REAL-TIME CATHODIC PROTECTION INTEGRITY MONITORING SENSOR, SYSTEM AND METHOD

Abstract

A sensor (4) for monitoring cathodic protection (CP) levels, i.e. cathodic protection potential and current capacity, the sensor being arranged to perform measurements of galvanic current and polarized potential between, on one hand, a reference object and, on the other hand, one of: i) a sacrificial anode (2) and ii) a protected component (1). The sensor comprises a reference electrode (5) in electrical and electrochemical contact with a metal sensing element (6) which has a defined surface area (6) exposed to an electrolyte, the sensing element electrically coupled to one of the sacrificial anode (2) or the protected component (1) via a resistor (15) and a switch (12).

Claims

1. A sensor (4) for monitoring cathodic protection (CP) levels, i.e. cathodic protection potential and current capacity, wherein cathodic protection comprises supply of cathodic current to protected components, the sensor being arranged to perform measurements of galvanic current and voltage potential between, on one hand, a reference object (6) and, on the other hand, one of: i) a sacrificial anode (2) and ii) a protected component (1), characterized in that the sensor comprises a reference electrode (5) in electrical and electrochemical contact with a metal sensing element (6) which has a defined surface area (6) exposed to an electrolyte, the sensing element electrically coupled to one of the sacrificial anode (2) or the protected component (1) via a resistor (15) and a switch (12).

2. The sensor of claim 1, wherein the sensor is arranged to generate a first output voltage (V1) indicative of the polarized potential between the sensing element (6) and the reference electrode (5), and a second output voltage (V2) indicative of the galvanic current flowing to the sensing element (6) from one of the sacrificial anode (2) or the protected component (1).

3. The sensor of claim 2, wherein the sensor (4) is an integral structure comprising the reference electrode (5) and the sensing element (6) embedded in a body (17) of non-conductive material.

4. The sensor of claim 3, wherein the reference electrode (6) is a wire which extends centrally through the sensing element (6) in the form of a tube, the ends (5, 6) of the wire and tube exposed to the electrolyte in one end of the body (17) of non-conductive material.

5. The sensor of claim 1, wherein the sensing element (6) is an element of high nobility, preferably one of palladium, platinum, gold, silver, titanium, Cu-based alloys, or stainless steel with a pitting resistance equivalent (PRE) greater than 40.

6. The sensor of claim 1, wherein the exposed area (6) of the sensing element (6) is from about 1 to 15 cm2 in size.

7. The sensor of claim 1, wherein the reference electrode (5) is an Ag wire with an AgCl surface layer, a Zn, Pt, or In wire, or a Cu wire with a CuSO4 layer.

8. The sensor of claim 1, wherein the resistance of the resistor (15) is in the range of 1-100 Ohm.

9. The sensor of claim 1, wherein the switch (12) is frequently controlled between on and off for cycling the supply of current to the sensing element (6).

10. A system for real-time monitoring and control of cathodic protection (CP) levels, i.e. cathodic protection potential and current capacity, in underwater equipment the operation of which is controlled via a subsea production control system (PCS), wherein cathodic protection comprises means for supplying cathodic current to protected components of the underwater equipment, the system comprising: a distributed network of sensors (4) installed on the underwater equipment, the sensors arranged to perform measurements of galvanic current and polarized potential between, on one hand, a reference object and, on the other hand, one of: i) a sacrificial anode (2) and ii) a protected component (1) of the underwater equipment; a subsea, electronic, cathodic protection control (CPC) unit (33) comprising a plurality of input terminals (34) and a processor (37) configured to receive and individually process sensor signals indicative of changes in the CP levels, wherein the CPC unit (33) uses the PCS for communication, wherein the CPC unit (33) is in communicative contact with the cathodic current supply means and configured to initiate current control commands for regulating the cathodic current supplied to individual components or component groups of the underwater equipment in response to detected CP levels.

11. The system of claim 10, wherein the CPC unit (33) is integrated in a subsea electronic module (SEM) (27) of the PCS.

12. The system of claim 10 or 11, wherein the plurality of sensors (4) are connected to the CPC unit (33) via a distributed network of the PCS.

13. The system of claim 10, wherein the sensors (4) are powered by cathodic current supplied to the CP system.

14. A method for real-time monitoring and control of cathodic protection (CP) levels, i.e. cathodic protection potential and current capacity, in underwater equipment the operation of which is controlled via a subsea production control system (PCS), wherein cathodic protection comprises means for supplying cathodic current to protected components of the underwater equipment, the method comprising: arranging a distributed network of sensors (4) configured for generation of voltage outputs indicative of changes in galvanic current and polarized potential between, on one hand, a reference object and, on the other hand, one of: i) a sacrificial anode (2) and ii) a protected component (1) of the underwater equipment, communicating the sensor outputs via the PCS to a cathodic protection control (CPC) unit (33), and generating in the CPC unit current control commands for regulating the cathodic current supplied to individual components or component groups of the underwater equipment in response to detected CP levels.

15. The method of claim 14, further comprising arranging each sensor (4) with a reference electrode (5) in electrical (7) and electrochemical (8) contact with a metal sensing element (6) which has a defined area (6) exposed to the water, coupling the sensing element electrically to one of the sacrificial anode (2) or the protected component (1) via a resistor (15) and a switch (12).

16. The method of claim 14 or 15, further comprising configuring the sensor (4) for generation of a first output voltage (V1) indicative of the polarized potential between the sensing element (6) and the reference electrode (5), and a second output voltage (V2) indicative of the galvanic current flowing to the sensing element (6) from one of the sacrificial anode (2) or the protected component (1).

17. The method of claim 14, further comprising: operating the sensors (4) on cathodic current supplied by the cathodic current supply means.

18. The method of claim 15, further comprising: cycling the supply of current to the sensors (4) to prevent deposits on the sensing area (6).

19. The method of claim 14, further comprising regulating the CP levels individually for protected components of the underwater equipment via a topside operator or optionally from the CPC unit (33) directly without involvement from the topside operator.

20. The method of claim 14, further comprising determining the status of the cathodic protection (CP) by comparing detected changes in galvanic current and polarized potential with the corresponding levels of a cathodic protection system in balance, wherein deviations from the levels of the balanced system are ranked in categories of adequate CP, suboptimal CP and inadequate CP.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0035] Embodiments of the invention will be described below with references made to the accompanying drawings. In the drawings,

[0036] FIG. 1 is a diagram showing the setup of a sensor in a cathodic protection (CP) monitoring system,

[0037] FIG. 2 is an end view of the sensor,

[0038] FIG. 3 is a longitudinal section through the sensor of FIG. 2,

[0039] FIG. 4 is an overview of an integrated CP monitoring system,

[0040] FIG. 5 is a diagram showing an interface between CP monitoring and production control (PCS) systems,

[0041] FIG. 6 is a diagram illustrating the tree structure of signal pathways in a CP monitoring system which is subordinated the subsea electronic module (SEM) of a PCS system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0042] Embodiments of the invention are illustrated schematically in the drawings.

[0043] With reference to FIG. 1, a component 1 to be protected is electrically connected to a sacrificial anode 2 via a connection 3. The sacrificial anode 2 and the subsea component 1 constitute the anode and the cathode respectively of a cathodic protection system.

[0044] A sensor 4 comprises a reference electrode 5 and a sensing element 6. The reference electrode 5 and the sensing element 6 are in electric contact via a wire 7. When in use the reference electrode 5 and the sensing element 6 are submerged in water or other form of electrolyte, the reference electrode 5 and the sensing element 6 are thus also in electrochemical contact as schematically symbolized by reference number 8.

[0045] A first voltmeter 9 is arranged to detect the polarized potential between the reference electrode 5 and the sensing element 6. The output from the first voltmeter 9 is transmitted to an output terminal 10 on the sensor.

[0046] The sensing element 6 is electrically connected to the protected component 1 via a connection 11. An ON/OFF switch 12 is arranged in this connection 11 for closing and opening, i.e. for feeding and non-feeding electrical current from the component 1 to the sensing element 6. A second voltmeter 13 is arranged on a wire loop 14 which connects to the electrical connection 11 on either side of a 1-100 Ohm resistor 15. The output from the second voltmeter 13 is transmitted to an output terminal 16 on the sensor.

[0047] One embodiment of the sensor 4 is illustrated schematically in FIGS. 2 and 3. The embodiment of FIGS. 2 and 3 is arranged as an integral unit. More precisely, the elements of the sensor, including the reference electrode 5, the sensing element 6, the first and second voltmeters 9 and 13, the resistor 15, the switch 12 and associated wiring are embedded in a body 17 of non-conductive and pressure-resistant material. The body 17 may be inserted and protected inside an external shell 18 made of non-corrosive and durable material. In this embodiment the reference electrode 5 is a wire which extends through the central region of a sensing element 6 in the form of a tube. The ends 5 and 6 of the reference electrode 5 and of the sensing element 6 respectively are uncovered an exposed to the electrolyte (such as water) in one end of the sensor (the bare ends 5, 6 are visible in FIG. 2). The output terminals 10 and 16, as well as a control input 19 to the switch 12, project from the other end of the sensor. A contact plate 20 is arranged to feed cathodic current to the switch 12 when the sensor is mounted to a subsea component included in the cathodic protection system.

[0048] Integration of the sensor 4 in a production control system, PCS, for a subsea hydrocarbon production plant is illustrated schematically in FIG. 4. The hydrocarbon production plant comprises a number of wells 21, jumpers 22 connecting the wells to a manifold 23, a pipeline end termination assembly 24 and a pipeline 25 for transport of hydrocarbon fluid recovered from the wells. The flows of production fluid, injection water or chemicals are controlled and regulated by means of valves on wellheads and valve trees, on manifolds and on pipeline termination assemblies. Regulation of these flows is governed through subsea control modules (SCM) 26 which are distributed to the operational components of the hydrocarbon production plant. The SCM 26 can be seen as the executive means of the PCS system, the SCM controlling the administration of electrical power, signals and hydraulic power that is distributed within cables, hoses and wiring of the PCS system. In FIG. 4, the widespread character of the PCS system is illustrated symbolically by the section-marked tree structure. At the root end of this tree, a subsea electronics module (SEM) 27 is arranged to control, within the PCS system, the flows of electrical power 28, control power 29 and hydraulic fluid 30 which are received via an umbilical 31 and the subsea umbilical termination assembly (SUTA) 32.

[0049] In a system aspect of the present invention, a distributed network of sensors 4 can be permanently installed on components to be protected in a hydrocarbon production plant. The sensors are connected to a cathodic protection control (CPC) unit 33 for upstream communication of measured values and for downstream communication of switch control signals. The CPC unit 33 is subordinated the SEM 27 for topside communication via the umbilical. Although illustrated as a separate module, the CPC unit may alternatively be integrated as part of the SEM 27.

[0050] With reference to FIG. 5, the CPC unit 33 comprises a plurality of input terminals 34 arranged to receive inputs from the corresponding number of sensors 4. The sensor signals may be introduced via an amplifier circuit 35 and an analogue-to-digital converter 36, from where the signals are fed to a micro-processor 37 for treatment. The outputs from the micro-processor are fed to a transceiver 38 which provides two-way communication with the SEM module via a multiple wire interface 39. An IC (integrated circuit) power supply 40 feeds DC current to the IC modules of the CPC unit.

[0051] In one embodiment, the micro-processor 37 has the processing capacity and program codes required to evaluate the status of the cathodic protection, based on the inputs from the sensors. The micro-processor 37 may additionally be configured to generate current control commands for regulation of the cathodic current to be supplied to the subsea components. In another embodiment, evaluation of the status of the cathodic protection is performed in the SEM module 27, whereas the micro-processor 37 operates as a switch bank to feed sensor data sequentially to the SEM module. This embodiment is illustrated in the diagram of FIG. 6. A plurality of sensors a-n are assigned to individual addresses under respective address nodes 1 to 9 on a superior level. The micro-processor 37 is configured to transfer sequentially the data from the nodes 1-9 to the SEM for computation, such that the 1st iteration involves data from sensors 1(a), 2(a) etc. to 9(a), the 2nd iteration involves data from sensors 1(b), 2(b) etc. to 9(b), until completing the nth iteration involving data from sensors 1(n) to 9(n).

[0052] From the disclosure, it will be appreciated that the present invention avoids the main disadvantages of currently practised solutions, which are typically ROV operated, are limited to spot measuring, and which do not provide real-time monitoring nor allow for spatial potential and current mapping.

[0053] In contrast, the present invention proposes an integrated sensor network that will monitor the health of the CP system in real time. The monitoring system can be integrated in the subsea production control system for data logging, risk assessment, and for actioning from surface equipment or automatically without intervention from the operator.

[0054] The sensor network will rank the health of the CP system by monitoring current and potential vs. time. The monitoring device is based on measurement of the galvanic current and potential (i.e. the polarization of the structure) between a sensing surface of known exposed area and either i) a sacrificial anode or ii) a subsea component connected to the CP system.

[0055] By way of integration with the PCS system and SEM electronics as disclosed, a plurality of sensors can be employed to provide a CP status monitoring system and method with high resolution.