JPH02160184A - Production of electric welded pipe - Google Patents

Abstract

PURPOSE:To prevent the generation of welding defects by measuring and calculating the temp. difference in respectively heated both-side edges on the inner and outer sides of an open pipe and correcting the quantity of heat input based on the relation between the previously determined temp. difference and the adequate quantity of heat input. CONSTITUTION:The open pipe 1 is formed into a cylindrical shape, the both-side edges of which face each other, by passing a band-shaped metallic sheet through forming rolls. The open pipe is passed in a high-frequency current coil r disposed on the outer periphery to heat and melt the both-side edges and the edges are butt-welded by squeezing rolls 3 by which the electric welded pipe 2 is formed. Lenses a, 6a are installed to the prescribed positions on the outside and in the inside of the pipe 1 and are connected respectively to pattern thermometers 7, 8 via optical fibers 5, 6. The respective thermometers determine the temp. difference between the inside and outside surfaces of the both-side edges and input the same to an arithmetic unit 9. The correction quantity DELTAP of heat input is calculated in accordance with the prescribed equation in the arithmetic unit and is inputted to a weld heat input control device 10. The control device 10 outputs the control signal corresponding to DELTAP to a welding machine 11 and controls the input voltage (electric power) of the coil 4. The generation rate of the weld defects is lowered in this way even if the difference in the wall thickness exists.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for welding in order to provide an appropriate amount of heat input in accordance with the wall thickness difference when there is a wall thickness difference between the edge portions on both sides to be butt welded. The present invention relates to a method of manufacturing an electric resistance welded pipe in which the amount of heat is corrected.

[Conventional technology]

In general, ERW pipes are made by bending a band-shaped metal plate such as a hot-rolled coil or a cold-rolled coil into a cylindrical shape so that both edges in the width direction face each other to form an open pipe. It is manufactured by passing a high frequency current through the parts, heating and melting these parts, and then butt welding them with a squeeze roll.

[Problem to be solved by the invention]

By the way, the band-shaped metal plate has a so-called plate crown where the wall thickness changes in the width direction during the manufacturing process, and due to bending of the band-shaped metal plate, uneven wear of the forming rolls, etc. Due to various reasons such as processing limitations, it is unavoidable that a difference in wall thickness and also a difference in level occur at the edge portions on both sides of the band-shaped metal plates that are to be butted together.

FIG. 6 is an explanatory diagram showing the state immediately before butt welding of the edge portions 11.1r on both sides, where there is a difference in wall thickness, with squeeze rolls 3, 3. Both side edge parts 14 to be welded! ,
It can be seen that there is a wall thickness difference in lr, and a step is caused by this difference.

As a countermeasure to this problem, a cold rolling machine for strip metal plates is installed on the entrance side of the pipe making machine to eliminate uneven thickness of the strip metal plates (Japanese Patent Application Laid-Open No. 60-82217), or a device for controlling the rolling reduction of the forming rolls is used. Although various methods have been proposed, such as installing a device (Japanese Patent Application Laid-open No. 133929/1982), it is difficult to correct a one-step difference in wall thickness using these methods.

When there is a difference in wall thickness between the edges to be butt welded, the rate of temperature rise at the thinner edge is greater than that at the thicker edge when heated, and the thinner edge at the welding point The weld zone becomes overmelted, and a penetrator-like welding defect, which is seen when there is excessive heat input, occurs in the weld zone. On the other hand, in the thicker edge portion, insufficient melting occurs at the welding point, and cold welding defects that occur when the heat input is low occur in the welded portion.

According to the results of experiments conducted by the present inventors, the relationship between the wall thickness difference and the temperature of the edge portion is as shown in FIG. 7, for example.

Figure 7 is a graph showing the temperature rise state of each edge part on both sides, with the horizontal axis representing the distance from the welding point (1m), and the vertical axis representing the temperature (1) of the inner and outer surfaces of each edge part. This is an indication.

In the graph, the Δ symbol indicates the inner temperature of the thin edge, the mu symbol indicates the inner temperature of the thick edge, the O symbol indicates the outer temperature of the thin edge, and the . mark indicates the inner temperature of the thick edge. ing.

As is clear from this graph, the outer surface temperature is approximately the same at the thicker edge and the thinner edge, but the inner temperature is lower at the thicker edge and higher at the thinner edge. I understand.

In order to prevent either such overmelting or insufficient welding, it is necessary to set the heat input appropriately.
This amount of heat input varies depending on the difference in wall thickness between the edge portions on both sides.

The inventors of the present invention set the reference wall thickness to 6 fl and set the proper welding input to 125 kW when the wall thickness difference between both edges is zero. As shown in the figure.

FIG. 8 is a graph showing changes in the appropriate welding input, with the vertical axis representing the appropriate heat input ratio, and the horizontal axis representing the wall thickness difference (crane) from the reference wall thickness. In the graph, the ○ mark indicates the value for the inner surface of the thick edge portion, and the △ mark indicates the value for the outer surface.

As is clear from this graph, the appropriate welding heat input changes depending on the wall thickness difference.

Therefore, in order to eliminate this inconvenience, it is desirable to determine the difference in wall thickness between the edge parts on both sides, but measurement in the state of a strip-shaped metal plate cannot take into account changes in the subsequent forming process, and also Currently, it is difficult to perform stable measurements to determine the thickness of each edge portion in a state where the edge portion is formed in a shape.

The present invention has been made in view of the above circumstances, and its purpose is to perform proper welding without directly measuring the wall thickness difference even when there is a wall thickness difference between the edge portions on both sides to be butt welded. To provide a method for manufacturing an electric resistance welded pipe in which the amount of heat can be set.

[Means to solve the problem]

In the method for manufacturing an electric resistance welded pipe according to the present invention, before butt welding the edge portions on both sides, the temperature of the heated edge portions on both the inside and outside of the open pipe is measured to determine the temperature difference between the edge portions on both sides. Based on the relational expression between the temperature difference calculated in advance and the appropriate amount of heat input, the corrected amount of heat input necessary to obtain the appropriate amount of heat input is determined, and the amount of heat input is corrected.

[Effect]

According to the method of the present invention, an appropriate amount of heat input can be set regardless of the level difference between the edge portions on both sides to be butt welded.

(Principle) As mentioned above, both edges to be butt welded lj! ,
When lr has a thickness difference as shown in FIG. 1, a temperature difference occurs between the edge portions 1j1.1r on both sides during heating, but this is considered to be the result of the following two factors.

In other words, if there is a difference in the electrical load between the edges on both sides, and there is a difference in the heating state of the edges on both sides, ■ heating in the thickness direction of each edge will be uneven due to the difference in proximity effect. This is a case of becoming.

Therefore, assuming that there is a wall thickness difference between the two edge parts IL1r to be butt-welded with a squeeze roll as shown in FIG. Letting the temperature difference between the inner surface temperature Tb and the inner surface temperature Tb be ΔTr, it can be expressed as shown in the following equation (11).

Tb − Ta = ΔTr ・”
(1) Furthermore, if the temperature difference caused by the above-mentioned (2) is ΔTt, it can be expressed as in the following equation (2).

Tb - Tc = ΔTr + ΔT t
-(21 Furthermore, the temperature difference is not necessarily caused only by the difference in wall thickness. For example, even if the wall thicknesses of both side edge portions 11Ar are the same, a temperature difference also occurs when there is a step as shown in FIG.

FIG. 3 is a graph showing the temperature at both edge portions and their vicinity when there is a step in the radial direction at both edge portions lN and 1r to be butted, and the vertical axis represents the temperature ('C).
, and the circumferential position (dragon) is shown on the horizontal axis.

In the graph, T" indicates the temperature on the outer surface side of the edge portion 11 that protrudes outward and is located high, and Te indicates the temperature on the outer surface side of the edge portion 1r that is concave inward and is located low.

As is clear from this graph, both edge portions B.

It can be seen that when lr is displaced inward or outward to create a step, the temperature of the edge portion located on the outside becomes lower than the temperature of the edge portion located on the inside, resulting in a temperature difference.

In this way, there is no difference in wall thickness between both edges, but if the temperature difference when there is a step is ΔTδ, then +11. (2) 2 is expressed as in the following (3), +41 formula.

Tb - Ta = ΔTr - ΔTδ - (3
) Td - Tc = ΔTr + ΔTt + Δ Ta ・
(4) Therefore, the temperature difference between both edges is (1), (2)
The sum of formulas, i.e. f3), (Since it is the sum of formula 41, the following (
5) It is expressed as in the equation.

(Tb-Ta) + (Td-Tc) = 2ΔTr+Δ
T t ・(5) Since Δ7r<<ΔTt (
Equation 5) is expressed as equation (6) below.

(Tb-Ta) + (Td-Tc)=ΔTr+ΔT
t ・+61 As is clear from equation (6), by measuring the temperature difference between the inner and outer surfaces of both edge portions IC1r immediately before butt welding with squeeze rolls, the temperature difference between the inner and outer surfaces of both edge portions H! , 1r can obtain the temperature change when there is a difference in wall thickness. Edges on both sides ll.

A corrected heat input amount ΔP for obtaining an appropriate heat input amount to avoid being influenced by a temperature difference of 1r is given by the following equation (7).

ΔP=α・(ΔTr+ΔTt)・P, −
(7) However, Po: Current heat input α: Correction coefficient Note that the correction coefficient α has a unique value that differs for each pipe making machine, so it is determined in advance by experiment.

〔Example〕

The method of the present invention will be specifically explained below based on the drawings.

FIG. 4 is a schematic plan view showing the implementation state of the method of the present invention, in which 1 indicates an open pipe, 2 indicates an electric resistance welding tube, and 3 indicates a squeeze roll.

The open pipe 1 is constructed by passing a band-shaped metal plate (not shown) through a number of forming rolls and forming it into a cylindrical shape so that the edge portions 11°1r on both sides in the width direction face each other, and is arranged around the outer periphery of the movement area of the oven pipe 1. Coil 4 that passes high frequency current
Pass through both edge parts lj! , lr are heated and melted and butt welded using a squeeze roll 3 to form the electric resistance welded tube 2.

Both edges of open pipe 1 N! , 1r is coil 4
The point where it passes through and the edge portions 14 on both sides which are in a heated state! ,l
Both edge portions 11. of the open pipe l during heating between the point where r first contacts (welding point V). An optical fiber /'
Let's look at one end of each.

The other end of each optical fiber 5, 6 is a pattern thermometer 7, 8, respectively.
It is connected to the.

Each pattern thermometer 7.8 calculates the temperature difference Tb-Ta, Td-Tc between the edge portion 11.1r on the inner surface and outer surface of both edge portions of the open pipe 1 taken through the lenses 5a+6a+optical fibers 5 and 6, respectively. Difference Tb-T
a, Td-Tc are input to the arithmetic unit 9.

The calculation device 9 calculates the corrected heat input amount ΔP according to the above equation (7) and outputs it to the welding heat input control device 10.

The welding heat input control device 10 outputs a control signal corresponding to the corrected heat input amount ΔP to the welding machine 11, and the welding machine 11 controls the coil 4.
control the input voltage or input power to the

In addition, in the figure, 12 indicates a mandrel inserted from the open pipe 1 side, 13 indicates a cutting blade provided at the tip of the mandrel 12, and 14 indicates an impeder.

Next, the test results of the method of the present invention conducted using the pipe making machine shown in FIG. 4 will be shown.

The composition of the band-shaped metal plate used is shown in Table 1, and the dimensions and test conditions are shown below.

Table 1 Width dimension of band-shaped metal plate? 60.5 dragon wall thickness
, 6.0Tsuru Wall thickness difference between both edges 0.25m, 0.04m pipe manufacturing speed, 40 kw/min welding input power (initial value), 557kw For the performance comparison of manufactured ERW pipes, UST ( Judgment criteria N
The number of welding defects was investigated based on the notch depth (5% of the thickness). The results are shown in FIG.

FIG. 5 is a graph showing welding performance, with the UST failure rate (%) plotted on the vertical axis. In the graph, the Q mark indicates the results when the thickness difference between the edge portions on both sides is 0.04 m, and the - mark indicates the results when the wall thickness difference is 0.25 m.

As is clear from this graph, in the conventional method, the UST defective rate (%) is 0.4% or more when there is a large difference in wall thickness, but in the case of the method of the present invention, there is almost no difference in wall thickness. Regardless, it can be seen that the UST defective rate remains below 0.1%.

〔effect〕

As described above, the method of the present invention can significantly reduce the incidence of welding defects even when there is a difference in wall thickness, especially when manufacturing alloy steels with a narrow appropriate welding heat input range. It has excellent effects when applied to

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the state of both edge parts when the wall thickness is different, Figure 2 is a schematic diagram showing the state of both edge parts when there is a step, and Figure 3 is a schematic diagram showing the state of both edge parts when there is a step. Fig. 4 is a schematic diagram showing the implementation status of the method of the present invention together with its control system, Fig. 5 is a graph showing the welding performance test results, Fig. 6 is a graph showing the temperature difference occurring at both edges. A schematic diagram showing the state immediately before the open pipes with a difference are butted together with a squeeze roll, Figure 7 is a graph showing the state of temperature increase on the inner and outer surfaces of the edge, and Figure 8 is a graph showing the relationship between the wall thickness difference and the appropriate welding input. It is a graph showing a relationship. 1... Open pipe 2... ERW pipe 3... Squeeze roll 4... Coil 5, 6... Optical fiber 7.8... Pattern thermometer 9... Arithmetic unit 10
...Welding heat input control device 11...Welding machine 12...
・Mandrel 13...Cutting blade 14 River Impeder Patent Applicant

Claims (1)

[Claims] 1. A band-shaped metal plate is curved so that its widthwise edges face each other to form an open pipe, and the edges are butt-welded using squeeze rolls while heating and melting. In the method of manufacturing a sewn pipe, before butt welding the edges on both sides, the temperature of the heated edges on both sides is measured on the inside and outside of the open pipe, the temperature difference between the edges on both sides is calculated, and the temperature difference between the edges is calculated in advance. A method for manufacturing an electric resistance welded pipe, characterized in that the corrected heat input amount necessary to obtain the appropriate heat input amount is determined based on the relational expression between the determined temperature difference and the appropriate heat input amount, and the heat input amount is corrected.