Corrosion-Detecting Probe Inspects Storage Tanks Without Emptying Them

Inspecting the inside of a large storage tank is an expensive, time-consuming, and hazardous operation. The tank must be taken offline, drained, cleaned of residual chemicals or hydrocarbons, and then entered by workers operating in a confined and potentially toxic space. For industries that rely on dozens or hundreds of such tanks - oil and gas, municipal water, aerospace, manufacturing - the costs of that routine process add up quickly.

A probe developed at Southwest Research Institute eliminates the need to empty the tank at all. The device attaches to the exterior wall, sends acoustic waves through the metal, and analyzes the reflections to produce a detailed two-dimensional map of the interior surface showing where corrosion has formed and how severe it is.

The probe, called the SwRI MST 8x8, uses a technology known as magnetostrictive transduction. A magnetostrictive material changes shape when exposed to a magnetic field, generating mechanical vibrations - in this case, ultrasonic waves - that travel along the tank wall. Eight sensors arranged in a flexible strip allow the probe to transmit and receive signals from multiple angles simultaneously, which is critical for building detailed spatial images.

How the Waves Find Flaws

The specific wave type the probe uses - shear horizontal guided waves - is well suited to detecting metal loss and other structural anomalies. Unlike bulk ultrasound waves, guided waves propagate along the thickness of a plate or shell, covering large surface areas with a single measurement and maintaining sensitivity to small defects.

When a guided wave encounters a region of thinned or pitted metal, some of the wave energy reflects back toward the sensor array. The eight-element configuration allows the probe to collect these reflections from multiple angles in a technique called full matrix capture. That data is then processed with the total focusing method, an advanced imaging algorithm that synthesizes all the captured signals into a single high-resolution image.

"Data from the probe is processed with an advanced imaging algorithm, the total focusing method, that generates these maps," said Dr. Sergey Vinogradov of SwRI, the paper's author. "As a result, instead of just indicating the presence of an anomaly, it can create a high-resolution map of the structure, showing areas with potential corrosion. This helps users assess the extent of damage to decide when to schedule expensive, time-consuming tank repairs."

Field Testing and Performance

SwRI performed field testing of the MST 8x8 on a series of storage tanks. The probe's flexible strip design allows it to conform to curved surfaces and structures with attachments or welds that would interfere with rigid inspection tools. Both the walls and the bottom of tanks - two areas where corrosion most commonly causes structural failure - can be inspected.

The same technology can apply beyond storage tanks. The research paper describes applications including ship hulls, wind turbine towers, rocket bodies, and pipelines. Any large metallic structure that requires periodic corrosion assessment and is expensive or dangerous to access from the inside is a potential candidate.

"Many industries require storage tanks to be inspected regularly," Vinogradov said. "This can be a very expensive process, as it requires the tank to be emptied, cleaned and manually inspected. By allowing inspection without emptying the tank, our probe reduces expensive down time and improves inspection safety, by avoiding work in hazardous, confined spaces."

Availability and Limitations

SwRI plans to make the technology available through equipment sales, licensing agreements, and technology transfer to inspection service companies. The study validating the probe was published in MDPI Sensors, providing a publicly accessible technical basis for potential adopters to evaluate the approach.

The published field testing focused on storage tanks. The probe's performance on very large diameter tanks, on tanks with complex interior configurations, or in environments with extreme temperatures or chemical exposure has not yet been fully characterized in the published literature. Those factors may influence detection sensitivity in specific industrial applications.