Tig Welding 316 Stainless

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Hi,I have to tig weld 20", 10mm (3/8) thick 316 stainless pipes.Any advice on root gap and how to prevent it to close? How should I do the tack welds, and in what sequence should the weld be done?The positions are 2G and 5G.Thanks
Reply:As a rule the less heat input less distortion. place your tacks at even distances around the circumference. "nice heavy tacks" Fitup is generally never "perfect" especially in the field as most of us pipe welders know. If you find you have a slightly tigher gap on one side of the pipe versus the other obviously weld on the opposite side first to allow it to open up. I know on heavier stainelss pipe ive done 1" wall and up i always do bridge tacking which almost eliminates any major distortion and lets the pipe relax after the root and its forced into that position. Just make sure you have your purge setup right and your golden! Id suggest learning to put in stick roots on stainless, definatly alot less hassle although is not easy to learn. Id suppose it totally depends on the procedure your given, your procedure should by rights have all the steps in which your to weld this pipe ex: amperage, landing, root opening, diameter of wire, number of tacks and how long, purge pressure, damming setup if required.
Reply:Pressure welder,What is bridge tacking?
Reply:We usually use Solar B weld flux for back shielding our 316 stainless pipe tig welds. Just another option.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Maarty:Bridge tacking can be done a number of ways i suppose but i will share two that i use quite often. It requires you to fill up the groove with your tack. First you make all of your small tacks to hold the pipe in place then in sequence you fill up each teach right to the top of the goove, proceeding to feather it so you can have a nice tie in of course. Another way is to place your tacks and instead of filling up your tacks with weld material, using a heavy piece of round bar and tacking on either side of the groove. This practice is usually applied to heavy wall piping to prevent distortion and to maintain a consistant root opening.
Reply:Originally Posted by Pressure_WelderMaarty:Bridge tacking can be done a number of ways i suppose but i will share two that i use quite often. It requires you to fill up the groove with your tack. First you make all of your small tacks to hold the pipe in place then in sequence you fill up each teach right to the top of the goove, proceeding to feather it so you can have a nice tie in of course. Another way is to place your tacks and instead of filling up your tacks with weld material, using a heavy piece of round bar and tacking on either side of the groove. This practice is usually applied to heavy wall piping to prevent distortion and to maintain a consistant root opening.