I will not give a response of yes (unless it is a perfect world) to your question because there are to many factors involved. But if welding on the same material with the same wire you can achieve the same results. This is one reason to have a procedure that has proven that it will work. Under most codes a change from vertical up to vertical down is an essential variable and will require a PQR for vertical downhill welding. If you are bound to any code you may want to check before welding
I'll agree with Wildturkey on this one. You need to run a PQR to be sure you are indeed getting full pen. I agree also by checking to see if you are bound by a particular code which may prohibit down hill verticals.
Are you planning on using a backing strip or are you back-gouging the second side?
More variables to consider to achieve full pen. I would be worried more about achieving full pen with the backing strip than with back-gouging. If you back-gouge the second side, you can make sure that you get the joint clean at the root, before filling it back up. If you use the backing strip, your root pass is a lot more critical to keep clean and to get good penetration (which is harder to do using down hill).
John Wright
This is VERY dependent upon the technique, thickness of base metal, current setting etc..
In my opinion it is MUCH easier to make a good looking weld downhill that will not hold together as well as an "ugly" weld made uphill.
In most cases if the arc cannot be kept on the leading edge of the puddle melting the base metal, the chances for poor fusion are increased. This becomes more evident with thicker material.
Achieving full penetration at the root is not difficult with downhill GMAW. The problem arises during the subsequent fill passes.
If I had a choice of ging across a bridge made with pretty downhill welds and "ugly" uphill welds. I'm going for ugly!
Weld a vertical up and vertical down plate say 3/8" thick. Or a multipass fillet weld in the same thickness. Cut a section of it out and break it by whatever means available. You will probably notice a difference.
Hope this helps
Gerald Austin
http://www.weldinginspectionsvcs.com
Most of us cannot say if your down hand weld is as strong as an uphill one or not. If I had to guess, I would say no, BUT as was pointed out, you need to conduct some tests under your circumstances to know for sure.
To some people, it may seem that using the same wire, same base metal, same welder, same everything except direction of welding, would give equal strength welds. But one major difference would be the heat input of the weld. Vertical down-hand will put less overall heat into the joint, which changes the cooling rate, which affects the metallurgical properties.
That was assuming proper fusion throughout the weld joint. Now if we add in the greater possibility for lack of fusion, overlap,& etc., you can see that even if the weld deposits were equal in strength there is a greater chance of a weaker weld.
Of course, down-hand welding has it's place and purpose. And a weld needs to be only as strong as it was designed to be. But without testing to prove it, I wouldn't say the strengths are equal.
Chet Guilford
I would haveto agree with all the responses posted. As stated before it not that hard to acheive full penetration at the root but subsequent passes are a different story. More time than not have I seen lack of fusion at the toes of welds especially fillet welds running downhill, even with a procedure.
Brian Maas
don't most prequalified procedures for GMAW on 3/8" plate, open root, full penetration call for downhill welding the root, and then uphill welding the fill passes? if so, then there must be a good reason for it. i think it would be hard to uphill weld an open root w/ GMAW, although it would be possible. but once you get that gap filled, you could easily uphill weld the rest of it.
Look at 3.7.1 for root welding for prequalified.
Brian Maas
thanks for all the input. I should have been a bit more specific in my first question. I am referring to steel that can be welded in one pass, like 10 gauge, maybe 3/16 with a 1/16th or 3/32 root opening and square edges. I do agree that it is probably impossible to do a downhill weld and input as much heat as uphill or flat but it is easier to create a more even root penetration downhill, which in steel like I refer to has a lot to do with tensile strength of the completed piece. I could do a A/B comparison tensile test, just thinking someone out there has done some kind of similar testing
SwellWelder, you bring up a very good question that I've had to try to explain a few times. I guess what it all boils down to is that if you're using filler metal with equal or higher tensile strength than the base metal, and the weld IS without defect AND maintains the full thickness property of the base metal, with one pass, why should it be a weaker weld than an uphill one?
I haven't done any detailed testing to find out for sure. All I know is that I've always been told that downhill welds are not structurally sound.
All the codes seem to reflect the same opinion of "You have to do another PQR & WPS & WPQ's etc. etc."
However, out of all the downhill welds I've actually made, none have had or caused any problems. It's just plain quicker, easier, & cleaner.
I bet the problem is in the fine details such as dilution and grain structure properties resulting from a comparatively lower heat input than vertical.
Perhaps Nieke and/or Professor Crisi will enlighten us with the true metallurgical explanation.
Thanks for bringing up the topic.
Tim
The problem does not arise from the mechanical properties of the weld metal. I would think the problem is related more to the ability to consistently maintain proper fusion to the base metal.
Thanks
G Austin
Granted, the good possibility of defects such as slag entrapment and lack of fusion are a big drawback when it comes to down hill welding.
However, defects can be repaired and parameters fine tuned in order to place a defect free down hill weld.
I guess my question is "Is a defect free, full penetration, down hill weld that is made with filler metal exhibiting equal to or greater physical properties than the base metal, capable of retaining said properties in service ?"
Thanks,
Tim
The company across the road from our plant builds wood stoves. All their welding is done down hill for appearance. After all they are only sealing the stove to keep smoke out of your house. Sure "looks" nice and pretty!
John Wright
I worked with a company that made all vertical welds downhill with FCAW Self shieded wire and I was never informed of any problem. Many a miles of downhill 60/70/80 10 roots exist in pipelines.
Those pipeline welds don't just have a downhill bead, they have downhill fill & cap too.
regards,
JTMcC.
Hi Tim
Thanks for the "vote of confidence" that I will be able to give a good answer on this one!
A number of issues have been raised in this string. Basically we can divide then into three categories:
1) A change from uphill to downhill progression may influence the propensity for obtaining defects.
2) A change in progression may change the metallurgical properties in some way.
3) Code compliance.
I believe that the intention of the question was to address the second issue. As such, I will go from the point of view that changeing the progression will not introduce any defects. In addition, any code compliance issues would be addressed adequately.
The major issue with changeing the progression from uphill, to downhill is that the speed of welding and therefore the heat input is generally reduced. The question is therefore what effect the decrease in heat input will have on the weldment?
There is no single answer to this question, because in some instances it will result in a hardened and brittle microstructure while at other times it will result in a tougher and stronger microstructure due to the reduced grain size that is typical with lower heat inputs. (Especially high speed low heat inputs.) It will depend on a number of different factors such as material composition and material thickness.
Assuming a thin material (to be welded complete in a single pass) that is not excessively hardenable (relatively low CE) I would expect that your downhill weld will be as strong and tough as your uphill weld, if not more so. This is so because thin materials typically heat up very quickly during welding, resulting in wide HAZ's with excessive grain growth. In addition, the weld metal (which would rarely harden, due to the low CE values) would tend to have a large grain size because the thin parent metal has little quenching effect.
The argument above would be doubly applicable if you were welding austenitic or ferritic stainless steels, or most of your austenitic non-ferrous alloys.
If however you were welding a hardenable material, you will end up with a harder, more brittle structure.
Hope this helps.
Regards
Niekie Jooste
Fabristruct Solutions
Thanks Nieke and everyone for your input.
I feel a bit better now about placing downhill welds on thin sheetmetal. :)
Hey SwellWelder, has your question been answered?
Tim
Yes, most of the questions I had have been cleared up, but I would still like to know if anyone has done an A/B tensile or bend test on single pass downhill/flat welded 10 ga or 3/16"? My money is still on downhill(if properly done) is as strong as flat.
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