As an example of one industrial need, a government review of the UK’s electrical energy requirements for 2025 has indicated that 60GWe of net new capacity will be required in order to meet demand. This will come from both new nuclear fission installations, as well as renewable energy sources (eg wind turbines). Both of these types of fabrications will require the joining of thick section (>30mm) ferritic and stainless steel grades, e.g. in pipework, pressure vessels and wind turbine support towers. In addition, fusion programmes (eg ITER) are now moving towards construction phases, and also require the joining of thick section stainless steels, amongst other materials (eg Cr-containing creep resisting ferritic steels).
The objectives of the proposed project are:
- Develop laser welding conditions for thick section butt welding of industry-relevant grades of steels and stainless steels, for thicknesses in the range 25-75mm.
- Evaluate the weld qualities with respect to relevant standards (ISO 13919, API 5L etc).
- Evaluate the weld properties with respect to relevant standards and codes (ISO 15614, ASME section IX etc).
- Carry out a techno-economic comparison of the process(es) developed with competing processes, in terms of equipment costs, deposition rates, welding speeds, joint completion rates etc.
A number of industries (including the power and oil and gas sectors) require processes for high quality, high productivity, low distortion welding of thick section steels and stainless steels. As an automatic, low heat input process, laser welding could prove suitable for such applications. This project will develop approaches for thick section laser welding, including:
- High power, single pass welding: TWI is aware of an increasing number of Yb-fibre and Yb:YAG disc laser sources (ie fibre-delivered, 1µm wavelength laser sources) with an output power ≥ 10kW being sold for primarily research, but also production welding activities. Currently however, examples exist predominantly outside of the UK (principally in Germany, US and Japan). These high power fibre-delivered laser sources are beginning to replace high power CO2 laser sources in industrial applications, due to their lower operating costs (eg increased wall plug efficiency) and increased flexibility from the fibre-delivery. Furthermore, the reduced operating cost of fibre-delivered laser sources is increasing the economic argument for their adoption in other industry sectors.
- Lower power, multi-pass welding: Research work with Nd:YAG and CO2 lasers has already shown that narrow gap, multi-pass laser welding (with wire feed) has potential for such applications. With the increases in beam power, power density (through reduced focused spot size) and stand-off distance offered by modern fibre and disk lasers, further advances in these capabilities are undoubtedly possible.
This project will raise the manufacturing readiness levels of welding processes based around these two approaches, using the latest fibre delivered laser technologies about to become available in the UK, along with, in cases to be selected, hybridisation with arc sources, seam tracking, and process monitoring and adaptive control of welding parameters, to increase industrial robustness and relevance.
Relevant Industry Sectors