Nondestructive Monitoring of a Multilayer Pressure Vessel: Strain Gages Instrumentation

Abstract

This paper presents a method that allows verifying the safety of operating multilayer pressure vessels when nozzle inspection that allows inserting ultrasonic testing equipment which is commonly known as Non-Destructive Examination (NDE) is not possible for such a purpose. In this context, strain gages were used to obtain strain values of the material related to stresses to which it is subjected by means of a pressurizing test. Once geometric characteristics and mechanical properties of the pressure vessel under study were known, it was possible to apply mechanics of materials concepts and obtain the biaxial state of principal stresses, thus inferring the actual thickness value of the accumulator. Moreover, it was possible to verify that although the use of strain gages takes longer than the ultrasound test, its degree of precision is remarkable and its applicability much wider, since geometric factors are not particularly concerning the shrinkage which occurs between the vessel layers. The data were also evaluated analytically and using finite element simulation, which demonstrated consistency with the results obtained by extensometry.