GB2471087A

GB2471087A - A Portable Cathodic Protection Monitoring System

Info

Publication number: GB2471087A
Application number: GB0910303A
Authority: GB
Inventors: Richard Holt
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-06-16
Filing date: 2009-06-16
Publication date: 2010-12-22
Also published as: GB0910303D0

Abstract

A portable cathodic protection monitoring system consists of a probe 1 and an electronics module (Figure 3) inside a pressure housing (14, fig 2). The probe 1 holds a number of half cells 11 along a single axis and has a sharp metal tip 12 for possible local contact readings. The probe may be held on a transport mechanism at any fixed orientation. The electronics will convert the local analogue signals to a digital data stream for ease of storage and to improve signal integrity. Data storage may be in the electronics module or an external device. By making a number of readings along a single axis it is possible to account for local noise sources and calculate the external field of the metal structure. Combining the data from contact readings with the 'noise' field values it is possible to calculate the cathodic protection potential of the item under investigation, together with current outputs from anodes and current density of metal surfaces.

Description

DESCRIPTION

Advanced Portable Cathodic Protection Monitoring System This invention relates to a method and apparatus to determine electric fields in water generated from corroding metals. The data may be used to determine the corrosion status of the material and the effectiveness of any related cathodic protection system.

BACKGROUND

It is usual when designing structural devices that the material of choice will be steel, as this will provide a structure which sufficient strength at a reasonable cost. When these structures are exposed to the environment corrosion will begin. It is possible to design in a corrosion allowance, but because the corrosion site cannot be pre-determined and the corrosion will not always be uniform across the structure it is difficult to be certain that a sufficient allowance has been made for all critical areas.

A corrosion allowance may also lead to additional overall weight and increased project cost. To mitigate the corrosion it is more usual to apply a coating system to the expose surfaces. This may be sufficient where the structure in question will only be exposed to aerobic corrosion. However, when the structure is to be placed in an offshore location and particularly when the importance of the structure is enhanced, then a coating system alone cannot be guaranteed to prevent all 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 guarantee to prevent any 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 it is regularly monitored. The monitoring should relate to the effects the cathodic protection system is having on the structure it is protecting.

The monitoring system should be versatile enough to cope with conditions that prevail, for example lack of direct access to the metal surface, and be applicable to a variety of methods of Transport System. The transport system will be supplied by others and could be for example Autonomous Underwater Vehicle (AUV), Remotely Operated Vehicle (ROy), manned submersible, or diver assisted.

The invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows a means of holding electrodes Figure 2 shows a means of submerging an electronics module.

Figure 3 shows suggested circuit diagram for the electronics module.

The advanced portable cathodic protection monitoring system consists of a probe unit (I) and an electronics module (Figure 3). The probe unit (1) is connected to the electronics module (Figure 3) using a multi-core cable. The probe unit connection (10) is designed to be suitable for the purpose of providing a watertight connection between the measuring cells (11) and the electronics module (Figure 3). The cells (11) are mounted along a single axis and are chosen to be well characterised. The probe body (1) is designed to hold a sharp metal tip (12) which is sufficiently durable to make regular contacts with the structure under investigation, should this be desired.

The equipment would be equally viable without the addition of the tip (12). The probe body (1) should be designed to have sufficient strength to prevent it deforming or flexing in use. The composition of the probe body (10) should be inert so that it will not to react with the conducting medium (electrolyte).

The electronics module (Figure 3) is in a pressure housing (14). The housing (14) is designed to provide a watertight connection (13) to the probe unit. The body of the pressure housing (14) should be inert to any chemical reaction with the conducting medium (electrolyte). Power is provided to the electronics module (Figure 3) through a watertight connection (15). This connection will allow commands to be transferred to the electronics module (Figure 3) and for data to be transmitted from the electronics module, if desired.

The circuit of the electronics module (Figure 3) indicates the method of deriving data.

Connection (16) from the probe half cells (11) will take signals from pairs of cells to differential signal conditioning blocks (17). The signal conditioning block (17) is the same for each of the pairs of cells. An analogue to digital convertor (18) transforms each of the voltages measured to a digital value. The microprocessor (19) ensures that the conversion of each of the values from the half cells (11) occurs at the same instant in time. The microprocessor can store the digital data in a non-volatile memory device (22) should this be necessary. Commands to the microprocessor are converted to a suitable form by the data transmission and reception module (24). This module will ensure the correct galvanic isolation of the microprocessor to external command sources. The module (24) will also convert data from the microprocessor to external devices creating the correct voltage levels and provide the necessary galvanic isolation. Power from an external source is galvanic isolated by the unit (20) which will also condition the power to be suited to internal requirements. Connection to outside power sources and data command and collection is through a suitable watertight connection (21).

A real time clock (23) can be synchronised with the main system clock at the start of the survey to enable later comparison of data collected. The clock may be periodically synchronised during the survey by receipt of command from the transport system through the watertight connection (21) and the data transmission and reception module (24). If appropriate the real time clock (23) may also be disabled.

Data recovered by the Advanced Portable Cathodic Protection Monitoring Unit (APCPM) will be a combination of the desired signal, noise from the transport system and other naturally occurring noise sources. For a given set of readings the noise source and the signal source will be at a fixed unknown distance from the probe. The voltage read between a pair of half cells can be expressed as a function of the noise source plus a function of the signal source. The value of the noise source will be proportional to the noise source and the distance of each half cell in the pair to that source. Similarly the value of the signal source will be proportional to the signal source and the distance of each half cell from it. For a horizontally mounted probe the distance between readings will provide sufficient information to extract the signal source value from the data by solving simultaneous equations. The exact position of the source will be determined as the potential maximum flips when crossing the source. For a vertically mounted probe the signal source value can be simply obtained, as long as the height of flight is known. If it is not known the solving simultaneous equations as for the horizontally mounted probe will provide the solution. A signal maximum will be recorded at the exact moment the probe passes over the signal source.

STATEMENT OF INVENTION

Equipment to measure an electric field in a conducting medium on a single axis. The measurements can be interpreted to determine the cathodic protection potential of the item under investigation. Where appropriate the measurements can be used to calculate the current output from current sources and the current density at current sinks.

ADVANTAGES

Preferably the measurement probe (Figure 1) will house a number of half cells (Ii).

The half cells will be distributed along a single measurement axis.

Preferably each half cell (11) will be housed in the probe, such that an electrical connection to the half cell will be insulated from the surrounding conducting medium.

Preferably the measurement probe (Figure 1) will include a sharp metal tip (12) capable of making a direct contact measurement on the item under investigation. The size, shape and material used to make the sharp metal tip should not unduly influence the potential of the item under investigation when in contact.

Preferably the sharp metal tip (12) will be housed in the probe, such that an electrical connection to the sharp metal tip (12) will be insulated from the surrounding conducting medium.

Preferably the probe will be sufficiently rigid in design to prevent any flexing or distortion in use. By design, the presence of the probe in the conducting medium should not unduly influence the electric fields present.

Preferably an electronics module (Figure 3) will be in close proximity to the probe.

This will reduce electrical noise pickup between the sensing half cells (11) and electronic conversion circuits.

Preferably electrical connections from the half cells (11) and the sharp metal tip (12) will join them to the electronics module in such a way as to insulate the connections from the surrounding conducting medium.

Preferably the electronics module will be in a housing (14) designed to remove any effects of water pressure on the performance of the electronics (Figure 3). The housing (14) may be part of the probe, or a separate assembly. The housing (14) will ensure that the surrounding conducting medium does not affect the performance of the electronics. The housing (14) itself will not affect the performance of the electronics.

Preferably the electronics module housing (Figure 2) will not unduly influence the

electric field present in the conducting medium.

Preferably the electronics module will receive power from the Transport System through a watertight connection (21). The design of the electronic will be to minimise its impact on the power budget of the Transport System.

Preferably the power supply module (20) will also provide galvanic isolation of the transport system power source.

Preferably the electronics module will read the voltage on each pair of half cells (11) at the same instant in time. This will mean that the magnitude of the signal and the noise will be fixed at that instant in time.

Preferably the electronics module will read the voltage between the sharp metal tip (12) and a half cell (11) at the same instant in time as reading other half cell to half cell voltages. The will allow a correction to be made to the contact reading to account for the half cell not being directly at the surface of the item being contacted.

Preferably the electronics module will record data measured in a non-volatile memory module (22). This may be replaced or supplemented by transmitting the data in real time to an external device connected through a watertight system (21). The protocol and voltage levels required to transmit this data will be determined by the data transmission module (24).

Preferably a real time clock (23) will provide a time stamp for each data stored. The real time clock (23) can be synchronised at any time before, or during the survey to ensure that data is coherent.

Preferably the transmission module (24) will provide galvanic isolation of the external data receiving device.

Preferably the non-volatile memory module (22) can be easily removed at the completion of a survey or its contents readily downloaded on demand.

Preferably all wire connections will be made using underwater connectors.

Claims

CLAIMSAdvanced Portable Cathodic Protection Monitoring System A monitoring system which can be transported from place to place and make measurements of an electric field in a conducting medium on a single axis generally as the result of a cathodic protection system on an offshore structure.
2 A monitoring system according to claim I which can store data on internal memory devices.
3 A monitoring system according to claim 1 which can be deployed at depth.
4 A monitoring system according to claim I which can be carried by an appropriate transport mechanism.
A monitoring system according to claim I which has a real time clock (23).
6 A monitoring system according to claim I which may receive power from a transport system.
7 A monitoring system according to claim I which can send data to external devices.
8 A monitoring system according to claim I which may receive commands from external devices.
9 A monitoring system according to claim 1 which can make a contact reading using a sharp metal tip.
A monitoring system according to claim 7 which can transfer the data in real time or on demand.
11 A monitoring system according to claim 5 which may reset, over-ride or ignore the real time clock if commanded.