Petroleum and liquid petroleum products -- Calibration of vertical cylindrical tanks

ISO 7507-3:2006 specifies a calibration procedure for application to tanks above 8 m in diameter with cylindrical courses that are substantially vertical. It provides a method for determining the volumetric quantity contained within a tank at gauged liquid levels. The measurements required to determine the radius are made either internally or externally. The external method is applicable only to tanks that are free of insulation. ISO 7507-3:2006 is suitable for tanks tilted up to a 3 % deviation from the vertical, provided that a correction is applied for the measured tilt as described in ISO 7507-1.

Pétrole et produits pétroliers liquides -- Jaugeage des réservoirs cylindriques verticaux

Nafta in tekoči naftni proizvodi - Umerjanje navpičnih valjastih rezervoarjev - 3. del: Optična triangulacijska metoda

General Information

Status
Published
Publication Date
12-Jul-2006
Current Stage
6060 - International Standard published
Start Date
28-Jun-2006
Completion Date
13-Jul-2006

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INTERNATIONAL ISO
STANDARD 7507-3
Second edition
2006-07-15
Petroleum and liquid petroleum
products — Calibration of vertical
cylindrical tanks —
Part 3:
Optical-triangulation method
Pétrole et produits pétroliers liquides — Jaugeage des réservoirs
cylindriques verticaux —
Partie 3: Méthode par triangulation optique
Reference number
ISO 7507-3:2006(E)
ISO 2006
---------------------- Page: 1 ----------------------
ISO 7507-3:2006(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but

shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In

the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

© ISO 2006

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2006 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 7507-3:2006(E)
Contents Page

Foreword............................................................................................................................................................ iv

Introduction ........................................................................................................................................................ v

1 Scope ..................................................................................................................................................... 1

2 Normative references ........................................................................................................................... 1

3 Terms and definitions........................................................................................................................... 1

4 Precautions ........................................................................................................................................... 1

5 Equipment ............................................................................................................................................. 2

5.1 Equipment for measurement of angles .............................................................................................. 2

5.2 Stadia ..................................................................................................................................................... 2

6 Equipment set-up and procedure ....................................................................................................... 2

6.1 Preparation of tank ............................................................................................................................... 2

6.2 Establishment of calibration conditions ............................................................................................ 2

6.3 Set-up of theodolites and/or total stations......................................................................................... 3

7 Stadia set-up and procedure ............................................................................................................... 3

8 Measurement of horizontal distance between two theodolite stations using a stadia ................. 3

9 Measurement of horizontal distance between two theodolite stations using a total station ....... 5

10 Procedure for internal optical tank wall measurements................................................................... 5

11 Procedures for external measurements............................................................................................. 8

11.1 General................................................................................................................................................... 8

11.2 Reference circumference measured by strapping ............................................................................ 8

11.3 Reference distances measured between pairs of theodolite stations .......................................... 10

12 Tolerances ........................................................................................................................................... 11

12.1 Distances between theodolites ......................................................................................................... 11

12.2 Horizontal angles................................................................................................................................ 11

12.3 Reference circumference................................................................................................................... 11

13 Other measurements for tank calibrations ...................................................................................... 12

13.1 Tank-bottom calibrations................................................................................................................... 12

13.2 Other measurements and data .......................................................................................................... 12

14 Calculations and development of tank capacity tables.................................................................. 13

14.1 From the internal procedure.............................................................................................................. 13

14.2 From the reference circumference procedure................................................................................. 13

14.3 From the reference distances between pairs of theodolites.......................................................... 13

14.4 Corrections.......................................................................................................................................... 13

14.5 Tank capacity table............................................................................................................................. 13

Annex A (normative) Computation of internal radii from internal measurements.................................... 14

Annex B (normative) Determination of the radius of the circle by the least-squares method................. 15

Annex C (normative) Computation of internal radii from reference circumference and external

measurements..................................................................................................................................... 20

Annex D (normative) Computation of internal radii from reference distances between pairs of

theodolite stations.............................................................................................................................. 22

Annex E (informative) Calibration uncertainties ........................................................................................... 24

Annex F (normative) Procedure for checking the theodolite(s).................................................................. 36

Bibliography ..................................................................................................................................................... 38

© ISO 2006 – All rights reserved iii
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ISO 7507-3:2006(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 7507-3 was prepared by Technical Committee ISO/TC 28, Petroleum products and lubricants,

Subcommittee SC 3, Static petroleum measurement.

This second edition cancels and replaces the first edition (ISO 7507-3:1993), which has been technically

revised.

ISO 7507 consists of the following parts, under the general title Petroleum and liquid petroleum products —

Calibration of vertical cylindrical tanks:
⎯ Part 1: Strapping method
⎯ Part 2: Optical-reference-line method
⎯ Part 3: Optical-triangulation method
⎯ Part 4: Internal electro-optical distance-ranging method
⎯ Part 5: External electro-optical distance-ranging method
iv © ISO 2006 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 7507-3:2006(E)
Introduction

This part of ISO 7507 describes the calibration of vertical cylindrical tanks by means of optical triangulation

using theodolites. The circumference of the tank is determined at different levels by reference to a base line,

which can be either a reference circumference measured by strapping or a base line between two stations of

a theodolite measured by means of a tape or by an optical method. External circumferences are corrected to

give true internal circumferences.

The method is an alternative to other methods such as strapping (ISO 7507-1) and the optical-reference-line

method (ISO 7507-2).
© ISO 2006 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 7507-3:2006(E)
Petroleum and liquid petroleum products — Calibration of
vertical cylindrical tanks —
Part 3:
Optical-triangulation method
1 Scope

This part of ISO 7507 specifies a calibration procedure for application to tanks above 8 m in diameter with

cylindrical courses that are substantially vertical. It provides a method for determining the volumetric quantity

contained within a tank at gauged liquid levels. The measurements required to determine the radius are made

either internally (Clause 10) or externally (Clause 11). The external method is applicable only to tanks that are

free of insulation.

This method is suitable for tanks tilted up to a 3 % deviation from the vertical provided that a correction is

applied for the measured tilt as described in ISO 7507-1.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

ISO 7507-1:2003, Petroleum and liquid petroleum products — Calibration of vertical cylindrical tanks —

Part 1: Strapping method
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 7507-1 and the following apply.

3.1
total station

theodolite with built-in distance meter that coincides with the optical axis of the instrument

4 Precautions

The general precautions and safety precautions specified in ISO 7507-1 shall apply to this part of ISO 7507.

© ISO 2006 – All rights reserved 1
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ISO 7507-3:2006(E)
5 Equipment
5.1 Equipment for measurement of angles

5.1.1 Theodolite, with angular resolution equal to or better than 0,2 mgon (1 mgon = 0,25 s).

Each theodolite shall be mounted on a tripod that is firm and stable. The legs of the tripod shall be steadied by

means of magnetic bearers (or any equivalent system) when being used for the internal method. The

theodolites shall be checked either periodically or prior to the tank measurements as described in Annex F.

Alternatively, a total station can be used along with a prism mounted on the other station. The total station

shall meet the same requirements for the angular measurements as the theodolites. The distance

measurement shall have a resolution equal to or better than 0,1 mm. The distance meter shall be calibrated

together with the used prism with an extended calibration uncertainty on the order of 1 mm or better. It shall

be possible to mount the prism on the tripod in the same position as the theodolite/total station.

5.1.2 Laser-beam emitter, low-power, equipped with a device, such as a fibre-optic light-transfer system

and a theodolite-telescope eye-piece connection, by which the laser beam can be transmitted through a

theodolite. The laser beam shall be coincident with the optical axis of the telescope.

5.1.3 Weights, heavy, to set round the theodolite stations to prevent movement of the tank bottom plate.

5.1.4 Lighting, for use inside the tank to allow measurements to be read accurately.

5.2 Stadia
Stadia, at least 2 m long, of a material whose thermal expansion is known.

The graduated length between two marks shall be calibrated. Extended calibration uncertainty should be on

the order of 0,05 mm. It shall be possible to mount the stadia on the tripod in the same position as the

theodolite.

NOTE The stadia is not used when the calibration is carried out using a total station.

6 Equipment set-up and procedure
6.1 Preparation of tank

For new tanks or for tanks after repair, fill the tank to its normal working capacity at least once and allow it to

stand for at least 24 h prior to calibration.
6.2 Establishment of calibration conditions

If the tank is calibrated with liquid in it, record the depth, temperature and density of the liquid at the time of

calibration. Do not make transfers of liquid during the calibration.

Measure or estimate the worst-case gradient of tank-shell temperatures at the time of calibration.

NOTE 1 The temperature gradient is used to estimate the uncertainties of the measured tank radii (see 13.2 and

E.3.5.3).

NOTE 2 The highest temperature is usually found on the sunny side at the top of the tank, the lowest temperature on

the shady side at the bottom of the tank.
2 © ISO 2006 – All rights reserved
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ISO 7507-3:2006(E)
6.3 Set-up of theodolites and/or total stations

6.3.1 Set up each theodolite or total station with care, according to the procedure and instructions given by

the manufacturer. In addition, follow the procedures described in 6.3.2 and 6.3.3.

6.3.2 Set up the instrument so as to be stable.

For the internal method, steady the bottom of the tank near the theodolite or total station by installing weights

or other heavy objects around the station if there is a risk of the station moving during the calibration. Mount

the legs of the tripod on magnetic bearers (or any equivalent system) to prevent the legs from sliding on the

tank bottom.

For the external method, drive the legs of the tripod fully home into the ground.

6.3.3 Set the bed plate of the instrument as near as possible to the horizontal.

NOTE This ensures verticality of the swivel axis of the theodolite or total station.

6.3.4 The calibration equipment shall be placed at the site for typically 1 h in order to reach ambient

temperature before commencement of the actual calibration procedure.
7 Stadia set-up and procedure

7.1 Mount the stadia on the tripod with care according to the procedure and instructions given by the

manufacturer. In addition, follow the procedures described in 7.2 and 7.3.

7.2 Mount the stadia horizontally and perpendicular to the aiming axis by adjusting the device on the stadia.

7.3 Once setting-up is complete, lock the stadia in position and verify that it is horizontal and perpendicular.

8 Measurement of horizontal distance between two theodolite stations using a
stadia

8.1 This procedure for determining the distance using a stadia is not recommended if the distance between

the stations is above 25 m.

8.2 Take the measurement prior to the commencement of the optical readings. Set up the stadia as

described in Clause 7.

Measure the horizontal angle, 2θ, subtended at the theodolite (see Figure 1) by the two marks on the stadia,

using the theodolite.
© ISO 2006 – All rights reserved 3
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ISO 7507-3:2006(E)
Key
1 theodolite 1
2 theodolite 2 (laser)
3 stadia mark
4 stadia
Points T and L are interchangeable.
B, the distance between the two reference marks on the stadia, equals 2 m.
Figure 1 — Measurement of distance between two theodolites

8.3 Compute the horizontal distance, D, between the two theodolite stations from Equation (1):

D = (1)
2t×anθ
where

B is the distance between the two reference marks on the stadia (corrected for thermal expansion, if

necessary);
θ is half the angle subtended at theodolite, T, by the two reference marks.

8.4 Carry out the measurement of the angle 2θ and the computation of the distance, D, a minimum of five

times while turning and re-pointing the theodolite in between, and calculate and record the average value.

Two standard deviations of the mean of the distance, D, shall be less than half of the tolerance given in

Table 3 or the entire procedure shall be repeated.

8.5 Re-determine the distance, D, after completion of all the optical measurements described in 10.13.

The average distances computed before and after the optical measurements shall agree within the tolerances

given in Table 3. If they do not, repeat the calibration procedure until a set of measurements is obtained with

the average values for D at the beginning and end within the tolerances.

8.6 The average of all measurements of distance, D, shall be used in further calculations.

4 © ISO 2006 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 7507-3:2006(E)

9 Measurement of horizontal distance between two theodolite stations using a total

station

9.1 This procedure for determining the distance between theodolite stations is not recommended if the

distance between the stations is less than 10 m.
9.2 Set up the prism at the second tripod.

9.3 Carry out the measurement of the distance, D, a minimum of five times while turning and re-pointing the

total station in between, and calculate and record the average value. Two standard deviations of the mean of

the distance, D, shall be less than half of the tolerance given in Table 3 or the entire procedure shall be

repeated.

9.4 Re-determine the distance, D, after completion of all the optical measurements described in 10.13.

The average distances computed before and after the optical measurements shall agree within the tolerances

given in Table 3. If they do not, repeat the calibration procedure until a set of measurements is obtained with

the average values for D at the beginning and end within the tolerances.

9.5 The average of all measurements of distance, D, shall be used in further calculations.

10 Procedure for internal optical tank wall measurements

10.1 Set up two theodolite stations inside the tank as illustrated in Figure 2 and as described in 6.3.

T and L are interchangeable theodolite and laser theodolite stations.

Figure 2 — Example of locations of theodolite stations and wall points for internal procedure

10.2 Locate the two stations approximately on a diametrical plane and at least one quarter diameter apart.

Adjust the theodolites and measure the distance, D, between T and L as described in Clause 8 or Clause 9.

10.3 Set the reference axis, TL, optically on the horizontal planes (circles) of both instruments by sighting

from each instrument the vertical graticule wires of the other instrument as described in 10.4 to 10.7.

10.4 Ensure that the laser is shut off in order to avoid exposure.
© ISO 2006 – All rights reserved 5
---------------------- Page: 10 ----------------------
ISO 7507-3:2006(E)

10.5 Adjust the theodolite, T, to set the telescope to infinity and illuminate the eyepiece of this telescope with

a light source.

10.6 Sight the object lens of the theodolite, T, from the telescope of the laser theodolite, L, and continue

focussing until the graticules become visible. Make the vertical graticule wires coincide by using the adjusting

device on the laser theodolite, L.

10.7 Repeat the operation from the theodolite. Repeat the operation as many times as is necessary until the

vertical graticule wires coincide perfectly.

10.8 The TL axis is now set. Record the relative locations of the two theodolites by taking readings on both

horizontal scales as the horizontal reference angles.

10.9 Switch on the laser beam. This beam is then used to provide a series of points on the tank shell wall.

Sight these points in turn using the other theodolite and take and record the horizontal-scale readings on both

instruments. Do not locate measurement points closer to the reference angle (the line through T and L) than

10 gon (Figure 3, angle α or β, whichever is smaller).
Key
T theodolite station
L laser theodolite station
P arbitrary point on the tank

Figure 3 — Horizontal angles between sightings on points on the tank wall and the reference axis TL

10.10 The minimum number of points on the tank shell wall per circumference shall be as given in Table 1.

These points shall not be closer than 300 mm from the vertical weld seam.

For each course, there shall be two sets of points: one set on a circumference at about 1/4 of the course

height above the lower horizontal seam, and the other at about 1/4 of the course height below the upper

horizontal seam as shown in Figure 4.
6 © ISO 2006 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 7507-3:2006(E)
Dimensions in millimetres
Key
1 seam
Figure 4 — Location of sets of points on tank wall

10.11 Determine the horizontal angles, α and β, of all the points along a horizontal set, as shown in

Figure 3, by the theodolite and the laser beam. Then move to the next level.

NOTE This ensures that each set of points on the tank wall is at the same level for a given circumference.

Table 1 — Minimum number of points per circumference for internal procedure
Circumference Minimum number of points
u 50 10
> 50, u 100 12
> 100, u 150 16
> 150, u 200 20
> 200, u 250 24
> 250, u 300 30
> 300 36

To avoid systematic errors, the number of points divided by the number of plates in the tank segments should

not be equal to an integer (e.g. 1, 2, 3, etc.).

For riveted tanks, it is recommended that at least three points are sighted in every tank plate at every height,

one in the centre and two at the extremes of the plate width (near the vertical seams).

10.12 After completion of the optical measurement of all the points, re-determine the horizontal distance, D,

between T and L (see 8.5 and 9.4) and repeat the calibration if necessary.

10.13 Check the axis, TL, by switching off the laser and repeating the operations described in 10.3 to 10.8.

The original and final horizontal reference angles shall be within the tolerance specified in 12.2. If not, repeat

the calibration procedures until a set of readings ending in such agreement is obtained. Record the average

values of the horizontal reference angles.
© ISO 2006 – All rights reserved 7
---------------------- Page: 12 ----------------------
ISO 7507-3:2006(E)
11 Procedures for external measurements
11.1 General

The measurements shall be related either to a reference circumference using the procedure described in 11.2

or to reference distances measured between pairs of theodolite stations as described in 11.3.

11.2 Reference circumference measured by strapping
11.2.1 Reference circumference

The reference circumference has a direct impact on the calibrated volume of the entire tank. It is necessary,

therefore, that it be measured as accurately as possible.

Determine the reference circumference using the reference method described in ISO 7507-1 and the following

items a) and b).

a) Take multiple measurements of the reference circumference either prior to the commencement or after

the completion of the optical readings. If the first three consecutive measurements agree within the

tolerances specified in Table 4, take their mean average as the reference circumference and their

standard deviation as the standard uncertainty. If they do not agree within the tolerances specified in

Table 4, repeat the measurements until two standard deviations of the mean of all measurements is less

than the half of the tolerances specified in Table 4. Use the mean as the measured reference

circumference and the standard deviation as the standard uncertainty. Use standard procedures to

eliminate obvious outliers.

b) Take the measurement of the reference circumference at a position where work conditions allow reliable

measurements and that is within the focal range of the optical instrument. Strap the tank, aiming at one of

the following levels:
1) about 1/4 of the course height above the lower horizontal seam,
2) about 1/4 of the course height below the upper horizontal seam,

and repeat the measurement to achieve agreement within the tolerances specified in Table 4.

11.2.2 Theodolite readings

11.2.2.1 Set up the theodolite outside the tank, as shown in Figure 5 for eight theodolite stations and as

described in 6.3.

The minimum number of stations (T1, T2, etc.) per circumference shall be as given in Table 2.

8 © ISO 2006 – All rights reserved
---------------------- Page: 13 ----------------------
ISO 7507-3:2006(E)
Key
T1 …… T8 theodolite stations
Figure 5 — Example of theodolite station locations for external procedures
based on a reference circumference
Table 2 — Minimum number of theodolite stations for external procedures
Tank circumference Minimum number of stations
u 50 5
> 50, u 100 6
> 100, u 150 8
> 150, u 200 10
> 200, u 250 12
> 250, u 300 15
> 300 18

To avoid systematic errors, the number of stations divided by the number of plates in the tank segments

should not be equal to an integer (e.g. 1, 2, 3, etc.).

The theodolite positions should be such that the targets avoid the vertical welds between tank segments.

Care should be taken, especially for smaller tanks, that the target points are evenly distributed around the tank.

11.2.2.2 From each station and for each level (see 11.2.2.3 and 11.2.2.4), make a sighting tangentially to

the tank on either side of the theodolite as shown in Figure 5. Maintain the same vertical angle of the

theodolite in both sightings.

NOTE This ensures that the intended targets on the tank are at the same level for a given circumference.

Record the horizontal angles subtended by the tangents at the theodolite.
© ISO 2006 – All rights reserved 9
---------------------- Page: 14 ----------------------
ISO 7507-3:2006(E)

11.2.2.3 Make sightings at the height at which the reference circumference was measured (see 11.2.1).

The angles at the strapped height shall be measured twice (before and after measurements of the angles at

other heights; see 11.2.2.4). The subtended angles shall agree with each other to within 0,01 gon. If they do

not, repeat the measurements until two standard deviations from the mean fit within 1/2 of this tolerance. In

further calculations, use the average and standard deviation of the measurements.

If agreement is still not obtained, repeat the measurements at this station.

11.2.2.4 For each theodolite station (e.g. T1), sight each of the courses at two levels, one at about 1/4 of

the course height above the lower horizontal seam, the other at about 1/4 of the course height below the

upper horizontal seam.

11.2.2.5 Move the theodolite from station T1 to T2 to T3, etc., until the whole circumference is covered.

Repeat all the above steps at each station (i.e. T1, T2, etc.), for each level. Record the horizontal angles for

each of the points sighted.
11.3 Reference distances measured between pairs of theodolite stations

11.3.1 Set up the two theodolite stations outside the tank, as shown in Figure 6 for eight stations, and as

described in 6.3, using a theodolite (5.1.1) and a second tripod. The minimum number of stations (T1, T2,

etc.) per circumference shall be as given in Table 2.
Key
T1 …… T8 theodolite stations

Figure 6 — Example of theodolite station locations for external procedure based on reference

distances between pairs of theodolites

11.3.2 Determine the horizontal distance, T1 to T2, between the two theodolite stations by using the stadia

as described in Clause 8 (T1 to T2 = D) with the stadia mounted at T2 as described in 6.3, or by using

...

SLOVENSKI STANDARD
SIST ISO 7507-3:2007
01-december-2007
1DGRPHãþD
SIST ISO 7507-3:2006

1DIWDLQWHNRþLQDIWQLSURL]YRGL8PHUMDQMHQDYSLþQLKYDOMDVWLKUH]HUYRDUMHY

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Petroleum and liquid petroleum products - Calibration of vertical cylindrical tanks - Part 3:

Optical-triangulation method

Pétrole et produits pétroliers liquides - Jaugeage des réservoirs cylindriques verticaux -

Partie 3: Méthode par triangulation optique
Ta slovenski standard je istoveten z: ISO 7507-3:2006
ICS:
75.180.30 Oprema za merjenje Volumetric equipment and
prostornine in merjenje measurements
SIST ISO 7507-3:2007 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST ISO 7507-3:2007
---------------------- Page: 2 ----------------------
SIST ISO 7507-3:2007
INTERNATIONAL ISO
STANDARD 7507-3
Second edition
2006-07-15
Petroleum and liquid petroleum
products — Calibration of vertical
cylindrical tanks —
Part 3:
Optical-triangulation method
Pétrole et produits pétroliers liquides — Jaugeage des réservoirs
cylindriques verticaux —
Partie 3: Méthode par triangulation optique
Reference number
ISO 7507-3:2006(E)
ISO 2006
---------------------- Page: 3 ----------------------
SIST ISO 7507-3:2007
ISO 7507-3:2006(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but

shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In

the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

© ISO 2006

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2006 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 7507-3:2007
ISO 7507-3:2006(E)
Contents Page

Foreword............................................................................................................................................................ iv

Introduction ........................................................................................................................................................ v

1 Scope ..................................................................................................................................................... 1

2 Normative references ........................................................................................................................... 1

3 Terms and definitions........................................................................................................................... 1

4 Precautions ........................................................................................................................................... 1

5 Equipment ............................................................................................................................................. 2

5.1 Equipment for measurement of angles .............................................................................................. 2

5.2 Stadia ..................................................................................................................................................... 2

6 Equipment set-up and procedure ....................................................................................................... 2

6.1 Preparation of tank ............................................................................................................................... 2

6.2 Establishment of calibration conditions ............................................................................................ 2

6.3 Set-up of theodolites and/or total stations......................................................................................... 3

7 Stadia set-up and procedure ............................................................................................................... 3

8 Measurement of horizontal distance between two theodolite stations using a stadia ................. 3

9 Measurement of horizontal distance between two theodolite stations using a total station ....... 5

10 Procedure for internal optical tank wall measurements................................................................... 5

11 Procedures for external measurements............................................................................................. 8

11.1 General................................................................................................................................................... 8

11.2 Reference circumference measured by strapping ............................................................................ 8

11.3 Reference distances measured between pairs of theodolite stations .......................................... 10

12 Tolerances ........................................................................................................................................... 11

12.1 Distances between theodolites ......................................................................................................... 11

12.2 Horizontal angles................................................................................................................................ 11

12.3 Reference circumference................................................................................................................... 11

13 Other measurements for tank calibrations ...................................................................................... 12

13.1 Tank-bottom calibrations................................................................................................................... 12

13.2 Other measurements and data .......................................................................................................... 12

14 Calculations and development of tank capacity tables.................................................................. 13

14.1 From the internal procedure.............................................................................................................. 13

14.2 From the reference circumference procedure................................................................................. 13

14.3 From the reference distances between pairs of theodolites.......................................................... 13

14.4 Corrections.......................................................................................................................................... 13

14.5 Tank capacity table............................................................................................................................. 13

Annex A (normative) Computation of internal radii from internal measurements.................................... 14

Annex B (normative) Determination of the radius of the circle by the least-squares method................. 15

Annex C (normative) Computation of internal radii from reference circumference and external

measurements..................................................................................................................................... 20

Annex D (normative) Computation of internal radii from reference distances between pairs of

theodolite stations.............................................................................................................................. 22

Annex E (informative) Calibration uncertainties ........................................................................................... 24

Annex F (normative) Procedure for checking the theodolite(s).................................................................. 36

Bibliography ..................................................................................................................................................... 38

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Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 7507-3 was prepared by Technical Committee ISO/TC 28, Petroleum products and lubricants,

Subcommittee SC 3, Static petroleum measurement.

This second edition cancels and replaces the first edition (ISO 7507-3:1993), which has been technically

revised.

ISO 7507 consists of the following parts, under the general title Petroleum and liquid petroleum products —

Calibration of vertical cylindrical tanks:
⎯ Part 1: Strapping method
⎯ Part 2: Optical-reference-line method
⎯ Part 3: Optical-triangulation method
⎯ Part 4: Internal electro-optical distance-ranging method
⎯ Part 5: External electro-optical distance-ranging method
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Introduction

This part of ISO 7507 describes the calibration of vertical cylindrical tanks by means of optical triangulation

using theodolites. The circumference of the tank is determined at different levels by reference to a base line,

which can be either a reference circumference measured by strapping or a base line between two stations of

a theodolite measured by means of a tape or by an optical method. External circumferences are corrected to

give true internal circumferences.

The method is an alternative to other methods such as strapping (ISO 7507-1) and the optical-reference-line

method (ISO 7507-2).
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SIST ISO 7507-3:2007
INTERNATIONAL STANDARD ISO 7507-3:2006(E)
Petroleum and liquid petroleum products — Calibration of
vertical cylindrical tanks —
Part 3:
Optical-triangulation method
1 Scope

This part of ISO 7507 specifies a calibration procedure for application to tanks above 8 m in diameter with

cylindrical courses that are substantially vertical. It provides a method for determining the volumetric quantity

contained within a tank at gauged liquid levels. The measurements required to determine the radius are made

either internally (Clause 10) or externally (Clause 11). The external method is applicable only to tanks that are

free of insulation.

This method is suitable for tanks tilted up to a 3 % deviation from the vertical provided that a correction is

applied for the measured tilt as described in ISO 7507-1.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

ISO 7507-1:2003, Petroleum and liquid petroleum products — Calibration of vertical cylindrical tanks —

Part 1: Strapping method
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 7507-1 and the following apply.

3.1
total station

theodolite with built-in distance meter that coincides with the optical axis of the instrument

4 Precautions

The general precautions and safety precautions specified in ISO 7507-1 shall apply to this part of ISO 7507.

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5 Equipment
5.1 Equipment for measurement of angles

5.1.1 Theodolite, with angular resolution equal to or better than 0,2 mgon (1 mgon = 0,25 s).

Each theodolite shall be mounted on a tripod that is firm and stable. The legs of the tripod shall be steadied by

means of magnetic bearers (or any equivalent system) when being used for the internal method. The

theodolites shall be checked either periodically or prior to the tank measurements as described in Annex F.

Alternatively, a total station can be used along with a prism mounted on the other station. The total station

shall meet the same requirements for the angular measurements as the theodolites. The distance

measurement shall have a resolution equal to or better than 0,1 mm. The distance meter shall be calibrated

together with the used prism with an extended calibration uncertainty on the order of 1 mm or better. It shall

be possible to mount the prism on the tripod in the same position as the theodolite/total station.

5.1.2 Laser-beam emitter, low-power, equipped with a device, such as a fibre-optic light-transfer system

and a theodolite-telescope eye-piece connection, by which the laser beam can be transmitted through a

theodolite. The laser beam shall be coincident with the optical axis of the telescope.

5.1.3 Weights, heavy, to set round the theodolite stations to prevent movement of the tank bottom plate.

5.1.4 Lighting, for use inside the tank to allow measurements to be read accurately.

5.2 Stadia
Stadia, at least 2 m long, of a material whose thermal expansion is known.

The graduated length between two marks shall be calibrated. Extended calibration uncertainty should be on

the order of 0,05 mm. It shall be possible to mount the stadia on the tripod in the same position as the

theodolite.

NOTE The stadia is not used when the calibration is carried out using a total station.

6 Equipment set-up and procedure
6.1 Preparation of tank

For new tanks or for tanks after repair, fill the tank to its normal working capacity at least once and allow it to

stand for at least 24 h prior to calibration.
6.2 Establishment of calibration conditions

If the tank is calibrated with liquid in it, record the depth, temperature and density of the liquid at the time of

calibration. Do not make transfers of liquid during the calibration.

Measure or estimate the worst-case gradient of tank-shell temperatures at the time of calibration.

NOTE 1 The temperature gradient is used to estimate the uncertainties of the measured tank radii (see 13.2 and

E.3.5.3).

NOTE 2 The highest temperature is usually found on the sunny side at the top of the tank, the lowest temperature on

the shady side at the bottom of the tank.
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6.3 Set-up of theodolites and/or total stations

6.3.1 Set up each theodolite or total station with care, according to the procedure and instructions given by

the manufacturer. In addition, follow the procedures described in 6.3.2 and 6.3.3.

6.3.2 Set up the instrument so as to be stable.

For the internal method, steady the bottom of the tank near the theodolite or total station by installing weights

or other heavy objects around the station if there is a risk of the station moving during the calibration. Mount

the legs of the tripod on magnetic bearers (or any equivalent system) to prevent the legs from sliding on the

tank bottom.

For the external method, drive the legs of the tripod fully home into the ground.

6.3.3 Set the bed plate of the instrument as near as possible to the horizontal.

NOTE This ensures verticality of the swivel axis of the theodolite or total station.

6.3.4 The calibration equipment shall be placed at the site for typically 1 h in order to reach ambient

temperature before commencement of the actual calibration procedure.
7 Stadia set-up and procedure

7.1 Mount the stadia on the tripod with care according to the procedure and instructions given by the

manufacturer. In addition, follow the procedures described in 7.2 and 7.3.

7.2 Mount the stadia horizontally and perpendicular to the aiming axis by adjusting the device on the stadia.

7.3 Once setting-up is complete, lock the stadia in position and verify that it is horizontal and perpendicular.

8 Measurement of horizontal distance between two theodolite stations using a
stadia

8.1 This procedure for determining the distance using a stadia is not recommended if the distance between

the stations is above 25 m.

8.2 Take the measurement prior to the commencement of the optical readings. Set up the stadia as

described in Clause 7.

Measure the horizontal angle, 2θ, subtended at the theodolite (see Figure 1) by the two marks on the stadia,

using the theodolite.
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Key
1 theodolite 1
2 theodolite 2 (laser)
3 stadia mark
4 stadia
Points T and L are interchangeable.
B, the distance between the two reference marks on the stadia, equals 2 m.
Figure 1 — Measurement of distance between two theodolites

8.3 Compute the horizontal distance, D, between the two theodolite stations from Equation (1):

D = (1)
2t×anθ
where

B is the distance between the two reference marks on the stadia (corrected for thermal expansion, if

necessary);
θ is half the angle subtended at theodolite, T, by the two reference marks.

8.4 Carry out the measurement of the angle 2θ and the computation of the distance, D, a minimum of five

times while turning and re-pointing the theodolite in between, and calculate and record the average value.

Two standard deviations of the mean of the distance, D, shall be less than half of the tolerance given in

Table 3 or the entire procedure shall be repeated.

8.5 Re-determine the distance, D, after completion of all the optical measurements described in 10.13.

The average distances computed before and after the optical measurements shall agree within the tolerances

given in Table 3. If they do not, repeat the calibration procedure until a set of measurements is obtained with

the average values for D at the beginning and end within the tolerances.

8.6 The average of all measurements of distance, D, shall be used in further calculations.

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9 Measurement of horizontal distance between two theodolite stations using a total

station

9.1 This procedure for determining the distance between theodolite stations is not recommended if the

distance between the stations is less than 10 m.
9.2 Set up the prism at the second tripod.

9.3 Carry out the measurement of the distance, D, a minimum of five times while turning and re-pointing the

total station in between, and calculate and record the average value. Two standard deviations of the mean of

the distance, D, shall be less than half of the tolerance given in Table 3 or the entire procedure shall be

repeated.

9.4 Re-determine the distance, D, after completion of all the optical measurements described in 10.13.

The average distances computed before and after the optical measurements shall agree within the tolerances

given in Table 3. If they do not, repeat the calibration procedure until a set of measurements is obtained with

the average values for D at the beginning and end within the tolerances.

9.5 The average of all measurements of distance, D, shall be used in further calculations.

10 Procedure for internal optical tank wall measurements

10.1 Set up two theodolite stations inside the tank as illustrated in Figure 2 and as described in 6.3.

T and L are interchangeable theodolite and laser theodolite stations.

Figure 2 — Example of locations of theodolite stations and wall points for internal procedure

10.2 Locate the two stations approximately on a diametrical plane and at least one quarter diameter apart.

Adjust the theodolites and measure the distance, D, between T and L as described in Clause 8 or Clause 9.

10.3 Set the reference axis, TL, optically on the horizontal planes (circles) of both instruments by sighting

from each instrument the vertical graticule wires of the other instrument as described in 10.4 to 10.7.

10.4 Ensure that the laser is shut off in order to avoid exposure.
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10.5 Adjust the theodolite, T, to set the telescope to infinity and illuminate the eyepiece of this telescope with

a light source.

10.6 Sight the object lens of the theodolite, T, from the telescope of the laser theodolite, L, and continue

focussing until the graticules become visible. Make the vertical graticule wires coincide by using the adjusting

device on the laser theodolite, L.

10.7 Repeat the operation from the theodolite. Repeat the operation as many times as is necessary until the

vertical graticule wires coincide perfectly.

10.8 The TL axis is now set. Record the relative locations of the two theodolites by taking readings on both

horizontal scales as the horizontal reference angles.

10.9 Switch on the laser beam. This beam is then used to provide a series of points on the tank shell wall.

Sight these points in turn using the other theodolite and take and record the horizontal-scale readings on both

instruments. Do not locate measurement points closer to the reference angle (the line through T and L) than

10 gon (Figure 3, angle α or β, whichever is smaller).
Key
T theodolite station
L laser theodolite station
P arbitrary point on the tank

Figure 3 — Horizontal angles between sightings on points on the tank wall and the reference axis TL

10.10 The minimum number of points on the tank shell wall per circumference shall be as given in Table 1.

These points shall not be closer than 300 mm from the vertical weld seam.

For each course, there shall be two sets of points: one set on a circumference at about 1/4 of the course

height above the lower horizontal seam, and the other at about 1/4 of the course height below the upper

horizontal seam as shown in Figure 4.
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Dimensions in millimetres
Key
1 seam
Figure 4 — Location of sets of points on tank wall

10.11 Determine the horizontal angles, α and β, of all the points along a horizontal set, as shown in

Figure 3, by the theodolite and the laser beam. Then move to the next level.

NOTE This ensures that each set of points on the tank wall is at the same level for a given circumference.

Table 1 — Minimum number of points per circumference for internal procedure
Circumference Minimum number of points
u 50 10
> 50, u 100 12
> 100, u 150 16
> 150, u 200 20
> 200, u 250 24
> 250, u 300 30
> 300 36

To avoid systematic errors, the number of points divided by the number of plates in the tank segments should

not be equal to an integer (e.g. 1, 2, 3, etc.).

For riveted tanks, it is recommended that at least three points are sighted in every tank plate at every height,

one in the centre and two at the extremes of the plate width (near the vertical seams).

10.12 After completion of the optical measurement of all the points, re-determine the horizontal distance, D,

between T and L (see 8.5 and 9.4) and repeat the calibration if necessary.

10.13 Check the axis, TL, by switching off the laser and repeating the operations described in 10.3 to 10.8.

The original and final horizontal reference angles shall be within the tolerance specified in 12.2. If not, repeat

the calibration procedures until a set of readings ending in such agreement is obtained. Record the average

values of the horizontal reference angles.
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11 Procedures for external measurements
11.1 General

The measurements shall be related either to a reference circumference using the procedure described in 11.2

or to reference distances measured between pairs of theodolite stations as described in 11.3.

11.2 Reference circumference measured by strapping
11.2.1 Reference circumference

The reference circumference has a direct impact on the calibrated volume of the entire tank. It is necessary,

therefore, that it be measured as accurately as possible.

Determine the reference circumference using the reference method described in ISO 7507-1 and the following

items a) and b).

a) Take multiple measurements of the reference circumference either prior to the commencement or after

the completion of the optical readings. If the first three consecutive measurements agree within the

tolerances specified in Table 4, take their mean average as the reference circumference and their

standard deviation as the standard uncertainty. If they do not agree within the tolerances specified in

Table 4, repeat the measurements until two standard deviations of the mean of all measurements is less

than the half of the tolerances specified in Table 4. Use the mean as the measured reference

circumference and the standard deviation as the standard uncertainty. Use standard procedures to

eliminate obvious outliers.

b) Take the measurement of the reference circumference at a position where work conditions allow reliable

measurements and that is within the focal range of the optical instrument. Strap the tank, aiming at one of

the following levels:
1) about 1/4 of the course height above the lower horizontal seam,
2) about 1/4 of the course height below the upper horizontal seam,

and repeat the measurement to achieve agreement within the tolerances specified in Table 4.

11.2.2 Theodolite readings

11.2.2.1 Set up the theodolite outside the tank, as shown in Figure 5 for eight theodolite stations and as

described in 6.3.

The minimum number of stations (T1, T2, etc.) per circumference shall be as given in Table 2.

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Key
T1 …… T8 theodolite stations
Figure 5 — Example of theodolite station locations for external procedures
based on a reference circumference
Table 2 — Minimum number of theodolite stations for external procedures
Tank circumference Minimum number of stations
u 50 5
> 50, u 100 6
> 100, u 150 8
> 150, u 200 10
> 200, u 250 12
> 250, u 300 15
> 300 18

To avoid systematic errors, the number of stations divided by the number of plates in the tank segments

should not be equal to an integer (e.g. 1, 2, 3, etc.).

The theodolite positions should be such that the targets avoid the vertical welds between tank segments.

Care should be taken, especially for smaller tanks, that the target points are evenly distributed around the tank.

11.2.2.2 From each station and for each level (see 11.2.2.3 and 11.2.2.4), make a sighting tangentially to

the tank on either side of the theodolite as shown in Figure 5. Maintain the same vertical angle of the

theodolite in both sightings.

NOTE This ensures that the intended targets on the tank are at the same level for a given circumference.

Record the horizontal angles subtended by the tangents at the theodolite.
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11.2.2.3 Make sightings at the height at which the reference circumference was measured (see 11.2.1).

The angles at the strapped height shall be measured twice (before and after measurements of the angles at

other heights; see 11.2.2.4). The subtended angles shall agree with each other to within 0,01 gon. If they do

not, repeat the measurements until two standard deviations from the mean fit within 1/2 of this tolerance. In

further calculations, use the average and standard de
...

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