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Car Forum / MINI / June 2004Stainless steel fasteners?
Hello, all! After my question about nuts and bolts for the Mini, I got a couple of pointers to stainless steel fasteners. They probably look smashing, but I would be reluctant to use them for two reasons: A: Corrosion and B: Brittleness A: There are two types of corrosion to take into account: Crevice corrosion and galvanic corrosion. Crevice corrosion occurs where an electrolyte, such as water, is trapped in a crack. A good example is under the paintwork. You have a small dent with a little crack in the paint. Water seeps in and goes to work. The water contains oxygen from the air, and this oxygen reacts with the iron in your car. Rust. The water, having access to oxygen in one end and iron in the other turns into a small battery, tearing electrons away from your poor iron atoms, thus speeding up the rusting. I am sure you all have noticed how far and quick rust spreads under paint. That's crevice corrosion at work for you. See http://www.corrosion-doctors.org/Localized/Crevice.htm A quick fix, if you find your pride and joy dented in the parking lot: Rinse the crack with pure alcohol (pure, beer will not do). Alcohol does a good job at driving out moisture. Wipe the alcohol off, and seal the crack with a dab of nail varnish. This should stop the corrosion dead in its tracks until you can address the dent properly. Galvanic corrosion occurs where you have two different metals in contact with each other in the presence of an electrolyte. Yes, water will do nicely, but add salt for extra effect. The less noble metal will be eaten away, and the more noble metal will be left untouched. Example: http://www.corrosion-doctors.org/Aircraft/galv-exam1.htm See http://www.corrosion-doctors.org/Aircraft/galvdefi.htm (If you doubt the power of galvanic corrosion, take a look at your car battery. The current you get out of it is a result of a galvanic corrosion type reaction. The metals are lead/lead oxide and the electrolyte is sulphuric acid.) As if this is not enough, the two forms can also work in pairs. Let's think about a stainless (noble) bolt used to fasten a Mini subframe (ignoble!). Water seeps in, and the process starts as crevice corrosion. Once the water is full of ions, and notices those different metals, it shifts to galvanic corrosion. B: Finally, we get to the brittleness: I don't think it is a good idea to replace any bolt that has a torque specification with anything but a high tensile steel bolt. High tensile steel is not brittle, and can handle a lot of stress. Stainless bolts have different properties, which may or may not be the right ones for the application. The end result can be everything from OK to catastrophic failure. I don't know the tensile properties of the stainless bolts in question, so I cannot say Aye or Nay. I can only imagine the consequence of a broken bolt in the front suspension or steering due to corrosion or metal fatigue due to repeated shocks to an inflexible bolt. Any comments from anyone who actually knows what he/she is talking about would be most welcome! I'll climb off my soap box now. Happy motoring! RustEater > After my question about nuts and bolts for the Mini, I got a couple of > pointers to stainless steel fasteners. They probably look smashing, but I > would be reluctant to use them for two reasons: > A: Corrosion and B: Brittleness > A: There are two types of corrosion to take into account: > Crevice corrosion and galvanic corrosion. > Crevice corrosion occurs where an electrolyte, such as water, is trapped > in a crack. A good example is under the paintwork. An even better example is deep in the threads of a fasterner. And crevice corrision in stainlessfasterners is going to happen right where you can least afford it, causing worse stress concentraters at the base of the threads. > Galvanic corrosion occurs where you have two different metals in contact > with each other in the presence of an electrolyte. Yes, water will do > nicely, but add salt for extra effect. The less noble metal will be eaten > away, and the more noble metal will be left untouched. > Example: http://www.corrosion-doctors.org/Aircraft/galv-exam1.htm > See http://www.corrosion-doctors.org/Aircraft/galvdefi.htm The chromiumand nickel in stainless steels generally reduce but do not eliminate the tendency to galvanic corrosion. > B: Finally, we get to the brittleness: > I don't think it is a good idea to replace any bolt that has a torque > specification with anything but a high tensile steel bolt. Absolutely. If stainless steel bolts were as strong as high tensile bolts then they would be marked as (stainless) high tensile bolts. Don't replace a grade 5 bolt with anything less than a grade 5 bolt, regardless of the material. > High tensile steel is not brittle, and can handle a lot of stress. Actually the higher grades are more brittle and are more prone to fatigue failures. One common car model in Australia suffered frequent failures of con rod big end bearing cap bolts in the late 1980s which turned out to be caused by the engine manufacturer replacing the correct high tensile bolts with a higher grade of bolt which, whilst stronger, was not up to the cyclic loadings. You'd have to be very unlucky to get caught out like that, but it's a clear lesson that you should stick to the correct fasterners, especially anywhere which is subject to cyclic loading, such as powertrain or suspension components. > Stainless bolts have > different properties, which may or may not be the right ones for the > application. The end result can be everything from OK to catastrophic > failure. Stainless is magic stuff. But it's not the same as conventional steel and you can't use it in exactly the same way you would ordinary steels, just as you can't replace steels with aluminium without changning your designs. > Any comments from anyone who actually knows what he/she is talking about > would be most welcome! I'll climb off my soap box now. It's a well worn soapbox. Thats my muddy footprints on it from last time we discussed this here. >> After my question about nuts and bolts for the Mini, I got a couple of >> pointers to stainless steel fasteners. They probably look smashing, but [quoted text clipped - 12 lines] > least afford it, causing worse stress concentraters at the base of the > threads. This is true, but more people have seen rust under paintwork. If anyone insist on using stainless bolts, they should at the very least cover the upper part of the threads and the underside of the bolt head with grease to prevent water from penetrating. I prefer to use propeller axle grease, as it is very resistant to water. Normal grease may be washed away over time. >> Galvanic corrosion occurs where you have two different metals in contact >> with each other in the presence of an electrolyte. Yes, water will do [quoted text clipped - 5 lines] > The chromiumand nickel in stainless steels generally reduce but do not > eliminate the tendency to galvanic corrosion. Not quite, Graham. It does indeed reduce corrosion on the bolt itself, but it will actually worsen the corrosion in the surroundings of the bolt. Now, if you flip out your average garage electron microscope and take a really close look on a stainless bolt that has been strained, you will find that the grains can actually work against the bolt itself. Stress corrosion. >> B: Finally, we get to the brittleness: > [quoted text clipped - 22 lines] > anywhere which is subject to cyclic loading, such as powertrain or > suspension components. I am really out of my depth here, but I always thought you had two variables: Hardness and elasticity. The steel in your coiled springs having high marks in elasticity, whereas the tip of the tools in your lathe would excel in brute hardness. And, of course, any combination of the two. It sounds as if the manufacturer you mention upped the hardness and lowered elasticity. Hmm. I must find out more about steel grading! >> Stainless bolts have >> different properties, which may or may not be the right ones for the [quoted text clipped - 10 lines] > It's a well worn soapbox. Thats my muddy footprints on it from last time > we discussed this here. You think it can handle a few more goes? One thing is why do the construction industry and marine industries use stainless fastenings and fixings into steel bodies and have been doing for a long time. My employer just had fitted a new all singing all dancing good lift fitted right inside a roller shutter door which is open during the day. The frame is box section steel but all the fastenings are A2 graded stainless steel. We have a lot of machinery with steel and alloy components which are held together with Stainless A2 fixings and are subjected to warm air, saline solutions, and liquid polymeric materials which has got to be just as bad as the outside world for a breading ground for tin worm and we have very few problems. Stainless steel has a number of factors for and against, as long as you use graded fixings for general applications you should not have to many issues. it is when you fit bolts to areas where specific high tensile steels bolts where originally fitted internal engine components, brakes, will you get major problems. Most nuts you fit on your car are not high tensile steel and you would probably find they are a standard graded steel. > Hello, all! > [quoted text clipped - 60 lines] > > RustEater > One thing is why do the construction industry and marine industries use > stainless fastenings and fixings into steel bodies and have been doing for [quoted text clipped - 6 lines] > which has got to be just as bad as the outside world for a breading ground > for tin worm and we have very few problems. I'm not sure about the construction industry, but the marine industries most definitely does not. If you see a stainless bolt in contact with steel in a marine implement, you will find zinc or magnesium nearby. If you don't add a sacrificial anode to such a setup, you will have failure. I am not sure as to exactly what steel is in those A2 fastenings. Can you find it in this list? http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm Back in the early 1900s, when the fishermen around here started fitting engines in their boats, little was known about galvanic corrosion. But they did take a dim view of all the iron nails in their wooden boats disappearing. Iron nails and bronze propellers just didn't mix well. > Stainless steel has a number of factors for and against, as long as you > use graded fixings for general applications you should not have to many [quoted text clipped - 3 lines] > tensile steel and you would probably find they are a standard graded > steel. My point indeed. I am perfectly happy using standard steel bolts on standard steel parts. They will rust merrily away at the same speed as their surroundings. The speed can be reduced with other means of rust protection. But to slap in a stainless bolt in standard steel, you would need to be very picky about the quality of the bolt. The only alloy that would not create a corrosion problem is Stainless steel 430 (active). This is the only alloy of stainless steel (to my knowledge) that is less noble than steel. Only slightly less, so the bolt would corrode slowly. As to the tensile strength and hardness of this alloy, I just don't know. http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm "RustEater" <fossen@NONSENSEonline.no> wrote in message > news:pan.2004.05.05.11.21.08.718000@NONSENSEonline.no... >> Hello, all! [quoted text clipped - 61 lines] >> >> RustEater all major ships have cathodiic protection in built into them, this is to protect the hull from serious damage due to the effect of electrolytic reactions. It is very strange you say that as on a recent visit to my local stainless supplier, he had orders awaiting despatch to a number of boat yards, motorcycle repairers, classic car restorers. So if they are buying these items which see very extreme condiditions on items that will probably outlast Minis no end then who am I to go against them. > > One thing is why do the construction industry and marine industries use > > stainless fastenings and fixings into steel bodies and have been doing for [quoted text clipped - 106 lines] > >> > >> RustEater Returning to dry land, it is not a problem to use stainless steel in dry places, such as inside the car. My ranting is about using stainless bolts where they will be exposed to water, like in the subframe mountings. Sadly, judging from the state of my Mini, not even the inside of the car is safe... Ok guys I will declare my vested interst straight away. I supply stainless steel fastenings (mainly for minis). A properly manufactured stainless bolt ( ie from a cold headed blank NOT turned from a piece of hex bar) with a properly formed thread used correctly in the right application should have no greater a failure rate than a mild steel bolt of similar grade. Indeed as time goes on it will have less of a failure rate ( ever notice how easy it is to shear an old bolt as the dreaded time worm starts to attack it with time?) Stainless steel is harder but not more brittle ( 2 differant things altogether) Galvonic corrosion of your mini is unlikely to be a problem ( its all to do with relative size) it will rust anyway! no matter how hard we try. A2 stainless is 304, A4 is 316. I would never knowingly sell stainless bolts for the following applications as iot is not possible to achieve the disered tensile strength: Brake caliper and drive flange bolts (grade12.2). engine internals ( pointless and some critical properties do not match) seat belt bolts ( I have no idea what the rating is and restrictions on head shape from a safety point) Both mine and my business partners minis are held together with stainless fasteners and have been since 1997. No problems have been encountered ( and yes we have removed those where stress may be a problem and looked for any problems) Mr C is right, A2 bolts are used extesively in construction, water treatment and food industries in hostile environments and in contact with steel and alloy ( I worked at a Stainless fabricators serving these industries for 6 years). There is no such thing as a perfect bolt just suitable ones for the application. I will not give my business details in this newsgroup at this time as I dont want to be accussed of advertising but if anybody wants them please contact me (careful of the spam trap) Hope this helps Dave > all major ships have cathodiic protection in built into them, this is to > protect the hull from serious damage due to the effect of electrolytic [quoted text clipped - 124 lines] > > >> > > >> RustEater > Ok guys > I will declare my vested interst straight away. I supply stainless steel [quoted text clipped - 30 lines] > Hope this helps > Dave Thank you, Dave! This actually solves everything. Stainless 304 is close enough to mild steel to replace all mild steel bolts. The effect of galvanic corrosion would be so small that it can safely be ignored. Unless you make a habit of parking your car under the high tide line, that is. As for the A4 made from 316, it would be more noble than brass and thus more of a problem. The reason I am so hung up on this is that our road authorities salt the roads during the winter, and our winter is normally 8 months long. Anything that can accelerate corrosion is to be avoided. Thanks again for the info! RustEater To clarify the size point : it is ok to hold 2 large pieces of steel together with a stainless bolt - it is NOT ok to hold two pieces of stainless together with a mild steel bolt!! It is also not a good idea to use aluminium rivets for the same reason. er... arent pop rivits made from ally?? Dave > > Ok guys > > I will declare my vested interst straight away. I supply stainless steel [quoted text clipped - 48 lines] > > RustEater > To clarify the size point : it is ok to hold 2 large pieces of steel > together with a stainless bolt - it is NOT ok to hold two pieces of > stainless together with a mild steel bolt!! > It is also not a good idea to use aluminium rivets for the same reason. > er... arent pop rivits made from ally?? You can get pop rivets in various different materials including aluminium or monel. The packaging usually tells you what they're suitable for. > A properly manufactured stainless bolt ( ie from a cold headed blank NOT > turned from a piece of hex bar) with a properly formed thread used correctly > in the right application should have no greater a failure rate than a mild > steel bolt of similar grade. That is the crux of the matter. "similar grade" Don't go replacing high tensile bolts in high load, cyclic load or safety situations with stainless steel bolts which are not of the same grade. It is fair to say that many of the high tensile bolts in a car are high tensile not because they need to be, but to reduce the number of different fasteners in the vehicle. If every 5/16 UNF x 1" bolt in the car is the same, (and there are plenty of them in a Mini!) you can't put the wrong type back in a critical application. My point exactly Graham, it is important to take advice and use some common sense. Many of the fastenings used on the mini have over the years been of unkown grade ( if graded at all) and only replaced with "better" bolts as a variety reduction exercise. Personally I will not supply anything i am not happy about using myself. Dave > > A properly manufactured stainless bolt ( ie from a cold headed blank NOT > > turned from a piece of hex bar) with a properly formed thread used correctly [quoted text clipped - 12 lines] > car is the same, (and there are plenty of them in a Mini!) you can't put > the wrong type back in a critical application. > Hello, all! > [quoted text clipped - 60 lines] > > RustEater nobody likes a smart arse so bend over, i just seen a place to stick that soap box. >> Hello, all! >> [quoted text clipped - 63 lines] > nobody likes a smart arse so bend over, i just seen a place to stick > that soap box. Hello; You are perfectly right, its better to use metals that have the same tension difference than a irob bold with a gold nut, the iron will rust away even quicker and the gold stays.... The best thing to do is attach some neversees (aluminium paste) to the both the nut and teh bold. This way you are pretty sure it's possible to get it lose again.  SignatureGroeten Robert Oor > nobody likes a smart arse so bend over, i just seen a place to stick > that soap box. Never been seen in the group before? Replies to a post which is a month old in a thread which died off weeks ago? Abusive post? Don't even waste your time replying to this sad little troll. >> nobody likes a smart arse so bend over, i just seen a place to stick >> that soap box. [quoted text clipped - 7 lines] > > Don't even waste your time replying to this sad little troll. Actually, I'm impressed the guy read the post all the way through! It would of course be more informative if he expressed his misgivings about the post in a more verbal fashion, but I take it he disagrees with me... As to the point of the discussion, see the brilliant post from nite fire. Most informative and interesting. Cheers, RustEater |
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