By B. D. Garrett, Superior Continental Corporation
The mechanisms of fatigue in non-ferrous metals and designing against them in coaxial cable is a complex subject and one which can be especially difficult when designing for a 25-year plant. The life of any one expansion loop is determined by a plurality of variables, such as environment, installation temperature, span length, cable size and expansion loop position and dimensions, all of which are discussed. The use of brittle coatings for full-field strain analysis, strain gage measurement, and extensive fatigue testing have been conducted to better establish the mechanics of various expansion loop designs and to evaluate their potential worth. This data has then been transformed into analytical approximations for the engineer in order that loops of better known life can best be designed to the particular system.