The advantages and disadvantages of advanced NDT.

Alison Glover from Ashtead Technology describes the advantages and disadvantages of advanced Non-Destructive Testing equipment, and explains why her company has invested over £1m (€1.4m) in advanced NDT equipment.

Alison Glover

Alison Glover

Simple, conventional inspection methods such as ultrasonic thickness testing can provide a useful, fast, low-cost method for assessing materials. However, in comparison with advanced NDT, such methods are generally less repeatable, less recordable, and have a lower Probability of Detection (PoD).

There are many advantages to be gained from advanced NDT, some of which will be briefly described below. The major disadvantage of these high-end technologies is, of course, their cost. Advanced NDT instruments may cost tens of thousands of pounds and require significant levels of training to best exploit their benefits. For this reason, Ashtead Technology has chosen to invest over £1 million in advanced NDT equipment; the ability to rent this technology can dramatically lower the cost of entry to this market for our customers in applications such as crack and flaw detection, weld evaluation, tube testing, corrosion mapping, composite inspection etc.

The advantages of advanced NDT
In general terms, advanced instrumentation can, in the right hands, provide more accurate and reliable inspection data with an improved PoD. The data is more recordable and more repeatable. Advanced technologies such as Phased Array Ultrasound (PAUT) or Eddy Current Array (ECA) provide more intuitive displays, better ways of presenting data and generate inspection reports of higher value to clients. For example, a colour-coded C-Scan is an intuitive way of representing inspection data. Using different colours for different remaining wall thicknesses, for instance in PAUT inspection of corroded or eroded pipes, produces an image that is easy to understand. Similarly, many clients will find a colour-coded ECA C-Scan simple to interpret compared with the conventional eddy current impedance plane display.

Composite OmniScanMX2

Composite OmniScanMX2

With greater control over instrument configuration, advanced NDT procedures can be optimised for particular inspections. Setup files can be saved digitally and easily transferred to others. Digital recording means that data can be emailed to colleagues when a second opinion is required, or when complex data needs to be assessed by a higher level technician. The ability to store large inspection data files also means that new inspections can be compared with those done previously, to determine whether there has been further deterioration, and to monitor, for example, crack growth. In addition, the use of scanners improves repeatability and helps to ensure that sequential inspections are directly comparable and less subjective.

As a result of these advantages, there has been strong growth in the advanced NDT sector, and this has been reflected in the volume of advanced NDT instruments in the Ashtead Technology fleet that are out on hire.

The disadvantages of advanced NDT
In comparison with conventional methods the operation of advanced instrumentation requires a higher level of training and additional certification, which incurs more costs. However, as discussed above, the deployment of advanced NDT delivers a superior, and therefore higher £value service. Once advanced training is completed, as with any skill, it is important to practise what was learned on the training course. This can only be done if high-value advanced instrumentation is available. Again, purchase costs may be preclusive, so renting can be a preferable option. In addition, instrument purchase ties the user to a specific technology, whereas a rental fleet offers users the ability to deploy the most appropriate kit for each job, or to hire equipment from different manufacturers depending on the users’ training, experience and preference.

Purchase of a particular technology may also reduce or preclude access to other methods that may be developed at a later date.

It is important to remember that the capital expenditure on advanced NDT equipment is not the only cost. Instrument maintenance incurs a further cost, as does depreciation. Capital purchases will typically be written off in the company accounts over a 3 year period, which means that this equipment must generate substantial profit for a return on that investment. Also, there are borrowing and opportunity costs – the money used in equipment purchase or to pay interest could have been used for something else, such as training or hiring more staff.

To be a worthwhile investment, high value advanced NDT equipment must be used regularly. Without an assured steady flow of work, there is a danger of underutilisation. In contrast, renting provides a way to only pay for equipment when it is needed and not to incur any costs in the intervening periods.

In summary, the advantages of advanced NDT can be enormous if the financial implications are managed effectively. One way to achieve this is by taking advantage of rental instrumentation from Ashtead Technology.

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