Acoustic Emission Testing (AET) per ISO 24489 and ASME Section V

What Acoustic Emission Testing Tells You

Acoustic emission testing listens for the stress waves a structure releases while it is damaging itself: a corrosion product fracturing, a crack extending, a leak jetting through the floor. Piezoelectric sensors on the outside of the shell pick those waves up, and the arrival times across the sensor array place the source. It finds activity, not geometry.

• What it reports: where on the structure damage is active during the monitoring window, and how intense that activity is.
• What it needs: a stimulus. A settled liquid load for a tank floor, a controlled pressure rise for a vessel. A structure under no change of load is largely silent.
• What it does not report: remaining wall thickness, flaw size or pit depth. Those come from the follow-up NDT the AE result directs.
• Why operators use it: it covers the whole floor or shell from outside, without draining, cleaning or entering the tank, so the out-of-service inspection budget goes to the tanks and zones that are actually active.

How a Tank Floor Examination Runs

The floor cannot be reached while the tank is in service, so the sensors go on the lower shell and the product itself becomes the load. Most of the work is in getting the tank quiet enough to hear: a floor examination fails on noise far more often than on sensitivity.

1. Method statement. Written from the tank drawings: diameter, internal arrangement, the location of any repairs and patch plates, and how any cathodic protection anodes connect to the bottom plate.
2. Fill and settle. The tank is filled to at least 50% of its safe fill height, preferably 90%, isolated, and left to settle: 24 hours for heavy products such as crude oil, 12 hours for lighter products.
3. Silence the tank. Inflow and outflow stopped, penetrations sealed, pumps, agitators, heaters and bubbler or ultrasonic level gauges switched off, and vehicle movement and work on adjacent tanks held for the test window.
4. Noise survey. Background levels read at ground-level nozzles, valves, manholes and points along the stairway before any data is recorded.
5. Mount the sensors. Resonant low-frequency sensors on bare metal, coating removed at each position and a 20 × 20 cm window cut where the tank is insulated, held by magnetic holders over couplant and spaced equally around the circumference. A large tank takes two rings, one 0.3 to 0.5 m and one 1 to 2 m above the bottom plate.
6. Verify the array. Every sensor is checked with a pencil-lead break before monitoring starts and again when it ends, so a sensor that lost coupling during the test is found rather than read as a quiet zone.
7. Monitor. A minimum of one hour of data with the test conditions held. Rain, lightning and high wind stop the test.
8. Analyse and grade. Noise is filtered out, the remaining events are located zone by zone, leak-type activity is separated from corrosion-type activity, and the floor is graded.

A Worked Example: Five Sensors, One Hour Twenty-Five Minutes

The figures below come from TCR's acoustic emission demonstration report, the document that shows a buyer exactly what a TCR AET report contains. The tank is a vertical above-ground storage tank of 8,040 mm diameter; the plant and the owner are not named.

The analysis found 217 valid events across the floor, and 130 of them located in one zone, near sensor 1 on the pump-house side. The zones near sensors 2 to 5 showed low activity. No active leak was indicated.

• Grade: IV, localised to the zone near sensor 1; the rest of the floor low.
• Evidence in the report: channel against hits, amplitude against hits, counts against amplitude, a transient waveform from sensor 1, cumulative energy against counts, and a severity map of the floor.
• Recommendation: follow-up NDT in the active zone at the first available opportunity: visual inspection, ultrasonic thickness measurement, liquid penetrant testing of the weld joints and vacuum box testing.

That is the value of the method in one line: a whole floor screened in an hour and a half, and the out-of-service inspection pointed at one sector of it.

Who Runs the Examination

Acoustic emission is interpreted, not just recorded, so the people matter as much as the instrument. TCR's AE team combines an ASNT NDT Level III certified in the method with two Level II technicians, each certified in acoustic emission after a general, specific and practical examination. The field team is drawn from TCR Advanced Engineering in Vadodara, which also issues the AET report.

Both Level II certificates were issued on 10 February 2026 under written practice TCR/NDT/SNT-TC-1A Rev. 8, which follows ASNT Recommended Practice SNT-TC-1A, 2024 edition. A standard field deployment is one team of two: a Level II technician and an assistant. The broader Level III bench is offered as its own service, ASNT Level III consultancy.

What the Report Contains

A TCR AET report is written so that the reader who did not attend can check every step: how the tank was loaded, where each sensor sat, how the system was verified, what was recorded and why the grade follows from it. A preliminary report is issued within three working days of the site work, once all required data is in hand; the final report follows within ten working days of the team's return to the laboratory.

• Equipment and tank details, and the instrument by make, model and serial number.
• The procedure and the standards it is written to.
• The sensor layout as a table and a drawing: position, height above the floor and spacing around the circumference.
• Test parameters: location type, sensor count, noise level, evaluation threshold, filters, wave velocity and temperature during the test.
• Gain, noise and threshold for every channel at calibration.
• Site photographs of the system and of each sensor mounting.
• Results as graphs and a severity map of the floor.
• A summary, the grade, and the recommended follow-up with named methods.