§1. Term-paper topic selection [00:14]
Even welding in the aerospace industry is a little too broad. You don't have to do welding — you can do machining in some industry. Actually I'd sort of rather you take something that's hard to machine, like a carbide tool. It's hard to machine; you've got to machine it with diamond or boron nitride. There are super-abrasives. Explain to the class when you use diamond and why you don't like to use diamond on machining of steel — because the carbon diffuses in, and you'd like to use boron nitride. Steel doesn't diffuse when it gets hot to have the cutting surface; boron and nitrogen don't have high solubility in steel. I'm not saying that's the thing, but you should take something fairly specific, fairly narrow. If you want to do something big and broad, then we can set up and you can do a one-hour seminar for the class. No, seriously — I'm not trying to be funny. You can't do welding in the aerospace industry in ten minutes at anything except the most superficial level, okay.
If you're interested in that topic, I have a former student who wrote a paper with me about that. They won the award in Spain — that's where the conference was. We're done with the classes a week from Monday. There'll be a class every day next week. I'll be lecturing three days next week, Dr. Belmar two days. I'm going to be gone the third through the fifth. If people want more time, we'll see where I am when I finish up next Friday, and if you want more time I'm happy to come the 6th and 7th of March. If you haven't heard enough stories, I've got more stories than you've got time. Any other questions?
Student: [asks about presenting thesis work]
You could talk about your thesis. She made a presentation in another class and double-dips it. I don't mind double-dipping — I did it all the time. I want you to pick a topic that you're interested in. I was doing this in welding once with a bunch of Navy guys, and one guy decided he wanted to opt out of the Navy when he could, and he wanted to do masts on sailing vessels. Which is not exactly the Navy — they don't have a lot of masts on sailing vessels anymore except the Constitution. Another one wanted to do the failure of the American Airlines flight over Brooklyn that the composite tail rudder came off. What did that have to do with welding? I don't care. This is your chance to tell me something that you're interested in.
Weren't one of you the ones who did doorknobs, how to manufacture doorknobs, a few years ago? One student was interested in decorative doorknobs, and she came in and talked about how you make decorative doorknobs. That was when I was teaching a casting course, and it sort of fit in because the decorative ones are often cast. If you want to sit down and talk about it, I'm happy to discuss it, but you will do the best job on something you're interested in, or something you want to learn about, or something you already know about. I want it to be fairly specific. So talking about decorative doorknobs is fine. It doesn't have to be welding — this is a welding module, but you could be taking one of the other modules. I'm not that picky. We only do this for fun, okay.
We'll accommodate any of those scheduling things. Sometime next week, or before spring break, I'll give people a potential schedule. I don't want to give you the schedule quite yet because I don't know what my first half of April is. I'll know better in a couple of weeks. We'll be flexible. I've never had a problem accommodating your schedule. Anything else? Okay good.
§2. On-site stress relief and the loss of battleship welding technology [05:35]
So let's start talking about stress relief heat treatment. This is a company called On-Site Stress Relieving Services. Here's a vessel. They built a box that's on rails. The vessel is too heavy to just put on rails, so it was easier to put the furnace on rails. You just slide the furnace over the vessel and you raise this thing to eleven, twelve hundred degrees. There are lots of different ways to do this for on-site stress relieving. Here's a vessel that they just wrapped — they put electrical blankets around it, virtually over everything, and then they just wrap the whole thing in insulation. Here's another one down here. If you go to the web, there are a bunch of pictures of on-site stress relieving.
And it has to be done. You either have to do thermal stress relief or mechanical stress relief if the things get very large, because the residual stresses get to be huge. I told you the story about the big weld with 400 little welds in it — the big thing came off of a 7500-ton forging press. They didn't do proper preheat or post-heat, they didn't stress relieve, they didn't peen. Peening is when you hit it with a little hammer every half-inch of weld; you go in there and beat the surface to introduce mechanical stress relief by deforming the surface. Which is the way we used to put together battleships, 14-inch thick armor. No one remembers how to do it exactly, and no one wants to go out and build a battleship to prove how to do it. We don't really know how to weld 14-inch thick armored steels anymore, because all those people are dead.
Did I tell you the story about the battleship Iowa down in Puerto Rico? One of the sailors was upset with one of the other sailors, and he set off a shell in the turret and destroyed the turret. The Navy didn't know how to repair it. Of course, you don't need 16-inch shells anymore. They were firing shells that had been made in World War II, and the last time I think we fired shells was in the 1970s — they were sitting off Israel and they were lobbing them into Palestine, somewhere in Syria. The Missouri may have been the last battleship built during World War II — that's why they had the signing on the Missouri in Tokyo Harbor; it was the newest battleship. You want to go in there with your newest machine if you're going to sign an armistice. The Iowa may have been finished after World War II, I think it may have been the last one. They're getting to be old ships, old and rusty. But we lost the technology.
§3. The Wyman Gordon 50,000-ton forging press and its cracked I-beam [08:36]
To tell another story on big heavy stuff: I mentioned a big forging press. The Air Force after World War II wanted to build fighter jets, and they wanted to build bigger ones for bombers, and they needed big forgings, because no one trusts a weld in an aircraft. You haven't had the beginning of my welding course, where I say the number one rule of welding is to avoid all welds possible. These things will fail at the welds because they're the most highly stressed location. So the Air Force doesn't trust welding, and they need forgings the size of this room, the width of this room, for things like the wing boxes on swept-wing fighters. The government helped Alcoa and a company called Wyman Gordon both build, in the 1950s, a 50,000-ton forging press. These were the largest forging presses in what we used to call the free world. The Soviets may have had a larger one. The Air Force was considering building an even larger one. The problem is these things are so big — they'd picked out a mountain in Colorado that was solid granite, and it was going to be the foundation, because you couldn't afford to pour enough concrete for these things.
One of them is still here, in West Grafton, Massachusetts near Worcester. The other one's in Cleveland in the Alcoa plant. I was at the Alcoa plant once. They still forge big aluminum things for aircraft. But what happened to the Wyman Gordon plant: the press goes up about three or four stories above the ground. When you walk into the plant, you've got these great big four rods, two of them. You've got the ground, and this goes up about three stories, thirty, forty feet high. And you've got this big set of beams up here — there are six of these I-beams, and they're ten feet high. That's a story right there by itself. They're ten-inch thick web, and they were welded together out of big forgings. This is not a rolled beam. It's ten feet high and ten feet, and it's just thick. They were about fifty, sixty feet long. You couldn't make the whole thing as a single forging, because you didn't have a forging press this size until you built the forging press.
They went six stories into the basement. You had this huge anvil down there that you're going to press against. For all the hydraulics and other stuff, you basically had this thing going six stories down into the basement. This thing has to move up and down — you've got to have another three stories going down. The other I-beams down here, which were the same as those above, were six stories buried in the ground. And one of them developed a crack all the way through. Someone was down there doing the inspection. They said, oh, I see a crack — it's ten feet long. That's not good. They had six of these beams. They had to shut down the machine.
It turns out the beams from the side had a taper to them. What they had done in erecting this thing was, when you're trying to put it in the pit down here, they had welded on little pads on either end just so you'd have something to sit on, because this was a 45-degree slope. They were about the size of my notebook if you made it into a cube — they were not small. They were about ten inches wide. They were two-inch fillet welds, which means they had yield-level residual stresses. After about 30 years of use — this was in the mid-eighties — they developed a fatigue crack that started at the toe of one of these and went straight through. Ten-foot crack.
To build a new one of these, they estimated would cost two billion dollars. Because it's not just the machine, it's all the hydraulic pumps and everything else. Fills the whole building — a huge building. We only own two of these in the United States: one at Wyman Gordon, which the Germans bought, and the Alcoa one. It was weld residual stresses. It wasn't a hydrogen crack — it was 30 years old. But it was weld residual stresses and the stress concentration. I got to go down in the elevator and see this thing. It's a little bit greasy down there — about two inches of grease everywhere. They had an elevator to go down there, and I looked at it, inspected it. They said, well, how do we weld this? I said, you're going to have to preheat it. We talked for a couple of hours about what you might have to do and how you'd stress relieve it. I said, the best thing for stress relief is if you can put it in a furnace. Can't we do it in place? Because it's not the easiest thing in the world to get a 50-ton beam out of the sixth-floor basement when the only access you have is an elevator shaft. They were going to have to disassemble a fair amount of this forging press in order to even get the beam out of there. Eventually they did decide to spend the millions of dollars to rig it out, weld it, stress relieve it in a furnace, and put it back in. Cost tens of millions of dollars to make that repair.
They had to grind the crack open. This is a ten-inch thick weld. You've got two pieces and you're going to have to prep the ends. You don't do a 45-degree angle, because then you're going to be putting in tons of weld metal. How narrow a groove? Should you do a straight bevel, or can you do a compound bevel where you have two different angles that you machine on here? Or do you do a J-groove? There are lots of things you can do. We were talking about how to minimize the amount of weld metal but still have enough fusion on the end — enough angle that you still get good fusion. Straight sides, you won't get good fusion. We do have something called narrow-gap welding. The Japanese spend a lot of time and money on narrow-gap. We use it on the top deck of aircraft carriers for thick steel. But you've got to develop the procedure. It could take you a year to develop a good reliable narrow-gap procedure.
A new forging — we probably have a one-and-a-half-year lead time. They thought about that. But they didn't want to be down for a year and a half. They got the turnaround in about three months. They were doing all the economic analysis on, well, do we go buy a new one? Buying a new one doesn't solve it, because it was still welded together up here. The flanges were welded to the beam, so you still had to weld the thing. The thing had been welded in 1950. I found an article in 1954 in the Welding Journal that talked about this, because it was such an unusual weld at the time they made a special feature article in the Welding Journal about building these presses. Come 1985 when we need to weld them again, we had to find out. So we were going back and looking through the literature to see what procedure anybody used. They had lost the procedure. It can take months to develop a procedure. It took us a month, and it wasn't just me — they brought in half a dozen consultants because it was tens of millions of dollars.
Student: [asks what the press can forge]
This forge will do titanium, steel, whatever you want. It's just 50,000 tons. Once you've got a 50,000-ton hammer, you can put anything under there. It's just a question of what dies you put in and how you change your parameters for forging aluminum. There are applications for huge steel forgings — like the tokamaks. These guys will probably buy time to do a 50-ton forging of stainless steel. The Germans, Krupp, bought this forge shop, and they'll forge anything for a price.
§4. Wyman Gordon, crankshafts, and product-liability exit [18:35]
This forging facility in West Grafton, before Krupp bought it, was Wyman Gordon. Krupp buys Wyman Gordon, and Wyman Gordon at the time was forging crankshafts for airplanes — Lycoming, Textron Lycoming, Teledyne Continental engines. If you're a small aircraft pilot, like a Piper Cub, you have these half-million-dollar engines that are aluminum. I'm going to talk about welding of the aluminum cases on one of those when I get to the aluminum. They have steel crankshafts, because you need the strength of steel. You don't want the weight, but you can't get anything else that has the fatigue life. Krupp buys Wyman Gordon, and they start looking at the order book and they see, we're making — I don't know — maybe two thousand crankshafts a year for Continental and Lycoming. They said, we don't want this liability. We don't make enough money on two thousand of these things, and if one of them fails you've got a ten-million-dollar lawsuit. There are people out there who just love to sue any manufacturer of an aircraft.
We can talk about that for half an hour. Congress passed a law in 1992 or so, called the General Aviation Revitalization Act, because all the Piper and Beechcraft and Cessna companies were going bankrupt with lawsuits whenever some guy fails to maintain his aircraft and ditches it and kills himself and his family. Some attorney comes in and sues them and they get tens of millions of dollars in front of juries, because no one wants to even think about falling from the sky. Krupp looked at this and said, we don't want this liability. We can't make enough money off the few things we're selling. So they gave one year's notice. They couldn't just cut them off because that would be restraint of trade. They gave them one year to find another supplier. They found a company down in Kentucky that had been manufacturing crankshafts for International Harvester engines — the big trucks going down the highway. Those guys were looking for business, and they said, sure, we'll forge your crankshafts. Problem was, they didn't have quite as good quality control, particularly since they were building a new plant. In the process of building the new plant they weren't paying too much attention to what was going on in the old plant. They produced about three thousand crankshafts for Teledyne Continental that Teledyne Continental had to do a recall on. They had about ten failures; only one or two killed somebody.
There's a certain liability you have to worry about in these businesses. The Germans didn't want the liability, and they were probably right. Who are you going to find that wants to do this? You often run into these questions about — you don't want to sue someone in manufacturing, because you're liable to put your supplier out of business. A lot of times you just sort of eat the cost of these lawsuits without passing them back to other people who screwed up. Other questions? No? Just a lot of scratching out there, okay.
§5. Post-weld heat treatment: the three reasons to temper [22:33]
So anyway — I think I told you enough about that one. They left a detail on there that created a stress concentration when everybody thought, well, it's not loaded. Well, it is loaded, and there was a stress concentration and it did create a problem. They did fix it, but they had to post-weld heat-treat it in a special furnace. Now we've talked about preheat; we haven't talked as much about post-weld heat treatment. There are three reasons to temper the steels. You lower the hardness — I'll just call it HV, Vickers hardness, but I mean Rockwell C, whatever. You temper it, you relieve residual stresses, and the third thing you do is you eliminate hydrogen.
Think of the Venn diagram I did. I relieve the stresses, I've reduced the hardness, and I've reduced the hydrogen. So this is hardness HV, stress, and H2. By post-weld heat treatment I do lots of good things. If I properly post-weld heat-treat, I probably won't get a hydrogen crack. And I told you about the Helms project. Now, how do you do it? What procedures do you use? Mike Boomforth [Bumforth?] was talking about the structural welding code yesterday, and here are some of the welding procedures per the structural welding code.
Mike mentioned that you can take the certified welding engineer exam by using either API 1104 or the structural welding code. He showed you that API 1104 was this little thin thing. The other code that's used most often is the ASME Boiler and Pressure Vessel Code. The problem with the ASME Boiler and Pressure Vessel Code is — it's this thing, okay. If I take all the parts of the ASME Boiler and Pressure Vessel Code — you don't want to take a full-day exam, or a three-hour exam, on the Boiler and Pressure Vessel Code. You probably need about five years' experience daily to understand it. It's sort of like the US tax code: there is no one who understands the whole thing. It's just a little too complex. It's the granddaddy code. It's about a hundred and five years old, and it is the highest quality standard, because if a pressure vessel blows it does really bad things, okay.
§6. The North Andover hot isostatic press explosion [26:01]
Which leads me to another story. About 20 years ago now, I'm sitting in my office — I was department head at the time — and I get this call that they had an explosion up in North Andover. There were only 16 tons; it was only a quarter-mile away. I was one of the first two people down in the pit when they finally cleared out enough space, and they had a crane. The other guy was the chief engineer for Travelers Insurance, and I was the other guy. We were the two guys who got down there first to look around. A lot of trash down there, okay.
This pressure vessel was a hot isostatic press, and it weighed about 300 tons. It was threaded at the top, also threaded at the bottom. The top cap and the bottom cap were 50 tons each, and the cylinder was 200 tons. It was about ten or twelve inches right here, and it opened up to about 28 inches at the top. They had designed this in the mid-eighties on a Cray supercomputer. A Cray supercomputer is probably a $500 PC today in terms of computing power. They had done all the thermal stresses on this. It had been operating for a number of years. The inside diameter was 60 inches, and it was probably 20 feet tall on the inside. It wasn't a small vessel. It weighed 300 tons.
It had been forged in Japan by Japan Steel Works — one of the only places in the world that had both the steelmaking technology and a big enough forging press to do this. Alcoa doesn't forge a lot of steel, and Wyman Gordon in Cleveland — you'd have to make the steel over in Japan and then bring it over here. The Japanese have maybe thirty-thousand-ton forging presses. So they had forged the pieces. Usually you make something a little bit longer — they call it a prolongation — so you can cut it off and cut out tensile specimens, Charpys, you can do all your quality control tests on the heat treatment. They did that, except it failed the mechanical properties after the heat treatment. Darn. I could scrap it — that's only going to cost me twenty, thirty million dollars — or I can just re-heat-treat it.
How do you re-heat-treat it? You don't have exactly the same chemistry. You take something that's very similar to it. You can't weld on a prolongation on something like this. So you just take a piece of the material and put it in next to it in the furnace. But that doesn't cool exactly the same way as this piece. This one's 200 tons; this one might be two tons, and they cool differently, they get different grain sizes. The second time, the heat rate, it passes. Great — ship it. They did, and it goes out. It's a hot isostatic press. They used to put Harley-Davidson — I remember walking around the rubble of the building from the explosion, because it just wiped out the whole building. They had a bunch of Harley-Davidson aluminum cylinders. They were cast cylinders and they would hot-isostatic-press to get rid of all the shrinkage porosity from the casting, because guess what — when you're on a Harley-Davidson motorcycle, guess what's right between your knees. If it blows up, not a good day. So they have very stringent quality control standards for these cylinders.
They put a bunch of these in a rack and they heat-treat it. It takes about a day to do a heat treatment, and a furnace like this probably costs a couple of thousand dollars an hour — well, only a thousand dollars an hour back then — so you might be talking about a $25,000 heat treatment. So you put more than one cylinder in. It was very convenient — it was sixty inches, and that was just big enough for all the discs that Pratt & Whitney and General Electric were going to make for the big jet engines. This was the only one in the world of this size for three months. Fortunately, people were building another one, because all the jet engines were going into high-bypass — big fat engines — and this thing couldn't keep up with all the work being thrown at it. About three years before, they'd started ordering another one. Unfortunately, when this thing let go, the other one came on stream three months later, otherwise it would have been three years before anyone in the world could have built an engine. Pratt & Whitney, Rolls Royce — think of the damages. Fortunately they had the other one almost ready to go, and they replaced this with another one, because there was no other unit that could take something that big.
Why did it let go? It's partly a hydrogen cracking story. It's not a welding story, but it's a hydrogen cracking story. In fact they called it stress corrosion cracking, so I might as well call it stress corrosion cracking. For stress corrosion cracking, you have to have a stress, you have to have a susceptible microstructure — in this case low toughness, read low toughness there. And then you have to have a source of hydrogen, and you'll get stress corrosion cracking.
If you did the fracture mechanics on this thing originally, it had about a 12-inch critical flaw size if it had the toughness it should have had when they did the heat treatment. But it didn't have that toughness. They took Charpys out — it failed. So they redid it, and this little piece passed, and that little piece had enough toughness. But when they went out to test this thing after it exploded, in one of these pieces — you're right, Jonathan, that piece right there — the crack ran right from that corner stress concentration, and it just ripped off a piece about a third of the way around. It weighed 16 and a half tons, and it was found a quarter-mile away. Took a lot of energy to move 16 tons a quarter-mile. Another 5-ton piece — we pieced the whole thing back together. Actually, you don't piece it back together, you don't pick up 5-ton pieces. It was in like 70 different pieces. The average piece — 200 tons, 70 pieces — that's 3 tons per piece, pretty heavy.
One 5-ton piece landed right on top of the operator's chair. It happened at 2 a.m. This thing runs 24/7. The operator had, just seconds before, gotten up to change the paper on one of the chart recorders. If this had happened 15 seconds earlier, he would have been underneath the 5-ton piece. He was sort of rattled, okay, but it landed right there. The chair was not in very good shape.
What happened — fracture mechanics and everything — you try to design something like this for leak-before-break. Leak-before-break means if you get a crack it will grow and grow until eventually it creates a leak in the vessel before the vessel just blows up as a brittle fracture. You want it to leak before it breaks. Break-before-leak is not good — no warning. On pressure vessels, if you read the ASME code for pressure vessels, they actually impose duties to have a leak that warns you. Typically the leak — it has high-pressure gas inside. This thing has 20,000 psi argon inside it. The argon is compressed as a gas, but it has a density like a liquid. You should have a leak-before-break on the original design if it had the toughness.
The toughness — K1c is proportional to — well, if you want to be precise, but it's not precise — 1.12 sigma square root of pi C, for a planar crack. Stress times the square root of pi times half the crack length. A would be the crack depth. It should be about ten inches or greater. Pi is the constant. Sigma is the stress. We know what the stress is when you're under 20,000 psi. They've done this finite element model and —