Hi all, I just wondered if anyone had any thoughts on a problem I encountered last week. I was fabricating a fuel tank from 3mm plate which was a sheet that was around a month old. When it came in I had painted one side of the sheet with red oxide. I cut out the tanks plates using a 9" grinder and slitting discs. All edges were ground a couple of inches back using a 40 grit flap disc. I tacked the tank together using stick with most of the tacks on the inside, I cleaned them up, drilled 3 x 1/2 holes for pipe connections and tacked on the lid. Thats when the problems started, my plan was to tigweld the seams, I did the long runs autogenously and they went pretty ok, a little bit of porosity but I put it down to a stray draught and when I ran over them they were ok. Then I tried welding the ends and the porosity probs got worse, I dropped from a 2.4 tungsten to a 1.6, changed the gas lens(16mm ceramic) and upped the gas to around 15 lpm. The welder was a Kea 160 amp Ac/Dc and I was working around 95 amps. No real improvement. I took the job back to my main workshop and attacked it with my Fronius magic wave 2200. I got on better with that especially when I upped my gas flow and changed it to a bigger ceramic but I am still getting some porosity on the seam welds. It seems to be coming through from within, where in some cases I get a crater that is right through. I finished it with a mixture of 1.6 tig rods and autogenous. When I welded on the pipe fittings I had no problems at all, it only seems to be a problem on the seams. I use these to machines on almost a daily basis and have never had a problem with stainless, alloy or mild steel. I am using pure argon ( 2 different bottles) and at one point I took the reg of the fronius's bottle and fitted an Elga optimator which I had in the store. (This is a regulator with the flow gauge as part of the reg). The rods were triple de-ox bohler steel rods A15 i think, I tried varying the torch angle but nothing seemed to work. The red oxide was all kept to the outsides of the tank in case it reacted with the diesel. I was inside, in two different workshops with the doors closed ( No draughts). I wondered if back purging the tank would help or could it be a problem in the plates themselves? Any thoughts would be appreciated.
- Thread starter lincoln17
- Start date
Possabilities that come to mind include...
Tacking with stick- missed slag etc
Welding autogenously- A15 filler wire contains deoxidisers for a reason. Oxy fuel mild steel wire doesn't contain deoxidisers and the result of using it with the TIG process is typically... porosity problems
Contamination from the cutting/grinding/paint as mentioned
Gas issue less likely with all the changes but a back bad cap seal can cause problems, high flow rates can cause problems on outside corners although less likely with a gas lens
Given the lack of problems with the fittings on the tank i'm thinking it's a combination of stick tacks and the autogenous runs
Tacking with stick- missed slag etc
Welding autogenously- A15 filler wire contains deoxidisers for a reason. Oxy fuel mild steel wire doesn't contain deoxidisers and the result of using it with the TIG process is typically... porosity problems
Contamination from the cutting/grinding/paint as mentioned
Gas issue less likely with all the changes but a back bad cap seal can cause problems, high flow rates can cause problems on outside corners although less likely with a gas lens
Given the lack of problems with the fittings on the tank i'm thinking it's a combination of stick tacks and the autogenous runs
