© 2019 Department of Petroleum Resources. All rights reserved Department of Petroleum Resources (DPR) PROCEDURE GUIDE

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purpose of drawing up a calibration chart for the tank to show quantity of petroleum and
petroleum products at any given depth.
2.5.3 Frequency of Calibration
2.5.3.1 All new tanks shall be calibrated before commissioned to service and mandatorily
after every five years of its operational life.
2.5.3.2 A tank shall also be automatically due for recalibration, if the circumferential reading
shows a difference of 0.015% and above, at a reference point, over the reading of the
last calibration of the tank.
2.5.3.3 A tank shall be recalibrated whenever the deadwood has changed in configuration
or arrangement.
2.5.3.4 A tank shall be recalibrated on relocation of the tank to another position.
2.5.3.5 A tank shall be recalibrated after any major repair or maintenance of the tank
2.5.4 Applicable Standard
Calibration method shall be as outlined in latest American Petroleum Institute Manual of
Petroleum Measurement Standard (API MPMS) Chapters 2.2A, 2.2B, 2.2D, 2.2F, API Standard
2555 (Method of Calibration by Liquid Calibration) as well as ISO 7507-5.
2.5.5 General Practices
2.5.5.1 Before a tank is calibrated, it shall be ascertained that the tank has been filled at least
once with a liquid of a density equal to or greater than the normal service liquid.
2.5.5.2 All tanks in service shall be cleaned out and checked for bottom alignment every five
years.
2.5.5.3 Any maintenance or repair job that involves replacement of plate sections or
alteration of the “Deadwood” of the tank shall automatically invalidate the existing
tank capacity tables and a new calibration of the tank shall be carried out before re-
commissioning.
2.5.5.4 Any modification to the tank changes its capacity by more than 0.015% of the original
shall invalidate the existing tank table.
2.5.5.5 There shall be no movement of petroleum or petroleum products into or out of the
tank during calibration.
2.5.5.6 Before a tank shall be deemed ready for calibration, it shall be thoroughly cleaned
and degassed.

2.5.6 Manual Tank Strapping
2.5.6.1 Calibration Equipment
These shall be as stated in the reference standards and shall comply with appropriate
specifications. The essential equipment shall be the same with those for taking
measurements of tank shells above ground and shall always be maintained in good
condition. Both the tape for height measurement and that for circumference measurement
shall themselves have been calibrated in accordance with the Part III Section 2.4 or possess
a current certificate of recent calibration at 68ᵒF (20ᵒC) in accordance with a recognized
National Bureau of Standard. Also, the equipment for determining temperature and gravity
shall be as follows: -