The corrosion reaction is unavoidable during the use of stainless steel pipes, so how to alleviate the corrosion is a key aspect of maintenance process. The following article describes the methods of avoiding or alleviating corrosion of stainless steel pipes.
Because stainless steel pipes are usually corroded in the circuit, corrosion prevention needs to be started from the angle of interference circuit.
The first is cathodic protection, which is a good way to prevent corrosion of stainless steel pipes. It uses the external current from the fixed anode to interfere with the circuit in the corroded battery. For most forms of external stainless steel pipe corrosion is 100% effective.
Galvanic CP connects high-energy metals (such as zinc or magnesium) to pipes (anodes). Zinc or magnesium is used as a sacrificial anode to protect the pipe. The sacrificial anode acts as a current anode and applies voltages up to -1.4 to -2.1V. If the reverse current applied from the sacrificial anode is more negative than -0.85V, the corrosion in the stainless steel will stop. If the reverse applied current is between -0.8V and -1.00V, the corrosion of aluminum will stop. If the current exceeds -1.00V, an alkaline solution will be formed on the aluminum and corrode the metal. In some cases, conversion to -0.003 V is enough.
Using a DC rectifier to drive the current to a suitable stable anode such as carbon, plating platinum titanium or magnetite in an applied current system, a proper CP level can also be reached. One end of the rectifier is connected to the pipe, and the other end is connected to the bed of the piezoelectric current anode or anode. Then the rectifier current rises until the line voltage reading of the copper sulphate half cell is less than -0.85V. We must pay attention to not too high, otherwise the coating will be stripped.
The second is electrical connection, which is used to prevent the corrosion of AC and DC current. This is a simple application of the illegal current source between the conduit and the grounding system. The bonding line provides a safe way to return to other utilities’ grounding systems, not from the surface of pipes. It also provides a security element to protect workers from fatal shocks that may occur on insulated pipes near high voltage wires, trams and trolley systems. The electrical connection can also be achieved by the free use of the electrified anode, which places the pipeline at the same voltage as the illegal application. Care must be taken to ensure that all pipe flanges are in electrical contact. If they are not in contact with each other, the installation of jumpers from the bottom up ensures that the entire pipeline is protected.
The third is the coating. The coating can be used to stop or reduce the corrosion of inner diameter (ID) and outer diameter (OD). In order to select the appropriate coating system, engineers need to consider the design, environment, content, pressure, external impact, design life and cost of the piping. Traditional external coatings such as mastic, as well as many new epoxy resins and polymers have been proven to be successful inhibitors. The internal coating can be used for corrosion control of contents, traction and friction reduction of cables, and erosion (impact) corrosion control.
Source: China Stainless Steel Pipelines Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)