Y N Tiwari

Residual life prediction of service exposed main steam pipe of boilers in a thermal power plant

This paper deals with residual life prediction methodology for more than 12.5 years service exposed main steam pipes of various boilers in a thermal power plant. Health assessment was made using destructive accelerated stress rupture and tensile tests at different temperatures, and some nondestructive tests. There was no evidence of localised damage in the form of surface cracks, cavitation or dents in the service exposed main steam pipes of all the boilers. So far as the remaining life at 550°C is concerned, it is possible to obtain a life of greater than 100,000 h at the hoop stress level of the service exposed pipes, provided no localised damage in the form of cracks or dents have been developed. It is recommended that a health check may be carried out after 50,000 h of service exposure at 550°C.

Evaluation of mechanical properties and assessment of residual life of a service-exposed water wall tube

This paper is aimed at investigating the residual life, spanning 32 years, of a service-exposed water wall tube from one of the steam generating boilers of a thermal power station. The remaining life prediction and safety assessments were made using destructive accelerated stress rupture and tensile tests at different temperatures, as well as some non-destructive tests. There was no evidence of localised damage in the form of surface cracks, cavitation or dents in the service-exposed water wall tube. So far as the remaining life at 425°C is concerned, it is possible to obtain a life greater than 100,000 h at the hoop stress level of the service-exposed tube, providing that no localised damage in the form of cracks or dents have been developed. It is recommended that a health check may be carried out after 50,000 h of service exposure.

Remnant life assessment of service-exposed pendent superheater tubes

Remnant life assessment and life extension has become an integral part of plant maintenance activities, Cr–Mo steels are widely used in thermal power plants at a temperature of about 550°C. This paper deals with the high temperature tensile and creep rupture properties of 1Cr–0.5Mo steels for pendent superheater tubes in a boiler of a thermal power plant after five years service exposure for 43,000 h. Based on stress vs Larson Miller Parameter plot and at the operating hoop stress level, the pendent superheater tubes in general are found to be in a good state of health and can continue to remain in service for a length of 10 years, provided the temperature of the tube is brought down below 500°C. This observation may not be true for those selected tubes where already expansion in the diameter has taken place. Such tubes should be identified and replaced. In the case that it is not possible to bring down the temperature below 500°C, it may be desirable to use a superior grade of material like 2.25Cr–1Mo or 9Cr–1Mo steel. A thicker tube of the same grade may also be considered provided the overall load of the panel does not exceed the limit. It is, however, recommended that a similar health check be carried out after five years.

High temperature mechanical properties of thermal barrier coated superalloy applied to combustor liner of aero engines

High temperature load controlled fatigue, hot tensile and accelerated creep properties of thermal barrier coated (TBC) Superni C263 alloy used as a candidate material in combustor liner of aero engines are highlighted in this paper. Acoustic emission technique has been utilised to characterise the ductile-brittle transition temperature of the bond coat. Results revealed that the DBTT (ductile to brittle transition temperature) of this bond coat is around 923 K, which is in close proximity to the value reported for CoCrAlY type of bond coat. Finite element technique, used for analysing the equivalent stresses in the bond coat well within the elastic limit, revealed the highest order of equivalent stress at 1073 K as the bond coat is ductile above 923 K. The endurance limit in fatigue and the life of TBC coated composite under accelerated creep conditions are substantially higher than those of the substrate material. Fractographic features at high stresses under fatigue showed intergranular cleavage whereas those at low stresses were transgranular and ductile in nature. Delamination of the bond coat and spallation of the TBC at high stresses during fatigue was evident. Unlike in the case of fatigue, the mode of fracture in the substrate at very high stresses was transgranular whereas that at low stresses was intergranular in creep.

Mechanical Property Evaluation and Remaining Life Assessment Of Service-Exposed Steam Pipe of Boilers in a Thermal Power Plant

This paper is aimed at investigating the residual life of more than eleven years service - exposed main steam pipes of various boilers in a thermal power plant. The remaining life assessment for safety were made using destructive accelerated stress rupture and tensile tests at different temperatures, and some nondestructive tests. There was no evidence of localised damage in the form of surface cracks, cavitation or dents in the service exposed main steam pipes of all the boilers. So far as the remaining life at 823 K is concerned, it is possible to obtain a life of greater than 100000 hours, both at the allowable as well as operating hoop stress levels of the service - exposed pipes, provided no localised damage in the form of cracks or dents has been developed. It is recommended that a health check should be carried out after 50,000 hours of service exposure at 823 K.

Life prediction of service exposed reactor and distillation column materials used in a petrochemical industry

Determination of mechanical properties is a powerful method for investigating and assessing the performance of service exposed materials. The present paper highlights the trend recently observed in service exposed (38 years) plain carbon steels used as reactor and distillation column materials in a petrochemical industry. Health assessment of both base and welded joints was made using destructive accelerated stress rupture and tensile tests at different temperatures, and some nondestructive tests. So far as the remaining life at 520°C is concerned, it is possible to obtain a life of about 1.00 lakh h at the respective hoop stress level of both materials, provided no localized damage in the form of cracks or dents have been developed. It is recommended that a health check may be carried out after 5 years of service exposure at 520°C.

Remaining life assessment of service exposed reheater and superheater tubes in a boiler of a thermal power plant

This paper presents the high temperature tensile and the stress rupture properties of 150,000 hours service-exposed superheater and reheater tubes made of 2.25Cr-1 Mo steels in a 120 MW boiler of a thermal power plant. These were used to estimate the remaining life for safety. Experimentally determined yield strength and ultimate tensile strength as well as estimated 10,000 hours - 100000 hours rupture strength as obtained from experimental data in the temperature range of 793 to 853K exhibit a decreasing trend with increasing temperature. Microstructural study did not reveal any significant degradation in terms of creep cavities, cracks, graphitization etc. In general, analysis of tensile and stress rupture data reveal that the service exposed superheater and reheater tubes can remain in service for a length of more than ten years at the operating hoop stress level 40 MPa / 813K, provided no localised damage in the form of cracks or dents has been developed. It is recommended that a similar health check should be carried out after 50,000 hours of service exposure at 813K.

Mechanical Property Evaluation and Remaining Life Assessment of Service Exposed Steam Pipe of Boilers in a Thermal Power Plant

This paper is aimed at investigating the residual life of more than eleven years service exposed main steam pipes of various boilers in a thermal power plant. The remaining life assessment for safety was made using destructive accelerated stress rupture and tensile tests at different temperatures, and some non-destructive tests. There was no evidence of localised damage in the form of surface cracks, cavitation or dents in the service exposed main steam pipes of all the boilers. So far as the remaining life at 550°C is concerned, it is possible to obtain a life of greater than 100,000 hours, both at the allowable as well as operating hoop stress levels of the service exposed pipes, provided no localised damage in the form of cracks or dents has been developed. It is recommended that a health check should be carried out after 50,000 hours of service exposure at 550°C.

Life Prediction of Service Exposed Tubes in a Boiler of a Thermal Power Plant

Boiler tubes in power plants have finite life because of prolonged exposure to high temperature, stress and aggressive environment. Platen superheater and reheater tubes, made of 2.25Cr-l Mo steels, service-exposed for 148,900 hours in a 120 MW boiler of a thermal power plant, underwent detailed metallurgical assessment to analyze their remaining safety life. The investigation included hot tensile, hardness measurement, dimensional measurement, microscopy and a few accelerated creep tests. Analysis revealed that experimentally determined yield strength and ultimate tensile strength, as well as estimated 10,000100,000 hours rupture strength as obtained from experimental data in the temperature range of 520°C to 580°C, exhibited a decreasing trend with increasing temperature. Microstructural study did not reveal any significant degradation in terms of creep cavities, cracks, graphitization etc. In general, analysis of tensile and stress rupture data revealed that, although there was degradation of the tubes due to the prolonged service exposure in terms of the ultimate tensile strength values, stress rupture plots showed that the service exposed superheater and reheater tubes could remain in service for a length of more than ten years at the operating hoop stress level 40 MPa / 540 °C, provided that no localised damage in the form of cracks or dents developed. It is recommended that a similar health check should be carried out after 50,000 hours of service exposure at 540 °C. Key w o r d s : Service exposed, superheater, reheater, boilers, stress rupture test, tensile properties, residual life.

Prediction of remaining life of a FCCU reactor plate

Evaluation of mechanical properties is a powerful tool for investigating and assessing the performance of service exposed materials. The trends recently observed in service exposed (32 years) plain carbon steels used as a reactor vessel material in a petrochemical plant have been highlighted in this paper. Health assessment of both base and welded joint was made using impact tests at room temperature, destructive accelerated stress rupture and tensile tests at different temperatures, and some nondestructive tests. From the stress rupture tests it could be concluded that a life of more than 10 years at the hoop stress level of the material can be obtained, provided no localised damage in the form of cracks or dents have been developed. It is recommended that a health check should be carried out after 5 years of service exposure at 485°C.