IRIS vs eddy current vs APR for tube inspection
IRIS measures tube-wall thickness ultrasonically. Eddy current techniques detect selected metal-loss and cracking indications, depending on the material and probe. Acoustic pulse reflectometry (APR) detects changes in the bore's internal geometry without a traversing probe. Each has limits. The owner and qualified inspection provider select methods, preparation and coverage for the expected damage mechanisms; a screening result does not by itself establish fitness for service.
How do the three methods compare?
| Dimension | APR (acoustic pulse reflectometry) | IRIS (ultrasonic) | Eddy current | Source |
|---|---|---|---|---|
| What it measures | Internal restrictions, through-wall holes and internal-surface metal loss; suitable analysis required for sizing. Not a general OD wall-loss or tight-crack test. | Quantitative wall-thickness map around and along the tube | Cracking, pitting, wall thinning; characterizes defect type | ASTM APR practice; Eddyfi method descriptions |
| How it reads the tube | Acoustic pulse in the air column, launched from the open tube end; no probe enters | An ultrasonic probe with a rotating reflector scans the wall in a water-filled tube | Electromagnetic probe traverses the bore | ASTM APR practice; Eddyfi method descriptions |
| Cleanliness needed | Can detect internal deposits; obstructions and masked indications can limit evaluation | Clean bore and adequate water coupling to the inspection procedure | Clean bore for probe passage and signal quality | Talcyon geothermal case study (higher-end cleaning named as the ultrasonic constraint); standard practice |
| Blocked tube | Can locate an obstruction; no evaluation beyond complete blockage from that end | A restricting deposit limits passage; accessible segments may still be examined | A restricting deposit limits passage; accessible segments may still be examined | Talcyon cleaning-validation case studies |
| Tube materials | Material-independent (acoustic) — published cases on carbon steel and titanium | Metals generally, including carbon steel | Non-ferromagnetic alloys; ferromagnetic tubes need adapted techniques (e.g. remote field) | Talcyon cleaning-validation cases; standard NDE method descriptions |
| Geometry | Published application notes on finned, U-tube, and twisted tubes | Straight sections; bends limit the rotating head | Handles bends with flexible probes, within limits | Talcyon resources library; standard practice |
| Published speed results | ~10 s/tube stated; 146 tubes under 1 h; 512 in 2 h; 7,541 in 24 h — varies materially by job | Depends on scan requirements, geometry, setup and preparation | Rapid acquisition possible; campaign rate depends on application | Manufacturer case results; rates are not a controlled comparison |
| Role in a program | Internal-condition screening within stated limits; can inform cleaning follow-up | Wall-thickness evidence over the specified coverage for engineering assessment | Selected flaw detection and characterization over the specified coverage | Method roles as described across the cited documents |
APR figures are Talcyon's statements and single-job case results, cited under Sources; field throughput varies materially with tube geometry, access, and site movement. IRIS and eddy current characteristics are stated at the level of standard NDE method descriptions; a specific campaign's capability is defined by the NDE vendor's written procedure, not by this table.
When is IRIS the right method?
When wall-thickness measurements are needed and the tube geometry, condition and preparation suit ultrasonic inspection. The resulting measurements inform engineering assessment; they are not, by themselves, a return-to-service decision. The inspection provider specifies calibration, scan requirements and coverage. An APR result does not automatically restrict IRIS work to flagged tubes.
When is eddy current the right method?
For suitable non-ferromagnetic tubes, eddy current techniques can detect and characterize selected metal-loss and cracking indications. Capability depends on probe design, calibration, material and the defect orientation. Carbon steel commonly requires other techniques such as remote-field testing. Tubes need sufficient clearance and preparation for the selected probe; a restriction may leave part of a tube inaccessible.
When is APR the right method?
When information about internal restrictions or internal-surface indications can help the cleaning or inspection programme. APR can examine suitable tubes from an open end without a traversing probe. Its limits include geometry, obstructions and tight cracks that do not significantly alter the bore. It does not replace examination for outside-surface damage or establish whole-wall integrity. Published and supplied manufacturer cases illustrate particular applications; required probe coverage remains the owner and qualified inspection provider's decision.
When can screening complement probe inspection?
APR screening may help identify restrictions and inform follow-up, but absence of a screen flag does not establish tube integrity. The owner and qualified inspection provider choose the required examination methods, coverage and acceptance criteria. Published Talcyon case results illustrate particular applications; they do not authorize a reduced inspection scope on another asset. Read the tube-inspection preparation guide for the cleaning interface.
Where does Dezu fit in this work?
Dezu has APRIS equipment in the Philippines and accepts scoped inspection and cleaning-validation enquiries. Its delivered record is heat exchanger tube cleaning — six recurring shutdowns at an HPAL nickel refinery since 2023, with cleaning verification agreed for the scope — and that cleaning helps provide the preparation required for a planned examination. Dezu offers APRIS scope review and operated rental, with bookings subject to confirmed equipment/software readiness, personnel, procedure and reporting responsibilities. Completion estimates follow scope review; Dezu publishes no tube-per-day capacity until it holds verified field actuals of its own. Tube integrity verdicts by IRIS or eddy current remain NDE-vendor work — Dezu's role there is the inspection-clean preparation those probes require. The cleaning service is at heat exchanger tube cleaning.
Does APR replace IRIS or eddy current testing?
No. APR detects changes in internal geometry, including restrictions and internal-surface metal loss, within the method and examination limits. It does not establish outside-surface condition or rule out tight cracks. The owner and qualified inspection provider select the required methods, coverage and acceptance criteria. No screen flag is not a tube-integrity verdict.
Which tube inspection method works on carbon steel tubes?
IRIS can measure wall thickness in ferrous and non-ferrous tubes with suitable preparation and coupling. Conventional eddy current is used for non-ferromagnetic tubes; carbon steel commonly requires techniques such as remote-field testing. APR is not dependent on the metal being magnetic, but its suitability still depends on tube geometry, access and the damage mechanisms of interest.
How fast is each tube inspection method?
Throughput depends on tube geometry, access, preparation, equipment, calibration and required data quality. Talcyon reports application-specific APR results; Eddyfi also reports rapid eddy current tube inspection. Those jobs are not a controlled comparison. Ask for a campaign estimate covering setup, examination, repeat readings and reporting; do not choose inspection coverage from a generic speed claim.
Sources
- Talcyon APRIS brochure (method description; ~10 seconds per tube) — talcyon.com material, mirrored
- Talcyon case study, Geothermal Plant (Turkey) — Isopentane Condenser Tube Inspection — ndt.talcyon.com
- Talcyon resources library (application notes on finned, U-tube, twisted-tube, boiler, furnace, and cooler inspections) — ndt.talcyon.com/resources
- Talcyon Pte Ltd case studies, Cleaning Validation — Heat Exchanger (Petrochemical) and Cleaning Validation — Condenser (Power Plant) — Talcyon-produced documents on file with Dezu; not in the public resources library as of August 2026
- ASTM E2906/E2906M-18(2022) — APR internal-surface scope, sizing and limitations.
- Eddyfi IRIS method and heat exchanger technique selection — instrument principles and method limits.
- Eddyfi tube-inspection case — application-specific ECT throughput, not a direct APR comparison.
Need more evidence about tube condition?
Review APRIS tube-screening and cleaning-validation enquiries · Review poor performance after cleaning · Plan chiller tube inspection
Deciding how to inspect a bundle this shutdown?
Send the exchanger list, tube material and sizes, what the inspection must decide, and the window. We reply with the cleanliness grade the method needs, whether APR screening is suitable, and a scope-based quotation for the cleaning side.