EN ISO 8311:1995

SLOVENSKI STANDARD
01-maj-1998
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Refrigerated light hydrocarbon fluids - Calibration of membrane tanks and independent
prismatic tanks in ships - Physical measurement (ISO 8311:1989)
Verflüssigte leichte Kohlenwasserstoffe - Kalibrierung von Membrantanks und
abhängigen Prismentanks in Schiffen - Physikalische Messung (ISO 8311:1989)
Hydrocarbures légers réfrigérés - Etalonnage des réservoirs a membrane et réservoirs
pyramidaux - Mesurage physique (ISO 8311:1989)
Ta slovenski standard je istoveten z: EN ISO 8311:1995
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.

INTERNATIONAL ISO
STANDARD 8311
First edition
1989-07-01
Refrigerated light hydrocarbon fluids -
Calibration of membrane tanks and independent
prismatic tanks in ships - Physical
measurement
H ydrocarbures Egers r6 frig&& - Etalonnage des r&ervoirs a membrane
et reservoirs p yramidaux - Mesurage ph ysigue
Reference number
ISO 8311 : 1989 (El
ISO8311 : 1989 (E)
Page
Contents
iv
..............................................................
Foreword
V
............................................................
Introduction
..............................................................
1 Scope
.................................................
2 Normative references
.......................................................... 1
3 Definitions
......................................................... 2
4 Precautions
5 Equipment .
5.1 Dynamometer .
5.2 End-to-end rule .
5.3 Lasertransmitter .
................................................. 3
5.4 Measuringtape
Opticallevel . 3
5.5
5.6 Steelrule .
................................................... 3
5.7 Thermometer
................................................. 3
5.8 Tension handle.
........................................................ 3
6 Measurement
6.1 Method .
.............................. 3
6.2 Determination of measuring positions
6.3 Marking .
........................................ 3
6.4 Tank length measurement
......................................... 4
6.5 Tank width measurement
Tank height measurement .
6.6
@ ISO 1989
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any
means, electronie cr mechanical, including photocopying and microfilm, without Permission in
writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-121 1 Geneve 20 l Switzerland
Printed in Switzerland
ii
ISO8311 : 1989 (E)
6.7 Bottom calibration . 6
6.8 Location of level gauge . 6
6.9 Temperature. . 9
6.10 Deadwood . 9
7 Calculation procedure . 9
7.1 Calculation of tank volume . 9
7.2 Effect of bottom undulation . 9
7.3 Area of chamfer Portion . 9
7.4 Trim corrections. . 9
7.5 List corrections .
7.6 Combined trim and list corrections . 9
7.7 Correction for tank Shell expansion or contraction . 9
8 Calibration tables. . 10
8.1 Calibration report . 10
8.2 Main gauge table . 10
8.3 Trim correction table . 10
8.4 List correction table . 10
............... 10
8.5 Correction table for tank Shell expansion or contraction
8.6 Correction for float-type level gauge . 10
Annexes
A Safety precautions for work in membrane tanks . 11
............... 12
B Example of calculation of errors for a typical membrane tank
C Example of a main gauge table. . 14
...................................... 15
D Example of a trim correction table
E Example of a list correction table .
........ 17
F Example of a correction table for expansion/contraction of tank Shell
. . .
Ill
ISO8311 : 1989 (EI
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of
national Standards bodies (ISO member bedies). The work of preparing International
Standards is normally carried out through ISO technical committees. Esch 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, govern-
mental and non-governmental, in liaison with ISO, also take patt in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all
matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
the ISO Council. They are approved in accordance with ISO procedures requiring at
least 75 % approval by the member bodies voting.
International Standard ISO 8311 was prepared by Technical Committee ISO/TC 28,
Petroleum products and lubrican ts.
Annexes A to F are for information only.

ISO8311 : 1989(E)
Introduction
Large quantities of light hydrocarbons consisting of compounds having 1 to 4 carbon
atoms are stored and transported by sea as refrigerated liquids at pressures close to
atmospheric. These liquids tan be divided into two main groups, liquefied natura) gas
(LNG) and liquefied Petroleum gas (LPG). Bulk transportation of these liquids requires
a special technology in ship design and construction to enable shipborne trans-
portation to be safe and economical.
Measurement of cargo quantities in ships’ tanks for custody transfer purposes has to
be of a high Order of accuracy. This International Standard, together with others in the
series, specifies methods of internal measurement of ships’ tanks from which tank
calibration tables tan be derived.
This International Standard covers calibration techniques applicable to membrane type
tanks, i.e. tanks in which the containment System comprises a relatively thin mem-
brane of either stainless steel or high-nickel steel alloy supported by insulation and
also, with some modifications, to tanks constructed of aluminium alloy or steel for low-
temperature Service that are independent, self-supporting and approximately prismatic
in shape.
Annex A gives recommendations on safety precautions to be observed during the
calibration.
Annex B gives an analysis sf the sources of error for a typical membrane tank.
Annex C gives an example of a calibration table relating partial filling volume as a func-
tion of liquid level and annexes D, E and F give examples of trim, list and temperature
correction tables.
V
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ISO 8311 : 1989 (EI
INTERNATIONAL STANDARD
Refrigerated light hydrocarbon fluids - Calibration
of membrane tanks and independent prismatic tanks
Physical measurement
in ships -
Measurements made to provide
1 Scope 3.1.1 bottom calibration :
calibration of the bottom part of a tank to take account of un-
dulation in the bottom plate.
1.1 This International Standard specifies a method for the
internal measurement of membrane tanks and independent
prismatic tanks used in ships for the transport of refrigerated
32 calibration table (main gauge table) : A table, often
light hydrocarbon fluids. In addition to the actual process of
referred to as a tank table or a tank capacity table, showing the
measurement, it sets out the calculation procedures for com-
capacity of, or volumes in, a tank corresponding to various li-
piling the calibration table and correction tables to be used for
quid levels measured from the gauge reference Point (sec 3.6),
the computation of cargo quantities.
with the ship on an even keel and upright.
1.2 For membrane tanks, the procedures of this International
3.3 chamfer : A slanting surface connecting the Walls of a
Standard utilize the scaffolding used for the installation sf the
tank with its top or bottom surface (see figure 5).
membranes to support the measuring equipment but, for in-
dependent prismatic tanks, other safe means of access to the
required measuring positions have to be used. 3.4 deadwood : Any tank fitting or structure, including
rounded corners or radiussed ends, which affect the capacity
of the tank. Deadwood is referred to as “positive deadwood”
when the capacity of the fitting adds to the effective capacity of
2 Normative references
the tank, or “negative deadwood” when the volume of the
fitting displaces liquid and reduces the effective capacity.
The following Standards contain provisions which, through
reference in this text, constitute provisions of this International
3.5 gauging : All the measurements taken in a tank
Standard. At the time of publication, the editions indicated
necessary to determine the quantity of liquid and vapour con-
were valid. All Standards are subject to revision, and Parties to
tained therein.
agreements based on this International Standard are encouraged
to investigate the possibility of applying the most recent editions
of the Standards listed below. Members of IEC and ISO main-
3.6 gauge reference point : The Point from which the
tain registers of currently valid International Standards
liquid depths are measured.
ISO 4512 : -l), Petroleum and liquid Petroleum products -
3.7 horizontal plane : A plane established parallel to the
Eguipment - Tank gauging and calibration - Manual
tank bottom.
methods.
ISO 7507-1 : - ‘1, Petroleum and liquid petroleum products -
3.8 liquid level : Height of the liquid surface measured from
Volumetric calibration of vertical c ylindrical tanks -- Part 7 :
the gauge reference Point. When the ship is in list or trim con-
S trapping me thod.
dition, the height is measured at a right angle to the tank
bottom.
3 Definitions
3.9 list : Transverse inclination of a ship.
For the purposes of this International Standard, the following
3.10 longitudinal fine : A line formed by a longitudinal
definitions shall apply.
plane crossing a horizontal plane.
31 . calibration : The process of determining the total
3.1’1 longitudinal plane : A vertical plane running parallel to
capacity or partial capacities of a tank corresponding to dif-
the centreline of the tank.
ferent levels.
1) To be published.
ISO8311 : 1989 (E)
3.12 : A line (Iongitudinal, transverse or ver- The calibrator shall provide detailed Sketches of any abnor-
measuring line
mality of the tank or its fittings where such Sketches will
tical) on a three-dimensional rectangular grid with a pitch not
materially assist the interpretation of the recorded data.
greater than 5 m. Measurement for calibration purposes is
taken along these measuring lines.
4.3 If drawings for the tank are available, all measurements
3.13 port : The left-hand side of a ship facing forward. taken shall be compared with the corresponding dimensions
shown on the drawings. Any measurement showing a signifi-
cant discrepancy in this comparison shall be rechecked.
3.14 reference line : A Standard line established by a string
or laser. A calibration method using this line is adopted as an
alternative to direct measurements, where it is considered im-
4.4 Measurements shall be taken twice to check whether
practical to take direct measurements.
they agree within the following tolerantes; if they do not agree,
measurements shall be continued until two consecutive
readings agree, and their average shall be taken as the result.
3.15 reference offsets : Clearances or offsets between the
tank bottom and a horizontal plane set over it, which are
measured along all the vertical lines drawn on the fore and aft Measurement Tolerante
end Walls.
up to 20 m + 2mm
+ 3 mm
over 20 m
3.16 reference plane : A plane parallel to a side Wall, end
for offset + 0,5 mm
Passes through a reference line.
wall or tank bottom which
If the measurements have been interrupted, the last measure-
ments taken shall be repeated. If the new measurements do not
3.17 section line : A line formed section plane crossing
bY a
agree, within the required tolerante, with the earlier measure-
a horizontal plane.
ments, then the earlier set shall be rejected.
3.18 section plane : A plane parallel with the fore and aft
end Walls of a tank.
4.5 When measurements are made with a measuring tape,
the tension specified in the tape calibration certificate shall be
applied.
The right-hand side of a ship facing
3.19 starboard :
forward.
4.6 The measuring tape shall be supported, if necessary, so
as to prevent it from sagging. If tape sag is unavoidable, the
3.20 trim : Longitudinal inclination of a ship.
calibrator shall note this and a catenary correction shall be ap-
plied during calculation.
3.21 vertical line : A line formed by a section plane on the
side Walls and formed by a longitudinal plane on the fore and
aft end Walls.
4.7 When measuring a membrane tank, care shall be taken to
ensure that the membrane is in contact with the supporting
material.
4 Precautions
-
NOTE In some cases it may be possible to ensure this contact
bY ap-
This clause outlines the precautions to be taken during
beneath the membrane.
a vacuum to the space
PMW
measurement in Order to ensure that the required calibration
precision is obtained.
4.8 The trim and list of the ship shall be kept unchanged
while the Optical level or laser transmitter is used.
4.1 Utmost care and attention shall be exercised in taking
measurements, and any unusual occurrence during the
measuring work which might affect the results obtained shall
be recorded.
5 Equipment
The calibration method described in this International Standard
may be applied to ships whether afloat or in a dry dock or on a the tension specif ied for a
5.1 Dynamometer r to check
building Slip. However, its use for ships in a dry dock is pre-
measuring tape.
ferred, because trim or list, if any, will remain the same
throughout the calibration procedure. The necessary adjust-
5.2 End-to-end rule, graduated in centimetres and
ment shall be made to any measurement by Optical level or laser
millimetres, to be used to measure deadwood, etc. A wooden
transmitter if the ship’s attitude has changed.
rule shall be free of warping. The rule shall bear the identifi-
cation of a recognized standardizing authority or certificate of
4.2 If unusual distortion is found in the tank, additional
identification.
measurement shall be taken by the calibrator as considered
necessary and sufficient to provide the required accuracy in the
5.3 Laser transmitter, emitting a Iow-power laser beam
calibration table. Notes by the calibrator detailing the extra
with a divergente of less than 4 mm at a distance of 35 m,
measurements and the reasons for them shall be included in the
which tan be rotated through 360° vertically and horizontally.
calibration report.
ISO 8311 : 1989 (El
complying with the specifications plates, horizontal and vertical lines on the fore and aft end Walls
5.4 Measuring tape,
and horizontal and vertical lines on the port and starboard end
given in ISO 4512, clause 20.
Walls.
5.5 Optical level, having an erect image and a magnification
6.4 Tank length measurement
of x 20 or greater, capable of being focussed to 1,5 m or less
and with a spirit Ievel sensitivity of 40 seconds of arc per 2 mm
Measure ta nk lengths along all the longitudinal lines at each
or less.
level of the horizontal planes as described in 6.4. 1 to 6.4.3.
5.6 Steel rule, to be used to measure clearances, etc.,
6.4.1 Length measurement on the bottom plate
graduated in millimetres. The rule shall bear the identification of
a recognized standardizing authority or certificate of identifi-
Measure distances between the fore and aft end Walls along all
cation.
the longitudinal lines marked on the bottom plate with a
measuring tape stretched thereon.
5.7 Thermometer, of suitable range, having an accuracy of
It 0,5 OC.
6.4.2 Length measurement on the top plate
5.8 Tension handle, fastened to the measuring tape to
Measure distances on the top plate in a manner similar to that
apply tension to pull it into a straight line (sec ISO 4512).
for the bottom plate (see 6.4.1). Care shall be taken to keep the
measuring tape in contact with the top plate.
6 Measurement
6.4.3 Length measurement in an intermediate horizontal
plane
6.1 Method
To avoid inaccurate measurement due to excessive sagging of
This clause and clause 7 set out a method of measurement and
the measuring tape, apply the reference line method using a
calculation applicable to tanks constructed using a membrane
string line (6.4.3.1) or laser beam (6.4.3.2).
containment System.
As shown in figure 1, lengths in these imaginary planes tan be
Measurements of the distances between opposite Walls of a
obtained by applying offset corrections at both ends, a2, a3 . . .
tank shall be taken by tensioning the tape as specified on the
a, -1 and !Q, b3 . . . b,, _ 1 f to the length measured directly on
tape certificate.
the side Wall.
Tanks constructed of aluminium alloy or steel for low-tempera-
ture Service, and of independent, self-supporting and approxi-
6.4.3.1 String line
mately prismatic shape, may exhibit significant deformation or
building inaccuracy. If such distortion has been identified, addi-
1) Mark PI and P2, SI and SZ, on both side Walls at equal
tional measurement, as indicated in 4.2, shall be carried out.
distances from the end Walls. Measure the lengths Kp, Ls)
between the fore and aft end Walls with a measuring tape ex-
The decision to adopt an alternative method shall be made by
tended along both side Walls, supporting the tape on the wall to
the calibrator. The reasons for the decision shall be included in
prevent it from sagging.
the field notes.
2) Stretch strings between the opposite Points PI and SI, P2
and S,, and measure the offsets between the strings and the
6.2 Determination of measuring positions
end Walls (aI, u2 . . . a, and b,, & . . . b,) with a rule.
Tank calibration is basically the measurement of the tank
measuring th offsets, take care to put the
3) In ese measuring
length, width and height between known positions. These
rule at a right angle to the string.
positions are determined by setting out a number of horizontal,
longitudinal and section planes.
6.4.3.2 Laser beam line
These planes intersect to form lines along which the measure-
ments of length, width and depth shall be taken. The various
1) Mount a laser transmitter on one of the end Walls with an
planes shall be set out at intervals not greater than 5 m; the in-
appropriate clearance, then align the laser beam horizontally
terval shall be adjusted so that the resulting measurements
and approximately parallel to the end Wall.
reflect any Change of section and adequately describe any
deformation. The positions at which measurements are to be
2) Mark PI on the port side wall where the laser beam strikes
taken shall be determined by the calibrator but shall not be
the Wall, then rotate the beam through 180° and mark S, where
more than 5 m apart.
the beam strikes the starboard Wall.
3) Measure offsets between the centre of the beam and the
6.3 Marking
end wall (~1, a2 . . . a,) with a rule.
Having determined the positions at which measurements are to
be taken, mark the lines which run on the tank inner Walls. 4) Repeat the same procedure on the opposite end Wall. Mark
Mark the section and longitudinal lines on the top and bottom
P2, SZ and measure 6,, 62 . . . b,.
1so8311 : 1989 (El
Port side wall
Aft end wall e M- Fore end wall
Longitudinal lines
String line
String line -
(or laser beam)
(or laser beam)
b
n-l
Starboard side wall
Figure 1 - Plan view of an intermediate horizontal plane
6.5.1 Width measurement on an intermediate
6.4.3.3 Average length
horizontal plane
The purpose of the measurement using a string line (6.4.3.1) or
laser beam (6.4.3.2) is to obtain the average length, L, of each
Measure tank width in the same way as in the length measure-
intermediate horizontal plane, which is calculated from the
ment by actual measurement of wf and w, in combination with
equation
the string or laser beam method as shown in figure 2.
n
The average width, w, for each intermediate horizontal plane is
(Qi + bi)
given by the equation
c
L, + Ls -
(LZl + 0, + bj + bn)
i=l
L= +
2 n
n
(Ci + d,)
Alternatively, another formula of equal or better precision may c
- (c, + c, + d, + d,)
Wf + wa i=l
be used when it is considered adequate in the light of the shape
W= +
of the tank. n
6.4.3.4 Laser beam plane
6.5.2 Chamfer portions
As an alternative to the laser beam reference line method
described in 6.4.3.2, the Single beam laser may be replaced by a
Measure the width on the end Walls at the tank top as well as at
laser producing a laser plane. A rotating laser is set up adjacent
the bottom of the upper chamfer. Likewise, measure the width
to and approximately parallel with each inner surface. The
on the end Walls at the tank bottom and at the top of the lower
plane will pass through the laser reference lines described in
chamfer.
6.4.3.2. Offset measurements are taken between the plane and
the positions on the wall determined as described in 6.2.
6.5.3 Trapezoidal tank
6.5 Tank width measurement
If the tank width is less at one end, measure the width in the in-
termediate horizontal planes in the same way as in 6.5.1, as
Tank widths are measured along all the section lines set in each
shown in figure 3.
horizontal plane as described in 6.5.1 to 6.5.3.
ISO 8311 : 1989 (E)
Port side wall
String line (or laser beam)
- Section line
Aft end wall-
- Fore end wall
String line (or laser beam)
Starboard side wall
Figure 2 - Plan view of an intermediate horizontal plane
~ Port side wall
/
-T
b
i:::
p;
I
--
-L?
Aft end wali -
pt
--- -
Si -s
m Section line
/--
‘C
b
iJ \
\
- Fore end wall
s;
L Starboard side wall
-.
-7
Q
t
Figure 3 - Plan view sf an intermediate horizontal plane (trapezoidal tank)
ISO 8311 : 1989 (El
b) Measure height d, between this reference line and the bot-
The average
width ( Wo) of the fore end wall an d the average
tom plate along all the vertical lines, and take another measure-
width (w,) of the aft end wall are calculated from
the equations
ment d, between the reference line and the top of the lower
n chamfer at the corners of the tank.
(c; + dl)
c
c) The height h, of the lower chamfer is calculated from the
ci + C; + di + dn
i=l
Wf = wi - equation
+
n
h, = average value of d, - average value of d,
and
n
6.6.2.3 Height of upper chamfer h, at the fore and aft end
(c; + d;)
Walls
c
ci + C; + di + d; ,
i=l
w, = w; - +
and h, have been obtained, the
Now that heights h,, heig ht
n
2 hr-rl
of th e upper chamfer is calculated from the equation
h”
As shown in figure 3, the offsets to be taken in measuring the
h, = h, - h, - hl
widths should theoretically be the ones parallel to the fore and
aft end Walls (ci . . . c>, di . . . dh), and the offsets di
6.7 Bottom calibration
measured at right angles to the side wall should be corrected,
as shown in figure 4, to d: measured parallel to the fore and aft
Figure 6 Shows an oblique pr kojection view of a tank bottom to
Walls by the formula d: = di x sec 8 where 8 is the angle
indicate the positions
...