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 22.214.171.124.9, 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
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.
Shells shall be of a circular cross-section.
Shells shall be designed and constructed to withstand a test pressure not less than 1.3 times the design
pressure. The shell design shall take into account the minimum MAWP values provided in portable
tank instruction T50 in 126.96.36.199.6 for each non-refrigerated liquefied gas intended for carriage.
Attention is drawn to the minimum shell thickness requirements for these shells specified in 188.8.131.52.
For steels exhibiting a clearly defined yield point or characterized by a guaranteed proof strength
(0.2% proof strength, generally, or 1% proof strength for austenitic steels) the primary membrane
stress σ (sigma) in the shell shall not exceed 0.75 Re or 0.50 Rm, whichever is lower, at the test
Re = yield strength in N/mm2, or 0.2% proof strength or, for austenitic steels, 1% proof
Rm = minimum tensile strength in N/mm2.
The values of Re and Rm to be used shall be the specified minimum values according to national or
international material standards. When austenitic steels are used, the specified minimum values for Re
and Rm 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 values of Re and Rm used shall be approved by the competent authority or its authorized
Steels which have a Re/Rm ratio of more than 0.85 are not allowed for the construction of welded
shells. The values of Re and Rm to be used in determining this ratio shall be the values specified in
the material inspection certificate.
Steels used in the construction of shells shall have an elongation at fracture, in %, of not less
than 10 000/Rm with an absolute minimum of 16% for fine grain steels and 20% for other steels.
For the purpose of determining actual values for materials, it shall be noted that for sheet metal, the
axis of the tensile test specimen shall be at right angles (transversely) to the direction of rolling. The
permanent elongation at fracture shall be measured on test specimens of rectangular cross sections in
accordance with ISO 6892:1998 using a 50 mm gauge length.