Abstract
Nondestructive and destructive residual life evaluation techniques for high temperature component materials have been studied by many researchers, and recently some of these techniques have been applied to actual power plants. But in the case of creep damage evaluation of boiler tubes, these techniques have been applied only at typical locations because of a huge number of tubes to be inspected and the unreliability of metal temperature assessments.
For developing creep damage evaluation techniques for boiler tubes, 3 tubes (JIS STB52D) were taken from an actual power plant after a prolonged service and then examined. These tubes were metallographically observed, and several kinds of creep tests were carried out to evaluate the metal temperature in service and the extent of creep damage. The relationships of the area fraction of cavities and the diametral strain to the creep damage were also discussed. The results obtained are summarised as follows:
1) The metal temperature in service and the creep damage of each tube could be evaluated properly by using the results obtained from creep rupture tests.
2) The area fraction of cavities observed near the tube surface increased with creep damage, and this behaviour was similar to that of SUS321HTB.
3) The diametral strain εd showed a good correlation with the creep damage, and εd increased rapidly at the later stage of the creep life. The diametral strain can be an effective parameter to evaluate the creep damage of tubes.
