Welding Technology Requirements For Different Welded Steel Pipes

Welded steel pipes mainly include electric resistance welded pipes and submerged arc welded pipes. When the strength of the welding rod is determined, it is determined by the complexity of the specific shape of the welded structure, the thickness of the steel, and the load of the weldment. Static load or dynamic load) and the crack resistance of steel and the difficulty of obtaining DC power supply. Generally speaking, the requirements for plasticity, impact toughness and crack resistance are high. For the welds working under low temperature conditions, basic welding rods should be used; when limited by certain conditions, the rust at the groove of low carbon steel weldments cannot be cleaned. . For dirt such as oil stains and scales, acid rods with low sensitivity to rust, oil stains and scales and strong anti-porosity properties should be used.

Welding of dissimilar steel of welded steel pipes, such as low carbon steel and low alloy steel, and low alloy steel of different strength grades, generally use welding rods matched with steel of lower strength grade.
(2) Working conditions and performance of the weldment. Pearlitic heat-resistant steel is generally selected from electrodes with similar chemical composition to the steel, or according to the operating temperature of the weldment.
(3) Simplify the process, increase productivity and reduce costs.

Selection method of welding parameters of welded steel pipe The welding parameters of arc welding mainly include electrode diameter, welding current, arc voltage, number of welding layers, power supply type and polarity.
(1) Selection of electrode diameter. The choice of electrode diameter depends on factors such as weldment thickness, joint type, weld location and weld level. In order to improve labor productivity without prejudice to the quality of welding, it is generally preferred to select large diameter electrodes.
(2) Selection of welding current of welded steel pipe. It is mainly determined by factors such as the type of welding rod, the diameter of the welding rod, the thickness of the weldment, the joint type, the weld space position and the welding level. The most important factors are the diameter of the welding rod and the position of the weld space.
(3) Selection of arc voltage. The arc voltage is determined by the length of the arc. When the arc is long, the arc voltage is high; when the arc is short, the arc voltage is low.
(4) Selection of the number of welded steel pipes. Multi-layer welding is often used in arc welding of medium and heavy plate electrodes.
(5) Selection of power source type and polarity. DC power supply, stable arc, small splash, good welding quality, generally used in the welding of important welded structures or thick plates with large stiffness structure. In other cases, the AC welder should be considered first.

In general, the welding of alkaline electrodes or sheets is performed by DC reverse connection, while the acid electrodes are usually connected.
(1) When the carbon arc planer is working, only the AC and DC arc welders are needed, and no air compressor is needed.
(2) Submerged arc welding materials
1. Welded steel pipe welding wire According to the different welding metal materials, the welding wire for submerged arc welding has carbon structural steel welding wire and alloy structural steel welding wire. High alloy steel welding wire, various non-ferrous metal welding wire and surfacing welding wire. In addition to the stainless steel welding wire and the non-ferrous metal welding wire, the surface of the welding wire is plated with copper to facilitate rust prevention and improve electrical conductivity.
When a wire of a smaller diameter is used for the same current, an effect of increasing the penetration depth of the weld and reducing the melt width can be obtained. When the workpiece is poorly assembled, a thicker wire should be used.

2. Longitudinally Submerged Arc Welding Pipe flux Submerged arc welding flux is divided into steel flux and non-ferrous metal flux according to the application, and is divided into smelting flux, sintering flux and ceramic flux according to the manufacturing method.
(1) The flux should meet the following basic requirements:
l) has good metallurgical properties.
2) Has good process

(2) Classification of flux. Submerged arc welding flux is classified into steel flux and flux for non-ferrous metals according to its use, and is usually classified according to manufacturing methods, chemical composition, chemical properties and particle structure.
l) According to the manufacturing method, it is divided into: smelting flux, sintering flux and ceramic flux.
2) According to chemical composition: alkaline flux, acid flux and neutral flux.

(3) Selection of welded steel pipe flux and welding wire.
Low carbon steel can be welded with high manganese and high silicon type flux, with H08MnA welding wire, or low manganese and manganese free flux with H08MnA and H10MnZ welding wire. Low-alloy high-strength steels can be welded with medium-manganese or low-manganese silicon-type fluxes to match the strength of the steel.

Welding of heat-resistant steel, low-temperature steel and corrosion-resistant steel for welded steel pipes may be carried out with medium-silicon or low-silicon fluxes in combination with corresponding alloy steel welding wires. For high-alloy steels such as ferrite and austenite, smelting fluxes with high alkalinity or sintered and ceramic fluxes are generally used to reduce the burning of alloying elements and to add more alloying elements.