TECHNICAL PAPER Investigation of Microstructure and Mechanical Properties of A335 P11 Main Steam Pipe in Stesen Janaelektrik Jambatan Connaught Power Plant, Malaysia Taoheed Olohunde Sadiq 1,2 • Lukmanulhakim Mohd Daud 1 • Jamaliah Idris 1 Received: 28 February 2018 / Accepted: 9 July 2018 / Published online: 13 August 2018 Ó The Indian Institute of Metals - IIM 2018 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 prema- turely in comparison with other locations. Keywords Microstructure Á Mechanical properties Á Spheroidization 1 Introduction It has become imperative to study the possible component failure that usually occur in electric power plant system comprising a gas turbine, boiler and steam turbine. This will help to determine the reliability, the lifetime and the effi- ciency of a power plant. In this study, the Main Steam Pipe has been considered as the one of the main critical parts of the boiler system besides the boiler tubes. It is a piping system that connects the bundle of tubes in the superheater level in the boiler, and links the steam turbine system. The Main Steam Pipe is usually hot due to high temperature and high pressure while the plant is in operation. Therefore, the study is necessary to ensure that this component does not fail when the load is mounted. Considering the combined cycle plant of Connaught Bridge Power Station with accu- mulated service life of over 150,000 Equivalent Operating Hours (EOH), involving more than 500 start-and-stop operations for the past 15 years, then there is a need to study the existing pipe materials. & Jamaliah Idris Jamaliah@fkm.utm.my Taoheed Olohunde Sadiq adisaolohunde@yahoo.com Lukmanulhakim Mohd Daud lmhakim.mdaud@tnb.com.my 1 Faculty of Mechanical Engineering, Universiti Teknologi Malaysia (UTM), 81310 Skudai, Johor Bahru, Malaysia 2 Manufacturing Department, Engineering Materials Development Institute, KM4, Ondo Road, P.M.B 611, Akure, Ondo State, Nigeria 123 Trans Indian Inst Met (2018) 71(10):2527–2540 https://doi.org/10.1007/s12666-018-1383-z