Creep deformation of materials in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 50

212°F 600°F 1000°F 1500°F

100

10

1

15 20 25 30

T (20+Log 10 t r )

35 40 45 50

10 -3

3.19 Larson-Miller plot for various materials. 88

higher temperatures. It is then assumed to be equally valid for longer times
and lower temperatures thus allowing for extrapolation. The Larson-Miller
method 83 is based on this logic. The original Larson-Miller equation is given
by the following:

og

( l ),

[3.49 ]

LMP T C

= + t r

10

￿ ￿ ￿ ￿ ￿ ￿

where LMP is the Larson-Miller parameter and C is a constant which was
assumed to be equal to 20 and was found to be reasonably accurate for
many materials. Plots of applied stress versus the LMP would then allow
extrapolation of short term data for long term predictions. Figure 3.19
shows a LMP obtained from short term tests for a variety of materials. It
is interesting to note the change in slope as lower stresses are approached.
Some of the other parameters which fall under the category of paramet-
ric methods are by Dorn and Shepherd, 84 Manson and Haferd, 85 Murry, 86
etc. However, LMP is quite commonly used in creep life predictions and
extrapolations.
Under graphical methods, there are procedures which seek to extrapo-
late rupture curves by direct manipulation of the plotted data. Grant and
Bucklin, 87 Glen, 88 Mendelsohn and Manson 89 and others proposed methods