Establishing termination criteria for a partial-stroke test of a fluid driven safety valve, and determining the proper functioning of a fluid driven safety valve

A method for establishing termination criteria for a partial stroke test of a fluidically driven safety valve having a valve member and a spring return;

• wherein the valve member is configured to be moved into a safety position by the spring return in case of a complete loss of pressure of the drive fluid;
• wherein the safety valve has means for determining the pressure of the drive fluid;
• wherein the pressure of the drive fluid acts against the spring;
• wherein the safety valve has means for determining the position of the valve member;
• wherein the method comprises the following steps:
• performing a first partial stroke test of the safety valve by variation of the pressure in the drive fluid;
• wherein the first partial stroke test is performed at a point in time at which the safety valve is operable;
• recording at least the position of the valve member during the first partial stroke test;
• deriving a first relation from the recorded data, which puts at least two of the position of the valve member, the time, the pressure of the drive fluid, and a further parameter recorded during the first partial stroke test in relation to one another;
• defining and saving this relation as a reference curve for this safety valve while operable;
• defining at least one second relation having a predetermined distance from the reference curve;
• establishing the following as termination criterion for a repeated partial stroke test of the same valve to be performed at a later time:
• if the repeated partial stroke test is performed at the same valve;
• and
• if the same data is recorded thereby;
• and
• if a third relation is determined from said data in the same manner as the reference curve,
• then the repeated partial stroke test is considered failed if the third relation has a greater distance to the reference curve than the second relation at at least one point.