Electrostatic in Petroleum/Petrol Tank Lorries

Any vehicle going down the road can build up electrostatic energy. The carbon in the tires is a poor conductor, so to be safe the vehicle should be grounded when a fuel transfer is made -- whether it is from the tanker to the storage tank or from the storage tank to your car. (Usually just touching the body of your car when you open the fuel door is enough to ground it).

Airplanes flying through the air also build up static electricity and likewise need to be electrically grounded when they land.

.........which is why the velocity of a non-conductive low-flashpoint fluid is usually kept below 1ms^-1 in pipes.

PWSlack:

Coriosity, why and how they do that?

Why? To reduce the risk of static build-up.

How? By calculating the pipe size correctly during process design.

Who are "they"?

"They" are those people using it.

~Anon~

Your explanation for me is clear. I appreciate that.

Could you expand more on that if the fuel builds up static charge inside it or inside the tank materials?

What you mean by danger is when we connect the flexible hose to the system, the static sparks will jump from the flexible hose to the flange of the system? By this activity, fire will happen when there is a flow of fuel transferred from the hose to the system because the hose now has a reversed electric charge with the system.

Is my understanding same as yours?

Fuel cannot build a charge on it's own, it requires an outside source or movement. If you stir up a tank, that movement could build up a charge just as if you stir a box of polystyrene balls with a plastic rod. The electric potential can also change in the ground under your feet as thunder storms or other weather passes overhead, also wind blown dust or other materials can change the charge. In this second case, the tank would quickly change with the potential of the ground but the fuel could take several hours to get to the same potential.

Flexible fuel hoses are required to have a conductive wire to ensure conductive bonding between the lorry and the ground fuel system. You should first equalize the potential between the lorry and the ground system with an earthing wire. If this is not done, earthing will occur when the hose's conductive wire makes the connection. If there are vapours present when the cap is removed from hose or fittings that spark can ignite a fire.

I am not sure about the reversed electric charge as you explain it. Charge can build up on the lorry or be present in the grounded system. It doesn't matter what direction the charge is going, only that it is present. Usually the charge is in the lorry because of the motion of sloshing fuel and the truck. Aircraft can develop a very large charge during a long flight and must be grounded (often through the first person to touch ground and the aircraft) prior to refueling.

There could also be a development of charge as the fuel is offloaded (or loaded) into the lorry. This isn't usually a problem because the charge can also relax through the conductive wire in the hose. Many companies require a waiting time between receiving large batches of fuel through pipelines to allow the charge to relax and any water to settle and be drained off.

Thank you for your useful expansion,

So the charge built up is because of movement of fuel inside the tank. Now, the tank and the fuel are charged. Due to different potentials of the tank lorry and the system that make a spark when we connect the hose to the system. To eliminate this, the tank lorry and the system must be equipotential. Is that correct?

I am being more curious to know why the spark is created when I drop my steel spanner on the floor (or steel floor). To eliminate the spark in the flammable zone, I will need to bond my spanner to the system (here is the steel floor) or I will use the different kind of metal. Are they correct?

Yes, making the system and lorry the same potential will reduce the chance of a charge as the fuel moves into the system. This does not eliminate all chance of spark though. The fuel is not an efficient conductor so portions of it will remain at a different potential. The instant the lorry becomes the same potential as the system, the fuel will still be at it's original potential, this could lead to sparks from the fuel to the inside of the lorry or if your system pipes are empty a spark anywhere along the piping. This has occurred in filtration vessels and caused flashes within the filters.

Dropping a spanner involves the energy of the falling mass, bonding it will not eliminate the spark, for that you need special materials that don't spark. This is not usually possible because the special tools are not as strong as steel and they will bend before loosening the fittings in a fuel system. They are made from Copper Beryllium and Brass Heat treated for maximum toughness but I think Beryllium is slightly radioactive (or has another hazard I can't recall right now).