Corrosion mechanism and protection technology of fishplates
- What are the common types of corrosion of fishplates?
The main types include electrochemical corrosion, chemical corrosion, and abrasion corrosion. Electrochemical corrosion occurs in humid environments, where micro - batteries form on the surface of fishplates, and iron elements lose electrons to form rust, with a corrosion rate of 0.1 - 0.3mm/year. Chemical corrosion is caused by media such as acid rain and salt fog. For example, salt fog in coastal areas reacts chemically with iron in fishplates to form ferric chloride corrosion products. Abrasion corrosion is due to the friction between fishplates, rails, and bolts when trains pass, causing surface damage and accelerating the corrosion process. These three types often interact, aggravating the damage to fishplates.
- How does the corrosion rate of fishplates vary in different environments?
In dry inland environments, the corrosion rate is about 0.05mm/year. In humid coastal areas, due to high salt content and humidity, the corrosion rate reaches 0.2 - 0.4mm/year. In industrial - polluted areas, the corrosion rate can be as high as 0.5mm/year due to the presence of acidic gases (such as SO₂). In urban rail transit tunnels, the humidity remains above 80% for a long time, and stray currents accelerate the electrochemical corrosion of fishplates, making the corrosion rate 30% faster than that of surface lines. Through environmental monitoring and corrosion rate assessment, targeted protection schemes can be formulated.
- How does the coating protection technology improve the corrosion resistance of fishplates?
Multilayer composite coatings are used. The bottom layer is a zinc - rich primer with a zinc content of ≥90%, which protects the substrate by preferentially corroding the zinc layer based on the sacrificial anode protection principle. The middle layer is an epoxy micaceous iron intermediate paint, enhancing the coating thickness and shielding properties. The top layer is a polyurethane topcoat, providing wear resistance and UV resistance. The total coating thickness is controlled at 200 - 250μm, and the salt - fog resistance test time exceeds 1500 hours. Compared with uncoated fishplates, the corrosion rate is reduced by 80%. In the application of the Sichuan - Tibet Railway, coated fishplates remained in good condition after 5 years of service.
- What is the application principle of cathodic protection in the anti - corrosion of fishplates?
It is divided into the sacrificial anode method and the impressed current method. In the sacrificial anode method, a zinc - alloy anode block is installed near the fishplate, and a galvanic cell is formed through wire connection. The anode block is preferentially corroded to protect the fishplate, and the anode block needs to be replaced regularly (with a lifespan of 2 - 3 years). The impressed current method applies a cathodic current to the fishplate through an external power source, making its potential lower than the corrosion potential and inhibiting corrosion. This method is suitable for important areas such as large railway hubs. Both methods can reduce the corrosion current density of fishplates by more than 90%, significantly extending their service life.
- How to evaluate the anti - corrosion effect of fishplates?
The evaluation is carried out through visual inspection, coating thickness detection, and electrochemical testing. Visual inspection observes the surface for rust spots and coating peeling, recording the corrosion area and degree. A magnetic thickness gauge is used to measure the coating thickness to ensure that each layer meets the standard. Electrochemical testing uses electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) methods to analyze the coating resistance and corrosion current density and evaluate the anti - corrosion performance. A railway maintenance department conducts evaluations every six months, promptly detecting and handling fishplates with ineffective anti - corrosion, reducing track safety hazards.