The causes and forms of corrosion of diesel generator set wet cylinder liner

In general, high-power diesel generator sets use wet cylinder liner, that is, the circulating cooling water directly contact with the outer surface of the cylinder liner, so that when the engine runs for a period of time, the outer surface of the cylinder liner corrosion is serious, affecting the cooling effect, serious cylinder liner perforation, cooling water penetration into the cylinder, resulting in vicious accidents such as water strikes.

 

The cause of diesel generator set cylinder liner corrosion

 

At present, it is generally believed that the corrosion of the cylinder liner is mainly produced by the combined effect of electrochemical corrosion and mechanical.

 

1. Electrochemical corrosion of the cylinder liner

 

If the diesel generator set is used in a special environment such as mining, the cooling water used in the diesel generator set will be dissolved with carbon dioxide, oxygen, sometimes also contains sulfur dioxide and some minerals (such as magnesium, calcium, etc.), which forms an electrolyte solution. When the cylinder liner is in contact with the electrolyte solution, it will cause an electrochemical reaction. The iron hydroxide compound generated by the electrochemical reaction is a kind of loose texture and porous rust, which is the inherent cause of cylinder liner corrosion. When the diesel generator work, under the action of various mechanical loads, rust layer by layer peeling off, it will cause corrosion phenomena such as cavitation corrosion.

 

2. Mechanical action

 

By the professional staff by the scene disassembly and analysis can be seen, high speed and supercharged diesel generator set is more likely to produce cavitation corrosion. The whole process of cylinder liner cavity corrosion is: the beginning of the electrochemical effect of corrosion, and then because of the impact of the cylinder liner by the load, vibration, the corroded metal layer stripped off, revealing the new metal surface continues to be corroded, the process continues, the cylinder liner will produce a small cavity hole.

 

Diesel engine work, due to the swing angle of the connecting rod changes, the role of the side pressure on the cylinder liner is also constantly changing. When the piston is near the upper and lower stops, the side pressure changes direction, the piston impacts the cylinder liner, causing high frequency vibration of the cylinder liner, so that the cooling water on the outer wall of the cylinder liner attached layer (water film), producing local high pressure and high vacuum. In the case of high vacuum, the cooling water evaporates into vapor bubble, some of the vapor bubble by vibration squeezed into the cylinder wall microscopic holes, cracks, grooves (in the cylinder wall microscopic holes may also occur in the vapor bubble). When the vapor bubble by high pressure impact and rupture, the rupture area near the pressure shock wave (called "water strike", the instantaneous pressure can reach hundreds of atmospheres) constantly impact the outer wall of the cylinder liner, accelerating the electrochemical corrosion of the cylinder liner wall, while the corrosion layer flaking, the formation of cavitation corrosion.

 

The form of diesel generator set cylinder liner corrosion

 

From the above analysis of the reasons we can see that the corrosion of the cylinder liner damage from the metal surface, so the formation of the following different forms of corrosion.

 

1. uniform corrosion cylinder liner exterior corrosion, the formation of a layer of corrosion (rust), this corrosion on the mechanical strength of the metal does not affect. Diesel generator set overhaul, the cylinder liner will be pulled out, with a steel wire brush to remove slightly can continue to use.

 

2. local corrosion Most cases, corrosion are occurring in the upper and lower part of the cylinder liner, especially concentrated in the side of the larger pressure on both sides. The shape of this local corrosion has spot, point and ulcer shape.

 

3. Grain corrosion As the combination of grain and grain relaxation, corrosive media penetrate deep into the metal, the corrosion products generated in the metal between the grains. This is the most dangerous kind of corrosion, although the appearance of the metal has not changed significantly, but its mechanical properties have been significantly reduced, or even completely lost.