Track 1 Session 12

1:00 to 2:00 p.m. Thursday, June 17, 2010

Equivalency: The Key to Developing Good Weibull Life Models

How much is your product life increased by operating at conditions lower than maximum operating conditions? An equivalency equation that answers this question will enable development of a more accurate Weibull life model. This presentation will trace the development of two different product life models. One model applies to a pump component undergoing high cycle fatigue where every stress cycle elastically deforms the component. The other model applies to low cycle fatigue of tubing where every stress cycle plastically deforms the tubing. For the pump, an initial equivalency equation is developed directly from fatigue test data of coupons of the same material as the pump component. This equivalency equation is then fine tuned with actual usage data. For the tubing, an equivalency equation is developed based on the physics defining the failure and then fine tuned with surrogate test data. Details of how the data are captured for both cases will be presented.

Key Words: Weibull, Equivalency, Miner's Rule, High Cycle Fatigue, Low Cycle Fatigue, Fatigue Limit, Endurance Limit, Life Model, Tracking Usage, Model Validation, Elastic Deformation, Plastic Deformation

Stan Stephenson, Tim Freeney and Brice Hughes

Halliburton

Duncan, Oklahoma