Corrosion of Stainless - Fortunate Catch!


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Bill Balme
Bill Balme
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This thread posted from Facebook:
Anne Lloyd
[color=rgb(29, 33, 41)][font=inherit]So fresh from the challenge over the installation of new batteries, new wiring and installation of a new charger ( done by me with help of Large crimping handles and large friend), I went up the mast to refit the anti chafe hoses on the spreaders[/font][/color]





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[font=inherit][color=rgb(29, 33, 41)]What did I see during a cursory rig check?[/color][/font]
[font=inherit][color=rgb(29, 33, 41)]The through bolt holding the lower shrouds has sheared off[/color][/font]
[font=inherit][color=rgb(29, 33, 41)]That’s with no tough conditions at all since 3 bouncy days in May.[/color][/font]
[font=inherit][color=rgb(29, 33, 41)]Well except for a brief gale passing through last Saturday while we were tied up with a tornado passing 1/2 a mile away![/color][/font]
[font=inherit][color=rgb(29, 33, 41)]Still a 16mm bolt?[/color][/font]


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Bill Balme
s/v Toodle-oo!

Bill Balme
Bill Balme
Gaining Respect (104 reputation)Gaining Respect (104 reputation)Gaining Respect (104 reputation)Gaining Respect (104 reputation)Gaining Respect (104 reputation)Gaining Respect (104 reputation)Gaining Respect (104 reputation)Gaining Respect (104 reputation)Gaining Respect (104 reputation)
Group: Forum Members
Posts: 243, Visits: 1K
[font=Helvetica, Arial, sans-serif]Copied from various Facebook posts:[/font]
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[color=rgb(29, 33, 41)]David Heath[/color][/font][color=rgb(29, 33, 41)][font=Helvetica, Arial, sans-serif] [/font][/color][color=rgb(29, 33, 41)][font=inherit][font=inherit]I would guess, just from the photos, that it is crevice corrosion. Stainless that cannot get air, like where a bolt, or chainplate is bedded into/through the deck, it can and sometimes will 'crevice corrode' very quickly, with very little warning, or [/font][/font][/color][color=rgb(29, 33, 41)][font=inherit]rust, into two pieces. The U bolt that we clipped our "safety harness" into did this and we have no idea how many years we were only clipped in by a tiny dab of Sikaflex. We discovered the problem when it was about 8 yrs old, when we removed it to paint the bulkhead and immediately all of them with bronze U bolts, that are fine 30 yrs later.[/font][/color]

[color=rgb(29, 33, 41)][font=inherit]If the cross bolt can touch aluminum. there would be s serious electrolysis danger. And, I would need to see if there is a bronze with enough shear strength.[/font][/color]

[color=rgb(29, 33, 41)][font=inherit]Could you get those parts electro-polished? That would help a lot. If not, you could passivate the parts yourself. (Use caution. And there are other articles about this. This is just one that I had used before.) Try not to scratch them as you assemble it.[/font][/color]

[color=#365899]https://www.pfonline.com/articles/citric-acid-passivation-of-stainless-steel?fbclid=IwAR15bAdBzZ16w_wOnKwe7JZaXkUXP3dPVVxwXZTiWXVs7AspOfUjKSvoyno[/color]
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[font=Helvetica, Arial, sans-serif][color=rgb(29, 33, 41)]Jim Rolt[/color][/font][color=rgb(29, 33, 41)][font=Helvetica, Arial, sans-serif] [/font][/color][font=Helvetica, Arial, sans-serif][color=rgb(29, 33, 41)][font=inherit][font=inherit][font=inherit][font=inherit]It looks like a fatigue crack thats propagated right through the metal to me.[/font][/font][/font][/font][/color][/font]
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[font=Helvetica, Arial, sans-serif][color=rgb(29, 33, 41)]Lynne Gane[/color][/font][color=rgb(29, 33, 41)][font=Helvetica, Arial, sans-serif] [/font][/color][font=Helvetica, Arial, sans-serif][color=rgb(29, 33, 41)][font=inherit][font=inherit][font=inherit][font=inherit]Hi Anne, Alan thinks it looks like a stress crack, could the mast have been flexing/moving due to either over tightening, or under tightening of opposite lowers? We know you done the miles but you are not having much luck with the rigging, hope you get it sorted easily. Worryingly we have the same fittings although we have also just had a re rig.[/font][/font][/font][/font][/color][/font]
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[font=Helvetica, Arial, sans-serif][color=rgb(29, 33, 41)]Ken Montgomery[/color][/font][color=rgb(29, 33, 41)][font=Helvetica, Arial, sans-serif] [/font][/color][font=Helvetica, Arial, sans-serif][color=rgb(29, 33, 41)][font=inherit][font=inherit][font=inherit][font=inherit]It’s definitely a “shear” . The cause: either crevice or fatigue or both but difficult to say without micro analyses. The shear process would have been going on for some time. Because the bolt diameter at the bolt head has sheared it suggests fatigue being absorbed there. Likely causes are the angle of the stay at the mast is causing load to “pump” against the bolt head. Check the correct fittings were used in the first place “ design, dimensions, materials”. A machining crack at the bolt head could have initiated the shear so make sure the replacement is “proper “ and not something that looks close to being ok. Remove the bolt every two years to check on it especially when you are on Long ocean passages or after a Long hammering to wind.[/font]
[font=inherit]Well done in catching it in time.[/font][/font][/font][/font][/color][/font]
edited by bbalme on 11/28/2018

Bill Balme
s/v Toodle-oo!

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