Extrapolation of Creep Strain and Rupture Properties of 1/2 per Cent Cr,1/2 per Cent Mo,1/4 per Cent V Pipe Steel

Both 1 per cent total plastic strain data and rupture data of up to 21 000 h duration are presented for 1/2 per cent Cr, 1/2 per cent Mo, 1/4 per cent V pipe steel. Four parametric methods commonly used for extrapolation purposes are assessed for their accuracy of prediction within the time covered by the present experimental data. The Manson-Haferd parameter, which emerged as the most satisfactory of the four, is used as the basis for the long-time estimates of material properties.

Based on the full 1 per cent strain and rupture data, 10 000, 30 000 and 100 000 h predictions are compared with the current British Steelmakers' Creep Committee recommendations.

The tendency of both the Larson-Miller and Orr-Sherby-Dorn parameters to provide optimistic estimates at longer times is again demonstrated, and while the Manson Generalized parameter fits the data excellently within the experimental range, it is shown that care is required in selecting values of parametric constants if instability is to be avoided.

To meet the increasing need for long-time creep strain data, each individual creep curve is represented by a creep strain/time relationship.