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Keywords = cast reformer tubes

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21 pages, 19235 KiB  
Article
Insight to the Microstructure Analysis of a HP Austenitic Heat-Resistant Steel Under Short-Term High-Temperature Exposure
by Milica Timotijević, Olivera Erić Cekić, Petar Janjatović, Aleksandar Kremenović, Milena Rosić, Srecko Stopic and Dragan Rajnović
Metals 2025, 15(5), 486; https://doi.org/10.3390/met15050486 - 25 Apr 2025
Viewed by 589
Abstract
The HP40Nb alloy, commonly used in the petrochemical industry as a heat-resistant material, undergoes significant microstructural changes at high temperatures. This study examined samples from the HP40Nb radiant tube used in a reformer furnace, exposed to 950, 1050, and 1150 °C for 2 [...] Read more.
The HP40Nb alloy, commonly used in the petrochemical industry as a heat-resistant material, undergoes significant microstructural changes at high temperatures. This study examined samples from the HP40Nb radiant tube used in a reformer furnace, exposed to 950, 1050, and 1150 °C for 2 and 8 h. Metallographic analysis, including optical microscopy, SEM, EDS, and XRPD, revealed that the as-cast alloy has an austenitic dendritic matrix with primary eutectic-like carbides (M23C6 and MC types). Prolonged exposure to high temperatures transformed the primary carbides into coarse M23C6 forms, losing their lamellar shape. The number of secondary carbides decreased with increasing temperature, and at 1150 °C for 480 min, secondary Cr23C6 carbides nearly decomposed, and Nb carbides dissolved into the austenitic matrix. Full article
(This article belongs to the Special Issue Novel Insights and Advances in Steels and Cast Irons)
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12 pages, 5366 KiB  
Article
Failure Analysis of Two HP-Nb Heat-Resistant Tubes after 46,000 h Exposure to Reformer Service Conditions
by Ali Nazemi Harandi, Abdoulmajid Eslami, Abbas Bahrami, Asghar Bakhtafrouz and Maryam Yazdan Mehr
Metals 2023, 13(2), 228; https://doi.org/10.3390/met13020228 - 26 Jan 2023
Cited by 2 | Viewed by 2680
Abstract
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 [...] Read more.
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 without titanium (Tube A) occurred due to the coalescence of creep pores and the creation of grain boundary cracks. Full article
(This article belongs to the Special Issue Structural Integrity and Failure Assessments in Metals and Alloys)
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15 pages, 109052 KiB  
Article
Weldability and Damage Evaluations of Fresh-to-Aged Reformer Furnace Tubes
by Chengming Fuyang, Yang Zhou, Bing Shao, Tianyu Zhang, Xiaofeng Guo, Jianming Gong and Xiaowei Wang
Metals 2021, 11(6), 900; https://doi.org/10.3390/met11060900 - 31 May 2021
Cited by 3 | Viewed by 2658
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue High-Temperature Behavior of Metals)
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10 pages, 5467 KiB  
Article
Aging Phenomena during In-Service Creep Exposure of Heat-Resistant Steels
by G. N. Haidemenopoulos, K. Polychronopoulou, A. D. Zervaki, H. Kamoutsi, S. I. Alkhoori, S. Jaffar, P. Cho and H. Mavros
Metals 2019, 9(7), 800; https://doi.org/10.3390/met9070800 - 19 Jul 2019
Cited by 13 | Viewed by 4236
Abstract
An investigation of aging phenomena during creep exposure has been conducted for HP-Nb cast reformer tubes for several exposure conditions. Aging was manifested by carbide precipitation, carbide coarsening, and carbide transformation. The transformation of primary M7C3 to the more stable [...] Read more.
An investigation of aging phenomena during creep exposure has been conducted for HP-Nb cast reformer tubes for several exposure conditions. Aging was manifested by carbide precipitation, carbide coarsening, and carbide transformation. The transformation of primary M7C3 to the more stable M23C6 carbide takes place at high exposure temperature (910 °C and above). The primary MC carbides transform to the Ni-Nb silicide or G-phase during creep exposure. The presence of Ti in the steel prevented the transformation of MC carbides to the G-phase. Morphological changes like needle to globular transitions, rounding of carbide edges, and carbide coarsening take place during creep exposure. The room-temperature tensile elongation and ultimate tensile strength are significantly reduced during creep exposure. The above aging phenomena are precursors to creep damage. Full article
(This article belongs to the Special Issue Failure Mechanisms in Alloys)
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