Static Electricity Basics
Where does the static electricity come from?
Static electricity is generated when a low conductivity fuel like petrol flows in a non-conductive pipe. Negative charges accumulate on the pipe wall and positive charges are carried away with the fuel. This charge separation is a similar to what happens when two non-conductive materials are rubbed against each other. Try rubbing a balloon against your skin or hair to experience electrostatic charging.
Since the non-conductive pipe cannot dissipate or lead away the charges they accumulate on the pipe wall. More charges are generated with low conductivity fuels, high flow velocities, turbulence cause by elbows, flame arrestors, filters etc. and by any impurities in the fuel. Tests on non-conductive pipes have shown that charges of 90,000 V can occur.
Click to play the animation of charge generation – Principle 1
The charges are not evenly distributed along the pipe wall, but dependent on the fuel flow and turbulence in the pipe. Discharges can occur between the pipe wall and a grounded object (metal flange or similar), between the pipe wall and the fuel or between differently charged areas on the pipe wall.
If there is flammable atmosphere in the pipe, it can be ignited by the discharge. This is known to have happened near the end of fill pipes at the filling point
The charges in the pipe also create an electrostatic field around the pipe. Ungrounded conductive objects in that field will get an induced electrostatic potential. This means that flanges, jubilee clips and other objects outside the pipe can have a dangerous potential unless properly bonded and grounded. Discharges can occur from these objects to any conductive object of different potential: grounded objects, tools or people.
Click to play the animation of electrostatic induction – Principle 2
Conductive piping dissipates static charges
In a conductive system, less charges are created by fuel flow and the charges that are created immediately dissipates to earth.
Click to play the animation of dissipation in a conductive pipe