Electrical potential surveys are often required on cathodically protected structures such as underground pipelines. However, proving that a cathodic protection system is providing the degree of corrosion protection expected can often be a time-consuming and error prone endeavor. It is usual to interrupt the CP source to carry out these surveys, the accuracy of which is affected by several factors, including the presence and design of DC decouplers.
In many applications, the capacitance of traditional DC decouplers used on pipelines can cause instant-OFF pipe potentials to be more electro-negative when compared to potentials measured on the same system without decouplers installed. Methods to obtain accurate polarized potentials in these scenarios exist. But for each method, there is some level of risk introduced to the pipeline and operating personnel and/or significant cost impact.
This paper explains this capacitance effect in detail as well as the traditional solutions and their associated risks. A new technology is introduced that allows for efficient, accurate instant-off measurements while providing the same safety and isolation performance provided by traditional DC decouplers. Field data will be presented to represent the performance of the new technology and compare it to that of traditional decouplers.