A pressure vessel is a housing designed and built to contain fluids (gases or liquids) under a higher pressure than the atmospheric. This fact turns pressure vessels into containers with internal energy, and thus they become potentially hazardous products where the main risk is the sudden release of the energy stored inside, which is directly proportional to the product of pressure by volume (PS·V). This value, together with the nature of the fluid stored, determines the hazard level of pressure vessels.
In order to guarantee the safety of THIELMANN pressure vessels, they are designed, manufactured and tested according to the demanding regulations and standards of each region.
In Europe, the requirements to be fulfilled are compiled in the Directive 2014/68/EU on pressure equipment (PED), which fully entered into force on 20 July 2016. Its compliance results in the homologation of THIELMANN pressure vessels and consequently in the affixing of the CE marking to them.
The PED defines the obligations of all the economic operators involved (manufacturers, authorized representatives, importers, distributors). As derived from our manufacturer role, THIELMANN has the obligation of identifying and analyzing the hazards and risks on account of pressure that apply to our pressure vessels. Consequently, these pressure vessels are designed, built and tested taking into account the risk analysis conducted, which ensures their safety when put into service in accordance with our instructions or in reasonably foreseeable conditions throughout their intended life.
In this regard, and according to the PED, THIELMANN provides adequate instructions of the pressure vessels manufactured, as well as completes a specified declaration of conformity and maintains a technical file of information about how the equipment was designed and manufactured. These instructions and declaration of conformity files are accessible to our customers, who can identify each pressure vessel because of being marked with our company name as the manufacturer, a unique identification of every model and its serial number, the year of manufacture, the maximum/minimum allowable pressure limits and the CE marking.
Specific aspects of the design, production and testing of the pressure vessels are the aim of a large number of harmonized standards published in the Official Journal of the European Union and developed in order to help to compliance the PED requirements. Hence, those pressure vessels in conformity with harmonized standards shall be presumed to be in conformity with the essential safety requirements covered by those standards or parts thereof.
Every pressure vessel is classified according to its hazard level, which is determined by the stored energy (PS·V) and the nature of the fluid stored.
It is thus essential to know the product to be stored in a pressure vessel in order to classify it within one of the two groups that the PED establishes:
- Group 1 consisting of substances and mixtures that are classified as hazardous in accordance with the following physical or health hazard classes (Regulation EC No 1272/2008):
- Unstable explosives or explosives of Divisions 1.1, 1.2, 1.3, 1.4 and 1.5;
- Oxidizing gases, category 1;
- Flammable gases, liquids or solids, category 1 and 2; and flammable liquids category 3 where the maximum allowable temperature is above the flashpoint;
- Self-reactive substances and mixtures, type A to F;
- Pyrophoric liquids or solids, category 1;
- Substances and mixtures which in contact with water emit flammable gases, category 1, 2 and 3;
- Oxidizing liquids or solids, category 1, 2 and 3;
- Organic peroxides types A to F;
- Acute oral, dermal or inhalation toxicity; category 1 and 2; and acute inhalation toxicity, category 3;
- Specific target organ toxicity – single exposure, category 1.
- Group 1 comprises also substances and mixtures contained in pressure equipment with a maximum allowable temperature TS which exceeds the flashpoint of the fluid;
- Group 2 consisting of substances and mixtures not referred before.
Once the product to be stored is classified within one of these groups, it is necessary to calculate the so-called “category”, since the assessment and conformity procedures (whereby the manufacturer fulfils defined obligations and ensures and declares that the pressure equipment concerned satisfy the requirements the Directive) are different for each category, ranging from self-certification (internal) for the lowest hazard level (category I) to full ISO 9001 quality management. Most of the procedures require the assessment from a Notified Body, which is an organization designated by an EU country to assess the conformity of certain products before being placed on the market. These bodies carry out tasks related to conformity assessment procedures set out in the applicable legislation, when a third party is required. The European Commission publishes a list of such notified bodies.
|CATEGORY||MODULE||CONFORMITY ASSESSMENT PROCEDURE|
|Category I||Module A||Internal production control|
|Category II||Module A2||Internal production control plus supervised pressure equipment checks at random intervals|
|Module D1||Quality assurance of the production process|
|Module E1||Quality assurance of final pressure equipment inspection and testing|
|Category III||Modules B (design type) + D||EU-type examination, design type + conformity to type based on quality assurance of the production process|
|Modules B (design type) + F||EU-type examination, design type + conformity to type based on pressure equipment verification|
|Modules B (production type) + E||EU-type examination, production type + conformity to type based on pressure equipment quality assurance|
|Modules B (production type) + C2||EU-type examination, production type + conformity to type based on internal production control plus supervised pressure equipment checks at random intervals|
|Module H||Conformity based on full quality assurance|
|Category IV||Modules B (production type) + D||EU-type examination, production type + conformity to type based on quality assurance of the production process|
|Category IV||Modules B (production type) + F||EU-type examination, production type + conformity to type based on pressure equipment verification|
|Category IV||Module G||Conformity based on unit verification|
|Category IV||Module H1||Conformity based on full quality assurance plus design examination|
The category for pressure vessels is generally determined by the following tables available in the PED that will depend not only on the group previously determined but also on the physical state of the product:
- Gases, liquefied gases, gases dissolved under pressure, vapors and also those liquids whose vapor pressure at the maximum allowable temperature is greater than 0.5 bar above normal atmospheric pressure (1013 mbar) within the following limits:
|Fluids in Group 1||Fluids in Group 2|
- Liquids having a vapor pressure at the maximum allowable temperature of not more than 0.5 bar above normal atmospheric pressure (1 013 mbar) within the following limits:
|Fluids in Group 1||Fluids in Group 2|
Once the adequate table is found, and considering the volume of the vessel (V) and its pressure (PS), the category can be defined and consequently, the corresponding conformity assessment procedure.
Considering a flammable liquid to be stored in a 100 l vessel at 9 bar, it is can be deduced that:
- It would be within the Group 1 because of its flammable character.
- Because of its liquid state, Table 3 is identified as that to be used for the categorization of the pressure vessel.
So, the resulting point from the combination of 100 l in volume (X-axis) and PS = 9 bar (Y-axis) in table 3 is in the area corresponding to Category I and thus, this pressure vessel has to be assessed by the procedure described for Module A (Internal production control) or by any other procedure of a higher category.
Despite the fact that PED applies to the design, manufacture and conformity assessment of pressure equipment and assemblies with a maximum allowable pressure (PS) greater than 0.5 bar, it has to be noted that the Directive establish some exceptions that include other THIELMANN containers such as:
- Vessels used for the transport of fluids while under pressure (i.e. containers used for the transport of fluids by road, rail, sea and air). These vessels are subjected to the Transportable Pressure Equipment Directive (TPED), which has different attestation and marking requirements (“π mark”).
- ‘Simple pressure vessels’, which are the subject of a separate Directive (SPVD 2014/29/EU) that essentially applies to receivers used on compressed air systems.
- Vessels designed for the transport and distribution of drinks having a PS·V of not more than 500 bar·l and a maximum allowable pressure not exceeding 7 bar. This is the case of the THIELMANN kegs worldwide used in the beverage sector.
There are also a number of other exclusions covering items of equipment for military use, for use in transport, for nuclear applications and several other classes of equipment.
 There are exceptions such as fired or otherwise heated pressure equipment with the risk of overheating intended for generation of steam or super-heated water at temperatures higher than 110 °C having a volume greater than 2 L, and all pressure cookers, etc. so this information shall always be checked in the legal text (http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex:32014L00689).