EN ISO 8311:2013
(Main)Refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels - Calibration of membrane tanks and independent prismatic tanks in ships - Manual and internal electro-optical distance-ranging methods (ISO 8311:2013)
Refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels - Calibration of membrane tanks and independent prismatic tanks in ships - Manual and internal electro-optical distance-ranging methods (ISO 8311:2013)
ISO 8311:2013 specifies a method for the internal measurement of membrane tanks used in ships for the transport of refrigerated light hydrocarbon fluids. In addition to the actual process of measurement, it sets out the calculation procedures for compiling the tank capacity table and correction tables to be used for the computation of cargo quantities. ISO 8311:2013, with some modification, can also be applicable to the calibration of independent prismatic tanks.
Gekühlte Kohlenwasserstoffe und verflüssigte, nicht auf Erdöl basierende gasförmige Brennstoffe - Kalibrierung von Membrantanks und unabhängigen Prismentanks in Schiffen - Manuelle Messung und Innenmessung nach dem elektrooptischen Distanzmessverfahren (ISO 8311:2013)
Diese Internationale Norm legt ein Verfahren zur Innenmessung von Membrantanks in Schiffen, die für den Transport von durch Abkühlung verflüssigten leichten Kohlenwasserstoffen vorgesehen sind, fest. Außer dem Messvorgang selbst werden die Verfahren beschrieben, mit deren Hilfe sich Tabellen für die Tankkapazität und Korrekturtabellen zur Berechnung der mengenmäßigen Schiffsladung aufstellen lassen. Diese Internationale Norm kann mit einigen Modifikationen auch für die Kalibrierung unabhängiger Tanks in prismatischer Form angewendet werden.
Für die in dieser Internationalen Norm beschriebenen Verfahrensabläufe wird bei der manuellen Messung von Membrantanks zum Abstützen der Messgeräte das Gerüst verwendet, mit dem die Membran aufgestellt wurde; für das interne elektrooptische Distanzmessverfahren (EDM) sollten jedoch andere Hilfsmittel für den Zugriff auf die benötigten Messpositionen angewendet werden.
Hydrocarbures réfrigérés et combustibles gazeux liquéfiés à base non pétrolière - Étalonnage des réservoirs à membrane et réservoirs pyramidaux - Méthodes manuelles et par mesurage électro-optique interne de la distance (ISO 8311:2013)
L'ISO 8311:2013 spécifie une méthode pour le mesurage interne des réservoirs à membrane équipant les navires transporteurs d'hydrocarbures légers réfrigérés. Outre le processus de mesurage proprement dit, elle établit les méthodes de calcul permettant d'élaborer la table de jaugeage du réservoir ainsi que les tables de correction à utiliser pour le calcul des quantités de cargaison. L'ISO 8311:2013 peut également s'appliquer, moyennant quelques modifications, au jaugeage des réservoirs pyramidaux autoporteurs.
Ohlajena utekočinjena plinasta goriva naftnega in nenaftnega izvora - Kalibracija membranskih rezervoarjev in samostojnih prizmatičnih rezervoarjev na ladjah - Ročne in notranje električno-optične distančne meritvene metode (ISO 8311:2013)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-februar-2014
1DGRPHãþD
SIST EN ISO 8311:1998
2KODMHQDXWHNRþLQMHQDSOLQDVWDJRULYDQDIWQHJDLQQHQDIWQHJDL]YRUD.DOLEUDFLMD
PHPEUDQVNLKUH]HUYRDUMHYLQVDPRVWRMQLKSUL]PDWLþQLKUH]HUYRDUMHYQDODGMDK
5RþQHLQQRWUDQMHHOHNWULþQRRSWLþQHGLVWDQþQHPHULWYHQHPHWRGH ,62
Refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels - Calibration
of membrane tanks and independent prismatic tanks in ships - Manual and internal
electro-optical distance-ranging methods (ISO 8311:2013)
Gekühlte Kohlenwasserstoffe und verflüssigte, nicht auf Erdöl basierende gasförmige
Brennstoffe - Kalibrierung von Membrantanks und unabhängigen Prismentanks in
Schiffen - Manuelle Messung und Innenmessung nach dem elektrooptischen
Distanzmessverfahren (ISO 8311:2013)
Hydrocarbures réfrigérés et combustibles gazeux liquéfiés à base non pétrolière -
Étalonnage des réservoirs à membrane et réservoirs pyramidaux - Méthodes manuelles
et par mesurage électro-optique interne de la distance (ISO 8311:2013)
Ta slovenski standard je istoveten z: EN ISO 8311:2013
ICS:
47.020.85 Prostori za tovor Cargo spaces
75.180.30 Oprema za merjenje Volumetric equipment and
prostornine in merjenje measurements
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN STANDARD
EN ISO 8311
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2013
ICS 75.180.30 Supersedes EN ISO 8311:1995
English Version
Refrigerated hydrocarbon and non-petroleum based liquefied
gaseous fuels - Calibration of membrane tanks and independent
prismatic tanks in ships - Manual and internal electro-optical
distance-ranging methods (ISO 8311:2013)
Hydrocarbures réfrigérés et combustibles gazeux liquéfiés à Gekühlte Kohlenwasserstoffe und verflüssigte, nicht auf
base non pétrolière - Étalonnage des réservoirs à Erdöl basierende gasförmige Brennstoffe - Kalibrierung von
membrane et réservoirs pyramidaux - Méthodes manuelles Membrantanks und unabhängigen Prismentanks in Schiffen
et par mesurage électro-optique interne de la distance (ISO - Manuelle Messung und Innenmessung nach dem
8311:2013) elektrooptischen Distanzmessverfahren (ISO 8311:2013)
This European Standard was approved by CEN on 9 November 2013.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2013 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 8311:2013 E
worldwide for CEN national Members.
Contents Page
Foreword .3
Foreword
This document (EN ISO 8311:2013) has been prepared by Technical Committee ISO/TC 28 “Petroleum
products and lubricants” in collaboration with Technical Committee CEN/TC 19 “Gaseous and liquid fuels,
lubricants and related products of petroleum, synthetic and biological origin” the secretariat of which is held by
NEN.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by June 2014, and conflicting national standards shall be withdrawn at
the latest by June 2014.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 8311:1995.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Endorsement notice
The text of ISO 8311:2013 has been approved by CEN as EN ISO 8311:2013 without any modification.
INTERNATIONAL ISO
STANDARD 8311
Second edition
2013-12-01
Refrigerated hydrocarbon and non-
petroleum based liquefied gaseous
fuels — Calibration of membrane tanks
and independent prismatic tanks in
ships — Manual and internal electro-
optical distance-ranging methods
Hydrocarbures réfrigérés et combustibles gazeux liquéfiés à base non
pétrolière — Étalonnage des réservoirs à membrane et réservoirs
pyramidaux — Méthodes manuelles et par mesurage électro-optique
interne de la distance
Reference number
ISO 8311:2013(E)
©
ISO 2013
ISO 8311:2013(E)
© ISO 2013
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested 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
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Published in Switzerland
ii © ISO 2013 – All rights reserved
ISO 8311:2013(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Precautions . 3
4.1 General . 3
4.2 Ship’s condition during calibration . 3
4.3 Tank distortion . 3
4.4 Comparison with drawings . 4
4.5 Measurements by measuring tape . 4
4.6 Measurements by electro-optical distance-ranging (EODR) instrument . 4
4.7 Condition of membrane. 5
4.8 Safety precautions for work in membrane tanks . 5
5 Equipment . 5
6 Determination of measuring points . 6
7 Calibration by manual method . 6
7.1 General . 6
7.2 Tank length measurement . 7
7.3 Tank width measurement . 9
7.4 Tank height measurement .12
7.5 Measurement of bottom undulation and gauge reference height .14
7.6 Correction for temperature .15
8 Calibration by electro-optical distance-ranging (EODR) method .16
8.1 General .16
8.2 Setting up of EODR instrument . .16
8.3 Calibration procedure .17
9 Additional measurements .19
9.1 Location of level gauge .19
9.2 Deadwood . .19
10 Calculation .19
10.1 General .19
10.2 Calculation of tank volume .20
10.3 Effect of bottom undulation .20
10.4 Area of chamfer portion .20
10.5 Trim corrections .21
10.6 List corrections .21
10.7 Combined trim and list corrections .21
10.8 Correction for tank shell expansion or contraction .21
11 Report and tables .22
12 Recalibration .23
Annex A (informative) Uncertainty associated with tank calibration .24
Annex B (informative) Example of tank capacity table (Tank No.3) .36
Annex C (informative) Example of trim correction table (Tank No. 1) .38
Annex D (informative) Example of list correction table (Tank No. 1) .40
Bibliography .42
ISO 8311:2013(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directives
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received. www.iso.org/patents
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 28, Petroleum products and lubricants, Subcommittee
SC 5, Measurement of refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels.
This second edition cancels and replaces the first edition (ISO 8311:1989), which has been technically revised.
iv © ISO 2013 – All rights reserved
ISO 8311:2013(E)
Introduction
Large quantities of light hydrocarbons consisting of compounds having one to four carbon atoms are
stored and transported by sea as refrigerated liquids at pressures close to atmospheric. These liquids
can be divided into two main groups, liquefied natural gas (LNG) and liquefied petroleum gas (LPG).
Bulk transportation of these liquids requires special technology in ship design and construction to
enable ship-borne transportation to be safe and economical.
Quantification of these cargoes in ships’ tanks for custody transfer purposes has to be of a high order of
accuracy. This International Standard (together with others in the group) specifies methods of internal
measurement of ships’ tanks, from which tank capacity tables can be derived.
This International Standard covers calibration techniques applicable to membrane type tanks, i.e. self-
supporting independent tanks in which the containment system comprises a relatively thin membrane
of either stainless steel or high-nickel steel alloy. This International Standard, with some modification,
can also be applicable to the calibration of independent prismatic tanks.
Annex A gives uncertainty associated with the measurement of membrane tanks.
Annex B gives an example of a tank capacity table relating partial filling volume as a function of liquid
level and Annexes C and D give examples of trim correction and list correction tables, respectively.
INTERNATIONAL STANDARD ISO 8311:2013(E)
Refrigerated hydrocarbon and non-petroleum based
liquefied gaseous fuels — Calibration of membrane tanks
and independent prismatic tanks in ships — Manual and
internal electro-optical distance-ranging methods
1 Scope
This International Standard specifies a method for the internal measurement of membrane tanks used
in ships for the transport of refrigerated light hydrocarbon fluids. In addition to the actual process of
measurement, it sets out the calculation procedures for compiling the tank capacity table and correction
tables to be used for the computation of cargo quantities. This International Standard, with some
modification, can also be applicable to the calibration of independent prismatic tanks.
For the manual measurement of membrane tanks, the procedures of this International Standard utilize
the scaffolding used for the installation of the membranes to support the measuring equipment but, for
the internal electro-optical distance-ranging (EODR) method, other safe means of access to the required
measuring positions are intended to be used.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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
ISO 7507-4:2010, Petroleum and liquid petroleum products — Calibration of vertical cylindrical tanks —
Part 4: Internal electro-optical distance-ranging method
IEC 60079-10-1, Explosive atmospheres — Part 10-1: Classification of areas — Explosive gas atmospheres
IEC 60079-10-2, Explosive atmospheres — Part 10-2: Classification of areas — Combustible dust atmospheres
IEC 60825-1, Safety of laser products — Part 1: Equipment classification and requirements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
automatic tank gauge
ATG
automatic level gauge
ALG
instrument that continuously measures liquid height (dip or ullage) in storage tanks
3.2
chamfer
slanting surface connecting the walls of a tank with its top or bottom surface
ISO 8311:2013(E)
3.3
deadwood
any tank fitting that affects the capacity of a tank
3.4
gauge reference point
point from which the liquid depth are measured
3.5
horizontal plane
any plane established parallel to the tank bottom
3.6
horizontal reference line
any horizontal line established by a string
Note 1 to entry: A calibration method using this line is adopted as an alternative to direct measurements, where
it is considered impractical to take direct measurements.
3.7
list
transverse inclination of a ship
Note 1 to entry: It is expressed in degrees.
3.8
longitudinal line
line formed by a longitudinal plane crossing a horizontal plane
3.9
longitudinal plane
vertical plane running parallel to the centreline of the tank
3.10
measuring point
one of a series of points on the inside surface of the tank shell from/to which the distance is measured by a
tape or a hand-held laser distance meter in case of manual method, or to which the slope distance, vertical
angles and horizontal angles are measured by use of the electro-optical distance-ranging instrument
3.11
port
left-hand side of a ship facing forward
3.12
reference target point
fixed point clearly marked on the inside surface to the tank shell or a prism mounted on a tripod
3.13
section line
line formed by a section plane crossing a horizontal plane
3.14
section plane
plane parallel with the fore and aft end walls of a ship’s tank
3.15
slope distance
distance measured from the electro-optical distance-ranging instrument to any measuring point or a
reference target point
2 © ISO 2013 – All rights reserved
ISO 8311:2013(E)
3.16
starboard
right-hand side of a ship facing forward
3.17
tank-calibration reference temperature
temperature at which the calibration of a tank has been calculated
3.18
tank capacity table
tank table
calibration table
capacity table
table showing the capacities of, or volumes in, a tank corresponding to various liquid levels measured
from a reference point
3.19
trim
difference between the fore and aft draught of the vessel
Note 1 to entry: When the aft draught is greater than the forward draught, the vessel is said to be trimmed by the
stern. When the aft draught is less than the forward draught, the vessel is said to be trimmed by the head.
3.20
uncertainty
U()
estimate characterizing the range of values within which the true value of a measurand lies
Note 1 to entry: Various types of uncertainty are defined in ISO/IEC Guide 98-3.
3.21
vertical line
line formed by a section plane on the side walls and formed by a longitudinal plane on the fore and
aft end walls
4 Precautions
4.1 General
This clause outlines the precautions to be taken during measurement. Utmost care and attention shall
be exercised in taking measurements, and any unusual occurrence during the measuring work, which
might affect the results, shall be recorded.
4.2 Ship’s condition during calibration
The calibration methods described in this International Standard may be applied to ships whether afloat
or in a dry dock. However, its use for ships in a dry dock is preferred, because trim or list, if any, will
remain the same throughout the calibration procedure. Adjustments, manually or automatically shall be
made to any measurement by optical level and EODR if the ship’s attitude has changed.
4.3 Tank distortion
If unusual distortion is found in the tank, additional measurement shall be taken by the calibrator as
considered necessary and sufficient. Notes by the calibrator detailing the extra measurements and the
reasons for them shall be included in the calibration report.
The calibrator shall provide detailed sketches of any abnormality of the tank or its fittings where such
sketches can materially assist the interpretation of the recorded data.
ISO 8311:2013(E)
4.4 Comparison with drawings
If drawings for the tank are available, all measurements taken shall be compared with the corresponding
dimensions shown on the drawings. Any measurement showing a significant discrepancy in this
comparison shall be rechecked; however, the tank capacity table shall be based on the actual
measurements.
4.5 Measurements by measuring tape
When measurements are made with a measuring tape:
a) the tension specified in the tape calibration certificate shall be applied;
b) the measuring tape shall be supported so as to prevent it from sagging. If tape sag is unavoidable,
the calibrator shall note this and a catenary correction shall be applied during calculation;
c) take multiple measurements. If the first three consecutive measurements agree within the
tolerances specified in d) below, take their mean as the measurement and their standard deviation
as the standard uncertainty. If they do not agree within the tolerances specified in d) below, repeat
the measurements until two standard deviations of the mean of all measurements is less than the
half of the tolerance specified in d) below. Use the mean as the measurement and the standard
deviation as the standard uncertainty. Use standard procedures to eliminate obvious outliers;
d) the following table shows the tolerances against the measurement distance:
Measurement Tolerance within
Up to 25 m 2 mm
over 25 m 3 mm
for offset 0,5 mm
e) if the measurements have been interrupted, the last measurements shall be repeated. If the new
measurements do not agree, within the required tolerance, with the earlier measurements, then the
earlier set shall be rejected.
4.6 Measurements by electro-optical distance-ranging (EODR) instrument
When measurements are carried out with an EODR instrument:
a) the electro-optical distance-ranging instrument shall be verified prior to calibration. The accuracy
of the distance-ranging unit as well as the angular measuring unit shall be verified using the
procedures given by ISO 7507-4:2010, Annex A;
b) the tank shall be free from vibration and air-borne dust particles. The floor of the tank should be as
free as possible from debris, dust and scales;
c) lighting, when required, shall be placed within the tank so as not to interfere with the operation the
EODR instrument;
d) the laser beam fitted to the EODR instrument shall be operated in conformity with IEC 60825-1.
The hazards, if any, in the area in which the calibration is to be carried out shall be assessed in
accordance with IEC 60079-10. The instrument to be used shall be declared (certified) as being safe
for use in the area of operation.
4 © ISO 2013 – All rights reserved
ISO 8311:2013(E)
4.7 Condition of membrane
Care shall be taken to ensure that the membrane is in contact with the supporting material. In some
cases, it may be possible to ensure this contact by applying a vacuum to the space behind the membrane.
4.8 Safety precautions for work in membrane tanks
a) All regulations covering entry into hazardous areas shall be rigorously observed.
b) Before a tank which has been in use is entered, a safe-entry certificate issued in accordance with local
or national regulations shall be obtained. All lines entering the tank shall be disconnected and blanked.
c) Hand lamps and other electric instruments shall be of a type approved for use in explosive atmospheres.
d) The safety of operating personnel shall be safeguarded by strict attention to the following.
1) Ladders shall be inspected before use, and extendable ladders used only within their safe
operating range. The footing for each ladder shall be level and firm, and all ladders shall be
securely lashed in position before being used.
2) Where painters’ cradles or boatswains’ (bo’suns’) chairs are used, blocks, falls, ropes, etc., shall
be tested before erection, and any item of questionable strength or condition shall be replaced.
Every care shall be paid to the securing of the equipment and its operational use.
3) If calibration cannot be carried out without the use of scaffoldings, properly constructed steel
tube or timber scaffolding shall be erected. Loose bricks, drums, boxes, etc., shall not be used to
form staging. Special attention shall be paid at the corners of the scaffolding. It is not uncommon
for a plank to be moved from its position on the scaffolding when the tank wall is being lined
with membranes.
4) Where appropriate, safety harnesses shall be worn by the calibrator working above ground level.
e) In some cases, edges of the anchor plates projecting from membrane can be sharp. The use of
protective gloves and helmets is especially advised.
f) Care shall be taken not to damage the membranes with shoes, measuring equipment, etc.
5 Equipment
The equipment used to calibrate the tanks in accordance with this International Standard are intended
to confirm to the relevant national or other standard.
5.1 Electro-optical distance-ranging (EODR) instrument, capable of achieving uncertainties of
tank volumes acceptable in legal metrology. The angular measuring part of the instrument should have a
−6
resolution of equal to or better than 3,142 × 10 rad (0,2 mgon), and the distance-measuring part of the
instrument, which is to be used for direct determination of distances, should have a resolution of equal to
or better than 1 mm.
The accuracy of EODR equipment can be affected by variations of temperature. The manufacturer’s
guidance should be followed.
5.2 Hand-held laser distance meter, which may be used, instead of measuring tape, to measure the
distance. The hand-held laser distance meter should have a resolution of equal to or better than 1 mm.
5.3 Measuring tape, complying with the specifications for strapping tapes given in ISO 7507-1 or equivalent.
5.4 Automatic level, having an erect image and a magnification of × 20 or greater, capable of being
focused to 1,5 m or less and with a spirit level sensitivity of 40 s of arc per 2 mm or less.
ISO 8311:2013(E)
5.5 Rule, with graduations in centimetres and millimetres, used to measure deadwood, the offsets
between the strings and the tank walls in the case of the manual method, etc. If a wooden rule is used, it
shall be fitted with a brass ferrule at each end and shall be free of warp.
5.6 Thermometer, having a suitable range, of an accuracy of ±0,5 °C.
A mercury thermometer should not be used.
6 Determination of measuring points
The calibration of membrane tanks is basically the measurement of the tank length, width and height
between known points. These measuring points are determined by setting out a number of horizontal,
longitudinal and section planes.
These planes intersect to form lines along which the measurements of length, width and height shall
be taken. The various planes shall be set out at intervals not greater than 5 m; the interval shall be
adjusted so that the resulting measurements reflect any change of section and adequately describe any
deformation. The points at which measurements are to be taken shall be determined by the calibrator
but shall not be more than 5 m apart.
Having determined the measuring points, mark the lines which run on the tank inner walls. Mark the
section and longitudinal lines on the top and bottom plates, horizontal and vertical lines on the fore and
aft end walls and horizontal and vertical lines on the port and starboard end walls. When measurements
are made by an EODR, coordinates of the planned measuring points may be stored in the instrument
instead of actually marking the lines or points on the tank inner walls.
7 Calibration by manual method
7.1 General
In the manual method, measurements of the distances between opposite walls of a tank shall be taken
by tensioning the tape as specified on the tape certificate. A hand-held laser distance meter, in place of a
tape, may be used for the direct measurements.
The lengths of the tanks shall be measured along all the longitudinal lines at each level of the horizontal
planes in accordance with 7.2.
The widths of the tanks shall be measured along all the section lines set in each horizontal plane in
accordance with 7.3.
The total heights, upper chamfer heights and side wall heights shall be measured and from these lower
chamfer heights shall be calculated in accordance with 7.4.
Annex A gives uncertainty associated with the measurement of membrane tanks with the manual method.
6 © ISO 2013 – All rights reserved
ISO 8311:2013(E)
7.2 Tank length measurement
7.2.1 Length measurement on the bottom plate
Measure the distances between the fore and aft end walls along all the longitudinal lines marked on
the bottom plate with a measuring tape stretched thereon. The average length on the bottom plate is
calculated using Formula (1):
n
L = L (1)
ll∑ ,i
n
i=1
where
L is the length of a longitudinal line on the bottom plate;
l,i
L is the average length of the bottom plate;
l
n is the number of longitudinal lines on the bottom plate.
7.2.2 Length measurement on the top plate
Measure the distances on the top plate in a manner similar to that for the bottom plate (see 7.2.1). Care
shall be taken to keep the measuring tape in contact with the top plate. The average length on the top
plate is calculated using Formula (2):
n
L = L (2)
uu,i
∑
n
i=1
where
L is the length of a longitudinal line on the top plate;
u,i
L is the average length of the top plate;
u
n is the number of longitudinal lines on the top plate.
7.2.3 Length measurement in an intermediate horizontal plane
To avoid inaccurate measurement due to excessive sagging of the measuring tape, apply the horizontal
reference line method using a string line.
As shown in Figure 1, lengths in these imaginary planes can be obtained by applying offset corrections
at both ends, a , a … a and b , b … b , to the length measured directly on the side wall. In practice,
2 3 n-1 2 3 n-1
carry out the following.
a) Mark P and P , S and S , on both side walls at equal distances from the end walls. Measure the
1 2 1 2
length (L , L ) between the fore and aft end walls with a measuring tape extended along both side
P S
walls, supporting the tape on the wall to prevent it from sagging.
b) Stretch strings between the opposite points P and S , P and S , and measure the offsets between
1 1 2 2
the strings and the end walls (a , a … a and b , b … b ) with a rule.
1 2 n 1 2 n
c) In measuring these offsets, take care to put the measuring rule at a right angle to the string.
ISO 8311:2013(E)
The average length of an intermediate horizontal plane, L is calculated using Formula (3):
m,p
n
ab+
()
∑ ii
LL+− aa++bb+
()
ps 11nn
i=1
L = + (3)
m,p
2 n
The averaged length of intermediate part, L , is calculated using Formula (4):
m
p−1
L = L (4)
m m,p
∑
p−2
j=2
where p is the number of intermediate planes.
Key
1 port side wall 4 string line
2 aft end wall 5 longitudinal lines
3 fore end wall 6 starboard side wall
L length of port side wall
P
L length of starboard side wall
S
P , P , S , S markings on both side walls at equal distances from end walls
1 2 1 2
a , a … a offsets between strings and end walls
1 2 n
and b , b
1 2
… b
n
Figure 1 — Plan view of an intermediate horizontal plane
8 © ISO 2013 – All rights reserved
ISO 8311:2013(E)
7.2.4 Tank length
The tank length, L, is calculated from L , L and L :
u m l
Lp×−()2 ++LL
mlu
L= (5)
p
Alternatively, another formula of equal or better accuracy may be used when it is considered adequate
in the light of the shape of the tank.
7.3 Tank width measurement
7.3.1 Width measurement on the bottom plate
Measure distances between side walls along all the section lines marked on the bottom plate with a
measuring tape stretched thereon. The average width on the bottom plate is calculated using Formula (6):
n
w = w (6)
ll,i
∑
n
i=1
where
w is the width of a section line on the bottom plate;
l,i
w is the average width of the bottom plate;
l
n is the number of section lines on the bottom plate.
7.3.2 Width measurement on the top plate
Measure distances on the top plate in a manner similar to that for the bottom plate (see 7.3.1). Care shall
be taken to keep the measuring tape in contact with the top plate. The average width on the top plate is
calculated using Formula (7):
n
w = w (7)
uu,i
∑
n
i=1
where
w is the width of a section line on the top plate;
u,i
w is the average width of the top plate;
u
n is the number of section lines on the top plate.
7.3.3 Width measurement on an intermediate horizontal plane
Measure tank width in the same way as in the length measurement by actual measurement of w and w
f a
in combination with the string as shown in Figure 2.
ISO 8311:2013(E)
The average width of an intermediate horizontal plane, w is calculated using Formula (8):
m,p
n
cd+
()
∑ ii
ww+−()cc++dd+
f1a nn1
i=1
w = + (8)
m,p
2 n
The average of the averaged length of intermediate part, w , is calculated using Formula (9):
m
p−1
w = w (9)
mm,p
∑
p−2
j=2
where p is the number of intermediate planes.
Key
1 port side wall 4 aft end wall
2 string line 5 fore end wall
3 section line 6 starboard side wall
w width of aft end wall
a
w width of fore end wall
f
P P S S markings on both end walls at equal distances from side walls
3, 4, 3, 4
C C C offsets between strings and side walls
1, 2. n
and d d d
1, 2. n
Figure 2 — Plan view of an intermediate horizontal plane
Alternatively, another formula of equal or better accuracy may be used when it is considered adequate.
For example, side wall may be approximated by a linear regression line of the x- and y-coordinates of
each measuring point on the side wall (see 8.3.3).
7.3.4 Trapezoidal tank
If the tank width is less at one end, measure the width in the intermediate horizontal planes in the same
way as in 7.3.3, as shown in Figure 3.
10 © ISO 2013 – All rights reserved
ISO 8311:2013(E)
The average width, w , of the fore end wall and the average width, w , of the aft end wall are calculated
f a
using Formulae (10) and (11).
n
′ ′
cd+
()
∑ ii
′ ′ ′ ′
cc+ +dd+
11nn i=1
′
ww= − + (10)
ff
2 n
and
n
′ ′
()cd+
∑ ii
cc′ + ′ +dd′ + ′
11nn i=1
ww= ′ − + (11)
aa
2 n
where c’ , c’ … c’ and d’ , d’ … d’ are the offsets between strings and side walls.
1 2 n 1 2 n
Key
1 port side wall 4 section line
2 aft end wall 5 starboard side wall
3 string line 6 fore end wall
w’
width of aft end wall
a
w’ width of fore end wall
f
P’ , P’ , S’ , S’ markings on both end walls at equal distances from side walls
3 4 3 4
c’ , c’ … c’ offsets between strings and side walls
1 2 n
and d’ , d’ … d’
1 2 n
Figure 3 — Plan view of an intermediate horizontal plane (trapezoidal tank)
As shown in Figure 3, the offsets to be taken in measuring the widths should theoretically be the ones
parallel to the fore and aft end walls (c’ … c’ , d’ … d’ ), and the offsets d measured at right angles to the
1 n 1 n i
side wall should be corrected, as shown in Figure 4, to d’ measured parallel to the fore and aft walls d’ = d
i 1 i
/cos θ where θ is the angle between the side wall and the plane at right angles to the fore and aft walls.
ISO 8311:2013(E)
Key
1 aft end wall
2 string line
3 fore end wall
d offsets at right angles to side wall
i
d’
i
d
'
i
parallel to fore and aft walls by a formula, d =
i
cosθ
θ angle between side wall and plane at right angles to fore and aft walls, taken from the drawings
Figure 4 — Correction of offsets
Alternatively, another formula of equal or better accuracy may be used when it is considered adequate
in the light of the shape of the tank. For example, side wall may be approximated by a linear regression
line of the x- and y-coordinates of each measuring point on the side wall and the width calculated as
distances between intersections of the fitted lines with the tank end walls (see 8.3.3).
7.4 Tank height measurement
7.4.1 Measurement of total height
On the top and bottom plates, draw section lines and longitudinal lines which will make grids on both
plates. Using a measuring tape, measure the distances between the intersections of these lines on the
top plate and the corresponding points on the bottom plate, i.e. along all vertical lines, and calculate the
arithmetic mean using Formula (12):
n
h = h (12)
tt,i
∑
n
i=1
where
h is the total height along a vertical line;
t,i
h is the average total height;
t
n is the number of vertical lines.
12 © ISO 2013 – All rights reserved
ISO 8311:2013(E)
Alternatively, another formula of equal or better precision may be used when it is considered adequate
in the light of the shape of the tank. For example, the arithmetic mean may be the weighted average in
case of trapezoidal tanks.
7.4.2 Measurement of side wall height
Measure the distance between the bottom of the upper chamfer and the top of the lower chamfer, along
all vertical lines drawn on both side walls, and obtain the arithmetic mean using Formula (13):
n
h = h (13)
mm∑ ,i
n
i=1
where
h is the side wall height along a vertical line;
m,i
h is the average side wall height;
m
n is the number of vertical lines.
7.4.3 Measurement of lower chamfer height
a) Set a reference plane with an optical level approximately parallel to the bottom and the end walls
with some clearance from the top of the lower chamfer.
b) Measure height d between this reference plane and the bottom plate along all the vertical lines, and
take another measurement d between the reference
...
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