Nanostructured surfaces

Operational Reliability Improving by Means of Substructural Strengthening
Hruzevyich A.V.1,2, Derecha D.O.1,3
1 Institute of Magnetism of the NAS of Ukraine and MES of Ukraine. Akad. Vernadskogo blvd. 36b, Kyiv-03142, Ukraine. 
E-mail: dderecha@gmail.com
2 Trypil’ska CHP, Ukrainka-08720, Kyiv Region, Obukhov District, Ukraine.
3 National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”. 37, Prosp. Peremohy, Kyiv-03056, Ukraine.

One of the main causes of emergency shutdowns of high unit capacity power units is damage of the boiler heating surfaces pipes. Thus, superheater pipes shutdowns, caused by metal overheating and accelerated by formation of creep flow, or typical damages of screen system connected with the emerging of corrosion-thermal fatigue and gas corrosion, occur after 10-15 thousand hours of work [1]. 
The crucial task of ensuring the operation reliability of the pipes of heating surfaces of supercritical pressure boilers units is solved by using of steel DIN 14MoV63 pipes strengthened by mechanical heat treatment (MHT).
As a result of the MHT, the strength of the steel at normal and operating temperatures increases on 27-9%, the yield stress increases on 58-12% (respectively) while maintaining the required level of plasticity. On trials for long-term strength time to shutdown of MHT pipes is 2-4 times higher than the standard.
During the operation, temporal systematic observations of the metal pipes condition were made on places and on the control cuttings. It showed that in the process of operation the microstructure of the pipes metal consistently deteriorates, but the dislocation polygonal substructure of the steel remains stable. The positive experience of long-term industrial operation of strengthened MHT pipes made of steel on heating surfaces of supercritical pressure units testifies technical and economic reasonability of using such pipes in heat power engineering, which provides an increase of the longevity of the responsible power-equipment units more than in 5-6 times.

1.	V.S. Ivanova, L.K. Gordienko. New ways to increase the strength of metals – Nauka: 1964.