High temperature corrosion of thermally sprayed NiCr and FeCr coatings covered with a KCl-K2SO4 salt mixture

Tommi Varis (Corresponding Author), D. Bankiewicz, P. Yrjas, Maria Oksa, Tomi Suhonen, Satu Tuurna, Kimmo Ruusuvuori, Stefan Holmström

Research output: Contribution to journalArticleScientificpeer-review

14 Citations (Scopus)

Abstract

Current boiler tube materials and designs are sensitive to changes in process conditions. The desire to increase efficiency through the increase in process temperature and the use of high-chlorine and alkali containing fuels such as biomass is challenging. The alloying of steel to increase the corrosion resistance leads to a significant increase in cost. Thermally sprayed coatings offer promising, effective, flexible and cost efficient solution to fulfil the material needs for the future. However, some heat exchanger design alterations have to be overcome before global commercialization. High temperature corrosion in combustion plants can occur by a variety of mechanisms, including passive scale degradation with subsequent rapid scaling, loss of adhesion and scale detachment, attack by molten or partly molten deposits via fluxing reactions and intergranular/interlamellar corrosion. The activated chlorine corrosion mechanism plays a key role in the thermally sprayed coatings due to their unique lamellar structure. In this study, the corrosion behaviour of NiCr and FeCr (HVOF and wire arc) thermally sprayed coatings was tested under simplified biomass combustion conditions. The tests were carried out by using a KCl-K2SO4 salt mixture as a synthetic biomass ash, which was placed on the coated materials and then heat treated for one week (168 h) at two different temperatures (550 °C and 600 °C) and in two different gas atmospheres (air and air + 30% H2O). After exposure, the metallographic cross sections of the coatings were studied with SEM/EDX. The results showed that the coatings behaved relatively well at the lower test temperature while critical interlamellar corrosion was observed in some cases at the higher test temperature. A few coatings (HVOF Ni49Cr, HVOF Ni21Cr, and wire arc sprayed Fe30Cr) showed promising performance even at 600 °C in both atmospheres (dry and wet).
Original languageEnglish
Pages (from-to)235-243
JournalSurface and Coatings Technology
Volume265
DOIs
Publication statusPublished - 2015
MoE publication typeA1 Journal article-refereed

Fingerprint

sprayed coatings
corrosion
biomass
Salts
Sprayed coatings
Corrosion
salts
coatings
Coatings
Biomass
Chlorine
chlorine
low temperature tests
Ashes
arcs
high temperature tests
wire
intergranular corrosion
Molten materials
costs

Keywords

  • thermal spray coating
  • HVOF
  • wire arc
  • biomass
  • high temperature corrosion
  • corrosion protection
  • ProperPart
  • ProperTune

Cite this

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title = "High temperature corrosion of thermally sprayed NiCr and FeCr coatings covered with a KCl-K2SO4 salt mixture",
abstract = "Current boiler tube materials and designs are sensitive to changes in process conditions. The desire to increase efficiency through the increase in process temperature and the use of high-chlorine and alkali containing fuels such as biomass is challenging. The alloying of steel to increase the corrosion resistance leads to a significant increase in cost. Thermally sprayed coatings offer promising, effective, flexible and cost efficient solution to fulfil the material needs for the future. However, some heat exchanger design alterations have to be overcome before global commercialization. High temperature corrosion in combustion plants can occur by a variety of mechanisms, including passive scale degradation with subsequent rapid scaling, loss of adhesion and scale detachment, attack by molten or partly molten deposits via fluxing reactions and intergranular/interlamellar corrosion. The activated chlorine corrosion mechanism plays a key role in the thermally sprayed coatings due to their unique lamellar structure. In this study, the corrosion behaviour of NiCr and FeCr (HVOF and wire arc) thermally sprayed coatings was tested under simplified biomass combustion conditions. The tests were carried out by using a KCl-K2SO4 salt mixture as a synthetic biomass ash, which was placed on the coated materials and then heat treated for one week (168 h) at two different temperatures (550 °C and 600 °C) and in two different gas atmospheres (air and air + 30{\%} H2O). After exposure, the metallographic cross sections of the coatings were studied with SEM/EDX. The results showed that the coatings behaved relatively well at the lower test temperature while critical interlamellar corrosion was observed in some cases at the higher test temperature. A few coatings (HVOF Ni49Cr, HVOF Ni21Cr, and wire arc sprayed Fe30Cr) showed promising performance even at 600 °C in both atmospheres (dry and wet).",
keywords = "thermal spray coating, HVOF, wire arc, biomass, high temperature corrosion, corrosion protection, ProperPart, ProperTune",
author = "Tommi Varis and D. Bankiewicz and P. Yrjas and Maria Oksa and Tomi Suhonen and Satu Tuurna and Kimmo Ruusuvuori and Stefan Holmstr{\"o}m",
year = "2015",
doi = "10.1016/j.surfcoat.2014.11.012",
language = "English",
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journal = "Surface and Coatings Technology",
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publisher = "Elsevier",

}

High temperature corrosion of thermally sprayed NiCr and FeCr coatings covered with a KCl-K2SO4 salt mixture. / Varis, Tommi (Corresponding Author); Bankiewicz, D.; Yrjas, P.; Oksa, Maria; Suhonen, Tomi; Tuurna, Satu; Ruusuvuori, Kimmo; Holmström, Stefan.

In: Surface and Coatings Technology, Vol. 265, 2015, p. 235-243.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - High temperature corrosion of thermally sprayed NiCr and FeCr coatings covered with a KCl-K2SO4 salt mixture

AU - Varis, Tommi

AU - Bankiewicz, D.

AU - Yrjas, P.

AU - Oksa, Maria

AU - Suhonen, Tomi

AU - Tuurna, Satu

AU - Ruusuvuori, Kimmo

AU - Holmström, Stefan

PY - 2015

Y1 - 2015

N2 - Current boiler tube materials and designs are sensitive to changes in process conditions. The desire to increase efficiency through the increase in process temperature and the use of high-chlorine and alkali containing fuels such as biomass is challenging. The alloying of steel to increase the corrosion resistance leads to a significant increase in cost. Thermally sprayed coatings offer promising, effective, flexible and cost efficient solution to fulfil the material needs for the future. However, some heat exchanger design alterations have to be overcome before global commercialization. High temperature corrosion in combustion plants can occur by a variety of mechanisms, including passive scale degradation with subsequent rapid scaling, loss of adhesion and scale detachment, attack by molten or partly molten deposits via fluxing reactions and intergranular/interlamellar corrosion. The activated chlorine corrosion mechanism plays a key role in the thermally sprayed coatings due to their unique lamellar structure. In this study, the corrosion behaviour of NiCr and FeCr (HVOF and wire arc) thermally sprayed coatings was tested under simplified biomass combustion conditions. The tests were carried out by using a KCl-K2SO4 salt mixture as a synthetic biomass ash, which was placed on the coated materials and then heat treated for one week (168 h) at two different temperatures (550 °C and 600 °C) and in two different gas atmospheres (air and air + 30% H2O). After exposure, the metallographic cross sections of the coatings were studied with SEM/EDX. The results showed that the coatings behaved relatively well at the lower test temperature while critical interlamellar corrosion was observed in some cases at the higher test temperature. A few coatings (HVOF Ni49Cr, HVOF Ni21Cr, and wire arc sprayed Fe30Cr) showed promising performance even at 600 °C in both atmospheres (dry and wet).

AB - Current boiler tube materials and designs are sensitive to changes in process conditions. The desire to increase efficiency through the increase in process temperature and the use of high-chlorine and alkali containing fuels such as biomass is challenging. The alloying of steel to increase the corrosion resistance leads to a significant increase in cost. Thermally sprayed coatings offer promising, effective, flexible and cost efficient solution to fulfil the material needs for the future. However, some heat exchanger design alterations have to be overcome before global commercialization. High temperature corrosion in combustion plants can occur by a variety of mechanisms, including passive scale degradation with subsequent rapid scaling, loss of adhesion and scale detachment, attack by molten or partly molten deposits via fluxing reactions and intergranular/interlamellar corrosion. The activated chlorine corrosion mechanism plays a key role in the thermally sprayed coatings due to their unique lamellar structure. In this study, the corrosion behaviour of NiCr and FeCr (HVOF and wire arc) thermally sprayed coatings was tested under simplified biomass combustion conditions. The tests were carried out by using a KCl-K2SO4 salt mixture as a synthetic biomass ash, which was placed on the coated materials and then heat treated for one week (168 h) at two different temperatures (550 °C and 600 °C) and in two different gas atmospheres (air and air + 30% H2O). After exposure, the metallographic cross sections of the coatings were studied with SEM/EDX. The results showed that the coatings behaved relatively well at the lower test temperature while critical interlamellar corrosion was observed in some cases at the higher test temperature. A few coatings (HVOF Ni49Cr, HVOF Ni21Cr, and wire arc sprayed Fe30Cr) showed promising performance even at 600 °C in both atmospheres (dry and wet).

KW - thermal spray coating

KW - HVOF

KW - wire arc

KW - biomass

KW - high temperature corrosion

KW - corrosion protection

KW - ProperPart

KW - ProperTune

U2 - 10.1016/j.surfcoat.2014.11.012

DO - 10.1016/j.surfcoat.2014.11.012

M3 - Article

VL - 265

SP - 235

EP - 243

JO - Surface and Coatings Technology

JF - Surface and Coatings Technology

SN - 0257-8972

ER -