Mobile on-site repair equipment is used to laser-clad the lower ring steel plate with cobalt-based corrosion-resistant and wear-resistant materials. The total laser cladding area is 19.2 square meters, and the average coating thickness is 0.68mm. During the cladding process, two methods were used to measure the temperature field in the cladding area and nearby. The first method is to attach a temperature chip array near the cladding area to monitor the highest temperature at this location during the cladding process. The measurement range is 70~100°C. The second method is to use an infrared thermal imager, which can simultaneously measure the cladding area and nearby temperature fields in time and space, with a measurement range of -20~350°C.

Repair and strengthening of steel plates in the runner chamber

From February to March 2017, laser cladding repair and on-site construction strengthening were performed on the lower ring steel plate of the runner room of Unit 9 of Gezhouba Power Station, and good results and evaluation were achieved. During the long-term use of the unit, the lower ring steel plate has been thinned due to the combined effects of cavitation, abrasion, erosion, etc., and there are also serious erosion pits and local surface defects on the surface. The state before repair is shown in Figure 6. In the past, if severe cavitation occurred, the entire steel plate would be replaced with a new steel plate or repaired using traditional manual surfacing methods. The overall cost of replacing the new steel plate is high; the surface accuracy of manual surfacing is poor, the manual workload is large, and excessive heat input can easily cause the steel plate to deform and form a hollow drum. A severe hollow drum will change the gap between the runner body and the blades, and even cause damage during operation. blade.

Mobile on-site repair equipment is used to laser-clad the lower ring steel plate with cobalt-based corrosion-resistant and wear-resistant materials. The total laser cladding area is 19.2 square meters, and the average coating thickness is 0.68mm. During the cladding process, two methods were used to measure the temperature field in the cladding area and nearby. The first method is to attach a temperature chip array near the cladding area to monitor the highest temperature at this location during the cladding process. The measurement range is 70~100°C. The second method is to use an infrared thermal imager, which can simultaneously measure the cladding area and nearby temperature fields in time and space, with a measurement range of -20~350°C.

The temperature chip measurement results show that the steel plate temperature can reach a maximum of 100°C about 30mm outside the cladding area, and this temperature is only reached in the later stages of the cladding process. The thermal imager measurement results are basically consistent with this. As shown in the right picture of Figure 7, the infrared temperature measurement thermal imaging immediately after the laser cladding stops shows that the peak temperature is at the last position of the laser cladding, and the peak temperature does not exceed 120 degrees. This is mainly because laser cladding is a localized high-energy rapid prototyping, the overall heat input is small, and it is not easy to cause the overall temperature rise of large-area materials. During on-site operations, a dial indicator is used for deformation testing and three-dimensional laser scanning to measure the cladding size and deformation. The results show that there is no obvious thermal deformation, no hollowing phenomenon, and the thickness of the cladding layer is close to 1mm. The surface roughness of the cladded steel plate after polishing is 1.9~2.1μm, and there are no defects through PT flaw detection (see Figure 8).

In April 2018, Changdian (Maintenance Plant) organized experts to conduct an acceptance review of the laser coating project of the lower ring steel plate of Unit 9 and tested the coating after one year of power generation operation. All indicators met the requirements, and the laser cladding coating technology of the runner chamber steel plate is evaluated as a technology that can be promoted and applied.