Cr-S Phase Diagram

[SMF1964]

Does anyone have access to one? I have a chromized steel that is in a boiler (coal combustion, low NOx firing). Un-chromized steel will react with the sulfur and form iron sulfur compounds that melt at lower temperatures. The same with nickel and sulfur. Does the same thing happen with chromium and sulfur?

 

[metengr]

SMF1964;
According to the information that I have seen, chromium that is either diffused into or deposited on waterwall tubing as a spray coating in excess of 30% chromium content should not react with flue gas that contains H2S (500-600 ppm) and 8% CO (reducing atmosphere). However, there have been mixed results in field testing.

I would suggest you review a newsletter from EPRI (dated August 1, 2002) that is available over the internet. One of the articles is titled "Long-Term Test Results for Protective Coatings on the Furance Walls of a Supercritical Boiler". This should help you.

 

[SMF1964]

metengr:

Thanks. The tube I have is a diffusion/pack chromized process. Where I have slag on the tube's surface, in some places I have perforation of the chromizing and a heavy oxide on the surface that is rich in chromium (no surprise, since the surface is up around 90% Cr). At the interface between this oxide/slag and the chromium, there is a sulfur-rich band on the X-ray map that is lower in iron content than usually seen with unprotected tubes and the question was asked if this is indication of a sulfidation reaction with the chromium.