| 1. |
- Pompe, Robert, et al.
(författare)
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Evaluation of ceramic sacrificial coatings for improved alkaliinduced corrosion protection in biofuel-fired boilers
- 2013
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Ingår i: NACE - International Corrosion Conference Series. - 0361-4409. - 9781627481458 ; , s. (9 pp)-
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Konferensbidrag (refereegranskat)abstract
- In the combustion of bio-based fuels the critically exposed burner parts in small boilers are typically uncooled and are usually made of FeCrNi alloys. These materials can suffer attack from the ashes because of the formation of alkali chromate. The reaction depletes the protective oxide in chromia, leading to accelerated corrosion. Selected "acidic" ceramic coatings based on Ti, Si, B and P have been evaluated for use as sacrificial layers to prevent the initial reaction of alkali and chromium. An accelerated oxidation test method including mild thermal shock has been utilized that previously proved useful to provide application-relevant results. A comparison of coated and uncoated specimens was performed with an austenitic high temperature steel as a substrate. The results indicate that the alkali released from the ash reacts with the respective "acidic" elements in the deposited coatings. This reaction has promoted initial formation of a thin and continuous chromium-rich protective oxide sub-layer. In addition, the oxide scale formed on the coated specimens appeared more coherent and crack-free. A significant enrichment of Ni at the steel-oxide interface also occurred that can promote high temperature corrosion resistance.
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| 2. |
- Pompe, Robert, et al.
(författare)
-
How to screen high temperature steels for optimal use in biofuel-heated burners for residential boilers: Role of alkali
- 2011
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Ingår i: NACE - International Corrosion Conference Series. - 0361-4409. ; , s. 12p-
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Konferensbidrag (refereegranskat)abstract
- Hot parts of burners for residential boilers are subject to irregular heating cycles up to 800 °C and higher, simultaneously exposed to alkali salts, variable oxygen partial pressure - and thermal shock. Fundamental hot corrosion studies under well-controlled conditions, in combination with simple ranking tests simulating the effect of ash deposited on the alloy surface, have been performed. The investigation included four types of high-alloyed steel and two types of ash from wood and bark pellets. The work was complemented with field studies of selected damaged parts. Two mechanisms involving interaction of potassium as well as carbon under intermittent oxygen-deficient conditions with chromium from the alloys have been corroborated. A simple ranking test procedure has also been designed. It proved relevant as a screening method only after incorporating a mild thermal shock in the heat treatment sequence. A significant difference in corrosive effect, particularly on a lower chromium-alloy like 304 L, has been observed for the ash derived from the wood and bark pellets, respectively.
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