Safety-related design of hydraulic cylinders: standards & verification

Legal & normative framework: What really applies

Hydraulic cylinder safety does not begin on the test bench, but in the specifications. The legal basis is the EU Machinery Directive 2006/42/EC. It requires that every cylinder design excludes all foreseeable hazards.

Specific guidelines are provided by DNV-ST-0194, ISO 19704 or AD-2000 data sheets, depending on the industry. These are supplemented by the FKM guideline or standard works such as Roloff-Matek for general strength assessments. There are also standards that deal exclusively with standard cylinders, such as DIN EN ISO 6020 or DIN EN ISO 6022.

For cylinder design, this means that the relevant standards must be derived from the application if necessary. For example, wall thicknesses, sealing systems and weld seams must be calculated and verified not only statically but also dynamically. Corresponding standards provide verifiable key figures, safety factors and material strengths for this purpose.

Complete documentation of all boundary conditions, calculation methods, manufacturing protocols and material certificates is a prerequisite for compliance with the EU Machinery Directive.

Practical verification: buckling, pressure, vibration

Hydraulic cylinder calculations in safety-related projects often include the following core verifications:

• Buckling:

  For cylinders operating under pressure with a long stroke, such as hydraulic cylinders for cranes, sudden buckling of the piston rod poses a major safety risk. Either conservative methods, such as Euler's method, or a precise FEM analysis are used for assessment: The Euler method assumes equal moments of inertia for the tube and rod, often resulting in oversized, cost-intensive cylinders, while the FEM analysis realistically maps all geometric and load influences, provides reliable safety verifications and enables a leaner, more economical design.

• Pressure:

  The permissible internal pressure load is first verified by analytically determined nominal stresses. A subsequent FEM analysis checks for stress peaks, for example at weld seams and flanges, and the design is adjusted if necessary. Finally, a burst test is performed at approximately 1.5 times the operating pressure, which confirms the calculation model and provides a standard-compliant safety verification – without unnecessary oversizing.

• Vibration & fatigue:

  Goodman, Haigh or Smith diagrams form the mathematical basis for dynamic strength assessment. A detailed FEM analysis simulates real load collectives including stress peaks. Since a static analysis does not reflect the actual operating conditions in numerous applications, a dynamic calculation is necessary to assess the system behaviour in a practical and reliable manner.

• Cover-pipe connections:

  Another key verification must be carried out for the connection between the pipe and the base or between the pipe and the head. For bolted connections, this is done in accordance with VDI 2230, and for welded connections in accordance with the FKM guideline. The choice of the appropriate verification method depends on the type and level of stress occurring. The aim is to safely and reliably achieve the required number of load cycles under real operating conditions.

In addition to the above mentioned calculation verifications, other aspects must be taken into account, including, for example, the assessment of tightness, temperature influences, media compatibility and corrosion.

How we meet the highest safety standards at ACONA

Standards check at the start of the project

Each specification is systematically checked against the applicable standards and customer-specific guidelines. All relevant data is entered into a digital specification sheet. This means that the basis for the design can be transparently traced at any time.

FEM-supported dimensioning

A comprehensive FEM analysis maps all static and dynamic load cases using structural mechanical equivalent models. The stress and deformation data derived from this is incorporated directly into the hydraulic cylinder calculation. All simulation and calculation results are documented and archived in an audit-proof manner in a load-bearing capacity certificate.

Engineering & manufacturing under one roof

Design, calculation and manufacturing up to a piston diameter of 800 mm are all carried out under one roof at our site in Herzogenrath near Aachen. This shortens coordination paths, minimises interface risks and accelerates change loops.

deep-R roll hardening process

Our proprietary deep-R process increases service life by up to 100% thanks to surface hardening, allows up to 25% higher performance and reduces volume and weight by 35%. Together with the Machine Tool Laboratory at RWTH Aachen University, we had this process tested in order to empirically confirm the added value of the deep-R process.

Testing and acceptance

Every hydraulic cylinder we develop undergoes rigorous pressure, leakage and functional tests under overpressure. Only after passing these tests is the cylinder approved for release. All test reports are digitally archived and made available to the customer.

Conclusion: a trio of factors in every ACONA project

Anyone planning cylinders for critical applications needs more than just strong materials: application- and standard-compliant calculations, well-founded FEM analyses including safety certificates and a comprehensive risk analysis form the foundation.

If this triad is anchored early on in the project, cylinders are created that function reliably even under extreme conditions – thus ensuring plant availability, personal safety and budgetary considerations in equal measure.

At ACONA, we provide our customers with precisely this complete package – reliably, transparently and in accordance with all applicable standards – and beyond, if desired. We plan and produce customised hydraulic cylinders, tailored precisely to your individual requirements.