I am not a professional welder;however,30 years ago I learned to weld at the local community college where I taught.Two nights a week and three years later I passed their tests. The instructors were from the Norfolk Naval Shipyard and the school there was very technical(not the college one)and was upgraded by the navy after the submarine disaster in the 60's.Later, I taught Physics at the yard,but did not have the clearance to see the advanced welding school.But,I could watch welding on ships.Heater bars were placed on either side of the weld(I do not know the temperature) and low hydrogen rods were used-7018.I used 6010 for rough work and 7018 for clean steel.I then had a side business doing repair welding.From what I learned from teaching at other shipyards, hydrogen was the enemy as it will invade the crystal structure of steel and cause cracking.This is just a comment as I am not qualified in metals technology.
Dead on right, Sir- the cracking at the edges of the HAZ on mild and mild alloyed steels is from hydrogen enbrittlement-- What makes AWS 7018 (70,000 PSI minimum tensile as stress relieved) such a fine SMAW electrode (we always used Lincoln 70 LH for code work on fab and schedule pipe steels (not on stainless of course) is that if handled properly- the flux is hydroscopic in nature, like a sponge, so it must be kept in a heated container or storage dry box- especially after you open the seal on a tin of electrodes- also it runs best with DC Reverse polarity, the same as your AWS 6010 and 7010 pipe rods- and unlike Lincoln 5P and HYP (we called it "Hippie Rod", 7018 has a heavy flux run off, and can be only run "out of position" Uphill--but as all the elements of the Lo-Hy rod are in the flux, you can't just take a stick of 7018- 3/32" is usally the smaller dia. made in 7018, scrape off the flux, and use it for TIG-- I use my Miller 250 TIG (Linde water cooled torch, soft start Hy-Freq and foot pedal rheostat for both mild, HSLA, Tool and Die (Air, Water and Oil hardened grades) and also for aluminum (AC Hy-Freq for alum.) Pre-heating and using a Tempil stick is the best way to get pre-welding temperature on your unknown alloyed gun barrels- 300 to 350 F in the adjacent areas of the HAZ- and then post heat and wrap in asbestos sacking until the entire section is cool to bare handed touch- but what the rest of the lads here have overlooked are three things, seemingly small, but crucial-- I sense a pattern of undercut as well as cracking on the edges of the weld beads- (1) the root pass is the key- you must "skip" weld or stagger the passes around the 360 degree circumference- and avoid grinding each section to a shear or sharp edge- leave a "land" where both section touch- you can't use alignment clamps and a backing ring as we do with API and ASTME code pipe welding-- (2)maintain that same 350 degree after the root pass by re-checking with the Tempilstick-- then add the fill passes, also skip weld, and in reverse rotation to the root pass- when you add the cap pass, increase slightly the gap from your tungsten in the torch, this will give the final pass a flatter "crown" and better flow to the edges, preventing undercut- with proper travel speed of course (3) One thing you all have overlooked, so far- use 100% Argon- right? Nope- more expensive, but I use a 50-Helium-50 Argon and a larger cup on the Torch- and make sure there is no debris on the inside dia. of the ceramic torch cup- that can cause turbulence and a void in the shielding gases in the molten arc/filler rod pool- also, only grind your 2% thoria tungstens on a designated clean wheen, and on the side, not the normal way- a contaminated grinding wheel will cause problems with your tungsten electrode- also make sure your filler rods are wiped clean of oil, debris- etc-- even sweat or acids from human hands can cause this- wear clean welding gloves when handling filler rods-- remember, 90 percent of a successful welding job is in the preparation-
