Identifying Rectifier Impacts on CP Systems: Simplifying Rectifier Interference Studies - Virtual Brew 07/17/25

Discover insights from Cole Finney, Virtual Brew Product Manager, on how rectifier interference can impact your cathodic protection (CP) systems.

✅ Tailored for corrosion technicians and engineers, learn best practices for identifying interference sources.

✅ Simplify rectifier interference studies using MicroMax Portable Current Interrupters and Bullhorn Remote Monitoring Units.

✅ Save time during setup, effectively analyze results, and develop actionable plans.

Transcript

Introduction and Agenda

[Presenter]
We have a lot of content today, so I’m going to try my best to squeeze as much as I can into our 20 minutes. I wanted to talk about how you can identify impacts to your CP system through interference studies, utilizing our products, as well as some basic best practices across the board.

Brief agenda: I’ll give a brief introduction to influence and interference studies as a whole, then we’ll go through some methods and best practices for performing INI studies — I’ll bounce around between “INI” and “influence and interference” today, since INI rolls off the tongue a bit better. I also have a real-world example — we performed a study several years ago, so I’ll show everything in action — and then some conclusions, moving into questions and answers.

Influence and Interference Studies: Overview

I’d be curious to know how many people in the audience are already familiar with influence and interference studies. This is a pretty common topic these days — it’s become more common, especially with crowded corridors, less land to lay pipelines, and more requirements to move product. There are more systems inside crowded corridors, and you’re having to share systems, which sometimes gets challenging.

A lot of people say influence and interference studies keep them in the same wheelhouse, and they’re the same thing — technically, yes, but they’re also technically different.

Influence Study vs. Interference Study

These are really critical studies that operators use to determine the level of interference or influence, but they are different. An influence study is focused on the extent that a specific cathodic protection system impacts a structure or the area surrounding it — so this is much more focused on your CP system, maybe a specific rectifier in your system, or a galvanic anode, and how that’s influencing the CP on your system. An interference study is more dedicated to actually finding stray currents, or focusing on other sources of electrical input that could disrupt your cathodic protection.

Example Waveform: Influence Study

Here’s an example on the influence study side — a waveform from our FDC application, a normal three-on, one-off interruption cycle. This pipeline has a Dairyland PCR on it, so you can see at the bottom of the waveform, there’s some slight influence on your off whenever you perform an on/off study.

Key points for what goes into an influence study: it’s focused on specific system impacts to your CP system — things like your decouplers, your anodes, potentially bonds, and your own rectifiers, and whether there are any power sources on your line affecting your own compliance. This is super helpful because engineers use it to understand the level of protection provided by your CP system — it’s performed alongside close interval surveys, as well as periodic and annual surveys. It’s a good look at how your assets and power sources are interfering or influencing your CP, and it’s also helpful for identifying where you might need to make adjustments if your CP isn’t adequate in a certain area because of your own assets.

Interference Study: External Sources

An interference study is much more focused on finding external sources of interference — things like a high-voltage AC line, or another operator’s rectifier, or other items that could affect your CP system. Here’s a waveform from our field data collector application, affected by a high-voltage AC line — a similar three-on, one-off, but you’ll see the waveform is a lot less crisp than the one from the influence study example.

Why Perform an INI Study

I include a NACE standard reference — this is probably a newer version of that study than the one I have on hand. The reason these studies are performed isn’t just that interference can cause accelerated corrosion at a site — it’s also best practice and standard to identify and mitigate interference. If you’re known to have interference, whether from your system or another system, you should know where it is and how to mitigate it — otherwise, it could be auditable.

Common Sources of Influence vs. Interference

In an influence study, you’re really looking at potentially interruptible items that influence your CP system — your own rectifiers on your own pipeline, or a neighboring pipeline from a foreign operator if you have shared systems, or bonds. These influence your CP system, and they’re also usually interruptible — things within our control that we can look at to understand the influence on our CP system.

With an interference study, these are things that are a bit more difficult to interrupt and identify — dynamic stray current, like a DC transit line if your pipeline is next to a DC transit system, or if you’re near a mine or a welding shop. Most commonly, and coming up more and more frequently in our industry, high-voltage AC power lines — these corridors are pretty crowded, there’s not a lot of new land to lay pipeline, so we’re sharing a lot of these corridors with power operators, and whatever they do interferes with what our CP systems look like. And lastly, for those in the far north or far south of the globe, telluric currents are also a very common source of interference that has to be found — usually through an INI study.

Regulatory Compliance

The biggest reason to perform one of these surveys is to ensure you’re still in regulatory compliance — you may have unexplained CP system issues or corrosion in an area you’re not paying attention to, and if you go into an audit, you’re going to be asked about it, and if you don’t have anything to back it up, you’re going to be in a lot of trouble.

Here’s an example: my test station reads -910 volts when my CP system is on — I’m within PHMSA criteria, I’m within compliance. But I’m not aware that there’s a foreign rectifier from a neighboring CP system affecting my pipeline, providing me 200 volts of extra current I wasn’t aware of. So whenever that foreign operator interrupts their pipeline, my on reading is actually -710 volts — I’m actually not in compliance, I just happened to be in compliance when I looked at my asset. This is a very common thing that happens, especially as we’ve done more research into understanding interference and how these systems next to each other actually influence each other.

Goals of an INI Survey

The goals of performing an INI survey: you want to understand where the potential influence or interference sources are, and you want to make sure you have a plan for how to mitigate those sources. If you’ve found them through testing and know where they are, you’ll be able to make mitigations that protect your assets longer, rather than allowing them to perform as expected and slowly start corroding in an accelerated way.

The other important outcome is documentation. If you have documentation that you’ve performed this study, identified interference, and mitigated it, that will go over well if you’re ever audited, or if you want to maintain your compliance ecosystem — especially in PCS, where it’s all documented and you have an auditable, traceable record that can be reviewed with others.

Testing Process: Identifying an Area to Study

There’s a pretty solid testing process for performing an INI survey. It may seem daunting — where do I even start? — but it’s pretty manageable once it’s laid out as a simple flowchart.

It starts with identifying an area you want to study — usually this means you ran a pig and found a large amount of metal loss in a certain area, or you performed your periodic and annual survey and your measurements were off by several hundred millivolts, outside of what you were expecting or outside of criteria. You may also want to ask: how close am I to my neighbors, do I have a shared system, am I bonded to somebody I wasn’t aware of, or wasn’t documented well, or just forgot about? And finally: is my environment kind of volatile — is my soil resistivity changing every season, is my pH changing, was there a landslide, an inclement weather event? There’s a lot that goes into identifying where you want to start.

Coordinating with Neighbors

Once you find your area, everyone’s favorite next step is coordinating with other people. A really successful INI survey cannot be completed without collaborating and contacting your neighbors — especially with a shared corridor, you’re going to want to call your fellow operator in that corridor, or even your own technicians if you have multiple in an area, and identify the pipelines, facilities, and other operators you’ll need to bring into the survey. After talking with them, you’ll want an agreement between everyone to actually begin the test — that’s probably the most important piece of this. You can have all the technology in the world, but if you don’t have buy-in from your other operator, your INI survey isn’t going to be successful.

Tools and Equipment for INI Surveys

You’ll also want to make sure you have the right tools and equipment ready. Three specific items: portable current interrupters — I’ll call out the Micromax specifically, a very common use case for our Micromax current interrupters, more on that later. Remote monitoring units — if you have access to Bullhorn remote monitors, this will vastly speed up your INI survey. And finally, a data collection device capable of capturing waveforms — in the photo here, Lon Duke has an Allegro field computer, but we also use the PCS field data collector tablet, a very common way to capture a waveform like this.

Staggered Interruption Cycles and Interference Mode

It all comes together when you coordinate with your neighbors and use Bullhorn remote monitors and Micromax current interrupters — you coordinate and begin an interruption cycle, a staggered interruption cycle, to begin capturing your INI data. You’ll identify the various current sources — rectifiers, in this case — that you want to interrupt to find out how they’re influencing each other. You’ll begin interrupting these one by one, in targeted groups, all at once, and then in staggering mode from there.
All of the Micromax and Bullhorn products include a mode called interference mode, which allows them to sync with each other and perform this type of staggered interruption cycle.

Manual Interruption Testing vs. Group Synced Interruption

Before we get into more of the tools, let’s talk about manual interruption testing versus group synced interruption. Group synced interruption using Bullhorn and Micromax is now probably the most common way to perform an INI survey. Manual interruption testing means your best tool is a walkie-talkie or a cell phone — you’re at one rectifier, cycling it manually at the cycle you want, while another technician is at a test station looking at his measurements, trying to understand where the interference may be. That’s probably not nearly as common anymore, especially with Micromax, Bullhorn, and other tools being so common and available.
Group synced interruption is definitely the way to go — you’re able to synchronize and interrupt almost all of your rectifiers in one go, then gather test point data very easily at your site with PCS field data collector. It makes gathering that data way more reliable and manageable than doing it manually on a piece of paper.

Setting Up the Interruption Cycle

You’ll want to make sure you set your interruption cycle in that isolated, staggered pattern — using Bullhorn remote monitors and Micromax current interrupters, you’ll set this up in interference mode. Here’s an example — an Excel spreadsheet showing exactly how these units are set up, alongside an animation of how the interruption cycle works. All of your units start in the off mode, then go on, and after that — say you’re doing a three-on, one-and-a-half-off cycle, like this one — you stagger each rectifier throughout the interruption cycle. This is for a total cycle of a minute.

Synchronized Waveform Capture

I want to talk about Bullhorn and why it’s important to use a GPS-synchronized tool to capture your influence and interference survey data. When you’re not synced, your data is going to be bad — that’s the blunt way to look at it. Here’s an example, in PCS field data collector, of capturing a waveform on a test point that had interrupters set on it for two separate cycles that weren’t synced with each other — a three-on, one-off on one asset, and a second interrupter set on the same schedule but not synced. You get a really wacky waveform, and you’re not going to get accurate off or on data. If you’re trying to perform an INI survey like this, you might as well stop — you’re not going to get good data out of it.

That’s really where Bullhorn and Micromax come in handy, since they both have a mode called interference mode, which allows you to coordinate staggered interruption with up to 99 other units — other rectifiers and interrupters — coordinating using the GPS clock and GPS sync. I’d planned to show how easy that is in Bullhorn Web, but for the sake of time I may hold off — I’ll bring it up at the end if we have time.

Capturing Waveforms with FDC and Survey Manager

Lastly, on having a tool to collect the data — you’ll want to use a DVM or tool with a five-minute window to capture a waveform. I say FDC, because we do this out of the box in our DVM application — as long as you set that window to five minutes, you’re able to capture a waveform with timestamps over the entire five minutes. After capturing that waveform, you can take that wave print and upload it into Survey Manager for easy analysis. Using this ecosystem of tools, you’re able to digitize this data, capture it remotely, and send it into our software to be analyzed — it’s a whole lot easier than porting all this data into an Excel file and turning that into a pivot graph to try to analyze it that way.

Real-World Example: 11 Rectifiers, 3 Test Stations

For the sake of time, I’ll speed through this, but here’s a real-world example — taking everything we’ve talked about, using specific tools to set up an INI survey correctly, capturing that data with the PCS field data collector application, and putting it into real life.

In this case, we had a single pipeline with 11 sources of impressed current — 11 rectifiers — and three separate test stations. Using Bullhorn remote monitors and Micromax current interrupters, we were able to set up all 11 assets to be interrupted in just under an hour, and perform our interrupted survey at a three-on cycle across all 11 assets — the same interruption cycle from the Excel sheet shown earlier.

Following our process for an INI survey: we had all of our assets off at the beginning, then all of them on for 9 seconds, and began our staggered interruption cycle, where cycle one is the first power source interrupted out of 11, cycle two the second, and so on through the third and fourth. In the waveform we captured, once we labeled which assets were affecting which, you could see which areas had the most IR drop and voltage change based on interruption — this was at the second test station.

At our third test station, this is the exact same cycle, but you can see where that voltage impact shows up differently — that helps you identify which power source is actually affecting your CP system. You’ll see a trend on cycle two — it wasn’t as bad at test station two, but at test station three it increased dramatically. So you can tell: my third rectifier is affecting test station three, that area, however many miles away, more than others — so I probably need to adjust that rectifier, adjust that CP system.

Key Takeaways

This was all done in an hour, by one technician — versus in the past, having to get multiple technicians together, which could easily take a full day of setting up portable interrupters and doing this manually. Using Bullhorn remote monitors and other tools to do this within an hour is pretty amazing when you think about it.

We’re also able to easily identify sources of influence using field data collector and Survey Manager — uploading that data into our cloud environment and overlaying it, understanding very easily which asset and which power source is affecting you where. It’s a whole lot easier to identify how you’re being influenced and where you can make mitigations, versus having a notepad or an Excel sheet and trying to piece together how everything works.