Tube inspection after cleaning — cleanliness decides what the inspection can see
Tube cleanliness affects probe access and inspection quality. Cleaning to remove fouling and preparation for an integrity examination can have different acceptance criteria. IRIS, eddy current and acoustic pulse reflectometry (APR) see different features and have different limits. Agree the preparation and examination coverage before the shutdown. Dezu delivers cleaning with scope-specific verification; APR screening support can be reviewed on request as part of a cleaning scope.
How clean do tubes need to be for inspection?
As clean as the inspection method demands — and that is the detail that catches plants out, because the two cleanliness grades in circulation are different scopes with different acceptance criteria.
| Grade | What it is for | How it is checked |
|---|---|---|
| Production clean | Remove fouling to the agreed cleaning condition. Performance recovery and return to service require separate confirmation. | Agreed checks such as water flow and nozzle passage, recorded with restrictions and accepted exceptions. These checks are not interchangeable. |
| Inspection clean | Prepare tubes to the chosen inspection method’s requirements. IRIS and eddy current have different preparation needs. | Surface condition to the NDE vendor's specification — gauge pull-through, borescope spot checks where specified. |
Define the cleaning acceptance criteria in the contract. If integrity testing is planned, include the inspection provider's preparation requirements before work starts. A generic instruction to clean tubes does not establish either standard.
Does leftover scale change what an inspection sees?
Deposits can affect probe clearance, ultrasonic coupling and signal interpretation. A probe may inspect an accessible segment but cannot pass a restriction smaller than its clearance requirement. APR can detect internal restrictions without a traversing probe. That does not make deposits irrelevant: a complete blockage prevents evaluation beyond it from that end, and other indications may be masked. The report must identify examination limits and unevaluable regions.
What is acoustic pulse reflectometry (APR)?
APR sends sound into an open tube end and analyses reflections from changes in internal geometry. ASTM E2906 describes detection of blockages, through-wall holes and internal-surface wall loss such as ID pitting or erosion. It is not a general test for outside-surface wall loss or tight cracks without a significant change in bore geometry. Sizing requires suitable signal analysis, and coverage depends on tube geometry, access and obstructions. Talcyon markets APRIS as one implementation. Its manufacturer timings are application examples, not Dezu production rates or a promise of complete defect detection.
How can screening help validate cleaning? (cleaning validation)
Screening can add evidence against specified cleaning criteria. Two Talcyon-produced case documents supplied to Dezu describe residual deposits found after water jetting. In a petrochemical heat exchanger of 146 carbon steel tubes (19 mm OD, 2.14 m long), initial cleaning was done by water jetting; APRIS then screened all 146 tubes in under an hour and found tubes still carrying blockages of 50–80% cross-section reduction. The flagged tubes were re-cleaned and re-tested with no remaining blockage indication reported. The client's stated alternative was to plug those tubes. In a power plant condenser of 7,541 titanium tubes (28.58 mm OD, 0.5/0.7 mm wall, 19.8 m long), APRIS screened 100% of tubes in 24 hours, found blockage of roughly 62% cross-section reduction, and reported the restrictions cleared after re-cleaning. These are the manufacturer's case results; they do not establish a general acceptance threshold or tube integrity.
Agree the checks, record the results, investigate restrictions and repeat the relevant checks after further cleaning. Dezu's cleaning records use scope-specific tube maps, witnessed flow or passage checks and exception disposition. Accepted residual restrictions remain visible in the record; acceptance does not mean every bore is unobstructed.
What does full tube-sheet screening establish?
Examining every accessible tube can broaden the evidence available for the features a method can detect. It does not prove every part of every tube is sound. The owner and qualified inspection provider select methods and coverage for the asset's materials, damage mechanisms and inspection objective. An APR indication may prompt further examination; absence of a flag does not authorize reducing required IRIS, eddy current or other inspection coverage. Talcyon's linked geothermal case is an example of one plant's use of APR, not a plug-or-keep rule for another plant.
Where else does APR screening apply?
Well beyond straight condenser tubes. Because the pulse travels the air column, published Talcyon case studies and application notes cover fin-fan air coolers at an oil refinery, U-tubes and twisted tubes, depropanizer reboilers, boiler tubes on an LNG carrier and an FPSO vessel, furnace tubes at a petrochemical plant, cooler tubes in a mining plant, and vaporizers in LNG regasification service — the vaporizer note reports 240 complex finned, multi-bend tubes screened in about 2 hours 15 minutes across six racks. A waste-heat boiler case at a chemical refinery in Italy reports 356 tubes screened in 1 hour 15 minutes. For the Philippine industrial base — geothermal condensers and brine exchangers, refinery and petrochemical bundles, HPAL and mineral processing circuits, power plant condensers — these examples are relevant to planning, but each asset still requires a suitability review.
What does Dezu do on tube inspection today?
Dezu's delivered record is cleaning, including recurring shutdown work at an HPAL nickel refinery since 2023. Verification is agreed for each scope, with recorded restrictions and exceptions. Dezu can prepare tubes to the inspection provider's specified condition. Dezu now has APRIS equipment in the Philippines and accepts APRIS inspection and cleaning-validation enquiries, including separate operated rental. Project bookings follow confirmation of equipment and software readiness, personnel, procedure and reporting responsibilities. Completion estimates follow scope review. The owner and qualified inspection provider retain responsibility for the examination programme, interpretation and integrity decisions. Compare the methods in IRIS vs eddy current vs APR; the cleaning service itself is at heat exchanger tube cleaning.
How clean do tubes need to be for IRIS inspection?
IRIS needs a sufficiently clean, water-filled bore for ultrasonic wall-thickness readings. Deposits and poor coupling can impair the result. The inspection provider must specify preparation and verify suitability. Eddy current has different preparation requirements. APR can detect internal restrictions without a traversing probe, but deposits and blockages can limit what else can be evaluated.
Can fouled or blocked tubes be inspected at all?
Some examination may be possible, depending on the method, deposit and access. A probe may inspect an accessible segment but cannot pass a restriction smaller than its required clearance. APR can identify internal restrictions from an open tube end; a complete blockage prevents evaluation of the tube beyond it from that end. Record inaccessible or unevaluable lengths instead of treating a screening result as full coverage.
What is cleaning validation for heat exchanger tubes?
It is checking the cleaning against agreed acceptance criteria. Checks may include a tube-status map, witnessed water flow, nozzle passage or suitable inspection. In a Talcyon case document supplied to Dezu, APRIS found residual restrictions after water jetting in a 146-tube exchanger; the affected tubes were re-cleaned and re-tested. That supports cleaning follow-up, not an independent fitness-for-service verdict.
Should tube inspection be part of a cleaning shutdown?
Cleaning and integrity examination are separate scopes. Agree the preparation, methods, coverage and acceptance criteria with the owner and qualified inspection provider before cleaning starts. APR may complement an inspection programme; it does not automatically justify examining only flagged tubes. Return to service remains a separate owner decision.
Sources
- ASTM E2906/E2906M-18(2022) — APR scope, internal-surface indications, sizing and limitations.
- Eddyfi heat exchanger inspection — technique selection by material and defect type.
- Talcyon APRIS brochure (manufacturer method description) — talcyon.com material, mirrored
- Talcyon case study, Geothermal Plant (Turkey) — Isopentane Condenser Tube Inspection (512 tubes in 2 hours; 23% corrosion; 4% plugged) — ndt.talcyon.com
- Talcyon case study, Chemical Refinery (Italy) — Waste Heat Boiler Tube Inspection (356 tubes in 1 h 15 min) — ndt.talcyon.com
- Talcyon application note, Inspection of Vaporizers in Regasification (240 finned multi-bend tubes, ~2 h 15 min) — ndt.talcyon.com
- Talcyon resources library (application notes: fin-fan coolers, U-tubes, twisted tubes, boiler and furnace tubes, mining plant coolers) — ndt.talcyon.com/resources
- Talcyon Pte Ltd case study, Cleaning Validation — Heat Exchanger, Oil & Gas (Petrochemical) (146 tubes, under an hour, 50–80% blockages found after jetting) — Talcyon-produced document on file with Dezu; not in the public resources library as of August 2026
- Talcyon Pte Ltd case study, Cleaning Validation — Condenser (Power Plant) (7,541 titanium tubes in 24 hours, ~62% blockage found) — Talcyon-produced document on file with Dezu; not in the public resources library as of August 2026
Need more evidence about tube condition?
Review APRIS tube-screening and cleaning-validation enquiries · Review poor performance after cleaning · Plan chiller tube inspection
Planning a shutdown where inspection follows cleaning?
Send the exchanger list, tube counts and sizes, the inspection objective, and the window. We reply with the cleanliness grade the inspection needs, whether APR screening is suitable for the scope, and a scope-based quotation.