Life Assessment and Creep Damage Monitoring of High Temperature Pressure Components in South Africa's Power Plant

摘要

The accumulation of creep damage with time of High Temperature and Pressure Components (bends, branches and weldments) is monitored by utilising both off- and on-line systems.rnEskom has a base line and progressive inspection philosophy and policy which forms an essential part of the life management system.rnA core technology utilised for this purpose is the metallographic replica technique supported by creep damage models. Nearly 60000 replica are taken, evaluated and archived each year. This represents 15000 locations and approximately 1500 components. Material varies from low alloy to 12 % chromium steels. The cumulative number of replica archived over the last 25 years is rapidly approaching the million mark.rnCritical life monitoring, life prediction and maintenance management are further enhanced by utilising capacitive and passive strain gauges. The experience in field monitoring is extensive and it is further supported by the monitoring of scaled down welded vessels in the laboratory.rnLiterature has often superimposed the evolution of creep micro and macro damage on a creep strain versus time curve and thereby implied that a manageable residual life exists even beyond the point of micro-void linkage. This paper demonstrates that component geometry, strain rate, void size, damage gradient and material homogeneity are some of the key factors to be considered otherwise this approach could lead to catastrophic failures. From an economic risk point of view the damage could be orders of magnitude higher than the short term benefit derived from such a practice. Human fatalities however can not be expressed in monetary terms.