۱٫ Introduction

۲٫ Description of the quarter-turn heavy-duty actuator

۳٫ Fundamental of the adopted criteria for fatigue life assessment

۴٫ Numerical analysis

۵٫ Results and comparison

۶٫ Conclusions and research developments

۷٫ Acknowledgments

۸٫ References

Fatigue design of structural components under multiaxial loading often relies on fatigue life calculations based on a post-processing of the full-field elastic stress/strain maps obtained from finite element (FE) analysis. In the present article, a post-processing tool is adopted to compute the fatigue life of a structural component, and multiaxial fatigue assessment is carried out by considering different criteria such as that of Smith-Watson-Topper and of Fatemi-Socie. The present paper focuses on a specific structural component related to a quarter-turn heavy-duty valve actuator, called scotch yoke, commonly used in many application sectors such as oil & gas, power and chemical industries. The fatigue assessment of the component is carried out by employing a full-model FE analysis, considering fillet-welded joints exposed to in-phase constant amplitude cyclic bending-torsion fatigue load with load ratio R=-1, with applied maximum load according to EN 15714-3, which is the standard in the valve actuator sector. The elastic stress/strain field extracted from the FE model is used to perform the fatigue assessment of the fillet-welded joints, where the potential fatigue crack initiation points (weld toe and weld root) are described by adopting an effective radius at the weld notches.

Introduction

Pneumatic or hydraulic scotch yoke valve actuators are commonly used in many industrial sectors and have many different applications. Among the most challenging scenarios for heavy-duty actuation are high-cycle applications, which impose high frequency of operation often at relatively high operating speed. In order to improve the performance of FLOWSERVE – Limitorque LPS/LHS heavy-duty actuator series, a fatigue assessment is carried out using numerical analysis supported by experimental evidence, to evaluate the high cycle application behavior of one of the main component of the actuator center body, the scotch yoke. The LPS/LHS actuator series, developed by FLOWSERVE – Limitorque in Italy is currently in accordance with the European norm [1], which imposes a minimum number of cycles for a specific loading condition. However, the number of cycles required by high-cycles applications can be very different, sometimes by orders of magnitude. For example, for an actuator like Limitorque model LPS-15, with a design output torque of 6000Nm, the minimum number of cycles required by the norm is with a stroking time of 30s, while in high-cycles applications, a minimum of cycles are frequently requested. The use of standard actuator series inevitably involves some uncertainties and oversizing, decreasing the competitiveness on the global market and increasing the cost of the machine.