Patent Number: 
Section: claims

1. A method for monitoring the health of a hydraulic control system comprising:a) capturing a layout and parameters of the hydraulic control system;b) capturing a valve signature during a System Integration Test;c) generating a simulated valve signature to match the valve signature captured during the System Integration Test by using a simulation algorithm and adjusting parameters of the hydraulic control system;d) recording the parameters of the hydraulic control system used to generate the simulated valve signature that matches the valve signature captured during the System Integration Test; subsequent to steps c to d:e) capturing a valve signature for a subsea valve opening/closing;f) generating a simulated subsea valve signature to match the subsea valve signature captured for the subsea valve opening/closing by using the simulation algorithm and adjusting parameters of the hydraulic control system;g) recording the parameters of the hydraulic control system used to generate the simulated subsea valve signature that matches the valve signature captured for the subsea valve opening/closing;h) repeating steps e), f) and g); andi) tracking changes in the parameters of the hydraulic control system over time. 2. The method of claim 1, further comprising detecting problems with the hydraulic control system based on the changes in the parameters of the hydraulic control system over time. 3. The method of claim 1, wherein the parameters of the hydraulic control system include data on tubing, hydraulic fluid properties, supply pressure, accumulator, actuator and flow restrictions imposed by different equipment in the system. 4. The method of claim 1, wherein the parameters of the hydraulic control system are selected from the group consisting of line length, line inside diameter, line wall thickness, line wall roughness, source pump pressure, accumulator volume, accumulator pre-charge, actuator volume, spring force, flow resistance imposed by equipment, hydraulic fluid properties, and directional control valve drop-out pressure. 5. The method of claim 1, wherein the system comprises a subsea directional control valve, and further wherein the valve signature comprises pressure readings recorded during opening or closing of the actuator. 6. A method for maintaining performance of a hydraulic control system comprising:a) monitoring the health of the system according to the method of claim 1; andb) performing preventative maintenance on the system based on analyzed performance of the system. 7. The method of claim 1, wherein steps (b) and (e) comprise recording valve signatures comprising pressure readings recorded during accumulator recharge from pressure sensors; and further comprising comparing the valve signatures, wherein:an increased pressure differential of the valve signatures with increased pressure indicates a leak; andthe valve signatures being parallel indicates sensor drift. 8. The method of claim 1, wherein step (b) comprises recording valve signatures from pressure sensors in the system during system integration testing, and further comprising:calculating an initial flow resistance, Cν0, using the recorded valve signatures during system integration testing and actuator volume, Vact;recording valve signatures from the pressure sensors during operation of the system; andcalculating a value for      ∫    0    T    ⁢            Cv      0        ⁢                  ⅆ        p              ⁢                  ⁢          ⅆ      t      during operation of the system, wherein dp is a pressure differential between the pressure sensors over time during operation of the system, and T is actuator opening time;wherein a calculated value for      ∫    0    T    ⁢            Cv      0        ⁢                  ⅆ        p              ⁢                  ⁢          ⅆ      t      greater than Vact indicates leaking and/or clogging in the hydraulic control system. 9. A method for maintaining performance of a hydraulic control system comprising:a) determining performance of the system according to the method of claim 7; andb) performing maintenance on the system if a comparison of the valve signatures indicates a leak or sensor drift. 10. The method of claim 8, wherein calculating Cν0 comprises using the equation:      Cv    0    =                    V        act                              ∫          0          T                ⁢                                            ⅆ              p                                ⁢                                          ⁢                      ⅆ            t                                .   11. A method for monitoring the health of a hydraulic control system comprising:determining whether a leak and/or clog exists in a hydraulic control system according to the method of claim 8; andperforming maintenance on the system if calculating a value for      ∫    0    T    ⁢            Cv      0        ⁢                  ⅆ        p              ⁢                  ⁢          ⅆ      t      indicates leaking and/or clogging in the hydraulic control system. 12. The method of claim 8, wherein there is not a filter located between the pressure sensors. 13. The method of claim 8, further comprising calculating a leak volume in the system using the equation:      V    leak    =                    ∫        0        T            ⁢                        Cv          0                ⁢                              ⅆ            p                          ⁢                                  ⁢                  ⅆ          t                      -                  V        act            .       14. The method of claim 8, further comprising calculating a margin of error for the leak volume based on accuracy of the pressure sensors. 15. The method of claim 8, wherein a calculated value for      ∫    0    T    ⁢            Cv      0        ⁢                  ⅆ        p              ⁢                  ⁢          ⅆ      t      greater than Vact plus the leak volume in the system indicates clogging in the hydraulic control system. 16. A method for maintaining performance of a hydraulic control system comprising:determining whether a leak exists in a hydraulic control system according to the method of claim 14; andperforming maintenance on the system if the leak volume exceeds a predetermined amount.