Compatibility of Molten Sulphur and 304L SS 1

[bobnecciai]

Does anyone have any experoence using 304L SS for molten sulphur storage? We have a tank designed and installed three years ago that has experienced extreme chloride cracking, inside and out.

Tank is not blanketed, no sweep, temp is 270 degrees.

 

[Metalguy]

If you have Cl in/on that tank, it's no wonder it failed.

Something with 6%+ Mo like 254SMO *might* work.

 

[bobnecciai]

That is my question, I suppose. I am not a metallurgist, I am trying to figure out where the Chlorides would have come from in a molten sulfur environment.

Any published documents I have seen state that 304L is either "good" or "resistant" when exposed to molten sulfur.

Thanks for the response.

bobnecciai

 

[Metalguy]

Most likely as a "minor" contaminant. It would only take a few ppm Cl at that temp. to cause SCC. Your SCC was probably TGSCC (trans-granular) rather than IGSCC, right?

 

[bobnecciai]

The full results of the metallurgy testing will come in tomorrow. I am looking at alternative materials to the 304L since I do not think we can expect completely uncontaminated sulfur from a crude refinery, and I can not find any history anywhere of a stainless 304L tank in similar service to compare to.

Thanks

 

[hacksaw]

typically carbon steel is the material of choice.surprised that external cracking is reported; most sulfur tanks are insulated.

suspect that you are operating in a coastal environment and pulling in salt laden air during sulfur transfers.

if you are using level bubblers then you tend to purge out the ambient air. If not then you need to install gas blanketing. If you use air then you'll also need provision for fire extinguishing (steam is commonly used).

 

[grampi1]

Standard upgrade in the liquid/gas interface of molten sulfur storage would be Alloy 20.

If at any time the sulfur came from a pit as is common in refinery Sulfur Recovery Units, groundwater can seep in via cracks in the concrete pit wall. CS steam heating coils are another source after they perforate from corrosion.

Running a molten sulfur tank with no inert gas blanketing is dangerous.