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 metallic materials 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 suitably 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. Aluminium may only be used as a construction
material when indicated in a portable tank special provision assigned to a specific substance in
Column (11) of Table A of Chapter 3.2 or when approved by the competent authority. When
aluminium is authorized, it shall be insulated to prevent significant loss of physical properties when
subjected to a heat load of 110 kW/m2 for a period of not less than 30 minutes. The insulation shall
remain effective at all temperatures less than 649 °C and shall be jacketed with a material with a
melting point of not less than 700 °C. 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 from materials which are:
(a) Substantially immune to attack by the substance(s) intended to be carried; or
(b) Properly passivated or neutralized by chemical reaction; or
(c) Lined with corrosion-resistant material directly bonded to the shell or attached by equivalent
Gaskets shall be made of materials not subject to attack by the substance(s) intended to be carried.
When shells are lined, the lining shall be substantially immune to attack by the substance(s) intended
to be carried, homogeneous, non porous, free from perforations, sufficiently elastic and compatible
with the thermal expansion characteristics of the shell. The lining of every shell, shell fittings and
piping shall be continuous, and shall extend around the face of any flange. Where external fittings are
welded to the tank, the lining shall be continuous through the fitting and around the face of external
Joints and seams in the lining shall be made by fusing the material together or by other equally
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, linings and accessories, shall not
adversely affect the substance(s) intended to be carried 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.
For portable tanks that are intended for use offshore, the dynamic stresses imposed by handling in
open seas shall be taken into account.
A shell which is to be equipped with a vacuum-relief device shall be designed to withstand, without
permanent deformation, an external pressure of not less than 0.21 bar above the internal pressure. The
vacuum-relief device shall be set to relieve at a vacuum setting not greater than minus (-) 0.21 bar
unless the shell is designed for a higher external over pressure, in which case the vacuum-relief
pressure of the device to be fitted shall be not greater than the tank design vacuum pressure. A shell
used for the carriage of solid substances (powdery or granular) of packing groups II or III only, which
do not liquefy during carriage, may be designed for a lower external pressure, subject to the approval
of the competent authority. In this case, the vacuum valve shall be set to relieve at this lower pressure.
A shell that is not to be fitted with a vacuum-relief device shall be designed to withstand, without
permanent deformation an external pressure of not less than 0.4 bar above the internal pressure.
Vacuum-relief devices used on portable tanks intended for the carriage of substances meeting the
flash-point criteria of Class 3, including elevated temperature substances carried at or above their
flash-point, shall prevent the immediate passage of flame into the shell, or the portable tank shall have
a shell capable of withstanding, without leakage an internal explosion resulting from the passage of
flame into the shell.
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 18.104.22.168.12, the safety factor to be observed shall be as follows:
(a) For metals having a clearly defined yield point, a safety factor of 1.5 in relation to the
guaranteed yield strength; or
(b) For metals 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.