Following the rapid development trend of high-quality strip continuous rolling production and the development of electric welding and testing technology, the continuous improvement of welding quality, the types of 316L stainless steel industrial welded pipes are also increasing, and it has replaced stainless steel in many industries. Sew the tube. In the production process of welded pipes, the weld reinforcement can be said to be a very critical problem.
Excessive weld seam height of 316L stainless steel industrial welded pipe has many hidden dangers, as follows:
(1) Stress corrosion cracks are prone to occur at the weld toe
The key to the stress of the butt joint is formed by the welding height, and the in-situ stress at the weld toe of the butt joint is relatively large.
The dimensions of the stress index are the weld height h, the intersection angle θ at the weld toe and the corner semi-warp r. The increase of the welding height h increases the angle θ, and the decrease of the value will increase the stress index.
The greater the reinforcement of the weld, the more serious the stress level, but the compressive strength of butt welding will decrease. After welding, flatten the excess height, if it is higher than the butt weld, reduce the stress. Sometimes it can increase the compressive strength of butt welding. The external weld has a large residual height, which will endanger the tube shape after pressure expansion.
When the straight arc welded pipe is expanded under pressure, the seamless steel pipe is wrapped according to the left and right two-part outer molds with the same inner wall and no steel pipe expansion specifications. Therefore, if the reinforcement of the weld is too large, when the diameter is expanded, the shear stress assumed by the weld is prone to "small straight edges" on both sides of the large weld.
However, work experience has proved that when the external weld reinforcement is manipulated at 2mm or less, it is not easy to have "small straight edges" when the pressure is expanded. The pipe type is not easy to suffer damage. This is because the reinforcement of the outer weld is small, and the shear stress borne by the butt weld is also small. If this kind of shear stress is within the range of ductile deformation, after unloading, a resilience is formed, and the water pipe will return to normal.
(2) The internal weld seam has a large residual height, which increases the power and energy damage of transport materials.
If the outer surface of the arc welded pipe for transportation is not coated with anti-corrosion solution, the welding seam has a large residual height, and the frictional resistance to the transportation material is also large, which will increase the energy consumption of the transportation pipeline.
(3) The external welding thickness is large, which is unfavorable to prevent corrosion.
If the epoxy resin laminated glass cloth is used for anti-corrosion during work, the extra height of the outer weld seam will make it difficult to press firmly at the weld toe. In addition, the higher the welding seam and the more the anti-corrosion layer should be thickened, the thickness of the standard anti-corrosion layer is calculated based on the end of the weld seam, which increases the cost of anti-corrosion.
Compared with the internal scraper type internal weld removal equipment, Hangao Tech (SEKO Machinery)'s air-cooled internal weld flattening equipment has less scratches on the inner wall of the stainless steel pipe. Its working principle is to use the built-in mandrel to interact with the rolling die to perform repeated rolling 30 times/min on the inner weld seam, so that the weld seam and the base metal are more integrated and the stress is reduced.
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