The Bathycorrometer® is used as a sub–sea inspection tool, by divers, to determine the corrosion status of an immersed structure.
The hand-held unit measures the electrochemical potential of the structure under investigation against its own internal silver/silver chloride/sea water reference electrode. The potential is then displayed on the Bathycorrometer® multimeter. This potential may be noted by the diver at the time the inspection is carried out or can be transmitted to the surface by the use of a Surface Display Unit.
The Bathycorrometer® allows a diver/inspection engineer to select a given location, on an immersed structure, at which the structure to sea water potential is to be measured. The electrochemical potential of the structure under investigation at this location can be determined to a high degree of accuracy (+/- 5mV ).
The measured potential will enable an assessment of the level of cathodic protection on the structure under investigation to be obtained. If the potential is less than 800 mV vs an Ag/AgCl reference electrode in aerobic conditions, then insufficient levels of cathodic protection are being achieved. If the potential is in excess of 1100 mV vs an Ag/AgCl electrode then excess levels of cathodic protection are being applied and there is a danger of cathodic disbondment, detachment of the structure coating. Indeed, in the case of high tensile steels, a high negative potential may cause hydrogen embrittlement.
underwater diver
The potential readings provided by the Bathycorrometer® will provide the structure’s operator with information on the efficacy of the installed cathodic protection system and locations of any areas where only partial levels of cathodic protection are being achieved. If there is a likelihood of corrosion the electrochemical performance of sacrificial anodes can be checked to determine if there are any areas of over protection. In the case of impressed current cathodic protections there is the possibility of coating damage due to over protection. This can be detected using the Bathycorrometer® and suitable measures for mitigating against excess levels of cathodic protection can then be taken.
Measurement of the structure to sea water potential with a portable silver/silver chloride electrode from the surface will provide information on the mixed potential of the structure over a large area. However, there may be areas of low protection on a given structure that will not be detected using a portable half cell. The information from portable half cells can sometimes be misleading and will in all instances require an electrical connection onto the structure under investigation.
The Bathycorrometer® enables measurements of the structure potential at a precise location and can provide a considerably more accurate assessment of the levels of cathodic protection, the spread of the cathodic protection current and likelihood of corrosion than other inspection tools. This is particularly important in the case of cathodic protection systems for offshore structures, where the levels of cathodic protection at critical locations (e.g. nodes) can be accurately determined. The data provided by the Bathycorrometer® will enable the structure’s operator to ensure the structural integrity of the structure under investigation, satisfy the certifying authority that the structure has an adequate level of protection against corrosion and ensure the structure design life can be achieved.
The Bathycorrometer® can be used to check the performance of cathodic protection systems on a wide range of structures, from offshore platforms, buried pipelines, sub sea modules, ships and jetties. It is particularly useful for measurement of the structure to sea water potential in instances where it is not possible to make electrical contact with the structure under investigation using any other technique.
The Bathycorrometer® can be provided with K series electrodes for calibration purposes to check the accuracy of the internal electrode each time a dive is conducted and a set of potential readings are taken. This will assist in providing a high level of confidence in the results being obtained.
In brackish waters the Bathycorrometer® can be provided with a gelled silver/silver chloride/sea water electrode. This electrode will provide a known electrochemical potential that will not vary with chloride concentration in the water. Thus the inspection engineer has no need to adjust the potential readings obtained to compensate for variations in water salinity.
The Bathycorrometer® can be provided with a Surface Display Unit (SDU) as an optional extra . The measured structure to sea water potential is then transmitted from the Bathycorrometer® to the surface by a 4 to 20mA signal. The surface display unit then converts this signal to a direct voltage read out, for interpretation by a corrosion engineer on board the survey vessel.
It is important to note that divers using the Bathycorrometer® and working in the vicinity of impressed current cathodic protection systems must follow national and local guidelines for the safe use of electricity under water.
The Bathycorrometer® has gained international acceptance as a diver–operated inspection device, has a proven track record, and is used throughout the world.
Note: Bathycorrometer® is a registered trade mark and is manufactured by Buckleys (UVRAL) Ltd.
