The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform

Ashok K Ray - One of the best experts on this subject based on the ideXlab platform.

  • structural integrity of service exposed primary Reformer Tube in a petrochemical industry
    International Journal of Pressure Vessels and Piping, 2016
    Co-Authors: Ashok K Ray, Nilima Roy, A Raj, B N Roy
    Abstract:

    Abstract This paper aims at quantifying creep damage, in terms of Kachanav's continuum damage mechanics (CDM) model and Bogdanoff model of service exposed primary hydrogen Reformer Tube. Quantification of creep damage was made from scatter in voids which was quantified from light optical microscopy (LOM), SEM (scanning electron microscope) equipped with image analyzing technique and EDX analyser, in terms of two damage parameters A and A*. Scatter in creep deformation behaviour of the material, is probably due to variation in mode of fracture and scatter in voids. Probability of rupture due to void area, shifts towards the higher population of void with increase in true strain. Experimental data for estimating creep damage agrees well with both the simulation based models. The value of damage tolerance parameter λ infers that growth of cavities has been attributed to a purely diffusion controlled mechanism, grain boundary sliding mechanism, or a combination of both.

  • Simulation and quantification of creep damage
    International Journal of Damage Mechanics, 2015
    Co-Authors: Nilima Roy, Avimanyu Das, Ashok K Ray
    Abstract:

    This paper highlights the assessment of creep damage of 11 years service-exposed Reformer Tube made up of HP-40 grade of steel of a petrochemical industry from replicated creep data. The existence ...

  • Life Estimation and Creep Damage Quantification of Service Exposed Reformer Tube
    High Temperature Materials and Processes, 2015
    Co-Authors: A Raj, Nilima Roy, B N Roy, Ashok K Ray
    Abstract:

    AbstractThis paper deals with evaluation of creep damage of ~11 years service exposed primary hydrogen Reformer Tube made of HP-40 grade of steel in a petrochemical industry, which has been carried out in terms of Kachanav’s continuum damage mechanics (CDM) model (K-model) and Bogdanoff model (B-model) based on Markov process. Residual life of the Tubes was estimated based on hot tensile, conventional creep deformation under identical test conditions, optical microscopy and fractography. Accumulation of damage due to creep has been quantified through microstructural studies. The as received Tubes did not reveal any degradation in the material like creep cavitation or voids, but there was indeed loss of tensile strength from room temperature to 870°C for the bottom portion of the Tube due to ageing and overheating. Scatter in creep deformation behaviour of the material is probably due to variation in mode of fracture and scatter in voids. From statistical point of view, Weibull distribution pattern for analysing probability of rupture due to void area shifts with increase in true strain towards the higher population of void. The estimation of mean time to reach a specific damage state from K- model and B-model is in close agreement with that of experimental data and can describe the sudden changes of the creep damage in the tertiary region as well. A remnant life of >10 years is estimated at the operating stress–temperature conditions of the top as well as bottom portion of the Tube.

  • Creep deformation and damage evaluation of service exposed Reformer Tube
    Canadian Metallurgical Quarterly, 2014
    Co-Authors: Nilima Roy, A Raj, B N Roy, Ashok K Ray
    Abstract:

    AbstractThis paper aims at studying the creep deformation behaviour and quantifying creep damage of ∼11 years service exposed primary hydrogen Reformer Tube made of HP40 grade of steel in a petrochemical industry, in terms of Kachanov’s continuum damage mechanics model (K model) and Bogdanoff model (B model) based on Markov process. Hot tensile, conventional creep deformation under identical test conditions, optical microscopy and fractography were extensively carried out. The as received Tubes did not possess any sign of degradation including voids or creep cavitations and decarburisation. There was indeed loss of tensile strength from room temperature to 870°C for the bottom portion of the Tube due to aging and overheating. Accumulation of damage due to creep has been quantified through microstructural studies in terms of two damage parameters A and A*. Experimental scatter observed in creep deformation and creep strain rate curves of the material at 870°C and at various stress conditions, is probably d...

  • Damage Analysis of Service Exposed Reformer Tubes in Petrochemical Industries
    High Temperature Materials and Processes, 2014
    Co-Authors: A Raj, Nilima Roy, G Krishna, B.k. Goswami, S B Kumar, Ashok K Ray
    Abstract:

    Accelerated creep or stress rupture data is used for remaining life assessment for life management studies of elevated temperature components, e.g. for Reformer Tubes where packed nickel catalysts are used for synthesis of hydrogen, ammonia etc. This research has become a regular task because of large range of time for failure (3 to 15 years) compared to designed life (11.4 years or 100,000 hours) and huge loss associated to damage, production and safety hazards. Utilization of appropriate inspection during plant shut down has been strategic short term life assessment. Tests have been typically done by high temperature mechanical properties, microstructure analysis and accelerated creep. Inspection of micro-cracks, hot spot formation, carburization/metal dusting for inner wall and oxidation, Tube diameter increment for outer wall inspection have been traditional symptoms of expiry of Tubes after service exposure. Aim of this review has been to study damage analysis of Reformer Tube in response to so wide time frame for failures and accidents involved, even after stipulation of designed time schedules.

P. S. Robi - One of the best experts on this subject based on the ideXlab platform.

  • High-temperature Tensile Properties and Creep Life Assessment of 25Cr35NiNb Micro-alloyed Steel
    Journal of Materials Engineering and Performance, 2016
    Co-Authors: Amitava Ghatak, P. S. Robi
    Abstract:

    Reformer Tubes in petrochemical industries are exposed to high temperatures and gas pressure for prolonged period. Exposure of these Tubes at severe operating conditions results in change in the microstructure and degradation of mechanical properties which may lead to premature failure. The present work highlights the high-temperature tensile properties and remaining creep life prediction using Larson-Miller parametric technique of service exposed 25Cr35NiNb micro-alloyed Reformer Tube. Young’s modulus, yield strength, and ultimate tensile strength of the steel are lower than the virgin material and decreases with the increase in temperature. Ductility continuously increases with the increase in temperature up to 1000 °C. Strain hardening exponent increases up to 600 °C, beyond which it starts decreasing. The tensile properties are discussed with reference to microstructure and fractographs. Based on Larson-Miller technique, a creep life of at least 8.3 years is predicted for the service exposed material at 800 °C and 5 MPa.

Johanne Laigo - One of the best experts on this subject based on the ideXlab platform.

  • creep resistance of fe ni cr heat resistant alloys for Reformer Tube applications
    Materials Science and Technology, 2019
    Co-Authors: Franck Tancret, Johanne Laigo, Jader Furtado
    Abstract:

    Relations between microstructure, phase transformations and creep resistance of austenitic Fe–Ni–Cr alloys are investigated. As-cast alloys with different silicon contents and an ex-service Tube ar...

  • phase transformations in fe ni cr heat resistant alloys for Reformer Tube applications
    Materials Science and Technology, 2018
    Co-Authors: Franck Tancret, Frederic Christien, Johanne Laigo, Rene Le Gall, Jader Furtado
    Abstract:

    Fe–35Ni–25Cr–0.4C alloys with different compositions are aged between 750 and 1150°C up to ∼10,000 h. As-cast microstructure contains interdendritic carbides of type M7C3 (‘Cr7C3’) and MC (‘NbC’). ...

  • phase transformations in fe ni cr heat resistant alloys for Reformer Tube applications
    Materials Science and Technology, 2018
    Co-Authors: Franck Tancret, Frederic Christien, Johanne Laigo, Rene Le Gall, Jader Furtado
    Abstract:

    ABSTRACTFe–35Ni–25Cr–0.4C alloys with different compositions are aged between 750 and 1150°C up to ∼10,000 h. As-cast microstructure contains interdendritic carbides of type M7C3 (‘Cr7C3’) and MC (‘NbC’). At service temperatures, M7C3 transform into M23C6 (‘Cr23C6’) within hours. Then, a hardening precipitation of secondary intragranular M23C6 occurs over hundreds of hours, the nose of the ‘temperature-time-hardening’ curve being around 1000°C. G phase forms after long aging; its solvus temperature and formation kinetics depend on silicon content. Z phase is observed after long aging at 950°C or above. G and Z phases form at the expense of MC. Very long aging causes nitridation under air, with first a transformation of M23C6 into chromium-rich M2X carbonitrides (X = C,N), then of MC into chromium-rich MX carbonitrides.

  • The combination of modeling techniques to predict the service behaviour of heat resistant alloys
    Materials Science Forum, 2007
    Co-Authors: Franck Tancret, Johanne Laigo
    Abstract:

    It is here demonstrated that combinations of various modeling techniques can be used to predict the service behaviour of heat resistant alloys, and sometimes to design “made-to-measure” alloys for specific high temperature applications. A first example is given, where an affordable creep-resistant nickel-base superalloy for operation around 750°C has been designed without any experiment. Based on the analysis of huge databases on existing alloys, Gaussian processes were used to predict its thermomechanical properties. Thermo-Calc allowed to design its fabrication process and to assess its weldability and its thermodynamical stability at service temperature. The alloy has then been tested and the validity of the modeling approach verified a posteriori, in particular a creep rupture life of 100 000 h at 750°C under 100 MPa. A second example is given, in the case of high-carbon Fe-Ni-Cr based alloys for Reformer Tube applications (HP steels). Their mechanical properties are predicted through the analysis of existing data with artificial neural networks. Parallelly, their thermodynamical stability in operating conditions is assessed using Thermo-Calc in combination with Dictra, to simulate the precipitation of carbides in the austenite matrix during service. It is therefore tried to understand microstructural evolution in service, damage mechanisms, and durability.

  • the influence of phase transformations on creep resistance in fe ni cr alloys for Reformer Tube applications
    Volume 9: Eighth International Conference on Creep and Fatigue at Elevated Temperatures, 2007
    Co-Authors: Johanne Laigo, Franck Tancret, Rene Le Gall, Fre De Ric Christien, Jader Furtado
    Abstract:

    Heat resistant steels of the HP-series have widespread uses in the petrochemical industry in pyrolysis and Reformer furnaces. The alloys are carbon-rich Fe-Ni-Cr alloys, with additions like Mn, Si, Nb, Ti, W... The typical microstructure of as-cast HP alloys is an austenite matrix with intergranular eutectic-like primary chromium carbides of the M7 C3 type and niobium carbides of the MC type. Upon ageing, phase transformations occur. Intragranular secondary M23 C6 carbides precipitate, which is thought to restrict dislocation motion, and intergranular M7 C3 transforms into M23 C6 . Under certain thermal conditions, a partial transformation of the primary niobium carbides into a nickel-niobium silicide called G phase can occur. These phases may play a critical role during creep, but neither their role on mechanical properties nor the mechanisms of phase transformations are clearly identified. The aim of this study is to understand the role of each phase or phase transformation in the creep resistance of HP alloys. Consequently, a critical review of phase formation and transformations in such alloys is presented using a set of experimental and modelling techniques (electron microscopy, Castaing microprobe, creep tests at high temperature and neural networks modelling of mechanical properties...).Copyright © 2007 by ASME

Jader Furtado - One of the best experts on this subject based on the ideXlab platform.

  • creep resistance of fe ni cr heat resistant alloys for Reformer Tube applications
    Materials Science and Technology, 2019
    Co-Authors: Franck Tancret, Johanne Laigo, Jader Furtado
    Abstract:

    Relations between microstructure, phase transformations and creep resistance of austenitic Fe–Ni–Cr alloys are investigated. As-cast alloys with different silicon contents and an ex-service Tube ar...

  • phase transformations in fe ni cr heat resistant alloys for Reformer Tube applications
    Materials Science and Technology, 2018
    Co-Authors: Franck Tancret, Frederic Christien, Johanne Laigo, Rene Le Gall, Jader Furtado
    Abstract:

    ABSTRACTFe–35Ni–25Cr–0.4C alloys with different compositions are aged between 750 and 1150°C up to ∼10,000 h. As-cast microstructure contains interdendritic carbides of type M7C3 (‘Cr7C3’) and MC (‘NbC’). At service temperatures, M7C3 transform into M23C6 (‘Cr23C6’) within hours. Then, a hardening precipitation of secondary intragranular M23C6 occurs over hundreds of hours, the nose of the ‘temperature-time-hardening’ curve being around 1000°C. G phase forms after long aging; its solvus temperature and formation kinetics depend on silicon content. Z phase is observed after long aging at 950°C or above. G and Z phases form at the expense of MC. Very long aging causes nitridation under air, with first a transformation of M23C6 into chromium-rich M2X carbonitrides (X = C,N), then of MC into chromium-rich MX carbonitrides.

  • phase transformations in fe ni cr heat resistant alloys for Reformer Tube applications
    Materials Science and Technology, 2018
    Co-Authors: Franck Tancret, Frederic Christien, Johanne Laigo, Rene Le Gall, Jader Furtado
    Abstract:

    Fe–35Ni–25Cr–0.4C alloys with different compositions are aged between 750 and 1150°C up to ∼10,000 h. As-cast microstructure contains interdendritic carbides of type M7C3 (‘Cr7C3’) and MC (‘NbC’). ...

  • the influence of phase transformations on creep resistance in fe ni cr alloys for Reformer Tube applications
    Volume 9: Eighth International Conference on Creep and Fatigue at Elevated Temperatures, 2007
    Co-Authors: Johanne Laigo, Franck Tancret, Rene Le Gall, Fre De Ric Christien, Jader Furtado
    Abstract:

    Heat resistant steels of the HP-series have widespread uses in the petrochemical industry in pyrolysis and Reformer furnaces. The alloys are carbon-rich Fe-Ni-Cr alloys, with additions like Mn, Si, Nb, Ti, W... The typical microstructure of as-cast HP alloys is an austenite matrix with intergranular eutectic-like primary chromium carbides of the M7 C3 type and niobium carbides of the MC type. Upon ageing, phase transformations occur. Intragranular secondary M23 C6 carbides precipitate, which is thought to restrict dislocation motion, and intergranular M7 C3 transforms into M23 C6 . Under certain thermal conditions, a partial transformation of the primary niobium carbides into a nickel-niobium silicide called G phase can occur. These phases may play a critical role during creep, but neither their role on mechanical properties nor the mechanisms of phase transformations are clearly identified. The aim of this study is to understand the role of each phase or phase transformation in the creep resistance of HP alloys. Consequently, a critical review of phase formation and transformations in such alloys is presented using a set of experimental and modelling techniques (electron microscopy, Castaing microprobe, creep tests at high temperature and neural networks modelling of mechanical properties...).Copyright © 2007 by ASME

Amitava Ghatak - One of the best experts on this subject based on the ideXlab platform.

  • High-temperature Tensile Properties and Creep Life Assessment of 25Cr35NiNb Micro-alloyed Steel
    Journal of Materials Engineering and Performance, 2016
    Co-Authors: Amitava Ghatak, P. S. Robi
    Abstract:

    Reformer Tubes in petrochemical industries are exposed to high temperatures and gas pressure for prolonged period. Exposure of these Tubes at severe operating conditions results in change in the microstructure and degradation of mechanical properties which may lead to premature failure. The present work highlights the high-temperature tensile properties and remaining creep life prediction using Larson-Miller parametric technique of service exposed 25Cr35NiNb micro-alloyed Reformer Tube. Young’s modulus, yield strength, and ultimate tensile strength of the steel are lower than the virgin material and decreases with the increase in temperature. Ductility continuously increases with the increase in temperature up to 1000 °C. Strain hardening exponent increases up to 600 °C, beyond which it starts decreasing. The tensile properties are discussed with reference to microstructure and fractographs. Based on Larson-Miller technique, a creep life of at least 8.3 years is predicted for the service exposed material at 800 °C and 5 MPa.