Correlation between full scale and small scale steady state (S4) tests for rapid crack propagation in plastic gas pipe

The lull scale and small scale, steady state (S4) tests are the principal methods for measuring the critical pressure above which rapid crack propagation can occur in a gas pressurised plastic pipe. The full scale test delivers a critical pressure which directly reflects service performance. The S4 lest is less costly, but produces a critical pressure which is significantly lower than that of the full scale test. The discrepancy in critical pressures is due largely lo differences in gas dynamics of the two tests. A well known gas dynamics analysis, which has previously been incorrectly applied, is used in the present work lo derive a correlation function, which compares well with limited experimental data. Further experiments and analysis illustrate some other factors that influence the correlation and suggest that the application of a more precise correlation function is impractical.