Sealing of thermally sprayed coatings

Maria Oksa, Erja Turunen, Tommi Varis

Research output: Contribution to journalArticleScientificpeer-review

15 Citations (Scopus)

Abstract

The use of coatings in fluidised bed boilers is increasing owing to the harsh conditions that modern boilers meet. High temperatures, combined with inhomogeneous, high chlorine and alkali containing fuels such as biomass, cause severe material wastage to metallic parts in boilers. Thermally sprayed coatings have been reported to provide protection to boiler tubes. However, thermally sprayed coatings have encountered serious problems, such as corrosion on the substrate material owing to voids and oxides in lamella boundaries. Sealing of the coatings can solve these problems. This paper investigates the sealing of coatings. Thermally sprayed metallic coatings were sealed with different commercial sealing agents and laser treatment. The coatings were tested after sealing by simulating fluidised bed boiler superheater conditions. Specimens were examined by optical microscopy and SEM and analysed by energy dispersive X-ray analysis. Some of the tested sealants protected the coatings adequately in a short term alkali chloride– alkali sulphate exposure test. The best sealant contained aluminium oxide and aluminium phosphate. Laser treated coatings had good corrosion resistance in a short term test.
Original languageEnglish
Pages (from-to)251-254
JournalSurface Engineering
Volume20
Issue number4
DOIs
Publication statusPublished - 2004
MoE publication typeA1 Journal article-refereed

Keywords

  • thermal spray
  • HVOF
  • metallic coating
  • sealing
  • sealant
  • lasers
  • corrosion protection
  • chlorine
  • alkali
  • fluidized bed boiler
  • fluidized beds

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