DISS Simular metals

[bigbad 4cyl x2]

i attached the hull to the deck with through bolts and 5200 . i did a rookie move and used silicon bronze bolts and flat washers . and stainless nuts and Finnish washer . my question is . how long can i expect this to last. before the corrosion kicks in.

 

[tashasdaddy]

Re: DISS Simular metals

depends and you is fresh or salt water.

 

[bigbad 4cyl x2]

Re: DISS Simular metals

salt occasionally

 

[studlymandingo]

Re: DISS Simular metals

Galvanic corrosion has already started! Have you ever seen the chromate fittings used around salt water, a few trips out and they can look 10 years old. I bought a boat recently that had new looking nuts on the bow eye, within a couple of months they had begun to crumble.

 

[bigbad 4cyl x2]

Re: DISS Simular metals

yea i just read some articles on the galvanic corrosion seems like it should be borderline ok . .... in the article you find the value for each metal then subtract the lower from the upper and see just how dissimilar they are and mine is just outside the acceptable range by a fraction of a point so uh ok ...... also i don't know if i was using 316 active or passive nuts ....crazy ill relay be looking at the harware closer from now on.

 

[studlymandingo]

Re: DISS Simular metals

I would put my eye to the fastners from time to time just to make sure. Better to catch it before it craps out, than after it does for sure!

 

[bigbad 4cyl x2]

Re: DISS Simular metals

they will be under the rub rail . i guess ill through bolt the rub rail with stainless fasteners in case the silicon bronze break . I'm just wondering a time frame for the sil brnz to corrode through . probably 20 years . hopefully not months . reading those articles sure did help though . allot to learn in the world of marine .

 

[Paul Moir]

Re: DISS Simular metals

To explain the passive and active business, you have to understand that stainless steel behaves somewhat like aluminium. There is a thin protective oxide layer that forms over freshly exposed stainless which is known as the passive layer, as opposed to the active material beneath it. For maximum corrosion resistance, freshly machined or forged stainless steel parts are often "passivated" which encourages a thick, more durable passive layer. Somewhat like anodizing aluminium.

In the case of a washer, likely some of the passive layer will get rubbed off the by the bolt head. So you can presume both active and passive stainless are in contact with your silicone bronze bolt.

Interestingly, it's the potential difference between the passive layer and the active material that premotes the formation of pits.

On a more practical note, since they're above the water line I doubt those fasteners will give you trouble in 40 years let alone 20. And if they do I'll bet the 5200 holds the halves together just fine anyway.