Installation of the Cathodic Protection
In order to avoid corrosion of the underground pipelines, for the sake of their protection, it is necessary to use cathodic protection stations (CPS) along the entire length of a pipeline. CPS has a constant direct current (DC) (protective installation), anodic grounding, control-measurement station, as well as cable and wires.
Protective installation can be connected to the alternating current (AC) 0.4, 6 or 10 kV, depending on the certain conditions (pic. 2.5).
Pic. 2.5. Typical constructive performance of the cathodic protection station (CPS).
1 – the 10 kV overhead line,
2 – step-down transformer,
3 – transducer,
4 – control-measurement station,
5 – cable-cathodic line,
6 – air-anodic line,
7 – anodic grounding,
8 – pipeline.
If the protection of multiline pipelines located in the same “corridor” is necessary, several installations and anodic groundings are mounted at the CPS.
It is possible to save a couple of pipe threads using only one installation when constructing protection circuit. However, it is necessary to keep in mind that during the break in system operation caused by the difference in natural potentials which are connected by the deaf pipe bulkhead, strong galvanic vapors cab may form, which in turn may lead to intense corrosion. Therefore, it is important to connect pipes using special blocks of joint protection. These blocks can help not only separate pipes but also install optimal potential for each pipe.
Uninterruptible power source for installation of cathodic protection is provided by the transducers connected to the 220 V power frequency. Transducer output voltage is adjusted manually by switching taps of the transformer winding. There is also automatic method of adjustment through faucet control (thyristors).
For the current rectification, bridge circuits with the midpoint of the secondary winding of the transformer are used. Such circuits have Efficiency from 60 percent to 75 percent and residual ripple of the rectified current to 48% at a frequency of 100 Hz.
In the systems of electrochemical protection, transducers with manual adjustment of the outflowing voltage are used. In such a scheme, resistance in the current circuit and required protective current stay unchanged for a long period of time.
As the environmental conditions where the installation systems of cathodic protection operate, constantly change (stray currents, change of soil resistivity and other factors), it is better to use transducers with automatic adjustment mode of the output voltage.
Such adjustment works by changing the capacity of facilities that are protected or by the current protection (galvanostats transducers).