The short version of the history behind digital radiography (DR) is that research in this field began in the 1970s. In the early 1980s, the use of computed radiography (CR) with imaging plates was introduced in the healthcare sector.
In 1987, DR was introduced for dentists, and throughout the 1990s the quality of imaging plates improved and the range of applications expanded. By the early 2000s, most players in the healthcare sector had moved away from film radiography in favour of DR.
As quality improved, the potential for CR in industrial radiography became increasingly relevant. Equipment became better adapted to industry, but the cost and quality of imaging plates and scanners were still a barrier. Around 2010, however, both equipment and image quality had become good enough for use on most welded structures and for corrosion inspection. During the same period, direct digital array (DDA) equipment for industrial use also became available.
This laid the foundation for the NDT industry in Norway to replace a large part of traditional film radiography with digital radiography from 2010 onwards. It started mainly with corrosion inspection as part of offshore in-service inspection, but over the past 5 to 6 years, parts of weld inspection have also been replaced by CR. In recent years, some companies have also moved to DDA for weld inspection, and this will certainly continue to develop in the coming years.
This brief history shows that the development of new NDT equipment requires patience and effort from many different parties. Economic incentives and environmental aspects have influenced the change in industrial radiography, but another barrier has been the development of international standards and, not least, strict image quality requirements for weld inspection.
Digital Radiographic Testing (RTD) in Norwegian industry
When the equipment entered the market, several of the major companies recognised its potential because they had high inspection volumes and high film costs. A digital solution could remove both film consumption and chemical consumption, while environmental considerations and space savings also played an important role.
At the same time, the challenge was that image quality was close to the limit of what was commercially acceptable for weld inspection. In practice, the only commercial use of RTD was therefore in corrosion inspection. As a result, in-service inspection and on-stream corrosion inspection led the way in the use of RTD. Several of the major oil companies invested in scanners and imaging plates and were therefore able to reduce film and chemical consumption on offshore platforms.
During this process, several parties pushed to use the same system for weld inspection, but acceptance was not automatic. In 2013, EN ISO 17636-2 was published, providing a sound framework for weld inspection using RTD. This made CR and imaging plates an acceptable alternative to radiographic film. However, this still required correct use and application on the correct dimensions with the correct radiation source. CR remained demanding on thin material thicknesses, and quality requirements measured by SRb detector, SNRN, and sensitivity still had to be met.
DDA, on the other hand, had a somewhat longer path towards acceptance for weld inspection. Even today, equipment that can be used down to material thicknesses below 4 mm is expensive, and DDA should preferably be combined with X-ray equipment with a small focal spot (b < 1 mm). This requires a thorough assessment of the need and application area before investing in DDA.
Equipment
With EN ISO 17636-2:2013, the industry gained a framework that made it possible to assess the transition from RTF to RTD. From around 2010, the equipment also continued to improve, and CR in particular could be used on most dimensions in weld inspection. However, price sensitivity was still a factor, and equipment costing between NOK 500,000 and NOK 1 million requires a certain volume before industrial use is justified.
The largest players in weld inspection took the lead here and replaced RTF with RTD. CR was introduced at several yards and has gained an increasing position in the industry. From around 2015, several smaller inspection companies also began using CR, and over the past 5 to 6 years, CR has become a real competitor to RTF, also for companies with medium inspection volumes.
DDA, however, has faced challenges in gaining market share because equipment with good sensitivity has a high investment cost. In addition, there are some limitations on use for the smallest dimensions and thicknesses, and X-ray tubes with a small focal spot are still generally required to achieve sufficient image quality. Nevertheless, DDA is becoming an attractive alternative to both film and CR when used in combination with X-ray tubes with a small focal spot (<1 mm).
Today, CR combined with X-ray tubes is a well-established and proven alternative to RTF and primarily requires a practical and financial assessment by the user. DDA is also an alternative to RTF and CR, provided that the right assessments are made in relation to application area, economy, choice of DDA panel and X-ray tube, and provided that the user understands what is required to achieve the correct image quality.
Courses
Until 2022, courses and certification in RTD had not been offered in Norway. Nor had there been unambiguous requirements for accredited NDT certificates in RTD in legislation or NORSOK, as the development of these standards often lags behind equipment development.
However, EN ISO 17636-2 has contained clear requirements for training and qualification since 2013. The standard clearly states that personnel working with RTD must be able to prove that they have completed training and qualification in RTD. Until now, this has been handled through courses from equipment suppliers, some courses abroad, or internal company training.
Furthermore, the 2022 version of ISO 9712 added an annex with tables specifying course requirements for different techniques. EN ISO 17636-2:2022 now requires the training of RTD personnel to follow ISO/TS 25107, which provides a detailed description of the content of an RTD course.
Regardless of the course format, it is extremely important that personnel who will work with RTD receive thorough training in the complexity of RTD and can document their competence. NORSOK in particular has moved increasingly towards certification and currently requires training and certification in UT on austenitic materials. In addition, the consultation draft for the next version describes requirements for training and certification in PAUT. Given the complexity of RTD, we believe that NORSOK will also require certification in RTD.
It is therefore very important that all companies intending to deliver RTD services in the market prepare a course and certification plan for their personnel, so that they are not left exposed if something unforeseen occurs. RTD is complex and involves several risks of error. Strong competence in RTD will reduce the risk of compensation claims due to image quality issues or defects that have not been detected.
Over the past 6 months, Force Academy (Force Technology's Norwegian training department) has developed an RTD Level 2 course covering both CR and DDA. Force Certification has also developed an examination and can now provide accredited certification in RTD. This means that formal training is finally available in accordance with ISO/TS 25107, together with an accredited examination and certification in accordance with ISO 9712.
The course has been developed for personnel who already hold RTF Level 2. It consists of 3 days of digital learning, which can be completed from home with instructor support, followed by 5 days of classroom teaching and practical training in Kristiansand, Norway. We have invested in completely new facilities that are very well suited to RTD courses for 8 students per course. The students have access to 4 complete X-ray stations that can be operated simultaneously. These are connected to 2 complete CR systems and 1 complete DDA system. Combined with 8 software licenses, this allows us to run the course with the best possible balance between group training and individual learning.
The first course was held in October with 7 participants, and the December course is fully booked. 3 new courses will be held before the summer, and we see that more companies in the industry recognise the need to train their NDT technicians in RTD.
Certification
The examination is based on the framework in ISO 9712 and consists of a combination of theoretical and practical tasks. The theoretical part consists of 20 multiple-choice questions (1 hour) and the preparation of an instruction (1.5 hours). The practical part consists of two technical assessments of CR and DDA respectively (2 hours) against EN ISO 17636-2, and 2 complete exposures using CR and DDA, respectively, against the same standard (2 hours).
The pass requirement is 70% or better in all parts. When a candidate passes the examination, a certificate is issued for the RTD technique linked to the candidate’s RTF certificate.
The technique certificate follows the method certificate and is valid for as long as the main certificate is valid. This is because the technique certificate does not include sufficient film interpretation and therefore rests on certification in film interpretation under the main certificate.
The road ahead for RTD
The industry is now at a crossroads where RTD is a real competitor to RTF. This means that more and more companies will gradually choose RTD over RTF. As a result, courses in RT will shift from RTF as the standard solution before 2022 to RTFD as the estimated standard solution from 2024. In 2023, there will be a transition period in which many people with RTF Level 2 will add RTD Level 2.
How long it will take before RTD becomes the standard certification and RTF becomes an optional addition is difficult to say. Force Academy will follow the industry closely in the coming years and will naturally adjust according to the needs and wishes of our customers.
The history of RTD confirms that things take time, and there are many reasons for this. Image quality, standardisation, economy, and a certain degree of industry scepticism mean that the market does not necessarily embrace new techniques immediately. CR and DDA were introduced as alternatives 10 to 15 years ago. Even so, it is only in recent years that the techniques have become real challengers to RTF in industrial radiography.
