Dangerous Goods by Road
Calculation of the shell thickness
The pressure on which the shell thickness is based shall not be less than the calculation pressure, but
the stresses referred to in 6.8.2.1.1 shall also be taken into account, and, if necessary, the following
stresses:
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In the case of vehicles in which the tank
constitutes a stressed self-supporting member,
the shell shall be designed to withstand the
stresses thus imposed in addition to stresses from
other sources.
Under these stresses, the stress at the most
severely stressed point of the shell and its
fastenings shall not exceed the value σ defined in
6.8.2.1.16.
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Under each of these stresses the safety factors to
be observed shall be the following:
- for metals having a clearly-defined yield
point: a safety factor of 1.5 in relation to the
apparent yield strength; or
- for metals with no clearly-defined yield
point: a safety factor of 1.5 in relation to the
guaranteed 0.2% proof strength
(1% maximum elongation for austenitic
steels).
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1 In the case of sheet metal the axis of the tensile test-piece shall be at right angles to the direction of rolling. The
permanent elongation at fracture shall be measured on test-pieces of circular cross-section in which the gauge length l
is equal to five times the diameter d (l = 5d); if test-pieces of rectangular section are used, the gauge length shall be
calculated by the formula
where Fo indicates the initial cross-section area of the test-piece.
The calculation pressure is in the second part of the code (see 4.3.4.1) according to Column (12) of
Table A of Chapter 3.2.
When "G" appears, the following requirements shall apply:
(a) Gravity-discharge shells intended for the carriage of substances having a vapour pressure not
exceeding 110 kPa (1.1 bar) (absolute pressure) at 50 ºC shall be designed for a calculation
pressure of twice the static pressure of the substance to be carried but not less than twice the
static pressure of water;
(b) Pressure-filled or pressure-discharge shells intended for the carriage of substances having a
vapour pressure not exceeding 110 kPa (1.1 bar) (absolute pressure) at 50 ºC shall be designed
for a calculation pressure equal to 1.3 times the filling or discharge pressure;
When the numerical value of the minimum calculation pressure is given (gauge pressure) the shell
shall be designed for this pressure which shall not be less than 1.3 times the filling or discharge
pressure. The following minimum requirements shall apply in these cases:
(c) Shells intended for the carriage of substances having a vapour pressure of more than 110 kPa
(1.1 bar) at 50 °C and a boiling point of more than 35 °C shall, whatever their filling or
discharge system, be designed for a calculation pressure of not less than 150 kPa (1.5 bar)
gauge pressure or 1.3 times the filling or discharge pressure, whichever is the higher;
(d) Shells intended for the carriage of substances having a boiling point of not more than 35 °C
shall, whatever their filling or discharge system, be designed for a calculation pressure equal to
1.3 times the filling or discharge pressure but not less than 0.4 MPa (4 bar) (gauge pressure).
At the test pressure, the stress σ at the most severely stressed point of the shell shall not exceed the
material-dependent limits prescribed below. Allowance shall be made for any weakening due to the
welds.
For all metals and alloys, the stress σ at the test pressure shall be lower than the smaller of the values
given by the following formulae:
σ ≤ 0.75 Re or σ ≤ 0.5 Rm
where
Re = apparent yield strength for steels having a clearly-defined yield point; or
guaranteed 0.2% proof strength for steels with no clearly-defined yield point (1% for
austenitic steels)
Rm = tensile strength.
The values of Re and Rm to be used shall be specified minimum values according to material
standards. If no material standard exists for the metal or alloy in question, the values of Re and
Rm used shall be approved by the competent authority or by a body designated by that
authority.
When austenitic steels are used, the specified minimum values according to the material standards
may be exceeded by up to 15% if these higher values are attested in the inspection certificate. The
minimum values shall, however, not be exceeded when the formula given in 6.8.2.1.18 is applied.
Minimum shell thickness
The shell thickness shall not be less than the greater of the values determined by the following
formulae:
where:
e = minimum shell thickness in mm
PT = test pressure in MPa
PC = calculation pressure in MPa as specified in 6.8.2.1.14
D = internal diameter of shell in mm
σ = permissible stress, as defined in 6.8.2.1.16, in N/mm2
λ = a coefficient not exceeding 1, allowing for any weakening due to welds, and linked to
the inspection methods defined in 6.8.2.1.23.
The thickness shall in no case be less than that defined in
| 6.8.2.1.18 to 6.8.2.1.21. | 6.8.2.1.18 to 6.8.2.1.20. |
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Shells of circular cross-section 2 not more than
1.80 m in diameter other than those referred to in
6.8.2.1.21, shall not be less than 5 mm thick if of
mild steel3, or of equivalent thickness if of
another metal.
Where the diameter is more than 1.80 m, this
thickness shall be increased to 6 mm except in
the case of shells intended for the carriage of
powdery or granular substances, if the shell is of
mild steel3, or to an equivalent thickness if of
another metal.
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Shells shall be not less than 5 mm thick if of mild
steel3 (in conformity with the requirements of
6.8.2.1.11 and 6.8.2.1.12) or of equivalent
thickness if of another metal.
Where the diameter is more than 1.80 m, this
thickness shall be increased to 6 mm except in
the case of tanks intended for the carriage of
powdery or granular substances, if the shell is of
mild steel3 or to an equivalent thickness if of
another metal.
Whatever the metal used, the shell thickness
shall in no case be less than 3 mm.
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Where protection of the tank against damage
through lateral impact or overturning is provided
according to 6.8.2.1.20, the competent authority
may allow the aforesaid minimum thicknesses to
be reduced in proportion to the protection
provided; however, the said thicknesses shall not
be less than 3 mm in the case of mild steel3, or
than an equivalent thickness in the case of other
materials, for shells not more than 1.80 m in
diameter. For shells with a diameter exceeding
1.80 m the aforesaid minimum thickness shall be
increased to 4 mm in the case of mild steel3 and
to an equivalent thickness in the case of other
metals.
Equivalent thickness means the thickness given
by the formula in 6.8.2.1.18.
Except in cases for which 6.8.2.1.21 provide, the
thickness of shells with protection against
damage in accordance with 6.8.2.1.20 (a) or (b)
shall not be less than the values given in the
table below.
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Where protection of the tank against damage is
provided according to 6.8.2.1.20, the competent
authority may allow the aforesaid minimum
thicknesses to be reduced in proportion to the
protection provided; however, the said
thicknesses shall be not less than 3 mm in the
case of mild steel3, or than an equivalent
thickness in the case of other materials, for shells
not more than 1.80 m in diameter. For shells of a
diameter exceeding 1.80 m this minimum
thickness shall be increased to 4 mm in the case
of mild steel3, and to an equivalent thickness in
the case of other metals.
Equivalent thickness means the thickness given
by the formula in 6.8.2.1.18.
The thickness of shells with protection against
damage in accordance with 6.8.2.1.20 shall not
be less than the values given in the table below.
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Diameter of shell |
≤ 1,80 m |
> 1,80 m |
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Minimum
thickness of
shells
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Austenitic stainless steels | 2,5 mm |
3 mm |
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Austenitic-ferritic stainless
steels
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3 mm |
3,5 mm |
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| Other steels |
3 mm |
4 mm |
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Aluminium alloys |
4 mm |
5 mm |
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Pure aluminium of 99.80% |
6 mm |
8 mm |
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For tanks built after 1 January 1990, there is
protection against damage as referred to in
6.8.2.1.19 when the following measures or
equivalent5 measures are adopted:
(a) For tanks intended for the carriage of
powdery or granular substances, the
protection against damage shall satisfy the
competent authority.
(b) For tanks intended for the carriage of other
substances, there is protection against
damage when:
1. For shells with a circular or elliptical
cross-section having a maximum radius
of curvature of 2 m, the shell is
equipped with strengthening members
comprising partitions, surge-plates or
external or internal rings, so placed that
at least one of the following conditions
is met:
- Distance between two adjacent
strengthening elements of not more
than 1.75 m.
- Volume contained between two
partitions or surge-plates of not
more than 7 500 l.
The vertical cross-section of a ring,
with the associated coupling, shall have
a section modulus of at least 10 cm3.
External rings shall not have projecting
edges with a radius of less than
2.5 mm.
Partitions and surge-plates shall
conform to the requirements of
6.8.2.1.22.
The thickness of the partitions and
surge-plates shall in no case be less
than that of the shell.
2. For tanks made with double walls, the
space between being evacuated of air,
the aggregate thickness of the outer
metal wall and the shell wall
corresponds to the wall thickness
prescribed in 6.8.2.1.18, and the
thickness of the wall of the shell itself
is not less than the minimum thickness
prescribed in 6.8.2.1.19.
3. For tanks made with double walls
having an intermediate layer of solid
materials at least 50 mm thick, the
outer wall has a thickness of at least
0.5 mm of mild steel3 or at least 2 mm
of a plastics material reinforced with
glass fibre. Solid foam (with an impact
absorption capacity like that, for
example, of polyurethane foam) may be
used as the intermediate layer of solid
material.
4. Shells of forms other than in 1,
especially box-shaped shells, are
provided, all round the mid-point of
their vertical height and over at least
30% of their height with a protection
designed in such a way as to offer
specific resilience at least equal to that
of a shell constructed in mild steel3 of a
thickness of 5 mm (for a shell diameter
not exceeding 1.80 m) or 6 mm (for a
shell diameter exceeding 1.80 m). The
protection shall be applied in a durable
manner to the shell.
This requirement shall be considered to
have been met without further proof of
the specific resilience when the
protection involves the welding of a
plate of the same material as the shell to
the area to be strengthened, so that the
minimum wall thickness is in
accordance with 6.8.2.1.18.
This protection is dependent upon the
possible stresses exerted on mild steel3
shells in the event of an accident, where
the ends and walls have a thickness of
at least 5 mm for a diameter not
exceeding 1.80 m or at least 6 mm for a
diameter exceeding 1.80 m. If another
metal is used, the equivalent thickness
shall be obtained in accordance with the
formula in 6.8.2.1.18.
For demountable tanks this protection is not
required when they are protected on all sides by
the drop sides of the carrying vehicle.
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The protection referred to in 6.8.2.1.19 may
consist of:
- overall external structural protection as in
"sandwich" construction where the sheathing
is secured to the shell; or
- a structure in which the shell is supported by a
complete skeleton including longitudinal and
transverse structural members; or
- double-wall construction.
Where the tanks are made with double walls, the
space between being evacuated of air, the
aggregate thickness of the outer metal wall and
the shell wall shall correspond to the minimum
wall thickness prescribed in 6.8.2.1.18, the
thickness of the wall of the shell itself being not
less than the minimum thickness prescribed in
6.8.2.1.19.
Where tanks are made with double walls with an
intermediate layer of solid materials at least
50 mm thick, the outer wall shall have a
thickness of not less than 0.5 mm if it
is made of mild steel3 or at least 2 mm if it is
made of a plastics material reinforced with glass
fibre. Solid foam with an impact absorption
capacity such as that, for example, of
polyurethane foam, may be used as the
intermediate layer of solid material.
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The thickness of shells designed in accordance with 6.8.2.1.14 (a) which either are of not more than 5 000 litres capacity or are divided into leakproof compartments of not more than 5 000 litres unit capacity may be adjusted to a level which, unless prescribed otherwise in 6.8.3 or 6.8.4, shall however not be less than the appropriate value shown in the following table: |
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Maximum radius of curvature of shell (m) |
Capacity of shell or shell compartment (m3) |
Minimum thickness (mm) |
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Mild steel |
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2 |
5.0 |
3 |
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2 - 3 |
3.5 |
3 |
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> 3.5 but 5.0 |
4 |
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Where a metal other than mild steel3 is used, the thickness shall be determined by the equivalence formula given in 6.8.2.1.18 and shall not be less than the values given in the following table: |
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Maximum radius of curvature of shell (m) |
2 |
2-3 |
2-3 |
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Capacity of shell or shell compartment (m3) |
5.0 |
3.5 |
> 3.5 but 5.0 |
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Minimum thickness of shell |
Austenitic stainless steels |
2.5 mm |
2.5 mm |
3 mm |
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Austenitic- ferritic stainless steels |
3 mm |
3 mm |
3.5 mm |
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Other steels |
3 mm |
3 mm |
4 mm |
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Aluminium alloys |
4 mm |
4 mm |
5 mm |
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Pure aluminium at 99.80% |
6 mm |
6 mm |
8 mm |
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The thickness of the partitions and surge-plates
shall in no case be less than that of the shell.
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Surge-plates and partitions shall be dished, with
a depth of dish of not less than 10 cm, or shall be
corrugated, profiled or otherwise reinforced to
give equivalent strength. The area of the surge
plate shall be at least 70% of the cross-sectional
area of the tank in which the surge-plate is fitted.
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Welding and inspection of welds
The ability of the manufacturer to perform welding operations shall be verified and confirmed by
either the competent authority or by the body designated by this authority, which issues the type
approval. A weld quality assurance system shall be operated by the manufacturer. Welding shall be
performed by qualified welders using a qualified welding process whose effectiveness (including
any heat treatments required) has been demonstrated by tests. Non-destructive tests shall be carried
out by radiography or by ultrasound and shall confirm that the quality of the welding is appropriate
to the stresses.
The following checks shall be carried out for welds made by each welding process used by the
manufacturer in accordance with the value of the coefficient λ used in determining the thickness of
the shell in 6.8.2.1.17:
λ = 0.8: All weld beads shall so far as possible be inspected visually on both faces and shall
be subjected to non-destructive checks. The non-destructive checks shall include all
weld “Tee” junctions and all inserts used to avoid welds crossing. The total length
of welds to be examined shall not be less than:
10% of the length of all the longitudinal welds,
10% of the length of all the circumferential welds,
10% of the length of all the circumferential welds in the tank ends, and
10% of the length of all the radial welds in the tank ends.
λ = 0.9: All weld beads shall so far as possible be inspected visually on both faces and shall
be subjected to non-destructive checks. The non-destructive checks shall include all
connections, inserts used to avoid welds crossing, and welds for the assembly of
large-diameter items of equipment. The total length of welds to be examined shall
not be less than:
100% of the length of all the longitudinal welds,
25% of the length of all the circumferential welds,
25% of the length of all the circumferential welds in the tank ends, and
25% of the length of all the radial welds in the tank ends.
λ = 1: All weld beads throughout their length shall be subjected to non-destructive checks
and shall so far as possible be inspected visually on both faces. A weld test-piece
shall be taken.
In the cases of either λ = 0.8 or λ = 0.9, when the presence of an unacceptable defect is detected in a
portion of a weld, the non-destructive checks shall be extended to a portion of equal length on both
sides of the portion that contains the defect. If the non-destructive checks detect an additional defect
that is unacceptable, non-destructive checks shall be extended to all remaining welds of the same
type of welding process.
Where either the competent authority or a body designated by this authority has doubts regarding
the quality of welds, including the welds made to repair any defects revealed by the non-destructive
checks, it may require additional checks.
3 For the definitions of "mild steel" and "reference steel" see 1.2.1. "Mild steel" in this case also covers a steel
referred to in EN material standards as "mild steel", with a minimum tensile strength between 360 N/mm² and
490 N/mm² and a minimum elongation at fracture conforming to 6.8.2.1.12.
5 Equivalent measures means measures given in standards referenced in 6.8.2.6.
Other construction requirements
The protective lining shall be so designed that its leakproofness remains intact, whatever the
deformation liable to occur in normal conditions of carriage (see 6.8.2.1.2).
The thermal insulation shall be so designed as not to hinder access to, or the operation of, filling and
discharge devices and safety valves.
If shells intended for the carriage of flammable liquids having a flash-point of not more than 60 ºC
are fitted with non-metallic protective linings (inner layers), the shells and the protective linings shall
be so designed that no danger of ignition from electrostatic charges can occur.
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Shells intended for the carriage of liquids having
a flash-point of not more than 60 ºC or for the
carriage of flammable gases, or of UN No.1361
carbon or UN No.1361 carbon black, packing
group II, shall be linked to the chassis by means
of at least one good electrical connection. Any
metal contact capable of causing electrochemical
corrosion shall be avoided. Shells shall be
provided with at least one earth fitting
clearly marked with the symbol
 capable
of being electrically connected.
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All parts of a tank-container intended for the
carriage of liquids having a flash-point of not
more than 60 ºC, flammable gases, or UN
No.1361 carbon or UN No.1361 carbon black,
packing group II, shall be capable of being
electrically earthed. Any metal contact capable
of causing electrochemical corrosion shall be
avoided.
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