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

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From the above example, the readings obtained during the 2nd and 3rd gauging are
acceptable while 6m 400mm is the tank dip.
2.3.6.1.4 The dip readings are noted in the gauge tickets. This procedure is followed to
determine the accurate level of petroleum or petroleum product in a tank before and after
cargo off-take from the tank while the procedure outlined under computation and
documentation is followed to determine actual quantities.
2.3.6.2 Ullage method
For the ullage method, the gauge reading shall be defined as the measure of the linear
distance along a vertical path from the surface of the liquid being gauged to the tank
referenced gauge height. When the ullage method is used, the tank reference gauge height
for both opening and closing conditions shall be periodically verified to ensure it has not
changed.

2.4 Manual Sampling of Tank Contents
2.4.1 Purpose
The purpose of sampling is to obtain a true representative composite sample of the
contents of a tank to be used in determining the quality of the petroleum and petroleum
product in the storage. The device used for manual tank sampling is called a thief can.

2.4.2 Specification of Manual Sampling Apparatus
2.4.2.1 Sample “thief-can” shall be made of a corrosion- resistant material.
2.4.2.2 The can should have a minimum length of 12” (304.8mm) with inside and outside
diameter of 1.75” (44.45mm) minimum and 3.5” (88.9mm) maximum.
2.4.2.4 The can shall neither be of the bomb or core thief-trap type with outside graduations
of at least 0.125” (3.175mm)
2.4.2.4 It shall be equipped with a wind shield to be used when taking the temperature of
the sample.
2.4.2.5 It shall have attached, a marked cord for samplings at predetermined depths of the
tank and a secured hook for hanging the can.
2.4.2.6 It shall be equipped with a mechanical shutter to permit filling and retention of
sample at any desired level of the tank.
2.4.3 Guideline for Manual Tank Sampling
2.4.3.1 The number of samples to be withdrawn from petroleum or petroleum products in
tank storage shall depend on the depth of the petroleum or petroleum product in storage
and shall be in accordance with the ASTM D4057. The general guiding principle for sampling
vertical cylindrical tanks is as follows:
2.4.3.2 Only one sample is withdrawn from a tank of petroleum or petroleum product’s level
of 10ft (3.048m) and below. The single sample is taken from the middle of the oil column.