REDUCED PRESSURE EBW

Conventional electron beam welding (EBW) requires components to be contained in a vacuum environment to achieve high integrity operational results. This factor can introduce a time and cost penalty and may preclude work requiring welding in-situ or all position welding.

Although in-air EB welding processes have been developed in the automotive industry for welding thin section steels and aluminium, the technology is of limited scale and suitability. Under licence from TWI, CVE are now able to offer a solution that allows welding of thicker materials and a wider range of metals at a coarser vacuum.

Typical thick section EB welding is often performed at a vacuum in the 10^-3 mbar range or better. Reduced Pressure Electron Beam Welding (RPEBW) has been demonstrated to weld up to 200 mm in steel in a single pass and a range of thick section light alloys at pressures around 0.1 to 10 mbar. Coupled with techniques to rapidly make a local vacuum using clamp-on chambers and seal both external and internal diameters of circular structures make RPEBW a valuable engineering technology.

Process advantages of RPEB

• A typical 100 kW RPEB gun system produces a tightly controlled beam at a stand-off distance of 50 – 500 mm
• Power and control affords single pass thick section high quality welding with low distortion on a variety of metals
• Operating at a lower vacuum brings significant reduction in pump down time – typically 75% reduction using only low-cost roughing pumps
• Welds can now be free from contamination by atmospheric gases
• Clamp-on chambers and local seal performance is less critical
• Enables sliding seals for continuous welding of pipe and plate sections

Suitable Applications

The use of RPEBW welding techniques have been explored in a variety of applications that use thick section steel and light alloys.

The first industrial use of the process is by SKB in Sweden for the proposed encapsulation of spent nuclear fuel in 50mm thick copper storage vessels.

RPEBW avoids problems caused by outgassing of these large components (they are 5m high and 1m diameter) and has an improved tolerance over In-Vac electron beam welding to seal leaks.

Other suitable industrial applications include the Power Generation and Distribution, Construction and Marine Engineering sectors.

Above is a schematic diagram of Reduced Pressure Electron beam gun column for welding copper nuclear waste storage canisters.