National Standard of the People’s Republic of China
Petroleum and Liquid Petroleum ProductsMeasurement
of Liquid Level in TankManual Method
Issued on: Dec. 10, 1992 Implemented as of: Nov.01, 1993
Jointly Issued by: State Technical Supervision Bureau
National Standard of the People’s Republic of China
Petroleum and Liquid Petroleum ProductsMeasurement
of Liquid Level in TankManual Method
1. Subject Content and Applicable Scope
The standard has specified the method to use an oil dip rod to measure the level of petroleum and liquid
petroleum products in the vessel and the height of free water at the bottom of the vessel.
2. Reference Standard
GB 13236 Specification for oil dip rod of petroleum and steel tape
3.1 Scale measure: the process to use an oil dip rod to measure the level height (referred to as oil height) of
oil product in the vessel.
3.2 Scale measure hatch (gauge hatch): to cut an opening on top of vessel for scale measure, temperature
measurement and sampling.
3.3 Reference point: a fixed point or marking on scale measure hatch, i.e. to start the measuring from this
3.4 Scale measure plate (reference plate): a piece of horizontal metal plate welded at the bottom of the
vessel (or on the wall of the vessel), located just below the reference point, is used as the contact surface of
3.5 Scale measure point (reference point): at the bottom of vessel or on scale measure plate, the point that
the dipstick weight contacts during measuring.
3.6 Reference height: the distance from the reference point to scale measure point.
3.7 Oil height: the distance from the level of oil product to scale measure point.
3.8 Water height: the distance from the oil water boundary to scale measure point.
3.9 Empty distance: the distance from the reference point to the level of oil product in the vessel.
4. Measuring devices and materials
4.1 Oil dip rod: shall be in compliance with the technical requirements of GB 13236.
4.2 Scale measure for water: is cylindrical or square, made of brass. The complete length of scale is 300 mm, the minimum division is 1 mm and the mass is approximately 0.8 kg.
4.3 Metering rod: it is made of painted hard wood or other corrosion resistant materials and is used for measuring the liquid depth of small type oil drum, tank truck and railway tanker. The height of vessel to be measured is regarded as a standard for the length of rod (the length of tank truck is about 3 m), the width is approximately 25 mm and the thickness is approximately 20 mm. The bottom end of wooden rod shall be attached with a metal head or metal cap to avoid damage. There are graduations on one side of rod with the minimum division of 1 mm. The zero is at the bottom or top of the rod.
4.4 Empty distance bar: it is made of painted hard wood or other corrosion resistant materials and used for measuring oil tank truck. The length is about 1 m, width about 20-25 mm and thickness about 10-20 mm. There is a common zero at a place 300 mm to the bottom end, and the graduations begin from here to the top and bottom in mm. There is a brass angle on the bar. When the bar is vertically placed and the angle lies on the tank wall of oil tank truck, the zero graduation coincides with the inner edge of tank proper. 4.5 Oil indication paste: it is a kind of paste substance. While measuring the level height of oil product in the vessel, apply it on the oil dip rod and it can clearly indicate the level position of oil product on the oil dip rod.
4.6 Water indication paste: it is a kind of paste substance, which will change color when it meets water and will remain unchanged when it meets oil. While measuring the water height at the bottom of vessel, apply it on the scale measure for water and the portion in water changes color, thus clearly indicating the position of water level on the scale measure for water.
4.7 Water indication paper: it is a paper strip that will change color when it meets water and remain unchanged when it meets oil. While measuring the water height at the bottom of vessel, fix it on the scale measure for water and the portion in water changes color, thus clearly indicating the position of water level on the scale measure for water.
5.1 General precautions
184.108.40.206 On the vessel, the scale measure hatch or other openings for measuring oil height or empty distance shall be provided with a proper marking for reference, and the location of the oil dip rod that shall be kept during operation of scale measure is indicated. The markings for reference shall be selected and located in a place where the dipstick weight can contact the scale measure plate or the bottom of vessel without any blockings.
The reference point shall be provided on the place where the location of scale measure is indicated, and the height from the scale measure to the reference point shall be clearly marked near the scale measure hatch on top of vessel. The height shall be detected when the vessel is being calibrated, and checked on a regular basis.
If the scale measure may probably have deviation due to the bending of vessel top plate, the reference point shall not be marked on the scale measure hatch, but marked on the rigid attachment that firmly fixed on the straight wall of vessel.
220.127.116.11 If there will be a scale measure provided in the vessel, it is better to locate it on the place where the influence caused by deformation of vessel bottom is minimized or the influence caused by expansion or shrinkage of vessel wall is minimized.
18.104.22.168 When a number of gauge hatches are provided on the vessel, each gauge hatch shall have a number or a clear marking. The gauge hatch for calculating the volume of vessel shall be used to measure oil height or empty distance.
22.214.171.124 The scale measure of the vessel must directly lead to the liquid within the vessel. If gauge tube is used on pressure constant vessel, there must be a slotted hole that improves the accuracy of measurement. 5.1.2 Measuring device
126.96.36.199 The measuring devices must be in compliance with the requirements and checked periodically. 188.8.131.52 The oil dip rod must have no twist, rusty spots etc. All markings on the graduation portion must be visible and readable.
184.108.40.206 The metal measuring device used in an inflammable atmosphere shall be made of a metal which can not produce sparks when collided.
5.2 Safety precautions
5.2.1 All safety regulations, including the regulations for entering the hazardous area, shall be closely observed.
5.2.2 The staircases, ladder on tank, platform and handrails shall maintain the safety condition on the structure.
5.2.3 The devices used by the measuring operators shall be put into the bag so as to save the hands to climb the ladder on tank.
5.2.4 The head lamp or flashlight shall be of explosion-proof.
5.2.5 When the scale measuring is performed on the vessel that contains inflammable liquefied hydrocarbon, if the storage temperature of liquefied hydrocarbon is higher than its flash point temperature, the following points shall be observed to avoid the risk of occurrence of static electricity. 220.127.116.11 In case the volatile product is filled into the fixed top oil tank, road or railway tanker, oil tanker or barge, due to increase of inflammable vapor in the upper space of the vessel, one of the following conditions must be satisfied when a metal oil dip rod is used to measure it:
a. Perform the measurement starting from the gauge tube that is properly installed; b. For the fixed top oil tank, the floating cover which is properly grounded shall be installed; c. The oil product shall contain adequate static electricity dispersion additives to ensure that the
conductivity of oil product is more than 50 pS/m and no mist and fine particles will form in the upper space of the vessel.
18.104.22.168 In case there is no gauge tube, floating cover or static electricity dispersion additives, the volatile
product can not be measured by the metal oil dip rod within 5 minutes after the pump stops. If it is possible
that the product will be polluted by water, the time has to be extended to 30 minutes at least.
22.214.171.124 When the metal oil dip rod is used to perform the measurement, it always keep contacting with the metal of scale measure hatch during the complete lowering and lifting operations.
126.96.36.199 Do not wear shoes that can produce sparks in the working area. It is not recommended to wear rubber shoes in the dry area.
188.8.131.52 Clothes shall be of anti-static electricity.
184.108.40.206 Scale measure shall not be performed during thunder, hail and rainstorm period. 220.127.116.11 In order to make the static electricity of body to be grounded, the measuring operator shall contact one component of vessel structure prior to the operation of scale measure.
5.2.6 Carefully open the cover of measuring opening at the location of windward side (especially on air-tight vessel, there is pressure in the vessel), first loosen the clamp holding the cover, but keep it in its
original position until the pressure is relieved completely.
5.2.7 The measuring operators must receive a strict training about the safety on inflammable gases, including operation and limits of fire extinguishers.
5.2.8 A tool kit can be installed near the gauge hatch on the top of vessel that contains non-volatile product, and the kit is to hold the measuring tools after use.
5.2.9 The substances or waste cotton fabrics immersed with oil shall not be put randomly, but collected in a proper container.
5.2.10 If any non-volatile oil product is splashed on the top of vessel, it shall be wiped out. 5.3 Special safety precautions
5.3.1 Lead gasoline
The complete regulations for measuring the vessel that contains lead gasoline shall be strictly observed.
5.3.2 Floating roof oil tank
When the measuring operator goes down to the floating roof upon the special requirement and as the toxic
and inflammable vapors may accumulated above the floating roof, he shall be monitored by another
operator standing on the top of platform at all times. In case of following conditions, the measuring
operator shall wear a safety belt, or the measuring operator or monitoring person shall wear the respirators
before the measuring operator goes down to the floating roof:
a. In case the product in the oil tank contains volatile mercaptan;
b. In case the floating roof stops on the support or is partially immersed;
c. In case the floating roof is not round or the seal ring of floating roof is damaged;
d. In other cases when there exists the vapor in a dangerous concentration.
5.3.3 When operators contact the lower-concentration vapor of the toxic oil product repeatedly or for
a long time, the risk will go up, they shall wear respirators and complete protection working suits.
5.3.4 When you are walking on the cone-shape top or arched top of the oil tank, you shall pay a special attention, for you will encounter special risks at any times, such as frost, snow, drips of oil, wind and corroded steel plate etc.
6. Scale measure method
6.1 Operation notes
6.1.1 For the vessel without obstacles or deposits at bottom, the method of directly measuring the oil height shall be used; for the vessel with obstacles or deposits at bottom and for the very thick oil products or asphalt, the method of measuring empty distance shall be used.
6.1.2 For the oil tank with its bottom deformed, it is better to use the method that the oil height readings shall be obtained though several gauge hatches (if the oil tank is provided with them) to reduce errors caused by the deformation of tank bottom, or the bottom of tank is always maintained the oil product above 1 m so as to reduce the changes of tank bottom.
6.1.3 When many gauge hatches are provided on the vessel, the regulations shall be given for using these gauge hatches. For the measurement before and after transfer of every batch of oil product, it shall be performed at the same location according to the same method.
6.1.4 The measurement must be repeated, and the measured values obtained must be recorded immediately. 6.1.5 When it is suspected that the readings obtained is affected by liquid level “creeping” and the indicated liquid level or “liquid trace” is always irregular in its profile, the oil indication paste shall be used.
Note: Creeping means the rise of liquid trace that the liquid level of oil product in the vessel moves on the oil dip rod caused by the capillary function, or means the continuous movement of liquid film caused when the oil dip rod is lifted out of the vessel.
6.1.6 When the oil is stored in the metering vessel, all inlets and outlets must be closed, and keep the condition of oil in piping completely same as that before transfer.
6.1.7 After the oil in the vessel is transferred and before the fluctuation in liquid level stops, the measurement shall not start. For the sticky oil, the measurement must be performed only when the air entered into the oil product is released out completely. When there are foams on the surface of oil product, the measurement of oil height must not be performed until the foams disappear or the foam on the surface of oil under the scale measure hatch is removed.
Note: regarding the stable time of liquid level, usually it is not shorter than 15 minutes for the light oil: it is not shorter than 30 minutes for the heavy oil.
6.1.8 For the floating roof oil tank, attention shall be paid for the following conditions in order to have a accurate measuring:
a. Before measurement, accumulation like water, snow, etc. shall be removed from the floating roof. If there are any water and snow that are irremovable, marking shall be indicated. b. If the floating roof moves, measurement shall be made only when the oil product in the tank and the floating roof become stable.
c. It shall be avoided to make measurement when floating roof is under half-floating
d. If the floating roof is not completely floated or below the normal floating liquid level, measurement shall not be made
e. Before and after the transportation of the oil product, the floating conditions of the floating roof shall be as same as possible, and then the displacement of the floating roof can be negligible.
f. As long as it is possible, the changes in immersion length of the floating roof should be measured.
g. Measurement can be made only when the oil is of enough fluidity. 6.1.9 When the horizontal oil tank is tilted with its axle and provided with several gauge hatches, special attentions shall be paid that oil level and water level can be measured only through the gauge hatches specified in Tank Volume Table.
6.1.10 The train tank should stop at horizontal section of the track and measurement shall not be made until the oil product in the tank becomes still.
6.1.11For measuring the oil level in the train tank, the empty distance bar with linear scale can be used.
6.2 Measurement of oil height
6.2.1 Use the depth oil dip rod
18.104.22.168 Selection of oil dip rod: When measuring the low-viscosity oil, the oil dip rod with light plumb bob (0.7kg) shall be used. When measuring high-viscosity oil or the container has a certain quantity of rusty chips or deposit, gauge rod with heavy plumb bob (1.6kg) shall be used.
22.214.171.124 The oil dip rod shall be carefully and continuously descend through the gauge hatch leaning against the point near the reference point all the way, and avoid swing until the plumb bob just touches the scale measure point at the bottom of the container. If the oil dip rod becomes slack, i.e., the plumb bob is tilted, raise the oil dip rod out to a proper height, rub away the oil and measure it again.
126.96.36.199 Check the reference level, if the reading on the oil dip rod is different from the reference level, it is probable that the plumb bob touches the obstacle in the container bottom. At this time, the plumb bob shall be used to detect the container bottom until the exact reading is got. If the exact reading can’t be got, measuring operator shall keep a record and report it in time.
188.8.131.52 After checking the reference level, take out the oil dip rod and read the its immersion height, taking the scale value near the liquid trace. Then rub away the oil on the gauge rod and measure the oil height again. If the difference of measuring values between the second time and first time is more than 1mm, measurement shall be repeated until the difference between the two continuous times is no more than 1mm. Record the measuring values and take the measuring value for the first time as the oil height.
184.108.40.206 When measuring the oil height, before the plumb bob lightly touches the tank bottom, there shall be a period for quieting down the stirring liquid. For thick oil, it is necessary to keep the plumb bob touching the container bottom for 3~5 seconds so that the oil surface around the oil dip rod gets to the level position to avoid the low readings. For the volatile oil, generally rub away the oil dip rod and a clear reading can be obtained. If it is difficult to obtain the reading, apply the oil indicating paste near the liquid level reading on the gauge rod. But don’t use chalk or other porous materials.
6.2.2 Use the measuring rod
220.127.116.11 For small containers like horizontal oil tanks and oil tank truck, measurement of oil height can be done by the method described in 6.2.1 or by the measuring rod. 18.104.22.168 Descend vertically the measuring rod from the reference point and stop its lower end at the scale measure point. Record the reading when the measuring rod is at the same horizontal level with the reference point.
22.214.171.124 Raise the measuring rod out to an enough height and rub away the oil around the level surface. Descend the measuring rod again. Before the measuring rod will just touch the gauging point, stop it for a while to have a period for quieting down the stirring liquid. Then slowly descend the measuring rod until it touches the scale measure point. Take out the measuring rod and record the reading of oil height.
126.96.36.199 Repeat this operation until the difference of the measuring values between the two subsequent times is not more than 1mm. Record the measuring values and take the measuring value in the first time as oil height.
6.3 Empty distance measurement
6.3.1 Use the oil dip rod for empty measurement
188.8.131.52 For the vessel that is provided with several gauge hatches and volume table is calculated according to the empty distance, when making the reference to the volume table, the empty distance value measured through the gauge hatch for preparing the table should be used.
184.108.40.206 The oil dip rod for empty measurement shall descend into the vessel, leaning against the point near the reference point on the gauge hatch.
220.127.116.11 When the plumb bob of oil dip rod for empty measurement gets into the oil surface, stop descent until the oil surface quiets down and then continue to slowly descend (only the portion with scale on the plumb bob can be immersed into oil) until the nearest cm/dm scale line of the oil dip rod is at the same horizontal line as the reference point. 18.104.22.168 Take out the plumb bob for empty measurement, read the oil immersion length on the plumb bob for empty measurement and the length when the oil dip rod is at the reference point, and make records. The sum of the reading on the oil dip rod and level surface reading of the plumb bob for empty measurement (when the liquid trace is shown below the zero graduation of the plumb bob for empty measurement) is exactly the empty distance value to be measured.
22.214.171.124 Repeat this operation until the difference of the measuring values between two
subsequent times is not more than 2mm. If the difference of the measuring values between
two subsequent times is not more than 1mm, take the measuring value in the first time as the
oil height. If the difference of the two measuring values between two subsequent times is
more than 1mm, take the average of two measuring values as the oil height.
6.3.2 Use oil dip rod for depth
126.96.36.199 For measuring the empty distance, only when there is no oil dip rod for depth, can this
alternative method be used. This method is similar to what is described in 6.3.1, but the oil dip
rod for empty measurement is replaced by the oil dip rod for depth.
188.8.131.52 When measuring the empty distance, the plumb bob shall be descended from the
reference point. When it just gets into the liquid, keep the plumb bob at that position until the
liquid surface becomes stable.
184.108.40.206 Continue to descend the plumb bob slowly until an integral meter scale on the oil dip
rod is exactly at the same horizontal line as the reference point.
220.127.116.11 Take out the oil dip rod and record the oil immersion length of the rod and value of
scale on the oil dip rod that is at the same horizontal line with the reference point. The
difference between the two values is the empty distance value.
18.104.22.168 Repeat this operation until the difference of the measuring values between two
subsequent times is not more than 2mm. If the difference the measuring values between two
subsequent times is not more than 1mm, take the measuring value in the first time as the oil
height. If the difference the measuring values between two subsequent times is more than
1mm, take the average of two measuring values as the oil height.
Note: In some cases that are necessary, the empty distance value can be converted into oil
height value. The oil height value can be obtained from the reference height minus empty
distance value. When using the oil dip rod and depth plumb bob, the equivalent oil height can
be directly obtained by the following methods. First, record the reference height and descend
the plumb bob below the liquid surface until the scale on the oil dip rod that has same cm/dm
number as the reference height is in the same horizontal line with the reference point. Take
out the oil dip rod and record the measured value. The difference between the reading of the
oil dip rod on the reference point and the reference height indicated shall be integral
centimeter. The sum of this value and the oil immersion length of the oil dip rod is the
equivalent oil height. The calculation method is as below:
1136.45 The height from scale measure point of the vessel bottom to the reference point
636.45 Subtract: the reading of the oil dip rod at the reference point
500.00 Value difference
87.98 Add: immersion length of the gauge rod
587.98 The equivalent oil height
6.3.3 Use shell outage stick
22.214.171.124 For oil tank truck, horizontal tank or other small vessels, their oil filling level is just below the reference point, so the empty distance bar vertically hanged with the horizontal strip can be used to measure the empty distance value.
126.96.36.199 Before using the empty distance bar, check visually the place below the horizontal strip and conditions relating to the zero scale. If the horizontal strip is found shifted, this empty distance bar shall be rejected and another empty distance bar shall be used. 188.8.131.52 Slowly descend the empty distance bar into the oil in the vessel until the horizontal strip horizontally stops at the hatch or the top of opening on the oil tank. The attention shall be paid that liquid surface shall not be stirred.
184.108.40.206 Take out the empty distance bar, directly read the non-immersed length of the empty distance bar on the scale.
220.127.116.11 If the vessel has a fixed reference point, when the empty distance bar stops at the top of the gauge hatch and the point dose not coincide with the lower side of the horizontal strip, the distance between the top of the gauge hatch and reference point must be corrected according to the reading observed.
6.4 Measurement of the water at the bottom of vessel
6.4.1 Use water scale measure and water indication paste/paper
18.104.22.168 If the height of the water does not exceed 300mm, the water scale measure shall be used.
22.214.171.124 The water scale measure attached to the strap of the oil dip rod shall be applied with a thin layer of water indication paste or vertically clamped with one or several strips of water indication paper by the clamp.
126.96.36.199 The water scale measure and strap of the oil dip rod shall be close to the reference point and lean closely against the gauge hatch to be descended into the vessel until it lightly touches the scale measure point.
188.8.131.52 The strap of the oil dip rod must be strained to guarantee the verticality of the water scale measure. The water scale measure shall maintain at this position for a quite enough time so that water can remove the water indicating paste or change the color of the water indication paste, or change the color of the water indication paper.
Note: Generally speaking, when using water indication paste, for petrol and kerosene, it needs to immerse for 3~5 seconds; for heavy oil, it needs to immerse for 10~30 seconds. Regarding the water indication paper, it needs even longer time, depending on the oil products on the water surface.
184.108.40.206 Take out the water scale measure, read the water height value and make the record. 220.127.116.11 If the clear reading of water layer can’t be obtained in immersion of the water scale
measure for the first time, it is necessary to remove the water indication paste/paper which have been used. Before doing the nest measurement, the water scale measure shall be wiped