sometimes it depends on the use of the pipe . welding with stick electrodes vert. down uses fast travel speeds and high welding currents with several small beads to make joints. this is used on cross country pipelines . because of the wall thickness this makes it economical . vert. up uses slow travel speeds , low currents and often low hydrogen electrodes with fewer heavy beads . this method is used for many reasons ( high pressure hi or low temp piping, X-ray requirements cleaning time and of course the alloy of pipe and thickness ) hope this helps . willie
But why is it that fittings are all welded in the up-hill only?
aj , what code are you using ? what material ? what quality application ?. willie
If you are comparing the same process and electrodes in trying to figure out why up or down and on pipe of similar wall thickness. Vertical down is often used on thinner wall pipe when welding an open-root butt joint - all passes in many cases. Vertical up root passes on some of these are fairly impractical. On that same pipe vertical up may be required when welding fittings on later. If there is a flowing substance inside the pipe that could (and does) accelerate the cooling rate. The uphill travel could offset this rapid cooling, or at least control it more than vertical down would allow. And I assume most are familiar with the consequences of rapid cooling.
Thinner wall pipe can be 0.120-5 inch thickness requiring 3 vertical down passes at a pretty fast travel speed to 0.250 inch versus the use of a very slow single or multiple pass uphill weld progression.
I'm not sure when down hill ever became appropriate. On my jobs, you get cought downhilling and your kicking cans down the road.
Downhilling is quite a bit faster which is where the problem comes in. The pool rolls down the weld creating lack of fusion problems.
There is gas distribution steel pipe that is 6" and 4" diameter with a wall thickness of .156 in. Vertical-up root passes on this are very impractical with SMAW. So there is a situation where it's appropriate.
The things that let you go uphill or downhill is the electrode type and process type. Different electrodes hold different characteristics because of there chemical compositions.
for example:
stick welding:
6010...very sweet for running downhill on pipe. Good for your root and hot passes. Easy to run a keyhole a get CJP....and even caps well because it burns fast and hot.
7018...you HAVE to go uphill. Stringers or weave beads.
Like others have said, depending on the application of the pipe will determine what type electrode/process you will be using, and that will determine which way you will running your beads.
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