Slag inclusion in welded steel pipes is the slag remaining inside the weld. From theoretical analysis, the main reasons for slag inclusion in submerged arc automatic welding are as follows: ①There are many inclusions in the raw materials (including base metal, welding wire, and flux); ②The cleaning between layers is not clean during multi-layer welding; ③Improper welding process parameters are selected, which is not conducive to the emergence of slag.
According to the production characteristics of LSAW steel pipes, it can be ruled out that slag inclusions in the weld due to poor cleaning between layers during multilayer welding can be eliminated.
Since there are many inclusions in the raw materials that cause slag inclusion in the weld, after taking a pre-weld inspection of the base material, replacing the welding wire and flux, the proportion of slag inclusions in the weld fusion line is only slightly reduced, indicating the inclusions in the raw material Objects are not the main cause of slag inclusion.
Therefore, the main reason for slag inclusion in the fusion line of thick-walled LSAW steel pipe is improper welding process parameters. The welding process parameters of thick-wall LSAW pipes mainly include heat input, welding current, welding voltage, welding speed, welding wire spacing, groove size, etc.
From the perspective of welding metallurgy, we can see that the main cause of slag inclusion in the weld fusion line is that the temperature of the fusion line is too low, which makes the liquid slag too late to precipitate; the reason for the too low temperature of the fusion line is that the peak temperature of heating is too low. Low or too fast cooling rate.
The well-known method of cutting straight seam steel pipes is gas cutting. Gas cutting uses the heat generated by the combustion of oxygen and acetylene to melt the cut metal at high temperature to produce iron oxide slag, and then blow the slag away from the metal with a high-pressure oxygen stream When the straight seam steel pipe is cut.
Cutting the straight seam steel pipe with gas cutting is efficient and easy to operate. The cut section is also relatively neat, but an oxide film will adhere to the surface of the cut. Need to be removed before welding. In the installation of straight seam steel pipes, gas cutting methods are commonly used to cut various straight seam steel pipes, steel plates, and profiles with larger pipe diameters.
The gas cutting tool for cutting straight seam steel pipes is a cutting torch. According to the difference of acetylene pressure, it is divided into two types: jet suction type and equal pressure type. Oxygen for gas cutting is supplied by an oxygen cylinder, and the acetylene gas is supplied by an acetylene cylinder or an acetylene generator.