Stainless steel - how to know is it 304 or 316?

[sailreve]

I am wondering if there is a way to easily tell if the rigging wire is made of 304 or 316 stainless still. Friend of mine came back from the Bermuda, all trip took about 3 weeks. His NEW rigging is full of rust stains, especially between the strands. Is it normal? This is fresh water boat.

Max

[killarney_sailor]

I am also a fresh water sailor and have done the Bermuda circuit several times. First time in St Georges I was rafted at the customs dock off a big British cutter returning to UK from a dozen years in the Caribbean. I made a comment to the lady aboard about being surprised about my stainless rusting after less than a week in salt water. She looked at me like I should not be out of the institution by myself and said, "Of course, stainless rusts"

The secret is to protect the stainless, before exposure with one of the many protectorants that are available. I have used Lanacote and it seems to work pretty well.

Bruce

[sailreve]

My rig is 30 ears old and looks better than his after 3 weeks in salt water. My boat spent 28 yeras in salt water.

Max.

[Tom H]

You might try using a magnet. 304 becomes sensative to a magnet when it is cold worked, 316 much less so. If a magnet sticks or is pulled towards the wire, it is most likely 304. If the magnet doesn't pull, you still don't know - it could be either 304 or 316.

[Rick Beddoe]

sailreve

I had this exact conversation with many folks while a dilemma I was having with my chainplates.

The magnet test that Tom H mentioned was the only one I came across. It wasn't very conclusive for me. Otherwise, I believe there are some sophistacted $$$ tests that could probably be done.

With regards to 304 vs 316, most Yacht designers seem to spec 316 for it's corrosion resistance. 304 is about 20% stronger than 316.
But, considering a boat designed for 316, what you gain in strength, you lose in corrosion resistance. OTOH, just because a boat was 'spec' designed with 316, that doesn't mean the manufacturer used 316. Taiwanese boats from the late 70s were known for using whatever was lying around at the time.

I've been told there are various grades of 304 and some of them are more prone to rust than others. Most people switch to 304 for cost reasons then try to use strength as the 'real' reason so as not to sound cheap (I know I do) :wink:

On the other hand, one of the companies I work with (http://www.mesabi.com/) builds industrial radiators for offshore drilling rigs. These are built completely of 304. Built in obsolescence perhaps?

But, as killarney_sailor mentioned, even Stainless will rust. However, I'm not so sure about coatings. Trying to apply 'before exposure' is like being 'a little pregnant'. What I've been told the biggest cause of rust is when SS can't 'breathe'. If it is in contact with moisture without any exposure to air, SS will rust (304 or 316). Putting on a coating could trap moisture.

It typically starts with pitting then grows from there. Polishing my help as it reduces the surface area which in turn may reduce the possibility of crevice corrosion.

It is a bit odd to hear that the rigging is full of rust stains after only 3 weeks. Are you sure it's stainless? Here's another weird possibility...did he (or anyone else) use steel wool to 'clean' the riggin? Sounds dumb, but I've seen it happen.

Hope that helps.