View Full Version : lMetalurgry of Silicon Bronze Screws
07-15-2003, 10:36 AM
The screws on my Penobscot trawler appeared to have deteriorated before their time (ten years);anyone know someone who can check out these screws? Nhwhite@aol.com
Mr. Know It All
07-15-2003, 11:04 AM
Where did you buy them? I'd be sending some to whoever sold them to you.
07-15-2003, 11:45 AM
This place sould be able to do it, or know where to get it done.
metal testing (http://www.conaminsp.com/)
07-17-2003, 01:36 AM
Hold on there! Before you go around running up expensive lab bills just to find out whether or not the fasteners were the proper alloy; I think you need to back up and think about this. Besides, the most a lab is going to be able to do (without destructive testing) is to perform an acid spot test which will tell you that the fastener is of a particular alloy group but it will not be accurate enough to identify the specific alloy itself.
You have stated that the fasteners were deteriorated before their time. Ok, this sounds like galvanic corrosion. Have you investigated the possibility of stray electrical current? This can be not just from your boat but from a neighboring boat. Also, bronze may be resistant to corrosion but it isn't invulnerable. Passivated nickel and stainless steel alloys can be more noble (cathodic) then bronze (source: Handbook of Corrosion Engineering: Pierre R. Roberge ). Then there is the one item that alot of people forget about - carbon. Right up there at the top of the galvanic series is graphite (carbon) and along with it goes alot of greases which contain carbon (that is why naval vessels use special greases for underwater lubricating).
07-17-2003, 06:02 AM
Wrong, a lab can put the screws in a spectrum analyzer that will identify the exact percentage of every element in the piece, which is non destructive. The test only takes a few seconds to do so shouldn't be very expensive. They can also do hardness testing, which is non-destructive. Now for destructive testing, and so what the screws are no good anyways, a microcsopic exam would show things like grain size, intergranular attack, porosity, etc. While they are at it have them do tensile test on a few.
If I was still working and my former employer hadn't closed the lab at the plant I worked at I would have offered to get the testing done. Any other forumites out there work at a place that has a lab?
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