Practical application of welding repair technology for casting plug valve

The boiler equipment of 3 × 350 MW supercritical unit in a power generation company is provided by Dongfang Boiler Works. The boiler is a spiral tube coil once through boiler with supercritical parameters and variable pressure operation, single furnace, one intermediate reheat, front and rear wall opposed combustion mode, balanced ventilation, tight sealing, solid slag discharge, all steel suspension structure Π type boiler.

High temperature reheater block valve d2500.11l. The valve body is made of ASME sa217c12a with a maximum thickness of 900 mm, which belongs to martensite heat-resistant cast steel. The steel is a cast steel developed on the basis of 9Cr1MoV, and its corresponding forging grade is ASME sa82f91.

During the overhaul of unit 2 in 2019, the magnetic particle inspection was carried out on the left block valve at the outlet of boiler reheater. It was found that there were cracks with different lengths on the outer surface of the block valve, and the length of the magnetic mark was between 3 mm and 10 mm. The typical defect morphology is shown in Figure 3, and the depth of the crack was 24 mm after being removed.

The steel has high oxidation resistance, high temperature steam corrosion resistance, good impact toughness, high and stable permanent plasticity and thermal strength, excellent thermal conductivity and small coefficient of linear expansion. The steel has no hot crack and hot crack, but has certain cold crack sensitivity.

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