Sanitary welding?

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I have a question about sanitary welding.  I've read alot about back purging, ie when welding stainless exhaust pipe or piping for food/liquid transfer, you back purge with argon on the inside of the pipe and weld on the outside.What happens in the situation where you can in fact weld from the side that is in contact with food?  EG lets say I wanted to make a "vat" that would hold a food of some sort out of 5 panels of stainless steel.  In this case since the top would be open I could weld it from the inside.  In this case would you need to back purge?  What would be gained by protecting the non contact side?More curious than anything.B
Reply:Huh???   Just weld it and clean it.   For food, always use stainless. Clean off the soot, carbon and/or slag and your done.  You're thinking way too much.Lincoln Power Mig 216Lincoln AC/DC-225/125Miller  625 X-Treme PlasmaMiller 211 Forney 95FI-A 301HF 91110Victor Journeyman O/PMilwaukee DaytonMakita  Baileigh NRA Life Member
Reply:Still best to back purge.  Even if just done locally by building a dam around the joint.  That will keep the sugaring under control.My name's not Jim....
Reply:As long as you dont have sugaring in the backside of the weld you dont need to worry about the purging.
Reply:Solar Flux, and be done with it.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:My knowledge is food products will require 316 grade.....and any sugaring at all is a reject......Last edited by B_C; 09-11-2013 at 12:48 PM.  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:A mix of replies.  Sugaring on the backside does not concern me as it would never be in contact with food anyway.  I know it can make a brittle weld, but this is of no real concern either as the piece wouldnt' be subject to vibration.  My thought had been in line with superarc where by welding on the inside the shielding gas would protect the food facing weld surface from sugaring, then just polish and clean and be done with it.No tig, so might have to do some testing with my miller 211.Thanksb
Reply:agree with being brittle and sugar affect ( burnt ) in the field we would have a purge hose connected to a screen for the a torch.  have someone get inside the tank and just follow the glow. now depending on thickness would depend on penetration on one pass or two. if thin .065 - i would run one pass at 50 amps and fully penetrate with someone holding a back purge. just be careful on how much back purge as it can blow back at the welder. making a hole or an arched weld and to much argon on the torch can burn a hole or sink the weld just communicate with back purger for burning (sugaring) or not enough heat.  now on the other hand if it is a thicker material back purge so it dosent burn just fallow the glow then switch side and finish the inside and back purge from out side. its hard to see but the sink on the left side was done with back purge both sides then polished  add a argon line to this screen screw a cup and hold on just give your self a 6 inch coupler as it will get hot.Last edited by tgall82; 09-11-2013 at 10:54 PM.
Reply:There's A LOT more to sanitary welding than you'd think.You cannot have sugaring anywhere. It will fill with food/liquid and grow rust and bacteria. It doesn't matter if food will come in contact with it or not, because the whole thing needs to be washable. All surfaces have to be cleanable and be bright shiney stainless.You can't even use many common construction techniques, the thing could be beautiful and their food inspector could still condemn the thing for having too small of bend radii in the inside corners, flat surfaces facing up, other non-self draining areas, non-sanitary mill finished or brushed surfaces, visible welds, non-passivated stainless with specs of free iron (from fabricating), etc.I'd try to get approval before you build anything.It's not something that can be done correctly unless you know what is and what is not acceptable.Last edited by MikeGyver; 09-11-2013 at 10:59 PM.Welding/Fab Pics: www.UtahWeld.com
Reply:I think it would help a great deal if we knew what you are trying to do. If you are welding something for a restaurant I think there are some very exacting standards you will be required to meet. If you are welding a feed bin on your farm there may not be any requirements but still concerns you would want to address. For me even if it was a personal project I would still consider sugaring unacceptable. The advantage of welding from the inside out is you can use solar flux on the outside without needing to worry about contamination. You will then need to be concerned with heat and sheilding on the inside otherwise you will loose your stainless properties and get rust in your container.Lincoln precision TIG 275Millermatic 140 MIG
Reply:Excellent feedback all thank you.  I certainly don't intend to make it seem as though sanitary welding is simple and understand there is a lot to it.  But it does make for good discussion.  The project I have in mind is making a pan for a cider press.  I converted a harbor freight arbor press into a cider press by building a base frame out of steel, a cylinder ( hdpe ), and a pressing plate (hdpe).  The idea behind the sanitary welding was to see if it would be possible to fabricate the drain tray out of stainless instead of HDPE.  This is by no means something that would be in a restaurant, just something used by a buddy and me to make hard cider.   tgall's picture is something like I am thinking but flat with the sides only say 4 inches high.  I will have to look into solar flux in more detail.  If all else fails I will just make the tray out of the hdpe, i even have the material, just thought it might be an interesting learning experience to work with stainless.b