ASTM Piping materials in Hydrogen Cyanide environment 1

[vic56]

We have to select piping and valve materials suitable for a hydrogen gas stream containing 95 mol% H2, 2%N2, 3%CH4, 0.25%H2O, 0.1%CH3CN, 0.01%HCN, 50ppm NH3. Design conditions are 33 barg at 100°C. We design units for hydrogen gas streams on a regular basis using carbon steel piping and valves. However the presence of the HCN combined with the water concerns us and raises the question should we be using stainless steel ? Does anyone have any input please ?

 

[metengr]

Based on your stated gas stream and constituents, I would not recommend carbon steel valves or piping because of the extreme solubility of HCN with water to form hydrocyanic acid. This information is based on an independent review of corrosion data from two valve suppliers.

I would probably specify 316 ss.