PED: equivalent overall level of safety

1. PED: equivalent overall level of safety PED Annex 1, clause 7: The following provision 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.

2. PED: equivalent overall level of safety – Annex 1 clause 7 Allowable stresses: 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: (See Guidelines: 7/14) - 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

3. PED: equivalent overall level of safety – Annex 1 clause 7 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.

4. PED: equivalent overall level of safety – Annex 1 clause 7 Hydrostatic test pressure: For pressure vessels, the hydrostatic test pressure referred to in 3.2.2 must be no less than: (See Guidelines: 3/6, 8/2) - 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.

5. PED: equivalent overall level of safety – Annex 1 clause 7 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. (See Guidelines: 7/13, 7/17, 7/18, 7/22)

6. PED: equivalent overall level of safety – guideline 8/6 Question:The first paragraph Annex I section 7 explicitly provides for exceptions to the general rules specified subsequently. How should the achievement of "an equivalent overall level of safety" in such a case be demonstrated? Answer:The specific quantitative requirements given in section 7 of Annex I are related to particular failure modes. If different values are used, the corresponding failure modes and their combination shall be identified and the measures taken to maintain an equivalent level of safety shall be provided in the technical documentation, with appropriate justifications. The achievement of "an equivalent overall level of safety" may be assumed if the measures taken provide adequate safety margins against all relevant failure modes in a consistent manner. Safety margins are adequate, and deviation from a particular value is justified : a) by a reduced risk in the respective failure mode, or b) by additional means to ensure no increase of the risk. When using a harmonised standard for pressure equipment which has been published in the Official Journal of the European Communities, no further justification is needed for the quantitative values which have been used as regard Annex I section 7 .(refer also to guideline 7/1) The requirement to demonstrate an equivalent overall level of safety applies to the product itself, and to the measures taken to meet the essential safety requirements. The use of a "recognised" code is not, in itself, sufficient to demonstrate an equivalent overall level of safety .(refer also to guideline 9/5)

7. PED: equivalent overall level of safety – guideline 9/6 Question:In which conditions is it possible to use a document other than a harmonised standard (national standard, professional code or private technical document) for the design and manufacture of pressure equipment for the application of PED ? Answer: The use of the harmonised standard is not mandatory. However, the directive did not include provisions to give presumption of conformity to documents other than harmonised standards. A manufacturer using another document shall describe in his technical documentation the solutions adopted to meet the essential requirements of the directive. The notified body (or the user inspectorate) shall validate, if required by the module chosen, these solutions. 3) The technical requirements of the Directive are given in Annex I. When using a national standard, a professional code or a private technical document for fulfilling Annex I, only the technical content of this document is relevant. Further provisions of this document (e.g. about bodies or certification procedures) are not relevant for the application of PED.

8. PED: equivalent overall level of safety Failure modes: • Global plastic deformation • Instability • Cyclic Fatigue (depends on the service time) • Corrosion (depends usually on the service time) • Creep (depends on the service time)

9. PED: equivalent overall level of safety The equivalent overall level of safety is used within the framework of the PED, i.e. it concern the safety of the pressure equipment to be put on the European market. Thus it applies to the design, manufacture and conformity assessment of pressure equipment. In service examinations, specific or periodically, may - depending on the amount and frequency - increase the in-service-safety of the equipment, but have obviously no influence on its safety level when it is put on the market. Thus, planed in service examinations cannot be used to claim an overall level of safety. But service restrictions shall be noted in the operating instructions.