GB2026699A - Detection of Submarine Potentials & Corrosion - Google Patents

Abstract

In the detection of submarine potentials and corrosion, a method of testing the variation of electric potential at the surface of a submarine object 2 in which the electric potential of the seawater at a location adjacent to a point on the surface of the object is compared with a reference potential, said location being within a confined space, preferably as small as possible, between the surface of the said object and an insulating barrier 4. The reference potential may be measured at the same point without the insulating barrier. <IMAGE>

Description

SPECIFICATION Detection of Submarine Potentials and Corrosion This invention relates to detecting submarine potentials, and in particular relates to a method of detecting corrosion occurring in reinforcing bars in concrete (or other highly electrically resistive substance) used in marine applications. Corrosion in reinforcing bars of this type may be due to improperly constituted concrete, or to the bar being too close to a surface of the concrete immersed in the sea.

A survey of the potential over the surface of an object may be used to detect corrosion. A difficulty that may arise when surveying submarine objects particularly objects in which the area of suspended corrosion is covered with a highly electrically resistive substance that cannot be penetrated, is that the relatively high electrical conductivity of seawater tends to cause the potentials measured over the external surface of the object to be relatively constant, and thus the effect of corrosion is obscured.

Accordingly the present invention provides a method of testing a submarine object for variation of electric potential at its surface in which the electric potential of the seawater at a location adjacent to a point on the surface of the object is compared with a reference potential said location being within a confined space preferably as small as possible between the surface of the said object and an insulating barrier. The insulating barrier, which may be in the form of a conical (preferably obtuseiy conical) shield, inhibits the oufflow of current from the confined space and the consequential equalization of the potential over the surface of the object.

The said reference potential may, for example, be the potential measured at the same location when the said insulating barrier is not present.

A preferred method of the invention will now be described with reference to and as illustrated in the accompanying drawings in which: Figure 1 illustrates schematically a first stage of the method; and Figure 2 illustrates schematically a second stage of the method shown in Figure 1. In Figures 1 and 2 a submarine piece of concrete 2 shown in cross-section contains a reinforcing bar 3 running beneath the surface of the concrete 2. If is desired to survey the concrete 2 for possible corrosion of the reinforcing bar 3 two measurements of potential are made in a first and a second stage of the method.

In the first stage, illustrated in Figure 1, a first electrode 1 of a pair of electrodes is brought to a location in the seawater adjacent to the part of the concrete 2 which is to be surveyed. The second electrode of the pair is at a remote point and is not shown. The potential at the location of the first electrode 1 is then measured in a standard manner to give a reference potential. For the second stage of the method illustrated in Figure 2, a second measurement of potential is made at the same location as the first measurement but with the location enciosed in a volume defined by an insulating barrier 4 and the surface of the concrete 2. The insulating barrier 4 is shown in cross-section and is obtusely conical in shape, the first electrode 1 is situated on the axis of the cone and is lead through a hole at or near the apex.The edge 5 of the insulating barrier is in contact with the surface of the concrete 2 and the diameter of the insulating barrier 4 at its edge 5 is large in comparison with the distance from the first electrode 1 to the reinforcing bar 3.

If corrosion of the reinforcing bar 3 is taking place a current will be flowing from the point of corrosion through the surrounding concrete 2 and seawater. The paths of the current will be substantially different when the first and second measurements of potential are made, and consequently the second measurement of potential will differ from the first, reference potential. When the insulating barrier 4 is in position, the component of the flow of current perpendicular to the surface of the concrete 2 present when the reference potential is measured will be substantially absent; if no corrosion is taking place in the vicinity of the first electrode 1 such a variation between the reference potential and the potential measured with the insulating barrier 4 in position will not be observed.

Thus the method may be used to detect corrosion in the reinforcing bar 3 or the presence of a point in the concrete 2 acting as a cathode.

Claims

1. A method of testing a submarine object for variation of electric potential at its surface in which the electric potential of the seawater at a location adjacent to a point on the surface of the object is compared with a reference potential said location being within a confined space, preferably as small as possible, between the surface of the said object and an insulating barrier.

2. A method as claimed in Claim 1 in which said reference potential represents the potential at said location if said insulating barrier were not present.

3. A method as claimed in Claim 1 or Claim 2 in which said insulating barrier is conical, preferably obtusely conical and said potential is measured by an electrode situated on or near the axis of the conical insulating barrier.

4. A method of detecting corrosion as claimed in Claim 3 in which said electrode is one of a pair of electrodes, the other situated at a relatively distant location.

5. A method of detecting corrosion as claimed in any previous claim in which said object is of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Detection of Submarine Potentials and Corrosion This invention relates to detecting submarine potentials, and in particular relates to a method of detecting corrosion occurring in reinforcing bars in concrete (or other highly electrically resistive substance) used in marine applications. Corrosion in reinforcing bars of this type may be due to improperly constituted concrete, or to the bar being too close to a surface of the concrete immersed in the sea. A survey of the potential over the surface of an object may be used to detect corrosion. A difficulty that may arise when surveying submarine objects particularly objects in which the area of suspended corrosion is covered with a highly electrically resistive substance that cannot be penetrated, is that the relatively high electrical conductivity of seawater tends to cause the potentials measured over the external surface of the object to be relatively constant, and thus the effect of corrosion is obscured. Accordingly the present invention provides a method of testing a submarine object for variation of electric potential at its surface in which the electric potential of the seawater at a location adjacent to a point on the surface of the object is compared with a reference potential said location being within a confined space preferably as small as possible between the surface of the said object and an insulating barrier. The insulating barrier, which may be in the form of a conical (preferably obtuseiy conical) shield, inhibits the oufflow of current from the confined space and the consequential equalization of the potential over the surface of the object. The said reference potential may, for example, be the potential measured at the same location when the said insulating barrier is not present. A preferred method of the invention will now be described with reference to and as illustrated in the accompanying drawings in which: Figure 1 illustrates schematically a first stage of the method; and Figure 2 illustrates schematically a second stage of the method shown in Figure 1. In Figures 1 and 2 a submarine piece of concrete 2 shown in cross-section contains a reinforcing bar 3 running beneath the surface of the concrete 2. If is desired to survey the concrete 2 for possible corrosion of the reinforcing bar 3 two measurements of potential are made in a first and a second stage of the method. In the first stage, illustrated in Figure 1, a first electrode 1 of a pair of electrodes is brought to a location in the seawater adjacent to the part of the concrete 2 which is to be surveyed. The second electrode of the pair is at a remote point and is not shown. The potential at the location of the first electrode 1 is then measured in a standard manner to give a reference potential. For the second stage of the method illustrated in Figure 2, a second measurement of potential is made at the same location as the first measurement but with the location enciosed in a volume defined by an insulating barrier 4 and the surface of the concrete 2. The insulating barrier 4 is shown in cross-section and is obtusely conical in shape, the first electrode 1 is situated on the axis of the cone and is lead through a hole at or near the apex.The edge 5 of the insulating barrier is in contact with the surface of the concrete 2 and the diameter of the insulating barrier 4 at its edge 5 is large in comparison with the distance from the first electrode 1 to the reinforcing bar 3. If corrosion of the reinforcing bar 3 is taking place a current will be flowing from the point of corrosion through the surrounding concrete 2 and seawater. The paths of the current will be substantially different when the first and second measurements of potential are made, and consequently the second measurement of potential will differ from the first, reference potential. When the insulating barrier 4 is in position, the component of the flow of current perpendicular to the surface of the concrete 2 present when the reference potential is measured will be substantially absent; if no corrosion is taking place in the vicinity of the first electrode 1 such a variation between the reference potential and the potential measured with the insulating barrier 4 in position will not be observed. Thus the method may be used to detect corrosion in the reinforcing bar 3 or the presence of a point in the concrete 2 acting as a cathode. Claims

1. A method of testing a submarine object for variation of electric potential at its surface in which the electric potential of the seawater at a location adjacent to a point on the surface of the object is compared with a reference potential said location being within a confined space, preferably as small as possible, between the surface of the said object and an insulating barrier.

2. A method as claimed in Claim 1 in which said reference potential represents the potential at said location if said insulating barrier were not present.

3. A method as claimed in Claim 1 or Claim 2 in which said insulating barrier is conical, preferably obtusely conical and said potential is measured by an electrode situated on or near the axis of the conical insulating barrier.

4. A method of detecting corrosion as claimed in Claim 3 in which said electrode is one of a pair of electrodes, the other situated at a relatively distant location.

5. A method of detecting corrosion as claimed in any previous claim in which said object is of concrete containing metal reinforcing bars near its surface.

6. A method of detecting corrosion substantially as hereinbefore described with reference to the accompanying drawings.