The European main gas transmission system is now some 50 years old and in the transition to renewables another 50 years of service are foreseen. This long term service has not been anticipated during design and construction. Nevertheless, gas transmission systems operate satisfactory and with very low failure rates. Thus, questions are raised how the existing gas transmission system can safely contribute to the total energy system in coming decennia. Where a lot of developments are toward integrity assurance of pipelines (ILI etc.), facilities receive less attention although they are an integral and essential part of the system. In this paper a systematic approach for assessing integrity of new and existing facilities is presented, leading to a structured inspection and test plan. The system based approach will be introduced and explained, with implementation in practice with 2 real life examples of recent cases.