The influence of prolonged exposure to operating temperatures and strain aging on the material properties of nuclear power plant reactor vessels and pipings

Effect of Long-Term Thermal Influence on Mechanical Properties of Welded Joints for Carbon Steels used in Power Engineering

“…As the degradation of mechanical properties of carbon steel is practically absent during the designed service life was recommends to carry out inspection after 200000 hrs of operation and not 100000 hrs and the basis for this conclusion was presented. On the base of earlier performed investigations (Karzov, 1993) we can mention a high stability of strength and ductile properties of this steel at 20°C independent of temperature and a prolonged thermal exposure. In this case the level of mechanical properties after thermal exposures does not decrease below the normative requirements for the initial period of operation.…”

“…The equipment and pipe-lines of NPP manufactured in carbon steel are operated at elevated temperatures up to 360°C that lay within the temperature range of dynamic strain ageing which manifests itself in strength properties improvement and plastic properties deterioration under single loading (Karzov, 1993). The variation of mechanical and fatigue properties of steels in the temperature range from 20 to 400°C can be attributed to different reasons, including carbon and nitrogen atomic hardening around screw dislocations, strain ageing due to internodes carbon and nitrogen atoms, and also to dislocation precipitation of carbide and nitride particles.…”

Degradation of structural steel properties under the prolonged influence of operating temperatures

“…It is easy to note the high constancy of the stan dard characteristics (σ B , σ 0.2 , δ, ψ) during the pro jected service life, and also the fact that the actual val ues of 22K steel properties and its joints after operating for 100000 and 200000 h are practically equal to the values specified in the regulations [26]. As follows from the data presented in [6], practically no changes in mechanical properties of either the base metal or the metal of welded joints of pipelines from carbon steels during the design lifetime occur. Therefore, the reserves of strength adopted at the design stage are provided in the course of a 30 year period of opera tion.…”

“…The influence of thermal aging at operating tem peratures on a longer time base has been evaluated by [6], and Fig. 1 gives the general trends of changes in the steel and its weld standard properties (welding performed by automatic welding under a layer of flux at 350°C in a limited time-20000 hbasis).…”

“…In making an estimation of the ser vice life, it is necessary to determine degradation of mechanical properties and take into account that for years these materials are subjected to constant and variable loadings and high temperatures and also cor rosion and radiation. In Russia, these studies are car ried out within 10-15 years [6][7][8][9][10][11][12]. Their results are generalized in this review for the following groups of materials: heat resistant steels; carbon steels such as 22K and 20; high alloyed austenite stainless steels such as 08Cr18Ni10Ti.…”