MSE_F2017_04

Okay so we were talking about strength of materials, and I showed a ratio analysis diagram for steel. And unfortunately I forgot my pointer, okay. Well it doesn't really matter. If you look at the ratio analysis, this is just a toughness — a measure of toughness, which is dynamic tear energy versus a yield strength. And if you look at this region right in here, you'll see that here about a hundred and eighty ksi is where it starts to drop off, and your maximum up there for toughness is ten thousand foot-pounds.

If I go to the same diagram for aluminum, it turns out your drop-off is at forty ksi and your toughness is one-fifth as much, it's around two thousand foot-pounds. Your critical flaw sizes are going to be similar because that basically comes out of the geometry of the material and the yield strength. But if you drop the yield strength, then you'll get the same critical flaw sizes — that, actually, say, yield-toughness ratio, so far as that goes. In any case, that's for aluminum.

And that's why the guy, when I was a student or a young faculty member, who was director of research at U.S. Steel used to call aluminum the near-metal. It was almost ductile in his opinion, okay. It has about one-fifth the strength and one-fifth the tough— toughness.

If you go to titanium — and the reason we only have three ratio analysis diagrams is because this is what the U.S. Navy is interested in, building submarines out of, back in the 1950s and 60s when what's-his-name, probably no I wouldn't, Rickover. It was the father of fracture mechanics, George Irwin, was head of mechanical engineering at Naval Research Laboratory, and he's considered the father of fracture mechanics because he took this idea that Griffith had, that you could study the fracture of a brittle material like glass, and you come up with this — I put it up the other day — the fracture toughness is equal to this times the square root of pi c. That's the fundamental equation of fracture mechanics, came out from Griffith in 1925. Everyone thought it only applied to brittle materials. Irwin showed it also can be applied to ductile materials, so it's much more general than just brittle materials.

It was originally — no I don't have my pointer, alright, just looked in the wrong place. But anyway, so everyone was trying to study this because of the Liberty ships after World War II, trying to understand it and how to apply it. And he found he could use the fracture mechanics formula of Griffith from 1945 — this was thirty years later — he applied it to steels and titanium. If you look at titanium, you find you have about one-third the toughness of steel, and the strength is actually about two-thirds, okay. The drop-off here is about a hundred and twenty rather than 180 ksi.

So the materials have different properties. These are only ratio analysis diagrams. You could do one for copper or nickel or something. Copper would have a very high toughness, it's a very ductile malleable metal. It wouldn't have fantastic strength, but some copper alloys can actually go to about 200 ksi. I actually should have brought it. Anyone know what copper alloy has 200 ksi? Beryllium copper, okay. You put a little bit of beryllium, get a precipitation, and you can get 200 ksi. And the example I have is just a regular old 10-inch adjustable wrench made out of beryllium copper, because you can get the same hardness as steel with only a little bit of a toxic metal. It's not toxic when you use it, it's only toxic when you breathe it, so that's another problem. But you can buy a full set of tools just like you'd buy yours out of steel — you can buy a set of socket wrenches and pliers and screwdrivers for five hundred dollars, you can buy the same thing out of beryllium copper for five thousand dollars, okay. Copper's a little more pricey.

Why do you use beryllium copper tools? They use it a lot in the mining industry. Probably now, not fatigue. Student: Spark resistance? Spark resistance. Copper has better thermal conductivity. So if I took a piece of copper — and if I had two pieces of metal and I won with steel, I took two pieces of steel and I'm banging them together, I could get a spark. You take two pieces, you take copper even against a piece of steel, the high thermal conductivity won't generate the spark, it won't give the high temperatures because of the high thermal conductivity. You know what sparks in the bottom of a mine, where you could have a lot of gas, and it could go kaboom and kill a lot of people. So for ten times the price you can get different strengths and different materials. But there are technological limits, and some of these diagrams they actually call the upper curve, there on this bending-down curve, the technological limit, okay, so far as that goes.

We can also look at strength versus maximum service temperature of materials, and this is the Ashby plot. Remember Ashby plots typically go over about five orders of magnitude, maybe six, in both directions, okay, sometimes seven, but usually about five orders of magnitude. And this is maximum service temperature. So room temperature — well actually room temperature's back here — and you can see where foams and plastics and stuff are very good around room temperature. But if you want to go above 300 degrees C, which is not that high, but if you want to get up to a couple thousand degrees C, you're really limited in the types of materials you can use. In fact most metals can't go to 2,000 C, they only go up to about — actually they won't — no, they don't go to 2,000 C, they only go up to about a thousand C in operating temperature, and they tend to melt around 1200 C, most of the common ones, unless you get to refractory alloys. But the ceramics just keep on coasting, okay. Problem is they tend to be brittle, and that's a problem.

So that kind of concludes the strength part of comparing strength. And strength has to be measured by two parameters. One parameter is force and the other is energy, right? Good, okay. Nobody knew that until fifty years ago, when George Irwin came along, okay. Well actually the Liberty ships. And they still don't have energy in most of the codes. I mean civil engineers got it in the 1990s because of the Northridge earthquake, and they found that buildings built in the 60s, when we knew about the need for fracture energy but it wasn't part of the code, it wasn't required, so no one's going to pay for it back then — you have an earthquake coming along and those buildings' connections just snapped. And it cost billions of dollars, and so the civil engineers decided, hmm, maybe energy of fracture is important, okay.

But there's still plenty of other industries where people still — until they have a big failure many times they don't start requiring things. In fact there's a guy who was elected to the National Academy of Engineering same year I was, from Duke University, and he wrote a book, To Engineer Is Human, and that's what made him famous — that he didn't do anything famous in engineering, he basically wrote a book about engineering. And said that engineering progresses historically, over thousands of years, due to failures. We have a failure like the Tacoma Narrows Bridge — if you've seen Galloping Gertie and things like that — you have something like that, and people just keep on pushing the limit and pushing the limit until they push it too far, it causes a major failure, and then everyone says, well why did that occur, okay. And they start developing codes and standards to keep it from happening again.

So now I wanted to go into something that used to bug me about thirty years ago. Material substitution. And the example I gave back then thirty years ago in a paper was refrigerators, okay. When I was your age, refrigerators were all made out of steel, an— outside, and enameled steel on the inside, okay. Might have been painted on the outside, it was enameled on the inside. Because what steel lacks is its lack of corrosion resistance, but you can enamel it and you would have something that was corrosion resistant. And then people decided that plastics would be a better material for the inside. They still keep steel on the outside of refrigerators and stoves and things. Well stoves you kind of need it because it gets hot — you start making stoves out of plastic and they tend to melt on you, okay. But refrigerators, you can make the inside out of something that has a low surface energy so it's easier to clean, things don't stick to it as easily with low surface energy. And you don't need strength on the inside, because if the little kid comes up on their trike and runs into it at full speed, the steel will resist the dents but the plastic is on the inside and it won't break — it would break, you forgot that impact, because the energy of fracture of plastics is nowhere as good as steel. So nowadays we make steel outside and plastic on the inside.

But what bugged me, because I lived through this transition in the 80s, okay — I would go and buy a nice refrigerator, and within three years it was a piece of junk because they screwed the shelves into the plastic. Well that's not how you design plastic, folks, okay. Plastic can't take screw holes and sharp stress concentration, it's a somewhat brittle material. I've shown you about fracture mechanics, you put a little notch in something and it breaks easily. Plastics don't have the toughness of steel. So if you're going to design a refrigerator, it turns out by the 1990s KitchenAid and other people learned, you slide the shelves in, you don't screw them in. Plastic has this wonderful property, it's easy to mold into complex shapes, so you mold a slot in there. And now you go look at virtually any refrigerator, it's made out of plastic but there's no screws on the inside. The other problem with screws on the inside, after time they would start rusting, and you'd have the little rusty drip on the inside, your refrigerator didn't look very good. Plastic is great, it's got great room-temperature corrosion resistance, okay.

They were essentially designing things the way they used to design things, and they didn't take this new material, plastic on the inside, and think about how do I design for plastic. And now there're handbooks that will tell you, don't design plastic as if you're designing something like it's out of steel, okay. Steel has different mechanical properties than plastics. You work to the advantages of each material. So that's my little — and now I can buy refrigerators that will last for fifteen years rather than falling apart in three years. There's a certain advantage to something that falls apart in three years. What's that? You get to sell more, okay, if you're the seller, okay. But it doesn't get a very good reputation.

In fact, what car nowadays, among cars used by people in the United States, a common car that sells a couple hundred thousand copies a year, what brand has got the highest reliability? Typically Toyota is usually up there, but Honda is also up there. Do you know why Honda has such a good reputation? Because in 1973 they came out with a Honda Civic and it would rust through in one year. It had terrible — I mean Honda got terrible reviews, no one would buy a Honda after 1973 because it was junk in terms of corrosion resistance. So the people at Honda said, we've got to do something, and they did. They improved the quality much better than even Toyota in terms of corrosion resistance. And generally Toyota is known for their engines, that just will run forever, okay. But if you actually look at the body structure and everything else, Honda basically turned it around completely. They developed a terrible reputation in the 70s for the original Honda Civic, and now people don't remember how bad Hondas were. So they learned from their experience.

So if we review some things we've talked about in structural materials. There are externalities in different things. I actually have one other externality to talk to you about. The number one driver in selection of a structural material is just cost. We use structural materials in very large volumes, in some cases billions of tonnes a year, and so whatever we use had better be cheap. And the cheapest material, crushed stone, is by far the largest use because it's the cheapest. Availability — well it turns out, we also talked about that. And some things that are excellent materials, like nickel alloys, fantastic, except they're just not as available, okay. They cost a hundred times as much as steel, or fifty times as much as aluminum.

Strength and ductility, we've talked about that. Ductility is a measure of toughness in some ways, it's not exactly the same but it's somehow related. It's the ability to stretch and deform before something breaks, and brittleness is something that breaks before it stretches. So strength, ductility, and toughness. Stiffness, we talked about that. Lightweight, very important if something moves, and the faster it moves the more important it is, okay. And we can look at — why I throw this one in, I don't know if I threw this one in or one of my assistants did, but you can look at different materials, this actually shows everything else unhighlighted, but polymers have a certain advantage in specific strength and whatnot. We can also look at toughness of things, or stiffness of things can be a function of geometry as far as that goes.

Lots of different ways to look at things, and you have to look at what are the key parameters. And there's not generally one key parameter, there's probably two or three primary parameters for whatever your application is, and you pick your material based on that, okay. Any questions?

Let me give you the one other one that I guess I didn't even know about until they redid my office a couple of years ago, and I hadn't really paid attention to what was going on. Usually when you put copper pipe in a building, for a heating system or a water system or whatever, you would solder it, right. And then in 1978 you couldn't use lead-tin solder. You had to use, you had to get the lead out, and you had to start using tin-silver solders, tin-silver-antimony solders. And they're okay, but they tend to leak a little bit more. But the real problem, the thing that got expensive, is over time they had enough plumbers burn down buildings while they were soldering things, that they started saying, you have to have a fire watch.

And then in places like Massachusetts, you ever noticed we have policemen when they're doing work on the roads? That's actually a law in Massachusetts. This is something that helps keep the police from all going dishonest. They don't want to pay them enough to support a family in Massachusetts, so they allow them to do off-duty work and earn forty-five bucks an hour by being someone to stand there while other people are doing construction. It's basically a tax on the construction process, but it also allows a good honest policeman to make enough money to support a family. Otherwise they're gonna be tempted to keep some of that drug money and buy a TV for their kids or something.

Well, the firemen wanted something good like that. So in the city of Boston, you've got to have the fire watch. I mean it says — it's written into the OSHA regulations now — if someone is doing hot work, they're welding or they're soldering, anything that could start a fire, hot work, they have to have a fire watch. So in construction this is one of the reasons construction, whether it's bridges and buildings or anything, has gotten so expensive, because you generally have two or three people standing around watching one person work, okay. And one of the things is you've got to have a safety watch when someone's doing hot work, and they're supposed to be looking to see if they got to put some fire out that started, that no one knew about.

Well, it turns out in Boston that fire watch has to be a fireman. You have to be part of the Boston Fire Department, and I don't know if they're getting forty-five or sixty bucks an hour, but now one of your bigger costs is to pay some fireman to hang around for eight hours one day while you got the plumbers doing plumbing work in the building, because they're soldering things.

So some guy came up with a bright idea — and I don't have all the correct fittings here, but basically you got the regular old copper pipe, and for only thirty bucks you can get one of these fittings, kind of pricey, but it's got an o-ring in it, and you buy a special tool for $800 and it will squeeze it together, and you make a mechanical o-ring seal. No hot work. So basically this is — if you have plastic tubing that would go inside here and they squeeze it down, and they've gotten rid of a lot of the hot work. And this is an externality of regulation, and it's specifically safety regulation. Get rid of the firemen, send them home, let him find some other way to earn money beyond his salary, because you're not gonna pay him enough to support a family of four in Boston.

Okay, anybody know what it costs to support a family of four in Boston, according to the economists? $65,000 a year. Now a lot of firemen make that much, but not when you're starting out, okay. Some of the better jobs for a lot of people will not ever get you to the living wage in the Boston area or San Francisco area. If you're in the middle of South Dakota it might be a living wage. Well actually South Dakota is not a good example with all the fracking going on. Middle of Wyoming, $60,000 salary, you do quite well, okay. But not in Boston, okay. So there are other regulations that people come up with.

So material selection examples. Metals, moderate cost — they are more expensive than stone and concrete and wood. They have good strength and toughness and ductility. Ceramics, low cost — stone, concrete — they can have very high strength, but very low toughness. And these are not the same, okay. Concrete in compression has very high strength, it has lousy toughness. In tension it's brittle, okay. And glasses and other material, very important structural material. There's not very many things that have the property that you can see through them other than Harry Potter's cloak, okay.

Polymers, moderate cost, low strength, low temperature capability, and low stiffness, okay. But easily formed — I should have put down, more easily formed than the other two, as you can form at room temperature all kinds of neat ways. So there's different strengths and weaknesses of each material. And you can go back to the billion-dollar club and see which ones are the most popular.

Now let's talk about materials competition, okay. And the example I like to give is simple old food containers, or beverage containers, actually, more specifically. And I have some here, I didn't bring in something of all of them. We make some cans out of steel. We make some cans out of aluminum. This is an all-aluminum can. It actually has a different alloy at the top and on the sides, because you have to form this one by drawing and stretching. In this one you need some strength, and you've got to be able to have the pull-tab that works and stuff. There's certain advantages to that. And of course here's plastics. There's glass — and I could have brought in a, probably somewhere had a piece of glass in my office. But each one of them has its own strengths and weakness. Not mechanical strength and weakness, but advantages and disadvantages to its use, okay.

Steel has a problem of corrosion. So most of our beverage containers, ninety-eight percent of our beverage containers, are made out of aluminum. If you go to Japan, what will they make them out of? Steel. Why? Because the Steve— Japan had at one time the largest steel industry. Now it's China. The United States had the largest one after World War II, and then the Japanese took it over, and now the Chinese are the largest steel producers in the world. And Japan, because of politics, had all kinds of ways to keep aluminum cans out of the market, so they basically made beverage cans out of steel. And there's problems in joining of steel for cans and whatnot, but in fact we still make some cans out of steel.

[Tom holds up a pineapple juice can.] This is a pineapple juice can, except the top is made out of aluminum. Why? You need low toughness so you can do the pull-tab, rather the aluminum, and you can put a little seal around. Here at the bottom it's made out of steel, okay. But you also notice something else, and I compare these two metal cans, what do you see about the difference in those two? It's a more slender shape, okay. And why is that? That's because someone used calculus of variations. This was one of the problems they gave me as an undergraduate in one of my math classes — calculus of variations, to figure out what has the maximum volume to hold the beverage and the minimum surface area for the material that I'm paying for, okay. And it turns out you take a Campbell Soup can, and it's just about perfect, okay, for doing the calculus of variations, where you vary the diameter and the height, and you can, under certain constraints.

And it gets more complex when you start mixing materials. But you can still — the mathematicians just love this — you had another constraint, like I'm gonna make this part out of aluminum, this part out of steel, yeah. It turns out the steel being cheaper than aluminum, you want to use more steel for your outside area than you do aluminum. So you make a slender can, as opposed to — you know the Sprite can is sort of about the same aspect ratio of height to width as a Campbell Soup can, right.

So why did we make a composite can out of pineapple juice? Corrosion, okay. Now tomatoes are pretty corrosive, but aluminum is pretty good for the type of acidity we have with tomatoes — although there are some tomato things, that if you look on the inside the aluminum is painted for corrosion resistance. So look at the cans that have a white inside, and now you know how — if your food has aluminum. But it turns out for pineapple juice, it turns out the least cost when you consider protection against the acidity in pineapple juice and everything, is essentially make a steel can. And if it's sitting upright on the shelf, then the bottom is steel and the sides are steel, and the aluminum top has — it's adequate because it's not immersed in it all the time, you don't get the pitting corrosion, okay. Different types of corrosion. So it actually makes sense, okay.

Believe it or not, in the bigger cans of pineapple juice, what are they made out of? Steel. There's outside steel. So pineapple juice comes — see who never paid attention when you went to the grocery store, okay. There's lots of material sizes you could have — someone could have done a paper on that, right.

It turns out, when I first started making aluminum cans, they were pretty thick-walled, and they weren't controlling the shape. The better example, the reason I brought this plastic bottle, look how thin this has become, okay. You may not remember it when you were three years old, but the plastic was a lot thicker, and they've been getting it thinner and thinner. Why? Because one of the problems with plastics, one, they're permeable, and the other is cost, okay. Things will actually diffuse through the plastic.

I had a situation once where someone was interested — there was a big fire and someone had a plastic gas can that had survived the fire, and they wanted to know how much gas had been poured out of this gas can into the steel tank or aluminum tank, whatever it was, of this machine. And they went back three years later, and the plastic gas tank was empty. Why? Because all the gas had diffused through the wall of the plastic. It turns out — it had been full, and someone had actually opened it up and taken a picture right after this big fire, and there was gas in it, and they sealed it and put it in storage, and came back three years later and it was empty.

And originally General Motors and Ford used to use lead-coated steel to make the gas tanks. Not zinc-coated — it turns out zinc-coated steel will be corroded by some of the things in a gas tank, but lead has excellent corrosion resistance. And they would use what's called terne, T-E-R-N-E, terne-coated steel, which is lead-coated steel. But then when they wanted to get lead out of the environment, they said, well we just use plastic. So they started making plastic gas tanks. And the designers thought this was fantastic — the plastic could be molded, the steel had to sort of be stamped and formed, and you couldn't make it into these odd shapes that would fit into the little cubbies that you have around the axle and stuff in your car, whereas you get more volume because you could mold this plastic tank.

You might know how you would mold a plastic tank. It's like blowing up a balloon, but you blow it up into a form or a shape. And you take hot plastic and you blow air on it, and it's like blowing up a balloon into a form, and it takes on the shape of the form. Blow molding it's called, blow molding, okay. It's just blowing up a balloon into a cavity that's got a shape to it.

Well, the problem with that is the EPA came along, said, oh we're losing one percent of all the gasoline in the country as volatile organic hydrocarbons into the air by just the permeability through all these thirty million cars with the gas tanks out there. And so they said, no we're gonna stop that, we're going to put regulations on how much permeability you're gonna have. So this was twenty-five years ago, I had a student working at Ford, and he was actually working on another problem on the paint line where they made the bumpers — and they get the plastic bumpers and the gas tanks — but I went to see, and they were now using a seven-layer composite, okay. It wasn't just a simple balloon, it had seven layers of different plastics, some of which were for strength, some of which were for permeability resistance. But it was getting very complex, okay. But in fact they still use those plastic composites now for gas tanks on cars, and they have a low enough permeability so people don't usually think about it. But you do have permeability — more permeability in plastics than you do in metals.

Student: Why do they do seven layers? Well, that's why they do seven layers, okay. It's easier — when you're blow molding, you can make seven balloons inside one another, and now you've basically got a coating. Well, if you start — and I'm not an expert on the gas tanks, but I know they ended up with seven layers to meet all the requirements, they had to go with seven layers.

Student: Plastic bottles? Yes, the CO2 will diffuse out, yep. And they make them thinner and thinner too to get away from cost. You notice I didn't have cost up here. The two that don't have a cost disadvantage, okay, because these are the disadvantages, are steel and glass. One of the problems is weight.

Now people will tell you — your beer purists will tell you — that the best beer comes in, well it comes draft, but the next best is a glass bottle as opposed to a metal can. Because beer is not very acidic, it's like four point five or five pH, but it has a little bit, and it will pick up purest — just like the wine purists, the beer purists will taste the difference, and so they like glass bottles. But when they build a brewery for the beer, which might be producing eight million barrels, where do they put the glass plant? Right next door. Only a fence separating the two, because you can't afford to transport all that weight. And you can't just make glass bottles thinner and thinner because they're brittle. You have to still have a fair amount of weight, but they are considered for a number of things, like some medicines and things, the gold standard in terms of purity, okay. Glass has low surface energy, doesn't pick up things better than metals, it's going to last for a million years without decomposing if you do it properly.

So plastics, permeability and cost. I mean I've shown you where the plastics, just the energy content of plastics is five times the energy content of steel, and two and a half times that of aluminum. So if you're going to use plastics, you've got to blow-mold thinner. And you had mentioned the pressurizing the aluminum cans. Well the aluminum cans, the aluminum costs twice what the steel costs, so you got to make the aluminum thinner. And what they did, in the 1980s they were using supercomputers to design the aluminum cans. It's a huge — it's a multi-multi-billion dollar industry, okay. And they had to use supercomputers to figure out exactly how thin they could make it and still have enough impact resistance, if someone drops it on the floor, that it doesn't — they're shattering and leaking and everything.

Composites — I should have brought, I do have some juice boxes in my refrigerator, of some juice, and the juice boxes also have about seven layers, and one of those layers is aluminum foil, okay. That gets around the permeability problem. You don't do that on gas tanks because you're going to blow-mold them. But that makes a real problem for recycling when you've got seven materials that you've got to recycle, whereas typically plastic milk bottles, or, etcher, better than just talking about milk bottles, let's talk about the soda bottles, okay, which they also have gotten so thin. Some of the cheaper ones, you take the top off and it's no longer pressurized, and you try to pick up that 2-liter bottle and you can't do it because it collapses on you, right. You don't have the pressure holding — when it's still got pressure on the inside, it's easy to pick it up, it doesn't collapse on you. But it's the pressure that's giving it the strength, okay.

Basically when one material in the food-beverage business gets a little bit of an edge over some new increase in technology over the other, then the others will start doing things to get better. And we use virtually all materials for beverages, and so it's not something I can just tell you at a 40,000-foot level, you should always use aluminum for beer cans, no. If you're a purist you should use glass, okay, for beer. But it's a big deal — one, I remember a year and a half ago, one of the breweries was advertising, I think it was Coors, that they had plastic beer bottles, okay. Yeah, oh they had to do a lot of work to make sure you didn't taste like plastic, okay, the plastics are more permeable, and anyway you also have to make sure you don't have any monomers left in that plastic, that all of a sudden the EPA's gonna, or the health people are gonna be all over you.

So anyway, it's a pretty mundane material to think of, just beverage containers, but it's a tremendous volume, and you wouldn't believe the technology that goes into these things. Because saving a fraction of a cent on a billion bottles a year — it turns out, talked about that, a tenth of a cent times a billion, that's a hundred million dollars. So anyway, volume has disadvantages.

Selection of competition among materials for conveying water. In the old days — well the oldest days they would just dig a trough in the ground, and they let the water kind of come through the ditch, and the water would just kind of go through, till you had a muddy ditch. Then they learned they could heat up their clay and make pipe. And so here's a clay pipe from 4000 BC. The Romans used concrete and stone to make aqueducts to transport water. Back a hundred years ago, 150 years ago even, we were using cast-iron pipe, and then steel pipe to transport water. But that had a problem. So now people go in and they actually put a little layer of concrete on the inside of the steel pipe to keep it from corroding from the inside. It could still corrode on the outside, but you can protect that with cathodic protection. But now people like to use plastic pipe, and you can see the rubber o-ring in there, okay, just like these other fittings, the rubber o-ring. Concrete pipe particularly for large-diameter pipe. And we used to actually even use wood, okay, so far as that goes. Virtually every material has its strengths. But for water that's going to flow through there, it's not going to be stagnant, it turns out plastic is the advantage right now.

If you're going to convey gas, it turns out we started out in the old days with a wooden pipe. That is a wooden pipe from 1840. They would just take an old tree and they would gun-drill the inside, lay it in the ground, and transport gas from whatever their source of gas was. And originally most of this was for the utilities, for street lights in the cities, okay. And I have seen things, when Boston Gas — it's now National Grid or whoever it is — but when it was called Boston Gas, I've been down to their training facility down in Norwood, and they have examples where they're digging in the ground and they find one of these old wooden pipes from the gas lines from the 1800s, okay. Or one of the cast-iron pipes. I have some pictures of the cast-iron pipe somewhere.

But then people realized that wood didn't have a very long lifespan, maybe twenty years, thirty years before it rots. And so people started using cast iron. And we use cast iron for water mains. One of the biggest problems in most of the cities like Boston and New York is we've got hundred-year-old cast iron water mains, and every now and then one of them breaks, okay. And they're so brittle that when you work on it in this block, you know that about five, ten years down the road the next block is going to have a leak. Because in New York City, when you go and dig up the road to replace the pipe that broke, you're gonna disturb the pipe on either side, and you don't want to have to dig up a long section of road in New York City, it tends to disturb traffic, okay, for too long. And it helps me a lot, now you know, when I get a job in New York City they said we had a water pipe burst, I said when was the last one in that area, and usually you find there was one about three to five years earlier, okay.

About five percent of all the water distributed in the United States, potable water, is lost through leaks in the pipe, due to corrosion and other things, okay. I have a strip — my house is eighty years old, and I had some construction done on it, and this spring when the grass came up, the water line from the street into the house — the grass was growing great even though I wasn't watering it, because the line underneath is leaking so much, okay. Now that's the town's losing all that water once it gets beyond my foundation. Now there's the meter that I have to pay for that, but the town is — just everybody knows that five percent of the water in distribution is lost through leaks. That is also true in gas pipe, okay. About five percent of all the gas we distributed in this country — and we've got something like a half-million miles of major pipe for oil and gas in this country, much of which is sixty to seventy years old, and is corroding big-time.

So what have people done? Back in the 1980s the American Gas Association decided the solution was plastic. And so this is a piece of gas pipe. How can I tell it's gas pipe, anybody know? It's got a yellow stripe. Pipes carrying flammable gases are supposed to be color-coded yellow. This is a piece of stainless steel gas pipe with a plastic coating on the outside, but stainless steel on the inside. I won't pass these around today, well I can pass them around later. But most of the gas pipe that's been going in for the last thirty years is thermally welded plastic pipe, okay.

And when my gas pipe at my house twenty years ago — they go in, the regulators make them sniff. They put a — they just stick a probe down in the ground, and they have to do that about once every year in an older neighborhood. In a newer neighborhood they may not have to do it but once every three years, once every five years, to find the gas leaks. And as I told you, five percent of the gas is lost to distribution. When it gets really bad — like last winter, while my house was being worked on, my wife and I lived at my son's house, same town, and I was noticing this gas smell when I'd get up early in the morning to come in. And it turns out they finally got around to fixing the leak — they knew it was there, so we didn't have to tell them, we told them but we're smelling gas, and I would smell it early in the morning because the sun's not out, not a lot of wind at night, and so I would smell it first early in the morning. And they just fixed it about three weeks ago, okay. That gas leak — that one crew has 1,700 backordered leaks to fix, and it probably takes one or two days to go fix a leak, gotta dig a hole in the ground, find the leak, okay. So job security for, you know.

Anyway, so we use a lot of different materials. This other one down here is corrugated stainless steel tubing. This is another thing that the Gas Association came up with in the 1980s. It wasn't really approved for residential use until 1997. The problem with this, it's got the yellow coating on a corrugated stainless steel, and if you have lightning come through — like if you live in Florida, which is lightning alley, Florida has a higher density of lightning strikes than any other place in the world, it's surrounded by water that forms clouds that form lightning, thunder and stuff — you get hit by lightning, and you can perforate this, and now you have a flamethrower in your wall, in the interior of your house, okay.

I've got over a hundred cases of houses that have burned down. And you know what, I kept on looking at these houses, I thought, how come these people live in such nice houses? And then I realized rich people build their houses on tops of mountains. And where is the worst place for getting a lightning strike? And don't believe this thing that lightning never strikes twice in the same spot, it does, okay. I mean, anyway, so there have been some problems with corrugated stainless steel tubing when you go switching to different materials.

The advantage is, it's flexible, they sell it for about five bucks a foot, okay. This old carbon steel pipe, black iron pipe, they sell for about ninety cents a foot, okay. This goes for five bucks a foot. The advantage is, a plumber takes three days to plumb a house, a brand-new house, typically with this stuff, they have to thread it, they have to cut it to length. This stuff you just put a fitting on the end, and you can run for a hundred feet with no connectors in between, it's flexible, bends around corners and stuff. A plumber can plumb the house in one day. So the company that's selling this is making a very large profit, until they have to pay for the house that burned out, which cuts into their profit. But they're still profitable enough that they have been paying them off.

Student: Does it bend? Yep, bends. That's plastic bending — the steel, it's a bellows, okay, corrugated bellows. You can bend it more times than it will ever see in service. It doesn't fail by fatigue, it fails because the lightning hits it and goes to ground. And so very interesting physics in it, okay, of lightning strikes and where it goes in the house. And no one can predict where it will go in a house. They've tried, they've run tests in Germany and in Florida — they've built homes and instrumented them and then triggered lightning, sent a little rocket up with a little wire on it into a thundercloud and got the lightning to hit the house, because you got a wire running back down to it, and then monitor where the lightning went. And it's nowhere near where the physicists and electrical engineers have predicted. So lightning is very unpredictable, okay.

So I'll see you — well, I won't see you any more this week. Brian, or Simone, Dr. Belmar, will be lecturing the rest of this week, every day. I'll be back next Tuesday — I shall be back next Monday, but Dr. Belmar's got next Wednesday too, okay. Thanks. Anybody have any questions?