Investigation of microstructure and mechanical properties of A335 P11 main steam pipe in Stesen Janaelektrik Jambatan Connaught Power Plant, Malaysia

Abstract

This study aimed at examining the mechanical property, hardness and microstructure of the main steam pipe in the waste heat boiler electric power plant to prevent any possible failure and determine its lifetime, reliability and efficiency. A used alloy steel main steam pipe with ASTM standard grade (ASTM A335 P11) and standard chemical composition (1.25Cr–0.5Mo) was taken from the waste heat boiler electric power plant, Tenaga Nasional Berhad, Connaught Bridge Power Station, Klang Selangor, Malaysia. Specimen from each critical point P1 (incoming from WHB1B) at 485 °C and 39 bar, P2 (incoming from WHB1A) at 485 °C and 39 bar, P3 (joint of WHB1A & WHB1B) at 110 °C and 65 bar and P4 (outgoing to ST1C) at 212 °C and 4 bar were cut for sample preparations. Microstrural spectra of all the samples revealed that all the points were being transformed from pearlite to spheroidite and critical point P3 (at 110 °C and 65 bar) contained cavities in its grain boundaries. Also, the results showed that the P3 (at 110 °C and 65 bar) had the highest ductility (34.17), Poisson’s ratio (0.2683), lowest yield strength (286.83 MPa) and lowest ultimate tensile strength (423.26 MPa) against other locations. Other critical points; P1 (at 485 °C and 39 bar), P2 (at 485 °C and 39 bar) and P4 (at 212 °C and 4 bar) showed the average of tensile properties which is slightly low compared to new pipe material due to stress and high temperature exposed in main steam pipe for a long period time with little increase in ductility. Hardness test showed that the critical point P3 (at 110 °C and 65 bar) possessed the lowest hardness strength value (140.7 HV) due to complex state of stress which assisted in modification of microstructure prematurely in comparison with other locations.