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The Pressure Equipment Directive 2014/68/EU defines procedures for the production control of pressure equipment and is relevant for process plants, particularly for the sizing and procurement of vessels and pipes.
Vessels and pipes with a design pressure of more than 0.5bar above the atmospheric pressure of 1.013bar(a) are divided into five categories based on a pattern defined in the PED. There are no production control requirements defined in the PED for the first of these five categories. Instead, for this category, with reference to article 4 section 3, the production has to be done in accordance with "sound engineering practice". For the other four categories, identified with the roman numerals I, II, III, and IV, the production process has to be monitored by conformity assessment procedures defined in the directive.
The ranking according to the PED is taken into account during the sizing of the components already, as a higher ranking into the categories of the PED means higher procurement costs due to the more elaborate conformity assessment procedures required for the production.
The ranking of pressure equipment into one of the five categories depends on several factors. Vessels and pipes are treated differently. The process media is classified as either dangerous or not dangerous, and as either being in a gaseous or liquid state of matter. Liquids with a vapour pressure at the maximum possible temperature of more than 0.5bar above the atmospheric pressure of 1.013bar(a) are treated as gaseous. From these factors eight pressure equipment groups result, each with its own conformity assessment table. An exception within this ranking is fired or otherwise heated pressure equipment with the risk of overheating, intended for the generation of steam or superheated water. A separate, additional conformity assessment table exists for equipment of this type. Including this exception, there are a total of nine conformity assessment tables.
In the conformity assessment tables the x‑axis represents the design pressure and the y‑axis either the nominal diameter, in the case of pipes, or the volume, in the case of vessels. For each table, the covered area is divided by an individual pattern into the five categories of the PED. To determine the category applicable for a given plant component, the corresponding table is identified and then the design pressure and the volume or nominal diameter, respectively, are plotted on the corresponding axis.
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We consider the requirements of the Pressure Equipment Directive when determining the capacity and process conditions of the plant components in order to avoid the classification into higher categories and to reduce the procurement costs.
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