In the last couple of days I saw a youtube video where a farmer was talking about an old trick of having a prominent “gas tank” near the road into which you would put all of your oil slops (used motor oil, diesel with water in it, etc) knowing full well that would be the tank that thieves would steal from.
Excellent plan! For a while at least. I would think the thieves would get wise to that before too long. Then what happens?
You’re right, but it looks like maybe they just reprocess the “trans-mix”.
The multi-product pipeline scheduling system - ScienceDirect.
The mixture of different grades of refined products transported in a pipeline is called “transmix”. Transmix is separated out and stored in a different tank for re-processing. Transmix will have different values depending on what two types of products have been mixed. In many cases the octane value is used to determine the value and level of re-processing is needed.
You normally don’t ship crude oil and refined products into the same pipeline. There are different pipelines for each, as the fluidity, specific gravity and transmix problems would not work.
The majority of shippers on a refined products pipeline, like Colonial, are wholesalers of such products. They are typically not the retailers that operate the branded gas stations in your local market. The retailers buy the different grades of gasoline from the distribution points along the pipeline. So yes, the Shell station and the Exxon station across the street, are all selling the same gasoline from the same wholesale refinery that loaded the gas in the pipeline along the Gulf coast. They will put in their own additives for their branding purposes. But for all practical purposes it’s the same gas.
This account on how pipelines work in the US, says that Colonial publishes specifications for 100 different grades of gasoline their pipelines can carry.
I used to work for a fuel delivery company, and would drive a tanker to the terminal to fill up. I would connect the piping to the truck, and “place my order” on a simple touch screen. All the Diesel came out of the same hose, and it was all ultra-low sulfur blend.
There was an inspection window in the terminal’s pipe, at eye level, and you could watch the clear Diesel rushing through the 6" pipe at great speed. If you had ordered dyed, every 50 or 100 gallons or so, you’d hear a whooshing noise and could see the clear Diesel turn dark, dark red when it got a shot of the dye added from the injector right above the window. So yes, it’s at the very last moment of wholesale, as it’s going in to the delivery truck.
How do you measure the density of a moving fluid? If you have a tethered float, it will be moved by the flow.
Then they set your gas tank trap on fire.
Today I learn that pipeline operators are “common carriers”. Previously, the only time I had ever seen the term was in Airline / Courier documentation asserting “we are not a Common Carrier”. I’d often wondered if such a thing even existed.
Common carriers have a high degree of liability for loss & damage to goods, at common law. Which is why carriers tend to seek to make it clear they are not common carriers.
Ironically, IME at least in Australia carriers that would otherwise fit the definition of “common carrier” tend to be quasi governmental (eg railways) and tend to have specific statutes exempting them from any sort of liability whatsoever.
You can use a coriolis meter:
Thanks, Machine_Elf.
This is in the 80’s in training so we did it all manually. There was a tap on the incoming line as it got to the spider (the distribution rack where you would shunt fuel to/from any of the tanks in the tank farm). You would pull about a cup of fuel or so into a beaker and drop the hydrometer in and measure the density manually. From there it was look up the temperatures and adjust for those, then do it again until the density curve was right for the next batch of fuel coming through the line. Like everything military, there was a specific procedure for when and how often to draw samples during the flow.
Not surprised to see, as noted above, that there is a flow meter to take the readings for you automatically. Honestly, I figured by this time they likely had some sort of laser type rig to continuously measure temp and density so the computer could through the valves automatically.
For what’s it’s worth the Colonial pipeline system consists of two pipeline , one is generally dedicated to distillates ( diesel, heating oil jet fuel) the other is for gasoline products so they are not mixing very dissimilar stuff in a single pipeline.
I really wanted to answer this question—I used to design flowmeters, including Coriolis meters. But I missed my chance and you nailed it. 
You can theoretically measure density with an ultrasonic flow meter and a few other ways, but Coriolis meters measure density directly, and that’s how it’s typically done in the petrochemical industry.
I actually had a coriolis meter in the 80’s.