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Innovative Non-Destructive Corrosion Under Paint Integrated Detection System

Final Report Summary - CUPID (Innovative Non-Destructive Corrosion Under Paint Integrated Detection System)

Executive Summary:
Corrosion under paint (CUP) is a ubiquitous and persistent problem which affects almost every part of the entire infrastructure of modern civilization. Apart from the great economic damage which it causes annually, estimated to be 3% of Gross Domestic Product, it also compromises the safety, environmental and aesthetic characteristics of the affected structures, machinery and other artefacts. Due to the growth in the number of steel and metal structures which are susceptible to corrosion damage in critical sectors such as oil/gas offshore industry, bridges, refineries and chemical plants, there is an urgent need to develop technologies/techniques that enables and moves industries to adopt more cost efficient and reliable inspection and monitoring methods.

A pan-European consortium of SMEPs comprising Solid Offshore Technology (Norway), Tecnologia y Analisis de Materiales (Spain), Inray Solutions (Bulgaria), V-Viz (UK) together with RTDPs from Inspection Technologies (UK), and PRA Trading (UK) initiated a Cupid project for developing a novel solution of Corrosion Under Paint Integrated Detection system (CUPID). This system incorporates three separate, fully developed and complementary non-destructive testing (NDT) Techniques. The instrument combines a novel and inexpensive active diffuse, on-axis incoherent millimetre wave (MMW) and THz source of illumination. Incorporated into this same optical platform is a near infra-red (NIR) inspection system. Furthermore, the instrument also takes measurements from a novel planar capacitive imaging (CI) system. The results from this instrument represent a truly disruptive technology which can instantly detect corrosion under paint under large areas of painted surfaces. The CUPID system technology is filed under UK Patent Application GB1413566.9.

Developed system was validated first at laboratory scale in controlled conditions and subsequently in field conditions. Validation test results obtained by both PRA-T and SMEPs showed that the best method of the three was CI that is able to detect corrosion with the thickness over 100 microns, but MMW showed also promising results especially for detecting material loss, which is the most important criterion for evaluating the extent of corrosion in structures. During the course of the project it turned out that the NIR imaging technique is not able to penetrate through the paint systems containing micaceous metal oxide therefore it is not suitable for detecting CUP for structures mainly used in oil and gas sector that were under investigation in Cupid project. However, it can be used for NDT for other paint systems.

The Cupid consortium partners actively introduced the project and its results to specialist and public audience on a variety of conferences and seminars, published journal articles, and shared the latest project news on the designated project website (
Project Context and Objectives:
Large structures as ship hulls, ballast tanks, offshore platforms, buoys, refineries, chemical storage plants and bridges are all constructions and objects where structural failure due to corrosion may have severe economical and societal consequences and the problem of CUP will inevitably worsen with time as infrastructure and artefacts age. Early detection of corrosion is currently both costly and extremely difficult to achieve and often not possible at all until the problem has become severe enough to be visible to the naked eye. At this time most of the structural damage is already done and structures may have become potentially dangerous and maintenance much more costly than if done at an early stage.

The challenge for the inspectors in NDT sector working daily outdoors with inspection in all kind of weather, temperatures and at structures of wide variations of heights and difficult access conditions is the quality of the equipment, reliability and often necessity to raise scaffolding to get close access to the areas to inspect. Currently used NDT techniques for the detection of CUP such as radiography, ultrasonic, eddy current, require highly localised inspection. Some of these types of equipment are not easy to use outdoors and in difficult to access areas. Adverse weather conditions can also affect detection performance. Some of this equipment are too bulky and/or heavy to be easily portable. Due to small scanning area of these devices the inspection speed is slow for large structures and the overall inspection process is labour intensive requiring extensive preparation (e.g. scaffold raising) and often involve shutting down operation. This makes the whole process rather expensive and time consuming.

The main aim of the Cupid project is to deliver three novel, fully developed and complementary NDT Techniques. Cupid system combines Capacitive imaging (CI), Millimetre Wave (MMW) imaging and Near Infrared (NIR) inspection techniques into one system that would enable to detect CUP by scanning the surface of the inspected structure and subsequently visualizing and analysing the data in a specially designed software application able to detect areas of potential corrosion and cracks.

In order to realize this system several scientific and technological challenges had to be overcome.
First enhanced scientific knowledge had to be acquired about maximizing imagining resolution through thin scattering layers; investigate the use of incoherent (random phase and amplitude) free natural sources of background millimetre and THz waves for industrial applications; to combine millimetre waves and Near Infrared in a hyper-spectral and complementary fashion to produce an innovative defect detection which far exceeds current state-of-the-art (SoA).

In order to determine achievable lift-off it was important to characterize the defect resolution in terms of size of defect detected vs. distance from painted surface. From here to provide quantitative angular resolution measurements to act as a Figure of Merit for the NDT product and ensure a minimum angular resolution of less than 1 degree.

For Cupid application development it was important to optimize the algorithms and controls for fully automatic defect and corrosion detection. In order to optimise further industrial design the physical aspects of the system such as field of view, frame rate, minimum sensitivity etc. had to be determined.
In technology development phase of the project the main focus was on design and implementation of three separate modules of CI, MMW, and NIR imagers. Development of defect and corrosion detection was also undertaken with the aim of 3 sigma (99.7%) certainty of detecting specified sizes of corrosion and cracking, with false positive rates < 3%.

In integration phase it was first planned to integrate the MMW and NIR modules with their common optics into the same enclosure as a single combined instrument. After that it was envisaged to combine the CI with the MMW and NIR hyperspectral module.

An integrated Cupid prototype system (hardware and software) was then planned to validate under both controlled conditions and in the field.

Project Results:
During Cupid project the enhanced scientific knowledge was obtained and some novel technical solutions were developed.

For example in MMW imager development a truly novel, broadband, low-cost Microwave/Millimetre Wave/THz imager was accomplished by ITL which is capable of being used with an active single-mode microwave source, which does not experience the deleterious effects of specular reflection which have previously severely limited the field of near-field microwave imaging.
In recent decades, much effort and resources have been invested in developing uncooled, inexpensive, sensitive, millimetre wave (MMW) and terahertz (THz) detectors that can be used as pixels in focal plane arrays, in real-time imaging.
The linear pyroelectric imaging array resulting from the project has been demonstrated to be capable of exhibiting a continuous broadband response from microwave to THz wavelengths. This achievement represents a novel alternative to the extremely narrowband Schottky-diode based devices that are currently commercially available and at approximately 1% of the cost of these exiting commercial devices and has great potential for commercial exploitation extending beyond the original remit of the project.
Furthermore, the incorporation of a demodulating technique, for the first time makes it possible to use an active microwave/MMW/THz source which is not affected by standing wave effects between source and object and is totally immune to the normal disadvantages of using an active single mode microwave source and the deleterious effect of the dominance of specular reflections: hotspots, glare, glint and restricted viewing angle.
Thus it is now possible to have the best of both worlds in microwave/MMW/THz imaging by having the extremely high SNR of an active low-powered microwave source to obtain images that are not only (i) unaffected by the distorting effects of specular reflections and (ii) without the disadvantages of poor sensitivity and restricted dynamic range typical of passive imaging systems.
Combining the project result of the very low-cost alternative to state-of-the-art heterodyne Schottky diode devices with the fact that the demodulation technique removes a problem which for decades has limited the ability to perform near-filed microwave imaging, would be of great interest to many industrial sectors outside the immediate target market of NDT. For instance, security, in-vitro medical assay devices, inline industrial inspection and process control.

For NIR imager it turned out during the first testing (reported in D4.1 and 4.2) that it works in some paint systems - including those which contained layers of heavily loaded zinc primers - but not particularly well with those systems containing micaceous metal oxide. Thus, due to time constraints the decision was taken by the Technical Committee to concentrate on the other two aspects of the CUPID technology, CI and MMW.

The CI technique developed by ITL has proven able to detect corrosion layers under paint (including systems which contain micaceous metal oxide layers) which are 100 microns and more in thickness. Greater levels of corrosion and appreciable metal loss which conform to the detection criteria specified in standards such as the Common Structural Rules for Double Hull Tankers present little problem.
One aspect of this project result which differentiates it from competing SoA such as ultrasound inspection is that it requires no coupling medium and is sensitive to defects closer than 10 mm from the surface, where often diffraction and scattering can render many ultrasound inspection techniques, largely ineffective.

Additional markets outside of NDT could be the detection of defects and voids in all sorts of materials such as in the plastics and glass-fibre composite industries – and not just for inspection of product in service but also as part of inline quality audit inspection and process control.
Validation of Cupid system was carried out in three phases. First the laboratory scale testing was done by PRA where the Eddy Current based impedance spectroscopy (ECI) was used as a reference inspection technique. Test specimens used in these tests were prepared in controlled conditions (i.e. their corrosion pattern was known). Lab scale tests showed that the ECI and CI methods produce comparable results. However, ECI scans showed better spatial resolution than CI scans and scanner was capable of detecting areas less than 1 mm2. ECI method can determine early corrosion and scanned image is not influenced much on coating thickness. This technology can also give a profile of corrosion in terms of area and depth.

Field tests made by PRA in an industrial site showed that the CI scanner gave better results than the MMW scanner, but yet, CI scan showed only spots with severe corrosion, areas with minor corrosion were indistinguishable. Both scanners’ response to paint thickness showed that as the surface structure was uneven, early corrosion areas could not be resolved from non-corroded areas. This makes the inspection results unreliable.

Cupid technology was also validated by the SMEPs at the Statoil Subsea Pool facility in Kristiansund, Norway. The representatives of ITL demonstrated the technology to the representatives of SolidTech. In cooperation the validation tests were performed on subsea flow modules which had been retrieved from a depth of several hundred metres after a period of between four and eight years in service. Based on the field trials it can be concluded that the CI method could show regions of interest which extended around the usual visible signs of subsurface corrosion (deformation and bumps on the surface). These extended regions could not be seen with the naked eye.
The MMW did not seem to detect any regions of interest around the visible surface deformations normally associated with corrosion under paint. It would seem likely, however, from the MMW trials that had any appreciable corrosion or metal loss been present that this would be far more likely to be detected. Further testing is needed to support this assumption.
Potential Impact:
The aim of the partners of the Cupid project was to develop an innovative NDT system for the rapid stand-off detection of corrosion and cracks which are hidden under painted surfaces. The SMEPs participating in the project create a strong supply chain for the manufacture of the equipment and for bringing it rapidly to market through demonstration.

Now that the project has ended it can be concluded that even though the original target to develop a CUP detection instrument based on three different but complementary technologies did not fully realise, the results achieved have generated valuable IP for the participating SMEPs. Foreground intellectual property generated during the project has been protected by filing a patent application in UK (GB 1413566.9 System for non-destructive detection of internal defects).

As there is still the need and market potential for a rapid reliable and cost-effective CUP detection system SMEPs carefully analysed the results achieved by the end of the project and identified the specific areas that need further development. These concern mainly improvement of spatial resolution of both MMW and CI. Consortium has also discussed possibility to integrate the system on an unmanned crawler device that could access remote locations, for example.
Initial target is to address big oil and gas companies as important stakeholders of NDT field or public sources for further funding of the development.

The NIR imaging module that was found not to work on paint systems most relevant to Cupid project could be applied, for example, for paint systems not containing micaceous metal oxide particles. This technique could also be used for NDT of plastic or composite products in automotive or finished white goods for household appliances, for instance. By using sophisticated digital signal processing techniques and enhanced machine vision approach the NIR imaging could still be used also on paint systems used in the oil and gas sector.
It can also be summarized that the SMEPs have now gained new knowledge about novel techniques used in NDT and obtained IPR ownership that gives opportunity to generate revenue from licensing of knowledge rather than just trading of manufactured products or services. Participation in an R&D project like Cupid has taught SMEPs a valuable lesson about the challenges and risks associated with a high risk development projects like Cupid. Equally RTDPs gained experience in managing customer expectations and requirements in product development process.

Together with the identification of specific application services that can be developed using the results together with the international co-operation and marketing value within such a project, the consortium have succeeded in claiming the commercial potential originally intended.

The most up to date information is available on project’s public website ( ). Project partners have introduced the project results in several professional conferences and seminars like the 11th European conference on non-destructive testing, October 6 – 10th, 2014, Prague, Czech Republic, and in Overflate 2015 “Corrosion never sleeps”, November 4th-5th, 2015, Bergen, Norway.
During the project SMEPs met with over a dozen potential end-users of the Cupid system who showed interest in using such system for NDT. Such meetings are planned to be continued also post-project.
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