The Pipeliners Podcast is continuing a series on inline inspection (ILI) with Marc Lamontagne of the Lamontagne Pipeline Assessment Corporation. In this episode, host Russel Treat and Mr. Lamontagne discuss the use of ultrasonics for inline inspection.
In this episode, you will learn about the use of ultrasonic tools to capture information about corrosion and cracking, the advantages of using ultrasonic compared to MFL for inline inspection, the technology available for ultrasonic ILI, and more.
Stay tuned for more episodes in this inline inspection series covering corrosion, cracks, deformation, and the data that is used in inline inspection.
Ultrasonic for Inline Inspection: Show Notes, Links, and Insider Terms
- Marc Lamontagne is the president of the Lamontagne Pipeline Assessment Corporation. Find and connect with Marc on LinkedIn.
- Ultrasonic inline inspection uses sound waves to send a signal into a steel pipe to detect the presence of corrosion or cracks within the pipe.
- Compression Wave Ultrasonic testing measures pipe wall thickness and metal loss. This type of test uses compression waves to send signals longitudinally through the pipe and perpendicular to the surface of the pipe.
- Shear Wave Ultrasonic testing detects longitudinal cracks, longitudinal weld defects, and crack-like defects such as stress corrosion cracking.
- Piezoelectric Sensors measure changes such as pressure, temperature, or strain that indicate cracks or metal loss in a pipe.
- Miniaturization is the process of manufacturing smaller technological devices, such as Piezoelectric Sensors, to increase the number of tools that can be used in a given space.
- The phased array technique is an advanced method using sound waves to detect cracks in a pipeline, measure wall thickness, and perform corrosion testing to evaluate the integrity of the pipe.
- Stress corrosion cracking occurs when there is stress on a pipeline, causing cracking. The greater the tensile stress on the pipe, the greater risk of cracking.
- Circumferential cracking is typically the result of stress over a prolonged period of time or from local stress due to soil changes.
- Intergranular cracking occurs along or between the grains of the metal that are welded together in the pipeline. These are typically characterized by narrow, tight cracks along the grain.
- Transgranular cracking occurs across the grains of the metal. These are typically characterized by wide cracks, pointing to the likelihood of substantial corrosion.
Ultrasonic for Inline Inspection: Full Episode Transcript
Russel Treat: Welcome to the Pipeliners Podcast, episode 34.
Announcer: The Pipeliners Podcast, where professionals, Bubba geeks, and industry insiders share their knowledge and experience about technology, projects, and pipeline operations. Now, your host, Russel Treat.
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This week, we have Marc Lamontagne coming back to join us. We’re going to continue our conversation about inline inspection. This week, we’ll be talking about the use of ultrasonics for inline inspection. Marc, welcome back to the Pipeliners Podcast.
Marc Lamontagne: Thank you, Russel. It’s great to be here again.
Russel: We brought you back. We’re going to talk about another kind of technology in inline inspection, and that’s ultrasonic. Maybe you could explain to the listeners, Marc, what is ultrasonic in inline inspection? What is the technology and how does it work?
Marc: It’s certainly similar to the medical ultrasonics in that there is a sound wave that is created and imparted into the steel pipe. Depending on the wave type, it, then, provides a signal of corrosion or cracks within the pipe.
Russel: I’m familiar with ultrasonic in measurement because I grew up as a measurement guy. In an ultrasonic meter, you’re measuring how fast a signal moves through a liquid. You measure it in two directions. When it’s moving in the direction of flow, it moves a little faster than when it’s moving against the direction of flow.
With that and some other fancy math, you can figure out velocity and from that, you can get volume. I would assume that ultrasonic in ILI is kind of doing a similar thing. If I’m expecting to see a certain amount of wall thickness, I expect the signal to move at a certain rate. If that wall thickness isn’t there, I’m going to get something different in the signal return.
Marc: That’s correct. There is the medium of the product that is within the pipeline that the ultrasonic wave goes through initially. Then, into the steel wall. There’s a couple different speeds of ultrasound due to the properties of the two different materials. The time that it takes for the signal to return through the steel wall, generally dictates whether an anomaly is present or not.
Russel: Right. Like everything else in these kinds of conversations, it all confirms my basic belief that everything’s easy until you know enough about it.
Marc: That’s correct. There are, certainly, those professionals that know a heck of a lot more about this and these tools and analysis than I do but I hope that I can provide you a good summary of it.
Russel: I think this is great, Marc. How long has ultrasonic been around for inline inspection?
Marc: Ultrasonics generally came around in the late ’80s, early ’90s. That was, primarily, in the beginning, what the ultrasonic inspections for — metal loss. The cracking inspections came shortly thereafter.
Russel: I guess that makes the technology quite a bit newer than magnetic flux, which we talked about the last time we had you on the podcast, but it’s still been around for some time.
Marc: Yes, that’s correct. It, primarily had to do with not the technology itself, but compressing all the electronics and memory into a package that could be put into an inline inspection tool and making it self-sufficient and having enough memory to run the distances that the inline inspection tools demanded.
Russel: That makes a lot of sense because ultrasonics, same thing in measurement. They’ve been around a long time. They didn’t begin to proliferate until the electronics packages could get to a price point and a performance level where it made sense to use them.
Russel: It makes sense to me that, ultrasonics been around…I’m trying to think when I first came across an ultrasonic meter. Probably in the late ’90s, when I first came across an ultrasonic meter. It’s been around for some time but when they first started making them, they only made sense for the big meters.
Now they’re starting to make them for four and three inches, which is all because of the continuing improvements in the electronics and the computer processing.
Marc: Yes, that’s right.
Russel: How does an ultrasonic signal distinguish between corrosion and cracking?
Marc: These are two different technologies altogether. The metal loss inspection by ultrasonics use is what’s called a compression wave. It’s an ultrasonic wave, a sound wave, that is oriented perpendicular to the pipe wall. It’s going directly from the inner wall to the outside wall in that straight direction.
Whereas, the crack inspections are what is known as a shear wave. They try to go through the pipe wall at a 45 degree angle, such that it can reflect off of cracks, which are, themselves, perpendicular to the pipe wall.
Russel: That makes perfect sense. We’ve talked about the water analogy. It’s a little bit like if you think about the signal being a flow of water. If I’m looking for a pit…Think about an island or a rock in a river. I want to flow the signal right at the rock in the river.
Russel: That way, I’m going to see the disruption in the signal and be able to look at that disruption and quantify the obstacle, or in this case, the missing metal. In the case of a crack, if I go perpendicular, it’s like looking at a knife. I’m flowing the water right at a knife edge.
Marc: Yes, exactly.
Russel: If I turn the knife 45 degrees to the water, I’m going to see it and if I don’t, I’m not going to see any disruption in the flow at all. On an ultrasonic tool, do they have both a shear wave and a perpendicular wave on the same tool?
Marc: Yes. Yes, they do, actually, put both technologies on a singular tool. The tools that were initially created for ultrasonic inspection, both cracks and metal loss, contained sensors, known as piezoelectric sensors, that were approximately a half-inch in diameter.
Metal loss and cracking inspections were done individually, simply because the size of the sensors dictated that. Not to mention, early on, the memory requirements. Of late, sensors have decreased in size, which has allowed for the combination tools to exist. Of course, the memory capacities to exist, as well.
Russel: One of the things that I’m aware of is that one of the ways they’re reducing cost in these ultrasonic is…The initial devices had very high signal strength, lots of attenuation, and made it easy to pick the signal up. I didn’t have to do a lot of analysis on the signal to remove noise.
When I miniaturized the devices, I’m sending less signal and I’m using more processing to remove the noise and get down to the pure signal. That can reduce cost. It can reduce power. It can reduce size. All of that is driven by miniaturization and the increasing power of electronics. I would assume that that same kind of thing is happening on these tools.
Marc: Yes, exactly. There are not only singular type sensors that are combined with one another, there are also tools that used phased array techniques, as well.
Russel: Very similar to how radar is processed in aviation?
Marc: That’s correct.
Russel: That makes sense. I’m enough of a nerd to know about that stuff. I’m not enough of a nerd to talk about it intelligently.
Russel: What are the standards around these kinds of ultrasonic inline inspection tools? Is it the same standards for MFL as it is for ultrasonic?
Marc: Yes. The standards are generally built around all of inline inspections. There may be components within each that vary depending on threat type but, in general, the standards are quite the same.
Russel: What are the strengths of ultrasonic compared to MFL?
Marc: When you’re considering the metal loss, ultrasonics will give you more of a direct measurement as opposed to inferred by the magnetic signal. Simply put, the ultrasonics, based on the time of flight will give you a greater confidence, more accuracy within the sizing of the defects that are being examined for.
Of course, with respect to MFL, it is not readily available to find tight cracks, cracks without voids associated in them. Of course, that’s where the ultrasonics would shine.
Russel: That, actually, makes perfect sense. That raises a question. It’s easy to understand corrosions and damage as defects or features. It’s a little harder to understand what causes cracking in a pipe?
Marc: Cracking may occur with improper welding techniques, heat inputs, cooling too quickly, etc., or stress corrosion cracking that can be available with disbonded coating and a proper environment. Of course, the stresses available to the pipe. It could even be a manufacturing type anomaly — something left over from the manufacture of the pipe or even shipping of the pipe to the location where it was put into service.
The cracking is generally located along the seam welds for these manufacturing and shipping type issues. Whereas, for stress corrosion cracking, it can be along the seam, any welds, but it also can be within the pipe body itself.
Russel: I was actually at AGA operations conference last week. I sat down to have breakfast and was talking to somebody. It was a lady. She’s a civil engineer. She worked on soil erosion and soil movement and the impact on pipelines and calculated the stresses applied from those types of things.
It’s like a lot of other things in this world. Once you talk about it, that makes perfect sense. Soil is, to some degree, dynamic.
It moves. There’s erosion. There’s settlement. There’s water and drying, and all that causes soil to move. That implies stress on the pipelines. Stress would tend to evidence itself more as cracks, versus corrosion is going to evidence itself more as metal loss.
Obviously, I don’t know enough to know if that’s an absolute but maybe you can confirm what I’m noodling on here?
Marc: Yes. The secondary stresses, particularly in pipe movement, may cause the pipe to bend. That bending, of course, there’s a greater tensile stress, potentially, than what the pipe was designed for. That could create some circumferential cracking.
Russel: That makes sense, too. If I’m compressing the pipe — in other words, I’m taking it from round to oval — that’s going to create cracks more in the direction, the length of the pipe. Where, if I’m bending it, it’s going to be cracks more perpendicular to the length of the pipe.
Marc: That can be, yes. It all depends on the orientation of the secondary stresses.
Russel: Exactly. What kind of data do these tools put out and how do I do the analysis of that data?
Marc: The tools put out signals that are based on the reflections of the ultrasonic waves. They vary in intensity. The readings for each of the tools can be down to a quarter-of-an-inch spacing and potentially even less as the tool goes through the pipe.
That’s a very large number of readings. Say you’re inspecting a 100-mile pipe, a quarter-inch is quite a few readings.
Each one of those readings has a certain amplitude. That is all put together in the ILI vendor’s proprietary software, where it, then, looks for particular signal characteristics and will outline those that it deems as crack like indications. Each of these crack-like indications are, then, vetted by the analysts from the vendors as to their particular attitude and characteristics.
Russel: I always try to visualize this in my mind’s eye as to what that looks like. Basically, what I’m doing is I’m taking a snapshot of the ultrasonic signal every quarter inch?
Russel: I know how much signal I’m propagating, and I know how much signal’s coming back?
Russel: That’s telling me what I’m seeing. I guess, if I propagate the signal into a pit, it’s going to come back one way. If I propagate the signal against a crack wall, is it going to read back a different way? Does that question make sense?
Marc: Yes. The amplitudes will vary depending on the amount of signal, of course, reflected back. Also, the difference between the compression wave and the shear wave…There’s terms, for instance, if you’re thinking of a crack inspection where the shear wave reflects off a crack. It’s called skips.
That means that it has reflected one or two or three times off the inner and outer walls of the pipe before it hits the crack and then, reflects back. They count the number of skips to determine whether it’s an inner or outer wall defect.
The signal, when returned from a crack, can generally be more intense at specific locations within the crack, such as what’s known as a corner reflection, where the crack forms a corner with the pipe wall. This gives a very good idea of its location. Correspondingly, cracked tip reflections, which would, correspondingly, give a very good read of its depth, as well.
Geometry has a lot to do with the signal attenuation and signal characteristics that are returned to the tool. If you consider corrosion, it’s not necessarily flat and parallel to the pipe wall. It can be semi-circular.
Russel: It tends to have rounded edges versus cracks would tend to have sharp edges.
Marc: Right. It will disperse the ultrasound signal in various directions. Therefore, not all returning to the ultrasonic device, but it still can give a good reading of time of flight. The amplitudes would vary based on the characteristics and shape of the corrosion and, even, cracking because cracks are not all necessarily perpendicular to the pipe wall, either.
The major stress fields are actually 45 degrees to the cracked tip. They can grow at an angle. Also, various forms of stress corrosion cracking. They’re either intergranular or transgranular, which gets into a whole other topic. They’re not necessarily straight and perpendicular.
Russel: There’s all kinds of different failure mechanisms, is another way to say that. Each of those failure mechanisms will create a different kind of crack feature and what you’re looking at is the geometry of that failure mechanism. That’s giving you an idea of what’s going on.
Marc: That’s directly affecting.
Russel: It makes sense to me that I’m reading the way the signal comes back.
Russel: That makes a lot of sense. I could get us drug real deep into the weeds about how that works because I’m just naturally interested in that sort of thing, but I don’t know that’s going to help the listeners.
Russel: Or, me this early in the morning, before I’ve got my first cup of coffee fully consumed. It does help visualize what’s going on. What they’re doing is, they’re taking this series of snapshots. I would assume they plot that some way in some graphical representation. Then, somebody who understands what they’re looking at is looking at that signal and analyzing it.
Are there tools that’ll automate the signal analysis?
Marc: Yes. That’s their proprietary software that they’ve developed in-house. They’re quite robust. The development of those, obviously, continues. They can examine the signal right down to its bare minimum if you understand what I’m saying? They do look for trends in the signal to classify the anomalies that they’re seeing.
Russel: Basically, the buzzword de jour right now is artificial intelligence and what they’re doing to analyze those signals is a type of AI.
Marc: That’s correct.
Russel: Interesting. If I were brand new to ILI, and I am… [laughter] … what would you want me to know about ultrasonic tools?
Marc: Ultrasonic tools are a very good tool to capture information with respect to corrosion and cracking with great confidence. The tools, themselves, of course, require a medium to run in, a liquid medium to run in. Therefore, it’s obviously much more difficult for a gas pipeline to use the tools. Though, not totally out of questions in some circumstances.
I’m quite familiar with gas lines who have run them in water. The information gathered from the ultrasonic tools, again, is quite reliable in most instances.
Russel: Is it more expensive to run an ultrasonic tool versus an MFL?
Marc: Yes, it typically has been. There are not as many vendors that provide that service, but it also has been a more intense review for the analysts to describe the anomalies and to describe size and identify the various anomalies within the ultrasonic inspection. Yes, it is generally more expensive than MFL technology.
Russel: As a practice, I might run MFL more frequently and if I knew or thought I had some features where I needed more detailed analysis, I might come back with an ultrasonic?
Russel: I, likely, would not use ultrasonic as my primary tool? Is that a fair statement?
Marc: Yes. There could be, also, consideration given to defect geometry, which might affect the confidence for magnetic flux leakage or vice versa. Not all corrosion is the same between pipelines. It just depends on the threats and their formation in a particular pipeline.
Russel: Interesting. I guess what this begins to raise, and we probably ought to add this to the conversation is, if I’m managing an inline inspection program and I’m using multiple types of tools and the vendors are all doing their own proprietary analytics, how do I begin to combine this information and compare, maybe what I got from an MFL with vendor one, and an ultrasonic with vendor two?
How do I look at that stuff and compare it?
Marc: It’s not uncommon that operators are using different vendors for different tool runs. There is software available, of course — developed in-house by operators or can be purchased externally — that will combine these inspection informations and enable matching of anomalies, run over run.
If you are wanting to look at the raw signal, that, then, becomes more difficult, unless you do it on a singular inspection basis using the vendor’s proprietary software.
Russel: It makes sense to me that the vendor tools software would be proprietary because I would imagine that the analysis they’re doing with their tool is very closely tied to the types and the specific implementation of their instrumentation.
Marc: That’s right.
Russel: It makes sense that the vendors would do that with their own proprietary technology but there is this need for integration.
Marc: There is. It can either be strictly based on the size of the anomalies that have been provided by the vendors or it could get more in-depth if you are actually the operator, if the operator sticks to a single vendor. That would allow for a signal to signal comparison over various inspections.
Russel: I now know more about ultrasonics than I did before, so that’s a good thing. Hopefully, the listeners feel the same way. We’re going to be coming back next week and we’re going to talk about another type of inline inspection technology.
Marc, thanks for joining us. We look forward to having you back next week.
Marc: Thank you again, Russel. I hope you’re feeling better.
Russel: You, too. Thanks. Hope you enjoyed our conversation with Marc Lamontagne. I hope you’re running along with me and learning about inline inspection. I know I’m certainly learning a lot as I talk to Marc.
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Thanks again for listening. I’ll talk to you next week.
Transcription by CastingWords