The full 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 test 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 to 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 to 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. PRC/1515 (C) 1999 IoM Communications Ltd.
