Ref.: MpoFsu03-001

Methodologies to evaluate the environmental stress cracking (ESC) in polymers: Review

Apresentador: Guilherme Alves Berto

Autores (Instituição): Berto, G.A.(Universidade Federal do Rio de Janeiro); Da Costa Neto, C.A.(Universidade Federal do Rio de Janeiro); Farias, C.A.(Shell);

Resumo:
Environmental stress cracking (ESC) is a macroscopic brittle fracture that occurs due to a synergy effect of an applied stress and the medium in contact with the material. If the material failure would not occur only because of the applied stress or only because of the medium influence in the material, the dominant failure mode is the environmental stress cracking. The fracture process via ESC initiates at the surface where there is a stress concentrator or a crack, which under tensile stress and in contact with active fluid during certain period of time is able to locally interact with the material and making the crack to subcritically grow steadily or step wise way. The ESC process is quite dependent on the material, stress level applied, time, temperature, medium, severity of the defect and so on. Even though many polymers are known by their high chemical resistance, their low fracture toughness makes it necessary to carefully evaluate the fracture properties of these materials in different environments. In fact, ESC is a frequent failure mode of polymeric materials, becoming a worrying problem if long service times of the polymer are considered. It is estimated that this failure mode may account for between 15% and 30% of service failures that occur in these materials. In that regard there are many ESC tests methodologies in the literature, some set by standards and others not. The ASTM ESC standards are methodologies that, for the most part, have been designed and developed for polyethylene and ethylene plastics and paraffins in some cases, while the ISO standards are more general, not only in the methodological scope, but also in the scope of material and processing. Other ESC test methodologies that are not standardized are used in the literature and fill in the gaps left by the standards. This work compiled and appraised methodologies to evaluate the environmental stress cracking in polymers found on the literature.