Welding Couplers to Kegs

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I'm having some difficulty welding couplers to kegs and thought I'd post here to see if what I'm trying to do is just too tricky for a newbie like myself. What I'm trying to do is get a nice smooth sanitary weld on the back side of a keg that has a 1/2" 308 stainless coupler.I lathed couplers down for a very snug fit and used a step bit to drill a hole in the keg. The coupler sits halfway in the keg so there's a lot of material there. The coupler is back gassed and everything seems to be going well on the front, however...The back side of the weld comes out rather inconsistent. I'm running about 45-55a on a Miller 200DX. I'm just doing a fusion weld here, but what I'm having troubles with is getting full penetration to the back side. It seems as though the coupler is taking all the heat, but not fusing on the back of the weld completely. Where the coupler and keg wall meet, there is a hair line there where it looks as though the metal has not melted completely on the coupler. The keg wall seems to be melting quite nicely though.My question is how I can get things fusing together nicely without blowing things apart. I talked to a local gentleman that suggested upping the power, however when I do that it completely toasts the threads in the couplers. It seems if I get up over 80a it will just start melting the coupler threads.Some other people suggested leaving more of a gap and using filler rod to get a smooth finish on the back end. It seems there's lots of ideas on things to try, but I feel like they're coming from guys who don't tig.When I'm traveling, I'm getting a nice puddle on the coupler and then moving down to pull the thin keg wall metal into it. Moving back up and slowly progressing the puddle 90 degrees. I feel like this could be a problem with amperage, travel speed, torch angle etc... Perhaps someone with more experience can give me some suggestions.Any help would be appreciated! Thanks!
Reply:Hey insurgus,Doing fittings on a SS barrel can be a real PIA. I have a very simple method that has worked flawlessly. First, using TIG will be an issue if you can't purge the barrel. Using Solar Flux will not be conducive to getting a sanitary weld. I have encountered this issue many years ago & found that the only foolproof method is silver-solder. No need to purge, no Solar Flux to contaminate, a much reduced heat level & has a tensile strength at +32KSI. I made a simple fixture to hold the coupler in place & sil-sol the outside. With the capillary action of the sil-sol, there is no need to do anything to the inside & it will be quite sanitary as sil-sol is used in many food grade applications. The pics are self-explanantory.Denny Attached ImagesComplete Welding/Machine/Fab. ShopMobile UnitFinally retired*Moderator*"A man's word is his honor...without honor there is nothing.""Words are like bullets.... Once they leave your muzzle, you cannot get them back."
Reply:Here's the last pic. Hope this may provide some food-for-thought.....Denny Attached ImagesComplete Welding/Machine/Fab. ShopMobile UnitFinally retired*Moderator*"A man's word is his honor...without honor there is nothing.""Words are like bullets.... Once they leave your muzzle, you cannot get them back."
Reply:Open the hole up more and use the keyhole method to burn the edges away. If you can't do that, you need to hire someone who is familiar with pipe welding. This joint is just like welding a o-let, focus heat on the fitting and keyhole the base metal.
Reply:Did some keg welding for a guy here in town that sells brewing kits........To keep the inside looking "Sano"  (Being Stainless)  Solar B  was a must with as intimate fit as possible.......It has been my experience that Stainless doesn't like gaps.......Worked great for me?  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:I used homemade bullet shaped pullers, cut the holes smaller than what you need and pull the bullet shape slug thru the barrel prefferably the same size as the OD of the coupling.On a pipe coupling I would thin the welded end of the coupling to approximate the barrel thickness. I used these pullers anytime I needed to put a fitting on the side of a SS tank. It makes a nice finished type job out of installing a fitting on a tank. I had  fittings to purge thru the welded on fittings from the outside and taped aluminum foil on the inside and used argon to purge with.I cant get you a pic as I gave away those pullers when I retired.mike sr
Reply:Thanks for the replies!That puller looks interesting. I'm using a back gas manifold that I built to pull it from the back. It's threaded and just seats the fitting in the hole, however the flare on the coupler is on the front side thats outside of the keg.Do you suspect I'd get a better fit if I did things backwards with the larger lip of the coupler being on the inside of the keg? I can see how it would be easier to melt down the keg wall, but I wonder if you'd get full penetration into the fitting if that makes sense...
Reply:Originally Posted by insurgusThanks for the replies!That puller looks interesting. I'm using a back gas manifold that I built to pull it from the back. It's threaded and just seats the fitting in the hole, however the flare on the coupler is on the front side thats outside of the keg.Do you suspect I'd get a better fit if I did things backwards with the larger lip of the coupler being on the inside of the keg? I can see how it would be easier to melt down the keg wall, but I wonder if you'd get full penetration into the fitting if that makes sense...
Reply:That puller looks interesting.  The way I'm doing it on mine seems to work quite well. Perhaps some pictures of the back side of the weld might help clear up what I'm after.Basically I'm trying to figure out if its the cut of the fitting, a lack of power, travel speed or some other factor that might be causing poor penetration on the back side. If you look at the weld here, you can see the hair line gap between the fitting and the keg wall. I know the weld looks like ****, but it was an early attempt and I'm still learning.When I try to jack the heat up past 65-70a, the threads on the fitting melt down. The fittings most guys use are 150's and are ****ty chinesse parts. I got some 300's that I need to machine, so those may take more heat.Hope that helps.Last edited by insurgus; 12-12-2011 at 03:52 PM.
Reply:Side question. If I slow down travel speed, will the puddle start melting through the back side more with the same amperage? I have a tendancy to want to run it hotter, but I am curious if travel speed influences penetration if I slow way down.
Reply:Why are you worried about penetration?  All your doing is sealing the fitting it isn't going anywhere.....  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:these are 1/4 in.  thin wall tube fittings welded into stainless manifolds....  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:Originally Posted by B_CWhy are you worried about penetration?  All your doing is sealing the fitting it isn't going anywhere.....