GB2464972A

GB2464972A - Cathodic protection monitoring system

Info

Publication number: GB2464972A
Application number: GB0820048A
Authority: GB
Inventors: Richard Holt
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-11-03
Filing date: 2008-11-03
Publication date: 2010-05-05
Also published as: GB0820048D0

Abstract

The cathodic protection monitoring system consists of a mobile unit (1) a command unit (2) and a number of monitor stations (4). The command unit (2) is connected to the monitor stations (4) using a two wire power and communications array (3). The final monitoring unit (4) is connected to the command unit (2) with the return loop (5) to provide redundancy. The command unit will acquire data from the monitoring units and store a number of readings to await retrieval by the mobile unit. The time interval between readings may be commanded. The command unit is self powered. Data exchange and power transfer between the command unit and the mobile unit may be achieved using a non-contact inductive coupling. The monitoring system is employed in an offshore structure and the mobile unit may be a remotely operated vehicle, autonomous underwater vehicle or manned submersible.

Description

I

DESCRIPTION

Cathodic Protection Monitoring System This invention relates to a method and apparatus to monitor a cathodic protection system.

BACKGROUND

In the design of structures it is usual that the material of choice will be steel, as this will provide it with sufficient strength at a reasonable cost. When these steel structures are exposed to the environment corrosion will begin. It is possible to include a corrosion allowance in the design, but because the corrosion site cannot be pre-determined and corrosion is not always uniform across the structure it is difficult to be certain that a sufficient allowance has been made for all critical areas. A corrosion allowance will lead to increase in overall weight and increase cost of materials. To mitigate the corrosion it is more usual to apply a coating system to the exposed surfaces. This may be sufficient where the structure will only be exposed to aerobic corrosion. However, when the structure is located offshore and particularly when the risk of failure of the structure is unacceptable, then a coating system alone will not guarantee total protection against corrosion. In this instance it is likely that a cathodic protection system will be added to the design of the structure, which if operated correctly, will prevent corrosion occurring in the protected areas.

The critical nature of the cathodic protection system suggests that it is prudent, and in some cases it is mandated that its performance is regularly monitored. The monitoring should relate to the effects the cathodic protection system is having on the structure it is protecting. Although it is perfectly feasible to record values on an annual or less frequent basis, most observers would agree that the greater the frequency of the data recording, the greater its usefulness will be. Depending on a number of diverse factors, it may be impossible or impractical to obtain frequent readings of a repeatable quality.

STATEMENT OF INVENTION

An autonomous means which over a period of time will store a number of readings which relate to the effect of a cathodic protection system on an offshore structure and when interrogated will transfer those readings.

DESCRIPTION

The invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows an overview of the complete system Figure 2 shows the mobile part of the system which is used to recover data, to issue commands and if required to recharge the energy storage in the fixed part of the system.

Figure 3 shows the command part of the system which acquires data and stores it ready for upload to the mobile part of the system.

Figure 4 shows a typical monitoring unit which would be positioned to gather relevant data.

The cathodic protection monitoring system (Figure 1) consists of a mobile unit (1) a command unit (2) and a number of monitor stations (4). The command unit (2) is connected to the monitor stations (4) using a two wire power and communications connection (3). The final monitoring unit (4) is connected to the command unit (2) with the return loop (5) to provide redundancy.

The mobile unit (Figure 2) may be operated by a remotely operated vehicle, autonomous underwater vehicle, manned submersible, diver or other means. It has connections to a power source and data storage means through an underwater connector (6). The raw power is converted using a power conversion and isolation means (11) for use by the mobile unit. A microprocessor (7) will communicate with the data storage means connected through the underwater connector (6). The microprocessor (9) will also communicate with the command unit (2) when it comes into range. Communication will be through a data transmission means (8) for which isolation is provided by the capacitors (9). When the microprocessor detects a command unit it will activate the power conversion means (12) which will transmit the power through the isolation inductors (13) to the transponder means (10).

The command unit (4) receives power from the mobile unit (2) through the transponder means (14). The power is isolated from any data by the inductors (22) and is regulated by the power conversion unit (23) and used to direct power to the energy storage means (24). When power is not available from the mobile unit (1) the energy storage means (24) will provide power to the power conversion means (25) when commanded by the microprocessor (16). Commands from the mobile unit (1) are sent through the transponder (14) and is isolated by the capacitors (15). Data from the non-volatile data storage means (17) is uploaded to the mobile unit (I) on command from the mobile unit.

The command unit is an autonomous means (Figure 3) which will store a number of readings in non-volatile data storage means (17). The time interval between readings may be commanded and the time at which the reading is made will be stored with the cathodic protection data. A real time clock means (18) will be used for timing operations. At the predetermined time the real time clock will command the processor (16) to begin operation. It may provide power to the monitor stations (4) and interrogate each in turn to provide a reading. The power and commands will be sent over two wires through the underwater connector (21). The power will be enabled by switching on the power conversion unit (25) which is isolated from the two wires by the inductors (26). The microprocessor will determine the commands to be sent. The command data will be sent by a data transmission means (19) and is electrically separate from the power by capacitors (20). Commands and power are sent to the monitor station (4) through an underwater connector (21) and a wire attached to it (3) connecting the command unit (2) to the monitor unit (4).

The monitoring unit (4) is mechanically attached to the structure to be monitored. It may have a local electrical connection to the structure under investigation where this is required to provide an accurate reading. Connection from the command unit or preceding monitor unit is through an underwater connector (28). The power is directed through inductors (35) where it is converted by the power conversion means (36) to provide power to the monitor unit. Optionally the monitor unit may contain its own power storage means (37). The commands are directed through capacitors (29) to the microprocessor means (30). The monitor unit is capable of undertaking a range of measurement options. These may include but are not limited to structure potential, structure current density, local water temperature, local water conductivity. If the type of measurement requires that certain devices means are directly placed in the surrounding water then the connection from the signal conditioning means (32) will be made through an underwater connector (33). The monitor unit (4) will contain, if required a signal conditioning means (32) and an analogue to digital convertor means (31) to a sufficient accuracy to ensure the data is accurate and meaningful. The monitor unit is connected to the next monitor unit through an underwater connector (34). If there is no other monitor unit then the monitor unit is connected to the command unit (27) using a two wire cable (5). This will provide redundancy in the event of connector or wiring failure.

ADVANTAGES

Preferably at a single visit to the fixed part of the cathodic protection monitoring system (Figure 3) a periodic set of data can be recovered. The data provides an accurate record of the past performance of a cathodic protection system.

Preferably there is no direct electrical contact between the fixed part (Figure 3) and the mobile part (Figure 2) to avoid problems of silt ingress or marine fouling making a direct electrical contact fail.

Preferably the power storage means in the fixed part (Figure 3) will enable a number of monitors to be interrogated.

Preferably the locations of the monitor means will be fixed.

Preferably a monitor means (Figure 4) will receive power from the fixed part (Figure 3) of the system.

Preferably a monitor means (Figure 4) will measure the potential of the structure when activated.

Preferably a monitor means (Figure 4) will measure the current density of the structure when activated.

Preferably a monitor means (Figure 4) will measure the temperature of the electrolyte surrounding the structure when activated.

Preferably a monitor means (Figure 4) will measure the salinity of the electrolyte surrounding the structure when activated.

Preferably connection between the fixed part (Figure 3) and the monitor means (Figure 4) will be two wires, providing both power and bidirectional data communication.

Preferably the final monitor means will connect back to the fixed part (Figure 3) using 2 wires (5).

Preferably all wire connections will be made using underwater connectors (6, 21, 27, 28, 33, and 34).

Claims

CLAIMSCathodic Protection Monitoring System 1 A cathodic protection monitoring system which over a period of time will store a number of readings which relate to the effect of a cathodic protection system on an offshore structure and when interrogated will transfer those readings.
2 A cathodic protection monitoring system according to claim I which will transfer the data from the storage means on demand.
3 A cathodic protection monitoring system according to claim 1 which can be deployed at depth in an offshore environment.
4 A cathodic protection monitoring system according to claim 1 which will include power storage to enable it to operate autonomously.
A cathodic protection monitoring system according to claim I which has a real time clock (27).
6 A cathodic protection monitoring system according to claim I which provides power to at least one external monitor unit.
7 A cathodic protection monitoring system according to claim I which sends commands to at least one external monitor unit.
8 A cathodic protection monitoring system according to claim I which receives commands from at least one external monitor unit.
9 A cathodic protection monitoring system according to claim I which receives data from at least one external monitor unit.
A cathodic protection monitoring system according to claim 2 which can transfer the data with or without the requirement of direct electrical contact.
11 A cathodic protection monitoring system according to claim 6 will use the power to operate and act on commands (Figure 3).
12 A cathodic protection monitoring system according to claim 6 will use the power to make measurements (Figure 3).
13 A cathodic protection monitoring system according to claim 6 will use the power to send readings to the command unit (Figure 3).
14 A cathodic protection monitoring system according to claim 11 which receives power and commands and transmits data and commands on two wires.