Question

Using the Larson-Miller data shown below, predict what would be approximately the maximum allowable stress at 800 °C to have rupture time of 15000h? C-20 103 T(20+log t,)(°R-h) 25 30 35 40 45 50 1000 100 100 10 10 12 16 20 24 28 103 T(20+log t,)(K-h) From F.R. Larson and J. Miller, Trans. ASME, 74, 765, 1952. Reprinted by permission of ASME Stress (MPa) Stress (10 psi)

Answer 1

Ans:

T = 800 deg C = 800 + 273 = 1073 K

Rupture time = 15000 hr

Hence Larsen miller parameter can be calculated as follows:

T*(C + log(t_r)) = 1073*(20+log(15000)) = 1073*24.176 = 25.94*10³

From the graph setting x-value to 25.94 we get (y-value) stress of 70 MPa approx.

Hence maximum allowable stress is 70 MPa.