SERC's Daresbury Laboratory contracted VG Engineering Ltd (Chambers Division) to manufacture an absorber guide for use in the Synchrotron Radiation Source (SRS), a 2 GeV electron storage ring. The SRS is used for academic and industrial research.
After manufacture the guide was welded to the inner wall of a stainless steel vessel which forms part of the vacuum containment system of the SRS, its purpose being to collimate the synchrotron radiation. However, after welding the absorber guide was found to be distorted and unusable. To fit a replacement would involve cutting away the vessel section to which the guide was attached and replacing it with a new section complete with new absorber guide. VG Engineering approached TWI to undertake the precision welding required to salvage the expensive vessel.
The vessel which measures 3m x 1m x 63mm fits inside one of the 16 dipole magnets that form the storage ring in which the electrons circulate to give off the synchrotron radiation. Since the vessel is to be located in a magnetic field, both the vessel and the weld material must have a very low permeability. Stainless steel grade 316LN was used in the manufacture of the vessel and guide and because the vacuum within the storage ring is better than 10 9 Torr, special attention had to be paid to weld quality. Welding had to be carried out precisely with minimum distortion, as subsequent machining would not be possible. Full penetration welds were therefore required to avoid trapped volumes within the vessel and care was taken to avoid over penetration into the vessel, which would lead to outgassing problems.
The welding of the absorber guide into the original vessel was carried out with ease and precision using TWI's 75kW CNC controlled electron beam machine. The weld was completed to the specified tolerances and the vacuum vessel was salvaged, avoiding the loss of an expensive unit.
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