Clevis pin corrosion

[geem]

Ten years ago we had our rig replaced. Since then we have done 37,000nm. We broke a strand on the babystay a couple of years ago, so whilst we were in the UK I replaced the babystay with dieform wire and stalok terminals.
I survey the rig on regular basis. A couple of months ago I found a broken strand on one of the aft lowers. Since we have an Atlantic crossing to do next year and I was going to replace the rig when back in the UK, so I decided to replace it now.
We did the backstay and aft lowers a couple of weeks ago whilst at anchor. Old wires off, and new wires, bottlescrews and toggles. Yesterday we went on the dock to tackle the capshrouds. A more tricky job with the mast up. The clevis pins at the top of the mast seem to have corrosion. I suspect the company that replaced the rig when we first bought the boat reused the old clevis pins. These pins are 3/4" so plenty of meat on them but they don't look good. Has anybody ever seen a clevis pins fail?
I have replaced them with new but it would be interesting to know how close to failure they were?

 

[Boater Sam]

They will last you and your grandchildren out.

 

[rogerthebodger]

Ten years ago we had our rig replaced. Since then we have done 37,000nm. We broke a strand on thr babystay a couple of years ago, so whilst we were in the UK I replaced the babystay with deform wire and stalok terminals.
I survey the rig on regular basis. A couple of months ago I found a broken strand on on of the aft lowers. Since we have an .Atlantic crossing to do next year and I was going to replace the rig when back in the UK, I decided to replace it now.
We did the backstay and aft lowers a couple of weeks ago whilst at anchor. Old wires off, and new wires, bottlescrews and toggles. Yesterday we went on the dock to tackle the capshrouds. A more tricky job with the mast up. The clevis pins at the top of the mast seem to have corrosion. I suspect the Co pany thst replaced the rig when we first bought the boat reused the old clevis pins. These pins are 3/4" so plenty of meat on them but they don't look good. Has anybody ever seen a clevis pins fail?
I have replaced them with new but it would be interesting to know how close to failure they were?View attachment 162371

Classic crevice corrosion but as the clevis are mainly in shear and the loading is quite light very unlikely to give you any issues with regard to strength

If any new ones with anhydrous lanolin to reduce any seawater inclusion to reduce any water ingress.

Also insure the replacements are 316 stainless and less likely to crevice corrosion

 

[vyv_cox]

Yes, I agree crevice corrosion. Corrosion pits can very commonly initiate fatigue fractures but on a clevis pin loads are mostly compressive, making this unlikely. Just for fun you could inspect for cracks with a glass but I think you will be fortunate (unfortunate?) to find any.

 

[penfold]

The difficulty with SS is that it's impossible to judge without relatively expensive NDT and clevis pins are cheap; with that level of pitting I'd replace. What is the condition of the mast fittings? A smear of tefgel or something cheaper on the new ones wouldn't go amiss.

 

[geem]

The difficulty with SS is that it's impossible to judge without relatively expensive NDT and clevis pins are cheap; with that level of pitting I'd replace. What is the condition of the mast fittings? A smear of tefgel or something cheaper on the new ones wouldn't go amiss.

I have replaced them. The ones that corroded were at the top in tangs. They seem to have corroded in the section that is hidden in the stalok eye fitting. There is no movement there and it's hidden from view until you remove the clevis pin

 

[Tranona]

Classic situation for crevice corrosion. No movement and oxygen starvation .

 

[William_H]

As said they would last a longtime. Clevis pin is used in shear ie load trying to cut it in half. So very resistant to failure. That compared to hardware it is attached to with much less cross sectional area in tension. (more inclined to fail) so clevis pin would be vastly over strong compared to wire or threaded parts of turnscrews etc. ol'will

 

[Neeves]

If you are sufficiently questioning to look at clevis pins, removing each in turn, I'd have a bag of new ones and simply replace - the costs are minimal.

On a lighter note - people wonder what liveaboards find to do all day......

Jonathan

 

[cpedw]

Classic situation for crevice corrosion. No movement and oxygen starvation .

Does that suggest NOT using any grease/tefgel/lanolin?

 

[vyv_cox]

Does that suggest NOT using any grease/tefgel/lanolin?

All corrosion depends on having water in contact with the metal (ignoring any non-aqueous varieties). Any measures taken to exclude water will be beneficial.

 

[Zing]

As they are scrap it would be interesting and with no cost to try to find a crack. Whack them really hard with a heavy hammer to see if it exposes a crack or fails or slice it apart and dye test.

 

[Neeves]

As they are scrap it would be interesting and with no cost to try to find a crack. Whack them really hard with a heavy hammer to see if it exposes a crack or fails or slice it apart and dye test.

Yes...

I did ponder how to test the old clevis pins, cheaply. I did not come up with a sensible idea. The only idea was to make a toggle from HT steel - but this would not be easy. The other problem was that clevis pins are not made to a specification (or I have not seen one) in that they are (or should be) significantly over strength (they are not the the weak link).

Slicing apart has great appeal.

If I extrapolate to testing shackles - quite often the pin, though deformed, does not fail (as such) but the thread fails (the pin pulls out) and/or the eye fails (by deformation).

Jonathan

 

[penfold]

Whacking with a hammer won't really prove anything; slicing through at the point of greatest pitting, grinding the end flat, polishing it then etching may show signs of cracking but may not.

 

[vyv_cox]

Whacking with a hammer won't really prove anything; slicing through at the point of greatest pitting, grinding the end flat, polishing it then etching may show signs of cracking but may not.

Etching stainless steel is not easy. It is normal to use electrolytic methods in conjunction with fairly complex etchants. A crack would be visible by eye.

 

[rogerthebodger]

Etching stainless steel is not easy. It is normal to use electrolytic methods in conjunction with fairly complex etchants. A crack would be visible by eye.

What about dye penetration crack detection.

I was required to crack detecte my stainless steel prop shaft by the safety surveyor every 4 years

I would turn down those clevis pins to the next size down and reuse for a smaller fork end

 

[vyv_cox]

What about dye penetration crack detection.

I was required to crack detecte my stainless steel prop shaft by the safety surveyor every 4 years

I would turn down those clevis pins to the next size down and reuse for a smaller fork end

Dye pen is perfectly valid on any metal as far as I know.

 

[William_H]

Dye pen is perfectly valid on any metal as far as I know.

Dye penetrant crack testing is valid for metals if not fool proof. Any effort to sand down or clean up abrasively the surface to be checked can force metal in to the crack as it appears on the surface. This will then cover camouflage detection. A better method might be ultrasonic testing which looks at internals of the component where sound waves reflect off discontinuities. Looking at the results can be complex as surfaces reflect sound waves. So you need to know where a crack will be and what the return pattern will look like for a good one and a cracked one. So not so practical for generalised checking.
Eddy current method can be very effective and cheap. Works like a metal detector but in reverse identifying discontinuity of metal as in a crack. Although mostly effective for cracks appearing near the surface. Widely used for checking aluminium alloy wheels.
Magnetic particle NDT is very effective in steel components like crankshaft for engine. Component is magnetised or subject to magnetic field. Magnetic (iron) particles flood the area in a fluid that reflects UV light. The particles tend to congregate across any discontinuity at surface. Not sure how 316 stainless steel would react to magnetic field.
Then radiographic method might also be useful. Using either X rays or gama rays to penetrate the component to give a shadow on photographic plate. However only effective if orientation is aligned to crack. But does look at internals of component. You need to know where the crack will be.
All methods are time consuming and operator sensitive. Only practical on high value or critical components and really only if you know where a crack will be.
Don't waste your time on NDT use old ones as they are over rated compared to other components in load path or just replace them for peace of mind. ol'will

 

[rogerthebodger]

There was a story of a medical Doctor visiting a friends Engineering works and saw ultrasonic weld testing and crack detection.

The Doctor then looked into the Medical use of ultrasonics in the medical field hence the ue now of scanning babies in the womb