The mechanical properties and microstructure of P92 steel after 85 000 hours' service were analyzed by several test methods such as chemical composition analysis

mechanical property test and microstructure analysis

and the results were compared with that of the original tube. The results show that

after 85 000 hours' service at high temperatures

all the P92 steel's mechanical properties except high temperature tensile strength met the requirements of the standard for new pipes. Compared with the original pipe

the performance of the service pipe had been deteriorated obviously. The plastic elongation at room temperature decreased by 9.2%

the tensile strength at room temperature decreased by 3.0%

the elongation at room temperature after fracture decreased by7.7%

the longitudinal and transverse impact absorption energy at room temperature decreased by 73% and 65%

the hardness decreased by 2.5%

and the plastic elongation decreased by 6.1% at 600 ℃ compared with that of the original pipe at 610 ℃. Moreover

the microstructure of the service tube had obvious aging. Although the martensite morphology in the metallographic structure was still obvious

the local martensite lath in the substructure had the characteristics of recovery

sub-grain and equiaxed

the second phase precipitated greatly at grain boundary and lath boundary

and Laves phase coarsened obviously.