Ultrasonic Wall Thickness Gauges

Why Measure Wall Thickness with Ultrasonic Thickness Gauges?

Erosion

Erosion is the process by which a protective coating or substrate is worn away by friction resulting from repetitive mechanical interaction. Typical causes of erosion include cavitation, impingement by liquid or solid particles, and relative motion against contacting solid surfaces or fluids.

Corrosion

Corrosion is the process by which a substrate and its properties are damaged or worn away by a chemical action or change. In metals, deterioration attributed to corrosion is most often caused by an oxidation process.

Erosion and Corrosion Testing

Using non-destructive inspection methods minimize safety concerns, ensure code compliance, and reduce the frequency of major repairs (and subsequently costs). As an example, marine applications have a significant risk of catastrophic substrate failure due to undetected substrate corrosion or erosion. However, costs associated with corrosion or erosion damage can be more subtle. Consider the case of a propeller blade that has experienced wear or damage. A likely impact is a decrease in the efficiency of the propeller, translating directly to a decrease in horsepower and an increase in turbulence (vibration). This results in a decrease in maximum speed and an increase in fuel consumption. Furthermore, cavitation caused by the damaged propeller creates a surrounding environment that is even more damaging to the propeller itself.

What are some UT Measurement Applications?

With ultrasonic thickness gauges, an accurate measurement of the remaining wall thickness of a substrate can be taken on pipes, pressure vessels, storage tanks, boilers, or other equipment prone to erosion or corrosion.

Though many industries are affected by erosion and corrosion, the marine atmosphere is one of the most aggressive corrosion environments. Corrosion rates are affected by several elements including sea water, humidity, wind, temperature, airborne contaminants, and biological organisms. Erosion is also common in marine applications due to abrasion from the impact of water and contaminate particles, impingement due to turbulence in high speed liquids, and cavitation due to pressure waves produced by air bubbles. Erosion not only affects the substrate itself but may also damage protective coatings, increasing the likelihood of substrate corrosion. Ships, marinas, pipelines, offshore structures, and desalination plants are all systems that are subject to varying levels of marine erosion and corrosion.

What is the difference between the PosiTector UTG C, PosiTector UTG M, and PosiTector UTG P probes?

The PosiTector UTG C Ultrasonic Thickness Gauge (Corrosion) single echo probe uses a dual-element transducer, a focused “V-path”, and V-path compensation to accurately measure the thickness of metals with heavy corrosion or pitting. The UTG C single echo probe will not ignore the thickness of the exterior coating: for best measurement accuracy, it may be necessary to remove any coating present at the point of measurement.

The PosiTector UTG M Ultrasonic Thickness Gauge (Multi-echo) probe uses a single element transducer to accurately measure the metal thickness of a new or lightly corroded structure while ignoring the thickness of protective coatings. The ultrasonic beam travels in a straight path to the material’s back wall at 90° relative to the surface. When three consecutive back wall echoes are detected, the probe makes a time-based calculation to eliminate the coating thickness from the gauge reading.

The PosiTector UTG P Ultrasonic Thickness Gauge (Precision) probe uses a single element delay line transducer to accurately measure the thickness of thin materials including plastics and metals. It automatically switches between single-echo or multiple-echo modes depending on material and thickness.