WM_S2014_15

So we could track down whatever this year that was, and he said the oil in Venezuela is high in vanadium, because he had been studying for ten years different trace metals and where they are in different oils in different parts of the world. And they said, I didn't even know what vanadium was probably, but John Wulff had been studying corrosion and oxidation of steels and stuff, and it turns out chromium oxide mixes with vanadium ethoxide [pentoxide] I think it is, to form a low melting eutectic. And so the protective chromium oxide scale on the stainless steel, when they fired their boilers with this oil containing vanadium, just melted away. The chromium oxide protective scale for high temperatures, and the whole thing just destroyed overnight.

Today the American Petroleum Institute has specification to get the vanadium down to very low levels, okay. I had to work on a problem very briefly up in the tar sands of Alberta. There's a lot of vanadium in some of those tar sands. The American Petroleum Institute has a specification of a way to get vanadium out of the crude. And there's only two materials you can use that won't be corroded by vanadium pentoxide. And one is some ceramic, which is of course very brittle. You have to run this furnace to get rid of the vanadium in, like 2,000 degrees centigrade. And the other one is, I can't remember, it's a 50— it might even be vanadium titanium okay, or aluminum titanium alloy or something, it's a very expensive alloy. Anyway, they had a whole ballpark, uh, in their furnace up against tar sands and they wanted to know.

But anyway, John Wulff knew the reason, and he got a big fat consulting fee because he knew where to put the X, okay. So the right answer is worth a lot of money, and as John Wulff used to say, the right answer is worth a lot of money and the wrong answer is not worth a dime, okay. In fact it's sort of negative, because it sends people in the wrong direction. Okay, enough stories for today, unless you have questions.

Okay, what I wanted to do, I handed this out yesterday, and I've told you about post weld treatment now and preheating. But I haven't— and I've told you, you can go to Stout and Doty's book and you can look up what it says, but we actually have more sophisticated ways because we have more sophisticated steels than they had thirty years ago. And so if you go to the structural welding code, this is the best document that I know of in the last ten or fifteen years to explain how to determine preheat. And so you've already got a copy of this, but it says there are two methods to determine preheat of the steel. And it gets a little complex, but I think it will bring together a lot of the things we've been talking about. You can either do heat affected zone hardness control, or hydrogen control. Well, lo and behold, those are the two bottom circles on my Venn diagram, right? Okay, one or the other.

If I turn to the next page, it says you've got to first select the method, and this whole appendix is which method and how to use the method. The first thing you do is determine the carbon and carbon equivalent. Well, I told you carbon determines the hardness, which happens to be one of these things on the Venn diagram. And the other thing that's important is hardenability, which is the depth of hardening. So if I have a steel, I need to know whether it has low depth of hardening or significant depth of hardening. And so in the welding industry, since the next— for the last seventy years, we've been talking about carbon equivalent. The carbon equivalent is a measure of the hardenability of the steel.

To locate— wow. Okay, the carbon equivalent is equal to the amount of carbon plus manganese and silicon divided by six, plus chrome, moly, and vanadium divided by five, plus nickel and copper divided by fifteen, okay. I've also handed out just now, going around, is something out of another book, a book on welding metallurgy, that gives you in one of their appendices a whole list of different carbon equivalents. Because over the last eighty years there's a lot of people who wanted to develop their carbon equivalent. It's basically an empirical relationship of depth of hardening as a function of alloy composition. I told you hardness is a function of carbon, hardenability is a function of all the alloying elements. And this is just a formula which no one will tell you it's the hardenability, but in fact it's just a formula for the hardenability of the steel that you're using.

So you need to know— I told you, when these people ask me to develop a welding procedure, the first thing I want to know is the chemistry, because I got to figure out a carbon and a carbon equivalent. And then I need to know the things. Okay, so if I have— my method is going to be a hydrogen control, which is this in this section. It says I then have to go to figure I1, this is appendix I, and to figure out what zone I'm in. So let's go to that.

Believe me, if you don't have someone to take you through this the first time, it's a mess. I'm trying to figure this out, I spent— the first time I ever looked at this, it took me about two hours to figure out what they were saying, and I had some background. So here's the carbon content and here's the carbon equivalent. I'm going to plot the two, and I can be in zone one, I can be in zone two, or I can be in zone three. Zone one is carbon steel, it's easy to weld, okay, tolerate 30 ppm hydrogen, all kinds of things. Zone two is over here, this is some of your higher strength quenched and tempered steel. HY80 submarine steel is kind of right over here near this line but it's in zone two. 4340— oh no, this stuff is a real pain. Zone three, you're going to be getting up to these five and six hundred degree Fahrenheit preheat temperatures.

So I guess at this time, in the next couple of minutes, because we've basically done— that's about all you, well, you also have to determine whether you are willing to accept a carbon equivalent and cooling rate hardness of 400 Vickers or 350 Vickers. Hardness is one way of measuring the hardness. Usually more commonly metallurgists on steel use Rockwell C values, and all you have to do is take the Vickers and divide by ten and you will be within about one point Rockwell C. So this is Rockwell C40, this is Rockwell C35, okay. You have to decide which level of safety you want. And this graph allows you to calculate cooling rates and stuff, or estimate cooling rates for your weld, which we won't get into. But in general— well, if I told you, um, anything below Rockwell C30 is a difficult target hydrogen crack, that would be basically in zone one. So Rockwell C30 to 40 is zone two, and above Rockwell C40 is probably zone three.

So the story I'll tell you in the last couple of minutes we have before— uh, by the way, you can have Monday off, it's a holiday. Um, so the story I'll tell you is, um, I don't think I've told this story— maybe I've told it last year, I apologize. Did I tell you the story about the America's Cup? Yeah. If I did you don't remember, but maybe you do, you remember anyway.

So I get in about six o'clock in the morning, there's not a lot of other practice here at 6 a.m., but I get a phone call from— my name is Jerry Milburn [Milgram], who's a professor being course two now, in the Navy program. At that time it was ocean engineering, and at the time there were two professors of naval architecture at MIT. They were sort of competing with each other, each sort of competing with each other designing the next, um, sailing vessel for the America's Cup. This is like fifteen, twenty years ago or something. And he calls me up because they have been using HY80 at 130 ksi, four inches thick and like six feet wide, as the keel for the America's Cup prototype that they built. And when they were out there testing this ship, they actually bent this keel, four inches— that HY80 exits, HY130, which four inches thick, which is the highest strength steel plate steel they could buy, and it wasn't strong enough for the America's Cup keel. I also thought, so that's pretty heavy, but they actually put weight in the bottom of the boat, okay. They actually sometimes put lead in the bottom of the boat, it's way critical that they also don't like to capsize and tip over, so anyway.

So he wanted to know, he said, we can buy 4340, but we have to weld it, how do we weld 4340? Well, 4340 is clearly in zone three. And so I had to develop a welding procedure for them for 4340. And uh, I went over the same— anyway, so 4340, I don't remember, but it was probably a 600 degree F preheat, okay. And I may have included the post weld PWHT [post weld heat treat], but I don't remember all the details. I picked up Stout and Doty, picked up 4340, saw what they recommended, and kind of worked things out from there about what welding might go there.

Student: When you have a 600 degree preheat, are you actually having guys weld, or is it robotic at that point?

You have people standing right there. Now they may be wearing reflective suits, yeah okay, and I told you about the guys in the blue jelly suits. They may have suits that blow cold, you know, air-conditioned air through them. And they may have, you know, four welders where ordinarily you have one, because they're spelling each other, it's a terrible job. Okay, but when you have no other choice, that's what you have to do. Once you get— when you start getting above 300 degrees, I mean it's bad enough at 300 degrees, but you can sort of stand next to something 300 degrees and have fans falling on you and things like that, it's not too bad. You start getting up to 400 and 500 degrees, you've got real problems. Okay, that's enough for today.