Electrolysis question

[Dferr]

Does anyone know for a fact, if using two different types of stainless steel like 316 and 318 would cause an electrolysis problem.

The situation would be, if you had a 316 stainless bolt and you were using a 318 stainless nut. Could the two different grades cause electrolysis?

Thanks,
Don

[Sasha_V]

Where are you getting 318?

316 and 304 (A more common blend to find with marine stainless) will not cause big problems any time soon....BUT the area of 316 in contact with and a little beyond the 304 will corrode at the same rate as the 304.

So the simple way of looking at it is; 316 is much more expensive then 304 for its added corrossion and streak resistent properties....Bringing the 316 into contact with 304 parts negates those advantages and means that you might as well have used 304 all round.

Another thing to consider is that surface area corrossion is a way more serious factor then the two metals not being identical. This means that getting a buffing wheel or two and taking the surface (whether 304 or 316) to a high "superyacht" finish will actually go a huge way towards imrpving stain and corrossion resistence. Cheaper stainless tends to be amatt finish, whihc is another way of saying billions of fine scratches all over the surface, ready to trap moisture and impurities (mostly salts) and have them discolour the surface of the metal.

Some points ot consider when buying stainless.
high polish 304 may be more suitable to your needs then semi or matt finish 316...

It takes some thinking!



Sasha

[sailingdog]

One other point. 316 is about 85% as strong as 304, but 304 is much more susceptible to chloride stress cracking, and as such 316 is generally a better idea in a saltwater environment, where there are lots of chloride ions.

[Sasha_V]

You know, that should be right on the money. It really SHOULD work that way...
But I work on a lot of boats that are over 40 years old...and have lived somewhat hard lives (on moorings in salt water, rather then on trailer or in a sheltered marina) and the 304 on them is just fine, thanks.

At some point I went over to using 304 for staunchions instead of 316 because I liek it when they bend and I can heat and bend them back and shrink out the wrinkles instead of having them stress fracture and break. Same goes for bow rollers and such. So after a few years of doing custom hardware, I find that well finished 304 is actually pretty damned nice. I do still use a lot of 316...but as a rule I will use it where there is going to be a lot of human contact (hand rails and such). I find that the oils, sweat, and sunscreen residue form human contact promotes discolouration in 304 fittings much more than just salt and sun and ionised chlorine.

By the way, 316L greatly reduces the tendency to self harden and fracture when stressed, so you can always go that option for staunchions.

Sasha

[soul searcher]

Sasha,
what about 304 L. still too brittle?