Cathodic protection (CP) is an electrochemical system for corrosion protection that can be used with any metal object/structure that is underground or submerged in water. Cathodic protection is an active protection system, which differs from passive systems such as insulating coatings. By using active and passive protection systems at the same time, it is possible to obtain effective and economic protection of the structures and their operation without failures for long periods of time.
The principle of cathodic protection is to supply the structure to be protected with an electric current of sufficient density to produce the desired electrochemical effect. In case of low current availability, cathodic protection can be obtained with the aid of galvanic anodes. Furthermore, if the amount of electric current required to protect the structure is high (due to its size and/or the poor condition of the insulating coating), the best thing to do is to use the so-called impressed current system which exploits a power source in direct current (often a transformer-rectifier).
Cathodic protection is also used to solve the problem of stray currents, which can cause metal corrosion. One of the causes of stray currents is the presence of railways. Stray currents are particularly dangerous for pipelines because they can reach even pipes located at great distances, sometimes tens of kilometres, and where they arrive they are also capable of causing the walls to perforate in a short time. One way to protect infrastructure from stray currents is to install electrical drainage systems designed to divert stray currents away from the structure in a safe and controlled manner.
Since cathodic protection transformer-rectifiers and drainage devices are generally distributed over large surfaces and are often located in places that are difficult to access, it is almost always convenient to use telemetry systems to remotely control and monitor their operating parameters.
An application case
In this application, Inventia MT-652 modules, distributed and supported in Italy by ServiTecno, have been installed in cabinets containing transformers-rectifiers and drainage systems. The customer is the Polish gas distributor Gaz-System SA, which selected 126 sites to develop a telemetry system covering the activities of the Kraków, Pogórska Wola, Sandomierz, Jarosław and Jasło regional units. The selected installations mainly include transformer-rectifiers and various drainage devices.
Since the existing plants were built at different times and according to different standards, the installation of the telemetry modules required a specific method for each of the plants. In principle, the installation was done on a TS35 bar located on the right side of the cabinet. Along with the telemetry module, the following components have been installed on the bar located in the cabinets: telemetry module power system, measurement shunt and external relay, selected according to the rated current of the power source used for cathodic protection . Furthermore, magnetic reed switches have been fitted to signal the opening of the cabinet doors.
In order to ensure the possibility of measuring the IR-free potential, plates with a surface area of 10 cm2 were also installed at the drainage devices in order to be able to simulate failures. At these sites, the polarized drainage devices are not connected to the mains, so external batteries were used to power the telemetry modules. The low power operation of the MT-652 allows it to operate without maintenance for several months or even several years depending on how many measurements are made and how often the measurements are transmitted to the master system.
The telemetry modules installed allow remote reading of the operating parameters of the cathodic protection devices, such as output voltage and current and ON/OFF potential at the connection point of the drainage system. The devices also allow remote activation of the transformer-rectifier and time synchronization of the measurements. The synchronized measurement of the IR-free potential is also performed on the plates mounted on the drainage devices. The devices were fitted with customer-supplied SIM cards and plugged into the customer's TelWinSCADA telemetry system.
The MT-652 and MT-651 telemetry modules
Inventia has developed and introduced two new telemetry modules, the MT-652 and the MT-651, designed to monitor the parameters and control the cathodic protection systems of pipes, tanks and other metal structures underground or immersed in water. Based on many years of experience in telemetry and an in-depth knowledge of cathodic protection, the modules meet the needs of integrators and users of this type of installation.
Both modules are housed in a compact glass-fibre reinforced plastic case which guarantees IP65 protection. They can make measurements through two separate and independent sets of analog inputs. Each of these groups includes:
- two analog inputs configurable with a range of ± 10 V or ± 100 V and a measurement resolution of 1 mV
- an analog input with a range of ± 100 mV and a resolution of 1 μV
This means that each telemetry module offers up to 6 measuring channels, which allows, for example, the simultaneous monitoring of 2 cathodic protection rectifiers. In addition to the analog inputs described, the terminal has two digital inputs and two digital outputs that can be used to signal any status, such as the opening of the cabinet door. The purpose of the digital outputs is to perform typical tasks, i.e. measuring the IR-free potential of the texturer chip, manual off/on switching of any circuit, or synchronized control of the output at a predefined time.
Both the MT-652 and the MT-651 they come with an internal GPS receiver, which is an extremely important feature in this case. In addition to geolocation, the receiver is used for precise time synchronization, based on the sequential measurements taken, which are subsequently marked with an individual timestamp.
There are five signaling LEDs on the front panel of the module. These are used by the module to display the status of the GSM modem, the GPS receiver, and the status of the inputs and outputs. This information can be useful when checking the status of the device or troubleshooting its operation. The input and output connectors, to which signals from the field can be connected, are located on the front side of the MT-652 module. To facilitate the installation of the module in a cathodic protection test station, where the available mounting space is very limited, in the MT-651 instead the signal connectors have been arranged in the lower wall of the unit, with a connector 19-pole hermetic. At the top of the device are two SMA connectors, one for a GSM antenna and the other for a GPS antenna. In the MT-651 telemetry module, the GPS antenna is placed directly inside the housing.
These telemetry modules can be powered with an external voltage of 7–30 VDC. In addition, the MT-652 has an internal 2,6 Ah rechargeable Li-ion battery with a nominal voltage of 3,7 V, which ensures its uninterrupted operation in the event of a mains power failure. The MT-651's main power comes from an internal 17,4 Ah battery with a nominal voltage of 10,8 V. Therefore this unit is designed to operate autonomously in places where external power is not available.
All the new solutions offered by Inventia support two SIM cards as standard and the same is true for these two new modules. This ensures high reliability in packet data transmission with GPRS. When the primary SIM card has no coverage, the device will attempt to switch to a backup SIM to successfully establish a data connection.
Forms MT-652 and MT-651, like the entire family of telemetry devices offered by INVENTIA, are supported by the free MTManager configuration environment and the MTData Provider communication software. The software communicates with the devices and delivers data through a standard OPC interface. In the case of historical data, it is possible to save them in SQL relational databases using ODBC sources or directly save the received data as a CSV file. INVENTIA therefore offers designers, integrators and users a wide range of integration functions with supervisory systems.