By the PICA Corp Engineering Team  |  Updated June 2026  |  Est. reading time: 8 min

---

What Is Remote Field Testing?

Remote Field Testing is an electromagnetic, non-destructive inspection method that measures pipe wall thickness from inside a pipeline, with no direct contact with the pipe wall required. A specialized tool carries two coil sets: an exciter (transmitter) and a detector (receiver), spaced roughly 2 to 3 pipe diameters apart.

The exciter coil sends low-frequency alternating current into the pipe. The resulting electromagnetic flux travels radially outward through the pipe wall, propagates axially along the exterior surface, then re-enters the wall and reaches the detector coil downstream. Because the signal passes through the full pipe wall twice (once going out, once coming back), the method is called through-transmission.

Where the pipe wall has thinned from corrosion, erosion, or graphitization, the signal arrives at the detector with a measurable phase advance and higher amplitude. PICA analysts process those changes to produce a continuous wall thickness map along the full pipe run. The technique registers defects on both the internal (ID) and external (OD) surfaces with roughly equal sensitivity, which most short-range eddy current tools cannot match.

---

Why MFL and Ultrasonic Testing Fall Short on Complex Pipelines

Magnetic flux leakage (MFL) and ultrasonic testing (UT) are established NDT methods, but both have real limitations when the pipe wall is not a simple, clean metallic surface.

MFL works by saturating a ferromagnetic pipe with a strong magnetic field. Where the wall has lost metal, flux leaks outward and is detected by sensors riding against the pipe interior. The problem: MFL requires close magnetic contact with the pipe wall. Thick internal liners (HDPE, cement mortar, epoxy) block or distort the magnetic field before it reaches the steel. MFL tools also have limited inspection capabilities on non-ferromagnetic pipes, including PCCP and bar-wrapped concrete cylinder pipe. A lined steel transmission main is essentially uninspectable by MFL without first stripping the liner.

Ultrasonic testing in standard in-line form requires either direct contact between the probe and the pipe wall or a liquid coupling medium. Cement-lined, HDPE-lined, and heavily tuberculated pipes either block the UT signal or produce unreliable thickness readings.

RFT sidesteps both problems. Because the signal travels through the pipe wall rather than along its surface, internal liners do not block it. Over 100+ kilometers of HDPE-lined steel pipeline were successfully inspected in field trials and several projects over the last 20+ years, with consistent results through the liner and no liner removal required.

---

The Pipe Types RFT Can Inspect

PICA’s Advanced NDT service using Remote Field Technology covers five pipe material categories:

Cast iron and ductile iron. The most common materials in North American water distribution networks, many installed before 1970. RFT measures remaining wall thickness along the full run, detecting graphitic corrosion (where iron leaches out while a graphite shell stays intact, making the pipe look sound from the outside but structurally hollow), pitting, and erosion. For 6-inch and 8-inch cast iron and ductile iron water mains, PICA’s HydraSnake deploys via fire hydrant with no excavation required.

Steel pipelines with internal liners. Carbon steel lines with HDPE, epoxy, or cement mortar liners are common in both water infrastructure and industrial settings. RFT inspects through liners and coatings, detecting corrosion on both the ID and OD surfaces simultaneously, even where liner integrity is uncertain.

PCCP (Prestressed Concrete Cylinder Pipe). One of the most structurally demanding inspection targets in the water industry. PICA’s RFT tools detect all three PCCP deterioration mechanisms in a single deployment: broken prestressing wires, steel cylinder wall loss, and loss of pre-load on individual pipe segments. No other single method covers all three. For a deeper look at PCCP inspection, see the PCCP and CCP inspection overview.

Bar-wrapped concrete cylinder pipe (BWP/CCP). The steel cylinder plays a more critical structural role in bar-wrapped pipe than in standard PCCP, making wall thickness measurement essential rather than optional. RFT is the preferred method for bar-wrapped programs. Read more in PICA’s RFT for bar-wrapped pipeline inspection article.

For a complete overview of pipe types and service applications, see the service applications page.

---

What RFT Detects and How Sensitive It Is

PICA’s RFT tools capture the following in a single continuous inspection pass:

• Wall thickness reduction from internal corrosion, external corrosion, pitting, erosion, and graphitization, with equal sensitivity to both ID and OD defects although RFT signals cannot differentiate between ID and OD integrity issues, but does pick up both
• Cracks and local stress concentrators in metallic pipe walls
• Broken prestressing wires in PCCP or broken bars in bar-wrapped pipe
• Steel cylinder wall loss in PCCP and BWP
• Loss of pre-load on PCCP pipe segments: RFT can differentiate segments that have retained pre-load from those that have lost compression, which Near Field Testing (NFT) cannot do

Before inspection runs, PICA’s tools can be calibrated using reference specimens with known defect dimensions if there are sample pipes available. The company has also undergone independent blind verification testing on AWWA C303 bar-wrapped pipe, where the inspection crew had no prior knowledge of defect locations, confirming detection accuracy across a range of wall loss percentages and wire break densities. Results are validated by PICA analysts using specialized analysis software before the condition report is issued.

---

PICA’s RFT Tool Lineup

PICA operates several RFT tool variants matched to pipe diameter, material type, and operating conditions. Tool selection is part of the pre-inspection planning process.

HydraSnake is built for 6-inch and 8-inch cast iron and ductile iron water mains. It enters through a fire hydrant or tee adapter, operates with the main in service, and can navigate tees and short-radius elbows with no excavation required. Learn how the HydraSnake deploys in a live water main.

SeeSnake and Chimera (smaller diameter models) cover 2-inch to 36-inch pipe in both in-service and out-of-service configurations. These are the primary tools for smaller-diameter metallic and concrete pressure pipe programs. More on the platform at the SeeSnake inspection tools overview and the next-generation SeeSnake article.

EMIT covers 48-inch to 96-inch internally-lined AWWA C-301 and C-303 pipe or lined metallic pipe materials. It is assembled inside the pipe through standard maintenance hole access and operates as an autonomous, multi-channel, tethered tool. Out-of-service only.

RAFT handles 36-inch to 48-inch pipe via a collapsible design that inserts through manway-sized access ports for both concrete pressure pipes and lined metallic pipes. Also autonomous and tethered.

The full RFT service window runs 2 inches to 96 inches in diameter. A tool selection guide by pipe type is on the RFT technology service page.

---

RFT vs. NFT: When Each Method Applies

Near Field Testing (NFT) is PICA’s Standard NDT service, an electromagnetic method that detects five or more adjacent broken prestressing wires or bars in concrete pressure pipe. It is a useful tool for PCCP and bar-wrapped programs, but it has specific technical limits worth understanding before choosing a method.

NFT does not measure wall thickness of the cylinder. It cannot detect cylinder corrosion, and it cannot characterize loss of pre-load. It also cannot inspect metallic pipes with any reliability.

RFT covers all three PCCP deterioration mechanisms and works across both metallic and concrete pipe types. When RFT can be deployed, it is the preferred choice. NFT is deployed when RFT cannot be, for example in programs where isolated wire break counting is the specific objective.

Two situations make RFT particularly important rather than just preferred. First, bar-wrapped pipe: the steel cylinder is more structurally critical in BWP, so cylinder wall thickness data is necessary, not optional. Second, PCCP carrying corrosive fluids (salt water, brackish water, seawater): if an internal liner cracks, corrosive fluid can reach the steel cylinder and cause it to corrode before any wire breaks develop. RFT detects that cylinder corrosion. NFT does not.

For a detailed comparison of both technologies, see the NFT and RFT inspection tools article.

---

In-Service Inspection and Operational Requirements

For pipes under 36 inches, PICA’s RFT tools can operate while the pipeline stays in service. Utilities must reduce flow to keep tool travel speed in the 5–20 feet per minute range, but the line does not need to be isolated or dewatered. For transmission mains running continuous 24/7 service with no available outage window, this matters considerably.

For pipes at 36 inches and above, the pipeline must be taken out of service and dewatered before EMIT or RAFT deployment. PICA coordinates with utilities on dewatering sequences, prioritizes the most critical segments for each outage window, and runs a gauge pig before the inspection tool enters the line to check for restrictions.

PICA’s water main inspection services page covers pre-inspection support: access point preparation, site visit planning, flow management logistics, and post-inspection report delivery timelines.

---

Why Acoustic Monitoring Alone Misses Pre-Failure Deterioration

Some utilities rely on surface acoustic monitoring, pressure transient analysis, or break history to manage pipeline risk. These tools identify problems after structural deterioration is already advanced.

Acoustic leak detection finds where a pipe is leaking, not where it is weakening. A PCCP main with 30% of its prestressing wires broken and approaching the threshold for pressure-induced failure may show no acoustic signal until the day it ruptures. By then, a planned, lower-cost repair is no longer an option.

PICA’s Advanced NDT with RFT finds pre-failure deterioration: wall loss at 10–20% depth, wire break accumulation in a distress zone, cylinder corrosion behind an intact liner, while targeted repair or pipe segment replacement is still possible. The TRWD (Tarrant Regional Water District) case study is a real example of RFT finding significant PCCP deterioration before any surface indicators appeared. Read how that program was structured: how Remote Field Technology transformed PCCP pipeline inspection at TRWD.

For a full overview of how PICA approaches pipeline condition assessment, see the linked service page.

---

Frequently Asked Questions

What is PICA RFT inspection technology?

PICA’s Remote Field Testing (RFT) is an electromagnetic, non-destructive inspection method that measures pipe wall thickness from inside a pipeline with no direct contact with the pipe wall. The signal passes through the full pipe wall twice (through-transmission), giving equal sensitivity to internal and external defects. PICA uses RFT as its Advanced NDT service, covering pipes from 2 to 96 inches across cast iron, ductile iron, steel, PCCP, and bar-wrapped concrete cylinder pipe, with no cleaning to bare metal required before deployment.

What pipe types does RFT inspection work on?

RFT works on ferromagnetic pipe (cast iron, ductile iron, steel) and on concrete pressure pipes with steel cylinders (PCCP and bar-wrapped pipe). It does not work on pure plastic or asbestos cement pipe without metallic reinforcement, since the technique requires a steel element to interact with the electromagnetic field. It is particularly well-suited to lined steel and PCCP pipelines where MFL tools cannot penetrate the liner and standard UT tools struggle to deliver reliable through-liner wall thickness readings.

Can RFT inspect a pipeline without a full shutdown?

Yes, in some cases. PICA’s RFT tools can inspect pipes under 36 inches while the pipeline stays pressurized and in service. Flow must be reduced to keep tool speed in the 5–20 feet per minute range, but full isolation and dewatering are not required. For pipelines at 36 inches and larger, PICA deploys the EMIT (48 to 96 inches) or RAFT (36 to 48 inches), which require the pipeline to be taken out of service and dewatered before the inspection run.

What defects does RFT detect in PCCP?

For PCCP, PICA’s RFT tools detect all three primary deterioration mechanisms in a single pass: broken prestressing wires, steel cylinder wall loss, and loss of pre-load on individual pipe segments. This three-mechanism coverage matters because PCCP can fail along two distinct pathways. Wire break progression is the most discussed failure mode, but liner cracks can also allow corrosive fluid to reach the steel cylinder and cause corrosion before any wire breaks develop. RFT catches both pathways. No other single NDT method covers all three outputs on PCCP.

How accurate is RFT at finding pipe wall loss?

PICA’s RFT tools can be calibrated against reference specimens with known defect dimensions before some inspection runs and has been used in projects for 20+ years on all pipe materials with metallic components. The company has undergone independent blind verification testing on AWWA C303 bar-wrapped pipe, where inspectors had no prior knowledge of defect locations, and confirmed high detection accuracy across a range of wall loss percentages and wire break densities. Results are validated by PICA analysts using specialized analysis software before final condition reports are issued to the client.

What is the difference between RFT and NFT for PCCP inspection?

NFT (Near Field Testing) detects five or more adjacent broken prestressing wires in concrete pressure pipe but does not measure wall thickness and cannot characterize loss of pre-load. RFT measures all three PCCP deterioration mechanisms in a single pass. When RFT can be deployed, it is the preferred choice. NFT serves as a fallback when RFT cannot be deployed. For bar-wrapped pipe and PCCP carrying corrosive fluids, RFT is especially important because cylinder condition, not just wire count, determines whether the pipe is approaching failure.

How much does an RFT pipeline inspection cost?

RFT inspection cost varies by pipe diameter, linear footage, operating conditions, access complexity, and mobilization distance. A combined Advanced NDT program for large-diameter PCCP typically runs $100,000 to $200,000 or more per mile. For smaller-diameter cast iron or steel water mains, costs scale differently by tool type and project scope. The relevant comparison: an unplanned rupture on a major transmission main costs $200,000 to $1.5 million in direct repair alone (AWWA), before factoring in traffic disruption, service interruption, and liability exposure.

---