The subsea industry is meeting new challenges due to more extreme depths and wells with high pressures and temperatures. This has led to an increased focus on automatic safety systems and verifications of these. In order to properly verify that deep-water system works as designed, it is no longer enough with just an onshore FAT (Final Acceptance Test). This is because the behavior of accumulators are very different when tested onshore, versus under real operating environment. The significant difference is the (outside) operating pressure and temperature. This is particularly applicable when accumulator’s operating-pressure exceeds 5000 psi.