Dye Penetrant vs X-ray Testing of Chainplates???

[dlj]

Originally Posted by Wotname

The above is true. Crevice corrosion always starts on the outside however having started on the outside, it progresses internally and leaves very little evidence of its presence on the outside of the material. Hence my previous statement was "mostly unseen crevice corrosion inside SS" rather than "unseen crevice corrosion inside SS". The adjective 'mostly' was to indicate the bulk of the corrosion is internal and therefore the bulk is not seen. The surface will always show the entry point but it is easy missed by the layman or DIY sailor.

I agree that a qualified NDT operator is the best person to preform the inspection.

Ah, gotcha - indeed the external indications may not be large compared to the damage progression internally. That's why I said your statement was unclear to me.

I've listened to discussions about how these alloys corrode from the inside without anything on the outside as if they are self-destructing from the inside out - just not the case at all... Now there are alloys and conditions where degradation can be occurring from the inside with no outside visible indication, but that does not happen in the austenitic stainless alloys within the chainplate application on a sailboat.

dj

[sailingharry]

A couple of comments.

First, as happens so often in these threads, many members of this forum feel that sailing is the exclusive realm of those with unlimited resources. The number of times you hear that "don't worry about the money, it's well worth it" or "this is not a place to try to shave expenses" leaves the very strong impression that if you don't have the money to keep your boat at 110% all the time, you should take another hobby. For the vast majority of the rest of us, we have to take a risk based approach. The corroded thru hull is probably high on the list for replacement. 15 to 20 year old rigging is starting to catch attention. But routinely replacing chain plates simply because you have removed them is something for those with unlimited resources, and perhaps for those planning ocean crossings.

But enough of that rant. The point I wanted to make was that if you are going to do a dye test, you should not clean the chain plates before testing with anything aggressive. Polishing wheels, wire brushes, etc can cause cracks to be hidden. Solvents, rags, etc are fine, maybe careful use of a razor blade, but save polishing for after testing.

[dlj]

Originally Posted by sailingharry

A couple of comments.

First, as happens so often in these threads, many members of this forum feel that sailing is the exclusive realm of those with unlimited resources. The number of times you hear that "don't worry about the money, it's well worth it" or "this is not a place to try to shave expenses" leaves the very strong impression that if you don't have the money to keep your boat at 110% all the time, you should take another hobby. For the vast majority of the rest of us, we have to take a risk based approach. The corroded thru hull is probably high on the list for replacement. 15 to 20 year old rigging is starting to catch attention. But routinely replacing chain plates simply because you have removed them is something for those with unlimited resources, and perhaps for those planning ocean crossings.

But enough of that rant. The point I wanted to make was that if you are going to do a dye test, you should not clean the chain plates before testing with anything aggressive. Polishing wheels, wire brushes, etc can cause cracks to be hidden. Solvents, rags, etc are fine, maybe careful use of a razor blade, but save polishing for after testing.

Oh man! So well said! I've been sailing for over half a century and have watched the sailing world change such that the less than wealthy can hardly afford it anymore! So from my corner of the world, rant on!!!

Spot on with the cleaning advice.

Great post!

dj

[Cheechako]

I would probably replace them.

Or you can remove and take them in to qualified experts for dye penetrant inspection. Reading that inspection requires good knowledge and best done under a black light. You need to be able to tell an inclusion from porosity from a crack from a smear etc. You will need to clean the debris off without marring the surface because grinding etc will hide defects.

So in the end, just making new is often the best idea.

I assume they are SS not bronze?

[boatpoker]

40yr old chainplates have undergone literally billions of cyclic vibrations, nothing lasts forever ... replace them.

Below is an x-ray of single pin prick size pit in a propeller shaft. The other photo shows the inside of that shaft when it broke.

[dlj]

Originally Posted by boatpoker

40yr old chainplates have undergone literally billions of cyclic vibrations, nothing lasts forever ... replace them.

Below is an x-ray of single pin prick size pit in a propeller shaft. The other photo shows the inside of that shaft when it broke.

316 has an endurance limit, so as long as the design was such that the loading remained under the endurance limit, they can go on for another billion cycles. 40 years has nothing to do with it.

You specified 316 for a propellor shaft? Very bad choice of material.

Any NDE inspection of that shaft would have picked up the obvious opening to the surface seen in your image. Or your NDE inspection was sub-par.

Here's an image for you - nothing on the surface. This one you wouldn't pick up from dye penetrant. This is internal to the material - oh right - it's NOT 316 material... It's 440C that was improperly heat treated post coating. Scary photo for sure don't you think? But it has nothing to do with the issue with the chainplates. It's a different material, undergoing a different degradation mechanism. If your propellor shaft is not 316, as it shouldn't be, then don't compare apples to oranges.

[Fore and Aft]

Dlj so what is the ultimate shaft material then? I would bet that most pleasure boat shafts I have seen are 316 stainless steel.
Personally I would compare the costs of NDT testing to the price of new chainplates. Often a big cost and hassle is removing and reinstalling hardware. So if it's not too expensive then why not replace them instead of paying for the testing? I am all for refurbishing anything on my boat. But high load items I would rather replace.
Cheers

[thinwater]

Originally Posted by dlj

I've heard this before in a couple places, but I've never seen actual data or parts that exhibit what you are describing unless the penetrant testing has been done incorrectly.

The second part of the above statement "unseen crevice corrosion inside SS" is a unclear to me. Crevice corrosion always starts on the outside. It does not start inside. One of the reasons I typically suggest using someone qualified in NDE to do the penetrant inspection is so that the cleaning step of the test is done correctly. If that step is not done correctly, it can hide the surface indications.

dj

^^ This.


Unless you have been trained the methods and tested your ability to find cracks, it is probably a waste of time, not much more effective than a magnifying glass. (I've done many types of NDE as a professional, including dye, x-ray, and UT--it takes time and practice with known defects to develop the skills.) At a minimum, the stainless will need to be polished, both sides.

[boatpoker]

Originally Posted by dlj

316 has an endurance limit, so as long as the design was such that the loading remained under the endurance limit, they can go on for another billion cycles. 40 years has nothing to do with it.

You specified 316 for a propellor shaft? Very bad choice of material.

Any NDE inspection of that shaft would have picked up the obvious opening to the surface seen in your image. Or your NDE inspection was sub-par.

Here's an image for you - nothing on the surface. This one you wouldn't pick up from dye penetrant. This is internal to the material - oh right - it's NOT 316 material... It's 440C that was improperly heat treated post coating. Scary photo for sure don't you think? But it has nothing to do with the issue with the chainplates. It's a different material, undergoing a different degradation mechanism. If your propellor shaft is not 316, as it shouldn't be, then don't compare apples to oranges.

Please show me in my post where I said anything about "316".
Ya can't just make stuff up and be believable.

[Wotname]

Hundreds of thousands of sailboats spend most of their lives at the dock going nowhere. When they do venture out, they wait for a nice day to sail or use the motor; these boats can keep their aging chainplates. Some sail further afield but only when there is good weather window for the expected duration of the trip; these boats might get away with inspecting their aging chainplates.

However if the OP is planning to cruise further afield then the chance of significant loading on the chainplates increases rapidly. Risk management 101 tells us the likelihood of an adverse event times the severity of outcome of the event is that which determines the degree of the need to manage the risk.

Thus the dock queen can keep the 47 year old chainplate while the off shore voyaging sailor will need to replace them. The OP can determine where they are on this spectrum and where they need to manage the costs. The OP has told us he has the skills and access to the facilities to make new ones - it seems like a no brainer to me to put the dollars towards new material rather than inspecting the old material if he is planning to head off-shore.

[Jim Cate]

I would point out that if the expensive NDE shows flaws (as it well may) then one is stuck with the cost of both the examination and the replacement. If they are anywhere near the same, seems a no brainer to replace them now.

Jim

[dlj]

Originally Posted by Fore and Aft

Dlj so what is the ultimate shaft material then? I would bet that most pleasure boat shafts I have seen are 316 stainless steel.
Personally I would compare the costs of NDT testing to the price of new chainplates. Often a big cost and hassle is removing and reinstalling hardware. So if it's not too expensive then why not replace them instead of paying for the testing? I am all for refurbishing anything on my boat. But high load items I would rather replace.
Cheers

Well, you ask a tough question "what is the ULTIMATE shaft material".... 316 stainless steel is not rated for submersed service - meaning that in the world of metallurgy, you shouldn't choose this material if it is being used underwater in the marine environment - propellor shaft would fall in that category. Now, that being said, it is used that way, I'm not sure why.... I hope not a lot in propellor shafts, but I don't know if that is the case or not.

As far as the ultimate material - I'd say there are a range of materials that could be used. I'd also like to know the answer to that question. But I don't. I'd like to know what they are using on say nuclear submarine propellor shafts or the big cruise ships, that would likely be close to an "ultimate" material. Unfortunately the answer to this question is outside my wheelhouse... I'd have to research the answer to that question...

Looking at Aquamet - their Aquamet 17 looks like a 15-5 or 17-4 precipitation hardening alloy. 15-5/17-4 are two alloys that are very close in composition with overlapping compositions so pretty much all modern manufacturing produces mill runs within that overlapping range so that in a mill run the output can be dual certified. Same kind of thing they do with 304/ 304L and 316/316L. The Aquamet published data on their website indicates that they are using a very good material for propellor shafts and using the correct heat treatments for submersed application in the marine environment. I'm not trying to promote their product - I've nothing to do with them - just trying to give info on the question asked..

dj

[dlj]

Originally Posted by Jim Cate

I would point out that if the expensive NDE shows flaws (as it well may) then one is stuck with the cost of both the examination and the replacement. If they are anywhere near the same, seems a no brainer to replace them now.

Jim

Totally agree. If the cost of doing dye penetrant testing approaches the cost of making new chainplates - just replace them. For sure it's a balancing act. Back to the OPs original question - for sure I would not X-ray the plates, firstly because it won't give the info needed, and secondly the cost is such you'd simply replace the parts rather than do the testing given the price, as you aptly point out...

dj

[RaymondR]

Originally Posted by dlj

316 has an endurance limit, so as long as the design was such that the loading remained under the endurance limit, they can go on for another billion cycles. 40 years has nothing to do with it.

You specified 316 for a propellor shaft? Very bad choice of material.

Any NDE inspection of that shaft would have picked up the obvious opening to the surface seen in your image. Or your NDE inspection was sub-par.

Here's an image for you - nothing on the surface. This one you wouldn't pick up from dye penetrant. This is internal to the material - oh right - it's NOT 316 material... It's 440C that was improperly heat treated post coating. Scary photo for sure don't you think? But it has nothing to do with the issue with the chainplates. It's a different material, undergoing a different degradation mechanism. If your propellor shaft is not 316, as it shouldn't be, then don't compare apples to oranges.

Not rocket science to calculate a maximum level of stresses experienced by the
chain plates.

[MaTao42]

I presume the original are SS. What are you thinking of replacing them with?