Creep life assessment of an overheated 9Cr-1Mo steel tube M. Mazaheri a , F. Djavanroodi a, * , K.M. Nikbin b a Department of Mechanical Engineering, Iran University of Science & Technology, Narmak, Tehran 16846-13114, Iran b Department of Mechanical Engineering, Imperial College, London, UK article info Article history: Received 13 August 2009 Received in revised form 25 August 2010 Accepted 27 August 2010 Keywords: Life assessment LarsoneMiller parameter 9Cr-1Mo steel Rupture test Tensile testing abstract Crude oil heater 9Cre1Mo steel tubes from a refinery plant were studied, after 24 years of service at nominally 650  C and 27 MPa, to predict their remanent lives. The investigation included dimensional, hardness and tensile measurements in addition to accelerated stress rupture tests between 650  C and 700  C and microstructural examination. Tube specimens were taken from two sections, the overheated side and the side which only saw the nominal operating temperature. The method employed involved the prediction of the increase in temperature with increasing sediment deposition during the operating life times using an FEM model. In addition the predicted temperatures are used to derive appropriate creep properties at relevant temperatures in a 3D pipe FEM creep analysis to predict the pipe defor- mation rate. All compare well with the actual service exposed pipe measurements and layer deposition. The overheated side revealed a small loss of creep strength in a stress rupture test. A layer of sediment (appr. 10 mm thickness) consisting basically of sintered carbon (coke) spread over the inside of the tube was acting as a thermal barrier causing the temperature to rise above 650  C. Analysis for the overheated side predicted an upper bound temperature of z800  C and a life of about 50 h suggesting that failure by creep rupture could occur rapidly in the sediment region. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Internally pressurized tubes are critical components in heat- exchanger applications, such as boiler water tubes, steam superheater elements and chemical plant reformer tubes [1,2]. Such tubes in power plants have a finite life because of prolonged exposure to high temperatures, stresses and aggressive environments. Remaining life assessment of aged power plant components in the present highly competitive industrial scene has become necessary both for economic and safety reasons as most of the power plants are over 25 years old. In real life situations both premature retirement and life extension in relation to the original design life can be encountered [2]. The consequences of failure of a component in-use can be tragic and expensive. There are many cases of engineering disasters resulting in loss of life and property. For boiler components, utmost attention is required to ensure that such incidents cannot take place. Carbon and CreMo steels are extensively used in high temperature components in power plants. Even though most of these components have a specific design life of 20 years, past experience has shown that they can have significant remaining life beyond the original design specification [3]. One of the most widely used techniques for life assessment of components involves removal of service exposed alloy and con- ducting accelerated tests at temperatures above the service temperature [4]. The aim of the present work is to evaluate the remaining life of Crude oil heater 9Cre1Mo steel tubes from a refinery plant, after 24 years of service, based on experimental and numerical analysis. 2. Experimental program The material specification with service condition and history of operation of the exposed 9Cre1Mo steel superheater and reheater tubes from a refinery furnace that heats crude oil at 450  C are given in Table 1 . Due to impurities in crude oil, basically sintered carbon (coke) has been deposited on the lower half of the tube section (Fig. 1). In this section, the rate of heat transfer from the tube to the crude oil would therefore decrease. In order to keep the temperature of the crude oil constant at 450  C more heat is required and subsequently material at this section (Fig. 1) will experience a higher temperature in comparison to the other side. This increase of temperature leads to higher physical and metal- lurgical damage, hence leading to a shorter safe operating time. In this article an experimental comparison has been made between the overheated and not-overheated side. * Corresponding author. Tel./fax: þ9821 77240203. E-mail address: javanroodi@iust.ac.ir (F. Djavanroodi). Contents lists available at ScienceDirect International Journal of Pressure Vessels and Piping journal homepage: www.elsevier.com/locate/ijpvp 0308-0161/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijpvp.2010.08.013 International Journal of Pressure Vessels and Piping 87 (2010) 746e752