1. Safety valve regulations

Safety valves protecting equipment subject to the Pressure Directive 97/23/EC (pending transposition into French law of Directive 2014/68/EU of May 15, 2014, published on June 27, 2014, and applicable from July 19, 2016, after transposition into French law) are also safety accessories (pressure-limiting devices) under this directive. This (cf. section 2.11.2) stipulates that they must be designed in such a way that the pressure in the ESP does not permanently exceed the maximum allowable pressure PS. A short-term overpressure of 10% of this PS is permissible. As the maximum permissible diaphragm stress corresponding to this PS, in carbon steel pressure vessels, is of the order of 66.7% of the material's elastic limit, a stress of 73.3% of the elastic limit is temporarily allowed. This provides a significant safety margin when discharging the valve under the above conditions.