Can Dyneema Chafe through Stainless Steel? Yes!

[carstenb]

The picture below shows the stainless steel eye of our snubber. Note the 3 deep furrows in the steel. These have been caused by chafe from the Dyneema shackle we use to fix the snubber to the anchor.

The snubber and shackle have been used for slightly over 1000 nights at anchor i various anchorages around the world. The Dyneema shackle is the original shackle and note that there is no wear on the Dyneema.

For the curious, we have a 30 kilo Mantus anchor - 100 meters of 8mm chain and our boat weighs in at about 12 tons, fully loaded.

[flyingnut40]

Following with interest

[Pete7]

Any chance that whilst it's in use the stainless steel could touch the galv chain?

[carstenb]

Originally Posted by Pete7

Any chance that whilst it's in use the stainless steel could touch the galv chain?

yes, I suppose it could. If the shackle twists when we turn whilst at anchor (wind, swells etc) there is that possibility - but I don't think the chain would be in contact with the eye for any great length of time.

What are you thinking? some type of galvanic corrosion?

I have to say, the Dyneema fits exactly into the groves.....................

[tanngrisnir]

I wonder if it is more like crevice corrosion, not the chafing so much as the Dyneema providing a means for moisture and salt to be in close contact with the steel for a long time. The thimble may be stainless but perhaps a low grade alloy?

Given you use it frequently, if it was chafe alone I would expect the abraded area to be bright with wear. How about a forensic pic, scrape out some of the corroded metal and see how deep it goes and what it looks like really close up.


Thanks for sharing, never seen this before.

[thinwater]

That's not chafe, that's some manner of electrochemical corrosion. The mechanism is not jumping out at me, but the pattern is all wrong for chafe. It is too rough and it obviously happened in a very short time period, relative to the total time at anchor. I've seen corrosion like that on stainless in chemical plants.


The other thing is that there is VERY little motion when the shackle is under load.


A high res photo would help.

[thinwater]

a. Was the snubber typically in the water or above? I'm assuming above.



b. I'm guessing the boat was often anchored in this manner for extended periods, for example at least weeks?

[carstenb]

Originally Posted by thinwater

a. Was the snubber typically in the water or above? I'm assuming above.

The snubber is always below the water. the bridle si about 5 meters long so the eye will always be submerged.

b. I'm guessing the boat was often anchored in this manner for extended periods, for example at least weeks?

we have anchored for extended periods - Nuku Hiva - say 6 months in one stretch. Hawaii, the Big Island - say 6 weeks in one spot. Many other places 3 weeks at time, Fakarava, Kuenhi, Rangiora, Rareteria etc.

While in polynesia we spent over 18 months at anchor in various places - never tied to a dock or a mooring ball during those 18 months.

[thinwater]

Originally Posted by carstenb

we have anchored for extended periods - Nuku Hiva - say 6 months in one stretch. Hawaii, the Big Island - say 6 weeks in one spot. Many other places 3 weeks at time, Fakarava, Kuenhi, Rangiora, Rareteria etc.

While in polynesia we spent over 18 months at anchor in various places - never tied to a dock or a mooring ball during those 18 months.

Thank you for the reply. This is still baffling, since chafe of this type is unknown, and Dyneema is in very wide use. Certainly, this is the result of something other than simple chafe. The pattern is wrong and the stainless is (appears to be) rough and rusty, which does not add up, not one bit. There are skips in the wear, which does not happen with chafe. I think it is obvious that there is some other factor involved, either odd metalurgy, a surface hardening effect (I've seen this is cold rolled steel) or something electrochemical, but for now it is a mystery. I'm leaning towards some factor relating to how the steel was rolled and formed.



Did you observe this happen slowly, at a steady rate, over a period of years, or did you notice it only recently?

[OS2Dude]

Are you sure the thimble is solid stainless steel? It looks like it could be plated steel. The shiny part seems to be the only part that is worn (and it is shiny on the sides of the furrow), and the rust seems too dark to be stainless corrosion.

[oleman]

Originally Posted by carstenb

The picture below shows the stainless steel eye of our snubber. Note the 3 deep furrows in the steel. These have been caused by chafe from the Dyneema shackle we use to fix the snubber to the anchor.

The snubber and shackle have been used for slightly over 1000 nights at anchor i various anchorages around the world. The Dyneema shackle is the original shackle and note that there is no wear on the Dyneema.

For the curious, we have a 30 kilo Mantus anchor - 100 meters of 8mm chain and our boat weighs in at about 12 tons, fully loaded.

Don't know why this would come as a surprise. Rubber seal lips will eventually wear a grove in a steel rotating shaft. That is why the rear main crankshaft seal of an engine starts leaking.
Physics, interesting stuff.
Good luck with your advantures!

[Pete7]

Originally Posted by carstenb

What are you thinking? some type of galvanic corrosion?

Certainly something odd and as others have stated, I would have expected smooth possibly polished grooves.

Going forward, I think cut the splice off and replace with a good quality stainless thimble if you can find a well known make. A galvanised thimble won't do, the Dyneema will be through that in a week.

Well spotted though.

Pete

[vpbarkley]

If you abrade the thin oxide layer that protects stainless in the absence of air it will corrode. Stainless only remains 'stainless' if the oxide layer is intact.

[thinwater]

Originally Posted by Pete7

... A galvanised thimble won't do, the Dyneema will be through that in a week....
Pete

Nope. If this were even slightly true, he would have worn through the chain during some of the longer stays. No, this is just not something that is seen.


This is not wear. This is corrosion. It doesn't even look like wear. There was no movement. I've done wear testing of Dyneema on stainless (reciprocating chafe machine) and it looks nothing like this.

[Var Korall]

Does a magnet stick?