The history of high frequency straight seam welded pipe

1. The Development History of High Frequency
Longitudinal Welded Pipe
The production and use of steel pipes have a history of more than one hundred years. In the early
nineteenth century, due to the needs of war, people used steel plates to bend them into tubes,
then heated them on the overlapping edges, and forged short mandrels into tubes to make
barrels. Later, this method was achieved. A major development, the furnace welded steel pipe
method appeared around 1825. This method is to heat the metal strip to the welding
temperature and then pull it out of the pipe mold. Since then, the industrial-scale production of
welded pipe has begun.
After 1843, the production of seamless steel pipes has been greatly developed. By 1896, various
technologies and equipment for producing seamless pipes have appeared one after another,
making the production of seamless steel pipes from basic theory, production technology to
various auxiliary equipment Have established a relatively complete system.
At the same time, due to poor welding and forming technology, poor quality of welded steel
pipes, and in short supply of strip steel and steel plates used as raw materials for welded pipes,
the development of welded pipe production lags far behind seamless pipe production, and
welded pipe production only accounts for the entire a small part of steel pipe production.
At the beginning of the twentieth century, resistance welding technology using the Hall effect
began to be used in the production of welded pipes. Yost et al. discussed the welding
temperature, welding pressure, welding speed and their relationship with resistance welding, as
well as the metallographic structure and mechanical properties of the weld. The impact of the
company has been carefully studied. At the same time, a series of researches on other forming
and welding process issues have been carried out, which has significantly improved the quality of
welded pipes. In the 1930s, the production of electric welded pipes had achieved general
development. During this period, the forming technology of welded pipes had also been greatly
improved. A continuous longitudinally welded pipe forming machine appeared, which was
gradually improved and perfected.
In 1938, the contact resistance welded pipe machine designed by Karl Holzer (as shown in the
figure below) has the scale of a modern electric welded pipe machine. It has six forming frames
and a set of welding devices with guide rollers, including squeeze rollers and The burr cleaning
device was followed by three sizing machines and flying shears.

2. After the Second World War, the production of contact electric welded pipes developed rapidly,
especially in the United States. The series design of electric welded pipe machines was first
started. The first series in the United States were four specifications coded by M. They are as
follows:
The appearance of this series of equipment is shown in the figure:
M series pipe welding machine adopts rotary welding transformer with output power of 125, 300
and 500 kVA, current frequency is 50-60 Hz, and later increased to 150-180 Hz. The structure of
rotary welding transformer is shown in Figure 1-8. The working principle is shown in Figure 1-9.
When a current of intensity I flows along a conductor with a resistance of R ohms, the heat
generated in the conductor after t seconds is Q=0.24I²RT card. During the welding process, the
resistance at the slit of the tube blank is greater than the resistance of the current flowing
through the circumference of the tube blank. Therefore, the edge of the strip at the slit will

3. generate a lot of heat, which can heat the edge of the strip to Welding temperature. The electric
current passes through the rotary welding transformer and is sent to the broken edge of the tube
through the ring electrode 1 separated by the insulator 2 to heat the edge. Then, under the
pressure of the looting roller, the edges of the tube blank heated to the temperature of the
welded tube are welded together.
Due to the periodic change of the alternating current intensity, it is impossible to obtain uniform
heating along the length of the weld. When the current intensity reaches the maximum, the
corresponding points on the weld are heated to the temperature or higher than the welding
temperature, and when the current is When the value is zero, the corresponding points on the
weld are not heated enough or reach the welding temperature, so the other side is welded and
unwelded along the length of the weld, or the welded and welded parts are alternately
distributed with each other, which forms the so-called cycle Sexual distribution of solder joints.
The distance between the solder joints in the weld is proportional to the welding speed and
inversely proportional to the frequency of the current. The smaller the distance between the
solder joints, the better the air tightness of the weld and the higher the quality of the weld In the
case of the same welding speed, increasing the current frequency can use the quality of the weld.
Similarly, when the current is 50 Hz, the welding speed can reach 30-32 m/min. At this time, the
distance between the corresponding welding points It is divided into 5 and 5.33 mm. On this
basis, if the welding speed is further increased, the quality of the weld will be greatly
deteriorated, which cannot meet the actual demand.
Therefore, higher frequencies of 120-360 Hz were subsequently used in the production of
resistance welded pipes(ERW pipe). At the same time, DC resistance welding, induction welding

4. and arc welding are used to produce welded steel pipes, but the welding speed of these welding
methods is very low.
Low-frequency resistance welding with a frequency of 60-360 Hz was the most widely used in
this period. During this period, almost 80% of welded steel pipes in the world were produced by
this method, because this method is the simplest and the welding quality It has also been
significantly improved. It can not only produce general conveying pipes and structural pipes, but
also produce boiler tubes with higher requirements. Petroleum pipes with a diameter from
114-500 mm and a wall thickness from 4.75 to 14.3 mm can also be produced by this method. ,
The welding machine used has a capacity of 4400 kVA, and a welding speed of up to 60 m/min.
The most negative AC imposes less restriction on the chemical and physical performance of the
material, but it has less restriction on the surface of the strip, especially the strip in contact with
the welding electrode. The steel edge part has strict requirements, and no iron oxide scale, rust,
oil stain, etc. are allowed. Therefore, low-frequency resistance welding generally requires pickling
or sandblasting to treat strip steel. This welding method is still in use today.
Because the power supply equipment of DC resistance welding is too expensive and its
application range is limited, it can only be used for carbon steel welding, especially for the
production of welded pipes with high welding quality requirements, small welding burrs and
smooth surface. For example, small-diameter cooler tubes are produced by DC resistance welding
and do not need to remove internal burrs. Its outer surface can be compared with cold-drawn
tubes. This method is generally not used for the production of steel tubes with a diameter
greater than 76 or 102 mm and a wall thickness greater than 4 mm. Because the removal of burrs
in steel pipes with larger diameters is easier, and the requirements for surface quality are not as
high as for small diameter pipes, AC resistance welding can be used.
After 1950, a series of changes took place in production. Especially in 1953, high-frequency
contact resistance welding with a frequency of 450 kHz began to be used in the production of
welded pipes, but the initial development was slow. It was not until 1960 that countries around
the world adopted high-frequency welded pipes. There are still few units. After 1960, the
production of high-frequency contact resistance welded pipes has achieved extremely rapid
development. A large number of high-frequency welded pipe units have been built in various
countries. Subsequently, high-frequency induction that transfers energy by means of ring
inductors has also begun to be used. For the production of welded pipes. After high-frequency
contact has achieved recognized good results, the application of high-frequency induction
welding is still extremely limited, and it only plays a minor role in the production of
high-frequency welded pipes.
High-frequency welding has a series of advantages: the heat effect of the weld is small, the
heating speed is fast, and the metal can be heated to the welding temperature in one hundredth
of the time (1130-1350℃), which can greatly improve the welding speed and quality. It can weld
strip steel that is not pickled or shot blasted. At the same time, it can weld carbon steel
inconveniently. It can also weld stainless steel, aluminum alloy, copper alloy and other materials.
In addition, high-frequency steel pipes have low energy consumption and high efficiency Because

5. of these advantages of high-frequency welding, in the 1970s, not only the newly-built small and
medium-diameter electric welded pipe units generally adopted this welding method, but also the
original low-frequency welded pipe units in various countries were transformed into
high-frequency, so that the unit ’ s Production capacity and product quality have been
significantly improved, and product specifications and use ranges are also expanding.
Since 1960, there have been many major improvements and innovations in the forming
technology, quality control and inspection technology, and finishing equipment of small and
medium diameter electric welded pipes.