Remaining Lifetime Evaluation of High Temperature Components of Power Plant Steam Boilers: Case Studies

The energy producing power plants are designed for operational period of 20, 30 years. During this period, inspections are realized to investigate the operational capability of the respective components and the plant as a whole, and when the designed time is approaching its limit, the crucial questions are raised with respect to the following possible operation, its safety and risks that stem from the fact that the continuous degradation of material properties occured during the longtime service as a result of service conditions, e.g. high temperatures, fatigue loading etc. The inspection of the boiler and the assessment of its future operational capability should ensure the safe operation and minimazing the failure risks. In comparison with the more sofisticated and much more expensive methods that use numbers of variables that enter the evaluation process of the lifetime exhaustion, or the metallographic non-destructive or even destructive methods that do not result often in a quantitative lifetime assessment, a relatively simple assessment method was used to evaluate the remaining lifetime of the high temperature components. On the basis of accelerated creep test data performed on the degraded materials, the remaining lifetime hours were calculated for the three “safety” situations: 1. “ZERO SAFETY” (neither recommended k = 1, 5 safety coefficient for working stress nor +70deg Celsius increase of working temperature were taken into consideration). 2. “STRESS SAFETY” (1, 5 safety coefficient for working stress and working temperature were taken into consideration). 3. “FULL SAFETY” (1, 5 safety coefficient for working stress and working temperature +70 deg Celsius were taken into consideration). This paper summarizes the results of remaining lifetime calculation for three different cases of steam boilers inspected after longtime service by Skoda Research ltd. Recently. On the basis of performed examination, the results provided the customer the recommendations relating the future safe and reliable operation.