Microstructural examination of 2.25Cr1Mo Steel Steam pipes after extended service

Abstract

Microstructural investigation has been carried out for 2.25Cr1Mo steel taken from service-exposed steam pipes. Samples selected for study experienced a nominal temperature of 542°C, with a nominal internal pressure 17.4MNm⁻² for 5 and 18 years. The original microstructure of the pipes consisted of ferrite and pearlite. The service exposure caused carbide transformations and ferrite grain growth. In this work, color micrography taken from specimens examined in the light microscope, transmission electron microscopy, scanning transmission electron microscopy and energy-dispersive x-ray analysis on carbon extraction replicas and thin foils were utilized to understand the carbide distribution, morphology, and structure. A sequence for microstructural degradation is also proposed, and this provides a basis for understanding the behavior of steam pipes during extended service.