Protective coatings and claddings: Application/evaluation. [Coatings were applied by chromizing, aluminizing, or simultaneously aluminizing/chromizing pack-diffusion processes]

Technical Report · Fri Aug 01 04:00:00 EDT 1986

OSTI ID:7127074

Baxter, D J

The objective of the project is to develop corrosion-resistant coatings for the protection of low-alloy steels exposed in downstream waste heat recovery systems of coal gasifiers. A specification will be formulated for boiler-grade steels and established coating procedures that will serve as a guide for future designers of heat recovery systems. Corrosion test results show that chemical composition is an important factor influencing the corrosion resistance of both Al- and Cr-containing coatings. Coatings containing 20 to 29% Al generally exhibited protective oxidation behavior under isothermal conditions in the mixed-gas environments, but at 14% Al, even with 0.4 to 2% Cr, breakaway corrosion occurred. Under thermal-cycling conditions, approximately 30% Al was inadequate in preventing sulfide scale formation, although the additional presence of 5% Cr reduced the amount of sulfide formed in the scale and also reduced the severity of internal corrosive degradation of the coating. The corrosion resistance of chromized steels is critically dependent upon the coating composition and physical defects. With about 17% Cr on the 2-1/4Cr-1Mo steel, breakaway corrosion was observed in the high-p/sub S//sub 2/ gas mixture. However, with Cr contents in the range of 22 to 25%, protective oxidation behavior was sustained, even under thermal-cycling conditions, although thermal cycling caused an increase in internal corrosion. The intergranular nature of internal corrosion highlights the weakness of the sensitized grain boundaries. Chromium-rich intergranular carbides, formed upon cooling from the chromizing temperature of approx.1100/sup 0/C, resulted in the depletion of Cr from regions immediately adjacent to the carbide-containing grain boundaries. As a result, these regions had lower resistance to corrosion. Breakdown of protection of chromized carbon steel appeared to be caused by defects present in the coating. 7 refs., 1 fig., 2 tabs.

• Research Organization: Argonne National Lab., IL (USA)
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 7127074
• Report Number(s): CONF-860961-6; ON: DE87004659
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010404* -- Coal
Lignite
& Peat-- Gasification
36 MATERIALS SCIENCE
360105 -- Metals & Alloys-- Corrosion & Erosion
ALLOYS
CARBON STEELS
CHEMICAL COMPOSITION
CHROMIUM ALLOYS
CHROMIUM STEELS
CHROMIUM-MOLYBDENUM STEELS
COAL GASIFICATION PLANTS
COATINGS
CORROSION RESISTANCE
DATA
DEPOSITION
DIFFUSION COATING
DIMENSIONS
EXPERIMENTAL DATA
INDUSTRIAL PLANTS
INFORMATION
IRON ALLOYS
IRON BASE ALLOYS
MATERIALS TESTING
NUMERICAL DATA
PROTECTIVE COATINGS
STEELS
SURFACE COATING
TESTING
THICKNESS