Laser cladding of cobalt-based corrosion-resistant and wear-resistant alloy is used to repair and strengthen the runner’s body. After repair, there are no metallurgical defects such as cracks and holes. The cladding layer material and the matrix maintain good bonding strength without thermal deformation.

On-site repair and strengthening of the runner’s body

In March 2018, during the overhaul of the 3F Francis generator unit of the Three Gorges Hydropower Station, it was discovered that the edges and corners of the lower ring were mainly affected by cavitation during use, and serious defects appeared. Except for the edges of the blade roots, which were not seriously damaged, other edges and corners showed different shapes. There is a certain degree of zigzag damage, and severe cavitation pits appear in local locations. Most dimensions of the edges and corners are thinned by about 3mm, and bright edge cavitation also occurs on the inner edges of the edges and corners. In addition, there is an annular gap with a width of 1~2mm when the edge of the runner body is installed by thermal expansion. During long-term use, there is also severe cavitation in the area around the gap, especially on the lower side of the runner body, which has serious hidden dangers of accelerating the damage of the runner body and needs to be blocked, repaired and strengthened.

Laser cladding of cobalt-based corrosion-resistant and wear-resistant alloy is used to repair and strengthen the runner’s body. After repair, there are no metallurgical defects such as cracks and holes. The cladding layer material and the matrix maintain good bonding strength without thermal deformation. Figure 1 shows the state before laser cladding, and Figure 2 shows the appearance after the laser cladding process and grinding and modification. After expert review, the project passed acceptance.