To all those who claim that stainless steel doesn't rust, you need to be aware of several things. First as some people have pointed out, there are different grades of stainless steel and there ability to stand up to salt water varies. Additionally, ss is susceptible to a type of corrosion called chloride attack. Any solution that contains high levels of chlorides, is very corrosive to stainless. Sea water, contains over 20,000 ppm of salt (sodium chloride) dissolved in it. This is EXTREMELY corrosive and the corrosion that it causes, produces cracks along the crystal boundaries of the alloy. We NEVER use ss in situations where there are high levels of chlorides. Mild steel will work much better. On the ocean, where things get wet with salt water and there is a large amount of oxygen available, I would opt for a nickel, cadmium, or chrome plated metal. They will hold up to salt water. Steve Holtzman Advanced Chemical Technology, LLC Industrial Water Treatment www.actglobal.net *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Steve Holtzman wrote: > > To all those who claim that stainless steel doesn't rust, you need to be > aware of several things. First as some people have pointed out, there are > different grades of stainless steel and there ability to stand up to salt > water varies. > > Additionally, ss is susceptible to a type of corrosion called chloride > attack. Any solution that contains high levels of chlorides, is very > corrosive to stainless. Sea water, contains over 20,000 ppm of salt (sodium > chloride) dissolved in it. This is EXTREMELY corrosive and the corrosion > that it causes, produces cracks along the crystal boundaries of the alloy Another point to note about saltwater is that near shore, you get considerable differences in salinity from one place to another. It has to do with the relative depth, tidal patterns and lay of the surrounding land. My telltale on this has been my stainless steel Gerber knife. On some paddling trips, it emerges relatively unscathe. On others it looks like something picked up from the soil in an old rusting junkyard. I have not done this lately but I used to consult a table of relative salinity for the waters around here. It appeared in one of NOAA's book of currents tables. The place of greatest salinity around here was (is still, I guess) in the vicinity of City Island. The waters are relatively shallow, meaning they will suffer the greatest evaporation of water, leaving a greater concentration of salt. They are at the extreme end of the tides coming in from the Atlantic via Long Island Sound, meaning they will have the least amount of water change and exchange. The lay of the land and islands creates pockets that are relatively sheltered from the bigger mass of waters of Long Island Sound, i.e. little lagoons, islands-surrounded batches of water, etc. which tends also to limit the exchange with other water and build up concentration of salt thru evaporation. My conclusion is that the greater salinity there (shown in the tables), probably for the reasons I state above, is a real acid (or should I say chlorine) test for stainless steel as shown in the rusting of my knife. I also have detected differences on the Hudson River which I suspect vary with seasons and wind directions. Seasons?: more fresh water fills the area from the river in the Spring than in the Summer because of snow melt and April rains. Wind directions?: winds from our South and Southeast tends to drive more ocean water into the bays and river bringing in more salt. Some days of paddling on the Hudson, my arms are white with encrusted salt; other days there is barely a spot of white on me. The term in German for stainless is rostfrei, i.e. to be free of rust. It is true under many circumstances but clearly not all. A better term would be rostwiderstandsfahig, i.e rust resistant. ralph diaz -- ----------------------------------------------------------------------- Ralph Diaz . . . Folding Kayaker newsletter PO Box 0754, New York, NY 10024 Tel: 212-724-5069; E-mail: rdiaz_at_ix.netcom.com "Where's your sea kayak?"----"It's in the bag." ----------------------------------------------------------------------- *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
I don't want to beat a dead horse, and this is just a follow-up. . . There has been an interesting exchange about stainless steel, corrosion, rust and maintenance issues. I learned a few things, one of the most interesting being that the salinity of ocean water increases closer to shore. That's fascinating for many reasons, not least of which is the relevant corrosion, but also the fact that desalinators may better be applied further out (for other reasons, as well). A couple of questions that came up seem to have partial answers in a source I have, which I finally got out and looked at. The source is the "Boatowners Mechanical and Electrical Manual" by Nigel Calder. Among sailing types, this book is a sort of bible. The edition I have is 1996. Calder dedicates two pages (136-37) to the question "Is Stainless Steel Really Stainless." Calder states that "there are more than 500 different grades of stainless steel. . . " The grades relate to the relative combinations of iron, chromium and nickel. In the presence of oxygen, the chromium helps create a "skin" around the iron, which greatly increases corrosion resistance. There must be at least 12% chromium for this to happen, and then the ss is referred to as "passivated." Most "better" ss has at least 20% chromium. The addition of nickel enhances corrosion resistance. Product without any (or very little) nickel is known as "ferritic" or "martensitic" ss. The addition of nickel results in what is called a "austenitic" ss. Austenitic is non-magnetic; the others react to a magnet (thus, easy testing can be done). According to Calder, only austenitic ss is proper for a marine environment. He explains that non-austenitic ss is "all too often found on boats, steadily rusting away" -- especially on smaller fasteners (he describes undoing a fastener and finding corrosion, and discusses crevice corrosion). Austenitic ss is usually categorized in the 300 numbers (eg, 304, 316); ferritic and martensitic are in the 400's. Interestingly, Calder says that 304 is not the best metal for marine use. I say interestingly, because I see it used all the time. (304 is sometimes called 18-8, because it is 18% chromium and 8% nickel.) He says 316 is better, as it has a higher level of nickel, *and* the addition of a 2% quantity of molybdenum. Calder concludes by explaining why/when corrosion might occur in ss. Without repeating the details here, the general idea is that the surface layer created mainly by the chromium becomes compromised. He suggests using only 316 (but doesn't actually say that 316 *will not* corrode). He also suggests polishing the surface of ss and ensuring that fasteners are properly bedded in a waterproof sealant. For this, he suggests 3M 5200. He expressly states that silicone should *not* be used, because it is "minutely porous." (Interestingly, I just checked the West Marine catalog blurb on sealants, and it says silicone is an "excellent insulation barrier between dissimilar metals." I think I'll stick with Calder.) One further note. Calder devotes a paragraph to the question of rusting of ss welds (someone raised this earlier). His explanation is that by welding the ss, you remove the "chromium from its passivating film-forming role." There are ways to avoid the problem, but they don't sound very practical. Anyway, I apologize if I bored you. I've been meaning to check Calder since this issue came up, and since I got myself a little education this morning I thought I'd share it with the group. No earth-shattering conclusions, just a bit more information. Mark Lane *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
>From experience, plated steel will corrode severly after one or two days being used in saltwater. Even cheap stainless holds up much better. Nick At 10:29 PM -0700 4/11/00, Steve Holtzman wrote: >To all those who claim that stainless steel doesn't rust, you need to be >aware of several things. First as some people have pointed out, there are >different grades of stainless steel and there ability to stand up to salt >water varies. > >Additionally, ss is susceptible to a type of corrosion called chloride >attack. Any solution that contains high levels of chlorides, is very >corrosive to stainless. Sea water, contains over 20,000 ppm of salt (sodium >chloride) dissolved in it. This is EXTREMELY corrosive and the corrosion >that it causes, produces cracks along the crystal boundaries of the alloy. > >We NEVER use ss in situations where there are high levels of chlorides. Mild >steel will work much better. On the ocean, where things get wet with salt >water and there is a large amount of oxygen available, I would opt for a >nickel, cadmium, or chrome plated metal. They will hold up to salt water. > >Steve Holtzman >Advanced Chemical Technology, LLC >Industrial Water Treatment >www.actglobal.net Nick Schade Guillemot Kayaks 824 Thompson St, Suite I Glastonbury, CT 06033 (860) 659-8847 Schade_at_guillemot-kayaks.com http://www.guillemot-kayaks.com/ >>>>"It's not just Art, It's a Craft!"<<<< *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
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