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CMS (Compact Muon Solenoid) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10,000-ton return yoke. Its magnet coil is wound from a pure aluminum stabilized superconductor. In order to withstand the considerable magnetic forces the conductor is reinforced by attaching high-strength aluminum alloy profiles using an Electron Beam (EB) welding process. 20 unit lengths of conductor, 2.5 km each, are needed. Only a complete bonding ensures the required mechanical strength of the conductor. The quality control of the welding is a key element in the success of the fabrication. Hence, we have introduced into the production line, just after the EB welding unit, a specifically developed ultrasonic imaging system. A high-speed phased-array instrument copes with the challenge of a continuous monitoring of the welding quality over the whole width and the complete length of the conductor. The performance of the ultrasonic inspection system and the assessment of ultrasonic indications with respect to different types of welding flaws is shown. By now over 45 km of the CMS conductor have been successfully welded and inspected.Index Terms-Bond quality, electron beam welding, nondestructive testing, ultrasonic phased-array technology.

Damage analysis of the serious incident that took place on 29 December 2004 on the Mürren-Birg section of the Schilthorn aerial ropeway identified the cause of failure as hydrogen-induced stress corrosion cracking. The necessary preconditions for this damage mechanism, which was previously unknown in the aerial ropeway industry, were established by the complex interaction of various ancillary conditions. During periodic rope relocation in 1977, galling occurred between the track rope and a deflection saddle as a result of inadequate lubrication. The friction or galling processes resulted in changes in the grain structure (friction-induced martensite) as well as scale-like smearing on the wire surfaces. The formation of friction-induced martensite results in local stress changes (peak tensile stresses on the surface). Over time, corrosion processes took place in the area of the surface defects under dissociating conditions (absence of air), producing diffusible hydrogen. The hydrogen diffuses preferentially to points of peak stresses and gives rise to embrittlement of the material and intergranular cracks. The results of the investigation were immediately distributed to the licensing authorities and aerial ropeway operators in the form of specially designed training materials to enable appropriate inspections of systems of similar design. Detailed evaluation of this preventive measure is still in progress.