Safe solutions

Areas as diverse as nuclear power stations, medical instruments and rail tracks need constant inspection to ensure they remain safe. Colin Carter looks at the variety of technology on offer


Measuring the properties of a material and estimating how long it will last is big business — especially in safety-critical situations — so it’s comforting to know someone is keeping an eye on the state of aircraft wings or making sure nuclear power stations have pressure vessels that aren’t about to split in two.

Another safety-critical area is the medical sector, where there are obvious dire consequences of the failure of commonly-used devices such as needles, sutures, tubing and protective clothing such as gloves. One solution is provided by Instron, whose in situ 3300 single column medical device system is small enough to be kept within a medical laboratory.

The device can be configured with grips or fixtures to perform tension, compression, flex and peel testing with a load range from 500N to 5kN with a range of custom fixtures for testing specialist components such as biomaterials, dental pieces or orthopaedics.

The system also features its own ‘Bluehill’ software suite (or optionally a ‘TouchPanel’ controller) which can be configured to handle whichever type of test is run, handle data analysis and undertake pass/fail analyses.

The provision of software to control materials testing machines is also at the heart of Zwick’s Touch PC — the latest addition to its range. The machine contains an integrated embedded industrial computer with a touch screen which is mounted directly on to the company’s material testing machines.

The Touch PC comes equipped with ‘testXpert’software to control the test process as well as ‘FaststartXP’ to allow the operator to select either a read-only mode for shared workstations or ‘designtime’ mode with unrestricted access.

Of course not all measurement processes involve destruction-testing. US-based New England Precision Grinding tests the quality of its medical devices — such as micro-miniature needles and catheter-placed stents — using optical comparators.

These are manufactured from materials such as 304 stainless steel and super-elastic nitinol and are so small —they are made from wire with diameters from around 0.003in (0.08mm) — inspection is impossible by traditional methods.

The technique was developed by the UK’s LS Starrett using its optical comparators which use 50x or 100x power lenses to display the pieces so that processes such as laser cutting, electro-polishing, welding, electrical discharge machining (EDM) work and laser marking of parts can be analysed.

Inspection is also important for much larger systems such as railways. Both here and around the world a great effort is made to check the condition of track and train components to help ensure the rail system’s safety.

Forces at the interface between train wheels and the rail can be measured by Interfleet Technology’s Instrumented Wheelset Technology IWT4, which utilises the train’s standard production wheelset without any destructive modifications.

Interfleet claims the system can be used for the validation of simulation models, research and development, troubleshooting, system optimisation, demonstrating safety under varying speeds and axle load conditions, assessing ‘track friendly’ conditions, monitoring track quality and the investigation of both rail and wheel wear and the likelihood of fatigue problems.

Rail inspection is an area where non-contact laser methods can be used to analyse the surface of the rails themselves. Micro-Epsilon has supplied Scancontrol sensors for use in a system for monitoring rails on Russia’s network which the company claims is minimising maintenance and downtime costs.

The system works by projecting a laser line on to the rail’s surface, and collecting the back-scattered light by a complementary metal oxide semiconductor (CMOS) sensor array, which is capable of measuring light even from highly reflective surfaces such as a worn rail. A controller processes the sensor data and is able to plot a 3D representation of the rail at speeds up to 80mph (130kph).

There are also companies specialising in rail inspection, backed by teams of engineers to provide inspection analysis.

One example is OIS, a member of the Aberdeen-based Abbott Group, which uses GE Inspection Technologies’ Small Controlled Area Radiography (SCAR) system to test for defective rails and welds. This produces digital radiographs of rails, which is claimed to identify any problem areas in under three minutes.

The company has also supplied a phased array ultrasonic testing machine for use on Germany’s railway network. This system is used at regular intervals to check wheelset axles for flaws and cracks, which GE says has proved much more reliable than any manual methods.

A complete non-destructive testing regime for the rail industry is also offered by companies such as Material Measurements, which has expertise in dye penetrant, magnetic particle, ultrasonic, radiographic and eddy current testing of wheels and other railway components for potential failure-inducing cracks.

While destructive and non-destructive has throughout the years been important work, testing technology is constantly being developed and improved.