EN
The Pressure Equipment Directive 2014/68/EU defines safety requirements for pressure equipment depending on their level of hazard, as well as conformity assessment procedures that are applied during the design, the manufacturing, and the final assessment of the pressure equipment to check the conformity with the safety requirements. It is relevant for process plants, particularly for the sizing and procurement of vessels and pipes.
Vessels, pipes, and pressure accessories 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 safety requirements defined in the PED for the first of these five categories. Instead, for this category, with reference to article 4 section 3, the design, manufacturing, and final assessment 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, corresponding assessment procedures must be applied to check the conformity with the safety requirements 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 to be applied for the manufacturing.
The safety requirements for pressure equipment are defined in annex I of the PED. Among other things, these include specifications for the design of the pressure equipment, the manufacturing, the final assessment, and the materials.
As part of the design of the pressure equipment, the pressure resistance must be demonstrated considering reasonably foreseeable operating conditions either by calculation methods or by experimental design methods. For this, the impact of wear, corrosion and other chemical influences, as well as fatigue must be taken into account. Pressure equipment is to be fitted with safety accessories, if there is a possibility that the permitted pressure limits are exceeded. These accessories are to be designed such that the maximum allowable pressure (PS) is not permanently exceeded. However, a short term exceedance of the PS of not more than 10% is allowed.
The final assessment shall include a pressure resistance test, which is usually done in the form of a hydrostatic pressure test.
The conformity assessment tables defined in annex II of the PED are used for the ranking of pressure equipment into one of the five categories depending 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.
The conformity assessment procedures are defined in annex III of the PED in the form of modules.
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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