The quality of raw materials is the key to ensuring the quality of stainless welded steel pipes. Therefore, all raw materials that enter the factory must be inspected before use, the quality certificate is accepted, the appearance, and the width and thickness are measured, especially for straight-drawn materials, except for inspection In addition to the width and thickness, the chemical composition and tensile test must be checked, and the production can be put into production after passing the test.
In the welding operation of stainless welded steel pipe manufacturers, the market faces three common problems: unqualified seams, incomplete penetration or burned through, cracks and pores. Let’s learn about the causes and solutions of these problems and master the correct welding technology. , So as to complete the welding task scientifically, safely and efficiently.
①The weld is unqualified. Unqualified welds are due to improper selection of welding process parameters or unskilled operation techniques, resulting in different weld heights and widths, poor weld formation, and concave back welds. The weld seam is weakened too much and the weld seam strength is not enough.
②Incomplete welding or burn through. Insufficient penetration is mainly due to the following reasons. One is too small current, the other is unskilled operation technology, the welding speed is too fast, and the butt gap is small, and the third is that the arc is too long or the arc is not aligned with the weld seam. When the metals are not fused together or part of the welded metal is not fused, the part should be repaired in time. The cause of burn-through is that the welding current is too high, the temperature of the molten pool is too high, the welding wire is not added in time, the strip butt gap is too large, the welding speed is too slow, etc., resulting in single or continuous perforation on the weld. The strength of the weld is weakened and burned through.
③Cracks and pores. The frequency of cracks is very high. Generally, cracks are divided into two types: hot cracks and cold cracks. As the liquid metal is solidified or slightly below the solidus temperature, thermal cracks with oxidation color will be formed on the fracture along the intergranular boundary. Phase change occurs in the solid state, or there is the existence of diffusible hydrogen, and under the action of excessive welding shrinkage stress during cooling, cold cracks with transcrystalline properties, shiny fractures and no oxidation color will be generated. If the welding wire is not up to the standard, the high temperature residence time during welding is too long, causing oxidation, overheating and excessive grain size growth, the material itself has more impurities, or the material itself is easy to harden. However, it is easy to have oil stains, oxide scales, rust on the surface of weldments and welding wires, or welding in a humid environment, or low subgas purity, or poor subgas shielding gas, and high temperature oxidation and splashing in the molten pool. Produce pores.