Pressure vessel

Pressure vessels are closed containers whose internal pressure is higher than the environmental pressure and which always have a sealing function. The task of pressure vessels is to:

  • store sealed media
  • avoid loss of media
  • prevent foreign materials entering
  • initiate certain exchanges
  • set desired reaction conditions

Unlike pressurized gas containers and transportation containers, the operation of a pressure vessel is assigned to a particular location.
Pressure vessels can be categorized as following with regard to their function:

  • Storage containers for gases (liquid gas storage containers, liquefied gases storage cryogenically)
  • Pressure accumulator tanks (hydraulic accumulator of a pressure casting machine, s. Pressure accumulator, Membrane expansion tank)
  • Compressed air reservoirs
  • Pressurized silos for pneumatic transportation of granulated goods e.g. for a molding machine
  • Heaters in a thermal oil plant (e.g. in thermal fluid die heater/cooler units)
  • Separators, accumulators, filters (water extractors)
  • Heat exchangers (condensers)
  • Containers and apparatus for specific processes
  • Heated or cooled pressure vessels as a system component

According to European law on the free movement of goods, a distinction is made between “simple pressure vessels” (directive 2009/105/EC) and “pressure equipment" (pressure equipment directive 97/23/EC).

Since 2002, pressure vessels with a maximum permissible operating pressure of over 0.5 bar (overpressure) have been subject to EC directive 97/23/EC (pressure equipment directive). According to the pressure equipment directive, pressure vessels, in addition to pipelines, boilers and pressure accessories,  are defined as pressure equipment and must be placed on the market with an EC declaration of conformity and a CE mark. Depending on the hazard potential (criteria here are the maximum operating pressure, liquid gas or liquid fluid or medium, fluid group) are categorized in categories I to IV.

The manufacturer can chose from various conformity-assessment procedures (sample construction, quality management system, individual test) in order to fulfill the requirements in the pressure equipment guideline. The pressure vessel is given a manufacturer sign, on which the manufacturer number and permissible operational data such as pressure, temperature, volume and the CE mark are displayed. As part of the conformity-assessment procedure, the manufacturer must create a risk analysis report and operating instructions which contain information about proper use, assembly, initial operation and maintenance and, if applicable, improper use.
The operating specifications for pressure vessels must be contained in an operational safety regulation.

Literature references:
Pressure equipment guideline 97/23/EC
German Wikipedia article Druckbehälter

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