>The usage is natural gas, 50 PDI. max., the gas has a water
>vapor near freezing, and the water in the well is salty.

Sounds to me like the gas movement in the pipe is producing high voltages 
that then produce ESD type arcs.

The description on your sensor mounting, it sounds like there is no metallic 
housing that could be grounded to trap ESD events due to the gas motion, or 
weather conditions. I would be tempted to wrap the sensor in an aluminium 
foil shroud, and use shielded cable to a suitable grounding point. 

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