the detail calls for a 3/16 inch fillet weld,,,,,,,,,,everything looks good,except that its 3/8ths,,,,,,,,,is it accepted..........?
what if it were even larger.....???????????
Most codes and standards address minimum weld sizing but not maximum. A couple make statements like... oversized weld are acceptable as long as they don't interfere with adjoining parts... or similar wording. It's a shame really that criteria isn't better defined as oversized welds can, in some instances be more detrimental than undersized welds. In any case they're a gross waste of time and materials but you will be hard pressed to find criteria for rejecting them... not much an Inspector can do but the foreman, superintendent or management in general can (and should) correct such practices as wasteful.
If the codes were to address oversizing of fillets my opinon is that the standard should be quite liberal. Its better left up to produciton to determine waste, and engineering to determine detriment, leave to inspection to determine compliance.
It may be acceptable. It is also 4 times as much welding. Adding any labor to make it smaller only adds to the cost and does nothing to add to the quality unless there is a clearance/intereference issue.
Aside from a compliance point, Engineering point, and forgetting the wasted time and material point for just a moment. Please let me make a comment from a metallurgical point. "Oversized fillet welds" can very easily cause very high tensile stresses in that particular area. Just because something has a lot of weld on it does not necessarily make it stronger...usually it is just the opposite. Right along the line Jon pointed out.
More very unnecessary thermal cycles..
I think concern for oversized fillets would have a lot to do with the extent of oversizing and the alloy in question. There's always limits. Thermal cycles, heat input, multiple passes, grain enlargement, will certainly have a metallurgical effect. But as a practical result large fillets in reality would generally have very little effect on the viability of carbon steel weldments. In fact multiple passes will have a tendency to stress relieve previous beads. A process counted on with some CrMo's and other alloys. This is not to say that a 1/2" fillet is OK for 1/4" material. Engineering judgment cannot be replaced. As I said, there are always limits. But I think the broad allowable parameters under prequalified status for D1.1 really make liberal approach here implicit in code thinking.
I agree with what you said, but unwarranted thermal cycles affect the HAZ more than the previously deposited weld metal. I agree that each weld pass is a form of rapid heat treatment, but those extra passes are not helping the HAZ.
Chuck
Your point is well taken. I'm not even sure they are helping the weld metal that much. But some. Certainly enough to be really important for alloys like Grade 91. Probably not so important for CS. And nothing is more complicated than a multipass pattern of HAZ's. While some areas are being relieved, some areas are seeing grain growth. But if I had to guess, and this is just a general guess based upon what I've read, I think the effect is very similar to the effect you get with microstuctures as a whole. If you run microhardness traverses you'll often find really hard 'spots' mixed with generally much softer areas (if its welded right) as you hit carbides, etc. I think its theorized, or even demonstrated, that the softer areas take the bulk of the strain under stress. I think this would be the case with HAZ patterns as well. Even those in the original BM. But bottom line for me I'm just not sure there is evidence of failures from oversized fillets that would motivate code bodies to address this issue.
"Oversized" fillets, or any welding for that matter, that involves more than necessary heat (thermal) cycles is not done for the better. I don't have any documented evidence of failures, though there may be many that aren't published. But, there is definitely evidence that thermal cycles affect grain structure and HAZ's, and not for the better. I must agree that this normally in the higher alloyed materials.
There have been some folks that considered the J groove weld in the PWR reactor heads to be part of the cause in the recent years rash of cracking. There are many other factors involved, but the reinforcing fillet on those Jgrooves was part of it. It's my opinion that there are not many reported cases because there are most always other factors involved. Excessive undercutting, convexity, concavity, etc create potential stress risers etc., those are clear, but trying to pin down excessive weld as a root cause? Trying to sell a root cause failure analysis as excessive weld would be a hard sell. I think most reports are probably going to use terminology such as you've mentioned already; enlarged grain structure, excessive thermal cycles, HAZ cracking etc. I think there may be several of those failure reports using that particular verbage that are in fact due to excessive weld IMHO.
Gerald,
I was just trying to say that excessive weld is what very likely causes these situations as excessive grain growth, excessive thermal cycles, HAZ cracking, etc. We can certainly pin it on one of these conditions, but what caused the condition in the first place? These conditions you (and I) listed are normally a product of excessive thermal cycles, which can be attributed to excessive metal (oversized fillet). Even in other types of failure, generally the problem is not in the weld itself (oversized or not) but in the HAZ. Usually, that is where the problems occur. In any failure, potential failure, processes to eliminate potential failure, or whatever, it is wise to figure what CAN cause these conditions. I agree with you that verbage is important in a failure analysis report, and the final determination may be something like liquation cracking or any of the other scenarios you listed, but it should be noted just exactly what was the most probable cause of that condition so as to avoid it happening again. IMHO, too...My brain thinks along the lines of stainless steel, very little CS, so these conditions may vary with the grade of steel.
Chuck
The other posts bring out some very good points. I just want to add that whenever I see a weld that much oversize (4x the volume as Pipewelder pointed out) I have to wonder why. What is underneath that made it easier to make that weld so large? There may be nothing wrong with the weld but it raises doubts.
I think the very diversity of issues this subject has generated here may be part of the reason the codes have not addressed it aggressively, or definitively. Is there a problem being hidden? Is the oversize a series of low heat input stringers (not at all conducive to extensive grain growth) or one big whoppin bead with one big whoppin HAZ? What material are we dealing with? Is deleterious liquation generated? Deleterious unmixed zones? Deleterious stresses? Deleterious precipitations? Deleterious eutectics? Are these things consistently reflected in failed mechanical testing?
I think the bottom line is, oversizing of fillet welds does not 'necessarily' lead to an unviable weldment. And this may very well be a primary criterion for code reticence, and maybe should be. If we KNOW we have a problem the codes can accomodate it. But if all we have is metallurgical logic and inspection oriented opinions of bad practice, do we really want code bodies involved? This approach would certainly have ramifications well beyond what appears to some to be a slam dunk situation.
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