Larson-Miller Creep Life
Trade time against temperature for creep-rupture — solve the LMP, remaining life in hours, or allowable metal temperature.
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The engineering
The Larson-Miller parameter collapses creep-rupture data onto a single master curve: at a given stress, any time-temperature pair with the same LMP produces the same rupture life. That's what makes it the workhorse for extrapolating short lab tests (hundreds of hours) out to plant and engine lifetimes (10⁵ hours), and for remaining-life assessments on boiler tubes, turbine blades, and hot-section hardware. Pull the LMP-vs-stress curve for your alloy from ASME Sec II-D, API 530, or the vendor datasheet, then use this card to trade time against temperature.
The constant C is nominally 20 for ferritic and many austenitic steels, but real fits run roughly 15–30 — use the value published with the master curve, not the folklore default, or your extrapolation is meaningless. Sanity check: because temperature multiplies the whole bracket, a 15–20 K increase in metal temperature typically cuts rupture life by roughly half. If your solved life looks too good, verify the temperature is in Kelvin (a Rankine-basis LMP is 1.8× larger — mixing bases is the classic blunder).
Keep extrapolations within about one order of magnitude in time beyond the underlying test data. LMP assumes a single dominant creep mechanism; long-time microstructural degradation (carbide coarsening, sigma phase) can break the correlation and make the parameter optimistic.
Where this math comes from
F. R. Larson and James Miller were General Electric engineers with a gas-turbine problem: nobody could run rupture tests for the 100,000 hours a machine had to survive. Building on Hollomon and Jaffe's 1945 observation that tempering response followed T·(C + log t), they showed in their 1952 ASME Transactions paper that creep rupture obeyed the same time-temperature trade — and that a single constant near 20 worked across dozens of alloys. Short, hot tests could now stand in for long, cool service.
Competing parameters followed almost immediately — Manson-Haferd in 1953, Orr-Sherby-Dorn in 1954 — and each fits some datasets better. But the Larson-Miller form won on simplicity and stuck: ASME Section II-D stress tables, API 530 tube design, and API 579 fitness-for-service remaining-life calculations all lean on LMP master curves to this day.
- 1910E. N. da C. AndradeFirst systematic characterization of creep as a time-dependent flow law in metals.
- 1945J. H. Hollomon & L. D. JaffeTempering parameter T·(C + log t) — the mathematical seed of LMP.
- 1952F. R. Larson & James MillerGE engineers publish the time-temperature rupture parameter with C ≈ 20.
- 1953S. S. Manson & A. M. HaferdAlternative linear time-temperature parameter, sparking decades of comparison studies.
- 2004ASME / APIAPI 579-1/ASME FFS-1 codifies LMP-based remaining-life assessment; Sec II-D stress lines rest on the same master curves.
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