API MPMS Chapter 2 · API 2550
If blank, defaults to liquid temperature.
Volume displaced by floating roof (from tank table). Enter 0 for fixed roof.
Understand tank gauging methods, strapping procedures, CTL/CPL corrections, and custody transfer measurement practices
Tank gauging is the measurement of liquid level in storage tanks to determine the quantity of product. API MPMS Chapter 2 covers manual gauging methods including innage (measuring from the bottom) and outage/ullage (measuring from the top). The gauge reading is converted to volume using a strapping table (capacity table) specific to the tank dimensions.
A strapping table (or tank capacity table) correlates liquid level heights to volumes for a specific tank. It is developed by physically measuring the tank circumference at multiple heights (strapping) or by calculating from as-built dimensions. API 2550 covers the procedure for calibrating upright cylindrical tanks.
CTL (Correction for Temperature of Liquid) adjusts the observed volume to a standard temperature (typically 60 deg F / 15 deg C) to account for thermal expansion. CPL (Correction for Pressure of Liquid) adjusts for compressibility effects at elevated pressures. These corrections are defined in API MPMS Chapter 11 (Table 6A/6B for CTL, Table 5A/5B for CPL).
Innage is the measurement of liquid depth from the tank bottom (datum plate) to the liquid surface. Outage (or ullage) is the measurement of empty space from a reference point at the top of the tank to the liquid surface. Innage = Reference Height - Outage. Most custody transfer measurements use innage gauging.