In July 2016, The American Petroleum Institute (API) published Chapter 18.2 Custody Transfer of Crude Oil from Lease Tanks Using Alternative Measurement Methods of the API Manual of Petroleum Measurement Standards. This chapter defines the minimum equipment and methods used to determine the quantity and quality of crude oil being loaded from a lease tank to a truck trailer without requiring direct access to a lease tank gauge hatch.
The main driver behind chapter 18.2 is safety. It is in place to offer an alternative to truck drivers, often by themselves, climbing to tops of tanks and taking level measurements. Chapter 18.2 section 4 reads:
“Opening thief hatches of storage tanks can lead to the rapid release of high concentrations of hydrocarbon gases and vapors. Be aware that those may result in very low oxygen levels and toxic and flammable conditions around and over the hatch. This standard was developed to encourage uniform, technically defensible measurement and testing practices for crude oil gathered from lease tanks when access to the tank’s thief hatch may be restricted.”
Level sensors with an accuracy of +/- 3mm (1/8”) meet the accuracy requirements of Chapter 18.2 can be used on Automatic Tank Gauging Systems measuring in crude oil lease tanks. Chapter 18.2 also lists requirements for the ruggedness of the sensors, the speed of response, and the security of the adjustment configuration in the sensor. All of these requirements are met by VEGAPULS 60 and VEGAFLEX 80 series sensors.
For quite some time, VEGAFLEX 81 and VEGAPULS 62 devices with Modbus output have been used to report level information from crude oil lease tanks to SCADA systems. This information was used by crude oil trucking companies to schedule the transfer of crude oil from the lease tanks to truck trailers. Now these same sensors can be used to record the volume of crude oil transferred.