I've done it on lighter, non critical stuff but cranking up the machine and trucking like road runner to keep ahead of the puddle to keep the slag from contaminating the weld or the lack of fusion issue that would arise at the root if the puddle got ahead of you. Not really laying down that much filler metal as compared to an uphill run with 7018. Faster perhaps, just as good I could not tell you. Tommy and I did a job a few years ago and they attempted downhill 7018 and we gouged out many a weld where the root of the filet joint had been untouched by filler material. It looked as good as it did when they bought it and butted the plates together. For the intended purpose of this stuff we were working on it might have been ok but the owner knew a little about welding and it was not what he paid for from the first guys who did the job.
In my trails I have not run across many that consider this an acceptable practice. Older welders who have been doing boiler work for 20-30 years and others pretty much say the same thing, "there's no downhill in ASME or AWS". Not saying there isn't but I have not run across anything to date other than some farm repairs on thin metals or fence trash. Doing it and because your running so fast I have seen concavity in the welds, maybe a bigger rod, more heat would cure it but with that comes more flux. Concavity from my studies is a reason for failure past a certain measurement. In my minds eye if it tends to do this because you are trying to keep ahead of the puddle and you have to go over it again, again....why not run uphill where you can pile the weld in there and limit passes? I've also heard chatter about penetration. Whether you actually get as good of penetration running downhill with the 7018. In my experience running lighter metals is why I use it, less penetration as opposed to uphill. Take a 3/8" beveled plate and weld half uphill and watch the weld pool, penetration and then on the other side run downhill with 7018 and compare. If you cut it and etch it or shoot it with x-ray to compare that would be interesting to see. I bet there would be no comparison though.
Just my two cents, in my shop not acceptable for anything other than a galvanized pipe fence repair or fixing the 1/8" sides on my trailer. As I said though, maybe somewhere they've got it figured out and it's the cats meow. I tend to agree with Superflux on it, "Yes 7018 can be (and does get) welded down hill. Should it?? Nahhh."
There are specific DH rods for LH welding on pipelines. Not in favor as pipeliners do not like LH.
Hardheaded, etc.
However 7018 CAN be run DH just there are few people who can do it. In the days of wooden ships and iron men, there were no grinders. Or at least those that were able to be used by hand. Using 7018 as a wash pass leveled everything up and made the weld flat. A good wash pass hand was worth his weight on gold. In 20 years working around tanks I have seen 2 welders who knew how to run it. One was a old CBI honest to god tankee and the other was a import from Mexico. Both were slick LH hands and the smallest rod they welded with were 5/32 and perfered the 3/16's. The welder has to have another rod in their off hand and if the slag starts getting ahead of the weld puddle the welder flicks the slag off. You have to have a welding machine that can handle the heat as once you get started you do not stop until you get to the bottom.
