Correlation Between the Properties of Heat Affected Zone of Welds in Erw Welded Pipes and the Quality of Welded Pipes

ERW steel pipe construction pipe seam heat affected zone properties are closely related to the quality of welded pipe. The width of the heat affected zone of the weld, the angle of the metal streamline, and the metallographic structure of the weld under different process parameters are studied by examples to explore ways that are beneficial to the stability and improve the welding quality of the welded pipe from a micro perspective.

Erw Welded Steel Pipe

Correlation between the properties of weld HAZ and main welding process parameters:

The shape and width of the heat affected zone of the weld are closely related to the welding speed, temperature, extrusion force and even the thickness of the tube blank. When the welding speed is constant, the width of the heat affected zone is directly proportional to the welding temperature (ie, the higher the temperature, the larger the width), and inversely proportional to the extrusion force (the larger the extrusion force, the smaller the width); When the extrusion force is constant, the width of the heat affected zone is directly proportional to the welding temperature (ie, the higher the temperature, the wider the width), and inversely proportional to the welding speed (ie, the faster the speed, the smaller the width); The width of the heat affected zone is inversely proportional to the pressing force (ie, the larger the pressing force, the smaller the width), and also inversely proportional to the welding speed (ie, the faster the speed, the smaller the width). It can be seen that the welding process of the welded pipe should be within the safe allowable range, fully explore the potential of the welded pipe equipment, according to the thickness of the pipe blank, reasonably configure the position of the induction coil and the opening angle to ensure sufficient heat (power) output. Gradually increase the welding speed, apply an appropriate pressing force to form the ideal shape of the heat affected zone, and run stably under this state, the welding quality must be steadily improved.

It is generally believed that the width of the heat-affected zone should be 1/4 ~ 1/3 of the thickness of the tube blank, the width of the fusion line should be 0.02 ~ 0.12mm, and the angle of the metal streamline should be between 45 ° ~ 60 °. The experiment of the sample (including frequent re-expansion experiments as a control retest) and analysis of hundreds of metallographic pictures show that the width of the heat-affected zone can be greater than 1/3. For welded pipes with thick wall (wall thickness greater than 5mm ), Which can even approach 1/2 of the wall thickness; the angle of the metal streamline can be slightly less than 45 °, and it can be kept above 40 °; and the corresponding fusion line width can also be slightly wider, generally less than 0.14mm Just fine.

In the case of qualified ERW welded steel pipe produced by our company (such as chemical composition, mechanical properties, and grain size of metallographic structure F + P), the width of the heat affected zone of the weld, Measured data of fusion line width and metal streamline angle.