The welding temperature of welded steel pipe is mainly affected by the high frequency eddy current, according to the formula (2) shows that the eddy current is mainly affected by the high frequency current frequency, eddy current and current excitation frequency is proportional to the square of the current; excitation frequency and excitation voltage, electric current and capacitance and inductance. Steel pipe production process to meet a lot of conditions, for different situations and design principles, in the industry to continue to use and promote. The excitation frequency formula is:

F=1/[2 PI (CL) 1/2]. (1)

F- () excitation frequency (Hz); C- excitation circuit in the capacitance (F), capacitance = power / voltage; L- excitation loop inductance, inductance = magnetic flux / current

When the heat input is insufficient, is not up to the edge of the weld heating welding temperature, metal structure remains solid, forming fusion or incomplete penetration; when the heat input is insufficient, by heating over the edge of the weld welding temperature, burn off or droplet, the weld formation of weld hole.

Welded steel pipe in the welding process parameters and using the standard design and processing of the production process, in the process that the different design requirements, used in different industry scale, will strip into the pipe unit, the multi roller rolling strip rolls up and gradually formed a circular tube gap, adjustment extrusion roll press, the weld gap control in 1~3mm, and the welding ends flush. If the gap is too large, resulting in a reduction in the proximity effect, the eddy heat is insufficient, the welding seam between the poor bonding and produce no fusion or cracking. If the gap is too small due to proximity effect increases, excessive heat loss caused by welding, weld seam; or by extrusion and rolling after the formation of pits, affecting the quality of the weld surface.

Welded steel pipe for an important control squadron in the welding process temperature, capacitance and inductance is inversely proportional to the square root of square root, or with the voltage and current is proportional to the excitation frequency and excitation loop control tube, which can change the size of the excitation frequency as long as the change of capacitance and inductance, voltage or current loop, so as to achieve control the purpose of the welding temperature. For low carbon steel, the welding temperature is controlled at 1250~1460 degrees Celsius, which can meet the requirement of 3~5mm welding of pipe wall thickness. Welding temperature can also be achieved by adjusting the speed of welding.