...We are also assuming we understand the reason for the rod at the tank. We don't know that ... there might be another reason. For example, few people realize that fuel - be it oil, gasoline, propane, whatever - can generate it's own static when flowing. For all we know, that rod plays a role only when the tanker is filling the tank.
Again, GROUNDING will do little to nothing to equalize the charge separation created between two conductive bodies by the flow of liquids. BONDING of the liquid transfer equipment on the other hand, will help reduce the potential of static discharge.
The NPFA 77 establishs a value of 10 ohms for this purpose. However, it has been well established by both the NFPA and IEEE that bonding resistance in the area of 1,000,000 ohms is sufficient to reduce static charges on equipment.
On a side note, I am aware that my comments on grounding and bonding topics are sometimes radical and fly in the face of nearly 100 years of code practices. It has been sometime since I have been active on this forum, but I do visit the forum frequently and read most of the posts. While many of the members here know me from other forums and have come to know where I stand on cetain aspects of Article 250 and the NFPA 780, others may not and assume my comments are unfounded, unsupported, or uneducated. I apologize it it appears that I am being difficult rather than helpful. That is not my intent.
If this discussion was on the topic of say, communication towers, we may have some issues of grounding to cover. But, when it comes to the topic of "ground rods for gas piping", there really is no purpoe grounding can serve.