cyccommute 

Perhaps you should review your own assumptions before you go saying that my assumptions are false. Chains can crack but they don’t crack all that often. Even highly rusted chains are not necessarily going to crack or be cracked. I did the experiment on salt cracking a chain and it took weeks of soaking in salt water to do so. I provided the link to my experiment above.

I know that plates can crack. I even know what initiates the cracking…it’s the stamping of logos or numbers that causes stress risers. It’s not something that happens all that often, however. I’m not “heading down false paths” here because I also know that other chemical reactions can cause the cracking of the chain plates by exacerbating the stress risers in the plate. Simple rust really isn’t the issue since rust tends to passivate the surface of steel. Because the rust is insoluble in water, it tends to provide some protections.

Salt, on the other hand, can catalyze the oxidation of the iron and lead to much more iron removal than water exposure would due to the hygroscopic nature of chloride salts and the ability of iron chlorides to release the chloride ions in the presence of water…even a very small amount of water…so that the chloride can go back and oxidize more iron. It’s a catalytic process with little to no passivation occurring on the iron surface.

Now take a rusty chain and drop it into a solution that is designed to remove the rust through chemical reactions but is also capable of reacting with the iron and there is a much higher possibility of the chain cracking that from simple oxidation. Add to that that the observer heard audible sounds when the chain was added to the solutions and I’m on very stable ground in my explanation. My hypothesis is on much more stable ground than blaming this on “hydrogen embrittlement”.

Let me see if I get this straight? You are allowed to disagree with me but I’m not allowed to disagree with you?

Sauce for the goose. Sauce for the gander. What mechanism are you proposing for this to be a case of hydrogen embrittlement? This is clearly not hydrogen embrittlement, so why bring it up? The cracking of the chain can be explained using elfmachine’s observations and some knowledge of chemistry. Further chloride cracking is also a known mechanism of iron cracking.

cyccommute 

I circled the obvious lip on the top and bottom of the pin. The pin stands proud of the outer plate on all chains. You can see a small lip just below where the outer plate has worn the pin slightly. The pin is worn more severely from the inner plate but the pin is also worn from the outer plate rotation. The reason the pin doesn’t fall out is because the lip traps the pin to keep it from falling out. Additionally, the rate of wear on the outer pin is slower than the inner pin and few chains really get to this kind of wear. Further, modern chains from at least 9 speed on are peened to keep the chain from pushing the plate off the pin. That’s what pins should not be reinstalled on almost all modern chains. Plates falling off the pin was an issue in the era of transition from 8 to 9 speed (or perhaps 7 to 8) two to three decades ago. Chain breakage (from pin failure not cracking) was far more common than it is today.

smd4

Your reliance on alternative facts--and failure to rely on your own experience--means I cannot continue this discussion in good faith.

grumpus

I wouldn't be surprised if there were some slight fretting between the pin and outer plate - there's obviously enough movement that it's necessary to peen the pins, and peening may not be enough to eliminate all movement.

smd4

He's talking about the pin actually rotating in the outer side plate.

cyccommute 

The outer plates on a discarded chain can be moved relative to each other but I will admit that it took more force than I expected. This chain was a worn out chain >0.75% elongation but not a highly worn chain. I have handled highly worn chains where the outer plates are easier to move.



The pin shows little noticeable wear.



I will admit that I was mostly incorrect about the fit of the outer plates. However, this whole “outer plate force fit” argument is a red herring. The fact that the plates fit tightly on the pin does not mean that that is the cause nor even a contributing factor to the plate fracturing. A chain plate fracture is something of a rare event. I’ll remind you of what was said

If the force fit put that much stress on the plate at every pin, fracturing of pin plates would be a much more common experience. It happens, yes, but it doesn’t happen all that often nor do people put chains in highly acidic cleaners that have an affinity for iron and then notice that the chain makes a popping noise when they do so.

I have said over and over and over in this post not to use naval jelly on chains and that I also wouldn’t suggest any kind of cleaner for a very rusty chain. Chains aren’t worth that level of effort.

grumpus

Ah, so I see; that seems a strange claim to make.

cyccommute 

Grumpus’s point is closer to what I had in mind. There is obvious movement and wear between the outer plate and the pin. It’s not as pronounced as the inner plate wear which have freer movement but there is some wear. But, again, this whole argument has nothing to do with the cracking of the plate.

smd4

Thank you. Of course, I never made any claims about the force of the pins causing cracking. I will leave that argument to you and FBinNY. And I don't have to worry about rust on my chain, because I maintain it, so I definitely won't be using any naval jelly.

phughes

So, to recap. OP your lack of maintenance is to blame. Buy a new chain, install it correctly, then keep it lubed. Clean it when it's dirty, then lube it. Repeat as necessary. If the chain is clean, you will be able to notice bad spots in the chain easier.

Glad I have one particular person here on ignore, but I made the mistake of clicking to see one of his posts. Wow.

FBinNY 

This thread has reached new levels of rediculousness to the point that I don't remember what we're arguing about. Since Cycocommute and I seem to be the main protagonists, I offer a suggestion. We each post a short summary of our theory relating to the cause of the OP's then simply leave it there for others to consider on their own. Keep in mind thatthe goal is to stop arguing and post positive assertions for folks to consider, rather than attack each other.

I'll start.

---------------------

The proximate cause is hydrogen embrittlement resulting from the OP soaking the chain in an acid bath.

The specific mode of failure is stress cracking of the outer plates at the pin holes. Outer plates are stressed by virtue of the force fit over the pins, which press outward creating a tension stress akin to hoop stress. Normally this is OK and the loads factored into the design. However the embrittlement weakened the plates causing cracks to form at the hole (the point highest localized stress) which then propagated outward to the edge. It's a simple two step process, weaken the plate then let it's own internal stresses take their toll.

In support, crack formation due to hydrogen embrittlement of steel is a well documented phenomenon, with plenty of scholarly articles available on the net. The type of failure at the pins that I describe is also well documented, and a quick search for bicycle chain plate cracks will bring up countless images showing radial cracks running outward from the pin at all angles. The holes are the most common location for plate cracks, and you won't find similar cracks on inner plates which are not stressed the same way. Morevover, the all angle aspect is important because it implies a cause other than the normal tension load imposed by the rider. Note also that you'll see the same radial cracks or relatively new chains showing minimal wear, and no markings near the cracks.

----------------

Now it's Cycocommute's turn to post his theory,

Duragrouch

Exactly. +1. Both inner and outer links cannot both be press-fit or the chain would not swivel around the chainrings, cogs, and derailleur pulleys. If only the inner was press-fit, the outer would fall off. Now, some may say, not if the outside of the pin were peened to a cap. Actually, the peening seen, either a square-peen on the outside of the pin, or a divot on the inside, is to increase the press-fit with the outer links. Also, if both inner and outer links were slip fit, the chain would have too much lateral flex, with worse gear changes on a derailleur system (which is why, after cleaning, periodically, on "bushingless" (modern) chains, I pull out the chain tool and at each pin, tighten up the outer links together, not to a tight fit, but taking out any gap between the outer and inner links, as this a) reduces the total chain "stretch", and b) provides more positive gear changes.

Having said the above, it is possible for the outer links to wear open to a slip fit on the pin, from stress, or more likely, the link fracturing, removing the press fit. And then you will get "fretting wear" like seen in one of the pin pics above. And even before then, any looseness between pin and outer link, and the chain is not long for this world.

cyccommute 

Although I have gone on above ad infinitum, I’ll have a go.

First, let’s review what elfmachine said in the original post:

The chain was ridden while rusted which freed it up a little. elfmachine then put it in an acid bath during which elfmachine heard popping noises. The chain was not cleaned and then ridden but popped in the acid bath. elfmachine doesn’t tell us if the chain was inspected for cracks prior to the acid bath but audible noises are not generally associated with the use of naval jelly treatments.

The chain may have been compromised before the acid treatment but observations provided point to the acid treatment causing the cracking. Not through hydrogen embrittlement but through acid dissolution of the metal at the stress risers of the stamped logo. If the chain had been treated with a nonacidic or even less acidic rust remover, the chain likely would not have cracked.

To be clear, I am not saying that chains can’t crack. Nor am I saying that inner plates can crack. I am saying that cracking of the outer plates is a rare occurrence. And contrary to what you have stated earlier in the thread, I am also saying that the cracking of the outer plates in this case was caused by placement of the chain in the acid bath and by the acid in that bath.

Finally, I have never attacked you. I have never questioned your expertise nor your abilities nor your knowledge. You, on the other hand, have not offered me the same courtesy.

phughes

choddo

So I think you’re both saying the same thing? Cool. H ions are bad mmkay. Whether from salt solution or acid.

cyccommute 

Nope. Not at all. The anion (negatively charged particle) is the bad actor. Neutral salt solutions have no hydrogen ions to contribute and the cation (positively charged particle) stays out of the fray. The common “salt” solutions used on roadways are sodium chloride (table salt), magnesium chloride, and, perhaps, potassium chloride. The chloride ion is what has the affinity for the iron. You could use any other “salt” to take advantage of the colligative property of melting point depression such as sodium acetate or calcium phosphate or any number of water soluble salts but none of them would initiate iron oxidation like chloride can. I suspect that all halide salts…fluoride, iodide, and bromide in addition to chloride…would have a detrimental effect on iron to differing degrees. Chloride cracking is something that requires long term exposure to happen at ambient temperatures. My soaking experiment took weeks to crack a new chain. But the question raised in the original post of that thread was “why does my chain crack when soaked in (green) mineral spirits?”

In the phosphoric acid solution elfmachine used, the hydrogen ion helps get the ball rolling by providing a low pH but the real dancer in the party is the phosphate ion. It forms complexes with the iron. I suspect that the phosphate in this case worked very quickly (in the presence of the hydrogen ion) to pluck iron out of micro fractures in the chain plate. The audible cracking was likely from the phosphate unzipping the metal along crystalline boundries. The phosphate, unlike chloride, doesn’t release the iron after the work is done so there is no catalytic effect. But it is more efficient at removing metal.

If you were to use weaker acid like acetic or oxalic or other organic acids, the plucking effect would be slower. That may be due to the fact that those acids don’t dissociate completely like phosphoric acid does and the anion doesn’t form as strong a bond either. I suspect that sulfuric acid wouldn’t do the same rapid cracking as the sulfate anion has little affinity for the iron. Over time it would dissolve the iron but it is something of a slower process.

choddo

Interesting. Couldn’t it be H- being released fron the phosphoric acid once water escapes from the reaction between the acid and the rust? (I think H2O is a by-product of that)

This is probably not helping the OP any more though.

cyccommute 

In water, phosphoric acid is completely disassociated. The hydrogen ion is already in the solution. To balance the reaction, the hydrogen ions are consumed in the making of the water. This would reduce the concentration of the hydrogen ions (H+ by the way) as the reaction proceeds. In other words, the reaction becomes less acidic although there is still going to be a lot of hydrogen ions around to make the solution acidic.

The reason that I don’t think this is a case of hydrogen embrittlement is because it wouldn’t happen with most any other kind of acidic solution. Hydrogen ions are available with acetic acid, for example, but the chain wouldn’t have cracked audibly if it were placed in a vinegar solution. I doubt if it would have cracked at all. The same would be true if the chain had been treated in a chelating solution.

I also speculated that possible chloride contamination could have some effect.

Andrew R Stewart 

I'll add a few observations:

IMO pins are forced into the chain outer plate holes, "force" here to mean they don't enter the plate due to the force of gravity alone. Yes there is a range of "force fit/slip fit/interference fit" but I doubt most here have the experience, education or tooling to measure the forces along this range let alone claim that at some point the term changes from interference fit to force fit. If I'm wrong of readers having the equipment to measure this stuff I am all eyes and ears to learn more. But as we should all know modern derailleur gear systems can (and due to poor rider skills) and do get shifted under tremendous loads as seen by the teeth and links. So even a non deforming pin fit to the outer plate has been shown to not be able to retain the plate on the pin end under there loads. Shimano (Not sure if they are the original designer or they just bought into the design) came up with the idea of peening over the pin ends to create a lip to better capture those outer plates. This peening comes in varying amounts and the amount is usually indirectly refereed to as "strength of chain". This peening can and does create a larger hole in the outer plate if the pin were to be removed, or if a pin was already peened before installation. It is this last bit that drove Shimano to come up with the UG assembly pin. It has a disposable pilot shaft that also has a ramp at it's end by the portion of the pin that will remain in the chain. This assembly pin has a slightly larger diameter then the original pins have and the ramp better allows the install of this pin without further plate hole damage. I do know nothing has been said about the chain's earlier assembly onto the bike.

I have seen the results of what was explained to me as cleaning products caused cracking before too, just not common. That Super Agitene I mentioned would discolor Regina Oro chains if left to soak over night. The brassy colored outer plates would become silver colored. NOT what your customer who paid your price for that chain wants to find out when they pick the service job up...

While outer plate cracking is not a common issue there have been production errors that weren't caught till thousands of chains made their way to the market. The (IIRC) late 1980s saw Sedis (prior to their molding into SRAM) have a number of SedisSport (or the equivalent model for that year) chains suffer from cracking outer plates. I had a chain crack on a tandem we rode and I've seen a few more at work too. It was fairly well known in the LBS world back then. The story I heard was embrittlement from less than right heat treating. I have seen a few other brand and model chains crack at the pin holes over the years but as others have said it is not a common failure mode.

Much more common is a "mechanic" reassembling the chain without aligning the two outer plates so that the pin tries to enter the far hole off center. A small chain pin tool has way more then enough strength to deform that outer plate beyond safe use. This I have seem many times, less so in the last 10ish years as connecting links have become the home assembly method of choice. This thread is not about that though.

Another interesting experience I've had, unrelated to chain cracking but involve heavy rust, was back in the later 70s I had a Raleigh Twenty (not the DL-20) that I had fitted a SA FW . This was to be my ride to work in the winter bike, which I did a couple of times and really didn't like the slushy riding we have here. Away went the bike till summer and low and behold the chain was so rusty I could almost hold it out straight. I solvent cleaned it at work (Super Agitene) which did nearly nothing to the rust or to freeing up the links. Wire brushed off the outsides best possible. I worked the chain link by link till there was enough pivoting freedom to remount the chain. Oiled and tensioned the chain best possible knowing I would be removing it soon to again clean it out. Rode it to and from work for a few days, a flat 1.5 miles one way. When I was to remove the chain for the follow up cleaning I noticed it was drooping as though the wheel had slipped in the slot (those SA nuts do like to strip out their threads on the hardened and flat spotted axle)I flush out the chain and saw the rust was nearly all gone. The wear surfaces were shinny and only very light spec rust remained on the non critical surfaces. Reinstalling the chain showed the wheel was still well secured but now about 4ish mms too far forward for the right chain tension (which we all know that for a SA IGH is no tension. That was how much space the rust had taken up in each link adding up to the "longer" chain after abrading off the rust in that week of riding. Andy

cyccommute 

My objection to the “force fit” statement was the implication that it was the root cause of the chain cracking. The fit isn’t that “forced” or chains would crack all the time. Frankly, chain manufacturers could make the chains a bit stronger and even less prone to cracking by not stamping lettering into the plates at the point where the chain is under the most stress. But chain cracking isn’t enough of a problem to worry about it.

The SDS for the current “Super Agitene” solution has nothing in it that would cause any kind of damage to the chain, either physically nor cosmetically. It’s 97% “Distillates, Petroleum, Hydrotreated Light” which is related to mineral spirits and “Dipropylene Glycol Methyl Ether” which wouldn’t damage metal nor metal coatings. The formulation may have changed over time but there aren’t many organic molecules that can damage metal.

It may have been heat treating or it could have been related to the stamping of ID markings on the plates. Metallurgy is also significantly better now than it was in the 80s.

Iron oxide is harder than the steel it is formed from. It is also takes up significantly more volume as I’ve pointed out above. The reason that rust makes a chain “stiff” is because the rust is expanded into the gaps of the chain where it locks stuff up. But rust is also brittle so it will break apart under strain. The reasons that the chain was shiny is that the rust broke down into smaller particles and became a grinding compound. Eventually the rust would break down to small enough particles that it would fall out of the chain and leave the chain nice and shiny. Worn, but shiny.

This expansion of the oxide is also what is responsible for seized stems and seatposts. Steel posts can because they rust and expand. Aluminum oxide is similarly more voluminous than the metal that forms it. Both expand in an area where there is little room for expansion and, in the case of seat posts, little opportunity to move the part to break up the oxide.

Duragrouch

Cyccommute,

You mention phosphoric acid. There is a solution called Ospho, a dilute phosphoric acid solution, no issue if it splashes briefly on hands, that is a common treatment for rust, it turns the red rust to black iron phosphate, and then you paint over it (I've had issues with cosmetic white "runs" if painting over too soon, the Ospho needs to dry about a week, and even better if first covered with primer). But anyway...

I treated a shiny carbon steel knife with Ospho, to get the vintage look, like carbon steel Sabatier kitchen knives that have been used for decades, graying from many years of slicing acidic fruits, vegetables, and meats. I didn't soak the knife in Ospho, just actively brush it on for several minutes, then rinse and dry, left a nice flat gray finish. So my question is, did this risk embrittlement of the knife? Thanks in advance.

Many years ago I derusted some files with concentrated hydrochloric acid (outside with full PPE), as I recall, made green solution on surface, but then after rinsing and drying, left them on an electric radiator heater a couple hours in case they absorbed hydrogen, wasn't sure if that would cure. Comments?

CliffordK

The Wipperman Conex 8sx (8 spd), 9sx (9 spd), 10sx (10 spd), and 11sx (11 spd) chains have stainless link plates, although I believe the pins are not.

It should be more corrosion resistant. However, if you look at the price, you may determine that it is cheaper just to purchase a cheap chain, keep it oiled, and replace as needed.

cyccommute 

Probably not unless the knife has some kind of forging flaw. The issue with elfmachine’s chain and the chain I soaked in salt water has more to do with the stamping of the plate. The stamping is a stress riser and the exposure to oxidizing chemicals opens up the stress riser. Finishing on the outside of the knife probably won’t be an issue. Naval jelly is a good product that doesn’t usually cause problems but it was never meant as something to soak parts in.

Iron chloride solid is usually green but a solution can be yellow.

As for rinsing off any parts where you want to avoid rust, I would rinse with denatured alcohol or acetone rather than let it air dry. I treated a bunch of bolts from my co-op with Evapo-Rust, rinsed them, and let the air dry. I had to retreat them and then I used denatured alcohol on the second treatment and avoided the development of the rust the second time.

Chuck M 

The OP had a failure due to lack of maintenance. And among these three pages of discussing chain construction and what to use to remove rust, grumpus has the countermeasure for the root cause of the problem.

Duragrouch

Thanks for the above.

Absolutely. Some things rust amazingly fast, like a (low alloy) carbon steel skillet I was initially cleaning before seasoning, the bare metal would rust in seconds after washing. Files, due to alloying elements, while not stainless, will resist rust for the time it takes to blow water off with compressed air, then hit it with a blowdryer or place on a hot radiator.