Benefits and Challenges of Stainless Steels

Welcome to Corrosion Chronicles, an original podcast series produced by the Materials Technology Institute. I'm Heather Elaine, the Executive Director of MTI, and I'm here with my co-host, Mark Cook, Materials Specialist with the Dalchemical Company. Hey, Mark. Hi, Heather. So, Mark, I've been introducing you as a Materials Specialist with the Dalchemical Company, but I understand you're now living a life of sitting on beaches and drinking margaritas. Is that a. That is the plan. That is the plan. Yeah, I retire from now. At the end of February, after 27 years, boy, if I were planning on relocating the Panama, but I'm also going to work part-time for Trichlor medals, which is an MTI member, and so I'll still be able to participate in MTI. I think the co-host of this podcast. Yeah, yeah. Yeah, absolutely. I'm very excited about it. Thanks. Well, congratulations. It's been an exciting thing to be able to retire early and be able to just do some stuff you want to do, do something different and enjoy it, and you know, have a margarita for me. Okay. Okay. All right. We're here today with Gary Coates. Gary has worked for over 45 years with stainless steels and nickel alloys, including 24 years with a major stainless steel producer. Gary's been with a nickel institute for the last 25 years, and he does a variety of things there. Supporting applications of nickel and nickel alloys in every industry, really, because nickel and stainless steels are used to make everything throughout the world. So today he's heavily involved in the worldwide training of engineers in the proper selection and fabrication of stainless steels and nickel alloys and he lives in Toronto, Canada. So it's wonderful to have you with us, Gary. Today's topic is stainless steels, and on previous episodes we've talked about carbon steel, we've talked about duplex stainless steels, and we've talked about high nickel alloys. So today we're covering stainless steels, or there was a smaller subset of that spectrum of alloys. So can you give us a definition of stainless steels? Well, I'm really happy to be able to do this podcast that I've had there in Mark. Stay with steel is if we take pure iron and add increasing amounts of chromium to it, something special happens around 10 and a half percent chromium. The material will not rust when exposed to humidity and the water in air. So that was found to be something special, and people take the definition a minimum of 10 and a half percent chromium as the minimum or stainless steel. So that is an ASTM definition for that. The actual amount that's needed will depend on several other factors, but 10 and a half is the definition. And as we'll discuss more throughout this episode, I mean stainless steel doesn't mean that it's not susceptible to corrosion or staining, so to speak. But within that class of stainless steels, there's all these different number groupings, 200, 300, 400 and 600 series stainless steels. Wait, we're not just talking about 304 and 316 today. Oh, that's boring, Mark. The, yeah, no, the numbering system that is used, go back to the 1930s when the American Iron and Steel Institute came up with that numbering this stone for stainless steels. The 400 series was actually two types of structures, the Fridic structure and the Martin Siddic structure. The material set have any nickel in them or very little nickel. They just have chromium and iron and some of them will have malabdom in them. The Fridic stainless steels do not harden. The Martin Siddic stainless steels are like a tool steel. They harden by a quench and temper type heat treatment. So what you just described, those are all 400 series. Those are 400 series. Yeah, okay. Okay. So what about the Martin Siddics? Martin Siddics are 400 also? Correct. And you cannot tell from the number whether it's a Fridic or a Martin Siddic. So or 10 is actually an interesting version of that because with the iron carbon content of a 410, it is hardenable. So it's a Martin Siddic. But as you reduce the carbon content, it becomes a Fridic. So in the petrochemical industry, sometimes they'll use a 410L and that's a strictly, Fridic grade does not harden with heat treatment where the standard 410S or 10 material will harden. So it is complicated. So what did they use that for in the petrochemical industry? Well, it's where they need the minimal amount of corrosion resistant. So they'll use it as a cladding on a prone molly steel to give it a little higher corrosion resistant. So what about the ones that are hardenable with the higher carbon levels? Is that what we're using for a really high quality kitchen knife, for example? It is one type that is used for kitchen knives. Some of them are not stainless at all, but yes, third high carbon and high chromium. So they have the corrosion resistance. Now, the problem is that the carbon will actually tie up some of the chromium. So a 440C, for example, which would make a very good knife. It has 18% chromium in it, but the effect of chromium level is more like 13%, 14%. So these make the sharpest knives. They are stainless steel, even with the high carbon content. Okay. So Gary, where do the 300 series stainless steel fit in? Yes. So the 300 series stainless steels are one that contain a relatively high content of nickel, which makes them austenitic in the structure. And I'll tell you, I'm not a big fan of talking about faith, standard cubic and body standard cubic structures because it can be beautiful. But it's an austenitic structure. And the nickel in it gives the properties of ductility and weldability, which some of the furate stainless steels and the martensite stainless steels don't have them. So they have become the most popular stainless steels as a family. But today, roughly about 60% of all stainless steel being a 300 series. Now during the Korean War, there was a shortage of nickel. So they made stainless steel with a lower nickel content, but added more manganese and nitrogen to keep the austenitic structure. The 200 series is something that is made primarily in Asia, forthom low-race cookware. We don't use it very much in the chemical industry. Okay, so I just want to check what I heard there. The 200 series, the analysis basically came about as a result of mineral shortages during the war. So they kind of fill a niche, but it's mostly a cost reduction and ability to make stainless about if you've got a shortage of some of the important constituents. So one of the issues is that in the 1930s, duplex stainless steel were not common. So the only duplex stainless steel at the time was something called 329. And so even though it's duplexed, it got a 300 series number duplex meaning course, austenitic and ferritic structure, roughly 50, 50 there. So today, we don't use those numbers at all. So duplex doesn't have one of these old numbers for AISI in there. So it's kind of an odd. Okay. Alright, so what about the 600s? Yeah, so the 600 series is here are the precipitation hardenable alloys. So that is a family of alloys where they're not quenching temper. You heat it up to a certain temperature and with the potato form, which makes them hard and strong. And then you can cool it slowly. So those alloys, you don't have any problem with distortion versus the martensitic with the quenching temper. You can end up with a lot of distortion. So where are they used? The pH grades tend to have a little higher corrosion resistance than the martensitic stainless steels. It's mostly with bar products for pump shafts, valve stems, that sort of thing where you want a little higher corrosion resistant than you would get with the martensitic stainless deal. And are they weldable? They are weldable, but not easily welded. So if you do everything just right. After welding the pH grades, you really need to go through the whole heat treatment procedure again and that does make it fairly expensive. Yeah, that was a really good summary of just the different series and kind of where they all fit in together. I'm curious about, you know, with stainless steel, it's always talked about magnetism and that's used as a differentiator to determine if, quote, unquote, something is stainless. Can you speak to that with respect to the stainless classes that you just went through? The 400 series, whether it's frittic or martensitic, are all as magnetic as carbon steel. The 600 series is also magnetic. The 300 series, properly solution annealed, is not magnetic at all. Today it contains a little bit of ferrite in, especially 304. So there might be a slight magnetic attraction and ask material in the austenitic and the 300 series. It will have an intentional addition to give it a ferritic structure and that means that it will be somewhat magnetic and the same thing is true of welds. They are designed with a composition to give them some ferrite there and the ferrite is magnetic, but it is not as magnetic as a carbon steel or a ferritic stainless steel. Okay, but it's, it's normal for a 300 series stainless weld to be more magnetic than the sheet material. Correct. Okay. And then did you mention 200 series? Yeah, so the 200 series are all 4 austenitic, so they are all 4 completely. non-vegnet. Can you discuss a little bit about the effects of the typical alloying elements? I mean, we've discussed chromium already as really the threshold for it being a stainless steel. But can you go through some of the other major alloying elements and discuss the effects of it? We mentioned both nickel and of course I worked with an echoing altitude, so I do have to thermal that a little. Yes, definitely. But it's actually the most expensive of the alloying elements. So a lot of people want to try to reduce the amount of nickel that goes in there. And one way to do that is to add a slight nitrogen addition to it. Now when we talk about nitrogen, we're not adding nitrogen gas into the molecule. It's a monoatomic nitrogen that's being added. It is also an ostinatizer wanting to make the structure austinetic. You can only add a certain amount in it before you will end up getting nitrides instead of fully dissolved nitrogen. When you can think of nitrogen as carbon, you know, carbon goes in between the molecules of nickel and chromium and iron. We call that interstitial to get into the metallurgical term there. But the nickel does some good things for the corrosion resistant, not as much as chromium, but it works in more reducing environment. So once you are in an environment where, for example, there are some things that want to dissolve the oxide film that makes a stainless steel stainless, the nickel will help to decrease the corrosion rate there. Millevedin also does a great job of decreasing the corrosion rate in reducing environments. It's used especially where you have chlorides or fluorides and pitting as an issue. Millevedin is a very important element and sometimes we want to add a lot more to it, but the more millevedin you add, the more nickel you have to add. And a major distinguish between 304 and 316L, which are the two work car screens for the industry. Right. So Gary, the alloy producers have been able to really refine down how tightly they're able to control alloying elements and the inclusion materials, but then they're also using a lot more recycled material than they used to. So can you talk about how that is shifting the composition over the last several decades from what 304L, for example, used to be versus what it is now and minimizing the good stuff and some of the bad stuff being on the higher end of the level. No, that's a very, very interesting point, Heather. We are able to control the amount of alloying elements and that's what makes the cost rise is when you have higher amounts than what you actually need as a minimum. So today, for example, on the nickel content, if 304L, it's a minimum of 8.0 percent nickel, typically you'll find that it's about 8.05 or 8.1 percent neck out there. And they really try to keep it right at the bottom. Same thing with millevedin on 316L. At one time had maybe 2.3, 2.4. There was a European version that was a 2.5 minimum, 11 on content today. Again, it's around 2.0.5. They want to keep it right at the bottom. So you might think initially that that's going to reduce the corrosion resistance of the material. But on the other hand, we're making the stainless steels much pure these days, much cleaner. One of the more important elements outweighs sulfur. Sulfur is generally considered as an impurity maybe 40 years ago. It was really hard to remove and they kept the levels at 0.035 max because it was hard to remove it. Today with the AOD processing and a special sulfur reduction step, you can reduce it easily to 0.001 percent. In fact, often it's even below that. And we can't report 0.00 on the melt-teth certificate. So it's get reported as 0.001 even though it is actually less criminal. Are there any of those undesirable elements that it's difficult to control and that are higher because we're using recycled material? There is, there is from and I'll take copper as an example. Copper can have a benefit to certain stainless steels in terms of its resistance to sulfuric acid especially, but we're afraid that with higher copper levels that it will deteriorate the weldability of the austenitic stainless steel. We haven't reached that area yet, but they have put a limit in ASTM, a new limit on the maximum copper content for alloys that where it is not an intentional addition. So there is some concern when we do an analysis at the melt-stroke of all the elements that we can find in a stainless steel, we do have internal limit to limit anything that might be bad. Most of the impurities do get removed in the AOD process however and that's a good thing. And in Europe and in North America, they're basically all recycled stainless steel. stainless steel gets recycled to like 95% of anything that is the end of life gets recycled there and that's a good thing. That's fantastic. Yeah. I mean that's all reducing filling up landfills. Exactly. So is the market for stainless growing or shrinking? I mean I see competing pressures. I feel like more things that used to be maybe pated carbon steel or stainless now, but then you've got newer materials like duplex is really I think gaining in popularity. So is the market growing or shrinking? The market is definitely growing generally over the last let's say 20 years. It's been 6, 7, 8% per year which is huge for any material that's been around the 19, 10s. But yeah, no, it is growing and you bring up an interesting point about the duplex because people think wow, that is really important for the chemical or petrochemical industry, but it represents only about 1% of all stainless steel production in the world. So it's a very small percentage. Okay. Do you know the growth in the segment when we talked about the different series earlier? Where's the growth relative to those different series? Do you know that I'll pop your head? Yeah, going back about 20 years ago, the 200 series was a very small portion of the market, maybe only one or two per cent, but with the production coming out of India and China, and especially for household kitchen goods, it grew fantastically high, but it's leveled off now. So everything is about even in percentage of growth, all the different series. Okay. So Gary, I think one thing that's interesting that maybe gets missed sometimes by laypeople is when you get to things like stainless, you can't treat corrosion rate quite the same way as you would with steel. You know what I mean? You can't just weigh a corrosion coupon and then test it and weigh it again and know what your corrosion rate is because generalized corrosion is not necessarily your major concern. It's some of these localized mechanisms right like pitting. So you can talk about that a little bit. There most advanced corrosion data that you see in books and corrosion handbooks is general corrosion. So it's something that we do understand quite a lot, but most often as you indicate stainless deals don't fail by general corrosion. They fail by localized corrosion and that's everything from pitting crevice corrosion, stress corrosion cracking, corrosion fatigue, that sort of thing. And that's a much harder one to predict, but we have some good feelings for, you know, what level of chloride content that whatever pH and cause a problem that comes more from experience of where it has gone wrong in the past, but other corrosion mechanisms take time. So a general corrosion test, you can get good results in seven days. These other mechanisms you got to almost have real life experience, put corrosion coupons in your actual system and see how they behave. Not just a flat coupon, but a, but a crevice coupon or a U-Bend coupon. So they're well done. For everything at once. Well done. Right. And I think you're right. It absolutely does become an experience based thing for each process of which types of corrosion and how susceptible a process is. But, you know, materials engineers have tried for decades to try to give overarching quantitative, you know, get your arms around that. So they develop the PREN number, pitting resistance equivalent number that, you know, is based on a calculation of chemistry of the stainless steels, but my experience is they're fairly problematic. So can you talk about that, like how reliable do you feel like they are and how good of a method is it or are there better methods out there for trying to get your arms around that? It is one tool and the toolbox of a corrosion engineer and it really says that this is what a particular alloy is capable of doing if it's in ideal condition. And that there are so many other factors that affect pitting resistance, social finish, inclusion, content, whether it was properly annealed or not. All these things come into it. So if you take 316L, you can come up with the PREN number for it based on the actual composition, but from one producer to another producer to another heat of a from the thing producer, it can vary considerably. But it gives you a ballpark figure for what it should be capable of. The problem I find is that people love the PREN number because it's simple. 316L at this number, 317L at this number. Well, that means that 317L is always the same. better than 316L, not just in pitting, but in general corrosion in whatever environment it is. And of course, that's completely wrong. And so I do find it being misused a little. Right. Right. Well, and I think that's a good time to just talk about some of the specialized situations like nitric acid, for example. Can you just talk about that and the effect of malibu? Yes, sure. And nitric acid is an oxidizing acid. It's an acid that wants to form that chromium oxide, Belmont stainless steel, and a 304L is good. You increase the chromium content. It gets even better. There are some versions of 310 that do a 25% chromium instead of the 17% in the 316L or 18% in the 304L. So obviously the chromium content has a major effect. However, when it comes to welded material, especially in moleptinum, will react and form a intermachalic phase called sygma phase, which reduces the corrosion resistance in these oxidizing conditions. It ties up the chromium a little bit so you don't have that same effect of chromium content in a very small area of the material. And especially at the heat affected zone of welds. So 316 is not as good as 314L in welded condition. Right. And just where like that's the that's the exception, right? Because in most environments, 316 will outperform 304. So that's where it's really comes down to that. You've got to really know your process. You've got to do your corrosion testing and just have that experience to know that you're trying to make any kind of broad statement and saying this alloys better than that one or has a higher PRAN is just going to steer you wrong. And if you you mentioned about knowing your environment, the impurities in it can change the characteristics. So you add some fluoride to nitric acid and all of a sudden you don't have the oxidizing environment. You can reduce the environment and that changes it entirely. Right. Exactly. So while we're on the subject of hitting in these interesting mechanisms, we've got to talk about stress-persion cracking because that's really what stainless steels are. That's the nemesis. Yes. That's the question. For stainless steels. And it is the nemesis or Achilles heel of the 300 and 200 series, the austenitic ones. And the more nickel you add, and there again the benefit of nickel. I've got to throw that in that. If you have a high enough nickel, they will not chloride stress corrosion crack, but standard 304, 316 alloys. They are very highly susceptible to chloride stress corrosion cracking. The ferritic grades are virtually immune to that. Often they'll contain a little bit of nickel, so they're not completely immune, but they're quite immune to it. And the duplex, of course, contains both austenitic structure and ferritic structure. They're much better than the austenitic, not quite as good as the ferritics. Right. Right. And people are always trying to really get their arms around that window for when stainless steel, 300 series stainless steels are susceptible to stress corrosion cracking, chloride stress cracking. And that's not super straightforward and easy either because it's a combination of temperature, pH, and stress residual stress in the alloy. And so if any one of those are particularly high, it can throw off that window. It's not always straightforward. But like you said, you know, allowing up is an option. We talked a lot about this during our duplex stainless steel episode. That's one of the major benefits. Sometimes you're better off going down the food chain and using carbon steels if this is a real concern because they'll corrode in a uniform manner and that's safer and more predictable, easier to monitor and manage than the unpredictability of stress cracking in stainless steels. So play at the I was in. We had an incident where, you know, it was a split body valve and the valve manufacturer upgraded the body bolting from steel to stainless steel. And, you know, the investigation went on through like, why won't we notify to this change? And well, we didn't feel the need to notify you because it was upgraded. It's like, well, there's, and there's another, you miss cat case of them doing the same thing because the carbon steel bolts were always corroding on a HF heat exchanger. And when they upgraded, quote, in air quotes to stainless steel, when there was, when there was that minimal amount of fugitive emissions of hydrofluoric acid coming through the gasket, then it cracked the bolts in the entire head of the exchanger came off resulting in a fatality. That's why we never, in never use stainless steel bolting for, for HF war for chlorides. Like it can be, it can be very, very detrimental. So. And one thing which people often forget is because Heather, you mentioned about the stress levels and the material is that when you have a welded construction, you have very high levels of stress in the heat affected zone, usually close to 100% of the yield strength. And so that's normally where a 300 series bill stress corrosion crack. Yeah. We have a lot of chlorine based chemistry, but we see a lot of FCC happening externally. You can just have enough chlorine in the environment. And then of course, like you say, there's always an opportunity for residual stress somewhere on a component. If not applied stress, and it's a, it's a big issue. Yeah. I thought corrosion under insulation with all of years ago, and it keeps on coming up again. And a lot of it is people want to use these more common lower alloys, stainless steels like 304 or 316. And that's why duplex has been used a lot in Patrick chemical. Yeah, unfortunately, I don't think CU has been solved yet. We know about a solver. We don't know how to solve it. It should be easy. It should be easy. Exactly. Can we talk about low temperature limits for stainless versus steel? Because I think that's an important difference. Yes. And that's again, where the 300 series and the two other series, the austenitic structure really shines. You can, by use most of them down to almost absolute zero without being worried about them becoming brittle. Now, you do have to worry about half things because as I mentioned, they contain some ferrite and the ferrite will crack at a much higher temperature. So typically, the asmi code says minus 196 degrees above that temperature. You don't even have to test, let's say, a rot material, 300 series material. And you can weld them and still pass the tests, if you weld properly, to ensure that there's very low ferrite in the weld battles, for example. And then high temperature use limits, it's got an advantage there as well. Right. They're much stronger. And again, the nickel allows it to be much stronger at the higher temperatures, though, especially with creep strength. That's often the determining factor for high temperature usage and the 300 series are much superior. You can also add little bits of other things in myobium and titanium and theory on some of these other things, which will give them even improved high temperature strength. You see, you mentioned creep strength. How does that differ from like hot pencil? Yeah, do a 10-file test, which might take 30 seconds to perform. The material will yield and then finally break at a certain stress level. But if you were to hang a dead weight from the material at a relatively high temperature, it will actually creep. It will actually stretch, slowly, and we call that creep. So talk a little bit about high temperatures in general and what's happening inside related to this creep mechanism. First of all, at ambient temperatures, you've under degrees Celsius, you can have material and a thousand years from now, 304L will be the same 304L. Nothing will change with the structure. But when you get the high temperature, there's activation energy happening and changes will happen to the material. Greens will grow. You'll get some intermetallic phases forming at these temperatures. And that changes the property sometimes for the benefit, sometimes to the detriment of them. So you have to really look at high temperature applications differently than you do ambient temperature application. So Gary, let's go ahead and talk about some fabrication issues with stainless steels, particularly welding, wire stainless steel weld wires typically over alloyed. We want the weld to be slightly more corrosion resistant than the base material. And as I mentioned earlier, you do get a little bit of ferrite normally in most 300 series weld wires. And that can affect the corrosion resistance also. So we try to have them a little bit higher alloyed and that has an o-galvanic effect. You don't want it to mall area of lower corrosion resistance in a larger area of higher corrosion resistance. You want the opposite to occur. So you want the weld to be slightly over alloyed to the base metal. So are you forming some ferrite in the weld lint cools? Yeah. And you can control that with the composition. And you can predict that different ways. There's the Schupper diagram. There's the DeLong diagram and there's some WRC diagrams that will help you to predict the ferrite content of a weld without any delusion. So 100 percent weld metal sample. But of course, you get delusion from the base material you're welding and you have to take that into account. But for now applications [BLANK_AUDIO] your applications, you want to keep the ferrite content to a lower level because the ferrite will form intermetallic phases very, very quickly at high temperature. You don't want your weld to become brittle and also the low temperature will affect the sharp impact properties of the material. But you do want ferrite there because it will help to avoid hot cracking in welds. And this was especially when you had the higher sulfur contents, but even other types of contamination. And the ferrite has a capacity to absorb, for example, the sulfur a little bit better than the the austenitic structure of the austenite grains. What we're talking about fabrication, I've got a couple just pet peeve questions I want to ask. When I was a co-op way back in the 1900s, I had to go around and use a little strap-on flow meter to measure flows and pipes. And the strap-on flow meter had these pins, the head screw tight to clamp the thing to the pipe. And they were stainless steel threads. I think they were probably cut threads. And stainless Gauls so easy. I mean, it's so frustrating compared to like carbon steel fasteners. Why does stainless Gauls so easily? Well, it all relates back to the oxide film that makes it corrosion resistant. That oxide film when you have two surfaces rubbing together that have the oxide film, they want to literally weld on top of each other. So, Mark, I just have to say you're supposed to add some lubrication going down to the end of the going all down on there to make it work. If the only I had worked at a company that made something like molly code or something, oh, we've been doing. We, we, and the quality of the threads also, it's an important factor. Back in the days when I was working with the stainless steel company, we were importing threaded pipe component. And we were selling a lot to a potent paper mill. And we're just over what's happening. And they said, well, we're, we try to, um, thread them onto the pipe. And they go. And so we take them off and we throw them into the forest and, and try the next one. And then they bought these very inexpensively. So, uh, a lot cheaper than the higher quality ones that were made in North America. But the purchasing departments saw the price was only half out of, that's an old story. Yeah, it is, but it's true. Yeah. Now, I would just say that, yeah, purchasing is always half the price that, that's a common theme in a lot of worries. So, I've been involved in several projects where we get an intense arguments about passivation of the equipment piping. And that, that can be a really hot topic. It seems like there's a lot of differing information out there, depending on what you're looking for. Yeah. So I'd really be interested to hear your perspective on passivation. Well, there is conceptually complicated people want to make things simple, but basically, passivation is to ensure there's a good layer of passive oxides film on stainless steel. And so what will stop that from happening? Well, if you have, for example, iron contamination, free iron is rubbed against the component, the strapping material holding it on the palette. It will rust. And even if you passivated in the normal passivating solutions, which are either citric acid or nitric acid, that will not remove the iron contamination on it. So you don't passivate it even though you're the propagating liquid on it. It's you, first of all, degrease it to get a rid of the grease because none of these acid will remove the grease. And you peckle it, because the peckling will remove things like heat fans, any surface inclusions. It removes that the rusts in iron contamination underneath it. That will all cause the oxides film to build up on the material afterwards. The most companies will say, if you pickle it properly, you don't need to passivate it afterwards because the passivation will occur naturally. Now in the food industry, they often use nitric acid as a final step. And a lot of that is because the nitric acid is a journal chiller. It kills bacteria. I'm not sure it does anything to help the pathivation on it because most of the material is already in an ideal state, but it will kill all the germs there, which is of course very important. And you're more of an advocate of degreasing and tickling than you are passivating. Yes. And I mean, I've heard of passivation, like I'm aware of passivation being done more commonly for pharmaceuticals or food industry. And it seems like it makes sense there because you are concerned about that. You don't want contamination to be an issue from that initial corrosion of the surface, but in the chemical process industry, you know, where you're typically using it in an acidic environment, the process is mostly going to do the passivation once you put it in service, right? Yeah, it'll remove the heat tint and these other surface contamination. That's correct. So I'd like to ask, we mentioned the recycling at the beginning, how you said almost 90% of stainless steels are being made with recycled material, which is phenomenal. What else are stainless steel producers doing about their carbon footprint and sustainability? I mean, these are very energy intensive processes. Yeah, no, they are indeed. And they're all working on trying to reduce their carbon footprint as every other industry is. And there are ways of doing that. Certainly, the recycling using more recycled material helps, but it's also they use electric arc furnace pits. If you have green energy, that helps. Can you run those with a solar farm? Yes, solar farm wind turbines. So that sort of thing, even no clear, if I dare mention, nuclear, greener than burning coal. But yeah, we're all concerned about that. But really, what you also have to look at, if you have a bridge, for example, and you put in carbon steel rebar, maybe you coat it with some epoxy and up in Canada here, we add lots of road salt to keep the roads amicing, because you really are accidents. You kill somebody that's a huge social cost there. So we add lots of road salt and that road salt goes through the epoxy layer and causes it to corrode and then tracks the concrete. And then we have an expressed way in trotto that probably every 10, 12 years, they have to dig up the concrete and replace the rebar. Well, the last time they did it, they said, "Hmm, let's use stainless steel rebar." And that's been such a, it will last maybe a hundred years in those conditions. There's a bridge in Canada, in Quebec, the Champlain Bridge. It used 20,000 tons of stainless steel rebar. And because it was a key bridge, they don't want any traffic disruption for many, many, many years. So they said, as part of the design, the rebar had to last 100 years as a minimum. Yeah, I mean, that's certainly a fair point for all material selection. And picking the right alloy that will have the right lifecycle cost, the appropriate life is always going to be your most environmentally sustainable solution rather than picking something that's completely based on price. And that bridge is a great example because the rebar, such a small portion of the total cost of that bridge. And then, not all, not to mention like the downtime of having to redo the bridge every 10 years and stuff. That's the ending there. All the concrete, everything. Yeah, it's amazing. Yeah, both in my province, Ontario, they're starting to take into account things like the cost of disruption to the traffic. In other words, if you have to go from three lanes down to two lanes, it might make the trucks go half an hour late. So they have to leave a half an hour early. And those are social costs that need to be added to the equation, the cost that we've been doing. It's run a five, but it's definitely, you know, there's an efficiency. There's it's a real cost, yeah. Yeah, it's a real cost. Yeah. Well, that's, I mean, that definitely has applicability for the CPI as well. I mean, these are all important reasons to do your material selection correctly. Absolutely. So sheers to materials engineers worldwide. All right. Thank you so much for joining us, Gary. I think this was a really informative episode. It was, it was fun to talk about stainless steels, this kind of like narrow niche in the spectrum of alloys and materials that we have options of choosing. So thank you for joining us today. It was my pleasure, Heather and Mark. And thanks to everyone for listening to this episode of The Corrosion Chronicles. Join us each month as we continue our conversations with subject matter experts, discussing materials related challenges and successes of the process industries. Be sure to subscribe to our podcasts on Apple Spotify, Google, and wherever you listen to your favorite podcasts. For more information about the materials technology institute, visit us online at mti-global.org. Thanks for listening and we'll see you next time.