Slag inclusion in welded steel pipes is the molten slag remaining inside the weld. From a theoretical analysis, the main reasons for slag inclusions in submerged arc automatic welding welds are the following three points: ① There are many inclusions in the raw materials (including base metal, welding wire, and flux); ② The inter-layer cleaning is not clean during multi-layer welding; ③The selected welding process parameters are inappropriate, which is not conducive to the emergence of slag.
According to the production characteristics of straight seam submerged arc welded steel pipes, it can be ruled out that the reason for slag inclusions in the welding seam caused by incomplete cleaning between layers during multi-layer welding can be ruled out.
Given the large number of inclusions in the raw materials causing slag inclusions in the welds, after taking measures such as inspecting the base metal before welding and replacing the welding wire and flux, the proportion of slag inclusions in the weld fusion line was only slightly reduced, indicating that the inclusions in the raw materials Materials are not the main cause of slag inclusions. Therefore, the main reason for fusion line slag inclusion in thick-walled straight seam submerged arc welded steel pipes is improper welding process parameters. The welding process parameters of thick-walled straight seam submerged arc welded pipes mainly include line energy, welding current, welding voltage, welding speed, welding wire spacing, groove size, etc.
An in-depth analysis from the aspect of welding metallurgy shows that the main reason for slag inclusion in the weld fusion line is that the temperature of the fusion line is too low, which prevents the liquid slag from precipitating; and the reason for the too-low temperature of the fusion line is that the peak temperature of the heating is too high. Low or too fast cooling rate. The most common method for cutting straight seam steel pipes is gas cutting. Gas cutting uses the heat generated by the combustion of oxygen and acetylene to melt the metal being cut at high temperatures to produce iron oxide slag, and then uses high-pressure oxygen airflow to blow the slag away from the metal. When the straight seam steel pipe is cut off.
Using gas cutting to cut straight seam steel pipes is highly efficient, and easy to operate, and the cut section is relatively neat, but a layer of oxide film will be attached to the cut surface. Needs to be removed before welding. During the installation process of straight seam steel pipes, gas cutting is commonly used to cut various straight seam steel pipes, steel plates, and profiles with larger diameters. The gas cutting tool for cutting straight seam steel pipes is a cutting torch, which is divided into two types: jet-suction type and isobaric type according to the difference in acetylene pressure. The jet-suction type cutting torch we commonly use is the jet-suction type. Oxygen for gas cutting is supplied by oxygen bottles, and acetylene gas is supplied by acetylene gas bottles or acetylene generators.
Due to the dangers of gas cutting, the operating procedures must be strictly followed during operation. When cutting straight seam steel pipes with gas cutting, you should also pay attention to the following points:
1. Whether the straight seam steel pipe is rotating or fixed, the cutting nozzle should remain perpendicular to the surface of the straight seam steel pipe. After cutting through, gradually tilt the cutting nozzle forward to an angle of 70°-80° with the tangent to the cutting point.
2. When gas cutting and fixing the straight seam steel pipe, generally start from the lower part of 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 and 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 between the end of the flame center and the end of the flame center is 3-5mm.
5. After the straight seam steel pipe is cut, use a file or hand grinding wheel to clean the iron oxide slag at the cut to make it smooth and clean. At the same time, the end face of the straight seam steel pipe mouth should be kept perpendicular to the center line of the pipe.
6. After gas cutting, the cutting oxygen valve and acetylene valve should be quickly closed and the preheated oxygen valve should be closed.
Post time: Jan-12-2024