Welded steel pipe slag is the slag that remains inside the weld. Theoretically, there are three main reasons for slag inclusion in submerged arc automatic welding seam: 1) There are many inclusions in the raw materials (including base metal, welding wire, and flux); 2) The interlayer cleaning is not clean during multi-layer welding; ③ The selected welding process parameters are inappropriate, which is not conducive to the emergence of slag.
According to the production characteristics of the straight seam submerged arc welded steel pipe, the cause of the slag inclusion in the weld seam due to the poor cleaning between layers during multi-layer welding can be ruled out. Because there are many inclusions in the raw materials and the slag inclusions in the welds, after taking measures such as inspection of the base metal before welding, replacement of welding wires and fluxes, etc., the proportion of slag inclusions in the weld fusion line is only slightly reduced, indicating that the inclusions in the raw materials It is not the main cause of slag inclusions.
Therefore, the main reason for the fusion line slag inclusion in the thick-walled straight seam submerged arc welded steel pipe is the improper selection of welding process parameters. The welding process parameters of the thick-walled straight seam submerged arc welded pipe mainly include line energy, welding current, welding voltage, welding speed, welding wire spacing, groove size, etc. An in-depth analysis from the welding metallurgy aspect shows that the main reason for the slag inclusion in the weld fusion line is that the temperature of the fusion line is too low so that the liquid slag has no time to precipitate, and the reason why the temperature of the fusion line is too low is that the peak temperature of the heating is too high. Low or cooling too fast.
The long-standing method of cutting
straight seam steel pipes is gas cutting. Gas cutting is to use the heat generated by the combustion of oxygen and acetylene to melt the cut metal at a high temperature to produce iron oxide slag and then uses high-pressure oxygen flow to blow the slag away from the metal. When the straight seam steel pipe is cut. Using gas cutting to cut straight seam steel pipes has high efficiency and is easy to operate. The incision section is relatively neat, but an oxide film will be attached to the incision surface. It needs to be removed before soldering. In the process of installing straight seam steel pipes, gas cutting is often used to cut various straight seam steel pipes, steel plates, and profiles with large diameters.
The gas-cutting tool for cutting straight seam steel pipe is the cutting torch. According to the different acetylene pressure, it is divided into two types: jet suction type and isobaric type. We commonly use the jet suction type torch. The oxygen used for gas cutting is supplied by an oxygen cylinder, and the acetylene gas is supplied by an acetylene gas cylinder or an acetylene generator. Due to the danger of gas cutting, it is necessary to strictly implement the operating procedures during operation. When cutting straight seam steel pipes by gas cutting, you should also pay attention to the following points:
1. No matter whether the straight seam steel pipe is rotated or fixed, the cutting nozzle should be kept perpendicular to the surface of the straight seam steel pipe. After cutting through, the cutting nozzle is gradually inclined forward and inclined to an angle of 70°-80° with the tangent of the cutting point.
2. Gas cutting usually starts from the lower part of the straight seam steel pipe when fixing the straight seam steel pipe.
3. The selection of the cutting nozzle and oxygen pressure is related to the thickness of the straight seam steel pipe, which can be selected according to the actual situation.
4. The distance between the cutting nozzle and the surface of the straight seam steel pipe should be determined according to the length of the preheating flame and the thickness of the straight seam steel pipe. Generally, the distance from the end of the flame core is 3--5mm.
5. After the straight seam steel pipe is cut, apply the iron oxide slag at the incision of the file or the hand-grinding wheel to make it smooth and clean. At the same time, the end face of the straight seam steel pipe should be kept perpendicular to the center line of the pipe.
6. At the end of the gas cutting, the cutting oxygen valve, and acetylene valve should be quickly closed to preheat the oxygen valve.
