At 09:16 PM 6/30/99 -0500, barnacle42@ameritech.net wrote: >I`m getting much info together to make a decision on building a steel >boat.I`m looking for info on "corten steel".I was told corten( not sure >of the spelling) doesnt rust like regular steel.Does any one know the >ins and outs of this product?How does it compare in cost? Thanks for >your help Steve Corten is a very wonderful steel for what it was designed for, but not for boat building, for which it was not designed. It rusts away underwater at least as fast as any other steel, and faster than some. We learned this the hard way on a Navy contract I once worked on, to build a dock for Trident II submarines. All the pilings were pre-stressed concrete, of course; but the outside row was made from very large Corten I-beams. The reason for that was so that they would have a little bit of spring to them, as the forces from the fenders bore against them. (The "fenders" are called "camels," and weighed about 60 tons each. They bear against the submarine hull on one side, and against the dock on the other.) To make a long story short, after ten years all the Corten under water had essentially rusted away, such that a diver could poke his finger right through it; while the parts above water were still in very excellent condition, as expected. At the time, we talked to the steel company about it. They did not know for what application we had used their product, but when they found out they were not at all surprised by the results. Corten simply was not designed for underwater applications, and they showed us where we would have known that if we had read the literature they had sent us with it when we bought it. They then happily suggested several alternatives for the replacement fender row, but I don't remember what they were now. That was a long time ago, though; and steel technology is an ever improving art. The best thing to do is to talk with your steel suppliers and see what they suggest. For those who do not know, Corten corrodes very fast when exposed to the environment; but the corrosion layer is very hard and tough. It therefore serves as its own self-healing coating, which protects it against further corrosion. It is used for bridges, power line towers, street light poles, and many other non-marine structural applications. A few buildings have even been built, in which the steel has never been painted. It lasts just about forever, and quickly heals itself if you scratch or grind the rust layer off. Underwater, however; it behaves very much like plain mild steel. It is interesting to note, that at the time when we discovered our disappearing Corten on the Trident II dock, I had a very good friend who designed steel ships and yachts for a living. He sort of laughed at our troubles a bit, and loaned me one of his engineering text books on material selection. It became very obvious to me that we had simply goofed up bad, for even the text books warned us against such things. At the same time, I found the art of steel commercial ship and barge design to be fascinating. Some alloys at that time corroded at a rate of less than one mil per year, even when left bare on the deck of a coal barge used in a salt environment. As I said, this has improved since then. The designers know the rate of corrosion of the steel in these applications where they cannot paint it, and simply add enough material thickness to last for the designed life of the ship or barge. (Plain mild steel will corrode at about six mils per year under the same conditions, to give you a point of reference for comparison.) Frankly, the best place to research this subject is in the DejaNews archives for the mechanical engineering newsgroups. They have held long threads on this in the past. If you still have questions after reading the archives, I'm sure that they would be happy to discuss it further for your benefit. One of the more active people in those groups is a retired engineer who has actually built very large buildings out of Corten, and he is full of good information. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ :: Paul and Cindy Kruse :: KJV Joh 14:27 Peace I leave with you, 165 South Kenneth Court :: my peace I give unto you: Merritt Island, FL 32952 :: not as the world giveth, give I unto you. E-mail: plkruse@iu.net :: Let not your heart be troubled, 407-453-6206 :: neither let it be afraid. :: +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++