This week I almost got beat by a TIG weld project. The shop next door to my school is American Hose and Fittings. They build hoses and such for all sorts of things, but their main products are custom stainless flex hoses.
They take stainless flex tube of many diameters, sheath it in stainless braid, and weld it to various pipe ends and flanges for engine exhausts and other high temp applications. They do this all day every day, using rotating positioners and a couple of TIG machines.
Anyway... on Monday their head welder came over to my shop to ask my opinion on a troublesome weld.
They had built these 316 SS flex hoses about 14 inches long and 3 inches diameter with heavy flanges on each end and stainless braid on the outside.
They were returned by the customer because they needed them welded on the inside as well as the outside to satisfy a "sanitary" requirement.
The joint is a 4 inch length of 3 inch sched 40 316 SS pipe butted against the end of the SS flex hose. Flex hose is made from 26 gauge sheet so it is paper thin.
So you have an inside, blind, lapped, outside corner weld of 26 ga to
1/4" wall pipe at the inner end of 4 inches of pipe.I ended up taping an inspection mirror to my TIG torch so I could see my progress immediately.
If you tried to heat the edge of the pipe, add lots of filler and flow the bead over the edge to capture the flex hose edge, the edge would just vaporize away from the heat.
I wrestled with some practice pieces until I figured it out. The trick was to turn the machine down to 25 amps, and create a worm of weld metal on the edge of the 26 ga flex hose end. Once I had this 3/32" to 1/8" diameter worm of metal running completely around the inside of the pipe I could go back in and fuse the worm to the pipe wall using higher amps and a pulser. A 3rd pass flowed the worm over the edge and into the flex hose wall.
A complete pain in the $@#&@^ It worked and I figured out how to fill any pin holes I blew into it.