FASTENERS FOR STRUCTURAL BOLTED JOINTS TO BE ASSEMBLED IN REMOTE HANDLING

Fasteners are generally considered a matter of a mature technology wit h a variety of solutions ready to meet a wide range of applications, b ut their use in remote handling needs accurate considerations. The fas tening system has a substantial effect on the total time to perform ma intenance operations, and therefore care should be taken from the begi nning of the project to its standardization. The set of requirements t o be satisfied by a qualification activity on fasteners to be remotely handled within the environmental conditions relevant to the NET-ITER machine (high temperature, radiation, vacuum, cryogenic temperature) d eals with shape and dimensions, materials properties, surface finish o f mating parts, lubricant compatibility, precautions against galling a nd seizure, provisions of remedial actions from an emergency situation , fabrication process specification, methods of preload application an d control of its persistence under machine operation. The qualificatio n of high strength bolts at cryogenic temperature (4 K) and relevant f racture mechanics tests, and the qualification of suitable coatings an d lubricants has been extensively investigated on both specimens and f ull size components. In this paper we report final results of a three- year development programme on fastener technology.