Reformer Furnace Research Articles

Creep damage mechanism of 20Cr32Ni1Nb steel at high temperatures

In the petrochemical industry, the centrifugally cast austenitic 20Cr32Ni1Nb stainless steel used in steam reformer furnace's hot outlet manifold experiences creep failure and microstructural degradation, impacting its structural integrity. Understanding the causes of these issues is crucial for addressing the associated challenges. This study examines the creep deformation behaviour, damage mechanisms, and microstructural evolution of 20Cr32Ni1Nb steel under stresses of 22–50 MPa at temperatures of 1163 K (890 °C) and 1223 K (950 °C). Analysis of creep and creep strain rate curves revealed the presence of both primary and tertiary creep stages, with the power law relationship governing the stress-dependent minimum creep rate and rupture life. The variance of creep damage tolerance factor was also analysed, with results showing that in high-stress regimes, loss of section and necking along with cavity growth may initiate tertiary creep, while in low-stress regimes, microstructural degradation, specifically G-phase formation, may initiate tertiary creep. As the duration of creep exposure increases, microstructures were observed to degrade, with the growth and coarseness of NbC and M23C6 carbides. The structure of the space group for the Ni–Nb–Si enriched G-phase in 20Cr32Ni1Nb steel was found to be Fm3‾m, with a lattice parameter of about 1.14 nm.

Simulation and performance improvement of an industrial steam methane reformer: depreciation and ceramic coating effects

In this work, Computational Fluid Dynamic (CFD) is applied to compare the performance of an industrial reformer furnace in four cases. The first and tenth years of operation are two cases with different emissivity factors and fuel components. The results are validated with industrial data and with other CFD simulation typical plants reported in the SMR literature. The results show that a 10% increase in fuel consumption in the tenth year cannot compensate for all temperature drop in skin tubes, and there is still a 14 K temperature drop, leading to a 5% decrease in hydrogen production in tubes. This is due to the different fuel components of the tenth year compared to the first year. To examine the effect of fuel change more closely, the third case is defined with the fuel components of the tenth year and the emissivity factor of the first year. The comparison of this case with others shows that fuel components have a high effect on system performance. The major reason for efficiency reduction between the first and tenth years correlates to a 50% decline in the wall surface emissivity factor. Finally, in the fourth case, applying a ceramic coating with a high emissivity factor is considered via the CFD model for the reformer in the tenth year. This change leads to an increase of about 19 K in tube temperature in the tenth year, which is 3 K more than that in the first year. It can be concluded that the ceramic coating application in the wall of the refractory of the reformer can reduce 14% fuel consumption and enhance hydrogen production.

Relationship between pressure drop and tube deformation in a reformer furnace: a case study

Relationship between pressure drop and tube deformation in a reformer furnace: a case study

An improved creep damage mechanics model and its application to evaluate creep strain design codes for hot outlet manifold in steam reformer furnace

Considering the effect of carbide coarsening and cavity nucleation and growth on the creep damage of Fe–Cr–Ni-based austenitic stainless steels, an improved creep damage constitutive model is established based on the hyperbolic sine function. The material parameter optimisation procedure and the associated ABAQUS user subroutine CREEP of the model are also developed. In addition, the improved model is calibrated and validated by comparing the extrapolated failure times for the three creep damage models, and applied to an idealized pipe bend to evaluate the inelastic strain limits in the ASME-NH code. The results show that the proposed model is capable to reflect the creep behaviour of a hot outlet manifold steel under different stress levels at 890 °C. During the long-term creep exposure of the manifold component, the limits of 1% creep membrane strain and 2% creep membrane strain + bending strain ruled in ASME-NH code may not be conservative. If only the cumulative inelastic strain is considered in the structural design, membrane strain is the primary rule for investigating the failure of the pipe bending.

Failure cause assessment of steam reformer radiant tube after long‐term service

AbstractThis study investigates the damage, microstructure, and mechanical evolution of service‐exposed HP40NbTi radiant tubes of a steam reformer furnace. Tube failure was reported after 6‐year of working at 525°C–830°C in the form of visible longitudinal and transverse cracks. The microstructure was evaluated using optical and scanning electron microscopy equipped with energy‐dispersive X‐ray spectrum analysis. The carbide phase transformation was determined by the method based on the matrix dissolution technique and X‐ray diffraction. The results of this study showed that the primary cause of the longitudinal crack formation is the local overheating and the oxidation of the dendritic grain boundaries. The M7C3 carbide transforms completely into the metastable M23C6 phase during high‐temperature service. Metallographic examinations revealed the shrinkage cavities and creep voids that are nucleated on both Cr‐ and Nb‐carbides. The continuous oxide layers of Cr2O3 and SiO2 formed near the inner and outer tube surfaces and the matrix's chemical composition near the outer tube surface was found to be depleted of Cr and C. Mechanical properties are irregular across the samples. A little margin of safety is noted, while the complete ductility dip is detected at room temperature. The root cause analysis of the failure under investigation showed that the tube failed due to the creep.

Weldability and Damage Evaluations of Fresh-to-Aged Reformer Furnace Tubes

The microstructures and tensile properties of fresh and aged reformer furnace tubes and a fresh-to-aged welded joint were investigated to assess the weldability of fresh-to-aged reformer furnace tubes. Damage evaluation of the fresh-to-aged welded joint was also carried out using the modified Kachanov–Rabotnov model. The experimental results showed that M7C3 carbide transforms into M23C6 carbide and secondary carbides precipitate in the matrix after aging treatment. With continuous exposure, the interdendritic precipitates coalesced and coarsened and the number of secondary carbides reduced gradually. Microdefects were absent in the fresh-to-aged welded joint, and the tensile properties of the welded joint were close to the as-cast alloy, which confirms the weldability of fresh-to-aged furnace tubes. According to the results of the simulation, stress redistribution occurred during the creep process and the peak damage of the welded joint was located in the aged tube. The maximum damage of the fresh-to-aged welded joint reached 34.01% at 1.5 × 105 h.

Energy intensification of steam methane reformer furnace in ammonia production by application of digital twin concept

ABSTRACT The Digital Twin concept undoubtedly emerges in different industries as a must-have option for improving energy efficiency, increase maintenance reliability, prevent environmental pollution, and mitigating safety issues. However, there is still no suitable solution specifically developed for continuous monitoring and optimisation of the complex process units such as steam methane reforming (SMR) furnace used in ammonia production. The current work addresses this problem with the main goal to save energy and reduce carbon footprint. The paper investigates the application of the Digital Twin concept in combination with already proven methods for the identification and optimisation of energy-saving opportunities and reduction of CO2 emissions. The results are total energy saving between 3 and 4% with CO2 reduction of approximately 0.890 tons/h.

Life Assessment of HP-40Nb Reformer Furnace Tube of a Petrochemical Plant

Life Assessment of HP-40Nb Reformer Furnace Tube of a Petrochemical Plant

Process design and simulation study: CO2 utilization through mixed reforming of methane for methanol synthesis

A case study is performed using Aspen HYSYS to investigate CO2 utilization for methanol synthesis. The base case is a conventional steam methane reforming process for methanol production. Two modified cases (mixed reforming with/without CO2 capture after the reformer) are developed with the aim to increase CO2 utilization. Simulation results revealed that both stoichiometric number and CO/CO2 ratio played an important role on syngas reactivity, which led to an overall increase in methanol yield. As a result, the volume of unreacted gas in the synthesis loop was reduced and allowed for a smaller reactor design. In terms of overall CO2 intensity, no significant improvements can be observed since the base case had a large volume of H2 rich purged gas sent to the reformer furnace. When the purged gas was not used as a reformer fuel, the CO2 intensity of the other cases became 50% less than the base case.

PEMODELAN TEMPERATUR DARI PROSES PEMBAKARAN DI REFORMER FURNACE PADA INDUSTRI BAJA

Conversion processes that involve large amounts of energy include processes in furnace reformers inthe steel industry. The reformer unit used to convert the process gas, namely a mixture of gas andsteam into CO and H2 gas with the help of a nickel catalyst. The heat energy used in the process is theresult of combustion from natural gas using combustion located above the furnace. The most importantthing in the conversion process is the radiative heat transfer in the combustion chamber to the reactionpipe wall so that enough energy is obtained to carry out the conversion process. One way to determinethe heat distribution of the reformer combustion chamber is to know the temperature profile along thereaction pipe, including the pipe wall temperature, the process gas temperature, and the temperatureof the combustion gas used as energy for the process in the reformer furnace. The performanceevaluation of the reformer furnace uses a mathematical model for combustion in the furnace which canlater be developed by knowing the fitting composition of the conversion results. The type of reformerstudied is the top-fired reformer. The results of modeling using data from the steel industry obtained thehighest temperature from the combustion of gas from the burner which is in the reaction pipe at aposition 3-4 meters from the upper end of the reformer around 1300 oC and the temperature of naturalgas-steam in the pipe reaches 860 oC at the end of the pipe. reaction. The pipe wall heating with naturalo ogas fuels provides a maximum temperature ranging from 890 C - 895 C on the outer wall of thereaction pipe, and the pressure inside the reaction pipe ranges from 8.0-8.5 atm.

Microstructure Evaluation During Short Term Creep of Cr35Ni45Nb Cast Alloy Reformer Tube

In this work, a Cr35Ni45Nb alloy tube for use in a reformer furnace is subjected to high temperature (871 °C and 927 °C) creep regimes, and the microstructural changes (e.g. carbide precipitation and phase transformation) and consequent creep damage are investigated. The results of creep tests under closely similar applied stresses give different values of the Larson–Miller parameter (LMP) at different temperatures. As a result, the calculated creep rupture time at 871 °C based on the LMP value measured at 927 °C is approximately twice that which was actually measured at 871 °C. The microstructure of the as-cast tube is found to consist of an austenitic matrix with networks of MC (NbC) and eutectic (M23C6) carbides located both at grain boundaries and between dendrites. It is noted that the M23C6 carbide is not a primary eutectic carbide that can be observed in the as-cast Cr35Ni45Nb alloys. It can be argued that the primary eutectic M7C3 carbides were transformed into M23C6 due to the heat of spiral welding during the tube manufacturing process. After creep, the NbC carbides at both locations were mostly transformed to the G-phase (Nb3Ni2Si) and all the precipitates formed inside the austenitic matrix were composed of the M23C6 and G-phase. Creep cavities were initiated around the G-phase and grew cracks along the grain boundaries due to the formation of a Cr-depleted zone and the G-phase.

Microstructural characterization and mechanical behavior of Cr25Ni35NbM alloy dissimilar weld joint for application in a hydrogen reformer furnace

The microstructural characterization and mechanical behavior of Cr25Ni35NbM/15CrMo and Cr25Ni35NbM/SUS321 dissimilar weld joints were studied in this paper. The microstructure, room temperature and high temperature (1173 K) tensile strength of dissimilar weld joints were analyzed through optical microscopy (OM), scanning electron microscopy (SEM) and electronic universal tensile testing machine. The microstructure of HAZ in 15CrMo steel of Cr25Ni35NbM/15CrMo dissimilar weld joint transformed from ferrite-pearlite into ferrite-martensite. A large volume fraction of α phase was found to have precipitated in the HAZ of SUS321 austenitic stainless steel for Cr25Ni35NbM/SUS321 dissimilar weld joint. At room temperature, the tensile strength and yield strength of these two type dissimilar weld joints is less than Cr25Ni35NbM alloy similar weld joint. The high temperature tensile strength of these two type dissimilar weld joints is less than Cr25Ni35NbM alloy similar weld joint. Both at room and high temperature, the fracture locations of two types dissimilar weld joints are the HAZ of the base metal 15CrMo and SUS321 stainless steel, respectively. It indicates that the weak part of the Cr25Ni35NbM alloy dissimilar weld joints is the low-performance base metals 15CrMo and SUS321 stainless steel.

Feasibility assessment of local repairment for reformer furnace tubes in service exposure

The reformer furnace tube in service exposure after local replacement was investigated on the microstructure and mechanical properties. Experimental results indicate that NbC carbide transforms into G phase in service exposure and the precipitates coarsen with the distance increasing. Meanwhile, the linked cavities distribute in the scope of 8.7 m–10.5 m. The tensile properties and micro-hardness exhibit a continuous decrease followed by a stable level and then a slight increase with the distance increasing for the “new” tube. Based on the microstructural observations and theoretical calculation, the highest damage part of the “new” tube is located at 8.7 m–10.5 m and the damage level is higher than that of the “old” tube. The damage distribution is comparatively homogeneous along the direction of wall thickness. Due to the good condition of the whole tube, the feasibility of the local repairment has been confirmed.

The Effect of Service Time on Carbide Volume Fraction and Hardness of Catalyst Tube Materials

The effect of service time on secondary carbides formation in reformer furnace tubes has been studied to obtain a relationship between carbide volume fraction, service time, and hardness. Tube material is Kubota KHR35CT which is part of ASTM A297 HP class. The study was performed by examinations of microstructural evolution and hardness. The microstructures were examined using optical and scanning electron microscopes of the new tube, and the other tubes that had been in service for 17,500; 96,300 and 113,800 hours at 850°C. Carbide volume fraction was measured using image analyzer. Carbide volume fraction of the new tube is 7.72%, and increased to 8.86% after 17,500 hours, 9.54% after 96,300 hours, and 10.95% after 113,800 hours. The increase in carbide volume fraction to 8.86 % did not affect the hardness substantially because the hardness only increases from 191 to 198 BHN. However, increasing exposure times to 96,300 and 113,800 hours decreased the hardness to 170 and 173 BHN respectively. These decreases in hardness may be corresponding to the coarsening and agglomeration of carbide particles due to longer exposure time at 850°C.

A new computation method for signature: Markov process method

AbstractSystem signature is a crucial measure in the description and comparison of system structures in the field of reliability, and it does not depend on the component distributions under the assumption that all components are independent and identically distributed. A Markov process method is proposed to compute signatures for general coherent systems in this paper, which is more efficient for the computation of the system signature. As applications of the method, signature formulas of consecutive‐k‐out‐of‐n: F systems and related consecutive‐type systems are investigated, including both the linear and circular ones. Particularly, the related signature formulas for consecutive‐type systems with sparse d are derived for the first time. Illustrative examples are presented for methane reformer furnace systems.

Integration of commercial CO2 capture plant with primary reformer stack of ammonia plant

The safety of primary reformers is essential to safe operation of large-scale petrochemical processes, especially when carbon dioxide is going to be recovered from an ammonia plant. In this study, a preliminary assessment is made to model an industrial stack as the stack gases are introduced into CO2 capture plant, during ammonia production. A CFD model was first developed in the absence of a commercial carbon dioxide recovery (CDR) unit to validate the model against industrial data under normal operation. At full capacity of the ammonia plan, the results provided by the CFD model match the measurement results well within about 3.87% margin of relative error. The calibrated model was then applied in combination with post-combustion, as part of the process, to verify the process safety constraints in reformer furnace. The effect of starting up and shutting down of CDR plant was explored in the event of emergency operation. From an operational view, in the event of startup or unplanned failure of the CO2 capture plant, the pressure fluctuations do not exceed the maximum allowable pressure of the firebox. Upon reaching the required operating conditions, both subsystems can be integrated operationally to continue production safely.

Failure Analysis of a Service Tube

One tube was cracked used in the primary reformer furnace in a fertilizer plant for two and half years. In order to find out the causes of cracking, the methods for chemical composition analysis, macro- and microstructure analysis, penetrant testing, weld analysis, crack and surface damage analysis, mechanics property analysis, high temperature endurance performance analysis, stress and wall thickness calculation were adopted. The integrated assessment results showed that the carbon content of the tube was in the lower limit of the standard range; the tube effective wall thickness was too small; local overheating leads to tube cracking in use process.

Failure analysis of TP304H tubes in the superheated steam section of a reformer furnace

Abstract The cracking failure of TP304H tubes in the superheated steam section of a reformer furnace was analyzed. Through the analysis of macro-appearance, micro-appearance of specimens with cracks, metallurgical structure of specimens from an intact pipe section and cracked pipe section, energy spectrum detection of fracture surface, residual stress measurement, and investigation of the service medium, the cracking mode was described as the stress corrosion cracking (SCC) of austenitic stainless steel. In this case, the materials in the heat affected zone were sensitized by inappropriate welding technology. This together with the higher pH value in the steam due to the failure of a gas-liquid separator led to the final cracking of the reformer furnace tube. So the inappropriate welding technology and the failure of the gas-liquid separator were the main factors in this fracture accident.

Effect of Long Term Service at Elevated Temperatures on Mechanical Properties of Manaurite XM Reformer Tubes

Abstract Microstructure transformations occur in the Manaurite XM cast steel tubes during long-term operation in the reformer furnace were revealed and described. The relationship between mechanical properties, an increase of internal diameter of the tube and microstructure degradation is discussed. Static tensile test was performed on two types of samples with different shapes. It has been shown differences in the results of tests and an explanation of this phenomenon.

Cracking Failure Analysis of Inlet Manifold in Hydrogen Reformer Furnace and Prevention

A study of cracking failure of three-way T junctions between inlet manifold and branch pipes in large-scale hydrogen reformer furnaces in terms of pipe material, operation medium, properties of cracking zone material, and vertical displacements of inlet manifold and branch pipes is presented. The results revealed that cracking failures of three-way T junctions can be attributed to the stress concentration, which was caused by incongruous vertical deformations of inlet manifold and branch pipes, as well as variations in horizontal deformation heights of branch pipes. The incongruous displacements of inlet manifold and branch pipes were significantly mitigated by optimization design of the suspension device of the inlet pipe using the finite element method. The vertical displacement differences between inlet manifold and branch pipes and the east–west vertical displacement differences between the five branch pipes were reduced by 48 and 91.5%, respectively. Bending of three-way T junctions was relieved and torsions were eliminated, resulting in mitigation of stress concentration. As a result, the maximum equivalence stress was reduced by 40%, satisfying strength requirements. In this way, cracking failures of inlet manifold in hydrogen reformer furnace were prevented and stable hydrogen production was guaranteed.