Directive 97/23/EC
ANNEX I: 7. SPECIFIC QUANTITATIVE
REQUIREMENTS FOR CERTAIN PRESSURE
EQUIPMENT
Guideline
The following provisions apply as a general rule. However, where they are not applied, including in
cases where materials are not specifically referred to and no harmonized standards are applied, the
manufacturer must demonstrate that appropriate measures have been taken to achieve an
equivalent overall level of safety.
This section is an integral part of Annex I. The provisions laid down in this section supplement the
essential requirements of sections 1 to 6 for the pressure equipment to which they apply.
7.1. Allowable stresses
7.1.1. Symbols
Re/t, yield limit, indicates the value at the calculation temperature of:
the upper flow limit for a material presenting upper and lower flow limits,
the 1,0% proof strength of austenitic steel and non-alloyed aluminium,
the 0,2% proof strength in other cases.
Rm/20, indicates the minimum value of the ultimate strength 20 °C.
Rm/t, designates the ultimate strength at the calculation temperature.
7.1.2. The permissible general membrane stress for predominantly static loads and for temperatures
outside the range in which creep is significant must not exceed the smaller of the following values,
according to the material used:
in the case of ferritic steel including normalized (normalized rolled) steel and excluding fine-grained steel and specially heat-treated steel,
2/3 of Re/t and 5/12 of Rm/20
in the case of austenitic steel:
if its elongation after rupture exceeds 30%, 2/3 of Re/t
or, alternatively, and if its elongation after rupture exceeds 35%, 5/6 of Re/t and 1/3 of Rm/t
in the case of non-alloy or low-alloy cast steel, 10/19 of Re/t and 1/3 of Rm/20
in the case of aluminium, 2/3 of Re/t
in the case of aluminium alloys excluding precipitation hardening alloys 2/3 of Re/t and 5/12 of Rm/20
Guideline
7.2. Joint coefficients
For welded joints, the joint coefficient must not exceed the following values:
for equipment subject to destructive and non-destructive tests which confirm that the whole series of joints show no significant defects: 1,
for equipment subject to random non-destructive testing: 0,85
for equipment not subject to non-destructive testing other than visual inspection: 0,7.
If necessary, the type of stress and the mechanical and technological properties of the joint must
also be taken into account.
Guidelines
7.3. Pressure limiting devices, particularly for pressure vessels
The momentary pressure surge referred to in 2.11.2 must be kept to 10% of the maximum allowable
pressure.
7.4. Hydrostatic test pressure
For pressure vessels, the hydrostatic test pressure referred to in 3.2.2 must be no less than:
that corresponding to the maximum loading to which the pressure equipment may be subject in service taking into account its maximum
allowable pressure and its maximum allowable temperature, multiplied by the coefficient 1,25, or
the maximum allowable pressure multiplied by the coefficient 1,43, whichever is the greater.
Guidelines
7.5. Material characteristics
Unless other values are required in accordance with other criteria that must be taken into account, a
steel is considered as sufficiently ductile to satisfy 4.1 (a) if, in a tensile test carried out by a
standard procedure, its elongation after rupture is no less than 14 % and its bending rupture energy
measured on an ISO V test-piece is no less than 27 J, at a temperature not greater than 20 °C but not
higher than the lowest scheduled operating temperature.
Guidelines
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