The overall objective of the RiaSoR 2 work package 4 (Data processing) is to provide methodologies for reliability evaluation and data processing to the Monitoring Framework (WP2). This report treats reliability methodologies and presents a case study that evaluates two design criteria for the structural reliability of the double rod pre-tension cylinder in CorPower Ocean's C3 half-scale prototype Wave Energy Converter (WEC). The pre-tension cylinder is subjected to internal pressure and the required wall thickness is assessed for static strength and fatigue strength design cases. The design calculations at CorPower are based on the pressure vessel standards. The case study re-evaluates the reliability assessment using Variation Mode and Effect Analysis (VMEA). The safety requirements based on the standard and on the VMEA assessment are evaluated, compared and discussed. The purpose of the re-evaluation is firstly to compare the VMEA methodology to the reliability design according to the pressure vessel standard regarding the safety judgements, and secondly to investigate if the VMEA evaluation gives a better ground for improvements and updating, compared to the standard. Additionally, the results will feed into the continued work on condition monitoring and maintenance planning.