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Safety and Technology: comparative study demonstrates competitiveness of the European Standard for Unfired Pressure Vessels (EN 13445)
A recent EC-sponsored study comparing the total costs of pressure equipment designed using the new EN 13445, which replaces respective national standards in 28 European countries, and American Society of Mechanical Engineers Boiler & Pressure Vessel (ASME Section VIII) code has underlined the economic viability of the European standard. Ten examples of widely used pressure equipment were considered, including a gas storage tank, hydrogen reactor, stirring vessel, autoclave, water separator, air cooler header and three different types of heat exchangers, and compared different approaches: design to EN 13445, ASME VIII and design to modified ASME VIII for compliance with the European Pressure Equipment Directive 97/23/EC (PED). Total costs were then assessed
with the collaboration of several European manufacturers. In 7 out of the 10 examples EN 13445 proved to be the most economic design code. Additionally a number of safety and legislative issues were also analysed.

"European standards are an important element for implementing a harmonised internal market for technically complex products. Their economic sustainability on an international playing field, technical excellence and wide usability are essential for achieving the Lisbon objectives of making Europe the world's most competitive society."

The term "pressure equipment" is used for products ranging from pressure cookers or compressor vessels via boilers for power stations to entire chemical plants. All of these can pose a safety hazard due to the pressurised fluid they contain. Harmonisation of the European market for pressure equipment is relatively recent: the PED, regulating the safety of pressure equipment, was published in 1997 and became mandatory in May 2002.

Although the use of European harmonised standards is not compulsory, they have a privileged position because products designed accordingly are presumed to comply with the requirements of the PED. EN 13445 is one of the most important European standards for pressure equipment, was developed by hundreds of experts from industry and academia under the auspices of the European Committee for standardisation CEN since the early 1990’s and continues to be extended and improved, e.g. to make it suitable for pressure equipment operating at very high temperatures above creep range. It endeavours to embrace the best features of former European national codes, e.g. the German AD-Merkblat, the British Standard and the French CODAP, but has also introduced several entirely
new technical concepts. In most cases for comparable duties EN 13445 allows for more efficient designs requiring less material, resulting in lower costs and lighter equipment. This particularly true for complex equipment and for serial production vessels.

ASME VIII has been developed by the American Society of Mechanical Engineers for more than 100 years. Its use is mandatory in most US jurisdictions and it is used voluntarily in many other countries, often with some local modifications. In general pressure equipment designed according to the ASME code is not compliant with the safety requirements of the PED, mainly due to less stringent requirements on material properties, welding and testing. However, the study suggests that in most cases the requirements of the PED can be met using ASME VIII as the base design code if some additional, relatively inexpensive but necessary measures are taken. On the other hand the study has raised some doubts whether ASME VIII meets the PED requirements on fatigue design for
welded regions, as ASME VIII has to be considered as non-conservative not only in comparison to EN 13445 but also to former European national codes. Fatigue damage is relevant for products which are subject to cyclic
pressure and temperature in autoclaves used for the disinfection of medical equipment, or cyclic stirrer forces and moments in stirring vessels.

The results of the study are available and can be downloaded from:
http://ped.eurodyn.com/standards/asme_comparative_study.html

More information about European Standards:
http://www.cenorm.org/

More information about PED:
http://ped.eurodyn.com/

More information about the US ASME code:
http://www.asme.org/

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