Damage characterization in two reformer heater tubes after nearly 10 years of service at different operative and maintenance conditions (original) (raw)
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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...
Damage assessment and maintenance strategy of hydrogen reformer furnace tubes
The states of damage along a reformer tube in service for 09 years are metallographically analyzed[ Damage levels are ranked relating to remaining life[ The damage distribution is obtained for the whole reformer tube[ The results show that the accumulated damage of the tube is non!uniform[ The damage level in the lower part of the reformer tube is signi_cantly higher than that in the upper part\ especially in the weld region[ The damage localization is also veri_ed by use of a continuum damage mechanics _nite element technique[ Accordingly it is proposed that local replacement might be a desirable method to extend the service life when the lower part of the reformer tube reaches the safe rupture life[ Þ 0888 Elsevier Science Ltd[ All rights reserved[
International Journal of Pressure Vessels and Piping, 2015
ASTM A213 T91 steel is used in power plants and petrochemical industry, for long-term service components. The improved mechanical properties of grade 91 are strictly related to its specific microstructure: a tempered martensite matrix with fine precipitates embedded in. Despite low alloy heat resistant ferritic steels, that have a well known operational experience, T91 service performances are still faintly consolidated, because this material has serviced only in a limited number of plants, since the eighties. Most of the available data were obtained by laboratory tests on relatively short term creep strength and corrosion properties. The investigations reported in this paper represent an important opportunity to describe and better evaluate the damage evolution of the grade T91 steel after more than 100000 h of exposure in severe conditions (580 C, 18e26 bar, combustion environment). Our results suggest that the steel suffered by different damage forms, which appear on definite portions of the tube cross section. The main degradation forms observed, in fact, into the tube bulk are both the martensite recovery and the microstructural evolution. This latter promoted mostly Laves phase precipitation and coarsening. On the other hand, both the outer and the inner wall side, suffered mainly by severe oxidation/carburization. Especially on the outer surface, the massive carbide precipitation has caused an evident loss of ductility so that the mechanical properties of the tube appear appreciably reduced.
Primary reformer tubes failure due to corrosion attack
Process Safety Progress, 2011
For the last 30 years, reformer tubes are gone through numerous changes in manufacturing processes and material of construction to improve performance and reliability. To increase plant throughout Qatar Fertilizer Company replaced the old HK40 tubes with HP modified alloy but within 24 months of operation, unexpected corrosion attack was observed on some of the reformer tubes. In this article, the potential root cause of the tube damage and remediation actions has been discussed.
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.
Analysis of failed reformer tubes
Engineering Failure …, 2003
Reformer tubes from a fertilizer plant made of modified HK 40 steel which failed after 4 years service were investigated for failure mechanism and life evaluation. The investigation included hot tensile tests, hardness measurement, dimensional measurement, microscopy ...
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.
Failure analysis of catalytic steam reformer tubes
Anti-Corrosion Methods and Materials, 2005
... In contrast, the scale developed by the inner surface was more dense and compact...' Failure analysis of catalytic steam reformer tubes HMTawancy, A. Ul-Hamid, AI Mohammed and NM Abbas ... moderately carburizing but coke is not formed (Blackburn, 1981). ...
Creep Failure of Reformer Tubes in a Petrochemical Plant
Metals, 2019
This paper investigates a failure in HP-Mod radiant tubes in a petrochemical plant. Tubes fail after 90,000 h of working at 950 °C. Observed failure is in the form of excessive bulging and longitudinal cracking in reformer tubes. Cracks are also largely branched. The microstructure of service-exposed tubes was evaluated using optical and scanning electron microscopes (SEM). Energy-dispersive X-ray spectroscopy (EDS) was used to analyze and characterize different phases in the microstructure. The results of this study showed that carbides are coarsened at both the inner and the outer surface due to the long exposure to a carburizing environment. Metallography examinations also revealed that there are many creep voids that are nucleated on carbide phases and scattered in between dendrites. Cracks appeared to form as a result of creep void coalescence. Failure is therefore attributed to creep due to a long exposure to a high temperature.
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.