System and method for estimating remaining useful life of pressure compensator

Abstract

A method for estimating the remaining useful life of a pressure compensator of a subsea arrangement, the method including determining displacement data related to displacements of the pressure compensator during a time period; and estimating the remaining useful life of the pressure compensator in relation to a failure mode of the pressure compensator based on the determined displacement data of the pressure compensator. A system including a subsea arrangement and a control system, a computer program product, and a computer program, are also provided.

Claims

1. A method for estimating the remaining useful life of a pressure compensator of a subsea arrangement, the method comprising: determining displacement data related to displacements of the pressure compensator during a time period during normal operation; and estimating the remaining useful life of the pressure compensator in relation to a failure mode of the pressure compensator based on the determined displacement data of the pressure compensator; wherein the estimation of the remaining useful life of the pressure compensator based on the determined displacement data of the pressure compensator includes: providing a compensator lifetime model for estimating the remaining useful life as a function of the displacement data of the pressure compensator; and estimating the remaining useful life of the pressure compensator based on the compensator lifetime model.

2. The method according to claim 1, wherein the method further comprises obtaining temperature data related to average temperatures of an internal fluid in fluid communication with the pressure compensator during the time period; and wherein the determination of the displacement data is made based on the temperature data.

3. The method according to claim 2, wherein the determination of the displacement data includes calculating a volume change of a compensation volume of the pressure compensator based on the temperature data.

4. The method according to claim 3, wherein the determination of the displacement data of the pressure compensator during the time period based on the temperature data comprises: providing a displacement model of the displacement data of the pressure compensator as a function of the temperature data; and determining the displacement data of the pressure compensator during the time period based on the temperature data and the displacement model.

5. The method according to claim 2, wherein the determination of the displacement data of the pressure compensator during the time period based on the temperature data comprises: providing a displacement model of the displacement data of the pressure compensator as a function of the temperature data; and determining the displacement data of the pressure compensator during the time period based on the temperature data and the displacement model.

6. The method according to claim 2, wherein the determination of the displacement data of the pressure compensator during the time period based on the temperature data comprises: determining the displacement data of the pressure compensator based on the obtained temperature data, historical temperature data and historical displacement data.

7. The method according to claim 2, wherein the method further comprises obtaining displacement values from a displacement sensor related to displacements of the pressure compensator during the time period; and wherein the determination of the displacement data is made based on the displacement values.

8. The method according to claim 2, wherein the determination of the displacement data includes determining or obtaining displacement values of the pressure compensator, filtering the displacement values, and determining the displacement data based on the filtered displacement values.

9. The method according to claim 2, further comprising determining a failure mode of the pressure compensator relating to the pressure compensator; and wherein the estimation of the remaining useful life of the pressure compensator is carried out in relation to the failure mode of the pressure compensator.

10. The method according to claim 1, wherein the method further comprises obtaining displacement values from a displacement sensor related to displacements of the pressure compensator during the time period; and wherein the determination of the displacement data is made based on the displacement values.

11. The method according to claim 1, wherein the determination of the displacement data includes determining or obtaining displacement values of the pressure compensator, filtering the displacement values, and determining the displacement data based on the filtered displacement values.

12. The method according to claim 1, wherein the compensator lifetime model is further based on depth data of the pressure compensator.

13. The method according to claim 1, further comprising determining a failure mode of the pressure compensator relating to the pressure compensator; and wherein the estimation of the remaining useful life of the pressure compensator is carried out in relation to the failure mode of the pressure compensator.

14. A system comprising a subsea arrangement and a control system, wherein the subsea arrangement includes: a main enclosure having a main enclosure volume; and at least one pressure compensator having a variable compensation volume in fluid communication with the main enclosure volume and configured to compensate volume variations of an internal fluid in the main enclosure volume; wherein the control system is configured to: determine displacement data related to displacements of the pressure compensator during a time period during normal operation; and estimate the remaining useful life of the pressure compensator in relation to a failure mode of the pressure compensator based on the determined displacement data of the pressure compensator, wherein the estimation of the remaining useful life of the pressure compensator based on the determined displacement data of the pressure compensator includes providing a compensator lifetime model for estimating the remaining useful life as a function of the displacement data of the pressure compensator, and estimating the remaining useful life of the pressure compensator based on the compensator lifetime model.

15. The system according to claim 14, wherein the subsea arrangement further comprises at least one temperature sensor arranged to measure a temperature of the internal fluid; and wherein the control system is configured to: obtain temperature data related to average temperatures of the internal fluid from the temperature sensor during the time period; and determine the displacement data based on the temperature data.

16. The system according to claim 15, wherein the at least one temperature sensor is provided in the main enclosure.

17. The system according to claim 15, wherein in the determination of the displacement data, the control system is configured to calculate a volume change of a compensation volume of the pressure compensator based on the temperature data.

18. The system according to claim 14, wherein the subsea arrangement further comprises a displacement sensor arranged to measure displacements of the pressure compensator during the time period; and wherein the control system is configured to obtain displacement values from the displacement sensor and determine the displacement data based on the displacement values.

19. A computer program product comprising a computer readable means holding computer-executable components for causing a control system to perform a method including: determining displacement data related to displacements of the pressure compensator during a time period during normal operation; and estimating the remaining useful life of the pressure compensator in relation to a failure mode of the pressure compensator based on the determined displacement data of the pressure compensator; wherein the estimation of the remaining useful life of the pressure compensator based on the determined displacement data of the pressure compensator includes: providing a compensator lifetime model for estimating the remaining useful life as a function of the displacement data of the pressure compensator; and estimating the remaining useful life of the pressure compensator based on the compensator lifetime model.

20. A computer program comprising computer program code which is able to, when run on processor circuitry of a control system, cause the control system to perform a method including: determining displacement data related to displacements of the pressure compensator during a time period during normal operation; and estimating the remaining useful life of the pressure compensator in relation to a failure mode of the pressure compensator based on the determined displacement data of the pressure compensator; wherein the estimation of the remaining useful life of the pressure compensator based on the determined displacement data of the pressure compensator includes: providing a compensator lifetime model for estimating the remaining useful life as a function of the displacement data of the pressure compensator; and estimating the remaining useful life of the pressure compensator based on the compensator lifetime model.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details, advantages and aspects of the present disclosure will become apparent from the following embodiments taken in conjunction with the drawings, wherein:

(2) FIG. 1: schematically represents a side view of a system comprising a subsea arrangement and a control system.

DETAILED DESCRIPTION

(3) In the following, a method for estimating the remaining useful life of a pressure compensator of a subsea arrangement, a system comprising a subsea arrangement and a control system, a computer program product and a computer program, will be described. The same reference numerals will be used to denote the same or similar structural features.

(4) FIG. 1 schematically represents a side view of a system 10 comprising a subsea arrangement 12 and a control system 14. The subsea arrangement 12 comprises a main enclosure 16 and a pressure compensator 18. In this example, the subsea arrangement 12 comprises one pressure compensator 18 but the subsea arrangement 12 may alternatively comprise several pressure compensators 18. The subsea arrangement 12 is submerged in ambient seawater 20. FIG. 1 further indicates a vertical direction 22 and a horizontal direction 24.

(5) The main enclosure 16 comprises a main enclosure volume 26. The main enclosure volume 26 may for example be constituted by one continuous chamber or by several chambers in fluid communication with each other. The main enclosure volume 26 is filled with an internal fluid 28, such as a dielectric oil. Power equipment 30 is arranged within the main enclosure volume 26. Non-limiting examples of power equipment 30 include transformers, switchgears, variable speed drives (VSD), high voltage conductors and combinations thereof. Heat from the power equipment 30 is absorbed by the internal fluid 28.

(6) The subsea arrangement 12 further comprises at least one temperature sensor 32 arranged to measure a temperature of the internal fluid 28. In this example, the temperature sensor 32 is arranged inside the main enclosure 16.

(7) The pressure compensator 18 has a variable compensation volume 34 in fluid communication with the main enclosure volume 26. Thus, also the compensation volume 34 is filled with the internal fluid 28. The pressure compensator 18 is configured to compensate for volume variations of the internal fluid 28, e.g. a volume expansion of the internal fluid 28 due to heating by the power equipment 30. The temperature sensor 32 may alternatively be arranged in the compensation volume 34.

(8) In the example of FIG. 1, the fluid communication is realized by means of a pipe arrangement 36 between the main enclosure 16 and the pressure compensator 18. The pipe arrangement 36 may be flexible and/or comprise flexible components to compensate for movements of the pressure compensator 18.

(9) The pressure compensator 18 of this example comprises an inner barrier 38 and an outer barrier 40. In FIG. 1, the inner barrier 38 is constituted by a double wall metal bellows and the outer barrier 40 is constituted by a rubber bellows or rubber enclosure. The two walls of the inner barrier 38 may be made of flexible metal sheets and air with a pressure of approximately 1 bar may be provided between the two sheets. The outer barrier 40 may be provided with a strengthening material on its inside. The provision of two barriers improves reliability of the pressure compensator 18.

(10) The pressure compensator 18 further comprises an upper end plate 42 and a lower end plate 44. Each of the upper end plate 42 and the lower end plate 44 may be made of metal. The inner barrier 38, the upper end plate 42 and the lower end plate 44 define the compensation volume 34 of the pressure compensator 18. The upper end plate 42 is guided up and down in the vertical direction 22 by means of guiding rods 46 as illustrated by arrows 48.

(11) During normal operation of the subsea arrangement 12, the pressure compensator 18 is displaced, i.e. contracts and expands, according to the volume changes of the internal fluid 28. In this example, the lower end plate 44 of the pressure compensator 18 is stationary and the displacement of the pressure compensator 18 is effected by the movements of the upper end plate 42 in directions 48. However, the pressure compensator 18 may have an alternative orientation in space or the displacement of the pressure compensator 18 may additionally take place in the horizontal direction 24 (radial deflection), or in any other direction.

(12) A closed intermediate volume 50 is formed between the inner barrier 38 and the outer barrier 40. The intermediate volume 50 is also filled with the internal fluid 28. However, the intermediate volume 50 may alternatively be filled with another fluid or a vacuum may be established in the intermediate volume 50. Due to the elasticity of the outer barrier 40, the pressure of the internal fluid 28 within the intermediate volume 50 is substantially the same as the pressure of the ambient seawater 20 outside the pressure compensator 18.

(13) The present disclosure is not limited to the particular type of pressure compensator 18 shown in FIG. 1. Alternative types of pressure compensators according to the present disclosure include pressure compensators comprising only one barrier and/or pressure compensators connected in series.

(14) The subsea arrangement 12 may be installed at great depth, for example at 3000 m (hydrostatic pressure of 300 bars). At great depths, the hydrostatic pressure acting on the pressure compensator 18 is practically constant. The volume change of the internal fluid 28 can thereby be accurately calculated based on the average temperature. Furthermore, the axial displacement of the pressure compensator 18 can be accurately calculated based on the volume change of the internal fluid 28. Thus, the average temperatures of the internal fluid 28 within the main enclosure volume 26 accurately and reliably correspond to axial displacements of the pressure compensator 18. The main enclosure volume 26 may be substantially larger than the compensation volume 34. In the example of FIG. 1, the main enclosure volume 26 is approximately ten times larger than the compensation volume 34.

(15) When the hydrostatic pressure increases due to a greater seawater depth, the inner barrier 38 and the outer barrier 40 may be brought into contact. When the hydrostatic pressure increases further, the rigidity of the inner barrier 38 and the outer barrier 40 increases. As a consequence, the lifetime of a pressure compensator 18 comprising two barriers 38, 40 may be shorter at greater seawater depths.

(16) The subsea arrangement 12 of this example further comprises a displacement sensor 52. The displacement sensor 52 is configured to detect displacements, such as positions and/or movements, of the pressure compensator 18, for example by detecting positions and/or movements of the upper end plate 42 relative to the lower end plate 44. The displacement sensor 52 may comprise, or may be constituted by, an optical sensor, an inductive sensor or the like.

(17) The subsea arrangement 12 may comprise only the temperature sensor 32, only the displacement sensor 52, both the temperature sensor 32 and the displacement sensor 52. Alternatively, the subsea arrangement 12 comprises neither the temperature sensor 32 nor the displacement sensor 52. In the latter case, the displacement data can be determined based on pressure measurements and/or based on the supplied power to the subsea arrangement 12, for example based on supplied power versus time and known thermal time constants of the subsea arrangement 12. The thermal time constants may be several hours, or even days.

(18) In the example of FIG. 1, the control system 14 is in signal communication with the temperature sensor 32 and the displacement sensor 52 by means of signal lines 54. However, a wireless communication may alternatively be implemented.

(19) The control system 14 is configured to determine displacement data related to displacements of the pressure compensator 18 during a time period. The control system 14 may further be configured to estimate or predict the remaining useful life of the pressure compensator 18 in relation to a failure mode of the pressure compensator 18 based on the determined displacement data of the pressure compensator 18. Alternatively, the estimation of the remaining useful life of the pressure compensator 18 based on the determination of the displacement data may be carried out online.

(20) Various methods for determining the number of oscillation cycles until failure (or other defined failure mode) of the pressure compensator 18 are applicable. One example of such method is the Miner's rule.

(21) The displacement data may be determined based on temperature data related to average temperatures of the internal fluid 28. The average temperatures may be obtained from, or determined based on, temperatures measured by the temperature sensor 32. Alternatively, or in addition, the average temperatures may be determined based on the power supplied to the subsea arrangement 12, such as to the power equipment 30.

(22) By knowing the thermal expansion coefficient of the internal fluid 28 and temperature data related to average temperatures of the internal fluid 28 during the time period, volume changes of the internal fluid 28 can be calculated during the time period. By also knowing the volumes of the main enclosure volume 26 and the compensation volume 34, volume changes of the pressure compensator 18 can also be calculated. The thermal expansion coefficient of the internal fluid 28 is often given by the supplier. The thermal expansion coefficient may alternatively be calculated or may be set to a fixed value.

(23) The displacement of the pressure compensator 18 is proportional to the volume change of the compensation volume 34 and also to the volume change of the internal fluid 28 in the main enclosure volume 26 and in the compensation volume 34. Any given temperature of the internal fluid 28 will correspond to a given volume of the internal fluid 28 during normal operation of the subsea arrangement 12.

(24) The determination of the displacement data of the pressure compensator 18 during the time period based on the temperature data may be based on a displacement model. The displacement model may express displacement data of the pressure compensator 18 as a function of the average temperatures of the internal fluid 28 during the time period. The displacement data of the pressure compensator 18 can thereby be determined based on the temperature data and the displacement model.

(25) The volume change of the internal fluid 28 within the main enclosure volume 26 and the compensation volume 34 is directly proportional to the change of average temperature of the internal fluid 28 within the main enclosure volume 26 and the compensation volume 34. In the example of FIG. 1, the pressure compensator 18 expands and compresses axially as indicated by arrows 48. A certain volume change of the internal fluid 28 thereby generates a certain axial displacement of the pressure compensator 18. Thus, the axial displacement of the pressure compensator 18 is directly proportional to the average temperature of the internal fluid 28.

(26) If the subsea arrangement 12 alternatively comprises a pressure compensator with only a rubber barrier, e.g. without the inner barrier 38 of metal, the pressure compensator may displace both axially and radially. The lifetime of such pressure compensator can be defined by temperature induced volume variations of the internal fluid 28.

(27) As an alternative, the determination of the displacement data of the pressure compensator 18 during the time period based on the temperature data may comprise determining displacement data of the pressure compensator 18 based on the temperature data (obtained from the temperature sensor 32 or calculated based on the power supply), historical temperature data and historical displacement data.

(28) Alternatively, or in addition, the displacement data may be determined based on displacement values of the pressure compensator 18 obtained from the displacement sensor 52. The displacement sensor 52 may for example provide positional data of the pressure compensator 18 relative to a neutral position of the pressure compensator 18.

(29) In any case, the displacement values (e.g. amplitudes determined based on the power supply, amplitudes determined based on temperature data from the temperature sensor 32, and/or amplitudes obtained from the displacement sensor 52) may be filtered. Thereby, the displacement data may be constituted by a simplified set of displacement values and the displacement data for use when estimating the remaining useful life of the pressure compensator 18 may be based on the filtered and simplified displacement values. The filtering of amplitudes may for example be made with an algorithm, such as a rainflow counting algorithm. One example of a rainflow counting algorithm is the ASTM standard E 1049-85. A model of damage of the pressure compensator 18 as a function of a simple set of amplitudes can be found by tests.

(30) A compensator lifetime model may be provided for estimating the remaining useful lifetime as a function of the displacement data of the pressure compensator 18. The compensator lifetime model may optionally comprise sea depth of the pressure compensator 18, temperature and/or hydrostatic pressure of ambient seawater 20 outside of the pressure compensator 18. The estimation of the remaining useful life of the pressure compensator 18 in relation to a failure mode of the pressure compensator 18 may then be made based on the compensator lifetime model.

(31) The failure mode of the pressure compensator 18 may be defined in various ways. One example of a failure mode is fatigue of the pressure compensator 18, or a defined number of oscillations of the pressure compensator 18 prior to fatigue, or a defined time prior to fatigue of the pressure compensator 18.

(32) The control system 14 may contain or may be loaded with a computer program product comprising a computer readable means holding computer-executable components for causing the control system 14 to perform methods according to the present disclosure. The computer program product may comprise a computer program comprising computer program code which, when run on a processor circuitry of the control system 14, causes the control system 14 to perform the methods.

(33) While the present disclosure has been described with reference to exemplary embodiments, it will be appreciated that the present invention is not limited to what has been described above. For example, it will be appreciated that the dimensions of the parts may be varied as needed. Accordingly, it is intended that the present invention may be limited only by the scope of the claims appended hereto.