Monitoring of corrosion induced loss of material by means of a plurality of electrical resistance measurements (field signature method, electrical resistance tomography)

A method of investigating loss of material from a location, the method including:

• defining the location and providing two or more electrical contacts in contact with the location,
• measuring the voltage between two or more electrical contacts at a first time and at one or more other times, a current being passed through the location at the time of the voltage measurements, the voltage measurements providing information on the loss of material from the location with time, the information on material loss being obtained using a relationships which links the voltage measurements to the loss of material,
• information on the relationship being obtained by a modelling process, the modelling process including generating a model of the location, the model including two or more points on that location, modelling the values generated values for the voltages which would be measured between the two or more points with a current applied to the location at a first time and at least at a second time, the model including a change in configuration of the location between the first time and the second time to model loss of material from the location, the relationship being an expression of the relationship between a factor related to the model voltage values and a factor related to the change in configuration of the model location.

A method according to any preceding claim in which the modelling process includes information on the electrical resistance of the material and/or materials forming the location and/or configuration and/or cross sectional profile and/or thickness of the material or materials forming the location.

A method according to any preceding claim in which a node is provided in the model for each pin in the actual measurement apparatus, the nodes have corresponding position and/or separation relative to the pins they represent.

A method according to any preceding claim in which the modelling process includes applying a model electric current to the model location and calculating the induced voltage at two or more of the nodes, and ideally at all of the nodes, forming the model of the location.

A method according to any preceding claim in which the modeling process includes the extraction of model voltages for the nodes corresponding to the pin positions in the actual apparatus and a calculation of voltage differences between node pairs.

A method according to any preceding claim in which the modelling process includes calculating such voltages and/or voltage differences at the first time, ideally with no material loss, and at one or more other times with material loss.

A method according to any preceding claim in which the change in the configuration of the model location involves a reduction in thickness of one or more parts of the location.

A method according to any preceding claim in which the method includes a comparison of the voltage differences for one or more nodes/pin pairs arising from the modelling process with a simulation of metal loss against the voltage differences arising for one or more pin pairs in the actual location, the method including the adoption of a simulation of material loss to equate to the material loss from the actual location if the comparison is acceptable and/or the consideration of an alternative model based on an alternative simulation of the material loss if the comparison is not acceptable.

A method according to any preceding claim in which the method includes the generation of a plurality of models based on different simulations of material loss and the consideration of which these models best represents the actual corrosion occurring, ideally due to the correspondence of the model voltage differences and the actual location voltage differences.

A method according to any preceding claim in which the relationship provides an expression of the corrosion as a thickness loss, proportion of material lost or other value, such as a rate of loss.

A method according to any preceding claim in which the factor relating to the model voltage values is a fingerprint coefficient and more particularly the maximum fingerprint coefficient measured for that configuration variation.

A method according to any preceding claim in which the relationship is used to provide information on the material loss in the measured location, and in particular by equating a measured factor relating to the measured voltage to a material loss.