Pipeliners Podcast


The Pipeliners Podcast is kicking off a new series on inline inspection (ILI) with Marc Lamontagne of the Lamontagne Pipeline Assessment Corporation.

Host Russel Treat and Mr. Lamontagne begin the series discussing magnetic flux leakage (MFL) technology. In this episode, you will learn about the value of MFL as the workhorse of inline inspection, how MFL can help discover metal loss, and the limitations of this technology.

Stay tuned for more episodes in this inline inspection series covering corrosion, cracks, deformation, and the data that is used in inline inspection.

Magnetic Flux Leakage 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.
  • Magnetic flux leakage (MFL) is a magnetic method of nondestructive testing that is used to detect corrosion and pitting in pipelines.
  • Ferrous metals contain iron, while non-ferrous metals do not contain iron, and are typically used in pipelines. Ferrous metals are also magnetic, allowing for MFL to use magnetism to inspect a pipeline.
  • NACE (National Association of Corrosion Engineers) or NACE International is a membership group whose stated goal is to “equip society to protect people, assets, and the environment from the adverse effects of corrosion.”
  • API 1163 is the industry standard for inline inspection systems qualification. The standard covers the use of inline inspection (ILI) systems for onshore and offshore gas and hazardous liquid pipelines.
  • The Pipeline Operators Forum (POF) brings together pipeline inspection and integrity engineers to establish good practices to improve the quality of pipeline integrity management. POF has released specifications and requirements for inline inspection of pipelines through a set of documents.
  • Axial and circumferential magnetic tools evaluate metal loss going down a pipeline. Axial refers to when the flux runs along the pipeline and circumferential refers to the flux running around the pipe.
  • Helically-oriented tools measure metal loss in the shape of a helix or spiral.
  • The Caliper tool uses geometry for inspection. The tool runs sensors along the wall of a pipeline to continuously measures the diameter and report back the data.

Magnetic Flux Leakage for Inline Inspection: Full Episode Transcript

Russel Treat:  Welcome to the “Pipeliners Podcast,” episode 29.

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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.

Russel:  Thanks for listening to the Pipeliners Podcast. We appreciate you taking the time. To show that appreciation, we’re giving away a customized YETI tumbler to one listener each episode. This week, our winner is Hans Sonneborn with Energy Transfer.

Congratulations, Hans. Your YETI is on it’s way. To learn how you can win this signature prize pack, stick around to the end of the episode. This week, we’re going to be starting another series on inline inspection with Marc Lamontagne. Without further ado, let’s welcome Marc.

Marc Lamontagne:  Thank you, Russel. It’s great to be back.

Russel:  I appreciate you volunteering to do a whole series with us on inline inspection. You might be dragging me along in this topic. It’s not something that I know a whole lot about. I’m hoping that I can help others learn as I’m learning along the way.

Marc:  I hope I can help make the basics of each technology more understandable and give a good introduction.

Russel:  Great. For the listeners, what we’re going to do is we’re going to do a series of episodes. We’re going to talk about the various technologies used in ILI or inline inspection. We’re going to start out with magnetic flux leakage, generally referred to as MFL. Marc, why don’t you tell the listeners what is MFL?

Marc:  Magnetic flux leakage — as the name implies — has a magnetic field that is magnetic flux imparted into the steel pipe, such that the steel pipe wall thickness is saturated with the magnetic flux.

If you can imagine the current going from North to South Poles filling the wall thickness, any deviation from that wall thickness, such as metal loss, will have a hole, therefore, some of the flux will escape. That is what is measured by these magnetic flux leakage tools to obtain the metal loss sizing.

Russel:  I’m an instrument guy, grew up around that stuff, so I’m trying to visualize this in my mind. I’m remembering RadioShack experiments I did as a kid. What I’m thinking about is if I have a piece of metal, and that metal has a very consistent thickness, that field is going to have one kind of signal.

Marc:  That’s correct.

Russel:  If it doesn’t, if that thickness is varying, that field’s going to have a different kind of signal.

Marc:  That’s right, exactly. These tools have permanent magnets that are quite powerful. As the tool moves along, it has to induce a large amount of magnetic flux. As you say, a more stable flux is important for the measurement of the metal loss.

Russel:  Okay. How long has this technology been around for pipelining?

Marc:  Well, the first MFL tools were developed in the early ’60s. These were low resolution tools that generally had, I guess, three degrees of metal loss, such as low, medium, and high, for the pipeliners to respond to with respect to repairs. Of course, the development and research into tools has greatly increased their resolutions and effectiveness over the years.

Russel:  I guess, like anything else, as computers have gotten smaller, lower power, and containing more memory, I can capture more signal. By capturing more signal, I can do more with it.

Marc:  Yes. More refined sensors, as well, which has increased the information dramatically.

Russel:  If I’m imparting this magnetic flux signal into the metal, does it have any negative impact on the metal itself?

Marc:  No. It does not. The magnetic flux that is imparted magnetizes the pipe, but over a short period of time, the pipe loses magnetization. There may be an issue if welding is to be taken place within a short period of time. As I mentioned, the magnetism dissipates over a short period of time.

Russel:  How would the pipe being magnetized affect the welding?

Marc:  The welding process is electrical, as well as the ferrous material being put into the void that is being welded. Magnetism with the iron going in could create an issue — and it has if it’s highly-magnetized. As I say, this generally is not an issue because repair welds, etc. do not happen, generally, that close to an inline inspection.

Russel:  I don’t know. It’s interesting, Marc, we’re having this conversation. I tend to think visually as I’m trying to learn something new. I’m reminded of the little game. I had some kind of game when I was a kid that had magnets and iron shavings.

You could play with the magnets and move the iron shavings around. You can see the magnetic fields by how the iron shavings responded to the magnets. It’s interesting. It’s like, “Huh, who knew? Who knew that I could have continued playing with magnets and made a whole career out of that.”

Marc:  That’s right. Would that have been better?


Russel:  Well, no. I’m not complaining. I’m just saying, “Who knew?” Right?


Marc:  Very good.

Russel:  That’s the thing about being a nerd when you’re a kid. You get curious about how things work. Then that takes you in a particular path.

Marc:  Right, exactly.

Russel:  I probably ought to ask this question. The technology has been around since the ’60s. Obviously, I’m sure that technology has evolved a lot. I mean if you think about how much computers evolved in that same time frame, I’m sure this technology has moved a similar amount. What are the standards involved in this? How has those standards evolved?

Marc:  The standards have really come around in more recent times just as the regulations have evolved. There are various standards. There’s a recommended practices from NACE. There’s API 1163 and Pipeline Operators Forum standards as well. They all delve into the inline inspection process to different degrees.

Some try to be an all-around standard such as API 1163 that looks at tool selection and right through the field data quality, etc. The POF standard better defines the definitions for metal loss in the respect of what you call various shapes and sizes of metal loss, whether it’d be axial grooving, general corrosion, etc.

Russel:  What are the strengths and limitations of MFL as it relates to inline inspection?

Marc:  MFL technology has really become the workhorse for inline inspection. It’s a very cost effective approach to information on metal loss for your pipeline. The recent advances within the last few years of sensors, as well as computing power, has dramatically increased this value to the operator.

The MFL tool itself is actually an indirect measurement of metal loss, such that the sizing of the anomaly is based on a flux leakage. It is not as direct as something like the ultrasonic tool, which we’ll get into in another episode, but still does provide very good estimates of the depth, length, and width of metal loss.

Russel:  I would assume that because this technology’s been around so long that it’s probably well understood in terms of how to apply it, which you’ll characterize as its strength.

One of the challenges in pipelining in general is that we are risk averse and for good reason. That makes it hard for us sometimes to adopt new technology and apply it. We tend to like the tools we’re most familiar with.

Marc:  Yes, that’s correct.

Russel:  It would seem to me that’s probably the case with MFL.

Marc:  Yes.

Russel:  What is MFL unable to do that’s important from a “managing the integrity of my pipes” standpoint?

Marc:  MFL is strictly for voids in the pipe such as metal loss. It cannot detect very tight cracks. Cracks with a certain opening may be able to be detected, but there needs to be a larger void.

Russel:  Yes. I guess the strength of the tool is it can identify missing metal. The limitation of the tool is that other features that are pipe weakness, but are not necessarily missing metal, it’s not going to pick up. What I’m thinking of is fatigue.

Marc:  Right. MFL tools can be oriented, axially or circumferentially. Generally, most of the cracking that is seen within pipelines runs axially or longitudinally down the pipe because of the pressure within the pipe.

There is a circumferential magnetic flux leakage tool, which is used to help define areas with cracking. Of course, these cracks need to have a sufficient opening to be able to be detected by MFL. Likewise, circumferentially oriented cracks may be found by an axially-oriented MFL with sufficient opening.

Russel:  Can you run on the same tool, axial and circumferential? Or would that with the field being generated conflict with one another?

Marc:  Well, they would be run as a separate sections in the tool. There are tools that are helically-oriented.

Russel:  Okay, you got to stop. You’re going to have to define helically for me.

Marc:  [laughs] Okay.


Russel:  I remember the last episode, the whole conversation about axial and circumferential and me having struggled getting circumferential right. Now, you’re throwing another one at me. It’s helical. You’re going to have to tell me what that is.

Marc:  Too early in the morning.

Russel:  [laughs] Yeah.

Marc:  As the word describes, sensors and magnets as well can be placed on a 45 degree angle. It’s not strictly axial or circumferential. It gives a response to a certain degree for either axially oriented features or circumferentially oriented features.

Russel:  All right, I got it. I can see that in my mind’s eye.

Marc:  There we go.

Russel:  I guess what I’m hearing in this is that one of the things to be aware of with MFL is the way that you generate the signal or the direction, maybe a better way to say it, that you’re generating the signal will indicate or better find different kinds of metal loss.

Marc:  Yes, that’s right.

Russel:  Orientation of the signal generation is going to find different orientations of metal loss.

Marc:  Yes, that’s correct. Having both technologies run through your pipeline might be of advantage. The shape of metal loss can greatly affect the magnetic flux leakage signal. When there is full wall thickness adjacent to a small metal loss area, the flux won’t necessarily resemble the full metal loss depth.

Russel:  Okay. All right.

Marc:  [laughs]

Russel:  I’m going to try to translate. [laughs]

Marc:  Yes, it’s Okay.

Russel:  Again, what I’m thinking about, if I have a crack, cracks got metal loss. The thing about a crack versus a corrosion loss is that crack is metal loss with full thickness on either side.

Marc:  Yes.

Russel:  My ability to see that is going to be dependent upon the direction of signal versus the direction of the crack. If you think about a crack and I’m looking at the bottom of the crack straight up, that’s going to look a lot different than if I’m looking across the crack.

Marc:  Yes.

Russel:  Okay. Got It. That makes perfect sense.

Marc:  That’s back to our analogy from the first episode of water running down a river and hitting a rock per se. It’s diversion of the water around the rock, where a crack would not disturb the signal, a larger void would.

Russel:  Yeah. Again, if you take the water running analogy, if I’ve got a piece of plywood and I set the piece of plywood so it’s inline with the flow of the river, the river is just going to flow right around it and disturb it almost not at all. But if I take and turn it, and it’s perpendicular to the river, then it’s going to make a major disturbance.

Marc:  That’s right.

Russel:  That’s really what we’re talking about in the way the signal works.

Marc:  Yes, that’s right.

Russel:  I love simplifying visuals. I want to help you with this, Marc. I want to help you with simplifying visuals.

Marc:  Perfect.

Russel:  That’s my role and mission through these episodes.


Marc:  And beyond.

Russel:  That’s what’s necessary for me to get it into my brain.

Marc:  Yeah, for these episodes and beyond because I have your phone number now. [laughs]

Russel:  Oh, goodness gracious. We’re in trouble. We talked before, in the first episode, about the need to use multiple technologies to find different features. I would think that MFL is going to be best at finding things like corrosion, where I have loss of wall thickness, any place where I’ve been scouring or anything like that.

It would be good at finding those kinds of features, but it’s going to be less effective at cracks depending on their orientation. I guess you really don’t get any indication of geometry off of the MFL.

Marc:  MFL tools can detect some geometry features. Geometry features are not as well defined by an MFL tool as they would be with a particular Caliper tool. The sensors do pick that up and you do see some deviation because the sensors ride along the wall. They do provide the difference in flux field when there are deformations.

Russel:  Once I’ve run one of these MFL tools, I download the data and then I’ve got to do my analysis of the data. How is that done? What is that mechanism like?

Marc:  Each vendor has their proprietary software. They download these files which can be very large, tens or hundreds of gigabytes, depending on length and diameter of pipeline as well as metal loss involved.

The process of analyzing these files has become fairly automated. The software will go through each of these inspections, automatically box the length and width of the features, and generate a depth based on algorithms created through pole tests, which are done when the tools are made or proved up before a run.

There’s automatic sizing that is depth, length, and width given to anomalies that the MFL finds. The more severe anomalies found are then manually analyzed to ensure that the sizing has been done appropriately.

Russel:  For all of those listeners that hear the buzzwords about data analytics, people, who have been doing inline inspection, have been doing data analytics for a long time. That’s basically what the process is?

I’m taking a signal. I’m using an algorithm to evaluate the signal. I’m identifying anomalies in the signal. Beyond that, I’m having an expert manually evaluate. I would assume that there’s probably a lot of work going on around automating the analysis of the anomalies.

Marc:  There is. It is important that the tool vendors have their pole test and algorithms created succinctly, so that they can better define these automatically created boxing of the anomalies.

Russel:  I’m hearing you use the word “boxing” and I guess that’s in the…I start visualizing a drawing of the pipeline and a box would be…you’re drawing a set of lines around the feature, so that you know physically where it’s located on the pipe.

Marc:  Yes. That’s right. It defines its length and width, and its orientation on the pipeline as well.

Russel:  Right, and where it is by mile marker, whatever the mechanism is for locating that.

Marc:  Yes. Flux leakage and the other tool types, you can easily see where each girth weld is, so you know each specific joint, the anomalies in there, the related position with respect to each girth weld and the clock type orientation. Orientations are defined like the dial of a clock. Looking downstream from 12:00 to 12:00.

Russel:  Right, 12 o’clock being the top and 6 o’clock being the bottom.

Marc:  That’s correct.

Russel:  Interesting. If somebody is new to ILI, what would you want them to know about the MFL tool?

Marc:  Magnetic flux leakage is the workhorse of the industry and has been well-defined over the years. It is cost effective as means to find corrosion and other metal loss for the integrity of your pipeline. It is the first go-to technology for metal loss inspection.

Russel:  Would it be fair to say that MFL is what you run first, and based on the result, you might determine what other kinds of tools you might need to run?

Marc:  Yes. What is typically done is to look at the history of the pipeline, the vintage, the coding, and define threats that could exist in your pipeline. Metal loss is a ubiquitous threat. The MFL is a standard for inspection in the pipeline.

Russel:  Cool. The thing I like to do is one of my key three takeaways. This will be a bit more challenging for me in this domain because this is something I’m learning as the listeners are learning.

Three things I would take away. One would be that MFL, magnetic flux is a workhorse. It’s been around a long time, and the technology is mature. By that I mean its use, its application, its analysis is well understood in the industry. That’s the first takeaway.

The second takeaway is that MFL is a great way to find metal loss in any kind of metal being largely underground. That’s a big deal. Lastly, that its limitations would be around finding features that didn’t present well as metal loss, things like cracking.

That’s what I would take away from this conversation. I feel I have a good understanding as a novice of magnetic flux. Next time somebody tells me they’re going to run an MFL tool, I’ll at least know what they’re talking about.


Marc:  Very good. Excellent.

Russel:  Marc, thanks for this. I’m looking forward to learning about the other kinds of tools as we move along through the process.

Marc:  Thank you, Russel. It’s always good to talk to you and I look forward to next time.

Russel:  All right. Thank you.

Marc:  Okay. Take care.

Russel:  I hope you enjoyed this week’s episode of the Pipeliners Podcast. I enjoyed the conversation with Marc. I’m learning about inline inspection and that’s a good thing. Just a reminder before you go, you should register to win our customized YETI tumbler branded with a cool Pipeliners Podcast logo. To win, visit pipelinerspodcast.com/win and enter yourself in the drawing.

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Russel:  If you have ideas, questions, or topics you’d be interested in, you can let us know by contacting us on the Contact Us page at pipelinerspodcast.com or you can reach out to me directly on LinkedIn. My profile name is Russel Treat. Thanks again for listening. I’ll talk to you next week.

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