11155 Life Assessment of Reformer Tubes from Strain Measurement

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Product Number: 51300-11155-SG

ISBN: 2011 11155 CP

Author: Charles W. Thomas, Ted L. Anderson and Tim Hill

Publication Date: 2011

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The life of reformer tubes is controlled by creep. However, the rate at which creep damage accumulates is not linear and is dependent on a number of complex factors including the large changes in creep properties as the material ages, the variable stress distribution through the wall of the tube and the uncertainties associated with actual metal operating temperature. This paper describes the development of a life assessment methodology to calculate level of damage from tube diameter inspection data.

At the heart of the methodology is a specifically developed model that describes the rate at which creep damage accumulates and relates that damage to strain and strain rate. A comprehensive database of tube material creep properties has been developed for input to the model. This data base has been created from reformer tube material that has been pre-aged to a range of metallurgical conditions.

The methodology is completed by detailed finite element analysis that takes into account the influence of plant cycling caused by start up- shut down and trips. Of particular note is the fact that the model has little dependence on measured tube metal temperature. In fact, temperature is an output from the model calculated from the knowledge of strain (inspection data) and creep behavior. Key Words: Reformer tubes, creep, inspection, life assessment.