Pipe Welding Series: Bevel Talk

The Hydrogen Problem

October 23, 2019 Season 4 Episode 1
Pipe Welding Series: Bevel Talk
The Hydrogen Problem
Chapters
Pipe Welding Series: Bevel Talk
The Hydrogen Problem
Oct 23, 2019 Season 4 Episode 1
Miller
Show Notes Transcript

Take a deeper dive into the reasons why preheat and post weld heat treatments occur in welding. Join induction heating specialist, Al Sherrill as he talks about when to heat, why it's important to heat and options available.  

https://www.millerwelds.com/products/induction-heating-systems



Speaker 1:
0:00
Welcome back to bevel talk. Thank you for joining us today. Again, we're joined with Tim Monday from team industries. You know, Tim, we left off talking a lot about, um, trends in the marketplace. What's going on, what you guys are seeing in industry as a code body member, but also in welding and heating. So let's take a little bit deeper dive into the welding and heating part of the codes. What trends are you seeing? How have you guys adapted to changes in technology at team industries?
Speaker 2:
0:30
Well, I think when it comes to, um, codes in general or even technology, um, one of the things that we find somewhat more, somewhat frustrating at times is our clients. Um, ability to adapt to those new technologies. Uh, very often the, uh, the clients have come up with a preestablished, uh, set of specifications. Um, it takes a huge amount of effort for them to change those. And so as a result, a lot of the new technologies that we see that we think we could benefit from, um, are not, are prohibited or they just don't know enough about it to allow it in their project. So it's, it's, it's really a challenge to sell it to our clients.
Speaker 1:
1:14
I often make the joke kind of tongue in cheek, the technology's 25 years ahead of industry and industry is 25 years ahead of code. And how do we combat that? How do we, how do we adapt to that?
Speaker 2:
1:26
Yeah. So, um, there's just, uh, just comment with regards to code. Um, you know, if the criticism is, is that the code doesn't keep up with technology, I would say that it's deliberate. Um, you have to, uh, you have to remember that everything that goes in the code has to have something that's well-proven a good track record. And, and if it doesn't, if it doesn't have a long period of time to evaluate whether or not that new technology works and does service or provides the safety level that is expected of the code committees, then they can't really put it in there until they've seen that proven out. And so it does, it's deliberate that it takes that long. The other part is, is that, you know, you're, you're dealing with a, a huge amount of experience on code committee. And each one of these on each one of these people who are reviewing the proposed changes, perhaps the inclusion of new technologies are looking at that and thinking, well, you know, I remember when this happened or this happened and they have a wealth of experience that they draw from to say, no, I don't think that this is what we should allow just yet.
Speaker 2:
2:36
I want to see more time, I want to see some more demonstration that it will work properly. And typically this'll be done under code cases. And that kind of thing is where they do that experimental type of work.
Speaker 1:
2:47
Right. Well and I think it's, it's, it's important to recognize that and understand that it's not just the codes aren't, they don't care about technology. But really what we're trying to do on what codes and standards are for is, is for safety
Speaker 2:
3:01
and then for service life to be able to extend or maintain service life. So we know what to expect from a product or a piece of equipment that's put together. Um, so how do you guys at team, with that being said about codes and standards, how do you guys adapt with new and changing technology and welding and heating? Well, I would say that one of the, the probably the biggest change in heating technology is probably induction. Induction has been a great tool for us. Um, but what we've seen, and this is again, one of those things that I've been exposed to as a result of being part of code committee is a lot of studies that have been carried out with regards to heating. Um, in this case particularly, um, induction heating. And one of the things that we're finding is that, uh, there's a, uh, the gradient to temperature gradient through the wall thickness as well as um, longitudinally direction of the, of the pipe is pretty steep because you can heat so fast with induction and we have electric resistance.
Speaker 2:
4:07
Um, typically you bring the temperature of that material up at a slower pace. With induction, you can get it up very quickly. And so as a result, um, you have a huge temperature gradient between where you're heating and right next to it that has no heating. Now I know that Miller has done some studies on this and they've actually done some, I think I'll Cheryl's done some, some studies on that and uh, written some white papers on it. Um, and this is, this is kind of the, some of the, the input that we on code committee need because right now I have the opposite. I have people who are doing studies, heat treatment studies, um, that are really kind of concerned about that whole temperature gradient and how quickly we're heating. We've been employing, um, induction heating and the concerns that I have that I see when we're using it is really to, first of all, um, we do some induction preheating but what I see is again, the ability to heat so quickly.
Speaker 2:
5:12
Uh, the temperature discipline dissipates about as quickly as it heats because you have this heat sink that draws away from it, right? So, um, uh, a while there will put the induction heating element on there and he'll put the temp stick on there right after that to say, Oh yeah, it's up at temperature. And then he'll start welding. Well, in the meantime, just from the time that it, that he's put the temp stick on and the time that he's getting his welding gear ready and he's going to start as well, the temperature of may have dropped below the minimum preheat temperatures. So that's a concern that you have to watch out for, which means really you have to be heating for wider area and a larger area than where you're actually going to be welding it. Those are all important things and I think it takes time. Understand
Speaker 1:
5:58
how induction heating works, how heating works, how the heat sync works to able to recognize and, and overcome and adapt in your shop to make sure that you're doing it correctly.
Speaker 2:
6:09
Right. The other, the other part that's a probably a concern of mine is that, so, uh, it's very regimented when you come to electric resistance heating, um, with regards to thermal couples, the placement of thermal couples and how you're measuring it, right? And when, when you measure that temperature, it, depending on where you're measuring the temperature, it's either giving you a good reading or a bad reading. So for an example, let's say that I have a huge, uh, flange that's welded onto the end of the pipe. I have about weld between this flange as a weld neck flange in a, in a pipe. And, um, you're heating that area right by the, the wild, right? Or in the case of pulsatile heat, treat your, your tree heat treating that well. Well, if I put a, if I put one thermal couple on right on the top of the world, um, what will I get right? What about the heat effected zone towards the flange? Do you think that that re reached posable heat treat temperatures,
Speaker 1:
7:07
right? You have to be able to verify and make sure that it did.
Speaker 2:
7:09
Right. So, um, so when we use electric resistance, we have numerous control thermal couples. Um, and then we only hit, but, but when we're induction heating, we only have one control thermocouple. Right. So it becomes difficult because if you think about the zones and how you heat with induction, you have wraps around it that you're wrapping around the weld. Well, what happens is, is that if I, if I put that, depending on where I put that thermal couple, which is, you know, anybody who's really understanding what's going on, you're going to put more than one thermal couple on there.
Speaker 1:
7:45
Absolutely. It's right. It's recommended to you use, you know, 12, three, six, nine o'clock at a minimum.
Speaker 2:
7:52
Well, it is, but it doesn't say you have to do that. Right, right. I see. So, and it depends on whether you go by D 10, 10, you know, the requirements of [inaudible] 10, 10 heating or you know, what is the client specifying? Right. Most of the time they don't say anything. So, uh, somebody could just put one thermal couple on at the top of the weld and, and they would have no idea what happened to the rest of the weld. Right. So, but heat sinks and, and it's really easy when you have one bar wild that's a pipe the pipe and there's no heat sinks that that's straight forward. You can, you can center the coils right on top of the weld and there's no problem. The problem really comes in is when all of these heat sinks, whether it's a branch connection or it's a, it's a con, you know, a pipe support that's welded on or there's a flange, all of those things have a huge effect on how it's heated and remember, right. Why are we doing post-weld heat treat, right? We're conditioning not only the weld metal, but also the heat effected zone is a very important part of it is that we're conditioning and heat effected zone. Right, right. I think it's, it's
Speaker 1:
8:56
very interesting, um, your thoughts and, and what you're thinking and how, and how your thought process is. Because a lot of people that aren't familiar with heating or aren't familiar with codes or aren't familiar with, with welding in general, they'll think, Oh yeah, there, there's my temperature all the way through, all the way around. I'm good to go. Yeah. And really understanding heating in general, not just injunction, not just induction, not just resistance heating, but how it is heating work. Why do we heat? What does it do when we pre heat? What does it do when we post-weld heat treat? What, what are the benefits of that? What if we go out of spec and why it's important is, is critical to, to a successful operation. Sure, sure.
Speaker 2:
9:37
When you think about the, you know, we say stress-relieving, right? Right. So what are we doing when we're stressed or relieving? Right? So, so, uh, obviously whenever you have molten metal that solidifies, you're going to be imposing, shrinking, right? And that's going to be happily, is a very localized level. So as it shrinks, you're going to impose all of these internal stresses that are in the weld, right. Um, the other thing is, is that, you know, you want to condition you, you, you, uh, raise the temperature in the heat effected zone and you quickly cool it off, right? Well, if you think about all the processes as steel is made from right, and how it's made, what happens is, is that we have to heat it up. We, we form whatever it is that we're making with the same pipe and we cool it off, but we could cool it off controlled.
Speaker 2:
10:25
We temper it, right? So, so you have to, you have to bring it, you first bring it up to is very high temperature where you're forming it, you bring it back down, they have to bring it back up temperate and then bring it back down. Right? Well, same thing happens in weld, right? And the heat affected zone is untempered. So we have to temper it. And that's what the, that's what we're doing. We're conditioning that, that heat, the heat affected zone as well as the wild know, right? So we're T we're tempering it, but we're also relieving stress, right? So how do we release stress where you raise the temperature until the, the yield point drops, right? And so as, as we raise the temperature, we meet the yield point and it yields, now they're words Gibbs, and it relieves the pressure, the T, the stresses within the weld and then they can lower it back down.
Speaker 1:
11:16
All right. It's the science behind heating is something that just amazes me how much we know and how much we can do to make sure that a weld or a joint or a configuration will do what is designed to do and intended to do. Um, but how, when misunderstood or misused, it can be detrimental to an entire project.
Speaker 2:
11:38
Yeah. So, uh, I, you know, and maybe this would be a probably a good time to lead into to some of the newer materials that have been used,
Speaker 1:
11:46
right? How, how do you guys adapt [inaudible] to lightweighting and high strength steels, um, in what you're doing? Yeah. Yeah.
Speaker 2:
11:52
So high strength steels typically, um, it's like the higher carbon content and that kind of thing require much higher preheat temperatures, right? So, um, you know, usually, you know, on the higher strength materials, we're usually at the three, three 50, you know, for a preheat. Now when we get into P 91, so this is primarily in the power market. Um, so that's a, that's a, it's a [inaudible] Chrome. Um, but the, the difference in [inaudible] for example, in P 91 is the, is the, uh, structure, the granular structure of the material. So, uh, it's primarily Martin site on, on P 91. And because of that green structure, it requires a very careful heat treated. Very careful. So an example of, we talked about improper heating. You had mentioned in proper heating, one of the concerns that we have with a P 91 is that the, the postal heat treat temperature is very close to the lower critical temperature.
Speaker 2:
12:51
So the lower critical temperature is where basically, um, the grain structure changes, right? So we don't want to give, get above that lower critical tablature because we want to retain the, the grain structure that's there, but we want to refine it, right? So intemperate. So to, to do that, um, we have to work in a very narrow zone. So typically interact about 14, 74 lower critical temperature, and you're usually at 14, 20 B know 1375 to 14, 24 plus will heat treat temperature. So there's not a lot of room between the upper end of the pulsatile hatred, temperature and the lower critical temperature. Right. So what has happened is, is that, uh, in the early days when they were implying a lot of this P 91, they were running into all kinds of problems because they were the local posts while heat treating it. Um, they didn't have a lot of thermal couples on it and they had heat sinks.
Speaker 2:
13:45
So for example, I've seen examples where, um, they had an Owlette, you know, uh, uh, integrally reinforced a branch connection, all that right that they welded on. And so they were heat treating that weld. And what they did is they put a couple of thermocouples on there on the actual weld for the Alana. Um, so the problem is, is that right above that was the thin wall pipe that welded right to the all that. And so when they heated it up, they put no thermal couples on there. So what do you think happened to the thin wall pipe that was wiling to the OLAP? It got overheated, went over the lower critical temperature and what Cotes says is says, you know, if, uh, if you go above the lower critical temperature, you have to treat it like [inaudible] not P 91. Well, the stress allowables for P 91 are much higher than P. so I'd seen where, um, there's big bulges in the pipe just above the Owlette where the mechanical properties of that material were ruined as a result of overheating. Yeah. And
Speaker 1:
14:52
again, I, you can't stress it enough that the heating is such a science and an art form. Um, anything you can do to make it easier and understand it better is, is critical to, to success in heating and post-weld heat treatment. Yeah, absolutely. Absolutely. We spent, we spent a lot of time in [inaudible]
Speaker 2:
15:09
committee just discussing those issues because they're so critical. And you know, we talk about, you know, the slow adoption of, uh, uh, code two technologies. P 91 was one of those technologies, right? And it presented such a huge, um, advantage to the manufacturers and to the, to the owners to use P 91 because thinner wall, lighter loads on the pipe supports less wiling to do, um, and longer life, you know, they could run at higher temperatures, all of those things. Um, there's a real advantage, a real push to do use P 91 over, for example, the typical chromes that you would see as a P nine P five, you know, P 22 type of stuff. So, um, when they did that though, um, they really, they wanted to adopt it but found out about some of these issues and they didn't get the safeguards in there right away. Right. Cause they just didn't know. Right. So it's, it's a, it's a process. Um, I think that given the, the problem was, is that it wasn't that the material wasn't good, the material is good. It's just the knowledge of the people handling it had to be increased.
Speaker 1:
16:24
All right. Well I think you think about it, how many hundreds and thousands of miles and hundreds of thousands of miles have been put down of [inaudible] now versus when it was first put out and how much data we have now versus then an experience. I mean, experience really leads to expertise, right? And how we handle it, how we deal with it has evolved as we've learned how to put it into service safely.
Speaker 2:
16:50
Yeah. And that's true. And I think every day, I mean, and appre is, is the electric, um, it's, it's their research body. Um, so everybody kind of chips into to appre the electric power research Institute is the name of it. And, uh, they have done huge amounts of research on, on the welding and [inaudible] and they've brought a lot of information to the code committee as well as to industry. So, um, it's, it's, uh, definitely an art.
Speaker 1:
17:24
Join us next time. As Tim and I talk more about how welders it team and while there's in general, have adapted to these high strength steels, um, and new technology and processes in welding.
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