The Acidic Stress Corrosion of GRP

Stress corrosion in GRP is a result of acidic attack of the fibres acting in concert with applied stress on the fibres. Accordingly. the effects of fibre orientation are in line with the magnitude of resulting resolved stress acting in the fibre directions. with the effect of fibre composition reflecting the susceptibility of the fibres to acid degradation. As a general rule the matrix has an important role to play during stress corrosion with tough ductile matrices favouring a good resistance to stress corrosion crack propagation. Whereas however certain systems have been found to provide good stress corrosion resistance on the basis of laboratory tests. any estimate of component lifetime is the result inevitably of extrapolation to longer times than may be covered in most laboratories. In practice. the long lifetimes required mean that if stress corrosion ceases to become an issue then more conventional corrosion resistance needs to be evaluated. It is likely that corrosion and stress corrosion have different requirements from resins ensuring that all selections are a compromise. The great dependence of the stress corrosion cracking process on stress concentrations and the sharp nature of the resulting cracks means that unusually great care must be taken to avoid geometric stress concentrators in the design of GRP process vessels and pipe work. Stress induced damage. especially in any protective barrier layer must be avoided at all costs in order to eliminate unexpected. early nucleation of cracks. Finally. it would be desirable to have access to intermittent monitoring procedures (e.g. acoustic emission) that may detect stress corrosion cracking in vessels that show no external signs of damage.