1、BRITISH STANDARD BS 7723-2: 1994 ISO 7507-2: 1993 Methods for calibration of vertical cylindrical tanks for petroleum and liquid petroleum products Part 2: Optical-reference-line method UDC 665.6:621.642.3:531.731:53.089.6BS7723-2:1994 This British Standard, having been prepared under the direction
2、of the Petroleum Standards Policy Committee, was published under the authority of the Standards Boardand comes into effect on 15January 1994 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference PTC/12 Draft for comment 87/52651 DC ISBN 0 580 22670 0 Commi
3、ttees responsible for this British Standard The preparation of this British Standard was entrusted by the Petroleum Standards Policy Committee (PTC/-) to Technical Committee PTC/12, upon which the following bodies were represented: Department of Trade and Industry (Gas and Oil Measurement Branch) De
4、partment of Trade and Industry (National Engineering Laboratory) Institute of Petroleum Royal Institution of Naval Architects Salvage Association The following body was also represented in the drafting of the standard, through subcommittees and panels: GAMBICA (BEAMA Ltd.) Amendments issued since pu
5、blication Amd. No. Date CommentsBS7723-2:1994 BSI 09-1999 i Contents Page Committees responsible Inside front cover National foreword ii Introduction 1 1 Scope 1 2 Normative references 1 3 Definitions 1 4 Precautions 1 5 Equipment 1 6 Procedure 2 7 Tolerances 6 8 Tank capacity calculation procedure
6、6 Annex A (normative) Method for calibrating bottoms of tanks 7 Annex B (normative) Specification for equipment used in strapping 7 Figure 1 Optical measurement of offsets from tank wall (typical case) 3 Figure 2 Determination of internal radius from offsets to external opticalreference line 4 Figur
7、e 3 Determination of internal radius from offsets to internal opticalreference line 4 Table 1 Minimum number of stations 5 List of references Inside back coverBS7723-2:1994 ii BSI 09-1999 National foreword This Part of BS 7723 has been prepared under the direction of the Petroleum Standards Policy C
8、ommittee. It is identical with ISO7507-2:1993 Petroleum and liquid petroleum products Calibration of vertical cylindrical tanks Part 2: Optical-reference-line method, published by the International Organization for Standardization (ISO). ISO7507-2 was prepared by Subcommittee3, Static petroleum meas
9、urement, of Technical Committee28, Petroleum products and lubricants, in which the United Kingdom participated. This British Standard forms part of a series, each Part of which is identical with the corresponding Part of ISO7507 and it is envisaged that BS7723 will consist of the following Parts: Pa
10、rt 1: Strapping method; Part 2: Optical-reference-line method; Part 3: Optical-triangulation method; Part 4: Internal electro-optical distance-ranging methods 1) ; Part 5: External electro-optical distance-ranging methods 1) . CAUTION. Attention is drawn to the Health and Safety at Work etc. Act1974
11、, and the need for ensuring that the methods specified in this Part of BS7723 are carried out with suitable precautions. The methods described in this Part of BS7723 are intended to be carried out by appropriately qualified and experienced persons or other suitable trained and/or supervised personne
12、l. Normal safety precautions should be observed in the use of the methods. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer
13、 immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 10, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated i
14、n the amendment table on the inside front cover. 1) In preparation. Cross-references International Standard Corresponding British Standard ISO 91-1:1992 BS 6441:1993 Schedule for petroleum measurement tables (Identical) ISO 7507-1:1993 BS 7723 Methods for calibration of vertical cylindrical tanks fo
15、r petroleum and liquid petroleum products Part 1:1993 Strapping method (Identical)BS7723-2:1994 BSI 09-1999 1 Introduction This method describes the calibration of vertical cylindrical tanks by measurement of one reference circumference by strapping and then determining the remaining circumferences
16、at different levels from measurements of radial offsets from vertical optical reference lines. These circumferences are corrected to give the true internal circumferences. This method is an alternative to other methods such as strapping (ISO7507-1) and the optical-triangulation method (ISO7507-3). 1
17、 Scope 1.1 This part of ISO7507 specifies a method for the calibration of tanks above8m 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 optical (offset) measurement
18、s required to determine the circumferences may be taken internally or externally. 1.2 Abnormally deformed, e.g. dented or non-circular, tanks are excluded from this part of ISO7507. 1.3 This method is suitable for tilted tanks up to3% deviation from the vertical provided that a correction is applied
19、 for the measurement tilt, as described in ISO7507-1. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this part of ISO7507. At the time of publication, the editions indicated were valid. All standards are subject to re
20、vision, and parties to agreements based on this part of ISO7507 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 91-1:1992, Petroleum measurem
21、ent tables Part 1: Tables based on reference temperatures of15 C and60degrees F. ISO 7507-1:1993, Petroleum and liquid petroleum products Calibration of vertical cylindrical tanks Part 1: Strapping method. 3 Definitions For the purposes of this part of ISO 7507, the definitions given in ISO7507-1 ap
22、ply. 4 Precautions The general precautions and safety precautions specified in ISO7507-1 shall apply to this part of ISO7507. 5 Equipment 5.1 Equipment for tank strapping, as listed in5.1.1 to5.1.5 below and specified inAnnex B: 5.1.1 Strapping tapes. 5.1.2 Spring balance. 5.1.3 Step-over. 5.1.4 Lit
23、tlejohn grip. 5.1.5 Dip-tape and dip-weight. 5.2 Thermometer. 5.3 Tank bottom calibration equipment, as specified inAnnex A. 5.4 Optical-reference-line device, e.g. a precision optical plummet, a precision engineers level with a pentaprism attachment, or a precision engineers theodolite with a penta
24、prism attachment. NOTE 1These are optical instruments with a means of attachment to either a tripod, magnetic bracket or other stable means of support. The instrument, when set on its support and levelled, either manually using bubble vials or automatically if an automatic levelling device is fitted
25、, shall be capable of giving a vertical line of sight. NOTE 2The instrument should preferably be of short focal length so that, when set up at a practical working height, it can be focused on the scale at the reference strapping level. The instrument shall have a resolution of at least1:20000 and be
26、 equipped with a telescope with a magnification of not less than20. The pentaprism attachment for use with an engineers level or engineers theodolite shall not introduce any collimation errors. NOTE 3Optical plummets may be fitted with either a single optical train, i.e. a zenith plummet, or a doubl
27、e optical train or a single superimposed optical train giving both upward and downward lines of sight, i.e.a nadir/zenith plummet. It is preferable that the plummet does not have any movable elements in its optical train, such as mirrors or pentaprisms, to ensure stability of the line of sight. 5.5
28、Magnetic trolley, of robust construction. Its design shall include the following features: a) The magnet(s) shall be of sufficient power to ensure that the trolley does not lose contact with the tank shall in conditions of high wind or when ring joints have to be negotiated or when there are heavy l
29、ayers of paint or scale.BS7723-2:1994 2 BSI 09-1999 b) The magnet(s) shall be adjustable for height so that the clearance between the magnet faces and the tank may be varied to suit the tank construction and condition. c) A cord or wire cable shall be attached to enable it to be raised or lowered fr
30、om the tank roof or, via a pulley system, from ground level. d) A graduated scale shall be attached securely to the trolley at its centreline. When the trolley is in its operational mode, the scale shall be perpendicular to the tank shell. e) The scale shall be attached to the trolley as closely as
31、possible to the centreline of an axle in order to reduce errors caused by deformations in the tank. 5.6 Graduated scale, made of translucent plastic and marked in millimetre increments. The length of the scale shall be as short as is practicable and shall be determined by the distance at which the o
32、ptical equipment can be set up from the tank side. 6 Procedure 6.1 Principle This calibration method is based on the accurate measurement of a reference circumference using a calibrated measuring tape at one level on an accessible, non-obstructed course. Repeat measurements agreeing within specified
33、 tolerances are made to avoid any systematic error in the derived circumferences. The derived circumferences are calculated from the reference circumference, and measurements of offsets taken at the specified levels and at the reference circumference. These offsets are a measure of the deviation of
34、the tank wall. They are measured at a specified number of vertical, optical reference lines spaced equally around the tank. NOTE 4For examples seeFigure 1 toFigure 3. 6.2 Preparation of tank Fill the tank to its normal working capacity at least once and allow it to stand for at least24h prior to cal
35、ibration. If the tank is calibrated with liquid in it, record the depth, temperature and density of the liquid at the time of calibration. However, if the temperature of the wall surface could differ by more than10 C between the empty part and full part of the tank, the tank shall be completely full
36、 or empty. Do not make transfers of liquid during the calibration. For floating-roof tanks where offset measurements may be taken internally, the roof shall be in its lowest position, resting on the legs. 6.3 Reference circumference Determine the reference circumference using the reference method de
37、scribed in ISO7507-1 and the following: a) Take the measurement of the reference circumference prior to the commencement of the optical readings. b) Take the measurement of the reference circumference at a position where work conditions allow reliable measurements, and which is within the focal rang
38、e of the optical instrument. Strap the tank at one of the following levels: 1) 1/5 to 1/4 of the course height above the lower horizontal seam, 2) 1/5 to 1/4 of the course height below the upper horizontal seam and repeat the measurement to achieve measurements agreeing within the tolerances specifi
39、ed in7.1. If the circumference cannot be measured on the outside, measure the inside diameters by a method that will provide a degree of precision equal to that obtained by using the external strapping method. c) After completion of the optical readings, repeat the reference circumference measuremen
40、t. d) The measurements required in a) and c) shall agree within the tolerances specified in7.1. e) If agreement is not obtained, take further measurements of the reference circumference until two consecutive readings do so agree. f) Record the arithmetic mean of two valid measurements as the referen
41、ce circumference. If no agreement between the two readings is obtained, repeat the calibration procedure. 6.4 Offset readings 6.4.1 Set up the optical-reference-line device (5.4), magnetic trolley (5.5) and graduated scale (5.6) successively at the measurement stations (see6.4.2) that are equally sp
42、aced around the tank, as close as possible, but not closer than100mm to the tank wall. No reference line shall be closer than300mm to a vertical seam. 6.4.2 The minimum number of optical-reference-line stations shall be as given inTable 1.BS7723-2:1994 BSI 09-1999 3 NOTEThe reference line stations a
43、re designated A to H in the plan view (see also6.4.2). Of these, only E and F are shown in the elevation. The horizontal levels are indicated by the numbers1to7(see6.4.4). Figure 1 Optical measurement of offsets from tank wall (typical case)BS7723-2:1994 4 BSI 09-1999 Figure 2 Determination of inter
44、nal radius from offsets to external optical reference line Figure 3 Determination of internal radius from offsets to internal optical reference lineBS7723-2:1994 BSI 09-1999 5 Table 1 Minimum number of stations 6.4.3 Verify the verticality of the optical reference line prior to the commencement of r
45、eadings by turning the optical instrument at the first station through180 , whereby the difference between the two readings of the diametrically opposite positions shall be within1in20000. Also verify the verticality of the optical reference line at each station by frequently checking the levelling
46、device. 6.4.4 Take a minimum of two radial measurements per course at each station, one at1/5to1/4of course height above the lower horizontal seam, the other at1/5to1/4of course height below the upper horizontal seam. Read the graduated scale to the nearest millimetre. The graduated-scale reading sh
47、all be repeatable to within1mm radial distance. 6.4.5 At all stations, measure the reference offset and then take offset measurements progressively on each course as the trolley is raised up the tank wall. After the last offset measurement has been taken on the top course, lower the trolley to the b
48、ottom course and repeat the reference offset. The initial and final reference offset readings shall agree to within1mm. If agreement is not obtained, take and record a further set of measurements until a set is obtained in which the initial and final reference offset readings agree to within1mm. Tak
49、e the average of these two reference readings as the reference offset. 6.5 Tank bottom calibration Calibrate the tank bottom preferably by filling with measured quantities of a non-volatile liquid (preferably clean water) as specified inAnnex A to a minimum level that covers the bottom completely, immersing the dip-plate and eliminating the effect of bottom deformations, or, alternatively, by a physical survey using a reference plane to determine the shape of the bottom. 6.6 Other measurements 6.6.1 Determine and process the followin
