Method for detection of a fluid leak related to a piston machine

1. A method for detection of a fluid leak related to at least one piston machine, the method comprising:

attaching a pressure sensor to at least an outlet side of the at least one piston machine;

measuring pressure on the outlet side of the at least one piston machine;

attaching a transmitter to the at least one piston machine, said transmitter rendering a signal for calculating a rotational speed of the at least one piston machine;

calculating the rotational speed of the at least one piston machine;

calculating a sum of nominal flow rates from each of the at least one piston machine;

calculating a flow rate compensation factor;

calculating a normalized pressure to be equal to a discharge pressure at the outlet side multiplied by said flow rate compensation factor; and

monitoring the normalized pressure to detect a leakage.

2. The method according to claim 1 , further comprising:

calculating a flow rate compensation factor that equals a quotient of the sum of nominal flow rates of the at least one piston machine divided by a chosen reference flow rate, the quotient raised to a power of a pressure exponent that is between 1.2 and 2.5.

3. The method according to claim 2 , wherein the pressure exponent in the flow compensation factor is between 1.5 and 2.

4. The method according to claim 1 , further comprising:

low pass filtering the normalized pressure; and

monitoring the normalized low pass filtered pressure to detect a leakage.

5. The method according to claim 2 , further comprising:

determining the pressure exponent in the flow compensation factor experimentally by measuring average discharge pressures at two different flow rates, where the pressure exponent is a quotient of a logarithm of a quotient of the two pressures divided by a logarithm of a quotient of the two flow rates.

6. The method according to claim 1 , further comprising:

measuring the temperature of fluid output from the piston machine;

determining a temperature compensation factor as a quotient of 1 divided by a difference of 1 minus a temperature sensitivity parameter multiplied by a difference between an actual fluid temperature and a reference temperature, and where the temperature sensitivity parameter is a quotient of a difference between two pressures divided by a product of a difference between two temperatures multiplied by one of the two pressures, the two pressures and the corresponding two temperatures being determined experimentally;

multiplying the normalized pressure by the temperature compensation factor;

monitoring the temperature compensated normalized pressure to detect a leakage.

7. The method according to claim 1 , further comprising:

measuring density of the fluid output from the piston machine;

determining a density compensation factor as a quotient of reference density and an actual density of the fluid;

multiplying the normalized pressure by the density compensation factor; and

monitoring the density compensated normalized pressure to detect a leakage.

8. The method according to claim 1 , further comprising:

activating an alarm when a low pass filtered version of the normalized pressure drops below an alarm limit.

9. The method according to claim 8 , wherein the alarm limit is automatically set by the following procedure:

ignoring transient changes of the normalized pressure during a quarantine period after a substantial change of the nominal flow rate;

monitoring the low pass filtered version of the normalized pressure during a subsequent base estimation period after the end of the quarantine time and determining a base value for the normalized pressure;

determining the alarm limit based on the normalized pressure measured during the base estimation period at the end of the base estimation period;

keeping the alarm limit constant after the base estimation period, while the piston machine is running at steady conditions.

10. The method according to claim 9 , further comprising:

determining the alarm limit as a function of at least one of an average, standard deviation, and extreme values of a low pass filtered version of the normalized pressure measured during said base estimation period.

11. A system, comprising:

one or more pumps, each of the pumps comprising:

a piston;

a crankshaft;

an outlet manifold; and

a transmitter arranged to measure a rotational angle of the crankshaft;

a pressure sensor coupled to the output manifold to measure outlet pressure; and

a computer coupled to the pumps, the computer configured to:

receive outlet pressure measurements and crankshaft rotational angle measurements;

compute a sum of nominal flow rates of the pumps based on the crankshaft rotational angle measurements;

compute a flow rate compensation factor;

compute a normalized pressure for the pumps based on the outlet pressure measurements and the flow rate compensation factor; and

detect a leak in the pumps based on the normalized pressure.

12. The system of claim 11 , further comprising: a temperature sensor disposed to measure temperature of fluid output from the pumps; wherein the computer is configured to compute the normalized pressure based on a temperature compensation factor; wherein the temperature compensation factor is based on temperature sensitivity of the fluid and fluid temperature measurements received from the temperature sensor.

13. The system of claim 11 , further comprising a density meter disposed to measure density of fluid output from the pumps; wherein the computer is configured to compute the normalized pressure based on a density compensation factor; wherein the density compensation factor is based on a reference density value and fluid density measurements received from the density meter.

14. The system of claim 11 , wherein the computer is configured to:

low pass filter the normalized pressure; and

detect a leak in the pumps based on the low pass filtered normalized pressure.

15. The system of claim 11 , wherein the computer is configured to compute the flow rate compensation factor as a quotient of the sum of nominal flow rates of the pumps divided by a reference flow rate, the quotient raised to a power of a pressure exponent that is between 1.2 and 2.5.

16. The system of claim 11 , wherein the computer is configured to:

activate an alarm based on the normalized pressure being less than an alarm limit value; and to determine the alarm limit value the computer is configured to:

identify a change in the nominal flow rate of the pumps;

initiate, based on the change, a quarantine period during which the computer disregards transient changes in the normalized pressure;

initiate, subsequent to the quarantine period, a base estimation period during which the computer measures the normalized pressure and determines a base value for the normalized pressure; and

determine the alarm limit value based on the normalized pressure measured during the base estimation period.

17. A device for detecting leaks in a piston machine, comprising:

a computer configured to:

receive output manifold pressure measurements and rotational angle measurements from one or more pumps;

compute a sum of nominal flow rates of the pumps based on the rotation angle measurements;

compute a flow rate compensation factor for the pumps;

compute a normalized pressure for the pumps based on the output manifold pressure measurements and the flow rate compensation factor;

low pass filter the normalized pressure; and

detect a leak in the pumps based on the low pass filtered normalized pressure.

18. The device of claim 17 , wherein the computer is configured to:

compute a temperature compensation factor based on temperature sensitivity of the fluid and measured temperature of fluid output from the pumps; and

compute the normalized pressure based on the temperature compensation factor.

19. The device of claim 17 , wherein the computer is configured to:

compute a density compensation factor based on a reference density value and measured density of fluid output from the pumps;

compute the normalized pressure based on the density compensation factor.

20. The device of claim 17 , wherein the computer is configured to compute the flow rate compensation factor as a quotient of the sum of nominal flow rates of the pumps divided by a reference flow rate, the quotient raised to a power of a pressure exponent that is between 1.2 and 2.5.

21. The device of claim 17 , wherein the computer is configured to:

identify a change in the nominal flow rate of the pumps;

initiate, based on the change, a quarantine period during which the computer disregards transient changes in the normalized pressure;

initiate, subsequent to the quarantine period, a base estimation period during which the computer measures the normalized pressure and determines a base value for the normalized pressure;

determine an alarm limit value based on the normalized pressure measured during the base estimation period; and

activate a leak detection alarm based on the normalized pressure being less than the alarm limit value.