High-frequency Welded Steel Pipe Production Process and Weld Defects

Henary Lee
 


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High-frequency welding steel strip is being fed into the machine, into a cylindrical tube by an induction coil contact welding angle, the induction coil near the magnetic field or current is induced by the edge of the strip, the strip edge due to the resistance caused by the resistance itself heat is heated, extruded strip edge heating roll extruded weld. High-frequency welding metal is not added, it is actually a forge welding.

The so-called high-frequency, relative to the alternating current of 50Hz frequency terms, generally refers to a high-frequency current of 50KHz ~ 400KHz. High-frequency current through the metal conductor, will have two peculiar effects: skin effect and proximity effect, high-frequency welding is the use of these two effects to pipe welding.

Frequency welded pipe production process depends mainly on the variety of products, from raw materials to finished products need to go through a series of processes, these processes need to complete the appropriate kinds of machinery and welding equipment, electrical control, testing devices and equipment in accordance with these different process process requires a variety of reasonable arrangement, high frequency welded steel pipe produced if control is good, it does not remain fused surface of molten metal or oxide. If cutting a weld specimen polishing, etching and observed under the microscope, the heat affected zone shaped like a drum, because the strip into the edge of the high-frequency current into the steel from the ends and edges of the strip edges with generating heat. HAZ color slightly darker than the base metal because welding carbon steel strip is heated to a diffusion edge, weld cooling is absorbed in the strip edges. Especially near the edge of the strip into CO and oxygen or carbon dioxide, the remaining iron without carbon, the color lighter.

Using a high frequency generator, high-frequency welded pipe mill generator past three circuits: the high-frequency generators; solid drive; electronic high-frequency oscillator, then basically improved to a single circuit. There are many high-frequency oscillator output power adjustment method, such as auto-transformers, reactance method, thyristors method.

High frequency tube is likely to be a variety of welding defects. Each defect has many different names, there is no recognized professional terminology. Here are names of defects, defects in brackets Another common name: (1) inclusions (burnt black oxide); (2) pre-arc (white burnt oxide); less than (3) fusion (open sewing); (4) lack of fusion edge (edge ??waves); (5) fused central deficiency (central cold welding); (6) adhesive bonding (cold welding); (7) cast welding (welding brittle); (8) pores (pinholes); (9) skip welding. These defects are not all but the most common high-frequency welding defects.

High-frequency welding is a resistance to flow through the workpiece with a continuous thermal contact surface high-frequency current generated by the heating and in the case of applying upsetting forces, the metal workpiece between each other to achieve a kind of successive welding method. It is similar to ordinary resistance welding, but there are many important differences.

High-frequency welding for carbon steel pipe production has been 40 years of history. High-frequency welding has a larger power supply, for different materials, diameter and thickness of the pipe can reach a higher welding speed (the maximum ratio of TIG welding speed higher than l0 times). Reasons therefore, high-frequency welding production of general purpose steel has high productivity because high-speed high-frequency welding, to the inner pipe burr removal difficult, high-frequency welded steel pipe(hfw steel pipe) which is currently not yet accepted by the chemical industry, nuclear industry one. From the welding material, the high-frequency welding can weld all types of steel, to meet different customer needs.

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