Dangerous Goods by Road
Capacity and setting of pressure-relief devices
NOTE: In relation to pressure-relief devices of closed cryogenic receptacles, maximum allowable
working pressure (MAWP) means the maximum effective gauge pressure permissible at the top of a
loaded closed cryogenic receptacle in its operating position including the highest effective pressure
during filling and discharge.
The pressure-relief device shall open automatically at a pressure not less than the MAWP and be fully
open at a pressure equal to 110% of the MAWP. It shall, after discharge, close at a pressure not lower
than 10% below the pressure at which discharge starts and shall remain closed at all lower pressures.
Frangible discs shall be set to rupture at a nominal pressure which is the lower of either the test
pressure or 150% of the MAWP.
In the case of the loss of vacuum in a vacuum-insulated closed cryogenic receptacle the combined
capacity of all pressure-relief devices installed shall be sufficient so that the pressure (including
accumulation) inside the closed cryogenic receptacle does not exceed 120% of the MAWP.
The required capacity of the pressure-relief devices shall be calculated in accordance with an
established technical code recognized by the competent authority1.
Approval of pressure receptacles
The conformity of pressure receptacles shall be assessed at time of manufacture as required by the
competent authority. Pressure receptacles shall be inspected, tested and approved by an inspection
body. The technical documentation shall include full specifications on design and construction, and
full documentation on the manufacturing and testing.
Quality assurance systems shall conform to the requirements of the competent authority.
1 See for example CGA Publications S-1.2-2003 "Pressure Relief Device Standards-Part 2-Cargo and Portable
Tanks for Compressed Gases" and S-1.1-2003 "Pressure Relief Device Standards-Part 1-Cylinders for Compressed
Gases".
Initial inspection and test
New pressure receptacles, other than closed cryogenic receptacles and metal hydride storage
systems,
shall be subjected to testing and inspection during and after manufacture in accordance with the
applicable design standards including the following:
On an adequate sample of pressure receptacles:
(a) Testing of the mechanical characteristics of the material of construction;
(b) Verification of the minimum wall thickness;
(c) Verification of the homogeneity of the material for each manufacturing batch;
(d) Inspection of the external and internal conditions of the pressure receptacles;
(e) Inspection of the neck threads;
(f) Verification of the conformance with the design standard; For all pressure receptacles:
(g) A hydraulic pressure test. Pressure receptacles shall meet the acceptance criteria
specified in the design and construction technical standard or technical code;
NOTE: With the agreement of the competent authority, the hydraulic pressure test may be
replaced by a test using a gas, where such an operation does not entail any danger.
(h) Inspection and assessment of manufacturing defects and either repairing them or rendering
the pressure receptacles unserviceable. In the case of welded pressure receptacles, particular
attention shall be paid to the quality of the welds;
(i) An inspection of the marks on the pressure receptacles;
(j) In addition, pressure receptacles intended for the carriage of UN No. 1001 acetylene,
dissolved, and UN No. 3374 acetylene, solvent free, shall be inspected to ensure proper
installation and condition of the porous material and, if applicable, the quantity of solvent.
On an adequate sample of closed cryogenic receptacles, the inspections and tests specified in
6.2.1.5.1
(a), (b), (d) and (f) shall be performed. In addition, welds shall be inspected by radiographic,
ultrasonic or another suitable non-destructive test method on a sample of closed cryogenic
receptacles according to the applicable design and construction standard. This weld inspection does
not apply to the jacket.
Additionally, all closed cryogenic receptacles shall undergo the initial inspections and tests
specified in 6.2.1.5.1 (g), (h) and (i), as well as a leakproofness test and a test of the
satisfactory operation of the
service equipment after assembly.
For metal hydride storage systems, it shall be verified that the inspections and tests specified in
6.2.1.5.1 (a), (b), (c), (d), (e) if applicable, (f), (g), (h) and (i) have been performed on an adequate
sample of the receptacles used in the metal hydride storage system. In addition, on an adequate sample
of metal hydride storage systems, the inspections and tests specified in 6.2.1.5.1 (c) and (f) shall be
performed, as well as 6.2.1.5.1 (e), if applicable, and inspection of the external conditions of the metal
hydride storage system.
Additionally, all metal hydride storage systems shall undergo the initial inspections and tests specified
in 6.2.1.5.1 (h) and (i), as well as a leakproofness test and a test of the satisfactory operation of the
service equipment.
Periodic inspection and test
Refillable pressure receptacles, other than cryogenic receptacles, shall be subjected to periodic
inspections and tests by a body authorised by the competent authority, in accordance with the
following:
(a) Check of the external conditions of the pressure receptacle and verification of the equipment
and the external marks;
(b) Check of the internal conditions of the pressure receptacle (e.g. internal inspection,
verification of minimum wall thickness);
(c) Checking of the threads if there is evidence of corrosion or if the fittings are removed;
(d) A hydraulic pressure test and, if necessary, verification of the characteristics of the material
by suitable tests;
(e) Check of service equipment, other accessories and pressure-relief devices, if to be
reintroduced into service.
NOTE 1: With the agreement of the competent authority, the hydraulic pressure test may be
replaced by a test using a gas, where such an operation does not entail any danger.
NOTE 2: With the agreement of the competent authority, the hydraulic pressure test of cylinders
or tubes may be replaced by an equivalent method based on acoustic emission testing or a
combination of acoustic emission testing and ultrasonic examination. ISO 16148:2006 may be used as
a guide for acoustic emission testing procedures.
NOTE 3: The hydraulic pressure test may be replaced by ultrasonic examination carried out in
accordance with ISO 10461:2005+A1:2006 for seamless aluminium alloy gas cylinders and in
accordance with ISO 6406:2005 for seamless steel gas cylinders.
NOTE 4: For the periodic inspection and test frequencies, see packing instruction P200 of 4.1.4.1
or, for a chemical under pressure, packing instruction P206 of 4.1.4.1.
Pressure receptacles intended for the carriage of UN No. 1001 acetylene, dissolved and UN No. 3374
acetylene, solvent free, shall be examined only as specified in 6.2.1.6.1 (a), (c) and (e). In addition the
condition of the porous material (e.g. cracks, top clearance, loosening, settlement) shall be examined.