Why do we measure Material Thickness?
Once a protective coating has been applied to a substrate, it will, inevitably, require either re-work or re-application over its lifetime. The timescale before this point is reached is dependent on the structure design, material used, specification, coating selection, initial preparation of the substrate, the correct application of the coating and the environment in which the coated substrate has been operating.
As part of any pre-inspection or pre-coating routine, it is important to assess the condition of the substrate as corrosion or erosion may have significantly reduced the substrate thickness meaning it may need;
1. Manual coating removal or blasting (to avoid further loss of substrate or pinching the substrate)
2. Replacement of a section of the substrate as part of any re-work
3. Replacement of asset
The substrate wall thickness provides the structural integrity of the asset, often defined by rules or regulations. General inspection of a structures’ wall thickness (independent of any coating inspection regime) is often required to avoid weakening or, in extreme cases, collapse.
Ultrasonic material thickness gauges are often used in situations where an inspector only has access to one side of a component, for example, an oil storage tank or pipeline.
They are also useful for when simple mechanical measurement is impossible or impractical for other reasons such as part size or limited access.
Ultrasonic thickness gauges can quickly and easily measure wall thickness from one side with no need to cut parts. Pits and flaws can also be detected using ultrasonic thickness gauges.
What is Ultrasound?
Ultrasound is a sound with a frequency greater than the limit of human hearing.
Transducer Probes
The key to accurately measuring the wall or material thickness is in the transducer probe selection.
Other Common Terminology
There are lots of terms used in ultrasonics that you will often hear in conversations on the subject.
Measurement Modes
We have discussed transmitted sound and received sound, we have also illustrated short pulses of sound.
Ultrasonic Gauges
Ultrasonic thickness gauges come in many forms, each with different features.
Precision Gauges
As discussed earlier there are several potential problems when measuring thin materials, not least the noise created by the pulse, making measuring difficult.
There is no point in wasting time and money in re-coating a substrate to protect it when the thickness is such that it will need to be replaced early in the life of the coating. Measuring the thickness of the substrate before beginning the process will prevent this waste.
Whilst mechanical gauges may be the simplest way of checking the thickness, this may not always be possible due to access limitations. Ultrasonic thickness measurement, therefore, becomes an invaluable non-destructive method for material thickness measurement.