How to prevent weld shrinkage when welding white steel pipes

How to prevent weld shrinkage when welding white steel pipes? Methods and steps for welding white steel pipes to prevent weld shrinkage: Use the short-cut welding method, which means welding a small section each time and stopping for a period of time. The general standard is: weld every 3-5 cm, stop (rest, do not continue welding) for 5-10 minutes. Repeat this! Note: When welding white steel pipes, it is best to use "stainless steel" electrodes and pay attention to the output current of the welding machine. It is best to heat the white steel pipe in advance before welding.
Methods to reduce internal stress
1. Hammering and Forging – Mechanical Method
When welding long cracks and surfacing layers, it is necessary to weld from one end to the other. During welding, the welding seam and surfacing layer are in a hot state, which can reduce the shrinkage of the welding seam and reduce the internal stress. When hammering, the temperature of the welding repair metal increases. The effect is better at 800℃. If the temperature drops, the hammering force will also decrease. If the temperature is too low, hammering is not allowed at around 300℃ to avoid cracks. The principle of the forging method is basically the same as the above, but the difference is that the weldment is hammered Must be heated before use.
2. Slow cooling and preheating - thermal method
This method is to place the workpiece to be welded in the furnace before welding repair and heat it to a certain temperature to prevent the heated workpiece from cooling rapidly during welding. The purpose of this treatment is to reduce the temperature of the welded repair part and the temperature of the base metal The difference between the two parts, thereby reducing the internal stress. The slow cooling method is to heat the welded workpiece to 600°C and put it into an annealing furnace for slow cooling.
3. "Destroy first and then establish" method
When welding with ordinary carbon steel electrodes, cracks are easy to occur. Here is a method for welding carbon steel electrodes: use a small current to cut along the weld, only grooving but not cutting through, and weld while it is hot, because local stress is removed during cutting. Therefore, no cracks will occur and the welding effect is good.
Methods to reduce and prevent deformation during welding repairs
1. Preheating method
Preheating the welded parts before welding can not only reduce internal stress, but also is a good way to reduce deformation.
2. Pre-added anti-deformation method
According to the properties of the metal to be welded, the direction of shrinkage deformation after welding repair is estimated, and the workpiece is pre-deformed by mechanical means before welding repair, so that the deformation after welding repair just offsets the pre-deformation.
3.Water cooling method
Use cold water to spray the weldment to reduce the temperature of the base metal and prevent deformation. Place the weldment into the cold water tank to expose the repaired parts, so that the temperature of the base metal will not rise and the weldment will not deform.
4. Clamping method
Use rigid clamps to fasten the weldment to prevent deformation of the weldment. However, this method will leave internal stress in the weldment, so it is mainly used for welding low carbon steel sheets with good plasticity.
5. Reasonable selection of welding specifications
Before welding, the reasonable selection of welding specifications has a great impact on reducing the deformation of the weldment. For example, as the current intensity increases, the deformation of the weldment also increases accordingly. The welding sequence of the welds is of great significance in reducing the deformation of the weldment, which is important for the structure. Welds, the welds between two connecting parts should be welded last. For cylindrical plate structures, the longitudinal (axial) welds should be welded first, and then the circumferential welds. Otherwise, the center of the structure will be deformed, deformed, or even cracked. If the weldment is composed of steel plates, first tailor-weld the transverse welds of the steel plates, use segmented welding, and weld in the opposite direction to the general direction of welding.