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Weldment failing after cyclical loading.

Weldment failing after cyclical loading.

Weldment failing after cyclical loading.

(OP)
Without getting into the weeds to much with specifics, my company does pretty specialized pile driving and we use shop made adapters to drive varying pile sizes, larger and variable shapes that need an adapter for the hammer. The adapters are usually weldments of some shape using usually carbon steel ASTM A572 Gr 50 plate, and structural pipes or tubes either A53 Gr B, or A500. Welded using Exx70 electrodes.

Our issue is these keep cracking and failing, and not always at the welded joints. Sometimes they fail in the base material not near the heat affected zone. Sometimes these adapters last 2-3 piles sometimes 50-100, but they always fail. The things we have tried are sizing the welds larger, sizing them smaller, radius all corners to delete stress risers.

Wondering if anyone has any input, should we try some PWHT, a different material (alloy of some type), casting? Any thoughts on expected lifetime, is forever unrealistic?

... my mind keeps rolling back to an anvil, while a man cannot put the same energy as a pile driving hammer can, these things are sometimes 100s of years old and may have been struck, what millions of times?

thanks in advance, Ill give more details if needed.

RE: Weldment failing after cyclical loading.

Have you tried vibratory pile drivers instead?

RE: Weldment failing after cyclical loading.

(OP)

Quote (chicopee)

Have you tried vibratory pile drivers instead?

Yes, we use those as well. Many of our applications aren't conducive to vibratory driving.

RE: Weldment failing after cyclical loading.

I don't want you to get in trouble with your firm about releasing a typical picture of a damaged adapter but pictures could help with additional responses. Off the top of my head, it is obvious that the impacts may be too much. I don't have any ideal about the piles you drive, however, the pile manufacturers may have other ideas.

RE: Weldment failing after cyclical loading.

How is the quality control in the shop? You may consider testing some of the weldments prior to putting them in service obviously NDT. And for kicks you could do some destructive testing. Have you reviewed best practices on the use of fatigue resistant details. AISC has ran a few articles in the past but here is some other article

RE: Weldment failing after cyclical loading.

Jmen68:
You said…, “Without getting into the weeds to much with specifics,…” Do you have any idea what a silly statement that is, and how unlikely that is to generate any meaningful discussion on your problem? The answer is, quit beating on them, and they’ll quit cracking. That keeps us out of the weeds. Alternatively, you want a perfect planer fit btwn. the hammer, the anvil plate and the top of the pile, and alignment of the leads and the pile, so you are not bending and flexing the anvil plate with every hammer impact. The anvil pl. btwn. the hammer and the pile top should be thick and everything else should just be guides to keep the two aligned and together in the driving process. As you suggested, these should be simple, clean details with a lot of ability to tolerate many impacts. You don’t need bigger welds, you need more forgiving, tolerant welds and details. Strength is not the issue, rather ductility and flexibility is. But, without much more detail on what things look like, we have no way of knowing how to comment. Didn’t they used to put an oak block/plank btwn. the anvil pl. and the pipe top or hammer to take up any irregularities, and this could be easily replaced as it got beat up?

RE: Weldment failing after cyclical loading.

Your management needs to take this extremely seriously.

I once investigated a case of fractured 1½" bolts from a pile driver. One such bolt segment fell from height and came within 6 inches of a direct strike on a worker's hard hat, which are not really designed for such an impact. The company had done nothing to monitor the condition of these bolts. So it is encouraging to hear you are doing something.

Sizing the welds larger (I assume you are talking fillets) will not help if cracks are propagating from the weld toe through the base metal. In fact making them bigger can actually enhance this failure mode. I see this a lot in socket welds and other piping fabrication arrangements.

ASTM A572 Gr 50 plate is HSLA, therefore microalloyed and hence should NOT be post-weld heat treated.

Given these problems chronic and considering the attendant cost and risk, I recommend you call in a 3rd party expert. There are too many things going on here that encompass design, material selection, construction and inspection.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Weldment failing after cyclical loading.

(OP)
GC - Our QC is good, I am confident the welders are producing good welds, and following procedures.

dhengr - I get that it is a silly statement. Just kinda wanted to direct focus to the point. I have attached a very poor sketch for everyone's entertainment. Failure on the really bad ones are around 10,000 blows from the hammer with an energy rating of about 9,000 ft-lbs.

Ironic - We take safety very seriously, fortunately these are not a current safety hazard to the employees during these operations. Many other things would hurt them before these will. Thanks for the tip on not PWHT, I need to expand my welding knowledge. Any clues on who to contact about something like this. I have reached out to some welding engineers at Lincoln Electric and they gave us some tips but nothing helped.

thanks for yalls input.

RE: Weldment failing after cyclical loading.

The person you want will be an engineer familiar with the issues and possessing specific experience with pile driving equipment, which has some unique challenges. Sorry I don't know where to send you other than manufacturers.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Weldment failing after cyclical loading.

The sketch give the impression that the material called out as pipe is failing and the weld is good. Do you use cushions while driving and are they replaced frequently? Are you driving beyond the capacity of the hammer?

RE: Weldment failing after cyclical loading.

Without getting into the weeds,

Your parts fail because the designers have inadequate understanding of metallurgy.

RE: Weldment failing after cyclical loading.

Forgive my ignorance of the configuration, but is the pipe on top a sleeve that guides the hammer to the thick plate, or does the hammer impact on the pipe?

RE: Weldment failing after cyclical loading.

Quote (jmen68)

Any clues on who to contact about something like this.
.
I'm interested. If you look up your 2017 post about fatigue design (see "my stuff" in the upper right-hand corner), you'll find my coordinates in the footer of one of my posts.

RE: Weldment failing after cyclical loading.

Usually the most effective means of determining the cause of the failure and its effective fix is to first send the damaged part to a metallurgist, then have the structure analyzed by a stress analyst to confirm the as build design faults then propose re-desinged fabrication procedures. The fix may be as simple as changing the welding fabrication sequence, or the selectio of materials or design of teh structure may need to be modified. Without the above 2 steps then you are simply behaving in a 18th century manner and can expect 18th century results.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: Weldment failing after cyclical loading.

Not really clear in the above posts is the subject of fatigue failure. For instance, pull a wire to failure and note the poundage. Next pull it to just below failure. No failure the first try. but pull it many times and eventually it breaks, from fatigue. The closer these pulls forces to the initial failure force, the quicker it fails. Do the repeated pulls at a poundage of half the earlier failure load and you may not ever break the wire at those forces. So, get into the subject of fatigue and it may help as to what to do.

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