The weld uses the high temperature of the welding heat source to melt the welding rod and the steel pipe at the joint to form a seam. After the welded steel pipe cools, the two welds are connected into a whole. According to the shape of the welded steel pipe and the relative position of the welds, it is divided into butt welds, fillet welds, plug welds, and electric riveting. Butt welds are often used for splicing plates and steel sections; fillet welds are often used for lap joints; plug welds and electric riveting are rarely used and are only considered to reduce the lap length of welds.
In order to prevent the workpiece from being deformed due to thermal expansion during welding, the spacing of the positioning steel pipe welds must be guaranteed, which can be selected according to the table below. The positioning steel pipe weld will be part of the weld in the future and must be welded firmly without defects. If the steel pipe weld requires single-sided welding and double-sided forming, the positioning steel pipe weld must be welded through. The weld of the positioning steel pipe must be welded according to the formal welding process requirements. If the formal steel pipe weld requires preheating and slow cooling, it must also be preheated before positioning welding and slowed after welding; the positioning steel pipe weld should not be too high to avoid welding to the positioning steel pipe weld. If this happens, it is best to grind the positioning steel pipe weld lower and grind the two ends into a slope to facilitate welding. If cracks, pores, and other defects are found on the positioning steel pipe weld, the section of the positioning steel pipe weld should be ground off and re-welded. Remelting is not allowed.
First, according to different welding processes, steel pipe welds can also have many forms:
1. According to the different combinations of steel pipe welds, they can be divided into five types: butt welds, fillet welds, plug welds, groove welds, and end welds.
(1) Butt weld: a weld welded between the groove surfaces of the weldment or between the groove surface of one part and the surface of another part.
(2) Fillet weld: A steel pipe weld welded along the intersection of two perpendicular or nearly perpendicular parts.
(3) End weld: A steel pipe weld formed by an end joint.
(4) Plug weld: A steel pipe weld formed by welding two plates in a circular hole when two parts overlap, one of which has a circular hole. A fillet weld only welded in the hole is not a plug weld.
(5) Slot weld: A steel pipe weld formed by welding two plates in a long hole when two plates overlap, one of which has a long hole. A fillet weld-only weld is not a slot weld.
Butt weld: According to the degree to which the weld fills the steel pipe, it is divided into a fully penetrated butt weld and an incompletely penetrated butt weld. An incompletely penetrated butt weld is subjected to very little force and has severe stress concentration. A fully penetrated butt weld is referred to as a butt weld. In order to facilitate construction, ensure construction quality, and ensure that the butt weld fills the gap of the parent material, different groove forms are adopted according to the thickness of the steel plate. When the gap is too large (3-6mm), a pad (arc starter plate) can be set under the V-shaped seam, single-sided V-shaped seam, and I-shaped seam to prevent the molten steel pipe from flowing and make the root weld through. In order to ensure the quality of welding, prevent the grooves at both ends of the steel pipe weld, and reduce the influence of stress concentration on the dynamic load, after the steel pipe weld is formed, unless it does not affect its use, the two ends can be left on the weldment, otherwise, they should be cut off after welding.
Fillet weld: The edge of the connecting plate does not need to be finely processed, the plate has no gap, and the welded steel pipe is directly filled in the right angle or oblique angle area formed by the two weldments.
2. According to the different spatial positions of the weld: it can be divided into four forms: flat weld, vertical weld, horizontal weld, and overhead weld.
3. According to the different intermittent conditions of the steel pipe weld, it can be divided into two forms: continuous weld and intermittent weld. Intermittent welds are divided into two types: staggered and parallel. In addition to the weld leg K, the weld size should also indicate the length L and spacing e of each section of the intermittent weld, and the symbol “Z” is used to indicate the staggered weld.
4. According to the different functions of the steel pipe weld, it is divided into load-bearing welds used to bear loads, connecting welds that do not directly bear loads but only play a connecting role, sealing welds mainly used to prevent fluid leakage and short-length positioning welds welded for assembly and fixing the position of the joint on the weldment before formal welding.
Second, there are several methods for flaw detection of steel pipe welding.
1. Radiographic flaw detection: Radiographic flaw detection is a method of detecting internal defects of welded joints by irradiating them with rays. Radiographic flaw detection can clearly show the internal conditions of welded joints, so it is widely used in the detection of various welded structures. In actual operation, radiographic flaw detection has high sensitivity and reliability, but it also has some disadvantages, such as expensive equipment and complex operation.
2. Ultrasonic flaw detection: Ultrasonic flaw detection is a method of detecting internal defects of welded joints by using the characteristics of ultrasonic waves propagating in solid media. Ultrasonic flaw detection can accurately locate and quantify defects, and has high sensitivity and reliability. In actual operation, ultrasonic flaw detection is widely used in welding inspection of various steel pipes, such as pipelines, pressure vessels, etc.
3. Magnetic particle flaw detection: Magnetic particle flaw detection is a method of detecting surface and near-surface defects by the property of magnetic powder adsorption on the surface of welded joints. Magnetic particle flaw detection can accurately detect surface cracks, pores and other defects of welded joints, and has high sensitivity and reliability. In actual operation, magnetic particle flaw detection is widely used in welding inspection of various steel pipes, such as steel structures, ships, etc.
4. Eddy current flaw detection: Eddy current flaw detection is a method of detecting internal defects by using the magnetic field changes generated by eddy currents in welded joints. Eddy current flaw detection has high sensitivity and reliability, and can accurately detect internal defects of welded joints. In actual operation, eddy current flaw detection is widely used in welding inspection of various steel pipes, such as stainless steel pipes, copper pipes, etc.
5. Liquid penetrant flaw detection: Liquid penetrant flaw detection is a method of detecting surface defects by the property of liquid penetrant penetrating on the surface of welded joints. Liquid penetrant testing can accurately detect surface cracks, pores, and other defects of welded joints with high sensitivity and reliability. In actual operation, liquid penetrant testing is widely used in welding inspection of various steel pipes, such as castings, pressure vessels, etc.
Post time: Apr-27-2025