything fits well it can IME. Sometimes once the purge is estabilshed i turn the thing down until the flow meter widget is just barely floating, kinda bobbing/rattling about just off it's seat. Obviously that only works on smallish stuff & closed joints with spot on fit up

 

[norlander]

might be something you can use here?

basic BP set shown.