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ASME Boiler and Pressure Vessel Code Stamped Vessels and the PED
The Pressure Equipment Directive (PED or Directive 97/23/EC) became mandatory in the European Union in May of 2002. Along with the Simple Pressure Vessel Directive (Directive 2009/105/EC) and directives addressing portable pressure vessels and aerosol cans, it sets mandatory requirements for pressure vessels in EU member countries. These directives establish the requirements for pressure vessels in what are generally very broad terms (the PED, which covers both fired and unfired vessels is only 58 pages long). The text of these directives may be found at http://ec.europa.eu/enterprise/sectors/pressure-and-gas/documents/ped. These directives set the requirements for a pressure vessel to receive the CE or "Conformite Europeene" stamp. In addition, the Committee for European Standardization (CEN) establishes standards, which are then adopted by all EU member countries. EN 13445 is the European Union standard for unfired pressure vessels, however, unlike the PED and the SPED, the standards are not mandatory. However, conforming to the appropriate standard will often lessen the reporting and inspection requirements to obtain a CE stamp.
Will an ASME U stamped vessel automatically qualify for a CE marking? At present, no. However, additional design documentation, welding process qualification / welder certification requirements, material certification, and quality control documentation will be required in order to obtain PED certification. Efforts to improve compatibility of the ASME code and the PED are likely to continue, however, it seems unlikely that the ASME code stamp and the CE designation will be interchangeable in the near future. In the PED, a Notified Body plays a role analogous to that of the Authorized Inspector in the ASME code. Most engineering firms which offer ASME code inspections are also qualified to serve as a Notified Body and can approve the issue of a CE stamp. These firms can offer guidance in navigating the PED requirements. The ASME also publishes guides intended to explain PED requirements to manufacturers of ASME code stamped vessels.
The PED classifies pressure vessels into categories I–IV according to their degree of risk, with category I vessels being the lowest risk. The category of a vessel is determined by the product of the volume and the maximum pressure, and by the type of fluid the vessel is intended to hold. Fluids are grouped into two types; hazardous or group 1 and non-hazardous or group 2. For each category, the manufacturer has a choice of modules. These modules govern the design, inspection, testing and quality control requirements for that vessel. For example, assume that we have a 10 gallon tank with a MAWP (maximum allowable working pressure) of 100 psi and an MDMT (minimum design metal temperature) of -320 F to be filled with helium gas. That helium is nontoxic and not flammable and that the product of the volume and maximum pressure is 1000 psi-gallons (260 bar-liters) make this a category III vessel. Annex II of the PED indicates that for a category III vessel we may choose between Modules B1+D, B1+F, B+E, B+C1 or H. The Modules are given in Annex III of the PED. Modules B and B1, for example, describe different approaches to the design review for the vessel while Modules D, E and F each deal with different approaches to quality control. For all Category III and IV vessels, the weld procedure and welder qualifications must be approved by a Notified Body (or an approved third party). This is also the case for individuals performing NDT. The European welding and NDT requirements are not very different from those of the ASME code, however, one cannot be substituted for the other. Welding procedures and welder qualifications tailored to the PED will be required and these must be approved by the Notified Body. A detailed design review, involving the Notified Body, demonstrating that the requirements of the PED are met will generally be needed. The material requirements must also be met. There are three ways in which material can be approved under the PED; using a material which complies with an appropriate EN standard, by using a material listed as Approved for European Pressure Vessels or by obtaining a particular material appraisal. A particular material appraisal requires that the suitability of the material for a particular application be demonstrated. For category III and IV vessels the particular material appraisal must be approved by the Notified Body. The manufacturer will be required to establish and document a suitable quality control system, details of which will depend on the combination of modules which are selected. Finally, how will our MDMT of -320F be treated under the PED? Annex I paragraph 7.5 of the PED states:
"… a steel is considered as sufficiently ductile… 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 20C but not higher than the lowest scheduled operating temperature."
Testing at the MDMT is one method of demonstrating that the material is sufficiently ductile. However, testing at the MDMT can be avoided if it can be demonstrated that the material selected is sufficiently ductile and tough by other means.
For manufacturers of ASME code vessels, certifying a product to the PED is far from automatic. Considerable work will be needed to document the design, the materials and the quality control program. The work required will scale with the size and operating pressure of the vessel. Working with a Notified Body will be required for any vessel bearing the CE stamp.
Will an ASME U stamped vessel automatically qualify for a CE marking? At present, no. However, additional design documentation, welding process qualification / welder certification requirements, material certification, and quality control documentation will be required in order to obtain PED certification. Efforts to improve compatibility of the ASME code and the PED are likely to continue, however, it seems unlikely that the ASME code stamp and the CE designation will be interchangeable in the near future. In the PED, a Notified Body plays a role analogous to that of the Authorized Inspector in the ASME code. Most engineering firms which offer ASME code inspections are also qualified to serve as a Notified Body and can approve the issue of a CE stamp. These firms can offer guidance in navigating the PED requirements. The ASME also publishes guides intended to explain PED requirements to manufacturers of ASME code stamped vessels.
The PED classifies pressure vessels into categories I–IV according to their degree of risk, with category I vessels being the lowest risk. The category of a vessel is determined by the product of the volume and the maximum pressure, and by the type of fluid the vessel is intended to hold. Fluids are grouped into two types; hazardous or group 1 and non-hazardous or group 2. For each category, the manufacturer has a choice of modules. These modules govern the design, inspection, testing and quality control requirements for that vessel. For example, assume that we have a 10 gallon tank with a MAWP (maximum allowable working pressure) of 100 psi and an MDMT (minimum design metal temperature) of -320 F to be filled with helium gas. That helium is nontoxic and not flammable and that the product of the volume and maximum pressure is 1000 psi-gallons (260 bar-liters) make this a category III vessel. Annex II of the PED indicates that for a category III vessel we may choose between Modules B1+D, B1+F, B+E, B+C1 or H. The Modules are given in Annex III of the PED. Modules B and B1, for example, describe different approaches to the design review for the vessel while Modules D, E and F each deal with different approaches to quality control. For all Category III and IV vessels, the weld procedure and welder qualifications must be approved by a Notified Body (or an approved third party). This is also the case for individuals performing NDT. The European welding and NDT requirements are not very different from those of the ASME code, however, one cannot be substituted for the other. Welding procedures and welder qualifications tailored to the PED will be required and these must be approved by the Notified Body. A detailed design review, involving the Notified Body, demonstrating that the requirements of the PED are met will generally be needed. The material requirements must also be met. There are three ways in which material can be approved under the PED; using a material which complies with an appropriate EN standard, by using a material listed as Approved for European Pressure Vessels or by obtaining a particular material appraisal. A particular material appraisal requires that the suitability of the material for a particular application be demonstrated. For category III and IV vessels the particular material appraisal must be approved by the Notified Body. The manufacturer will be required to establish and document a suitable quality control system, details of which will depend on the combination of modules which are selected. Finally, how will our MDMT of -320F be treated under the PED? Annex I paragraph 7.5 of the PED states:
"… a steel is considered as sufficiently ductile… 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 20C but not higher than the lowest scheduled operating temperature."
Testing at the MDMT is one method of demonstrating that the material is sufficiently ductile. However, testing at the MDMT can be avoided if it can be demonstrated that the material selected is sufficiently ductile and tough by other means.
For manufacturers of ASME code vessels, certifying a product to the PED is far from automatic. Considerable work will be needed to document the design, the materials and the quality control program. The work required will scale with the size and operating pressure of the vessel. Working with a Notified Body will be required for any vessel bearing the CE stamp.