Sealing of thermally sprayed coatings

Maria Oksa, Erja Turunen, Tommi Varis

Research output: Contribution to journalArticleScientificpeer-review

14 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

Fingerprint

sprayed coatings
Sprayed coatings
sealing
boilers
coatings
Boilers
Coatings
Alkalies
sealers
alkalies
Sealants
beds
Aluminum
Superheaters
Oxides
Lasers
Aluminum Oxide
Energy dispersive X ray analysis
Chlorine
lamella

Keywords

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

Cite this

Oksa, Maria ; Turunen, Erja ; Varis, Tommi. / Sealing of thermally sprayed coatings. In: Surface Engineering. 2004 ; Vol. 20, No. 4. pp. 251-254.
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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.",
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Sealing of thermally sprayed coatings. / Oksa, Maria; Turunen, Erja; Varis, Tommi.

In: Surface Engineering, Vol. 20, No. 4, 2004, p. 251-254.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Sealing of thermally sprayed coatings

AU - Oksa, Maria

AU - Turunen, Erja

AU - Varis, Tommi

PY - 2004

Y1 - 2004

N2 - 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.

AB - 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.

KW - thermal spray

KW - HVOF

KW - metallic coating

KW - sealing

KW - sealant

KW - lasers

KW - corrosion protection

KW - chlorine

KW - alkali

KW - fluidized bed boiler

KW - fluidized beds

U2 - 10.1179/026708404225016346

DO - 10.1179/026708404225016346

M3 - Article

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SP - 251

EP - 254

JO - Surface Engineering

JF - Surface Engineering

SN - 0267-0844

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