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- Andersson, Petter, 1970
(författare)
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Deposit Induced Corrosion in Biofuel Combustion
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Deposit induced corrosion is one of the main mechanisms for attack on heat exchangers in biofuel boilers. This severe corrosion decreases the obtainable steam temperature in boilers, thereby the efficiency in production of electricity is reduced. Deposit formation from the gas on superheater tubes are is generally referred to as fouling. Fouling decreases the heat transfer from the gas to the steam. Alkali and chlorine rich biofuels, and especially waste, will form deposit rich in alkali chlorides and sulphates that are corrosive. High sulphur contents in the fuel and gas reduces the corrosion attack. Waste can also be rich in heavy elements such as lead and zinc that can form low-melting-point eutectic chloride melts. Alloys rich in nickel, chromium and molybdenum are used to improve the corrosion resistance in biofuel boilers. In order to investigate candidate alloys for waste boilers a field test was performed including two test panels in the waterwall at 300 and 338 °C as well as a superheater test coil at 460-540 °C. The alloys ranged from carbon steel to nickel based Sanicro 65. The deposits and corrosion products were characterised by X-ray microanalysis (EDX), Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES) and X-ray diffraction (XRD). Secondary Ion Mass Spectrometry (SIMS) and X-ray Photoelectron Spectroscopy (XPS) were done on selected samples. Both in the waterwall and on the superheater thicker deposits formed on the ferritic steels. In the waterwall the addition of chromium and nickel only decreased the corrosion rate at the higher temperature. Protective Cr-Ni-Fe oxide separated the chlorides from the metal on Sanicro 28 and Sandvik 625. In the superheater the corrosion rates were high, up to 34 mm/year for T22. Sanicro 28 and the more Cr and Ni rich alloys performed the best. The austenitic alloys were preferentially attacked on the side of the deposit crest and Sanicro 65 directly under the deposit crest. Alloy 310 suffered severe pitting corrosion in a line at the side of the deposit crest. The scales in the superheater were porous and cracked. Chlorides were observed in the metal/scale interface. Sanicro 28 formed chromium oxide that separated the chlorides from the metal in the interface. Grain boundary attack and local attack under a thick porous chromium oxide was observed on Sanicro 65. Laboratory tests were done with coupons of the austenitic steels 310 and Sanicro 28 imbedded in KCl-tablets at 500 °C in 5%O2-10%H2O-N2 gas. The aim was to mimic the deposit and its morphology on superheater tubes and to investigate how this affects the corrosion. Consistent with field behaviour, it was shown that transport through the KCl-deposit controlled the corrosion rate. The corrosion rate decreased with increasing thickness after reaching a maximum at 1 mm. The rim of the coupons was preferentially attacked due to microcracks through the tablet. Scale growth was investigated after 24, 168 and 672h. The corrosion products after 24h consisted of FeCr oxide and potassium chromate. The chromates grew laterally, consuming the chromium in the surrounding oxide. After 168h an oxide was formed under the chromate and chlorine was enriched in the scale/metal interface. Finally after 672h the oxides were 5 μm thick and few chromates were seen. Similar to fouling, crystals of KCl formed near thicker iron oxide after 168h in these tests.
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- Andersson, Petter, 1970, et al.
(författare)
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Field test of superheater corrosion in a CFB waste boiler: Part II - Scale formation characteristics
- 2005
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Ingår i: Materials and Corrosion. - : Wiley. - 0947-5117 .- 1521-4176. ; 56:8, s. 550 - 560
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Tidskriftsartikel (refereegranskat)abstract
- This study concerns the scales formed on the steels T22, Alloy 310, Alloy 28 and the nickel-based Alloy 65 in a superheater test coil at 460-540°C in a CFB waste boiler. The methods used for the characterisation of the scales included SEM, EDX, Auger spectroscopy and XRD. The deposits on the tubes consisted mainly of alkali chlorides and calcium sulphate. The scales formed consisted of Fe 2 O 3 and Fe 3 O 4 on the T22 steel, NiFe 2 O 3 and Cr 2 O 3 on Alloy 310 and Alloy 28, and Cr 2 O 3 and NiO on Alloy 65. Rapid corrosion on the steel T22 was associated with the growth of an open columnar iron oxide below a thick porous chlorine-containing scale. Pitting corrosion on Alloy 310 occurred and it may be associated with selective corrosion, first following the grain boundaries then uniformly attacking the metal. The only protective oxide was observed on Alloy 28 that formed an inner chromium oxide separating the chlorides from the metal. Dense thin chromium oxides were observed in the scale on Alloy 28, but no major cracks were found perpendicular to the tube. Alloy 65 suffered from grain boundary attack and was locally attacked under thick porous chromium oxide with nickel chlorides in the advancing front. Molybdenum was enriched at the interface to the metal on both Alloy 28 and Alloy 65. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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- Andersson, Petter, 1970, et al.
(författare)
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Scale growth on austenitic alloys under KCl deposits at 500 deg C
- 2008
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Ingår i: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 595-598:I, s. 333-342
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Tidskriftsartikel (refereegranskat)abstract
- The scale growth on two austenitic alloys, Alloy 310 and Sanicro 28, under KCl deposits was examined. This is relevant to the long term corrosion of superheater tubes in biofuel combustion. Coupons were encapsulated in tablets so that 1 mm of KCl with a relative density of 91% covered the metal. Samples were tested at 500 deg C in 5%O2-10%H2O-N2 for 24, 168 and 672 h. After exposure the salt was broken off and the scale was characterised by using SEM-EDX and AES. After 24 h a 50 nm thick oxide surrounded 500 nm thick chromates on the surface. No oxide layer was detected under the chromates and no Cl was found under either layer. The chromate growth requires lateral transportation of Cr along the surface. This reduces the protectiveness of the oxide and accelerates the formation of less protective Fe rich oxides. The formation of chromates also releases HCl inside the KCl tablet. The chromates did not grow significantly between 24 and 168 h, but the oxide grew equally thick beneath and between them and Cl was enriched around the metal oxide interface. After 672 h the oxides were about 5 mum thick and only few chromates were seen. Crystals of KCl formed in areas with thick porous and Fe rich oxides on both alloys.
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- Brahma, Arindam, 1987, et al.
(författare)
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FUNCTION DRIVEN ASSESSMENT OF MANUFACTURING RISKS IN CONCEPT GENERATION STAGES
- 2023
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Ingår i: Proceedings of the Design Society. - 2732-527X. ; 3, s. 1995-2004
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Konferensbidrag (refereegranskat)abstract
- Decisions made in the concept generation phase have a significant effect on the product. While product- related risks typically can be considered in the early stages of design, risks such as supply chain and manufacturing methods are rarely easy to account for in early phases. This is because the currently available methods require mature data, which may not be available during concept generation. In this paper, we propose an approach to address this. First, the product and the non-product (manufacturing and/or supply chain) attributes are modelled using the enhanced function means (EF-M) modelling method. The EF-M method provides the opportunity to model alternative solutions-set for functions. Dependencies are then mapped within the product and the manufacturing models, and also in between them. An automatic combinatorial method of concept generation is employed where each generated instance is a design concept-manufacturing method pair. A risk propagation algorithm is then used to assess the risks of all the generated alternatives.
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- Stolt, Roland, 1970-, et al.
(författare)
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Design for Inspection : Evaluating the Inspectability of Aerospace Components in the Early Stages of Design
- 2017
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Ingår i: Procedia Manufacturing. - : Elsevier. - 2351-9789. ; 11, s. 1193-1199
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Tidskriftsartikel (refereegranskat)abstract
- One important part of the manufacturing process of aerospace components is making inspections using Fluorescent Penetrant Inspection (FPI). This mandatory inspection represents a non-negligible part of the manufacturing and service cost. It is therefore important to make the geometry of the components suitable for inspection i.e. practicing Design for Inspection (DFI). This has been studied at an aerospace company with the aim of bringing DFI to the early stages of product development process. In this paper, a tool is proposed for the evaluation of inspectability in the early design stages. The tool is applied on CAD-models of the components automatically ranking the inspectability of design proposals using a novel inspectability index. Thus, inspectability can be considered together with other performance and manufacturing aspects forming a powerful decision support. The tool has been run and evaluated together with manufacturing staff at the aerospace company with promising results.
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