§1. Soil corrosion and underground storage tanks [00:04]
Now in soils — you don't have a lot of soils in the Navy, but nonetheless soil is important. The Army has 15,000 underground storage tanks, at least when they did the study in 1991, for fuel and all kinds of other things. The Navy has them on their bases too, but the Army owns more than the Navy. So they did a big study at the Construction Engineering Research Labs out in Urbana-Champaign, Illinois.
Here's a plot of the soil aggressiveness value — I'll explain what that means in a little bit — the corrosion potential of the soil versus the age of the leaking tank. This is 108 tanks. The quickest leaks were in six years. Some of these tanks have about an eighth-inch-thick wall. Some might be a quarter inch if it's a great big tank, like you see at an aviation depot. But a lot of their tanks are little 500- or thousand-gallon tanks, and they might be an eighth of an inch thick. If we say, gee, it started to leak in six years, an eighth-inch wall — that's 20 thousandths of an inch per year. And it was an aggressive soil. But some of them last 30 years, and they've had some tanks last 40 years.
Last winter — anybody from West Virginia? Anybody remember what happened in West Virginia? They shut down all the water, because this company had some chemicals that they stored for the mine, and it turns out the tank started leaking, and it got over a protective barrier into the City of Charleston water supply. Well, those old tanks were riveted tanks from the 1940s. Someone might have thought that maybe they should have been inspected, okay. Some of them are just pure rust on the bottom. That company is now basically bankrupt — the company that owns the tank — but the Water Authority is being sued because they're not bankrupt.
What is the soil aggressiveness index? Here are the basic characteristics. We've got the soil resistivity in ohms, and the higher the resistivity the less aggressive. This is sort of like the megohms of water. If you can't transfer the electrical charge to have the chemical reaction — to have a chemical reaction you're transferring electrons from one atom to another, you've got to have an electrical circuit. So if the soil resistivity is high, you don't get corrosion. The soil pH: if you're very caustic, the Pourbaix diagram tells you that the steel becomes sort of immune at high pH; in a very acidic environment, the opposite. The soil moisture is just part of the whole resistivity loop. Dry, it's great. Saturated with water, it's not as aggressive as high resistivity.
They had a regression formula that took some of these things into account, so you get the cross effect. And then the sulfide content. If you had sulfide, this tends to be sulfide-reducing bacteria. There's a certain type of corrosion we now call MIC — microbiologically induced corrosion — which we really didn't recognize. The first I ever heard about MIC was about 1979. They had some MIC corrosion in a nuclear reactor, and these bugs were surviving forty thousand rad. A human would last for about three minutes. They were replicating their DNA so fast, repairing their DNA — it's just incredible. These bugs were right there in one of the hottest parts of the reactor, and they had this little colony.
They have to have something to eat. In this case some bugs will reduce sulfur compounds and that's what they eat. Don't ask me, I'm not a biologist, but they call them SRBs — sulfur-reducing bacteria. It wasn't something we thought about in the corrosion literature until about 40, 45 years ago, when we saw the stuff in nuclear reactors. Now you read a report on corrosion in a tank, and half the metallurgists in the world say, oh it must be MIC. So now everything is MIC. In fact I had a case once that someone said was MIC on copper. Well wait a second — copper actually kills bugs. If you had a copper-hull ship — in 1836 Humphrey Davy made a copper-hull ship for the British Navy to get rid of all the barnacles that would grow on there. Copper kills organic things at very low concentration. So copper is toxic — you shouldn't be eating lots of copper, but there's not enough copper in copper water pipes; it doesn't corrode fast enough. They worry about the lead in the pipes from the solder. They took lead out of solder in Massachusetts in 1978. But copper is not a problem.
If you could afford to, you'd have copper-lined boats. They've had some boats down in the tropics where the barnacles and other things grow very rapidly, and you can almost justify it, because within one year you can basically be dead in the water from the weight of the barnacles and the drag. Now, none of you are old enough to know what the Navy used to use. Anybody ever heard of tributyl tin? As recently as the early '90s — David Taylor had in the '70s or '80s come up with tributyl tin added to the paint, and this would kill any mollusk in the entire harbor. It was parts per billion or parts per trillion, and it would just wipe out all the mollusks.
Some of the fishermen and some of the harbors where they had the Navy ships were complaining to Congress, and finally Congress outlawed tributyl tin. The Navy was defending it — they'd say this is a military necessity. But the oyster men or the clam diggers — if the Navy ship came in that harbor, gone. That was back when I was working with David Taylor on a regular basis each summer. Most of the civilians working at David Taylor thought we shouldn't be using it, but it was such a cost saver. One person told me once, if you just take a submarine up to the Arctic you can freeze them off. But I've never been able to confirm that — I don't know if he's pulling my leg or what. Anyway, barnacles can be a problem.
§2. Forms of corrosion: pitting and the Florida condo case [08:58]
So what else about soils and wet-dry. You have to worry about moisture, but you've got plenty of moisture in most cases. We've been following the forms of corrosion. We talked about general attack earlier today — two thousandths to ten thousandths of an inch for carbon steels. General attack is just a general wasting, rusting everywhere. We talked about localized attack. We talked a little bit about pitting — a wearing away of the surface locally, and you get corrosion at a pit. One of the things I handed out on marine corrosion has a nice little picture of how you get acidic regions and basic regions right around the pit, and it's sometimes called autocatalytic. That drives the pit, just boring a hole.
I've seen pits — I talked about the pits and my mother-in-law and the dinnerware. My thesis advisor had a situation over 40 years ago. When copper prices went up in the early 1970s, the stainless steel industry thought they had a great solution: use stainless steel for piping in a home. The problem is you can't easily solder to stainless steel unless you use a very aggressive flux. So they decided to plate the outside of the stainless steel with copper, and that way they could solder to the copper. That sounded great.
So in order to plate stainless steel — you've got this stainless steel tube, this is iron-chrome alloy, and you want to plate on a very thin layer of copper. Copper is noble to stainless steel. But whenever you plate something, you have what we call holidays — little microscopic pinholes. What happens there is now you get the galvanic reaction: this is your cathode, your anode becomes your stainless steel right here, and all the area driving the electrons is focused right on that pinhole.
They put this in a 40-story condo down in Florida, right on the ocean. Turns out they have salt in the air, they have hurricanes come by. Within about a year and a half, they had a sprinkler system in their building. But it wasn't intentionally a sprinkler system — it was the water piping system. My thesis advisor was involved in that. For me as an assistant professor, trying to feed my family on the assistant professor salary, he gave me some work at $15 an hour, which was typical technician pay back then. I did some tests. I could take 100 ppm chloride water and just stick this stuff with the copper on the outside in, and at the splash line where I had extra oxygen, I could perforate — that was about half-millimeter-thick stainless steel, about 20 thousandths — I could pit right through it in 24 hours in warm water. You could look up and see the stars if you put a flashlight in there.
§3. The hydrocephalic shunt — Bob Rose's saline jar [12:55]
I had another story on that. My thesis advisor used to do a lot of biomedical work. Anybody know what hydrocephalus is? It's water on the brain. Certain people generate lots of fluid in the brain, it generates pressure, and it can damage the brain, sort of like a concussion. They actually will put a valve up here and run it down to your stomach, and it'll drain that excess fluid from the brain down into the stomach. I worked on a thing a few years ago with a design group here at MIT — students looking at a valve so they could implant this valve on top of the brain and you could push a button if you felt the pressure. You could just push at one particular point, open up the valve, and drain it.
They were having a corrosion problem. This was in the early 1970s. Some MD knew just as much about corrosion — now this is a good story, because none of you know enough about corrosion to go out there and become corrosion engineers after taking a few hours here. But this guy had read some textbook on corrosion and he knew gold was really good. I mean, I told you that the first day, right? Gold is very corrosion resistant. But if you put gold instead of copper, gold is even more noble and could attack the stainless steel even quicker. He convinced one of the valve manufacturers for hydrocephalus to make a gold-plated valve. Of course they couldn't put it in somebody until they got approval from the FDA.
My thesis advisor — Bob Rose — was consulting for this company. You have to understand why medical devices and instruments are designed. Usually some MD says, oh, this would be a great idea. The MD might know a lot about medicine, but they don't often know a lot about metallurgy or mechanics. But because they're the consultants being paid fifteen hundred dollars an hour, and they hire some metallurgist at one-third or one-quarter of that rate, they don't treat the engineer with the same respect as they do the medical doctor, because this person is a medical doctor — he knows everything. So they called Bob up and said, this famous doctor has this idea and he wants to gold-coat the hydrocephalic shunts — they're called shunts, not valves, because they shunt the fluid to the stomach. Bob says, not a good idea. They said, why not? He says, well, you put a noble metal on top of a non-noble metal and you concentrate all the corrosion current right there.
They said, we have to meet with this doctor — we're going to have a meeting in two weeks in New York, can you come? Bob says, yeah, but get me one of the valves ahead of time. He doesn't get it until the Friday before. What does he do? He takes the valve and puts it in some saline solution, just regular old stuff they'd use in a hospital. Sticks it in the saline solution, puts it in his briefcase. On Monday morning he goes to this conference room, and this doctor gets up and gives a half-hour presentation on galvanic corrosion and electrochemistry, and Bob's sitting there listening. And this is why they should gold-coat all these things. At the end he said, well Professor Rose, what do you think about that? And Bob just reaches over to his briefcase, pulls out this jar of saline solution which is all black and murky because it's been corroding all weekend. He says, I put one of the shunts in saline solution on Friday. Everyone just sort of got sick and walked out of the room. That was the end of that idea.
§4. Passivation: the New England Aquarium facade [17:24]
Which is not all that different than copper plating stainless steel. Now, the protective layers on things like stainless steel — stainless steel has to have a passive layer. The passive layer is just the oxide layer. People will often say Cr2O3, chromium oxide on the top surface. It's not really Cr2O3 — it's actually something much more complex, it's Cr2(OH)3. But if you actually analyze the surface of a steel that has more than 10 or 12 percent chrome, that top surface will be almost 100 percent chromium. And chromium oxides, hydroxides, or whatever — it's not a nice simple crystal like Cr2O3, it's maybe an amorphous layer, because it may only be 50 nanometers thick. But it imparts the corrosion resistance.
The problem is, if you just get stainless steel off the steel mill, it hasn't had time to oxidize any iron that might still be on the surface. It's what we call an active surface. You have to put that stainless steel in an oxidizing solution like nitric acid. Nitric acid is an oxidizing acid. It'll eat things up pretty well because it oxidizes things. You can put stainless steel in nitric acid — you can make stainless steel containers for nitric acid. Nitric acid will eat away all the free iron on the surface. Any iron on the surface will dissolve away as iron nitrate, and you'll end up with pure chromium. You go from an active surface to a passive surface.
Passivity is an important thing in not just stainless steels but lots of alloys. Some of your nickel alloys which have chromium, sometimes people talk about passivity in terms of some of the brasses. The Navy uses aluminum manganese bronze for propellers, and the aluminum forms a very protective aluminum oxide skin, makes a passive surface. As long as you don't break through that, don't get pitting, you can have a very good surface in terms of resisting corrosion. They had to plate the stainless steel — in order to put the copper on, you can't plate to a passive surface, because you've basically got a very thin layer of ceramic on the surface. Yes, you can get electric current through there and plate on it, but you won't get a metallurgical bond. You can take your fingernail and it will just flake off. So you have to activate the surface.
How do you activate the surface? You put it in HCl. That's what they do at the steel mill when they roll it. They have some oxide on there from high temperatures when they're hot-forming the stainless steel. They pickle the surface — it's called pickling — in hydrochloric acid. The hydrochloric acid eats away the black oxide that you don't really want. You get a nice shiny stainless, but now it's got some iron on the surface, it's not pure chrome. So you take it and put it in nitric acid at the steel mill, and you sell it as passivated stainless.
But in order for the stainless steel company to make this copper-plated tubing, they had to activate it to get the plating to adhere. Which meant that when you now have the little holiday, you didn't have a passive surface. Activated stainless steel will rust just like anything else. How many times have I had someone come to me, "this is supposed to be stainless, but it can't be, it's rusty." Oh, it can be. I can take stainless steel, put it in hydrochloric acid, then put it in a saline solution, and it will rust.
If you want to see this, go down to the New England Aquarium. The outside of the New England Aquarium has these little plates that are supposed to look like great big fish scales — part of the design. The specification was that they were supposed to use passivated stainless steel, so it would have marine corrosion protection, right there 20 yards from Boston Harbor. They purchased passivated stainless steel sheet. They formed it, stamped it, and cut it into these big things, and then to give it a little texture they took a grinder and ground away little grinding marks on the surface. When you grind away the surface, you leave active stainless steel underneath the grinding marks. After about a year, you go over there and see right there in the grinding marks a little rust, just following the pits.
The aquarium brought me in and said, what do we do? I said, you were supposed to use passivated stainless steel. "Well, the manufacturer did purchase passivated — it was in the specification." I said, yeah, and then they ground it. You could go over to where the food trucks deliver food for the cafeteria and see where the bumpers had run into some of these things. Now you had a whole band this wide of rust. Some stainless steel, if you activate it — if you're not right there in Boston Harbor with all the chlorides around, it might self-passivate over the next couple of weeks or months, just in the humidity of the air. You'll oxidize away the iron and end up with a passive surface. But if you're there with chlorides right there, it won't always self-passivate.
You need to do something. Were they going to have to take off all the facade of the New England Aquarium? It's going to cost a fortune. Take it in, put it in something to clean the rust off — there are less aggressive things than HCl — and then re-passivate it, or could we do it in place? If you do it in place, all the environmentalists are going to be worried if you start using nitric acid right next to Boston Harbor. All those little fish are used to eating, drinking nitric acid.
Milder solutions than nitric acid that can passivate are citric acid and phosphoric acid. So we had a little test program. We had them rub on citric acid, naval jelly — I can't remember what naval jelly's made out of, but I think naval jelly actually has some nitric acid in it. Naval jelly was something you used to clean metal. We tried naval jelly, phosphoric acid, citric acid, Coca-Cola, Diet Coke. Why did you try Diet Coke? Coca-Cola is phosphoric acid, folks. And what would be better than telling the neighbors that we were cleaning it with Coca-Cola, because they spill Coke into the harbor all the time, right? And citric acid is just lemon juice, sort of.
I think they ended up using the citric acid, and they did do it in place. But it's not as strong and it didn't work quite as well. But that's the story of the Boston Harbor and passivation of the stainless.
§5. Rinse-water pH: pacemaker cases and brass heating pipes [25:50]
Passivation of the stainless is something that comes up all the time. Most recently I was looking at, last night, one of my co-workers gave me this — a scanning electron microscope photograph of a pit. [Tom passes around a sample.] This is a titanium pacemaker case. This one's almost 35, 40 years old. They still make them sometimes out of titanium, but the battery cases are actually made out of stainless.
The company was making these battery cases for three of the largest pacemaker companies, and they were having corrosion problems. They were having little pits, and you can see here — I copied this one — the intergranular attack. This is the pit, you can see the oxides in the scanning electron microscope; they charge up and turn white. These are the grains of the stainless steel around. They probably had some chlorides. In fact that's what everyone's pointing to — where do the chlorides come from in the cleaning solution. But in fact, there's some data that says their deionized water, which was supposed to be like 10 megohm — their deionized water had a pH of three.
You have to actually change your deionized water sometimes. You're in the Coast Guard, right? You have to qualify ships. One of my first consulting jobs, when Quincy Shipyard was still in operation — I got a call because they were building some barges to transport a very heavy crude oil. They had to put some heating pipes in there so they could heat it up to pump it back out of the barge. They can pump it into the barge when it was warm — maybe it's number six fuel oil. Number six fuel oil, if you just let it come to room temperature, doesn't flow too well and doesn't pump very well. So they made these brass pipes like three-inch diameter and ran them through the inside of the barge, and you could run Dowtherm, which is a mineral oil type of heat transfer fluid.
They were finding stress corrosion cracks in the brass. They brought me in: we raised everything properly, why do we have these stress corrosion cracks? The pH of their rinse water was 2.3. It turns out — this stuff that I just put up there is a similar problem. You don't change your rinse water. So if nothing else today, you learn that if you don't do maintenance on your fire protection systems, you get hardening of the arteries because you're introducing oxygen. If you don't change your rinse water, you're carrying over all that other stuff with the rinse water. They decided afterwards that one way to solve the problem was to go from changing the rinse water once every two weeks to changing it every week. The best thing would actually be to monitor it every day. It's not too hard to measure the pH. They actually knew how to measure the pH, but they didn't bother to do it. It's probably going to put them out of business, but anyway.
§6. Under-insulation attack: the Manwich tank [29:17]
So we have localized corrosion — crevice, pitting, intergranular, local electrical differences caused by breaks in the coating or dissimilar metals. One of the dissimilar metals we already talked about — they call it galvanic attack on this little thing. This is the noble metal next to the base metal. This is just the copper on the stainless steel or the gold on the stainless steel for the hydrocephalic shunt. We're walking through these things. We talked about the pitting, crevice corrosion — I mentioned yesterday when I talked about the silt that got in the titanium heat exchanger.
If you put under-insulation corrosion — if you've got some piping and you have a flood and the insulation gets wet, the wet insulation creates this nice wet-dry type of environment, just like my roof out there in Arizona. Under-insulation attack is a common problem. They were making Manwich down in Knoxville, Tennessee — sloppy joes, right? When you're making the stuff continuously, everything's fine. But when you stop for some reason, you actually have to keep that product above 190 degrees Fahrenheit by the FDA standard, so you don't grow bacteria. They had this hot water tank that was supposed to be operating at 210 degrees. The set point was 210 degrees. Water boils at 212. They wanted to get as much out of this tank as they could.
There's a nice little story in this. The boiler and pressure vessel code requires that any pressure vessel more than 100 gallons has to be built to the ASME code, which has all kinds of requirements for quality and wall thickness. But water heaters are exempted, because people use water heaters for lots of things — or any vessel less than 100 gallons. So this was a 99-gallon vessel. People built a lot of 99-gallon vessels. If you looked at the size of hot water tanks in the world, you'd see a big peak right here in the number of vessels that are 99 gallons. That's because of the boiler pressure vessel code, whether you have to come under the code or not.
This tank was right there with all these others. It had been designed by a guy who I think had a year of trade school. Nothing wrong with that, but he's designing something that really should have been a boiler pressure vessel. He puts insulation around it because it's a hot water tank. They have to come in and disinfect. What do they disinfect with whenever they're cleaning this food processing plant? A nice chloride solution, right? They come in and they're spraying disinfectant every night to clean off the walkways. Some of it gets underneath the insulation. 304 stainless steel stress corrosion cracking, same thing as I showed you yesterday.
It's not quite as bad as this stuff. [Tom passes a cracked sample around.] Try to be gentle. Well, this one you don't have to be quite as gentle. The other one will actually fall apart if we're not careful. There's another one that really is in tough shape, but you can see all the little cracks. That's what basically happened to this vessel. The cracks didn't get all the way through — unfortunately, it blew up one day, and someone standing next to it got scalded with 200-degree steam. Under-insulation attack. Same thing as crevice corrosion — you actually get an acidic condition underneath the crevice, and get preferential corrosion underneath something else on top of it.
It can be dirt. I had a heat exchanger at a utility, and they'd made it out of admiralty brass. We don't use admiralty brass much anymore — we mostly use thin titanium tubes. But admiralty brass, if you didn't have filters to keep the solids out of your heat exchanger tubes and you get a little film of that stuff, you just pit right through that admiralty brass in about a year. So it's important to have filters. It's important to clean things. It's important to do maintenance to prevent the corrosion problems.
§7. Velocity effects: copper alloys and LaQue's data [34:24]
Now there are velocity effects on corrosion. One of the velocity effects is just erosion. If I look at copper alloys in particular — they're very susceptible to velocity effects. Here we've got copper, and this plot comes out of the book called Marine Corrosion which I mentioned is out of print, by Francis LaQue. Francis LaQue was the corrosion engineer at International Nickel Company. He later became senior lecturer at Scripps Institute of Oceanography. The International Nickel Research Center is named after Francis LaQue now.
If you've ever seen corrosion data, it comes from Kure Beach, North Carolina — there are two places where seawater corrosion data come from. Kure Beach, North Carolina, which is the International Nickel site — they own a piece of the beach in North Carolina. The other is good old David Taylor Annapolis, it used to be. They talked about corrosion in Severn River water. For those of you that went to Naval Academy, you look across the Severn and you see this nice white old antebellum house — that's the David Taylor Research Center. One of your classmates, Kirk Graham, once became head of that. The commanding officer of David Taylor used to be able to live in that great big old antebellum house. Severn River water was the Navy's facility. They shut down the Annapolis facility in the BRAC, and it all got moved to Carderock, the one outside the Beltway in Washington.
The probability of attack as a function of velocity in feet per second on copper — copper's got a fairly soft oxide. It's a protective oxide, just like the protective films on other things. But in all water we have some total dissolved solids — microscopic solids. At certain velocities, those solids in the water going by will just eat away that oxide skin, just abrade it away. If you use admiralty brass, you can get considerably higher velocities. Aluminum brass — you get a very tenacious aluminum oxide skin. If you want something even better, you go to cupronickel alloy.