I have a process vacuum system (20 torr operating pressure) that needs lined pipe for corrosion resistance, but I’m not sure if static buildup in the gas phase is credible or not. The gas that is being pumped is various organic solvents (e.g. acetone, hexane).
I am not finding discussion regarding static charge buildup in lined pipes with the fluid being transported is solvent gas as opposed to liquid. Is the gas phase static buildup negligible?
Edit: The piping is PTFE lined carbon steel, the metal portion of the piping will be bonded and grounded.
No. In a non-lined metallic pipe, static can build up in a flowing gas. That’s why they are grounded and should have electrical continuity across joints. In my mind, the liner and hexane make it worse. They tend to be non-conductive.
What I’ve found so far -
9th ed of Perry’s, pg 23-17:
Pure, standard-state gases do not accumulate static charges, and seldom, if ever, do they contribute to electrostatic scenarios.
FM Global DS 5-8:
NFPA 77, 2024 edition:
Section A.10.3
This is what I intuitively think - and for gasses I would think the friction with the wall causes charge buildup just like in liquids but so far I’m finding statements to the contrary.
The flammability concern is the main point of focus, and I believe other conditions mitigate that (connected equipment is nitrogen purged before adding solvent so the vacuum is pulled on an N2/solvent atmosphere).
Have you consulted NFPA 77, Recommended Practice on Static Electricity? Since retiring I no longer have a copy. IIRC, they do say as gases or liquids flow through pipes and hoses, static electricity can be generated.
NFPA 77 has the most discussion of this topic so far and most of it seems to agree with the other information. For my situation, I am reasonably confident the stream will be clean (i.e. free of particulate) and the information I’m reading is leading me to think my situation wouldn’t require a wetted path grounding elements. It’s certainly not where I thought I’d end up after reading up on the topic.
Feedback from the site has been that the existing system and a previous pilot plant that was at a larger scale operated with lined pipe like this with only the external metal shell being grounded for many years.
The consensus from the senior engineers at my company is that for these systems, they haven’t seen or designed the piping to have wetted path grounding.
The piping vendor SME had recommended grounding rings but that was in the context of expected 2 phase flow. The SME deferred to the operating experience to guide this new design.
