Cracked seal welds on a 25 Ton Crane

[fredhpe]

I have an issue with cracked circular seal welds on a 25 Ton Crane Assembly. The crane was manufactured some 40 years back. Tthe crane is well maintained and is still in excellent condition with the exception of the seal welds.
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These seal welds were applied by the manaufacturer (to the best of my knowledge), in place of filler material, to hide/fill 2 mis-zized holes (4 3/8" diameter instead of 2" diameter) in two (2) 1 1/4" thick plates for a horizontal 2" diameter shear pin that holds the vertical 25-Ton hook. There was no need for these seal welds in the first place, and whoever applied them had no clue about the minimum weld requirements in AWS/AISC nor did he realize the potential for a stress riser that could damage the 1 1/4" thick holding plates. The same manufacturer says he would have to inspect and engineer a solution at my company's cost when it is clearly a design/manufacturing flaw. The manufacturer's drawing clearly shows 4 3/8" diameter holes).
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Repair of these cracked welds now would be difficult and possibly unnecessarily very expensive. The welds cannot be easily accessed as they are located between the layers of the crane frame assembly (i.e. the crane assembly would have to be taken apart!!!). In addition, any rewelding would require retesting of the crane per ANSI N14.6. Additional NDT require space that is not available and cannot verify the actual size of the weld. An MPT did, however, verify that no additioanl cracks existed on the surface other than those around the outer surfaces of the inserts.
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My thoughts on this issue is that a surface (seal) weld whould not have required much heat to be applied to the material to cause a crack to propagate into the holding plates.
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Accordingly, can one leave these cracked seal welds as is (of course, cover them with a filler material and paint over them)?
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Your inputs would be greatly apreciated.

 

[metengr]

Because of the risk and service duty, remove the cracked seal welds, re-inspect the substrate material using wet fluorescent MT and be done with it. I would not leave cracked seal welds because you do not know the condition of the substrate. Yes, getting to the welds might be difficult but you need to remove them and make sure the structural member is acceptable for service.

 

[dhengr]

Fredhpe:
We can’t see what you are looking at from here. Just imagine the hundred of details and conditions which might be conjured up from you description (word picture). Each with a different answer to your concerns. Why not provide some sketches (free body diagram?, etc.) with some dimensions, sizes, loads, the weld in question, etc., enough real info. to allow a meaningful discussion. All we know so far is it’s a 40 year old, 25 ton crane. Thus, the manufacturers warranty probably doesn’t cover it any longer. But, after 40 years, I hope this isn’t the first inspection of the crane, and you just found these cracks, how old are they? If the cracks are old you may have some confidence that they are not propagating. They probably don’t support the “ horizontal 2" diameter shear pin that holds the vertical 25-Ton hook” as you implied, or they wouldn’t just be seal welds, but you make that perfectly unclear. Is this at the foot of the boom? What are the load paths around this opening in the heavy plates? When it’s welded in place it takes some load and vibration, and that caused the cracking. Where does that load go if the cover plate just hangs there?

Inspect the entire area, and make sure this crack can’t propagate into any important members. Then watch this area over time. Do some stress analysis of the immediate area to substantiate your opinion, and write a report for that crane’s file on your findings. Comment on the fact that any repair may do more damage than good, or why leaving well enough alone should be o.k. That’s called engineering experience and judgement, an informed decision. Don’t cover the crack up with caulking or anything like that, which suggests you are trying to hide it. That really drives inspectors and safety people crazy, and against you. I would talk with the manufacturer’s engineering people about this to confirm some of your suspicions, and findings. Have they seen this before, what was the fix, etc.? But, understand their position too, they should be helpful, but have no reason to stick their neck out to far without actually seeing it, after 40 years of your potential abuse.

 

[MiketheEngineer]

Then why did they crack?? If not supporting any load. Watch out - bet they do.....

 

[racookpe1978]

We;ll, maybe they weren't "supposed" to be holding any load ... But they WERE holding a load (or resisting a failure) at some point. If there was never a load on the welds, there would have never been a crack, as pointed out above.

But now? Now they are NOT holding any load at all, regardless of what design intentions ever were in the first place, or actual design conditions were then (before the crack), or now (after the crack in a supposed "seal weld". Therefore, you CANNOT make any assumptions about where your current load path is, nor how "safe" that load path is now against failure.

By the way, if a "seal weld" has cracked, how can you be sure the steel and welds underneath the previous water-tight seal are not not corroded and threatening to yield after 40 years wtaer, humidity, bird poop, and "no lookee, no see"

 

[chicopee]

About showing us a picture of the crane and of the locations of the resized holes with its cracks as you have not identified the type of crane and the type of cracks. It is unlikely that the crane manufacturer would have resized the original 4-3/8" dia. holes to 2" dia. for a shear pin to accomodate a 25 tons hook. Crane manufacturers have too much liabilty issues for using holes not intended to support loads. I suspect the owner did the resizing for that hook.

 

[stanweld]

fredhpe,
The described seal weld is highly prone to hydrogen embrittlement cracking; cracking may have initiated within hours of welding. If the involved welds were previously inspected during routine inspection and maintenance and no cracks were found, the weld has been under cyclic loading. Why would you believe that the load cannot be transferred from the loaded hook to the shear pin to the donut insertion piece, seal repair weld? As described the seal weld would be highly prone to fatigue cracking.