By the PICA Corp Engineering Team  |  Updated June 2026  |  Est. reading time: 9 min

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What Is Electromagnetic Pipeline Inspection Technology?

Electromagnetic (EM) pipeline inspection uses alternating magnetic fields to measure pipe wall condition from inside the pipe — without direct contact with the wall and without removing the pipe from service. A transmitter coil generates a magnetic field. Receiver coils downstream detect how that field changes as it passes through the pipe wall. Variations in field strength, phase angle, and signal amplitude reveal metal loss, cracking, or broken wire that would be invisible to a camera or a manual tap test.

The principle has been in industrial use since the 1940s. Its application to buried water and wastewater infrastructure was developed more systematically beginning in the 1970s, largely through the work of Dave Russell, whose research led to the founding of Russell NDE Systems Inc. — the company behind PICA’s inspection tools. The result of that work is a family of EM methods, each suited to a different pipe wall configuration and defect type.

The distinction between those methods is not academic. Using the wrong EM technique for a given pipe type produces either misleading data or no usable data at all. This article covers the four primary methods used in modern pipeline condition assessment — MFL, conventional eddy current, RFT, and NFT — and explains which pipe types and failure modes each is built to handle.

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The Four Core Electromagnetic Methods

Magnetic Flux Leakage (MFL)

MFL is the most widely deployed EM method for oil and gas transmission pipelines. A high-strength permanent magnet saturates the pipe wall with a magnetic field. Where the wall is intact, the field stays within the metal. Where corrosion, pitting, or mechanical damage has thinned the wall, some of the field “leaks” outward. Sensors riding close to the pipe wall detect this leakage flux and translate it into a defect map.

MFL is fast and sensitive for its intended application: clean-bore, ferromagnetic steel pipelines with full pigging access and no internal liner. Modern high-resolution MFL tools can classify defect geometry with enough precision to drive integrity management decisions on gas transmission mains. The limitation is just as clear: MFL requires near-contact between the magnet array and the pipe wall, which means it cannot penetrate internal liners, cement mortar coatings, or concrete encasement. It also relies on magnetic saturation, which does not work in the same way for PCCP, bar-wrapped concrete cylinder pipe, or cast iron. For municipal water infrastructure, MFL’s role is narrow.

Conventional Eddy Current Testing

Conventional eddy current works at close range. An excitation coil induces circulating electrical currents in a conductive material. A sensing coil detects how those currents change in response to surface or near-surface anomalies. The technique is highly sensitive to small, shallow defects — which makes it well-suited for aerospace heat exchangers, stainless steel tubing, and above-grade non-ferromagnetic metal structures.

For buried pipelines, conventional eddy current runs into hard limits. The field is confined to the immediate area around the coil, giving it minimal penetration depth in thick-walled or complex-wall pipe. Ferromagnetic steel is particularly problematic: the high magnetic permeability of the material overwhelms the near-field signal. Conventional eddy current cannot inspect through liners or coatings, and it cannot characterize internal and external wall loss simultaneously. In buried infrastructure programs, it is most commonly used for spot inspections at excavated locations, corrosion under insulation (CUI) screening using the Bracelet Probe, and above-grade structural components where direct access is available.

Remote Field Technology (RFT)

Remote Field Technology was developed specifically for buried, lined, and complex-wall pipelines. Its physics differs fundamentally from MFL and conventional eddy current. An RFT transmitter coil generates an alternating magnetic field that travels outward through the pipe wall, propagates along the outside of the pipe, and re-enters the pipe wall further downstream — arriving at the receiver in what is called the “remote field zone.” Because the signal has passed through the pipe wall twice, the receiver has equal sensitivity to defects at the inner surface and the outer surface simultaneously.

This through-transmission characteristic is what makes RFT the standard method for PCCP and bar-wrapped concrete cylinder pipe inspection. In those pipe types, deterioration can originate from either direction: corrosive fluid attacking the steel cylinder from inside if the liner cracks, or groundwater attacking from outside. A method that favors one wall surface will miss half the possible failure pathways. RFT sees both.

RFT also works through internal liners, cement mortar coatings, scale, and epoxy — without requiring cleaning to bare metal. This matters for aged water mains where liners developed over decades are protecting the pipe from further corrosion; removing them for inspection would destroy the protection being assessed. PICA’s RFT tools cover pipe diameters from 2 inches to 96 inches, using different configurations for in-service deployments (pipes up to 36 inches, no dewatering required) and out-of-service programs (36 to 96 inches, using EMIT and RAFT platforms assembled inside the pipe).

Near-Field Technology (NFT)

Near-Field Technology uses transformer coupling — inducing current directly in the prestressing wire tendon wrapped around a concrete pressure pipe. When a wire breaks, the coupling signal at that location changes measurably. NFT accurately detects and quantifies five or more adjacent broken prestressing wires or bars, making it a reliable broken-wire counter for PCCP and bar-wrapped pipe programs.

The distinction between NFT and RFT comes down to scope. NFT detects broken wires or broken bars. It does not measure cylinder wall thickness and cannot characterize steel cylinder condition. For PCCP carrying standard fresh water, NFT wire break counts can serve as an integrity indicator. But for bar-wrapped pipe — where the steel cylinder plays a more critical structural role than in standard PCCP — or for pipelines carrying corrosive fluids where cylinder corrosion can progress before wire breaks appear, NFT alone is insufficient. RFT is preferred when available; NFT is deployed as a fallback when RFT cannot be accessed for a given pipe configuration. PICA’s NFT tools cover pipes from 16 inches to 136 inches in diameter. A deeper comparison of PICA’s NFT and RFT inspection tools covers the deployment scenarios and output differences in detail.

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Matching the Electromagnetic Method to the Pipe Type

The right EM method for any pipeline inspection program follows directly from the pipe wall geometry. Specifically: what does the signal need to penetrate, what is it trying to detect, and where are defects most likely to originate?

For clean-bore ferromagnetic steel in oil and gas (natural gas transmission, crude oil trunk lines), MFL is the standard. It is fast, well-supported by regulatory precedent, and well-suited to the pipe types and operating environments where it was designed to work. For cast iron and ductile iron water mains, RFT is the right choice: it measures continuous wall thickness through scale and cement mortar lining, detecting graphitic corrosion and pitting that MFL would miss entirely. PICA’s HydraSnake is built specifically for 6-inch and 8-inch cast iron and ductile iron mains, deploying through a fire hydrant with no excavation required.

For PCCP and bar-wrapped concrete cylinder pipe, RFT is the preferred method because it measures wire breaks, cylinder wall loss, and loss of preload simultaneously — the only EM method that captures all three PCCP deterioration mechanisms in a single pass. NFT is deployed when RFT cannot be accessed for a given pipe size or access configuration, providing wire break count as a secondary output. Across all pipe types, PICA’s full range of pipe inspection applications is organized by material and failure mode, so the method selection starts with what the pipe is made of and what is likely to be killing it.

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What Electromagnetic Inspection Cannot Detect

EM methods are not a complete picture on their own. RFT requires a steel element in the pipe wall — it cannot inspect pure plastic or asbestos cement pipe without metallic reinforcement. MFL cannot penetrate liners or coatings. NFT detects wire breaks but not wall thickness, and cannot determine whether breaks resulted from corrosion or hydrogen embrittlement. None of the EM methods reveal internal surface condition visible by camera: joint offset, liner cracking, deposits, and physical damage to the bore.

This is why EM inspection is most useful when combined with CCTV and laser/lidar profiling where the application warrants it. A pipe segment showing EM wall loss anomalies alongside CCTV evidence of liner damage carries a different risk profile than one where the liner is intact. The TRWD case study documents how this combined approach changed rehabilitation decisions on a large PCCP transmission main in Texas.

Acoustic pre-screening rounds out the picture for leak and gas pocket detection in pressurized mains — tasks that EM methods do not address. PICA’s Navigator acoustic sphere covers this layer before EM inspection is deployed, identifying priority segments and flagging anomalies that guide where to focus the more detailed EM program.

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Why Using a Single EM Method Is Never Enough

The history of pipeline failures includes many cases where a single-method inspection program gave operators false confidence — either because the EM method in use was the wrong one for the pipe type, or because it addressed one failure mode while a different one was running in parallel.

For PCCP, the clearest example is the liner-crack pathway to cylinder corrosion. A program relying solely on NFT wire break counts will not detect cylinder corrosion that has progressed ahead of wire break development in a pipe segment carrying corrosive fluid. A program using RFT detects both. For cast iron mains, graphitic corrosion can leave a pipe looking structurally intact to a visual inspection while wall thickness has been reduced by half. MFL would miss this on a cement-lined main; RFT reports it directly.

PICA’s approach to water main inspection programs is built around selecting the EM method — or combination of methods — based on pipe material, age, operating conditions, and what the client needs to know to make a confident capital decision. For smaller-diameter in-service applications, PICA’s SeeSnake & Chimera RFT tools bring high-resolution electromagnetic inspection to pipes that previously had no viable in-line option. The goal across all programs is the same: the right data at the right resolution, collected without unnecessary service disruption.

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Frequently Asked Questions

What is electromagnetic pipeline inspection technology?

Electromagnetic pipeline inspection uses alternating magnetic fields to measure pipe wall condition from inside the pipe without direct contact or excavation. A transmitter coil generates a magnetic field; receiver coils detect changes in that field caused by wall loss, wire breaks, or corrosion. The four main methods are MFL, conventional eddy current, Remote Field Technology (RFT), and Near-Field Technology (NFT). Each differs in its underlying physics and is suited to a specific pipe wall configuration and defect type.

Which pipe types can be inspected using electromagnetic methods?

The range is broad but method-dependent. RFT inspects cast iron, ductile iron, steel, PCCP, and bar-wrapped concrete cylinder pipe. NFT inspects PCCP, bar-wrapped, and reinforced concrete cylinder pipe for wire and bar breaks only — it requires a prestressing wire or bar to couple to. MFL is suited to clean-bore ferromagnetic steel pipelines. Conventional eddy current is primarily used for non-ferromagnetic metals and above-grade applications. Pure plastic and asbestos cement pipe without metallic reinforcement cannot be inspected electromagnetically.

When is MFL preferred over RFT for pipeline inspection?

MFL is preferred for clean-bore ferromagnetic steel pipelines — particularly oil and gas transmission lines where the pipe has no internal liner, full pigging infrastructure exists, and inspection speed per mile is a program priority. For water and wastewater pipes that are internally lined, cement-mortar coated, or built with concrete encasement (PCCP, bar-wrapped), RFT is the appropriate method. MFL cannot penetrate these wall configurations, so applying it to lined municipal pipe produces unreliable results.

Can electromagnetic inspection detect PCCP prestressing wire breaks?

Yes. Both RFT and NFT detect broken prestressing wires in PCCP. RFT is the more complete method: it measures wire breaks, steel cylinder wall thickness, and loss of preload in a single tool deployment — covering all three primary PCCP deterioration mechanisms. NFT detects five or more adjacent broken wires and is used as a fallback when RFT tools cannot be deployed for a given pipe configuration. For PCCP pipelines carrying corrosive fluids, cylinder condition assessment is the priority and RFT is required, not NFT alone.

How accurate is electromagnetic pipeline inspection?

Accuracy depends on the method, the pipe type, and defect size. PICA’s RFT tools have been validated through independent blind testing on AWWA C303 bar-wrapped pipe — controlled tests where operators have no prior knowledge of defect locations. Published results from Water Research Foundation verification programs and independent AWWA testing show detection rates for significant wall loss and wire breaks exceeding 90%. Small, isolated defects below a minimum threshold size have lower sensitivity in all EM methods, which is one reason multi-method programs produce more complete condition data than any single technique.

Does electromagnetic pipeline inspection require taking the pipe out of service?

Not always. PICA’s in-service RFT tools — including the HydraSnake for 6-inch and 8-inch water mains and the SeeSnake and Chimera platforms for pipes up to 36 inches — operate in live, pressurized pipelines. Flow must be reduced to manage tool speed in the 5 to 20 feet per minute range, but full isolation and dewatering are not required. For pipes 36 inches and larger, out-of-service inspection using EMIT or RAFT platforms is required. In some cases, in-service acoustic pre-screening with the Navigator sphere identifies which segments warrant the more disruptive out-of-service EM program.

How much does electromagnetic pipeline inspection cost?

Cost varies by pipe diameter, linear footage, tool selection, access complexity, and mobilization distance. For large-diameter PCCP and concrete pressure pipe programs, combined electromagnetic NDT typically runs $100,000 to $200,000 or more per mile — a range that reflects the difference between a straightforward 36-inch single-access run and a complex 96-inch EMIT deployment with long mobilization. Smaller-diameter in-service programs using HydraSnake or SeeSnake cost considerably less per mile. The comparison that matters: EM inspection program costs are typically 10 to 50 times less than the repair cost of an unplanned failure on the same segment.