Nitridation of grate in a biomass-fired boiler

Melanie Montgomery*, Kristian V. Dahl, Flemming B. Grumsen, Frederik B. Kværndrup, John Hald

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

After a straw-fired power plant in Denmark had been in operation for 16 years with 93,815 hr operation, there was a need for overlay welding repair of the grate due to a decrease in wall thickness from erosion/corrosion. The grate consisted of 15Mo3 (Werkstoff nr. 1.5415) tubes where water/steam flows through, which were welded together with fins, and where one side faced the combustion zone coming into contact with the fuel (the side that required weld overlay). The water/steam temperature was 320°C and the surface metal temperature was estimated to be 350°C. However, there were difficulties when trying to overlay weld the grate as the weld pool was unstable. The microhardness measurements on cross-sections of the tubes revealed a higher hardness of the tube facing the combustion zone compared to opposite the combustion zone. In addition, there was higher hardness adjacent to the combustion side than the steam/water side. Analysis of etched cross-sections with light optical and scanning electron microscopy revealed the presence of acicular structures at the convex surface. Further analysis has been conducted with X-ray diffraction and a LECO nitrogen analyser indicating the presence of iron nitrides. Reasons for their evolution and implications for the repair welding are discussed.
Original languageEnglish
JournalMaterials and Corrosion
Volume70
Issue number1
Pages (from-to)1461-1475
ISSN0947-5117
DOIs
Publication statusPublished - 2019

Keywords

  • Biomass boiler
  • Iron nitrides
  • Straw
  • Welding problems

Cite this

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title = "Nitridation of grate in a biomass-fired boiler",
abstract = "After a straw-fired power plant in Denmark had been in operation for 16 years with 93,815 hr operation, there was a need for overlay welding repair of the grate due to a decrease in wall thickness from erosion/corrosion. The grate consisted of 15Mo3 (Werkstoff nr. 1.5415) tubes where water/steam flows through, which were welded together with fins, and where one side faced the combustion zone coming into contact with the fuel (the side that required weld overlay). The water/steam temperature was 320°C and the surface metal temperature was estimated to be 350°C. However, there were difficulties when trying to overlay weld the grate as the weld pool was unstable. The microhardness measurements on cross-sections of the tubes revealed a higher hardness of the tube facing the combustion zone compared to opposite the combustion zone. In addition, there was higher hardness adjacent to the combustion side than the steam/water side. Analysis of etched cross-sections with light optical and scanning electron microscopy revealed the presence of acicular structures at the convex surface. Further analysis has been conducted with X-ray diffraction and a LECO nitrogen analyser indicating the presence of iron nitrides. Reasons for their evolution and implications for the repair welding are discussed.",
keywords = "Biomass boiler, Iron nitrides, Straw, Welding problems",
author = "Melanie Montgomery and Dahl, {Kristian V.} and Grumsen, {Flemming B.} and Kv{\ae}rndrup, {Frederik B.} and John Hald",
year = "2019",
doi = "10.1002/maco.201810630",
language = "English",
volume = "70",
pages = "1461--1475",
journal = "Materials and Corrosion",
issn = "0947-5117",
publisher = "Wiley - V C H Verlag GmbH & Co. KGaA",
number = "1",

}

Nitridation of grate in a biomass-fired boiler. / Montgomery, Melanie; Dahl, Kristian V.; Grumsen, Flemming B.; Kværndrup, Frederik B.; Hald, John.

In: Materials and Corrosion, Vol. 70, No. 1, 2019, p. 1461-1475.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Nitridation of grate in a biomass-fired boiler

AU - Montgomery, Melanie

AU - Dahl, Kristian V.

AU - Grumsen, Flemming B.

AU - Kværndrup, Frederik B.

AU - Hald, John

PY - 2019

Y1 - 2019

N2 - After a straw-fired power plant in Denmark had been in operation for 16 years with 93,815 hr operation, there was a need for overlay welding repair of the grate due to a decrease in wall thickness from erosion/corrosion. The grate consisted of 15Mo3 (Werkstoff nr. 1.5415) tubes where water/steam flows through, which were welded together with fins, and where one side faced the combustion zone coming into contact with the fuel (the side that required weld overlay). The water/steam temperature was 320°C and the surface metal temperature was estimated to be 350°C. However, there were difficulties when trying to overlay weld the grate as the weld pool was unstable. The microhardness measurements on cross-sections of the tubes revealed a higher hardness of the tube facing the combustion zone compared to opposite the combustion zone. In addition, there was higher hardness adjacent to the combustion side than the steam/water side. Analysis of etched cross-sections with light optical and scanning electron microscopy revealed the presence of acicular structures at the convex surface. Further analysis has been conducted with X-ray diffraction and a LECO nitrogen analyser indicating the presence of iron nitrides. Reasons for their evolution and implications for the repair welding are discussed.

AB - After a straw-fired power plant in Denmark had been in operation for 16 years with 93,815 hr operation, there was a need for overlay welding repair of the grate due to a decrease in wall thickness from erosion/corrosion. The grate consisted of 15Mo3 (Werkstoff nr. 1.5415) tubes where water/steam flows through, which were welded together with fins, and where one side faced the combustion zone coming into contact with the fuel (the side that required weld overlay). The water/steam temperature was 320°C and the surface metal temperature was estimated to be 350°C. However, there were difficulties when trying to overlay weld the grate as the weld pool was unstable. The microhardness measurements on cross-sections of the tubes revealed a higher hardness of the tube facing the combustion zone compared to opposite the combustion zone. In addition, there was higher hardness adjacent to the combustion side than the steam/water side. Analysis of etched cross-sections with light optical and scanning electron microscopy revealed the presence of acicular structures at the convex surface. Further analysis has been conducted with X-ray diffraction and a LECO nitrogen analyser indicating the presence of iron nitrides. Reasons for their evolution and implications for the repair welding are discussed.

KW - Biomass boiler

KW - Iron nitrides

KW - Straw

KW - Welding problems

U2 - 10.1002/maco.201810630

DO - 10.1002/maco.201810630

M3 - Journal article

VL - 70

SP - 1461

EP - 1475

JO - Materials and Corrosion

JF - Materials and Corrosion

SN - 0947-5117

IS - 1

ER -