If my memory serves, there is a problem with using certain types of sealers in direct contact with stainless steel. I seem to remember that anything containing silicone is not good in such an application. Is this correct, or is there any similar problem with sealing stainless against other surfaces?
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need application information
There are a number of factors that you have to consider, when working with Stainless Steel: ~ Passivity: S/S gets it’s corrosion resistance from a thin oxide layer on it’s surface; hence it is preferred to maintain it’s contact with oxygen (not coated nor sealed, nor underwater) ~ Galvanic Compatibility: Dissimilar metals must be isolated. ~ more ... I’m not aware of any chemical incompatibility between Stainless Steel & Silicone. Some Silicones bond to Stainless Steel pretty well (remember, Silicone is NOT a Structural Bonding/Sealing agent), but urethane sealants often require a primer (actually a silane adhesion promoter). Teflon Sealants generally work well with Stainless. Stainless steel is relatively inert, hence adhesion of paints and sealants is often a problem. The first step is to remove any oily surface contamination. Adhesion to stainless steel is enhanced by using pre-treatments, such as: ~ Acid Etching ~ Surface Priming ~ Abrasion Although it is effective, I don't like to recommend hydrofluoric acid etches because of the extreme safety hazard. It must always be used under controlled conditions. Instead, muriatic acid may be just as effective. Another possible problem with using acids on certain grades of stainless is pitting and stress corrosion cracking. You can eliminate the acid and roughen the surface by abrading. This can be done by using non-metalic sandpaper, plastic abrasive pads, s/s wire wheels, s/swire brushes, or media blasting. It is important to note that the first step in any pretreatment is surface degreasing. After degreasing and abrading, apply the sealant as soon as possible. HTH, Gord
There are a number of factors that you have to consider, when working with Stainless Steel: ~ Passivity: S/S gets it’s corrosion resistance from a thin oxide layer on it’s surface; hence it is preferred to maintain it’s contact with oxygen (not coated nor sealed, nor underwater) ~ Galvanic Compatibility: Dissimilar metals must be isolated. ~ more ... I’m not aware of any chemical incompatibility between Stainless Steel & Silicone. Some Silicones bond to Stainless Steel pretty well (remember, Silicone is NOT a Structural Bonding/Sealing agent), but urethane sealants often require a primer (actually a silane adhesion promoter). Teflon Sealants generally work well with Stainless. Stainless steel is relatively inert, hence adhesion of paints and sealants is often a problem. The first step is to remove any oily surface contamination. Adhesion to stainless steel is enhanced by using pre-treatments, such as: ~ Acid Etching ~ Surface Priming ~ Abrasion Although it is effective, I don't like to recommend hydrofluoric acid etches because of the extreme safety hazard. It must always be used under controlled conditions. Instead, muriatic acid may be just as effective. Another possible problem with using acids on certain grades of stainless is pitting and stress corrosion cracking. You can eliminate the acid and roughen the surface by abrading. This can be done by using non-metalic sandpaper, plastic abrasive pads, s/s wire wheels, s/swire brushes, or media blasting. It is important to note that the first step in any pretreatment is surface degreasing. After degreasing and abrading, apply the sealant as soon as possible. HTH, Gord
B
Bob
Application
The application will be sealing the lifting tang on a centerboard - it will have to protrude through the fiberglass/resin layer, and I'm wanting to run a bead of something good, maybe 5200, around it at that point. Does stainless have to be exposed to free oxygen, or can it be an oxygen containing compound? I have seen 316 stainless that was totally immersed for quite some time and emerged with no corrosion whatever. Was the oxygen in the water sufficient to passivate it? Thanks for the input.
The application will be sealing the lifting tang on a centerboard - it will have to protrude through the fiberglass/resin layer, and I'm wanting to run a bead of something good, maybe 5200, around it at that point. Does stainless have to be exposed to free oxygen, or can it be an oxygen containing compound? I have seen 316 stainless that was totally immersed for quite some time and emerged with no corrosion whatever. Was the oxygen in the water sufficient to passivate it? Thanks for the input.
S/S
I don't think the "free-air" in water will allow the formation of a chromium-oxide (passive) film. Sealing the fibreglass (centreboard) to S/S (tang) joint with a flexible polyurethane sealant, such as 5200, should prevent the ingress of water, and prevent any hidden corrosion. "5200" bonds well to most grades of S/S. What makes stainless steel stainless? Stainless steel must contain at least 10.5 % chromium. It is this element that reacts with the oxygen in the air to form a complex chrome-oxide surface layer that is invisible but strong enough to prevent further oxygen from "staining" (rusting) the surface. Higher levels of chromium and the addition of other alloying elements such as nickel and molybdenum enhance this surface layer and improve the corrosion resistance of the stainless material. When the amount of chromium (in an iron matrix) exceeds 10 ½%, a complex chrome oxide forms instantaneously that prevents the further diffusion of oxygen into the surface and results in the "passive" nature of stainless steel and its resistance to oxidation (or corrosion). A chemical "dip" into 10% nitric acid acid bath will enhance the development of this "passive" oxide. Stainless does not "rust" as you think of regular steel rusting with a red oxide on the surface that flakes off. If you see red rust it is probably due to some iron particles that have contaminated the surface of the stainless steel, and it is these iron particles that are rusting. Look at the source of the rusting and see if you can remove it from the surface. If the iron is embedded in the surface, you can try a solution of 10% nitric at room temperature or slightly heated. Wash area well with lots and lots of water after use. Commercially available "pickling paste" can also be used. Some on-line S/S references: “Care & Cleaning of Stainless Steel”: http://www.ssina.com/download_a_file/cleaning.pdf “Stainless Steel for Coastal and Salt Corrosion Applications”: http://www.ssina.com/download_a_file/corrosionfinal.pdf
I don't think the "free-air" in water will allow the formation of a chromium-oxide (passive) film. Sealing the fibreglass (centreboard) to S/S (tang) joint with a flexible polyurethane sealant, such as 5200, should prevent the ingress of water, and prevent any hidden corrosion. "5200" bonds well to most grades of S/S. What makes stainless steel stainless? Stainless steel must contain at least 10.5 % chromium. It is this element that reacts with the oxygen in the air to form a complex chrome-oxide surface layer that is invisible but strong enough to prevent further oxygen from "staining" (rusting) the surface. Higher levels of chromium and the addition of other alloying elements such as nickel and molybdenum enhance this surface layer and improve the corrosion resistance of the stainless material. When the amount of chromium (in an iron matrix) exceeds 10 ½%, a complex chrome oxide forms instantaneously that prevents the further diffusion of oxygen into the surface and results in the "passive" nature of stainless steel and its resistance to oxidation (or corrosion). A chemical "dip" into 10% nitric acid acid bath will enhance the development of this "passive" oxide. Stainless does not "rust" as you think of regular steel rusting with a red oxide on the surface that flakes off. If you see red rust it is probably due to some iron particles that have contaminated the surface of the stainless steel, and it is these iron particles that are rusting. Look at the source of the rusting and see if you can remove it from the surface. If the iron is embedded in the surface, you can try a solution of 10% nitric at room temperature or slightly heated. Wash area well with lots and lots of water after use. Commercially available "pickling paste" can also be used. Some on-line S/S references: “Care & Cleaning of Stainless Steel”: http://www.ssina.com/download_a_file/cleaning.pdf “Stainless Steel for Coastal and Salt Corrosion Applications”: http://www.ssina.com/download_a_file/corrosionfinal.pdf
P
Patrick
Not stainless and not steel
like I said some time ago, it is stain resistant but is definitely subject to the corrosive effects of seawater. My friend had the 3/8" bolts which held his chainplates replaced recently. It was a big job. They were corroded almost completely through in places. Some of the bolts snapped from the torque of removing the nuts making the job of replacing them all the more difficult. As I recall, these areas were "sealed" with 5200 or something like it and well painted outside with some very expensive urethane paint (Sterling?). He had some "red rust" stains on his hull below the painted areas. The stains were not from anything else. Almost any sealant is permeable to some extent and it doesn't take much seawater to eat it up. My suggestion is to keep an eye on anything load bearing and do not paint it. If you see any faint red rust stains, that is probably a good warning sign of underlying corrosion.
like I said some time ago, it is stain resistant but is definitely subject to the corrosive effects of seawater. My friend had the 3/8" bolts which held his chainplates replaced recently. It was a big job. They were corroded almost completely through in places. Some of the bolts snapped from the torque of removing the nuts making the job of replacing them all the more difficult. As I recall, these areas were "sealed" with 5200 or something like it and well painted outside with some very expensive urethane paint (Sterling?). He had some "red rust" stains on his hull below the painted areas. The stains were not from anything else. Almost any sealant is permeable to some extent and it doesn't take much seawater to eat it up. My suggestion is to keep an eye on anything load bearing and do not paint it. If you see any faint red rust stains, that is probably a good warning sign of underlying corrosion.
Hydrofluoric Acid
Gord recommended using HF as part of a pickling solution. Hydrofluoric Acid is extremely dangerous and should not be used outside a qualified laboratory setting. It comes in polyethylene bottles because it dissolves GLASS. We used it to dissolve quartz and other siliceous minerals. There is a recommended treatment for treating skin exposed to HF. Cover the exposed skin with calcium gluconate solution and get to a doctor immediately. I strongly recommend that you avoid HF like poison or worse.
Gord recommended using HF as part of a pickling solution. Hydrofluoric Acid is extremely dangerous and should not be used outside a qualified laboratory setting. It comes in polyethylene bottles because it dissolves GLASS. We used it to dissolve quartz and other siliceous minerals. There is a recommended treatment for treating skin exposed to HF. Cover the exposed skin with calcium gluconate solution and get to a doctor immediately. I strongly recommend that you avoid HF like poison or worse.
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