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Corrosion of pipework in sulfuric atmosphere

Corrosion of pipework in sulfuric atmosphere

Corrosion of pipework in sulfuric atmosphere

(OP)
Good day all,

I have installed fuel gas piping in a plant barely 6 months ago and last week, a piece of flexible hose was found to have failed.

The plant operates some crucibles into which the workers regularly dose sulfur powder. The temperature of the crucibles is between 950 and 1000 deg C. I suspect that the sulfur had been oxidized at those high temperatures, turning into sulfur dioxide, which again reacted with moisture in the air to turn into acid. Relative humidity is at about 85% here. The piping had been installed about 4 meters away from the crucibles. I surmise that it had been the acidic fumes that had caused external corrosion on the pipework.

The thing that puzzles me is that a piece of corrugated flexible hose made of Stainless Steel grade 304 had failed completely at the weld seam (photo attached). The fuel gas piping operates at 4kPa (0.6 psi) so it could not have been stress cracking can it?

Furthermore, I have proposed to the plant to replace the corroded pipes with either Alloy 20 or the original SA-106 B, but coated with waterproof, high-solid epoxy. Has anyone had experience with this kind of environment? If so, can you share what had been done to address the matter of corrosion?

LiewNH

RE: Corrosion of pipework in sulfuric atmosphere

A flex hose at 950-F ??
seems like the hose would fail based on temperature.
Corrosion of the hose would require less than 300-F representing
H2SO4 dew point.

RE: Corrosion of pipework in sulfuric atmosphere

Good grief, you have people working in an atmosphere so acidic it can destroy stainless steel ?

Don't worry about your flex hose, shut the plant down until it can be safely re-designed, and worry about all the litigation that will surely follow the legal route from your local hospital.    

RE: Corrosion of pipework in sulfuric atmosphere

I couldn't see much in the photo, but because you say cracking in in the weld zones: moisture + S + weld zone (sensitized) > suggests the possibility of polythionoic SCC. That SCC would be intergranular vs trans for chloide SCC. 321 and 347 SS would be resistant and alloy 20 ( as I remember it is stabilized).

RE: Corrosion of pipework in sulfuric atmosphere

(OP)
Great, I'll be speaking to some vendors about the materials and to obtain some definitive texts on the resistance to polythionic SCC. In your experience, can any kind of coating reliably achieve the same effect? I am going for a design life of 10 years, with thickness inspections by UT every year and eddy current inspection every 2 years.
C2it, for your info, the plant had been shut down following medical complications of some workers and extensive corrosion to the steel structure and piping. It was badly thought out to operate it in that configuration to begin with, and another team is developing an entirely enclosed sulfur dosing system. It will only be allowed to operate again after the integrity and OSH improvement program had been fully implemented.

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