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Development of Quantitative Radiographic Tomography technology for the in-situ Inspection of welded austenitic safety critical pipework in the nuclear power generation and petrochemical industries

Final Report Summary - TOMOWELD (Development of Quantitative Radiographic Tomography technology for the in-situ Inspection of welded austenitic safety critical pipework in the nuclear power generation and petrochemical industries)

Executive Summary:
Austenitic steel is often used in the construction of pipework in the nuclear power industry due to its resistance to corrosion and its high fracture resistance. Pipelines are usually constructed by joining sections of pipe together, using welding. These welds can host many types of defects if not inspected, and under stress these defects can grow and lead to mechanical failure. Thus, detection of such defects is critical.

Currently, inspecting austenitic welds using ultrasonic techniques is very difficult due to the material’s inhomogeneity and anisotropy. In austenitic steel, an applied ultrasonic beam is subjected to many fluctuations, i.e. scattering (severely reducing signal to noise ratio and therefore defect detection capability), skewing and bending, beam distortion, velocity changes - all of which can make defect sizing and positioning difficult and inaccurate. In addition, there might occur ghost echoes resulting from the anisotropic and heterogeneous metallurgical structure of the welds which can disturb the results. Therefore radiographic inspection methods can offer numerous advantages.

Conventional film radiography is the current technique used for inspecting these materials, as the grain structure does not significantly affect the radiographic results. However, the drawback of using film radiography is the long exposure times, and the limited information available from the inspection results.

In general, there is a trend towards replacing radiographic film with digital detection media. This is due to digital detection technology generally allowing quicker X-ray image acquisition as a result of shorter exposure times, together with the added benefits for display, processing and archiving. However, even if a digital detector was used for the inspection of welds in austenitic steel as a replacement for film, there is still an inherent problem in that the inspection output yields a 2D image of a 3D object. This causes the superimposition of internal features (reducing the contrast sensitivity) and the inability to position the depth of defects in the direction of the X-ray beam. In addition, conventional 2D radiography can only detect planar defects (such as cracks) that are correctly orientated to the X-ray beam, i.e. sufficient through-thickness extent in the direction of the X-ray beam. The solution is the application of the multi-angle radiography inspection technique.

The TOMOWELD project aimed at developing a unique tomographic solution for non-destructive condition monitoring and inspection of thick pipework. The special focus was on large and thick austenitic steel pipes used in nuclear power plants (NPPs). In nuclear power plants, defects in e.g. welds may have very severe consequences if they lead to failure of the pipe. The TomoWELD project has developed a robust mobile X-ray tomographic system for the accurate inspection of austenitic steel welds at the sensitivity levels required in the nuclear industry. The application of X-ray computed tomography overcomes the limitations of current inspection techniques by providing 3D information of the internal structure, allowing detailed cross sectional analysis and dimensional measurements to be obtained. This is realized by a new concept of the scan geometry, an enhanced GPU based 3D data reconstruction, and the application of a new generation of photon counting DDAs. The new detector permits selection of energy thresholds to obtain an optimum energy range, and reduction of the influence of scattered radiation.

TomoWELD provides:
• A reliable NDT method for the volumetric examination of austenitic and ferritic pipework
• A higher level of confidence in the integrity of critical austenitic welds in nuclear power plants.
• Accurate sizing and characterisation of critical defects.
• Data related to the condition of critical pipework enabling maintenance work to be prioritised.
• A reduction in the overall in-service maintenance capital expenditure budget within the nuclear power plant industry.

Project Context and Objectives:
The TomoWELD project proposed to develop a robust mobile X-ray tomographic system for the accurate inspection of austenitic steel welds at the sensitivity levels required in the nuclear industry. The application of X-ray computed tomography will overcome the limitations of current inspection techniques by providing 3D information of the internal structure, allowing detailed cross sectional analysis and dimensional measurements to be obtained.

The main technical objectives for the project cover the development of:

1) An automated radiographic inspection technique and procedures for site work on nuclear power plant (NPP) to examine austenitic stainless steel pipe butt welds for pipe diameters up to 350mm and material thickness up to 35mm single wall (70mm penetrated thickness double wall). The technique to be capable of detecting planar and volumetric defects throughout the weld volume to a level of 2% of wall thickness or better for single wall up to the target thickness. This includes the determination of the performance requirements and system components (technical and functional specifications) of the proposed system, including all hardware and software components and their architecture.
2) Inspection work, underpinned by the development of modelling tools for image reconstruction from limited data of the test components. An existing radiographic simulation tool will be adapted for generation of synthetic tomographic projections for relevant configurations and to determine the optimum tomographic technique with respect to the theoretical and practical aspects.
3) Sample test-pieces required for the development work and the laboratory trials designed and fabricated.
4) A novel digital detector array (DDA) for the range of radiation energy levels to suit the component target diameters (up to 350mm) and material thicknesses (up to 35mm).
5) Image processing software algorithms for data acquisition and fast image reconstruction of the test component.
6) A lightweight mini-focus (<500µm focal spot size) miniature X-ray unit to operate at a maximum target output of >240kV - 270kV and medium power consumption (300W).
7) The required hardware will be developed, designed and built along with software components for the hardware control.

Project Results:
The main S & T results/foregrounds are:

1. Representative austenitic stainless steel weld sections/samples containing realistic defects for technique development and validation of the TomoWELD system, digital detector arrays (DDAs), robotic manipulator, imaging software and the developed inspection procedure.
2. Technical and functional specifications for the system to be agreed with the end-users, AREVA (pressure components manufacturer to the global nuclear and petrochemical industries).
3. Innovative digital radiographic tomography site applicable techniques and procedures to cover the radiation energy levels needed to adequately test the range of pipe sizes (i.e. diameter and thickness) within the scope of the project.
4. Innovative DDA for the detection of pipe-weld defects specified in WP1 and including a relevant planar (smooth and rough facet) and volumetric defects.
5. Innovative new miniaturised X-ray source with higher kV energy and large opening window and cathode to anode acceleration oriented parallel to the pipe axis to penetrate larger wall thickness pipe welds up to 30 - 35mm.
6. Innovative robotic manipulator carrying radiation source (X-ray unit) and DDA together with control system and data acquisition/display for high speed testing of pipe welds.
7. Innovative image data processing software algorithms for data acquisition and fast image reconstruction of the test component.
8. Innovative modelling tools for image optimisation of reconstructed image from limited test data.
9. Innovative prototype Integrated TomoWELD inspection system comprising of the robotic manipulator, radiation source, DDA and control system with data display software.

Potential Impact:
Improved competitiveness of SME Participants
Improved SME competitiveness will result from the new integrated radiographic tomography system and techniques that will enable a far higher integrity of on-site volumetric NDT inspections taking place on austenitic stainless steel pipe welds in nuclear power plants, petrochemical and process plants. This is compared to the current practice of using pulse echo ultrasonic testing and conventional film or digital radiography, both of which have limitations.

Economic Justification for the Research – Cost Effectiveness
The total REA and Consortium SMEs’ investment in the project is anticipated to yield an approximate 20:1 per year return on investment (ROI) per year 4 years following the project completion for the participating SMEs. The project’s overall ROI for the wider benefit of the EU is anticipated to yield approximately 85:1 ROI per year 4 years after project completion.

For Nuclear Power Plants (NPP)
The developed TomoWELD radiographic tomography technology targets in-service non-destructive inspection of austenitic stainless steel pipe welds operating in safety critical applications in nuclear power plants (and petrochemical plants). A TomoWELD inspection results in a defect detection level that cannot be achieved using existing ultrasonic techniques because of the adverse effects of the large columnar grain structure. Unlike existing film and digital radiographic techniques, the developed tomographic technique enables more detailed information to be deduced relative to detected indications and defects. For example, precise defect position and depth in the weld through-thickness is provided. This enables an engineering critical assessment (ECA) to be made to ascertain the impact of any detected defect on the continuing operational integrity and safety of the plant. The TomoWELD system is able to offer the following advantages:

1. Reduced assessment costs through inspections that provide a more thorough and searching examination with enhanced volumetric data imaging of suspect weld areas
2. Faster and more effective inspections, reducing outage time, thereby increasing plant availability and revenue earning capacity.
3. Reduced risk of critical weld failure and subsequent costs of litigation, clean up, lost production, personnel injuries and fatalities, and bad public relations because a more complete and searching inspection is undertaken.

Within the EU there are some 145 reactors, mainly pressurized water (PWR) but also some boiling water (BWR) and advanced gas-cooled (AGR) reactors, and 445 reactors world-wide. However, some countries currently operating NPP plan to phase out their nuclear capacity over the next decade, most notably in Germany. A further 62 reactors are under construction and a further 66 reactors are planned world-wide, including some in the EU, such as France, Finland and the UK with the majority being in the Russian Federation, India and China, who are purchasing reactors and associated technology from the EU and the USA.

In the European Union as a whole, 145 NPP provides about 27% of the electricity, and energy companies across Europe have expressed a strong interest in investing in new NPPs despite the high initial investment (€6billion) for construction.

Worldwide, Europe (Western Europe in particular) along with Japan and the Eastern seaboard of the USA has the highest concentration of NPPs. This demonstrates the fact that innovative nuclear plant inspection technologies such as TomoWELD can have a significant impact on the entire European economy and beyond.

The Consortium SMEs will benefit from increased opportunities in the EU and global nuclear power generation industry through sales of the TomoWELD products and provision of inspection services. Furthermore, Europe will benefit from the economic savings brought about with the introduction of the TomoWELD system, and the mechanism of ensuring the safety of Europe’s NPP, which would help ensure a continued, and uninterrupted power supply. The NPP operators are large corporations, and they are backed by government institutions. A vast majority of these NPPs outsource their inspection and NDT to SMEs in the inspection business. Moreover, SMEs also dominate the inspection equipment manufacturing market in Europe and serve their clients in the nuclear power generation sector.


For Non-Nuclear Plants
Sectors other than nuclear are not being targeted by the TomoWELD consortium until after 2018. However, it is possible to estimate that EU petrochemical, process plant and pharmaceutical industries could represent a €128.5million pa benefit for the EU. The EU petrochemical, process plant and pharmaceutical industries are represented by 110 refineries (700 worldwide including 40 terminal processors), 650 major [€500k minimum revenue per day] chemical plant (3300 worldwide) and 2,000 smaller [€200k average revenue per day] chemical, process and pharmaceutical plants (10,000 globally).

Total EU Economic Benefits
The total EU economic benefits are given as Economic Benefits to the participating SMEs, and Economic Benefits to the EU Industrial economy at large for the nuclear generation and the petrochemical/process plant market sectors.

(a) Participating SMEs Sales and Profit estimates
Summarising the sales and profits of the TomoWELD products, on-site services, technical support and licensing over a four year period following project completion: Each of the SME partners gain sales in their own rights in what will be an increasing market for decades to come. The annual profit in Year 4 is over €12million per year representing sales of over €31million per year for the five project participating SMEs 4 years after project completion.

It is estimated that there are over 14,000 potential end-user world-wide client plant operators (445 nuclear power plants, 700 refineries, 3,300 major chemical facilities, and 10,000 process plant, smaller chemical facilities and pharmaceutical plant). The percentage market penetration for each of the components resulting in the estimated number of units sold, and applied on-site radiographic services, is considered to be conservative at 25% for NPP and 10% for petrochemical plant.

In addition there are over 7,000 offshore oil & gas installations globally that could also derive benefit from the application of the TomoWELD system, but this is not included in this analysis scenario.

(b) Savings due to reductions in ‘outage days’ and pipe failures
NPP savings due to a reduced number of outage days per year is estimated at €46 million per year within the EU and €95 million globally.

New and Improved products and services with clear market potential: The TomoWELD product will produce a step change in industrial radiographic tomography inspection. It enables, for the first time ever, high energy radiation to be used under safe radiation protection conditions, on-site, to non-destructively examine safety critical austenitic stainless steel welds on nuclear power stations. Furthermore, this is to a standard that has not been achieved in the past. TomoWELD is far superior inspection method compared to using ultrasonic techniques which are severely limited in defect detection capability on austenitic welds. The new prototype radiation digital detector array (DDA) system provides significant improvements in image quality over current digital or film radiographic methods, achieving class B quality according to EN ISO 17636-2; enabling improved defect detection capability and the evaluation of potentially serious indications such as cracks, lack of weld fusion and undercut.

Further technical development, demonstration after completion, and time to market: Following completion of the project, which is targeted at the specific application of NDT of austenitic stainless steel pipe welds in the nuclear industry, further technical advancements will essentially be engineering based in terms of product development. The intention is to further miniaturise the apparatus, in order to gain access to pipes in difficult location in terms of inspection envelopes of less than 250mm height around the pipe, and to also improve production rates.

The technical engineering product developments required for commercialisation could be drawn from each, or a combination of, the following routes.

(a) Invest from individual or participating SMEs collectively
(b) Outside investment from banks or venture capitalists
(c) Investment from large scale end users
(d) Investment raised from future order down payments

Equipment and technique demonstration will take place, initially within the project, and post project as part of the marketing process from the participant SMEs and service inspection companies that have taken on the technology through licensing and purchase of the final engineered TomoWELD equipment.

Impact of participating SMEs: The most significant impact for the participating SMEs is the ability for early entry into a new applications global market for digital radiographic tomography in the nuclear and petrochemical industries, or for any industrial/engineering sector that uses austenitic stainless steel pipework in safety critical or economically critical processes, e.g. pharmaceuticals and food processing. For experienced radiographic service inspection company providers, the transition into this new market application will not be difficult as they already have the infrastructure and internal processes to meet international nuclear requirements, e.g. nuclear safety passbooks and records to work on NPP.

Economic Growth and increase in EU and International Markets: Unfortunately, the exploitation set-up envisaged in the project has suffered from the decisions in Europe following the Fukushima break-down. This has stopped a lot of investments, and all German NPPs will close over the next years. This has reduced the business potential, and also the possibilities of AREVA (Germany) to advocate for the TomoWELD system benefits. In the period before commercialisation a new evaluation of the potential market for TomoWELD should be made.

However, the main target market of nuclear power generation is still currently set to grow over the next two decades with a number of new nuclear power plants planned. Also, existing NPP operators are looking to extend the life of their plant, after first justifying the move based on sound engineering reasoning backed up by an enhanced inspection regime. This is despite a small number of countries (notably Germany in Europe) deciding to prematurely close down their existing NPP, although other EU countries (France, Finland and UK) are building new plants.

Employment: TomoWELD will create further employment opportunities for the partner SME companies, and those involved in NDT and inspection of NPPs and other energy related plant with installed austenitic stainless steel pressure retaining pipe welds, including petrochemical plant. It is estimated that the project will help create an additional job per €100k worth of sale.
List of Websites:
TomoWELD website address: http://www.tomoweld.eu

For enquiries regarding the TomoWELD system contact : Joergen Rheinlander, InnospeXion ApS,
Horseager 14, DK 4330 Hvalsoe - DENMARK
Tel:(+45) 4640 9070, Fax (+45) 4640 9044, e-mail: tw@innospexion.dk website: www.innospexion.dk

For enquiries regarding the detector contact: Klaus-Peter Finke-Harkonen
Oy AJAT Ltd, Tekniikantie 4 B, FIN-02150 ESPOO, Finland
Tel: +358 (40) 024-3929, e-mail: klaus@ajat.fi website: www.ajat.fi

For general enquiries contact: Ian Nicholson
TWI Ltd, Granta Park, Great Abington, Cambridge, CB21 6AL, UK.
Tel: +44 (0)1639 873100, e-mail: ian.nicholson@twi.co.uk website: www.twi.co.uk