JPH0133534B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing an electric resistance welded tube.

In general, the process of manufacturing an electric resistance welded pipe consists of forming, welding, seam annealing, cleaning, sizing, and running/cutting. In such a manufacturing process, the toughness of the welded part is temporarily improved by seam annealing, but there is a problem in that the toughness deteriorates again due to processing strain caused in the subsequent sizing process. As a method to remove the processing strain applied to the vicinity of the weld during this sizing process and improve the toughness of that area, it has been proposed to heat treat the weld using a seam annealing method after sizing, but this method does not Since only the vicinity of the weld is locally heated, heat is rapidly removed in the circumferential direction of the tube during the cooling process, and the weld is rapidly cooled, so that no significant effect can be expected in improving the toughness of the weld. In addition, the above-described local heat treatment tends to cause deformation such as bending due to thermal strain, resulting in a problem that the quality of the product deteriorates.

In addition, in the ERW pipe manufacturing process, there is a problem that the yield strength decreases due to the Paussinger effect during pipe making, and this decrease in yield strength is caused by the first
Particularly high strength (e.g. API standard 5LX) as shown in the figure
- X60 or more), and t/D (thickness/
The smaller the outer diameter (about 2%), the larger the diameter. Generally a size with a large t/D (small size)
As for pipes, the reduction is applied in the sizing process, so even if the yield strength decreases during pipe making, the strength is restored by the reduction, whereas in sizes with small t/D (large diameter sizes), buckling occurs. For reasons such as this, little drawing is applied in the sizing process, and as a result, the product is manufactured with a reduced yield strength. Furthermore, even if it is possible to reduce the weld to some extent by fine passes or sizing depending on the pipe size, strong drawing that restores the yield strength will result in deterioration of the weld toughness. Recently, low-temperature impact characteristics of welded parts are often specified in high-tension electric resistance welded line pipes, so there is a natural limit to the degree of throttling mentioned above, and the large effect of improving yield strength is not expected. Can not. In recent years, there has been a strong tendency for pipeline materials to have higher tensile strength.
For this reason, in the past, coils made of materials with a yield strength higher than the standard value (for X60, YS was 5
The reality is that it is possible to manufacture high-tensile resistance welded pipes by taking measures to compensate for the decrease in yield strength in advance by using a material with a high tensile strength (Kg/mm ² or higher).

In view of the above circumstances, the present invention aims to provide a method for manufacturing an electric resistance welded pipe that can simultaneously improve both the reduction in weld toughness and the reduction in yield strength due to the Bauschinger effect.

For this reason, the present invention provides a welder for seam welding after seam welding when manufacturing a pipe body with a wall thickness to outer diameter ratio of 3% or less and a strength of 5LX-X60 or more according to API standards. The welded part is heat treated with a post annealer, then cooled through a cleaning zone and a water cooling zone, after which the entire tube formed with a Xizer is annealed at a high temperature of 500°C or higher.

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 2 shows the implementation status after welding of the ERW pipe manufacturing method according to the present invention, in which the formed pipe P is seam welded by a welder 1, and then the welded part is heat-treated by a post annealer 2. After passing through a cleaning zone 3 and a water cooling zone 4, it is shaped by a sizer 5, and finally cut into a predetermined length by a traveling cutter 6. After passing through the sizer 5, the tube body P is heated and annealed in the circumferential direction at a temperature of 500° C. or higher by the whole tube heating device 7. In addition,
By providing a heat insulating dome 8 as shown in FIG. 3 on the exit side of the all-tube heating device 7, it is possible to secure the holding time at the annealing temperature and to bring the cooling conditions close to the furnace cooling state.

In this way, the deterioration of toughness caused by seam welding is improved by heat treating the welded part with a post annealer after seam welding, and then annealing the entire tube at high temperature after forming with a sizer. Processing strain during the process is removed, and the decrease in yield strength due to the Bauschinger effect during forming is also appropriately reduced.

Firstly, in the present invention, processing distortion in the sizing process is removed by heating the weld to a temperature of 500°C or higher. Since the entire weld is heated, rapid cooling of the weld zone is prevented, and thereby the weld zone toughness can be appropriately improved by annealing. As an example of the effect of this, the entire circumference of the pipe is
By heating to about 650℃, API5LX-
It has been confirmed that in X70 class high-tensile, high-toughness ERW pipes, the transition temperature of the welded part is approximately 15 to 20 degrees Celsius lower than that of normal material (as sized).
Figure 4 shows the welded part impact characteristics of the electric resistance welded pipe (X70 class) manufactured according to the present invention together with that of a comparative material (welded → seam annealed → sizing), a 20″ x 12.7 size test sample. 610 pieces of material
This shows the impact properties of welded parts (test piece 10 x 10 mm) when heated to ℃ and 720℃. According to this,
It can be seen that the impact properties of the material of the present invention are significantly improved compared to the comparative material that is sized as is.

Second, the high-temperature annealing appropriately reduces the decrease in yield strength due to the Bauschinger effect during forming. In other words, the Paussinger effect is greatly reduced due to the temperature effect and strain aging effect due to the above-mentioned annealing, and the yield strength can be rationally improved even in high-strength steels such as API 5LX-X60 or higher, and high-tensile resistance welding with a small t/D can be achieved. Tubes can be manufactured easily. FIG. 5 shows the effect of improving yield strength according to the present invention (material X70), and it can be seen that an appropriate effect of improving yield strength can be obtained for any pipe diameter size.

In addition, with the present invention, the carbon equivalent of the material can be lowered by improving the yield strength, thereby reducing the hardness of the circumferential welded part of the tube, which is expected to have an effective effect on stress corrosion cracking and hydrogen-induced cracking. can. Further, according to the present invention, by straightening the tube body that needs to be bent before the temperature decreases due to annealing, it is possible to appropriately eliminate the Bauschinger effect caused by the straightening.

Note that the upper limit of the annealing temperature is preferably 1000° C. or lower in order to prevent coarsening of the structure of the welded part.

According to the present invention described above, when manufacturing a pipe body with a wall thickness to outer diameter ratio of 3% or less and a strength of 5LX-X60 or more according to API standards, the toughness of the welded part by seam welding can be improved. In addition, it is possible to effectively improve toughness by suppressing the rapid cooling of the welded part after heating and eliminating processing distortion in the sizing process, and in addition, it can rationally reduce the decrease in yield strength due to the Bauschinger effect during pipe making. Therefore, it is possible to easily and economically produce high-tension electric resistance welded pipes for line pipes, etc., without using materials with a strength higher than the standard value or performing strong drawing during fin passes and sizing. It can be manufactured as follows.

[Brief explanation of drawings]

FIG. 1 shows the relationship between t/D of an electric resistance welded pipe and the amount of change in yield strength due to forming. FIG. 2 is an explanatory diagram partially showing the state of implementation of the present invention. FIG. 3 is an explanatory diagram showing an example of the tubular body heating situation in FIG. 2. FIG. 4 shows the impact characteristics of the welded part of the electric resistance welded pipe manufactured by the method of the present invention together with a comparative material. FIG. 5 shows the relationship between the annealing temperature of the tube after the sizing process and the amount of decrease in yield strength compared to when coiling. In the figure, 7 is a whole tube heating device.

Claims (1)

[Claims] 1 The ratio of wall thickness to outer diameter is 3% or less and the strength is API
When manufacturing pipe bodies that are 5LX-X60 or higher according to the standard, after seam welding, the welded part is heat treated with a post annealer following the seam welder, and then cooled in a water cooling zone after passing through a cleaning zone. After that, the entire tube formed by Xizer is high-temperature annealed at a temperature of 500 degrees Celsius or higher. This is a method for manufacturing electric resistance welded tubes with excellent yield strength and welded part toughness.