DE3913897A1 - Prodn. of thick-walled welded steel tubes - using two coils to heat edges up to welding temp. with first coil lying in welding direction - Google Patents

Abstract

The production method uses two coils. The two coils lie one behind the other in the welding direction. The first coil carries out the heating of the entire slit tube to between 600 and 800 deg. C. The second coil only heats the edges up to a temp. of 1400 deg. C. The first coil is operated with a medium frequency of 10,000 Hz and the second coil is operated with a high frequency of 100,000 to 300,000 Hz. ADVANTAGE - High and unpermitted current density at corners of edges is prevented. Risk of corner overheating is removed.

Description

The invention relates to a method for producing ge welded steel pipes where the edges to be welded are heated to welding temperature by high-frequency currents.

According to this known technique, steel strips are also used known devices made slot tubes, and the edges due to high-frequency currents in the range above 100,000 Hertz 1 400 ° C heated and welded.

For thick walls, 1/10 to 1/12 of the pipe diameter amount, arise during cold forming from the steel strip to Slotted tube undesirable stresses perpendicular to the tube axis, the endanger a perfect weld.

According to the known method is driven by and kali the rollers rolled the slot tube into the area at room temperature brought to the induction coil.

The induced currents heat up in a very short tube cut the edges to be welded, using one if possible uniform temperature distribution is sought.

With thick walls, however, there is a risk of inadmissible Overheating of the outer corners of the edges up to melting temperature doors around 1600 ° C.

In addition to the above-mentioned transverse stresses, these also pose a real threat wanted overheating to produce flawless welds.

Thick-wall welded steel pipes can be of high quality produced by induced currents only if two technical Prerequisites fulfilled and the resulting tasks solved will.  

• 1. The edges must be plane-parallel before welding exactly opposite each other without tension.
• 2. The corners of the edges must be protected from overheating will.

According to the invention, these technical problems are solved by a double coil arrangement. ( Fig. 1)

The first coil heats the whole slotted tube to a temperature below 800 ° C.

With this measure, the tensions within the slot pipe dismantled and because the Curie point was exceeded demagnetization also achieved.

In order to achieve a high depth of penetration, the first coil operated according to the invention with a center frequency of 10,000 hertz.

The second coil arranged at a clear distance increases the Temperature of the edges to the desired welding temperature of 1 400 ° C.

The welding does not begin as with the known methods with room temperature of 20 ° C, but begins according to the invention in the range of 800 ° C in a non-magnetic state.

The high and impermissible current density at the corners of the edges is avoided and the risk of corner overheating sides.

Claims (2)

1. Process for the production of welded thick-walled steel tubes characterized in that two in the welding direction consecutive coils are used, the first coil on the heating of the entire slotted tube 600 ° to 800 ° C takes over while the second coil the edges heated to 1400 °. 2. The method according to claim 1, characterized in that the first coil with medium frequency around 10,000 Hertz and the second coil with high frequencies from 100,000 to 300,000 Hertz is operated.