A compressed-air receiver may appear to be one of the simplest pieces of equipment in an industrial system. From a safety perspective, however, its shell, ends, welds, materials and design must safely contain stored pressure energy throughout the vessel’s intended operating life.
Directive 2014/29/EU establishes the European regulatory framework for certain series-manufactured welded pressure vessels commonly known as simple pressure vessels. These vessels are intended to contain air or nitrogen, are not intended to be fired and must satisfy specific material, pressure, temperature and geometrical conditions to fall within the Directive.
The distinction between the Simple Pressure Vessels Directive (SPVD) and the Pressure Equipment Directive (PED) is particularly important. A pressure vessel should not be classified under the SPVD merely because its construction appears simple. It must satisfy the specific scope criteria established by Directive 2014/29/EU.
For vessels whose product of maximum allowable pressure and capacity exceeds the threshold established by the Directive, conformity assessment involves a Notified Body. Design, materials, welding, manufacturing controls, testing and technical documentation all become part of the conformity process.
This GAR Insight explains SPVD scope, PS × V classification, essential safety requirements, vessel materials, welding, design calculations, manufacturing controls, testing, conformity assessment, Notified Body involvement, technical documentation and CE marking.
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Explore SPVD scope, vessel classification, essential safety requirements, materials, welding, testing, conformity assessment, technical documentation and CE marking.
Understanding Directive 2014/29/EU
Directive 2014/29/EU harmonises requirements concerning the making available on the European market of simple pressure vessels falling within its defined scope.
It is a recast of the previous European simple-pressure-vessel legislation and has applied since 20 April 2016.
The Directive establishes obligations for manufacturers, authorised representatives, importers and distributors and provides conformity assessment procedures involving Notified Bodies where required.
Which Vessels Are Covered by the SPVD?
Directive 2014/29/EU applies only where the vessel satisfies a specific combination of construction, material, pressure, contents, temperature and geometrical conditions.
Series Manufactured
The vessels covered by the Directive are manufactured in series.
Welded Construction
The vessel must be welded and intended to operate above 0.5 bar internal gauge pressure.
Air or Nitrogen
The vessel is intended to contain air or nitrogen rather than other gases or liquids.
Not Fired
The vessel is not intended to be subjected to firing as part of its operation.
Defined Materials
Pressure-resisting parts must use the steel or aluminium materials permitted by the Directive.
Defined Geometry
The pressure vessel must use one of the geometrical configurations specified by the Directive.
| Parameter | SPVD Scope Condition |
|---|---|
| Internal gauge pressure | Greater than 0.5 bar |
| Contents | Air or nitrogen |
| Maximum working pressure | Not greater than 30 bar |
| PS × V | Not greater than 10,000 bar·L |
| Minimum working temperature | Not lower than −50°C |
| Maximum temperature — steel | Not higher than 300°C |
| Maximum temperature — aluminium | Not higher than 100°C |
Simple Pressure Vessel or PED Pressure Equipment?
One of the first regulatory decisions for a pressure vessel is determining which European pressure-equipment legislation applies.
SPVD
Directive 2014/29/EU applies to the narrowly defined category of series-manufactured welded vessels satisfying its scope conditions.
PED
Directive 2014/68/EU covers a much broader range of pressure equipment and assemblies, subject to its own scope and classification provisions.
Vessels specifically designed for nuclear use where failure may cause radioactive release, vessels specifically intended for installation in or propulsion of ships and aircraft, and fire extinguishers are excluded from the SPVD.
↑ Back to Article GuideUnderstanding PS × V
The product of maximum allowable pressure and vessel capacity is one of the central parameters used by the SPVD to determine the applicable conformity requirements.
Consider a vessel with a maximum allowable pressure of 10 bar and a capacity of 500 litres:
| PS × V | General SPVD Position |
|---|---|
| ≤ 50 bar·L | The vessel must be designed and manufactured in accordance with sound engineering practice in a Member State and bear the inscriptions specified by the Directive, but it does not follow the CE-marking conformity route applicable to vessels above 50 bar·L under the SPVD. |
| > 50 bar·L | The vessel must satisfy the essential safety requirements in Annex I and undergo the applicable conformity assessment. |
| > 10,000 bar·L | Outside the upper PS × V scope limit of Directive 2014/29/EU. |
Essential Safety Requirements
Vessels whose PS × V exceeds 50 bar·L must satisfy the Essential Safety Requirements established in Annex I of Directive 2014/29/EU.
Material Suitability
Materials must possess characteristics suitable for their pressure-bearing and manufacturing functions.
Mechanical Strength
The vessel must withstand the pressures and loads that can reasonably occur during intended operation.
Weld Integrity
Pressure-bearing welds must provide characteristics consistent with the required safety of the vessel.
Corrosion Consideration
Vessel design must appropriately account for foreseeable corrosion where relevant to the intended conditions of use.
Manufacturing Quality
Manufacturing processes must not adversely affect the safety characteristics established by the design.
Inspection & Testing
Appropriate examinations and tests must confirm conformity of the manufactured vessel.
Material Requirements
The SPVD deliberately limits the materials permitted for the pressure-bearing parts and assemblies that contribute to vessel strength.
Steel Vessels
Pressure-bearing parts may be manufactured from non-alloy quality steel satisfying the applicable material requirements of the Directive.
Aluminium Vessels
The Directive also permits non-alloy aluminium or specified non-age-hardening aluminium alloys.
Material Properties
Materials should possess appropriate mechanical properties, ductility and suitability for the intended fabrication processes.
Material Traceability
Material identification and supporting documentation should allow pressure-bearing material to be connected with the manufactured vessel and conformity evidence.
Vessel Design & Pressure Strength
Pressure-vessel design must establish that the shell, ends, connections and pressure-bearing joints provide adequate strength throughout the intended operating conditions.
Maximum Pressure
The design must account for the maximum allowable working pressure specified for the vessel.
Working Temperature
Material properties and design must remain suitable throughout the specified temperature range.
Wall Thickness
Pressure-bearing sections require sufficient thickness to satisfy the applicable design and manufacturing criteria.
End Geometry
Vessel ends and transitions must correspond with the permitted configuration and applicable design calculations.
Openings & Connections
Connections and openings should not compromise the structural integrity of the pressure-retaining envelope.
Corrosion Allowance
Where foreseeable corrosion could reduce wall thickness, appropriate design provisions should be considered.
Welding & Manufacturing Requirements
Welding is one of the most safety-critical manufacturing activities for a simple pressure vessel because the principal pressure-retaining structure is permanently joined by welded seams.
Welding Procedures
Welding should be performed according to suitably controlled and technically appropriate procedures.
Welder Qualification
Personnel carrying out pressure-bearing welds require appropriate qualification for the applicable materials, process and joint conditions.
Production Consistency
Manufacturing controls should ensure that series-produced vessels remain consistent with the assessed design.
Joint Preparation
Forming, fit-up, preparation and welding conditions should support repeatable weld quality.
Heat Effects
Manufacturing operations should not degrade pressure-bearing material properties below those required by the design.
Inspection
Welded construction should undergo the examinations required by the applicable design and conformity route.
Inspection, Testing & Pressure Verification
Production vessels must be examined and tested as required by the applicable conformity procedure to demonstrate that they correspond with the assessed design and provide the required pressure integrity.
Visual Examination
Manufacturing condition, welds, identification and relevant construction details should be examined for conformity.
Dimensional Verification
Dimensions relevant to design strength and conformity should correspond with approved manufacturing information.
Pressure Testing
Applicable pressure testing provides evidence that the manufactured vessel can withstand the required test condition without unacceptable leakage or structural behaviour.
Weld Examination
Appropriate examination methods should be used where required to verify the integrity of pressure-bearing joints.
Material Verification
Material records should correspond with the materials used in the manufactured vessel.
Production Records
Inspection and test results should provide traceable evidence that production conformity has been demonstrated.
Harmonised Standards & Presumption of Conformity
Harmonised standards can provide manufacturers with technical specifications and methods supporting conformity with the essential requirements covered by those standards.
Vessel Design
Applicable standards can provide detailed rules for materials, design calculations, fabrication and inspection.
Welding
Harmonised or supporting standards can address welding procedures, personnel qualification and fabrication control.
Testing
Standards can provide recognised examination and test methods for demonstrating manufacturing and pressure integrity.
Presumption of Conformity
Correct application of a harmonised standard whose reference has been published in the Official Journal can provide presumption of conformity for the requirements it covers.
SPVD Conformity Assessment
For vessels whose PS × V exceeds 50 bar·L, the manufacturer must complete the applicable conformity assessment procedures required by Directive 2014/29/EU before CE marking and market placement.
Before manufacture, vessels above this threshold are subject to EU-type examination under the applicable SPVD procedure. Production conformity is then demonstrated through one of the permitted procedures selected according to the Directive and the vessel’s PS × V value.
| Stage | Purpose |
|---|---|
| EU-Type Examination | Independent assessment establishes that the technical design of the vessel type satisfies the applicable requirements. |
| Conformity to Type Based on Internal Production Control Plus Supervised Vessel Testing | Production is controlled by the manufacturer with the additional supervised testing required by the applicable procedure. |
| Conformity to Type Based on Internal Production Control Plus Supervised Vessel Checks at Random Intervals | Production conformity is supported by Notified Body checks performed at random intervals under the applicable procedure. |
| Conformity to Type Based on Internal Production Control | Where permitted by the Directive for the applicable PS × V range, the manufacturer fulfils the production-control obligations established by the relevant procedure. |
Technical Documentation
Technical documentation should enable conformity of the vessel with the applicable requirements to be assessed and should clearly describe the design, manufacture and intended operation of the vessel.
CE Marking, Identification & Traceability
Once the applicable conformity assessment has been completed, vessels subject to the CE-marking provisions of the Directive must carry the required marking and identification information before being placed on the market.
CE Marking
CE marking indicates that the manufacturer assumes responsibility for conformity with applicable Union harmonisation legislation requiring that marking.
Notified Body Number
Where required by the applicable production conformity procedure, the identification number of the Notified Body accompanies the CE marking.
Vessel Identification
Required vessel information must allow the product and its operating limits to be appropriately identified.
Manufacturer Identification
Applicable manufacturer name and contact information must be provided in accordance with the Directive.
Operating Information
Relevant pressure, temperature, capacity and other required information must accompany the vessel as applicable.
EU Declaration
The EU Declaration of Conformity formally records responsibility for the vessel’s conformity with applicable legislation.
From Vessel Design to EU Market Access
SPVD conformity is most efficient when the regulatory classification is established before detailed vessel design and production tooling are finalised.
Define Vessel
Establish pressure, capacity, contents, material, temperature and intended service.
Confirm Scope
Determine whether all Directive 2014/29/EU scope conditions are met.
Calculate PS × V
Establish the pressure-volume classification value.
Map Requirements
Identify applicable essential and other regulatory requirements.
Select Standards
Determine appropriate harmonised standards and technical specifications.
Engineer the Vessel
Complete material selection, calculations, drawings and manufacturing specifications.
Qualify Welding
Establish appropriate welding procedures, personnel and fabrication controls.
Select Assessment Route
Determine the conformity procedures applicable to the PS × V range.
Notified Body
Complete required independent design and/or production assessment.
Manufacture & Test
Produce, inspect and test vessels under the applicable controls.
Declare & Mark
Complete the EU Declaration and apply required conformity markings.
Maintain Conformity
Ensure series production remains consistent with the assessed design.
From a Welded Vessel to Demonstrable Pressure-Safety Conformity
The apparent simplicity of a compressed-air or nitrogen vessel should not obscure the engineering significance of the pressure energy it contains. A vessel’s safety depends on the relationship between pressure, volume, material properties, wall thickness, geometry, welded joints, manufacturing quality and operating temperature.
European conformity therefore begins with classification. The manufacturer must establish whether the product actually satisfies every condition necessary to fall within Directive 2014/29/EU rather than another pressure-equipment framework.
Once SPVD applicability is confirmed, PS × V becomes a critical parameter. It determines whether the vessel is subject to the essential safety requirements and influences the applicable conformity assessment route.
Materials, design calculations, welding, production controls, inspection and pressure testing should then provide a connected body of evidence demonstrating that the manufactured vessel corresponds with the assessed design.
The Engineering Question
Can the vessel safely contain its intended pressure throughout the specified operating temperature range and foreseeable service conditions?
The Conformity Question
Can the manufacturer demonstrate that every vessel placed on the market corresponds with the materials, calculations, welding, manufacturing controls, testing and conformity procedure on which its compliance is based?