Rated operating temperature of the P91 steel pipe was 541 ℃,the operating pressure was 17.5 MPa,and the specification wasφ194 mm ×25 mm.After about 78 000 h of service,its hardness was below the lower limit of the standard.Microstructure and properties of the P91 steel pipes used in a subcritical boiler after long-term service was investigated by means of metallographic,transmission electron microscopy,chemical phase analysis,creep-rupture properties and other test methods,respectively.The results show that the widening of martensite laths and the coarsening of the M23 C6 phase at the grain boundaries of the P91 steel pipes after long-term high-temperature service are the main reasons for the decrease in high-temperature strength.Specimens were taken from the P91 steel tubes for endurance testing,resulting in creep rupture strength value of 72 MPa for 100 000 h of extrapolation at 566 ℃.Data can be used as the reference for the assessment of the creep life of the P91 steel.
P91 steel pipelong-term high temperature servicemicrostructureproperties
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