Acoustic Emission (AE) Testing for Spheres & Pressure Vessels Singapore — Online Integrity Screening

What Is Acoustic Emission (AE) Testing?

Acoustic emission testing is a passive, global non-destructive testing (NDT) method. Rather than sending energy into a component and reading what bounces back — the way ultrasonics or radiography work — AE simply listens. When a defect is active under load, the material releases energy as it moves: a crack tip advances, a corrosion product fractures, a weld flaw yields, and each of these events radiates a burst of high-frequency stress waves through the vessel wall. Sensors bonded to the outside of the vessel detect those transient bursts, and the system records where and when each one arrives.

The defining characteristic of AE is that it only responds to defects that are actively growing while the vessel is stressed. A dormant, stable flaw that is doing no harm stays silent; a flaw that is propagating announces itself. This makes AE fundamentally a screening tool for structural significance — it separates the sources that matter from the ones that do not, across the entire structure at once. The methods are described in ASME Section V Article 12 for acoustic emission examination of metallic vessels, and in the ASTM E1139, E569 and E1419 practice and guide documents, with EN 14584 covering AE examination of metallic pressure equipment during proof testing.

Because the sensors sit on the surface and the whole vessel is monitored during a single controlled load, AE gives coverage that point-by-point inspection cannot match in the same timeframe. It is the natural first pass on large, complex vessels where inspecting every square metre by hand would be prohibitively slow.

Why AE Matters for Spheres and Large Vessels

A modern LPG storage sphere is enormous. The shell may hold thousands of cubic metres of pressurised gas, its surface curves in every direction, and almost none of it is reachable without full scaffolding or rope access. Inspecting such a vessel conventionally means gas-freeing, cleaning, entering, and then working across the entire internal and external surface — an operation that consumes a large slice of a plant turnaround and keeps the asset out of service for its duration.

AE changes the economics of that inspection. By assessing the whole vessel from a limited number of surface-mounted sensors during a controlled pressurisation, it screens integrity without the blanket internal access. The load sequence stresses the shell, any active source emits, and the array locates and grades those emissions. The result is a map of where the vessel is genuinely misbehaving under load — and, just as importantly, confirmation of the large areas that are quiet and sound.

That map is what makes AE so valuable for turnaround planning. Instead of scheduling detailed NDT everywhere "just in case", the inspection team can direct detailed vessel inspection and quantitative NDT precisely to the zones AE has flagged. Shutdown scope shrinks, high-cost access is concentrated where it earns its keep, and the risk of an unpleasant surprise deep into a turnaround falls sharply. On the crowded, high-throughput plants of Jurong Island, that difference in planning certainty is significant.

How AE Testing Is Performed

An AE examination follows a disciplined sequence, from sensor layout through to a graded source report. Each stage is designed so the final data can be defended against the acceptance criteria in the controlling code.

The load sequence is central. AE exploits the fact that a growing flaw emits when stressed, and that continued emission during a pressure hold — rather than emission only while the load is rising — is a strong indicator of a genuinely active, structurally significant source. Reading that behaviour correctly is what separates a competent AE examination from a stream of unfiltered noise.

What AE Screens For

AE is sensitive to the classes of damage that release energy as they progress. On a sphere or large vessel, that covers the failure modes that most concern an integrity engineer.

Where AE Fits in the Inspection Workflow

AE is a location and screening method, not a sizing method. It answers "where is the vessel active, and how significant is it?" — not "how deep is this flaw?". Used correctly, that is a strength, because it lets the far slower quantitative techniques be applied surgically instead of blanket-wide.

On a typical oil and gas or refinery asset, the workflow runs in sequence: AE screens the whole sphere or vessel during a controlled load; the graded source map identifies the zones that warrant closer study; then targeted ultrasonic testing, phased-array UT (PAUT) or magnetic flux leakage (MFL) is deployed to those zones to size and characterise the indications. Where internal visual confirmation is needed, drone-based confined-space pressure vessel inspection and remote visual inspection close the loop. AE and these detailed methods are complementary, and API RP 583 provides useful context where corrosion-under-insulation and external degradation feed into the same integrity picture.

The vessels that benefit most are the large, hard-to-access ones: LPG and LNG storage spheres, horizontal bullets, columns, reactors and large drums. These are exactly the assets where whole-vessel screening from a few access points delivers far more coverage per shutdown hour than starting with point-by-point inspection. AE sits at the front of the process precisely so the expensive work that follows is aimed, not sprayed.

Standards We Work To

AE examination of pressure equipment is a codified discipline, and a defensible result depends on applying the right standard for the vessel and load case. Our AE work is aligned to the recognised references for the method.

• ASME Section V, Article 12 — acoustic emission examination of metallic vessels, the core procedural reference for AE on pressure equipment.
• ASTM E1139 — standard practice for continuous monitoring of AE from metal pressure boundaries.
• ASTM E569 — standard practice for acoustic emission monitoring of structures during controlled stimulation.
• ASTM E1419 — standard practice for examination of seamless, gas-filled pressure vessels using AE.
• EN 14584 — AE examination of metallic pressure equipment during proof testing, including source location and grading.
• API RP 583 — recommended practice for corrosion-under-insulation, providing context where external degradation informs the integrity assessment.

Citing these standards is not the same as claiming a certificate for every one of them, and we are explicit about scope on each project. What matters to an integrity engineer is that the procedure, sensor layout, load sequence and acceptance criteria are anchored to a recognised code, so the resulting source map stands up in a fitness-for-service review.

Why Choose SG Drone Inspections

We are a Singapore industrial inspection specialist focused on getting the right data into the hands of your integrity and turnaround teams — combining AE screening with the drone-based access and NDT that follow it.

Frequently Asked Questions