[보관함:] Case Studies

Within the nuclear industry welding of “thick section” components can be completed through various processes that are cost-effective, but the presence of residual magnetism in the materials has hindered the effective application of these processes. For many years the aim has been to find a suitable process that can be used more widely across the nuclear industry.

Even though output within nuclear is low, the safety-critical nature of these components demands a solution. Typically, the welding of “thick section” components such as pressure vessels within the nuclear industry has traditionally been performed using arc-welding techniques, which require multiple weld passes with an interstage non-destructive examination (NDE) and preheating of the component to reduce the risk of hydrogen cracking.

For a nuclear plant, the joining of components is currently used through the use of the tungsten inert gas (TIG) process. TIG welding of “thick-section” pressure vessels such as the reactor pressure vessel is an expensive and time-consuming practice involving extensive pre-work including fixtures, tooling, pre-heating of the components and multiple weld passes. Another drawback to using the TIG process is that it can only penetrate to a certain depth so thick-section welding is executed by filling the weld groove with several passes. Typically, this involves up to 100 runs of weld for a typical reactor pressure vessel section of 140mm or greater.

Consequently, there are a few disadvantages of using this process, namely multiple runs requiring preheating, inter-pass temperature control and inter-stage inspection by NDE throughout the whole process. The welding, inspection and completion of an RPV, therefore, takes many weeks, even months thus accounting for a vast proportion of the fabrication cost and component lead-time. Historically, there have been many attempts to deploy electron beam welding (EB) with local vacuum pumping, but most were hampered by the need to work at a high vacuum.

Previously, trade organisation, The Welding Institute has demonstrated that operating the EB process in the pressure range of 0.1-10m bar, so-called ‘reduced pressure’ in preference to high vacuum ~10^-3mbar offers possibilities of more reliable deployment of local sealing and pumping for EB welding on a large structure. In the late 1990s, TWI developed a high power (60kW) EB welding system for girth welding of long offshore oil and gas transmission pipelines.

Excellent weld quality was achieved consistently with rudimentary pumping and flexible rubber seals and the process showed that there was a good tolerance to material cleanliness, fit-up, surface condition and working distance with the potential to fully girth weld 40mm wall thickness, 711mm diameter pipe sections, in less than five minutes.

The more recent developments of electron beam welding technology offer the opportunity to weld “thick-section” components in a single pass and negate the need for (NDE), which means there’s a significant saving in time and cost in the fabrication of nuclear pressure vessels. Furthermore, elimination of the preheating step is possible since the EB process is carried out in a vacuum environment.

Compared with other welding processes there are many advantages of using electron beam welding within the nuclear industry. It can offer significant savings in cost and time for “thick-section” fabrication due to the rapid joining rate resulting from the process of welding the full joint thickness in one single pass.

However, due to the physical size and geometry of nuclear pressure vessels, traditional vacuum chambers would be prohibitively expensive when considering the low volume of output in the nuclear industry. Currently being pioneered in Britain, Cambridge Vacuum Engineering has recently launched a revolutionary local vacuum EB technology called Ebflow.

The EBManPower project, which is a joint- collaboration between CVE, TWI, U-Battery and Cammell Laird, will implement and validate the first Ebflow system within a large-scale fabrication facility for cost-effective manufacture of large-scale power generation infrastructure.

The Ebflow technology will specifically focus on reducing the cost of “thick section” steel structures applicable for both nuclear and off-shore wind structures. The collaborative partners are hopeful that their project will be critical in helping Ebflow to reach the marketplace and work in a real-world environment.

Compared with other welding processes there are many advantages of using Ebflow technology within the nuclear industry.

This particular project aims to manufacture components for nuclear power plants. Similar processes have been successfully applied in other industrial sectors, but this is the first time this approach has been applied within the power sector.

The demand for “thick section” steel structures in the power generation is already strong and will continue to grow over the years. Currently to produce a typical 100-metre long monopile (100mm thick) it can take more than six thousand hours of ‘arc-on’ welding time. However, the Ebflow system, based on high productivity electron beam welding can reduce the welding time involved to less than 200 hours equivalent to a 85% cost reduction.

Due to complete in 2021, the EBMan Power project aims to will resolve many years of development of trying to attempt and deploy electron beam welding within the global industry.

This will become a reality, rather than a possibility and may help to relieve some of the production pressures the world currently faces as well as contributing to the solution of what is known as the “energy trilemma” (low carbon, secure and affordable energy) and enabling a low carbon economy.

Micro modular reactors (MMRs) are a type of nuclear fission reactor that are smaller than conventional reactors and manufactured at a plant and then brought to a site to be fully constructed. Modular reactors allow for less on-site construction, increased containment efficiency, and heightened nuclear materials security. MMRs have been proposed as a less expensive alternative to conventional nuclear reactors.

U-Battery is a micro modular reactor (MMR) that will be able to produce local power and heat for a range of energy needs. The original challenge was to design an economically viable, modular nuclear power generation system that is intrinsically safe. Putting this into context, large scale nuclear reactors require high capital investment and heavily rely on the infrastructure of nuclear sites.

Designers were therefore motivated to develop smaller-scale reactors, especially for developing countries and remote areas off main power grids. The development of micro modular reactors presents a host of economic, industrial and environmental opportunities, contributing to the solution of what is known as the “energy trilemma” (low carbon, secure and affordable energy) and enabling a low carbon economy.

Globally, 79% of electricity is generated by thermal processes, in which conventional power plants provide over 62% of the global electricity supply and the remaining 17% is by nuclear fission processes and this is expected to increase further (IEA, 2015).

Thermal power plants make use of a large number of thick section (greater than 20mm) components for many parts of the primary circuit; pump and valve bodies, ancillary systems and other safety-critical components. Furthermore, offshore wind demand in the UK requires more than one thousand structures (towers and foundations) or 1 million tonnes of steel to be cost-effectively fabricated on an annual basis.

The demand for “thick section” steel structures in power generation is already strong and continues to grow. The ability to fabricate these thick section structures cost-effectively is in part limited by the welding time and associated cost; to produce a typical 40-metre long monopile (60mm thick) can take more than six thousand hours of ‘arc-on’ welding time. The long term benefits of this partnership will be increased revenues and exports as well as the securing of high-value jobs in the manufacturing and low-carbon energy sectors.

To reduce cost the manufacturing time needs to be significantly reduced.

Cambridge Vacuum Engineering (CVE) has developed the Ebflow system, based on high productivity electron beam welding, which can reduce the welding time involved to less than 200 hours, equivalent to an 85% cost reduction. The EBManPower project will implement and validate the first Ebflow system within a large-scale fabrication facility to enable cost-effective manufacture of large scale power generation infrastructure.

Cammell Laird is one of the UK’s heavy fabrication shipbuilders and is the manufacturing partner for the U-Battery micro modular reactor (MMR) system. The EBManPower project is due to complete in 2021 and is valued at £1.5 million. The Ebflow system will be deployed at the Cammell Laird site in Birkenhead to fabricate a demonstration modular reactor pressure vessel for the U-Battery, and other related energy products in a cost-effective manner. This practical demonstration will be critical in driving the widespread deployment of the new cost-effective solutions to meet low carbon needs across the energy sector in the UK and overseas.

In the longer term, a key objective of EBManPower is to stimulate the development of a flexible and efficient advanced manufacturing technology (electron beam welding) for the manufacture of components for nuclear power plants. Similar processes have been successfully applied in other industrial sectors, but this is the first time this approach has been applied within the power sector.

The project is at its heart focused on reducing the cost of “thick section” steel structures applicable for both nuclear and off-shore wind structures. EBManPower will exploit CVE’s revolutionary EBFlow system and will innovate, demonstrate and provide a near to market result; validation in a real-world environment is the ultimate aim. The project will take a technology concept, the feasibility of which has already been proven, and make the final push to reach the marketplace. The results will be used to enable its UK based consortium to enter and compete in the power industry plant component supply chain as well as bringing opportunities for other sectors and clients.

“Our revolutionary Ebflow technology, fully developed and pioneered in Britain, will transform the productivity of fabrication processes throughout the world of heavy engineering. In many cases, the speed of welding can be 30 times faster than current methods.” Bob Nicolson, Managing Director at Cambridge Vacuum Engineering.

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Engineering specialist Sheffield Forgemasters is to lead a consortium of partners in its largest ever research and development project, with an overall project value of £10.5 million.

The company will explore industrialisation of electron beam welding (EBW) in civil nuclear assemblies, with the potential to integrate welding into the manufacturing process, offering material improvements and vast reductions in manufacturing time and cost.

Sheffield Forgemasters has been awarded £8 million of funding to lead strategic partners in the project, from the Government’s Department for Business, Energy and Industrial Strategy (BEIS), the largest single grant given under its £20 million Nuclear Innovation Programme.

Jesus Talamantes-Silva, Research, Design and Technology Director at Sheffield Forgemasters, said: “This is a landmark project for the UK, building on three years of work we completed in partnership with Innovate UK (the UK’s innovation agency), to refine the basic science of electron beam welding in nuclear applications.

“It is our largest research project to date, which launched in August, running until March 2021, and the implications of accelerating this technology for civil nuclear power are significant, but could also benefit other sectors including defence, offshore and petrochemical industries.”

Sheffield Forgemasters will collaborate with partners from CVE, TWI, Arc Energy, NAMRC, The University of Manchester and Cambridge University. It will also work with an invited steering committee of Rolls Royce Civil Nuclear, Rolls Royce (Submarines) Cavendish Nuclear, the MOD and the UK Atomic Energy Authority.

The company will install an electron beam welder capable of welding 3.0m diameter cylinders under localised vacuum and without traditional welding preparation, offering narrower welds than traditional methods plus the ability to weld as part of the manufacturing process, prior to quality heat treatment.

It will then manufacture a civil nuclear component to demonstrate a full-sized (4.3m high x by 3.0m diameter) small modular reactor pressure vessel and also produce several grades of steel alloys suitable for civil fission and fusion nuclear applications within the project’s research element.

Jesus Talamantes-Silva added: “This is a highly advanced manufacturing process which has not yet been brought to industrialisation in this sector. Although EBW exists elsewhere, it is used on a smaller scale than the 200mm welds that we will conduct.

“We aim to demonstrate how EBW can improve material characteristics over traditional welding, which heats up a larger volume of material, but also how this technology can integrate at manufacture to remove component weld properties at a later stage.

“Using EBW over traditional welding techniques, circumferential welding of pressure vessels can be reduced from approximately 150 days to 10 days. Through the science that we have already refined, we will be able to produce safer, stronger components for the next generation of nuclear power, with lower costs and vastly reduced production times.”