any tricks for ensuring an ideal purge?

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I can get good enough gas coverage to keep stainless from sugaring with no problem but I'm curious to know if there are any tricks or methods to know when all of the O2 is out of there?
Reply:what are you welding?what is the gas flow? a little more details would help.After the arc has died the weld remains
Reply:2" stainless .065 wall tubing, GTAW, pure argon on both sides. But what I'm looking for is a way to verify that my purge is perfect instead of "about 5 minutes at this flow rate" kind of response. How can I test my purge before I fire up on it?. Good enough is something I try to avoid in other words.
Reply:Light a bic lighter and hold at the oposite end of the purge hose and if it blows it out your good to go. If you wanted to get real technical they make sniffers that will measure the oxygen content but you don't need those unless your trying to follow a specific wps.
Reply:or a matchUA Local 598
Reply:Originally Posted by quasiI can get good enough gas coverage to keep stainless from sugaring with no problem but I'm curious to know if there are any tricks or methods to know when all of the O2 is out of there?
Reply:Originally Posted by Donald Branscom"to keep stainless from sugaring" what is that???BTW there are catalogs with many solutions for purging gas fittings ,end caps,round and square and many other things.
Reply:I thought the term 'sugaring' was pretty widely known, but then I'm the one asking questions.I tried a lighter thinking it would be a pretty straight forward test but the stream of gas seemed to interrupt the flame not put it out at any point( i got the same results at a couple of different intervals). Maybe holding a container over the outflow and then trying to maintain a flame inside it immediately after would be a better way?
Reply:Your over thinking this one dude. I always put my purge in the farthest from the weld so the argon can fill the whole tube ,pipe, or whatever your welding on. For example if I have a 12 ' long tube with a joint two feet from the end I put my purge in the other end as it seems to fill the tube with argon better[personal preference from experiance]. Wherever your purge is going in be sure to tape it off so your not pulling in air along with your purge. On the outlet you need a opening at least as big as your inlet hose size but I prefer a little bigger. You don't want your purge building pressure inside your work piece or you will know it when you try to close up your root. If you have a proper purge it will blow out your flame and if you ain't got no flame guess what you ain't got no oxygen. This isn't rocket science.
Reply:If you have a regulator on the purge line and know the volume of the section to be purged, it is a straightforward calculation.Example: 1 cubic foot of volume to be purged, 2 cfm purge gas flow = wait 30 seconds and you're good to go.In practice, as long as you're flowing argon on the inside, your chance to sugar the weld is minimal, so the lighter (or match) flickering is good enough.However, this leaves out what I think is the critical part of purging with thin wall tubing, pressure.  I like to run 1-2 psig on the inside to keep the purge from trying to push the puddle out.  This is most important on sanitary welds, but can cause other welds to fail as well.
Reply:http://www.airproducts.com/NR/rdonlyres/6AC2C3E9-40E1-4E21-8BBC-57CA2F3E27CE/0/stainless_pipe.pdfhttp://www.tubenet.org.uk/technical/whypurge.htmlCliff notes version...FWIW a flame will be extinguished long before all the O2 is gone. The lighter/match check is sufficient for some applications/to avoid sugaring of the root provided good purging techniques are used but it's possible to end up with a right mess tooArgon is denser than air and so will displace air from the bottom upwardsExcessively high flow rates when initially establishing the purge can cause turbulence and result in mixing instead of displacement of the atmosphere. When purging large volumes setting up a diffuser (think similar to a gas lens) helps in this regard as high flow rates are needed initially if you want to finish in time to go to the pubGenerally speaking it's recommended to have at least 6 changes of volumeOf course purge quality needs to a be a lot better for sanitary work than for say an exhaust pipe or similar high temp application
Reply:Originally Posted by hotrodderhttp://www.airproducts.com/NR/rdonlyres/6AC2C3E9-40E1-4E21-8BBC-57CA2F3E27CE/0/stainless_pipe.pdfhttp://www.tubenet.org.uk/technical/whypurge.htmlCliff notes version...FWIW a flame will be extinguished long before all the O2 is gone. The lighter/match check is sufficient for some applications/to avoid sugaring of the root provided good purging techniques are used but it's possible to end up with a right mess tooArgon is denser than air and so will displace air from the bottom upwardsExcessively high flow rates when initially establishing the purge can cause turbulence and result in mixing instead of displacement of the atmosphere. When purging large volumes setting up a diffuser (think similar to a gas lens) helps in this regard as high flow rates are needed initially if you want to finish in time to go to the pubGenerally speaking it's recommended to have at least 6 changes of volumeOf course purge quality needs to a be a lot better for sanitary work than for say an exhaust pipe or similar high temp application
Reply:Originally Posted by quasiI can get good enough gas coverage to keep stainless from sugaring with no problem but I'm curious to know if there are any tricks or methods to know when all of the O2 is out of there?
Reply:I'm surprised no one has mentioned solar flux. This is a powdered flux that you mix with denatured alcohol to make a paste. paint it inside both ends of tube to be welded and you don't have to purge.
Reply:Originally Posted by alabama-bmI'm surprised no one has mentioned solar flux. This is a powdered flux that you mix with denatured alcohol to make a paste. paint it inside both ends of tube to be welded and you don't have to purge.
Reply:Sugaring is also known as oxidation in the TIG process.A technical description might beGas Tungsten Arc Welding (often called TIG Welding) is an arc welding process in which the heat is produced between a non consumable electrode and the work metal. The electrode, the weld puddle, the arc, and adjacent heated areas of the workpiece are protected from atmospheric contamination by a gaseous shield. This shield is provided by a stream of gas (usually an inert gas), or a mixture of gasses. The gas shield must provide full protection; even a small amount of entrained air can contaminate the weld.When two pipes are welded together, inert gas is injected into the pipes to prevent sugaring or oxidizing of stainless or chrome steel pipe. "Sugaring" is a term used in the welding industry to mean oxidation of the internal "root pass," the first layer of weld material introduced into the pipe weld. Oxidation of the "root pass" is caused by a lack of an inert gas to purge a pipe of oxygen. The high nickel and chromium content of the base metal becomes reactive with oxygen in the melting process of the weld. When purge gas is initially introduced to the interior of the pipe, a groove or gap between the two pipes to be welded together is left open to the atmosphere. Approximately 90 to 95% of the purge gas, the inert gas within the pipes, will escape through this gap between the ends of the pipes. The inert gas is then displaced by air which is rich in oxygen, which reacts with the chrome or nickel in the metal of the pipe itself, resulting in sugaring.To combat this problem, welders commonly use masking tape or duct tape to inhibit the inert gas seepage through the gap in the pipes. In some applications, such as the construction of power plants, codes (ASME Pressure Vessel Code Sections 9 and 11) exist which require that the gaps between the pipes be blocked. A common means to accomplish this blocking is the use of masking or duct tape. However, there are problems associated with the use of tape. As the metal heats up, the masking tape or duct tape leaves an acidic residue which adversely affects the pipes. An inspector will require the welder to remove the residue. Two methods exist for removing residue. The pipes can be ground to remove the residue. This is an arduous and expensive process as it requires both time and labor. Alternatively, a welder can remove the residue with acetone. While the use of acetone is a simpler process, the risks involved with acetone are great. Acetone has a low flash point, whereas the temperature of the arc on a TIG welder is significantly more than 1500° F. Thus, the use of acetone on the cooling metal could have catastrophic repercussions. There exists a need for a shield which will inhibit the flow of inert gas from the interior of the pipes to be welded, without leaving a residue on the pipes.OK that concludes our daily lesson for the dayPS that description comes to you from the US Patent Office (did someone patent sugaring?) Acetone on hot weld can you say Boom Last edited by specter; 01-18-2011 at 09:37 AM.Co-Own CNC shop:Miller :1251 plasma cutter, MaxStar 700 TIG/Stick, & XMT 456 Multiprocess Welder.&  2 Hypertherm HPR260's Plasma CutterSorry I had a bad stroke but now I am back.
Reply:Originally Posted by FegenbushHowever, this leaves out what I think is the critical part of purging with thin wall tubing, pressure.  I like to run 1-2 psig on the inside to keep the purge from trying to push the puddle out.  This is most important on sanitary welds, but can cause other welds to fail as well.
Reply:Originally Posted by gofoffWhat?? Can you explain this to me? If your welding .065 wall tube properly there is no way you can have pressure of any kind inside the tube. Maybe I'm misunderstanding what your saying.
Reply:Use an 02 analyzer at the exit of the purge, when it reads <1% o2 then you have a good argon purge. In some applications you are required to also allow for six volume changes, you'll have to do the math for the volume of the pipe and the purge flow rate. Also an Alnor Dewpoint indicator can be used at the exit port, you must have a dewpoint reading of that equivalent to -11 degrees f. A magnahelic gauge can also be used to monitor pressure changes, your looking for <1".Last edited by embarr; 02-19-2011 at 10:07 PM.Reason: additional info.
Reply:I normally look at the size of the vessel in question and make a hasty determination of whether I smoke one or two butts before I start welding.Most SS pipe/tube that I do is a one butt wait.On the other hand, last week I repaired a couple of large SS marine mufflers.  Those were two butt jobs.Biggest factor though is that the vent is placed near the top of the chamber being purged, so as the argon (heavier than air) fills from the bottom up.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Volume(in. to the 3 power) = length(in in.)x Pi x radius to the 2nd power(in in.)flow rate(in. to the 3rd power/min)=cfh x 29flow time(min) = volume divided by flow rate.it's trust and character I need around me. You know, who you choose to be around you lets you know who you are. One car in exchange for knowing what a man's made of? That's a price I can live with. - Hans
Reply:Some info on the relationship of Oxygen content in purge gas to discoloration of SS.http://weldingweb.com/vbb/showthread.php...=stainless+ppm