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Through Optimum Use and Innovation of Welding and Joining Technologies
Improving Global Quality of Life
5
Needs and challenges in welding and joining technologies
5.3
Advanced technologies for maintenance, repair and life extension
As mentioned in the previous section, the revolutionary developments in microelectronics and computer
science are the reasons for advanced NDT technologies becoming available during the last decade. NDT has
been developed for maintenance, for better quality inspection after repair and for more reliable lifetime
prediction. The main areas of progress in NDT techniques applied in practice and reflecting the work in the
sub-commissions of IIW Commission V “NDT and Quality Assurance” are covered below.
5.3.1
NDT of welds by use of radiography, technical radiology & computer tomography
As long as radiography means irradiating a component by X-rays or Gamma rays and sensing the information
on a film, developing the film and analysing the developed film by human eye, the technique will suffer high
errors due to human factor influences. Some quality standards for instance in nuclear technologies, have
asked for film storage to have long-term documentation. Following the example of medical doctors who
have changed their standards, adopting the digitisation of the film material has tremendously enhanced
the technology. By applying automatic online working pattern recognition software, considerable success in
detecting imperfections can be achieved using the best trained NDT inspector as a benchmark.
After online digital radiology gained popularity, the more pixelised solid state flat panel devices became
available. Here also, by the use of pattern recognition software, reliability comparable to the best film
application can be achieved. The highest achievable capability for inspection is obtained by use of computing
tomography because of the multi-angle information taking into account imperfections that can lay with an
individual angle to the direction of the incoming energy. Here the synergic combination of digital detectors,
optimised reconstruction algorithms test and high-speed computing power is responsible for the progress.
A first inspection qualification according to the European Network for Inspection and Qualification (ENIQ)
recommendations in Europe for multi-angle radioscopic inspection of primary circuit pipe welds in Nuclear
Power Plants in Germany was successfully performed.
5.3.2
NDT of welds by use of ultrasound
5.3.2.1
Advanced UT techniques
In ultrasonic testing (UT) with the development of the so called array transducer the most intelligent and
flexible inspection probe was introduced into practice. The piezoelectric sensor membrane is divided into
multiple single source elements which individually are controlled in the amplitude and phase of the electric
pulses used for transmitting and receiving ultrasound. As micro-electronics becomes more miniaturised and
computing power becomes cheaper, systems are now available at reasonable prices. The advantage of the
transducer is the quick multi-angle-beam inspection which can detect individually oriented flaws.
Industrial phased arrays have been in development for decades, following medical phased arrays and other
areas like radar, sonar and geophysics. In the past, a small market, considerable flexibility demands, data
handling, software, and extensive training and experience requirements have hampered the wide use of
phased arrays for industrial applications. The first industrial commercial phased array systems appeared in
the early 1990s, but were large, expensive, and required good software skills. Most of these units were used
in the nuclear industry on specific advanced applications.
Currently, the phased array industry is maturing rapidly and phased arrays are becoming pervasive in
inspection markets worldwide. This is true both for industrial field applications as well as for more academic
applications in universities and research institutes. From a technical perspective, this is being driven by the
flexibility that they bring to an inspection task, with their ability to generate a wide range of ultrasonic beam
characteristics with one phased array unit.
