Laboratory testing of selected chromia-forming alloys was performed to rank the materials and gain further knowledge on the mechanism of KCl-induced high temperature corrosion. The investigated alloys were stainless steels EN1.4021, EN1.4057, EN1.4521, TP347H (coarse-grained), TP347HFG (fine-grained), Sanicro 28 and the nickel-based alloys 625, 263 and C276. Exposure was performed at 600 8C for 168 h in flowing N 2 (g)þ5%O 2 (g)þ15% H 2 O(g) (vol.%). Samples were covered with KCl powder prior to exposure. A salt-free exposure was also performed for comparison. Corrosion morphology and products were studied with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD). It was observed that in the salt-free exposure, stainless steels TP347H (coarse-grained) and EN1.4521 failed to form a thin protective oxide layer compared to the oxide formed on the other alloys. In the presence of solid KCl, all the alloys showed significant corrosion. Measurement of corrosion extent indicated that alloys EN1.4057, Sanicro 28 and 625 show a better performance compared to the industrial state of the art material TP347HFG under laboratory conditions. An additional test was performed with KCl vapor in static air for the same duration and at the same temperature. This was undertaken to investigate the role of the vapor phase and revealed that KCl vapor at 600 8C can initiate attack.
Pack cementation was used to produce Fe1−xAl and Fe2Al5 diffusion coatings on ferritic‐martensitic steel P91 and a Ni2Al3 diffusion coating on pure nickel. The performance of diffusion coatings against high‐temperature corrosion induced by potassium chloride (KCl) was evaluated by exposing the samples at 600 °C for 168 h in static lab air under KCl deposit. In addition, a salt‐free experiment was performed for comparison. Microstructure, chemical and phase composition of the samples were analyzed with scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS) and X‐ray diffractometry (XRD) before and after the exposures. It was found that all the diffusion coatings formed protective oxides under salt‐free exposure in air. Under the salt deposit, Fe1−xAl showed local failure while on large parts of the sample a protective layer had formed. Fe2Al5 was attacked over the entire surface and the dominant mode of attack was selective aluminum removal. Ni2Al3 showed excellent performance and no sign of attack was observed anywhere on the sample.
In biomass fired power plants, deposition of alkali chlorides on superheaters, as well as the presence of corrosive flue gas species, give rise to fast corrosion of superheaters. In order to understand the corrosion mechanism under this complex condition, the influence of the flue gas composition on high temperature corrosion of an austenitic superheater material under laboratory conditions mimicking biomass firing is investigated in this work. Exposures involving deposit (KCl)‐coated and deposit‐free austenitic stainless steel (TP 347H FG) samples were conducted isothermally at 560 °C for 72 h, under both oxidizing and oxidizing‐chlorinating atmospheres, and the resulting corrosion products were comprehensively studied with scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS), and X‐ray diffraction (XRD) techniques. The results show that deposit‐free samples suffer grain boundary attack only in an oxidizing‐chlorinating atmosphere, otherwise corrosion results in formation of a duplex oxide. Corrosion attack on deposit‐coated samples was higher than on deposit‐free samples irrespective of the gaseous atmosphere. Specifically, severe volatilization of alloying elements occurred on deposit‐coated samples under oxidizing‐chlorinating atmosphere due to enhanced impact of KCl and HCl.
Laboratory testing on selected alumina and silica‐forming alloys was performed to evaluate their performance against high temperature corrosion induced by potassium chloride (KCl). The alloys studied were FeCrAlY, Kanthal APM, Nimonic 80A, 214, 153MA and HR160. Exposure was conducted at 600 °C for 168 h in flowing N2(g)+5%O2(g)+15%H2O(g) (vol.%) with samples covered under KCl powder. A KCl‐free exposure was also performed for comparison. Corrosion morphology and products were studied with scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS) and X‐ray diffractometry (XRD). It was observed that alloying with aluminum did not lead to the formation of protective alumina for the studied alloys. The silicon containing stainless steel 153MA showed an analogous performance to low‐silicon austenitic stainless steels of similar chromium and nickel contents. For alloy HR160, a potassium‐chromium‐silicon‐oxygen containing layer forms as the innermost corrosion product. The layer was uniformly distributed over the surface and appears to render some protection as this alloy exhibited the best performance among the investigated alloys. To reveal further aspects of the corrosion mechanism, Nimonic 80A was exposed in static laboratory air for the same duration and temperature with either KCl or K2CO3 deposits. Comparison of results obtained with these experiments showed that both potassium and chlorine can play a role in material degradation by KCl.
Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.