Black oxide in SS steam pipe
Black oxide in SS steam pipe
(OP)
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During an upgrade at our pharmaceutical plant, we cut open some Clean Steam piping to weld in a tee for future expansion. I assumed the internals would be polished stainless like the Water for Injection (WFI) systems. No, it has a matte black oxide layer that is not tightly adhered. I can easily pick some up by wiping a finger across it.
It's 316L stainless tubing. As best I can figure, it's a magnetite oxide layer. Is this common? What is the mechanism? I'm sure it was polished at one point. The Clean Steam system is not required to be passivated like the WFI systems are, but I'm not sure what to think about this.
Thanks
Ben

During an upgrade at our pharmaceutical plant, we cut open some Clean Steam piping to weld in a tee for future expansion. I assumed the internals would be polished stainless like the Water for Injection (WFI) systems. No, it has a matte black oxide layer that is not tightly adhered. I can easily pick some up by wiping a finger across it.
It's 316L stainless tubing. As best I can figure, it's a magnetite oxide layer. Is this common? What is the mechanism? I'm sure it was polished at one point. The Clean Steam system is not required to be passivated like the WFI systems are, but I'm not sure what to think about this.
Thanks
Ben






RE: Black oxide in SS steam pipe
Depending on steam temp and quality that is highly possible.
Or it is Fe transported from someplace else that settled and oxidized here.
Either way I don't see it hurting anything.
If you need clean clean steam then put a filter at point of use.
By the way, this is similar to rouge in WFI systems, it doesn't actually hurt anything.
You are better off leaving it alone.
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P.E. Metallurgy, Plymouth Tube
RE: Black oxide in SS steam pipe
RE: Black oxide in SS steam pipe
But I believe that most of it is from transport as well.
Given that at least some of it can be wiped off that tends to favor the transported Fe theory.
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P.E. Metallurgy, Plymouth Tube
RE: Black oxide in SS steam pipe
For transport, would that mean that there is some non-stainless component upstream somewhere, or is this an oxide that stainless forms under particular conditions (such as rouging)?
RE: Black oxide in SS steam pipe
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Black oxide in SS steam pipe
RE: Black oxide in SS steam pipe