Damage assessment and maintenance strategy of hydrogen reformer furnace tubes (original) (raw)
Related papers
Model of Influencing Factors for Hydrogen Damages of Boiler Evaporator Tubes
11th International Conference on Fracture 2005 (ICF11), Turin, Italy 20-25 March 2005, Volume 6, Red Hook, NY: Curran Associates Inc., 2010, pp. 3998-4003, ISBN: 978-1-61782-063-2., 2010
""Hydrogen-induced fractures of metallic components of thermal fossil fuel power plants (TPP) presents very serious exploitation problem and often exert considerable influence on the loss of power plant availability. Hydrogen damage is one of the most disturbing of boiler tube failure mechanism, and from the international experience, remains as one of the leading causes of frequent outages of boiler tubing system. To clarify root causes and complexity of problems associated with hydrogen damages, it is necessary to apply a multidisciplinary approach which comprises research in the field of material quality, boiler design, operation and maintenance. The work reported here is based on the theory and, particularly, on the experimental tests performed on boiler evaporator tube samples, taken from a domestic 210 MW power plant, that had experienced hydrogen damages during service. Possible mechanisms for metal – hydrogen interaction are considered from materials point of view, fluid hydrodynamics in evaporator tubes and the complexity of structural – exploitation plant characteristics. The aim of this paper is to contribute to the analysis of hydrogen damaging in boiler evaporator tubes and to propose failure mechanism model based on ′′micro-departure from nucleate boiling′′ (micro-DNB) of working fluid. In addition, this paper elucidates some definitions of major root cause influences by proposing model for systematization of influencing and corresponding operating factors responsible for hydrogen damages of boiler evaporator tubes.""
Hydrogen embrittlement of the furnace walls tubing
Hydrogen embrittlement could be one of the several causes of rupture on carbon steel boiler tube. Cracking occurs primarily because of the precipitation of molecular hydrogen along the grain boundary. The result of this process is formation of methane due to reaction of dissolved hydrogen with carbon in the steel. The hydrogen cracks morphology is specific, i.e.significantly different from the cracks affected by the long time or short time overheating. During hydrogen embrittlement decreasing of steel plasticity is taking place. Also the intensive hydrogen decarburization of the waterside surface of the tube is the process which is simultaneously occurs. Deposits, which could be formed on the waterside of the tube, especially in localized area, may have a great influence on a probability of hydrogen precipitation on grain boundaries and cracks appearing. Disturbance of boiling regime as well as departure from nucleate boiling that is taking place in particular area of waterwall tubing has a great influence o heat transfer process as well as on intensity and localization of hydrogen attack process. Some experimental investigation results of failure of boiler water wall tubes made of 0,2 C 0,5 Mn 0,25 Cr steel are presented.
Metals
This study presents a failure analysis in two reformer tubes used for hydrogen production in a petrochemical industry. These tubes (Tube A and Tube B) were made by the centrifugal casting of HP-Nb alloy in such a way that one contained titanium as a micro-element, and the other was free from titanium in its chemical composition. Although the two tubes were subjected to similar creep conditions, Tube A failed after only 46,000 h of operation against the design life of 100,000 h. SEM images showed initiation and growth of creep pores next to chromium carbide particles, as well as the formation of microcracks in Cr23C6 carbides. Pore initiation occurs as a result of grain boundary sliding and is strongly dependent on structural morphology. The tube containing titanium (Tube B) showed higher thermal stability and higher creep resistance than the tube without titanium (Tube A), which was due to the formation of finer and more discrete carbide particles. The final fracture of the tube wit...
Microstructural evaluation of welded fresh-to-aged reformer tubes used in hydrogen production plants
Engineering Failure Analysis, 2018
Heat resistant reformer tubes comprise a significant fraction of petrochemical reforming plants cost considering their high alloy content (i.e. 25Cr-35Ni-1Nb-0.1Ti). The bottom portion of tubes experiences the highest temperatures in the furnaces leading to microstructural changes, creep damage, and loss of elongation over their service life which in this case is twenty years. There is a cost-and time-driven motivation to only replace this portion of tubes by welding in contrast with replacing entire set of tubes which is the common industrial practice. However, welding new to aged tubes may lead to reliability issues due to difference in mechanical properties as a result of microstructural differences. In the current study, the microstructure and tensile properties of aged and new tubes have been evaluated in an effort to qualify the mechanical integrity of weldments. Welding trials are carried out to investigate the microstructure of the aged-to-new weldments and correlate it with the tensile properties (particularly elongation). Findings reveal that the heat affected zone of aged tubes is prone to micro-cracking of bulky primary carbides and incipient melting particularly at the inner surface where the root pass is applied. Adopting preheating for the root pass is effective in reducing carbide micro-cracking by decreasing cooling rate which assists in the accommodation of stresses generated by thermal contraction. Despite presence of carbide micro-cracks, tensile elongation is not severely affected as aged-to-new welds exhibit comparable and slightly higher elongation than aged base metals (above 4%). It is proposed that this is partially due to the orientation of micro-cracks in carbides. Further microstructural and tensile property results are presented and discussed.
Damage analysis and integrity assessment of a few steam-reformer components at a syn-gas plant
Mechanics & Industry, 2017
Study deals with damage-analysis and integrity-assessment for a few components of a steamreformer at a syn-gas generation plant, including catalyst tubes and hot-collectors. Selected components include the ones which either suffered from a fluid-leakage in the service or noticed with a constant high-temperature exposure during normal plant operation. The field investigation activities included visual inspection, dimensional check, die-penetrant test and pressure-drop measurements. Laboratory investigation, made on selective samples, included precise and detailed dimensional-measurement, visual examination, die penetrant test, microstructural characterization, creep-rupture test, etc. As a result of diagnostic analysis, creep was identified as the principal mechanism of degradation of the studied components. Catalyst tubes were found to be in sound condition and, hence, recommended to continue in use for the remaining period of the service-life, even after high-temperature exposure in the past. Other items; however, were noticed with a limited residual creep strength, hence, rejected for future use. Further, recommendations were made for improvement in practices of process-and operation-management, to avoid premature deterioration of the reformer components. In addition, suggestions were given for enhancing the versatility and reliability of plant inspection and monitoring methods, using latest tools and technology of the field. Moreover, suitability and limitation of different analytical approaches regarding interpretation of test and inspection results are highlighted.
Failure analysis and remaining life assessment of service exposed primary reformer heater tubes
Engineering Failure Analysis, 2008
Catalyst filled heater tubes made of cast HP-microalloyed grade 35Ni25Cr1NbTi alloy used in the primary reformer furnace section of a fertilizer complex failed after 8 years in service. Failure analysis and remaining life assessment of the tubes were carried out based on mechanical strength evaluation, microstructural observations and accelerated stress rupture tests for Larson-Miller parameter (LMP) based remaining life prediction. Failed tube portions showed coarsened primary carbides of chromium and niobium at the inter-dendritic boundaries. Degradation of niobium carbide (NbC) in to Ni-Nb-Si phase and partial conversion this phase back to NbC was observed. Secondary carbides at the intra-dendritic regions were almost absent. Degradation in tensile strength was also observed. The unfailed regions which are from a relatively cooler region of the same tube showed comparatively lesser degree of coarsening of the carbides and a higher tensile strength. The failure was attributed to localized overheating leading to premature creep failure. Based on LMP curve the life extended for tubes with similar outer diameteral expansion.
Failure Analysis of Incoloy 800HT and HP-Modified Alloy Materials in a Reformer
Journal of Failure Analysis and Prevention, 2019
The main causes of creep failure in the pigtails and tubes made of high-temperature Incoloy 800HT and HPmodified alloy materials of two natural gas primary reformers operating at a petrochemical plant complex were studied. Optical emission spectroscopy, high-resolution optical microscopy, scanning electron microscopy, and energy-dispersive x-ray spectroscopy were performed to verify that creep was the prevailing failure mechanism in both cases. Creep was confirmed in both cases by the (massive) presence of intergranular voids (aligned in some cases) at the grain boundaries and cracks originating from the edge and longitudinal to the edge in some areas. Localized overheating due to burner flame impingement most likely accelerated the creep rate deformation for the HP-modified reformer tube material though the material surpassed its design life of 100,000 h. The findings substantiate that high priority should be placed on reformer burner management and ensuring the catalyst in the reformer tubes is packed optimally to avoid downstream flows issues in the outlet pigtails. These measures can serve to mitigate the effects of localized heating that can contribute to the failure of these components.
2004
Hydrogen induced damages in metallic components of fossil fuel power plants are usually followed by unpredicted events and very intensive. In the course of clarifying a very large complex of problems associated with hydrogen damage, it is necessary to apply a multidisciplinary approach. Much of this work is based on the theory and, particularly, on experimental tests performed on boiler water wall tube samples, taken from a domestic 210 MW power plant, that had experience hydrogen damages during service. Possible mechanisms for metal–hydrogen interaction are considered from material point of view; fluid hydrodynamics in furnace wall tubes; and from the complexity of structural – exploitation plant characteristics. The aim of this paper is to present a contribution to the methodology of hydrogen damaging of boiler water wall tube based on formulation of the model of damage – influenced by the "micro-departure from nucleate boiling" (micro-DNB) of working fluid.
Proceeding of: of 3rd Conference.of Macedonian Metallurgists Union, Ohrid, Macedonia, (2000), pp. 78-84 , 2000
Convective boiling beyond critical-heat-flux is encountered in a number of applications, one of which is water wall tubing of steam generators. Sometimes, the heat transfer process in particular zones of heated surfaces of boiling tubes system is combined with fluctuation of wall temperature. This phenomena is connected with heat transfer crises during departure from nucleate boiling (DNB) as well as dry out and causes the interruption of water layer along a tube wall provoked the formation of drying areas. This process has a great influence on intensity and localization of hydrogen attack and deposits formation on the waterside of the tube. Standard investigation procedure were applied on specimens taken from furnace walls tubing, made of 0.2C0.5Mn0.25Cr, steel in the purpose of failure analysis..