Pulsed Eddy Current for CUI: From Screening to Follow-up

Corrosion under insulation creates an awkward inspection problem: the surface you want to examine is hidden by the system intended to protect the asset. Removing insulation everywhere may be disruptive, but a screening result that is misunderstood can send the maintenance team to the wrong places. Pulsed eddy current, usually shortened to PEC, is useful when its result is connected to a clear follow-up decision.

For owners of insulated carbon-steel piping and vessels, the buying question is therefore broader than whether a probe can read through insulation. It is whether the proposed examination can identify areas that deserve further attention, document where it could not provide reliable information, and support a repeatable maintenance record. This guide explains how to specify that workflow without confusing screening with local thickness verification.

PEC, ECA and PECA: clarify the request

Pulsed eddy current is an electromagnetic technique used for wall-loss assessment on ferromagnetic structures. Eddyfi describes applications involving carbon steel and cast iron, including inspection through insulation and weather jackets. The instrument analyzes a transient response associated with the induced currents rather than simply taking a conventional ultrasonic point reading. 1

Array refers to a sensor arrangement. Eddy current array, or ECA, and pulsed eddy current array, or PECA, should not be treated as interchangeable purchase descriptions. Eddyfi markets PECA for CUI programs using multiple pulsed eddy current sensors. Ask a provider to identify the actual technique, probe and intended damage application when a request uses an imprecise phrase such as “pulsed array eddy current.” 2

This distinction matters when comparing proposals. One bid may address broad wall-loss screening through insulation while another addresses a different examination on an accessible surface. Both may mention eddy currents, yet deliver entirely different evidence. Start the scope with the material, insulation and inspection objective, then ask the supplier to explain why its proposed configuration fits.

Understand what the footprint means

A PEC result represents an area of influence rather than an infinitesimal point. Eddyfi’s technical explanation notes that increasing lift-off broadens the averaging area and that a small defect within that area can be underestimated. Its discussion of galvanized steel also identifies signal attenuation, a changed footprint and vibration-related interference. These are reasons to evaluate the complete insulation and cladding arrangement. 3

Do not convert a reported regional response into an unsupported statement about the deepest pit. If the maintenance decision depends on local minimum thickness, the inspection plan needs an appropriate local follow-up. Likewise, avoid describing a low-priority screening region as proven free of every damage mechanism. The report should explain the question the examination addressed and the questions left open.

A useful purchasing exercise is to ask the supplier to sketch the expected footprint for the proposed setup and identify the smallest relevant feature the trial will challenge. Keep that sketch with the trial results. It provides a concrete basis for discussing scan spacing, overlap and limitations without turning a nominal instrument specification into a universal performance claim.

Collect the information that changes the setup

Prepare an asset list before mobilization. At minimum, give each examination area a stable identifier and include material, nominal wall information, diameter or geometry, insulation thickness, jacket material, operating condition and access restrictions where known. Mark unknown fields explicitly. An empty cell should not silently become a default assumption in the contractor’s setup.

Photograph representative jackets, seams, supports and irregularities. Explain which areas can be reached safely and which need an alternative access arrangement. Ask the provider to separate exclusions caused by access from exclusions caused by technique limitations. Those categories lead to different corrective actions and should not be blended into one “not inspected” note.

For North American projects, specify both the reporting unit system and the authoritative asset identifiers. A US contractor and Canadian owner may use different unit conventions in their day-to-day work. Agree the stored unit, displayed unit and conversion rule at the start. Never rely on an unlabeled spreadsheet column or a color map to communicate a dimensional result.

Build a representative demonstration

Use a demonstration that reflects the important combinations of wall, insulation, cladding and geometry in the proposed scope. Ask the supplier which configuration changes are required between those combinations. Document the reference information available to the operator and the method used to establish it. Do not describe a successful test on a convenient specimen as qualification of every asset in the facility.

Include a repeatability exercise: remove and reposition the probe, repeat a selected line, and have the provider explain any material differences. Request the underlying record and the final interpretation. The purpose is to learn what ordinary positioning and setup variation does to the result, not to demand an unrealistic promise of identical numbers.

Eddyfi also describes permeability-related influences and an analysis tool intended to assist their assessment. A purchasing team should treat such features as specific supplier capabilities to demonstrate, rather than assume software can resolve every ambiguous response. Ask which indications require further investigation and how uncertain results remain visible in the report. 4

Agree the follow-up rules before scanning

Create a decision table with the responsible integrity team. It should distinguish a reportable screening response, an inconclusive response, an inaccessible area and a region examined within the agreed scope without a reportable response. Assign an action and an owner to each state. Keep the engineering limits and escalation times under the control of the appropriate technical authority.

Do not use this table to invent a universal rejection threshold. Its purpose is to keep decisions traceable. The asset owner’s competent team must choose the technical criteria, any immediate restrictions and the applicable inspection requirements for the particular equipment.

Budget for follow-up at the same time as screening. If the entire allocation is spent collecting screening data, a project can finish with a long list of unresolved locations. Ask for separate commercial allowances for access, insulation removal where appropriate, local examination, reinstatement and final reconciliation. That makes the cost of completing the decision visible.

Map coverage without hiding the gaps

Specify the coordinate reference used to locate each scan. On a pipe, this might include an agreed component identifier, an axial reference and a circumferential convention. On a vessel, the team needs an equally clear location system. The exact scheme can vary, but a second crew should be able to return to a nominated area using the delivered record.

Show examined, excluded and unresolved regions as separate states. A blank area on a heat map is ambiguous: it could mean no measurement, a processing failure, or a display choice. Require a legend and a coverage summary that explain the difference. Keep the raw location record available when the image is exported into a report.

As an illustrative planning example, suppose a project contains 120 nominated areas. If 90 are screened, 20 remain inaccessible and 10 require a different setup, the initial coverage is 90 of 120 nominated areas, or 75%. That does not mean 75% of the metal surface has been examined, because the areas may have different sizes. State the denominator before using a percentage in a progress report.

Close the loop after local examination

Preserve the original screening result when follow-up information arrives. Add the local findings as a linked record rather than overwriting the earlier response. The original record shows why the area was selected; the follow-up shows what additional evidence was obtained. Together they make the next campaign easier to design.

Review disagreements with the people responsible for the technique and the asset. A regional screening response and a local thickness reading sample different things, so a numerical difference does not automatically mean that one operator made a mistake. Check location, footprint, surface preparation, reference assumptions and units before drawing a conclusion.

Track unresolved items to an explicit disposition. Each item should have a named role, a due date established by the owner and a final status. A colorful report with no action ownership can be less useful than a modest spreadsheet that reliably closes the identified questions. The digital twin reporting guide explains how to connect those records to asset locations without losing the source evidence.

Ask for a quotation that can be compared

Send the same asset schedule and reporting requirements to each prospective provider. Request the proposed technique and equipment, personnel qualifications, demonstration basis, access assumptions, expected exclusions, source-data deliverables and follow-up arrangements. Require any productivity estimate to state the conditions on which it depends.

Separate the screening price from the cost of resolving findings. A lower day rate can become a more expensive campaign if travel, access, repeat work or report reconciliation are omitted. Conversely, a more extensive initial proposal may include work the owner does not need. The useful comparison is the price of the agreed decision workflow, with optional items identified.

For general context, read the CUI overview and the eddy current method guide. Use the inspection cost guide to organize quotation questions rather than treating indicative prices as a project budget. When ready, include your asset schedule in an inspection request so providers can respond to a defined scope.

Sources and reporting notes

Sources checked October 11, 2026. The cited pages are manufacturer explanations, not independent comparative trials. The workflow and planning example above are editorial guidance. No inspection accuracy, savings percentage or site-specific acceptance threshold is asserted.

1. Eddyfi: Pulsed Eddy Current technology.
2. Eddyfi: How PECA Transformed CUI Programs.
3. Eddyfi: Three Major Effects of Galvanized Steel on PEC.
4. Eddyfi: PermTool and PEC Advanced Analysis.