Portable tanks intended for the carriage of flammable 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
MAWP. For shells with vacuum insulation the test pressure shall not be less than 1.3 times the sum of
the MAWP and 100 kPa (1 bar). In no case shall the test pressure be less than 300 kPa (3 bar) (gauge
1 For calculation purposes g = 9.81 m/s2.
pressure). Attention is drawn to the minimum shell thickness requirements, specified in 22.214.171.124.2
For metals 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 greater values are
attested in the material inspection certificate. When no material standard exists for the metal 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.
Aluminium and aluminium alloys used in the construction of shells shall have an elongation at
fracture, in %, of not less than 10 000/6Rm with an absolute minimum of 12%.
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 6892:1988 using a 50 mm gauge length.
Minimum shell thickness
The minimum shell thickness shall be the greater thickness based on:
(a) The minimum thickness determined in accordance with the requirements in 126.96.36.199.2
to 188.8.131.52.7; or
(b) The minimum thickness determined in accordance with the recognized pressure vessel code
including the requirements in 184.108.40.206.
Shells of not more than 1.80 m in diameter shall be not less than 5 mm thick in the reference steel or
of equivalent thickness in the metal to be used. Shells of more than 1.80 m in diameter shall be not
less than 6 mm thick in the reference steel or of equivalent thickness in the metal to be used.
Shells of vacuum-insulated tanks of not more than 1.80 m in diameter shall be not less than 3 mm
thick in the reference steel or of equivalent thickness in the metal to be used. Such shells of more
than 1.80 m in diameter shall be not less than 4 mm thick in the reference steel or of equivalent
thickness in the metal to be used.
For vacuum-insulated tanks, the aggregate thickness of the jacket and the shell shall correspond to the
minimum thickness prescribed in 220.127.116.11.2, the thickness of the shell itself being not less than the
minimum thickness prescribed in 18.104.22.168.3.
Shells shall be not less than 3 mm thick regardless of the material of construction.