General design and construction requirements

Shells shall be designed and constructed in accordance with the requirements of a pressure vessel code
recognized by the competent authority. Shells shall be made of steel suitable for forming. The
materials shall in principle conform to national or international material standards. For welded shells,
only a material whose weldability has been fully demonstrated shall be used. Welds shall be skilfully
made and afford complete safety. When the manufacturing process or the materials make it necessary,
the shells shall be suitability heat-treated to guarantee adequate toughness in the weld and in the heat
affected zones. In choosing the material the design temperature range shall be taken into account with
respect to risk of brittle fracture, to stress corrosion cracking and to resistance to impact. When fine
grain steel is used, the guaranteed value of the yield strength shall be not more than 460 N/mm2 and
the guaranteed value of the upper limit of the tensile strength shall be not more than 725 N/mm2
according to the material specification. Portable tank materials shall be suitable for the external
environment in which they may be carried.

Portable tank shells, fittings and pipework shall be constructed of materials which are:
(a) Substantially immune to attack by the non-refrigerated liquefied gas(es) intended to be
carried; or
(b) Properly passivated or neutralized by chemical reaction.

Gaskets shall be made of materials compatible with the non-refrigerated liquefied gas(es) intended to
be carried.

Contact between dissimilar metals which could result in damage by galvanic action shall be avoided.

The materials of the portable tank, including any devices, gaskets, and accessories, shall not adversely
affect the non-refrigerated liquefied gas(es) intended for carriage in the portable tank.

Portable tanks shall be designed and constructed with supports to provide a secure base during
carriage and with suitable lifting and tie-down attachments.

Portable tanks shall be designed to withstand, without loss of contents, at least the internal pressure
due to the contents, and the static, dynamic and thermal loads during normal conditions of handling
and carriage. The design shall demonstrate that the effects of fatigue, caused by repeated application
of these loads through the expected life of the portable tank, have been taken into account.

Shells shall be designed to withstand an external pressure of at least 0.4 bar (gauge pressure) above
the internal pressure without permanent deformation. When the shell is to be subjected to a significant
vacuum before filling or during discharge it shall be designed to withstand an external pressure of at
least 0.9 bar (gauge pressure) above the internal pressure and shall be proven at that pressure.

Portable tanks and their fastenings shall, under the maximum permissible load, be capable of
absorbing the following separately applied static forces:
(a) In the direction of travel: twice the MPGM multiplied by the acceleration due to gravity (g)1;
(b) Horizontally at right angles to the direction of travel: the MPGM (when the direction of travel
is not clearly determined, the forces shall be equal to twice the MPGM) multiplied by the
acceleration due to gravity (g)1;
(c) Vertically upwards: the MPGM multiplied by the acceleration due to gravity (g)1; and
(d) Vertically downwards: twice the MPGM (total loading including the effect of gravity)
multiplied by the acceleration due to gravity (g)1.

Under each of the forces in 6.7.3.2.9, the safety factor to be observed shall be as follows:
(a) For steels having a clearly defined yield point, a safety factor of 1.5 in relation to the
guaranteed yield strength; or
(b) For steels with no clearly defined yield point, a safety factor of 1.5 in relation to the guaranteed
0.2% proof strength and, for austenitic steels, the 1% proof strength.

The values of yield strength or proof strength shall be the values according to national or international
material standards. When austenitic steels are used, the specified minimum values of yield strength
and proof strength according to the material standards may be increased by up to 15% when these
greater values are attested in the material inspection certificate. When no material standard exists for
the steel in question, the value of yield strength or proof strength used shall be approved by the
competent authority.

thermal insulation, the thermal insulation systems shall satisfy the following requirements:
(a) It shall consist of a shield covering not less than the upper third but not more than the upper
half of the surface of the shell and separated from the shell by an air space about 40 mm across;
(b) It shall consist of a complete cladding of adequate thickness of insulating materials protected
so as to prevent the ingress of moisture and damage under normal conditions of carriage and so
as to provide a thermal conductance of not more than 0.67 (W.m-2.K-1);
(c) When the protective covering is so closed as to be gas-tight, a device shall be provided to
prevent any dangerous pressure from developing in the insulating layer in the event of
inadequate gas tightness of the shell or of its items of equipment; and
 
1 For calculation purposes g = 9.81 m/s2.
 
(d) The thermal insulation shall not inhibit access to the fittings and discharge devices.

Portable tanks intended for the carriage of flammable non-refrigerated liquefied gases shall be capable
of being electrically earthed.

Design criteria

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