API MPMS CHAPTER 7.2:2018

This chapter describes the methods, equipment, and procedures for manually determining the temperature of liquid petroleum and petroleum products by use of a portable electronic thermometer (PET).
This chapter discusses temperature measurement requirements in general for custody transfer, inventory control, and marine measurements. The actual method and equipment selected for temperature determination are left to the agreement of the parties involved.
The manual method covers: —nonpressurized tanks and nonpressurized marine vessels;
—gas-blanketed tanks and gas-blanketed marine vessels.
It does not cover hydrocarbons under pressures in excess of 21 kPa (3 psi gauge) or cryogenic temperature measurement, unless the tank is equipped with a thermowell.