Welding preparation
(1) in order to prevent the hardened layer and carburized layer produced in the repair welding groove during the crack excavation process, the mechanical method is used instead of the faster carbon arc air gouging method. According to the depth of crack excavation, the groove is repaired to U-shape as shown in Figure 2. The groove depth h and the groove width l depend on the shape of the defect itself, the groove bottom angle radius R ≥ 5 mm, the groove angle α ≥ 10 ° to avoid the formation of dead angle in the welding process.
(2) penetrant inspection or magnetic particle inspection shall be carried out on the surface of groove and the base metal within 50m around it, and there shall be no crack and other defects.
(3) after passing the magnetic particle inspection or penetrant inspection, clean the groove and the area within 50 mm on both sides with absolute alcohol or acetone to thoroughly remove the surface dirt.
(4) the practice shows that the welding rod enicrfe-3 is a kind of welding rod with good plasticity and crack resistance, so the welding rod enicrfe-3 is selected for repair welding.
(5) enicrfe-3 belongs to alkaline electrode. According to the requirements of DL / t869-2012, nickel based electrode is put into the electrode drying oven in advance to dry the electrode at 350 ℃. The electrode is put into the electrode insulation bucket on site to keep the electrode warm when it is electrified. It can be taken at any time when it is used.
Welding requirements
(1) the welder who has obtained the corresponding welding qualification certificate should be familiar with the construction site and equipment, and fully understand the construction content and process requirements.
(2) preheat before welding. In order to prevent the temperature difference between the base metal and the weld from being too large and the cooling rate from being too fast, the hardening structure and welding cracks are produced. Before welding, the oxygen acetylene flame is used to preheat the welding area within 100 mm, and the preheat temperature is (100 ~ 150) ℃.
(3) welding layer. After preheating, the welding can be carried out. The diameter of welding rod is 2.5 mm, the welding current is 80-90 a, the direct current is reversed, and the straight-line welding rod is used for welding. Welding along the length direction, the length of one welding is less than 100 mm, the two sides are welded first and then the middle is welded, and the thickness of welding layer is controlled at about 2 mm.
(4) welding of filler layer. The electrode with diameter of 2.5 mm is still used for the second and third layers, and the electrode with diameter of 3.2 mm is used for the third layer and above. The welding current is 105-115 a, and the straight-line welding is still used. The next welding layer is staggered with the previous welding layer at 90 degrees, and the thickness of each welding layer is controlled at 2-2.5 mm. Weld both sides first and then the middle. When welding on both sides, the arc should be inclined to the base metal as far as possible to ensure good fusion with the base metal. The temperature of valve body shall be controlled as far as possible during welding, and shall not be higher than 100 ℃. After welding the second layer, hammer with air pick, the diameter of hammer is 10 mm, the weight is about 200 g, and the pressure of air pick is 0.35 MPa. Hammering starts from the middle of the weld and gradually hammers to both sides until there are dense pits on the weld surface. Hammering should avoid the fusion line to prevent weld cracking. No hammering is allowed for the welds of primer and cover.
(5) weld interlayer inspection. After each layer of weld is welded and hammered, the welding slag shall be cleaned, and the weld shall be inspected with 10 times magnifying glass. If cracks, lack of fusion and other defects are found, they shall be ground off and re welded.
(6) welding of cover layer. The welding seam of cover layer shall be fully filled with a certain amount of grinding. There shall be no crack, undercut, surface non fusion, slag inclusion and other welding defects in the cover welding.
(7) after welding, wrap asbestos cloth and other insulation materials, and slowly cool to room temperature.
Post weld inspection
After the repair welding, the surface of the workpiece is modified by mechanical method to restore its original shape. After 24 hours of welding, all repair welding areas were tested by Pt, and no cracks, no fusion and other defects were found in repair welding area, fusion line and heat affected zone. In order to prevent the occurrence of new defects, the repair area shall be rechecked regularly in combination with unit maintenance.