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Mechanical properties and structure of the Cr-Mo-V low-alloyed steel after long-term service in creep condition

Dobrzański J., Zieliński A., Krztoń H.

Journal of Achievements in Materials and Manufacturing Engineering

2007

Vol. 23, nr 1

39-42

Purpose: of this paper is to present the changes of the mechanical properties and structure in material components of the power station boiler after long-term creep service made of Cr-Mo-V low-alloyed steel. Design/methodology/approach: The investigated material has been obtained from the Polish power stations. All examined elements have exceeded their assessed life of 100 000 hours. Mechanical properties and structure examinations were carried out on materials after long-term service in creep conditions. The microstructure have been observed using a light and a scanning electron microscope. The investigation of the development of the precipitation processes were done by X-ray diffraction phase analysis. Findings: Carbide precipitations evolution in correlation to the life exhaustion extent were presented. Residual life in creep short tests was done. Residual life in correlation to changes structure and developed of carbide precipitation processes were presented. Practical implications: The presented methods can be used for materials evaluation operating in creep conditions. Originality/value: The presented results changes in the mechanical properties, structure and in the precipitation processes are applied to evaluation of the condition of the elements in further industrial service.

Methodology of classification of internal damage the steels during creep service

Dobrzański J., Sroka M., Zieliński A.

Journal of Achievements in Materials and Manufacturing Engineering

2006

Vol. 18, nr 1-2

263--266

Purpose: of this publication is to present the methodology of computer assisted method for analysis of the metallographic images obtained in the scanning electron microscope (SEM) from the elements after long time creep service. Design/methodology/approach: Stages in development of internal damage involving intercrystalline cavitation cracking were discussed and illustrated with micrographs. The method based on analysis of images, shape coefficients and neural networks was proposed as a tool to evaluate the internal damage classes of materials used for the high-pressure installations elements working in creep conditions. Findings: Combining of several methods making use of the image analysis, shape coefficients, and neural networks will make it possible to achieve the better efficiency of class recognition of damages developed in the material. Practical implications: The presented method can be use in industrial practice for evaluation and qualification of creep-damage of power station boiler components operating in creep regime (e.g., steam boilers, chambers, pipelines, and others). Originality/value: Original value of the work is applying the artificial intelligence method for the classification of internal damage in the steel during creep service.