Abstract
The study presents some strength parameters of structural materials, including steel grades 13HMF, P91 and P92, currently used in professional power engineering to produce pipelines, boiler super-heaters, steam tanks, steam pressure tanks and pipelines designed to operate at the temperature range up to 650° C. The author presented results of material stress tests performed by him for pipelines in as-delivered state as well as after 40 000 hours of operation. The tests were made using Mathar strain gauge method. Hardness test results for areas subjected to strain gauge tests and structural changes of tested samples are also presented. Stress test results indicate stress increase for operated material as well as for grain size growth compared to as-delivered material. It is caused by operating load (both thermal and mechanical) of the pipeline material.