G1

G1
G1(1974)(cont)(Rev.1
1979)(Rev.2
1997)(Corr.1
Sept 2003)(Rev.3June 2016)(Corr.1
May 2018)(Corr.2
Oct 2021)(Corr.3
Sep 2023)

Vessels with cargo containment system forliquefied gas
G1.1 General
G1.1.1 The present text gives the general principles which are applied by Classification
Societies for approval and survey of the relevant items of vessels with cargo containment
system for liquefied gas for classification purposes. They do not intend to cover full details ofsuch approval and survey procedures which are to be found in the individual Rules ofClassification Societies.
G1.1.2 Where appropriate, this Requirement refers to the basic tank types which are defined
under G1.2. Tanks differing from these definitions will be the subject of special consideration.
ssG1.1.3 This UR does not apply to vessels which must comply with the requirements of IMO
Resolution MSC.370(93) Amendments to the International Code for the Construction andEquipment of Ships Carrying Liquefied Gases in Bulk (IGC Code).
G1.2 Definitions
G1.2.1 Integral tanks
Integral tanks form a structural part of the ship's hull and are influenced in the same mannerand by the same loads that stress the adjacent hull structure. The design vapour pressure P0
is not normally to exceed 0,025 N/mm2 (0.25 bar). If, however, the hull scantlings are
increased accordingly, P0 may be increased to a higher value but less than 0,07 N/mm2 (0.7bar).
Integral tanks may be used for liquefied gases provided that the lowest temperature in any
part of the hull structure in no circumstances will fall below –10°C. A lower temperature may
be accepted by the Classification Society subject to special consideration.
G1.2.2 Membrane tanks
Membrane tanks are non-self-supporting tanks which consist of a thin layer (membrane)
supported through insulation by the adjacent hull structure. The membrane is designed insuch a way that thermal and other expansion or contraction is compensated for without
undue stressing of the membrane. The design vapour pressure P0 is not normally to exceed
0,025 N/mm2 (0.25 bar). If, however, the hull scantlings are increased accordingly, P0 may be
increased to a higher value but less than 0,07 N/mm2 (0.7 bar).

Note:
1.

Rev.3 of this UR is to be uniformly implemented by IACS Societies for ships contracted
for construction on or after 1 July 2016.

2.

The “contracted for construction” date means the date on which the contract to build thevessel is signed between the prospective owner and the shipbuilder. For further details
regarding the date of “contract for construction”, refer to IACS Procedural Requirement(PR) No. 29.

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(cont)The definition of membrane tanks does not exclude designs such as those in which nonmetallic membranes are used or in which membranes are included or incorporated ininsulation. Such designs, however, require special consideration by the Classification Society.
G1.2.3 Semi-membrane tanks
Semi-membrane tanks are a non-self-supporting tanks in the loaded condition and consist ofa layer, parts of which are supported through insulation by the adjacent hull structure
whereas the rounded parts of this layer connecting the above mentioned supported parts aredesigned also to accommodate the thermal and other expansion or contraction. The design
vapour pressure P0 is not normally to exceed 0,025 N/mm2 (0.25 bar). If, however, the hullscantlings are increased accordingly, P0 may be increased to a higher value but less than
0,07 N/mm2 (0.7 bar).
G1.2.4 Independent tanks
Independent tanks are self-supporting; they do not form part of the ship hull and are notessential to the hull strength.
Three categories of independent tanks are considered:(i)

Independent tanks type A which are designed primarily using Classification Society
classical structural analysis procedures. Where such tanks are primarily constructed ofplane surfaces (gravity tanks), the design vapour pressure P0 is to be less than 0,07
N/mm2 (0.7 bar).

(ii)

Independent tanks type B which are designed using model tests, refined analytical tools
and analysis methods to determine stress levels, fatigue life and crack propagation
characteristics. Where such tanks are primarily constructed of plane surfaces (gravity
tanks), the design vapour pressure P0 is to be less than 0,07 N/mm2 (0.7 bar).

(iii)

Independent tanks type C (also referred to as pressure tanks) are tanks meetingpressure vessel criteria and having a design vapour pressure P0 not less than:where Aσm=P0 = 0,2 + 0,1ACρ03/2(N/mm2)P0 = 2 + ACρ03/2

(bar)

 σ 
0,0185  m  ∆σ A 

2= design primary membrane stress (N/mm2)∆σA = allowable dynamic membrane stress (double amplitude at probability level
Q = 10-8)= 55 N/mm2 for ferritic-perlitic, martensitic and austenitic steels= 25 N/mm2 for aluminium alloy (5083-0) (for other materials the value of A will be
determined in agreement with the Classification Society)C= characteristic tank dimension to be taken the greatest of h: 0,75b or 0,45l

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with h:(cont)= height of tank (dimension in ship’s vertical direction) (m)b= width of tank (dimension in ship’s transverse direction) (m)l= length of tank (dimension in ship’s longitudinal direction) (m)ρ0= relative density of cargo (=1 for fresh water) at the design temperature.

However the Classification Society may allocate a tank complying with the above criterion totype A or type B dependent on the configuration of this tank and the arrangement of its
supports and attachments.
G1.2.5 Design vapour pressure
The design vapour pressure P0 is the maximum gauge pressure at the top of the tank which
has been used in the design of the tank.
(i)

For cargo tanks where there is no temperature control and where the pressure of the
cargo is only dictated by the ambient temperature, P0 is not to be less than the vapour
pressure of the cargo at a temperature of 45°C. However, lesser values of thistemperature may be accepted by the Classification Society for ships operating in
restricted areas or on voyages of restricted duration and account may be taken in suchcases of a possible insulation of the tanks. On the other hand, higher values of thistemperature may be required for ships permanently operating in areas of high ambient
temperature.

(ii)

In all cases, including (i), P0 is not to be less than the maximum allowable relief valve
setting (MARVS).

(iii)

Subject to special consideration and to the limitations given under G1.2.1 to G1.2.4 forthe various tank types, a vapour pressure higher than P0 may be accepted in harbour
conditions where dynamic loads are reduced.

G1.2.6 Design temperature
The design temperature for selection of materials is the minimum temperature at which cargo
may be loaded and/or transported in the cargo tanks.
Provisions to the satisfaction of the Classification Society are to be made so that the tank or
cargo temperature cannot be lowered below the design temperature.
G1.3 Design loads
G1.3.1 General(a)Tanks together with their supports and other fixtures are to be designed taking into
account proper combinations of the various loads listed hereafter:
Internal pressure
External pressure
Dynamic loads due to the motion of the ship
Thermal loads
Sloshing loads
Loads corresponding to ship deflection
Tank and cargo weight with the corresponding reactions in way of supports
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Insulation weight
Loads in way of towers and other attachments.

G1(cont)The extent to which these loads are to be considered depends on the type of tank.
(b)

Account is also to be taken of the loads corresponding to the pressure test mentioned inG1.10.

(c)

Account is also to be taken of an increase of vapour pressure in harbour conditions(see G1.2.5 (iii)).

(d)

The tanks are to be designed for the most unfavourable static heel angle within therange of 30° without exceeding allowable stresses given G1.5.

G1.3.2 Internal pressure(a)

The following formula gives the value of internal pressure head heq, in N/mm2 or bar,
resulting from the design vapour pressure P0 and the liquid pressure defined in G1.3.2(b) but not including effects of liquid sloshing:heq= P0 + (hgd)max.

Equivalent procedures may be applied.
(b)

The internal liquid pressures are those created by the resulting acceleration of thecentre of gravity of the cargo due to the motions of the ship (see G1.3.4). The following
formula gives the value of internal pressure head hgd, in N/mm2 or bar, resulting fromcombined effects of gravity and dynamical acceleration:hgd= aβ x Zβ

hgd= aβ x Z βρ1,02 × 10 5ρ1,02 × 10 4

(N/mm2)(bar)

where:aβ= the dimensionless acceleration (i.e. relative to the acceleration of gravity),
resulting from gravitational and dynamical loads, in an arbitrary direction β (seeFig. 1)Zβ= largest liquid height (m) above the point where the pressure is to be
determined measured from the tank shell in the β direction (see Fig. 2). Smalltank domes not considered to be part of the accepted total volume of the cargotank need not to be considered when determining Zβ.

ρ= the maximum density of the cargo (kg/m3) at the design temperature.

The direction β which gives the maximum value (hgd) max of hgd is to be considered. Where
acceleration in three directions needs to be considered an ellipsoid is to be used instead ofthe ellipse in Fig. 1. The above formula applies to full tanks.

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(cont)

G1.3.3 External pressure
External design pressure loads are to be based on the difference between the minimum
internal pressure (maximum vacuum) and the maximum external pressure to which any
portion of the tank may be subjected simultaneously.
G1.3.4 Dynamic loads due to ships motions(a)

The determination of dynamic loads is to take account of the long term distribution ofship motions, including the effects of surge, sway, heave, roll, pitch and yaw onirregular seas that the ship will experience during her operating life (normally taken tocorrespond to 108 wave encounters). Account may be taken of reduction in dynamic
loads due to necessary speed reduction and variation of heading when thisconsideration has also formed part of the hull strength assessment.

(b)

For design against plastic deformation and buckling the dynamic loads are to be taken
as the most probable largest loads the ship will encounter during her operating life
(normally taken to correspond to a probability level of 10-8). See Appendix 1 for
guidance.

(c)

When design against fatigue is to be considered, the dynamic spectrum is determinedby long term distribution calculation based on the operating life of the ship (normallytaken to correspond to 108 wave encounters). If simplified dynamic loading spectra areused for the estimation of the fatigue life, these are to be specially considered by theClassification Society.

(d)

In order to practically apply crack propagation estimates, simplified load distribution
over a period of 15 days may be used. Such distributions may be obtained as indicatedin Fig. 3.

(e)Ships for restricted service will be given special consideration.

(f)

The accelerations acting on tanks are estimated at their centre of gravity and include
the following components:

vertical acceleration:

motion acceleration of heave, pitch and possibly, roll (normal to theship base)transverse acceleration: motion acceleration of sway, yaw and rollgravity component of rolllongitudinal acceleration: motion acceleration of surge and pitch
gravity component of pitch.
G1.3.5 Sloshing loads(a)When partial filling is contemplated, the risk of significant loads due to sloshing induced
by any of the ship motions mentioned in G1.3.4 (f) is to be considered.

(b)When risk of significant sloshing induced loads is found to be present, special tests andcalculations will be required.

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(cont)

G1.3.6 Thermal loads(a)Transient thermal loads during cooling down periods are to be considered for tanks
intended for cargoes with a boiling point below -55°C.

(b)

Stationary thermal loads are to be considered for tanks where design, supporting
arrangement and operating temperature may give rise to significant thermal stress.

G1.3.7 Loads on supports
See G1.6.

Fig.1 Acceleration ellipse

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Fig.2 Determination of internal pressure heads

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(cont)

Fig.3 Simplified load distribution

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(cont)

G1.4 Structural analysis
G1.4.1 Integral tanks
The structural analysis of integral tanks is to be performed in accordance with the rules forhull structure of the Classification Society.
G1.4.2 Membrane tanks(a)For membrane tanks, the effects of all static and dynamic loads are to be considered todetermine the suitability of the membrane and of the associated insulation with respect
to plastic deformation and fatigue.

(b)

Before approval is granted, a model of both the primary and secondary barrier,including corners and joints, is normally to be tested to verify that it will withstand the
expected combined strains due to static, dynamic and thermal loads. Test conditions
are to represent the most extreme service conditions that tank will see in its life.
Material tests are to ensure that ageing is not liable to prevent the materials fromcarrying out their intended function.

(c)

For the purpose of the test referred to in G1.4.2 (b), a complete analysis of theparticular motions, accelerations and response of ships and tanks is to be performed,
unless these data are available from similar ships.

(d)Special attention is to be paid to the possible collapsing of the membrane due to an
overpressure in the interbarrier space, to a possible vacuum in the tanks, to thesloshing effects and to hull vibration effects.

(e)

The structural analysis of the hull is to be performed in accordance with the rules forhull structure of the Classification Society taking into account the internal pressure as
indicated in G1.3.2. Special attention is however to be paid to deformations of the hulland their compatibility with the membrane and associated insulation. Inner hull plating
thickness is to meet at least the requirements of the Classification Society for deeptanks taking into account the internal pressure as indicated in G1.3.2. The allowablestress for the membrane, membrane supporting material and insulation will be
determined in each particular case.

G1.4.3 Semi-membrane tanks
Structural analysis is to be performed in accordance with the requirements for membranetanks or independent tanks as appropriate, taking into account the internal pressure as
indicated in G1.2.3.
G1.4.4 Independent tanks type A(a)

The structural analysis is normally performed in accordance with the rules for hull
structure of the Classification Society taking into account the internal pressure as
indicated in G1.3.2. The cargo tank plating thickness is to meet at least therequirements of the Classification Society for deep tanks taking into account the internalpressure as indicated in G1.3.2 and any corrosion allowance required by G1.5.2.

(b)

For parts (structure in way of supports for instance) not covered by the Rules, stresses
are to be determined by direct calculations taking into account the loads referred to in
G1.3, as far as applicable, and the ship deflection in way of supports.

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G1.4.5 Independent tanks type B(a)

The effects of all dynamic and static loads are to be used to determine the suitability ofthe structure with respect to:plastic deformation
buckling
fatigue failure
crack propagation
Statistical wave load analysis in accordance with G1.3.4, finite element analysis orsimilar methods and fracture mechanics analyses or is equivalent approach, are to be
carried out.

(b)

A three dimensional analysis is to be carried out to elevate the stress levels contributedby the ship hull. The model for this analysis is to include the cargo tank with its
supporting and keying system as well as a reasonable part of the hull.

(c)

A complete analysis of the particular ship accelerations and motions in irregular waves
and of the response of ships and tanks to these forces and motions is to be performed
unless these data are available from similar ships.

(d)Buckling analysis is to consider the maximum construction tolerances.

(e)

Where deemed necessary by the Classification Society, model tests may be required todetermine stress concentration factors and fatigue life of structural elements.

(f)

The cumulative effect of the fatigue load is to comply with the following formula:ni 10 3
∑ N + N ≤ Cw
i
j
Where
ni

= number of stress cycles at each stress level during the life of the ship.

Ni= number of cycles to fracture for the respective stress level according to the
Wohler curve

Nj= number of cycles to fracture for the fatigue loads due to loading and unloadingCw≤ 0,5, except that the Classification Society may give special consideration to theuse of a value greater than 0,5 but not greater than 1,0 dependent on the test
procedure and data used to establish the Wohler curve (S – N curve).

G1.4.6 Independent tanks type C
Structural analysis is to be performed in accordance with G2.

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G1.5 Allowable stress – corrosion allowanceG1.5.1 Allowance stresses(a)

For integral tanks, allowable stresses are normally those given for hull structure by theClassification Society.

(b)

For membrane, see G1.4.2 (e)(c)

For independent tanks type A primarily constructed of plane surfaces, the bending
stresses for primary and secondary members (stiffeners, web frames, stringers, girders)when calculated by classical analysis procedures are not to exceed the lower of 0,75σF
or 0,38σB for carbon-manganese steels and aluminium alloys. However, if detailed
calculations are carried out for primary members, the equivalent stresses σc, as definedin G1.5.1 (g) may be increased over that indicated above to a value acceptable to theClassification Society; calculations have to take into account the effects of bending,shear, axial and torsional deformations as well as the hull/cargo tank interaction forces
due to the deflection of the double and cargo tank bottoms. For σF and σB see G1.5.1
(h).

(d)

For independent tanks B primarily constructed of bodies of revolution, the allowablestresses are not to exceed the following:σm ≤ fσL ≤ 1,5f
σb ≤ 1,5F
σL + σb ≤ 1,5F
σm + σb ≤ 1,5F

where
σm

= equivalent primary general membrane stressσL= equivalent primary local membrane stressσb= equivalent primary bending stressf= the lesser of σB/A or σF/BF

= the lesser of σB/C or σF/D

A, B, C and D have the following values:
Material

A

B

C

D

C-Mn steels and Ni
steelsAustenitic steels

3

2

3

1,5

3,5

1,6

3

1,5

Aluminium alloys

4

1,5

3

1,5

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(cont)For σB and σF see G1.5.1 (h).
(e)

For independent tanks type B, primarily constructed of plane surfaces, the Classification
Society may require compliance with additional or other stress criteria.

(f)

For independent tanks type C, see G2.

(g)

For the purpose of G1.5.1 (a)-(f) equivalent stresses σc (von Mises, Huber) aredetermined as follows:

σ c = σ x 2 + σ y 2 − σ xσ y + 3τ xy2
where
σx

= total normal stress in x direction

τxy= total shear stress in y-x planeσy= total normal stress in y direction

Unless other methods of calculation are justified, the total stresses are calculated accordingly
to the following formulae for independent tanks type B:

σ x = σ x.st ±∑ (σx .dynσ y = σ y.st ±∑ (σy .dyn)2)2

τ xy = τ xy.st ± ∑ (τ xy.dyn ) 2
where σx.st, σxy.st and τxy.st are dynamic stresses
σx.dyn, σxy.dyn and τxy.dyn are dynamic stresses
determined separately from acceleration components and hull strain components due todeflection and torsion.
(h)

For the purpose of G1.5.1 (a)-(g):σF= specified minimum upper yield stress at room temperature. If the stress-strain
curve does not show a defined yield stress, the 0,2 % proof stress applies. For
welded connections in aluminium alloys, the proof stress in the annealedconditions is to be used.

σB= specified minimum tensile strength at room temperature. For welded
connections in aluminium alloys, the tensile strength in annealed conditions is
to be used.

The above properties are to correspond to the minimum specified mechanical properties ofthe material, including the weld metal in the as fabricated condition. Subject to special
consideration by the Classification Society, advantage may be taken of enhanced yield stressand tensile strength at low temperature.
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(cont)(i)

Allowable stresses for materials other than those covered by W1 will be subject tospecial approval in each separate case.
Stresses may be further limited by fatigue analysis, crack propagation analysis andbuckling criteria.

G1.5.2 Corrosion allowance(a)

No corrosion allowance is generally required in addition to the thickness resulting fromthe structural analysis. However, where there is no environmental control around thetank (inerting, etc.) or where the cargo is of a corrosive nature, the Classification
Society may require a suitable corrosion allowance.

(b)

For pressure tanks, corrosion allowance is given in G2.

G1.6 Supports
G1.6.1 Cargo tanks are to be supported by the hull in a manner which will prevent bodily
movement of the tank under static and dynamic loads while allowing contraction andexpansion of the tank under temperature variations and hull deflections without unduestressing of the tank and of the hull.
G1.6.2 The tanks with supports are also to be designed for a static inclination of 30°without
exceeding allowable stresses given in G1.5.
G1.6.3 The supports are to be calculated for the most probable largest severe resulting
acceleration taking into account rotational as well as translational effects. This acceleration ina given direction maybe determined as shown in Fig. 1. The half axes of the 'acceleration
ellipse' are determined according to G1.3.4 (b).
G1.6.4 Suitable supports are to be provided to withstand a collision force acting on the tankcorresponding to one-half the weight of the tank and cargo in the forward direction and one
quarter the weight of the tank and cargo in the aft direction without deformation likely toendanger the tank structure.
G1.6.5 The loads mentioned in G1.6.2 and G1.6.4 need not be combined with each other orwith wave included loads.
G1.6.6 For independent tanks and, where appropriate, for membrane and semi-membranetanks, provisions are to be made to key the tanks against rotational effects referred to in
G1.6.3.
G1.6.7 Anti-flotation chocks are to be provided for independent tanks. The anti-flotation
chocks are to be suitable to withstand an upward force caused by an empty tank in a holdspace flooded to the load draught of the ship, without plastic deformation likely to endanger
the hull structure.

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(cont)

G1.7

Secondary barrierG1.7.1 When the cargo temperature at atmospheric pressure is below -10°C a secondary
barrier is to be provided, if required by G1.7.3, to act as a temporary containment for any
envisaged leakage of liquid cargo through the primary barrier.
G1.7.2 When the cargo temperature at atmospheric pressure is not below -55°C, the hull
structure may act as secondary barrier. In such a case:(i)the hull material is to be suitable for the boiling point at atmospheric pressure (see W1);(ii)

the design is to be such that this temperature will not result in unacceptable hullstresses.

G1.7.3 The requirements for secondary barrier in relation on tank type are as given in Table
1.
Table 1 indicates the basic requirements with respect to secondary barrier. For tanks which
differ from the basic tank types as defined in G1.2, the secondary barrier requirements will bedecided in each separate case.
G1.7.4 The secondary barrier is to be designed so that:(i)it is capable of containment of any envisaged leakage of liquid cargo for a period of atleast 15 days, unless different requirements apply for particular voyages. This condition
is to be fulfilled taking into account the load spectrum defined in G1.3.4.(d).

(ii)

it will prevent lowering of the temperature of the ship structure to an unsafe level in caseof leakage of the primary barrier (see G1.8.2).

(iii)

the mechanism of failure for the primary barrier does not also cause the failure of thesecondary barrier and vice-versa.

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Table 1
Cargo temperature
tb at atmosphericpressure
Basic tank typetb < – 55°C
Separate secondary
barrier whererequired–55°C ≤ tb < –10°C

tb ≥ –10°C

Hull may act as
secondary barrier

Integral

Tank type not normally allowed1

MembraneComplete secondary barrier

Semi-membrane

Complete secondary barrier2

Independent Type A

Complete secondary barrier

Independent Type B

Partial secondary barrier

Independent Type C

No secondary barrier required

No secondary barrier
required

NOTES:
1. A complete secondary barrier will be normally required if cargoes with a value of tb below–10°C are permitted in accordance with G1.2.1.
2. In the case of semi-membrane tanks which comply in all respects with the provisions
applicable to independent tanks, type B, except for the manner of support theClassification Society may consider the possibility of accepting a partial secondary
barrier.
G1.7.5 The functions of the secondary barrier are to be ensured assuming a static angle ofheel equal to 30°C.
G1.7.6 Where a partial secondary barrier is required, its extent is to be determined on thebasis of cargo leakage corresponding to the extent of failure resulting from the load spectrum
defined in G1.3.4.(d) after the initial detection of a primary barrier leak. Due account may betaken of liquid evaporation, rate of leakage, reliable pumping capacity and other relevant
factors. In all cases, however, the inner bottom in way of cargo tanks is to be protectedagainst liquid cargo. Clear of partial secondary barrier, provisions are to be made to deflect
any liquid cargo down into the space between the primary and secondary barriers and tokeep the temperature of the hull structure to a safe level (spray-shield).
G1.7.7 The secondary barrier is to be capable of being periodically checked for its
effectiveness. Checking may be a pressure vacuum test, a visual inspection or anothersuitable method acceptable to the Classification Society. Procedures for the periodic
checking of the secondary barrier during the life of the ship are to be submitted to theClassification Society as a condition of the approval of the cargo containment system.

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G1.8 Insulation
G1.8.1 When liquified gas is carried at a temperature below –10°C, suitable insulation is tobe provided to ensure that the minimum temperature of the hull structure does not fall below
the minimum allowable service temperature given for the concerned grade of steel in the IGC
Code Ch.6 Table 6.5 when the cargo tanks are at their design temperature and the ambient
temperatures are 5°C for air and 0°C for sea water. The above conditions may generally be
used for world wide service. However, higher values of the ambient temperatures maybe
accepted by the Classification Society for ships operated in restricted areas. On the other
hand, attention is drawn to the fact that lesser values of the ambient temperatures may be
fixed by National Authorities.
G1.8.2 Where a complete or partial secondary barrier is required, calculations are to bemade with the same assumptions as in G1.8.1 to check that the minimum temperature of thehull structure does not fall below the minimum allowable service temperature given for theconcerned grade of steel in the IGC Code Ch.6 Table 6.5. The complete or partial secondary
barrier is then to be assumed at the cargo temperature at atmospheric pressure.
G1.8.3 Calculations required by G1.8.1. and G1.8.2 are to be made assuming still air andstill water. In the case referred to in G1.8.2, the cooling effect of the rising boil-off vapour fromthe leaked cargo is to be considered in the heat transmission studies. For membersconnecting inner and outer hulls, the mean temperature may be considered for determining
the steel grades.
G1.8.4 In all cases referred to in G1.8.1 and G1.8.2 and for the ambient temperature
conditions of 5°C for air and 0°C for sea water, approved means of heating transverse hull
structural material may be used to ensure that the temperature of this material do not fall
below the minimum allowable values. If lower ambient temperatures are specified, approvedmeans of heating may also be used for longitudinal hull structural material, provided thismaterial remains suitable for the temperature conditions of 5°C for air and 0°C for sea water
without heating. Such a means of heating is to comply with the following requirements:(i)

Sufficient heat is to be available to maintain the hull structure above the minimum
allowable temperature in the conditions referred to in G1.8.1 and G1.8.2.

(ii)

The heating systems are to be arranged so that, in the event of a failure in any part ofthe system, standby heating can be maintained equal to not less than 100% of thetheoretical heat load.

(iii)

The heating systems are to be considered as essential auxiliaries.

(iv)

The engineering of the heating systems is to be in accordance with the requirements of
the Classification Society.

G1.8.5 In determining the insulation thickness, due regard is to be paid to the amount of
acceptable boil-off in association with the reliquefaction plant on board, main propulsion
machinery or other temperature control system.

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G1.9

Materials

G1.9.1 The shell and deck plating of the ship, and all stiffeners attached thereto, are to be inaccordance with the Rules of the Classification Society unless the calculated temperature of
the material in the design condition is below –5°C due to the effect of the low temperaturecargo, in which case the material is to be in accordance with the IGC Code Ch.6 Table 6.5,
assuming ambient sea and air temperatures of 0°C and 5°C respectively. In the design
condition the complete or partial secondary barrier is to be assumed to be at the cargo
temperature at atmospheric pressure and for tanks without secondary barriers, the primarybarrier is to be assumed to be at the cargo temperature.
G1.9.2 Hull material forming the secondary barrier is to be in accordance with the IGC Code
Ch.6 Table 6.2 and UR W1 Table 2a and 2b.
G1.9.3 Material used in the construction of cargo tanks are to be in accordance with the IGC
Code Ch.6 Tables 6.1, 6.2, 6.3 and UR W1.
G1.9.4 All other materials used in the construction of the ship which are subject to reduced
temperature due to the cargo and which do not form part of the secondary barrier are to be inaccordance with the IGC Code Ch.6 Table 6.5 for temperature determined by G1.8. This
includes inner bottom plating, longitudinal bulkhead plating, transverse bulkhead plating,floors, webs, stringers and all attached stiffening members.
G1.9.5 The insulation materials are to be suitable for loads which may be imposed on themby the adjacent structure.
G1.9.6 Where applicable, insulation materials are to have suitable properties of fire
resistance and are to be adequately protected against penetration of water vapour andmechanical damage.
G1.9.7 Insulation materials are to be tested and found acceptable with regard to thefollowing properties as applicable:compatibility with the cargosolubility in the cargoabsorption of the cargoshrinkageageingclosed cell content
densitymechanical properties
thermal expansion
abrasioncohesionthermal conductivity
resistance to vibrations
resistance to fire and flame spread
G1.9.8 The procedures for quality control of insulation materials during fabrication and/or insitu erection are to be to the satisfaction of the Classification Society.
G1.9.9 Where power or granulated insulation is used, the arrangements are to be such as toprevent compacting of the material due to vibrations.

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(cont)The design is to incorporate means to ensure that the material remains sufficiently buoyant tomaintain the required thermal conductibility and also prevent any undue increase of pressure
on the containment system.
G1.10

Construction and testingG1.10.1 All welded joints of the shell of independent tanks are to be of the butt-weld fullpenetration type. For dome to shell connections, the Classification Society may approve filler
welds of the full penetration type. Except for small penetrations on domes, nozzle welds arealso generally to be designed with full penetration. For tank type C, see G2.
G1.10.2 Workmanship is to be to the satisfaction of the Classification Society. Inspection of
welds including non destructive testing are to be in accordance with the IGC Code Para. 6.5.6
and/or the requirements of the Classification Society.
G1.10.3 For membrane tanks, quality assurance measures, weld procedure qualification,
design details, materials, construction, inspection and production testing of components areto be to standards developed during the prototype testing programme.
G1.10.4 For semi-membrane tanks the relevant requirements for independent tanks or for
membrane tanks are to be applied as appropriate.
G1.10.5 Integral tanks are to be hydrostatically or hydropneumatically tested in accordancewith the Rules of the Classification Society. The test is in general to be performed so that thestresses approximate, as far as practicable, the design stresses and so that the pressure at
the top of the tank corresponds at least to the MARVS.
G1.10.6 For ships fitted with membrane or semi-membrane tanks, cofferdams and all spaces
which may normally contain liquid and are adjacent to the hull structure supporting themembrane are to be hydrostatically or hydropneumatically tested in accordance with therequirements of the Classification Society. Pipe tunnels and other compartments which do notnormally contain liquid are not required to be hydrostatically tested.
In addition, the ship hold structure supporting the membrane is to be given a tightness testing.
G1.10.7 Each independent tank is to be subjected to a hydrostatic or hydropneumatic test.
For tanks type A, this test is to be performed so that the stresses approximate, as far aspracticable, the design stresses and so that the pressure at the top of the tank corresponds atleast to the MARVS. When the hydropneumatic test is performed, the conditions are tosimulate, as far as possible, the actual loading of the tank and of its supports. For tanks typeB, the test is to be performed as for tanks type A. Moreover, the maximum primary membranestress or maximum bending stress in a primary membrane under test conditions is not toexceed 90% of the yield strength of the material (as fabricated) as the test temperature. To
ensure that this condition is satisfied, when calculations indicate that stress exceeds 75% of
the yield strength, the prototype test is to be monitored by the use of strain gauges or othersuitable equipment. For tanks type C, see G2.
G1.10.8 All tanks are to be subjected to a tightness testing which may be performed in
combination with the pressure test mentioned above or separately.
G1.10.9 Requirements with respect to inspection of the secondary barrier will be decided ineach separate case.
G1.10.10 On ships using independent tanks type B, at least one tank and its support is to be
instrumented to confirm stress levels unless the design and arrangement for the size of theship involved are supported by full scale experience. Similar instrumentation may be required
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(cont)

by the Classification Society for independent tanks type C dependent on their configurationand on the arrangement of their supports and attachments.
G1.10.11 The ship is to be surveyed during the initial cool-down, loading and discharging of
the cargo to verify the overall performance of the containment system for compliance with thedesign parameters. Records on performance of the components and equipment essential toverify the design parameters are to be maintained and these records are to be available to
the Classification Society.
G1.10.12 Heating arrangements, if fitted in accordance with G1.8.4, are to be tested forcompliance with the design requirements.
G1.10.13 Inspection of the hull for cold spots is to be performed following the first loaded
voyage.

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(cont)

APPENDIX 1
Guidance formulae for acceleration components
In pursuance of G1.3.4, the following formulae are given as guidance for the components ofacceleration due to ship's motions in the case of ships with L> 50 m. These formulae
correspond to a probability level of 10-8 in the North Atlantic.
vertical acceleration2

a z = ±a0245   x  0,6 
1 +  5,3 −   + 0,05  L  L  CB 

3/ 2transverse acceleration2

a y = ±a0

z


x
0,6 + 2,5 − 0,05  + K 1 + 0,6 K 
B


L

2

longitudinal accelerationa x = ± a 0 0,06 + A 2 − 0,25 A
Lz  0,6 
A =  0,7 −+ 5 
1200
L  C B 


with
where
L

= length of ship between perpendiculars (m)CB= block coefficientB= greatest moulded breadth (m)x= longitudinal distance (m) from amidship to centre of gravity of the tank with
content, x is positive forward of amidship, negative aft of amidshipz= vertical distance (m) from the ship's actual waterline to the centre of gravity oftank with content, z is positive above and negative below the waterlineV= service speed (knots).

Generally, K= 1,0. For particular loading conditions and hull forms, determination of K
according to the formulae below may be necessary.

K=

13G M
B
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K ≥ 1,0where GM= metacentric height (m).
ax, ay and az are the maximum dimensionless (i.e. relative to the acceleration of gravity)
accelerations in the respective directions and they are considered as acting separately forcalculation purposes.
az does not include the component of the static weight.
ay includes the component of the static weight in the transverse direction due to rolling.
ax includes the component of the static weight in the longitudinal direction due to pitching.

End ofDocument

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