UNDERSTANDING ULTRASONIC THICKNESS MEASUREMENT

TO BETTER UNDERSTAND HOW THE TECHNOLOGY WORKS, AND HOW IT CAN BE APPLIED, MEPCA SAT DOWN WITH TECHNOLOGY SPECIALIST, CYGNUS INSTRUMENTS.

HOW DOES ULTRASONIC THICKNESS MEASUREMENT TECHNOLOGY WORK?

Taking ultrasonic thickness measurements is one of the most fundamental practices within a family of analysis techniques known as Non-Destructive Testing (NDT).

An ultrasonic thickness gauge (UTG) will allow an engineer to test the thickness of a material from one side only (as opposed to boring a hole in the material and using a calliper).

To operate the unit, a simple calibration is performed on the material to be measured and then ultrasound is passed in to the material via a transducer (sometimes known as a probe); the gauge measures the time taken for the ultrasound to pass through the material and return – and thus a thickness measurement can be calculated and is presented.

WHAT ARE THE TYPICAL APPLICATIONS FOR ULTRASONIC THICKNESS TESTING IN PLANT MAINTENANCE ROUTINES?
A thickness gauge can be used to measure any metal (or dense engineering material such as HDPE) and so the scope to involve ultrasonic thickness testing in plant maintenance is extensive. However, the most common application for the UTG is with pipework.

Pipework can be subject to myriad types of corrosion; galvanic corrosion, deposits, microbiologically influenced corrosion (MIC) and chemistry can all cause wall thinning in pipes. And, unlike some other assets within plant maintenance, pipework rarely stops working; as such erosion – due to flowing liquids (and air bubbles) – is a simple and ever-present cause of wall thickness loss. If ignored or forgotten, there is the threat of eventual pipe failure that can lead to potentially highly costly shutdown and, worse still, industrial accidents.

However, the simple act of using a UTG as part of regular, planned plant maintenance – or for more ad hoc inspections as and when needed – will help to ensure that wall thinning in pipework can not only be monitored, but also included as part of a predictive maintenance programme. Cygnus thickness gauges are equipped with the facility to record and report on findings. These reports can be exported (via cable, SD card or Bluetooth) and loaded into a spreadsheet, where they can be analysed and absorbed into a wider predictive maintenance programme.

SO, CAN A UTG BE USED IN SITUATIONS WHERE THE ITEMS BEING TESTED ARE COATED?
With most UTGs, it is not possible to measure through a coating simply and quickly. However, Cygnus Instruments does offer a particular ultrasonic technique called multiple echo. The benefits of this technique are that it is incredibly accurate, straightforward to use and that the method naturally ignores coatings (only the substrate that is subject to wear and tear is measured).