JPS617010A - Method for diagnosing factor for thickness deviation of seamless pipe - Google Patents

Abstract

PURPOSE:To diagnose exactly the factors for the thickness deviation of a pipe by measuring the wall thickness in the various parts along the axial direction of the pipe at plural circumferential points thereof and detecting the specific factors contributing to generating the change in the wall thickness from the distribution and period of the thickness deviation, and the max. and min. values of the circumferential thickness deviation. CONSTITUTION:The wall thicknesses in the various parts in the axial length direction of the seamless pipe are measured at the plural circumferential point thereof by using an electromagnetic ultrasonic method. The functions of the wall thickness distributions in the axial length direction are determined with the optional two points in the circumferential direction in accordance with the measured values. The cross-correlation functions are drived from these functions of the wall thickness distributions. Whether the peak value in the prescribed region of the cross-correlation functions exceeds a predetermined reference value or not is judged. The average values of the wall thickness in the axial length direction of the measured values described above are calculated and whether the difference between the max. value and min. value in the circumferential direction among the average values exceeds the predetermined other reference value or not is judged. The exact diagnosis of the factors for the thickness deviation is thus made possible and the adequate disposition is executed with a good timing.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is intended to solve problems in pipe manufacturing equipment such as drilling machines and mandrel mills,
Alternatively, the present invention relates to a method for diagnosing the cause of uneven wall thickness, such as poor heat treatment of a raw material for pipe making - a barrel billet, based on the distribution of the wall thickness of a manufactured pipe.

[Prior art]

When manufacturing seamless pipes using, for example, a Mannesmann mandrel mill, the raw material billet is heated to the required temperature in a heating furnace, and then a hole is punched along the center using a drilling machine to obtain a blank tube. After passing it through an elongator as necessary, or directly passing it through a mandrel mill and elongating it, it is manufactured by finishing it to the specified outer diameter and wall thickness using a stretcher or other rolling mill. There is. However, seamless pipes manufactured in this manner have variations in wall thickness due to various factors. The causes of such variations in wall thickness are not only due to the material of the tube material, non-uniform heating temperature, etc., but also often due to tube manufacturing equipment such as a punching machine, a mandrel mill, and a reducer. For example, it is known that uneven thickness can occur in drilling machines due to wear and eccentricity of the plug, and in mandrel mills due to roll misalignment, roll wear, deflection of the mandrel bar, etc. Inspection of processed tools, etc.

It is recognized that the degree of uneven thickness can be reduced by maintenance and replacement.

However, in the past, such inspections and maintenance, tool replacement, etc. were performed periodically, for example, based on the number of pipes being manufactured, so inspections and maintenance or tool replacements tended to be carried out early with safety in mind. There were problems such as frequent inspections and maintenance, and high tool costs.

The present inventors conducted experiments and research into the relationship between uneven wall thickness of manufactured pipes and defects in pipe manufacturing equipment such as punching machines and mandrel mills, which are the causes of uneven thickness, and defects in heat treatment such as billet charring. As a result, for example, if there is a defective plug in the drilling machine, especially if there is eccentricity, a spiral thickness deviation will occur on the inner surface of the tube, or if there is a defect in the mandrel mill or plug mill, especially if there is a defective roll gas sop alignment. If uneven thickness occurs at two 90° different positions in the axial direction of the tube, and if there are other defects such as billet burnt, the inner surface of the tube should be treated in the same manner as in the case of a defective punching machine. Spiral-like uneven thickness occurs,
It was found that the period of this uneven thickness was different from that in the case of a defective drilling machine. In addition, these characteristic wall thickness changes remain even in the final product stage of seamless pipes, so there is no need to measure the wall thickness distribution one by one by placing a wall thickness needle on each exit side of each pipe manufacturing device. For the final product, we measure the wall thickness in the axial direction at multiple points in the circumferential direction, analyze this, and separate the wall thickness variation for each cause of thickness unevenness to accurately identify the causes of uneven thickness. , and that it can be easily diagnosed.

〔the purpose〕

The present invention has been made based on this knowledge, and its purpose is to measure the wall thickness of each part in the axial direction of the tube at each of a plurality of circumferential locations using an electromagnetic ultrasonic method,
Based on this wall thickness measurement value, the uneven thickness distribution, period of uneven thickness, maximum and minimum values of uneven thickness in the circumferential direction, etc. are determined, and changes in wall thickness peculiar to the cause of uneven thickness can be detected and accurately measured. To provide a method for diagnosing the cause of uneven thickness of a seamless pipe by diagnosing the cause of uneven thickness of a seamless pipe and enabling appropriate treatment and maintenance and inspection at an appropriate timing without waste.

〔composition〕

The method for diagnosing the cause of uneven wall thickness of a seamless pipe according to the present invention is to perforate a billet using a punching machine, and to elongate and roll the obtained raw pipe, to determine the axial length of the seamless pipe at a plurality of locations in the circumferential direction. Measure the wall thickness at each part in the direction, calculate the wall thickness distribution function in the longitudinal direction of each axis at any two locations in the circumferential direction based on the measured values,
A cross-correlation function is derived based on these thickness distribution functions,
The present invention is characterized in that the cause of uneven thickness is determined based on the cross-correlation function.

Another method for diagnosing the cause of thickness unevenness in a seamless pipe according to the present invention is to perforate a billet using a punching machine, and then elongate and roll the obtained raw pipe to form a seamless pipe at multiple locations in the circumferential direction. Measure the wall thickness of each part in the longitudinal direction, determine the thickness distribution function in the longitudinal direction of each axis for any two points in the circumferential direction based on the measured value, derive the cross-correlation function based on these thickness distribution functions, It is determined whether the peak value within a predetermined region of the cross-correlation function exceeds a predetermined reference value, and the average value of the wall thickness in the longitudinal direction of each axis of the measured values is calculated, and the circumference of the average value is calculated. The method is characterized in that the difference between the maximum value and the minimum value in the direction is compared with another predetermined reference value, and the cause of uneven thickness is determined based on a judgment as to whether or not the difference exceeds the reference value.

[Example] The present invention will be specifically described below based on drawings showing examples thereof. FIG. 1 is a schematic diagram showing the pipe making process using the Mannesmann mandrel mill method and the control system of the method of the present invention.
5 is a reheating furnace, 6 is a trench reducer, and 7 is a cooling bed. The billet 1 is heated to a predetermined temperature in a heating furnace 2, perforated in the center with a perforator 3, then roughly rolled in a mandrel mill 4, cut into cropped parts with a hot saw, and then transferred to a reheating furnace 5. After heating, it is rolled to a predetermined outer diameter and thickness using a stretch reducer 6, and then cooled on a cooling bed 7 to produce a seamless pipe. Then, on the outlet side of the stretch reducer 6, the wall thickness is measured at a plurality of locations in the circumferential direction of the pipe P at predetermined pitches (0.1 to 10 cm) in the axial direction using the wall thickness measuring device 10.

Figure 2 shows 1 of the measuring section and signal processing section of the wall thickness measuring device IO.
It is a block diagram showing an example, in which an excitation coil a is arranged concentrically around the movement range of the seamless pipe P on the exit side of the trench reducer, and when a direct current is passed through this, the joint A DC magnetic field is applied to the tubeless P in its axial direction. On the other hand, 13 is a synchronous pulse generation circuit, and based on the trigger signal, the pulse current generation circuit 14 emits a pulse current, and each time the transmitting coil 11 is energized, the magnetic flux in the radial direction of the tube P changes. Accordingly, an eddy current is generated on the surface of the tube P. The Lorentz force caused by this eddy current and the magnetic field generates a strain (Fleming's left-hand rule) that changes in a direction perpendicular to the surface of the tube 2, and this strain propagates in a direction perpendicular to the surface of the tube P. That is, longitudinal ultrasonic waves are generated from the surface of the tube 2. This ultrasonic wave propagates through the tube P and is reflected by its inner circumferential surface, and this reflected ultrasonic wave reaches the surface (Fleming's right-hand rule) and generates an eddy current. It is detected as an induced voltage by the receiving coil 12, amplified by the amplifier 15, envelope-detected by the synchronous detector 16, and inputted to the time difference measuring circuit 17. A trigger signal is given, and this outputs a signal to the time difference measuring circuit 17 to cause counting to be performed from the time when the pulse current is applied to the transmitting coil 11 to the time when the first echo is detected.The time difference measuring circuit 17 The time difference between the time when the ultrasonic wave is generated on the surface of the pipe P and the time when the saw echo is detected when it is reflected on the inner surface is determined and sent to the wall thickness conversion circuit 21 of the arithmetic unit 20 through the interface 18.Thickness conversion circuit 21 measures the wall thickness of the pipe P based on the above time difference, the separately determined temperature of the pipe P, and the longitudinal wave propagation velocity at this temperature. The wall thickness over the entire length of the pipe P is calculated and output to the circuit 22 as '/jfJW, respectively.

The arithmetic circuit 22 calculates the thickness distribution function in the axial direction and the cross-correlation function based on the input wall thickness data, and further calculates the average value in the axial direction and the average value based on the wall thickness data. The maximum value and minimum value of the value in the circumferential direction are determined, the difference between these values is calculated, and each is outputted to the determination circuit 23.

The determination circuit 23 determines whether the uneven thickness formed in the seamless pipe is caused by the mandrel mill, the punching machine, or the billet sintering, based on each input calculated value.

First, the uneven thickness formed in the seamless pipe is processed using a mandrel mill.
In particular, the procedure for determining whether the problem is caused by roll gap alignment or the like will be explained with reference to FIG. First, the obtained tube has multiple locations i (i=1・
・・J-1 to n points for each part j in the axial direction of the tube (excluding the top and bottom parts, which are subject to large deformations) for k)
Measure the wall thickness Di3 of each part of the pipe (Step 2). Based on this wall thickness data, calculate the arithmetic average -b-1 of the measured values in the axial direction at multiple points in the circumferential direction of the pipe, that is, the When the arithmetic average '-D + of the wall thickness values in the axial length direction is calculated, this average wall thickness value Di is determined by eliminating the effects of the uneven thickness due to defects in the punching machine and side burning b3 of the fillet throat, and Only the resulting uneven thickness is extracted. The reason for this is explained as follows.

In other words, it is assumed that the wall thickness distribution in the axial direction obtained for the raw pipe is the result of a combination of uneven thickness due to a defect in the punching machine, single burning of the billet, and uneven thickness due to a defect in the mandrel mill, The uneven thickness due to defects in the mandrel mill is a(1,
Further, if the cycle of uneven thickness due to one-sided burning of the plug of the punching machine and the billet is ω, and the position in the axial direction is Lj, the uneven thickness distribution in the axial direction of the raw pipe is a. It can be expressed as +sinωLj.

By the way, if this is averaged in the axial length direction of the raw pipe (at least for several cycles of the uneven thickness cycle), the following equation is obtained.

Therefore, terms related to uneven thickness caused by a defective plug of the punching machine and uneven billet burnt are eliminated, and only the value of uneven thickness ao caused by a defect in the mandrel mill is obtained.

Next, among the average wall thickness values in the axial direction of the pipe obtained as described above, the maximum value Dimaχ in the circumferential direction and the minimum value Di
Find the difference ΔDi from min (step ■), and calculate this deviation Δ
Determine whether or not D+ is greater than 1 to the predetermined reference value (Step ■). If it is smaller than 1 to the reference value, the uneven thickness due to a defect in the mandrel mill is determined to be within the allowable range and diagnosed. end. In addition, if the reference value is greater than 1, the rolling conditions of the mandrel mill are deemed to be defective and the conditions are readjusted (step ■). When the adjustment is completed, the production of the next tube is started (step ■), and the step Return to step (3) and repeat the above process, readjusting the mandrel mill until ΔDi becomes smaller than 1 to the reference value.

Next, the process of detecting whether or not there is uneven thickness due to a defective plug in the punching machine or uneven burnt on the pireno 1 will be described with reference to the flowchart shown in FIG. 4 and the explanatory diagrams shown in FIGS. 5(a) to 5(d). First, for the tube obtained in the same manner as in the case described above, as shown in FIG.
Determine the wall thickness of each part in the axial direction, and calculate the thickness of each part in the axial direction.
As shown in c), the total number of wall thickness data for the middle part excluding the top and bottom parts (from the broken line position to the top and bottom parts, respectively) is N (j=1...N).
, the installation interval of the data is Δβ, and the wall thickness distribution function ψ1(j, Δ
l), ψ2 (j, Δl) (step ■), and based on this, the cross-correlation function C12' (k
, Δl) is derived according to the formula below (step ■)
.

C+2(k, Δβ) However: Coefficient The reason why ψ2 on the right side in the above equation is set to ψ2 (+Δβ for j-) is that Δβ changes depending on the pipe size.

If there is an eccentricity of the plug in the punching machine or if the billet is burnt on one side, the wall thickness distribution of the obtained tube will depend on each factor as shown in Figure 5 (B).

Periodic thickness deviations as shown in (c) are formed. In other words, when looking at the wall thickness distribution in the axial direction of the pipe, Fig. 5 (d) and (
A peak of uneven thickness appears at a predetermined period as shown in e).

Now, as shown in Fig. 5 (d) and (e), if the distance from the reference position to the position showing the peak value of wall thickness in the axial direction of the tube is caused by the drilling machine, it is 1Δl, which is caused by billet burnt. If the case is 2Δl, then the cross-correlation function Cl2(k,
4g) are also C+2(k,, ΔA) and CI2, respectively.
It has a peak at (k2, Δl).

Therefore, on the other hand, the uneven thickness period due to the eccentricity of the plug of the punching machine, the billet side burning, etc. should be experimentally and empirically determined in advance.
is set, and the cross-correlation function Cl2(k, ΔI2
) has a peak value exceeding the reference value in the vicinity of (k) as shown in FIG.
), if it does not have a peak value, it is determined whether or not it has a peak value in the vicinity of step 2 (Step ■), similarly, if it does not have a peak value, it is due to a defective plug in the punching machine or burnt part of the billet. It is determined that there is no uneven thickness, in other words, there is no need to adjust or inspect the punching machine or billet heating furnace, and the diagnosis is completed.

On the other hand, if the peak value of 1 is higher than the standard value, it is detected that uneven thickness due to one-sided burnt of the billet has occurred.
Adjust the heating conditions for the billet heating furnace (step ■), and when the adjustment is completed, determine whether or not the peak value is present in step 2 (step ■). If the peak value is found, replace the plug of the drilling machine and make adjustments. (Step ■), manufacture the next seamless pipe (Step ■), and calculate the cross-correlation function Cl
Return to step (2) and repeat the above process until 2(k, Δβ) no longer has a peak value at any of kl+k2, and readjustment of the heating furnace and/or drilling machine is repeated. As mentioned above, when determining J, it goes without saying that it is determined by taking into consideration the perforation speed of the perforator and the subsequent rolling ratio of the rolling mill.

In addition, the process of the above-mentioned steps (1) to (2) is more specifically carried out as follows. That is, 01. Regarding the cross-correlation function obtained based on the wall thickness distribution function in each tube axis direction separated by θ2...θn, □±Δk (n=1.2) is within the judgment range empirically or experimentally obtained in advance. is set, and the cross-correlation function peak value Cl2(kl ′,
ΔIri, C,2(k2'.

Δ12), k, −Δk<k, '<k, +Δ, J−Δk
Find <k2'<k2→-Δk. Then, find such peak values for each cross-correlation function and divide them into multiple values.
The average value will be taken, and only if the average exceeds a predetermined value will the necessary measures be taken to improve the plug failure of the drilling machine and the failure of the heating furnace.

〔effect〕

As described above, in the method of the present invention, the wall thickness in the axial direction is measured at each of multiple locations in the circumferential direction of the manufactured pipe, and the degree and period of wall thickness deviation are calculated based on this wall thickness data. It is now possible to extract the characteristic wall thickness variation pattern for each cause of thickness imbalance and determine the presence or absence of each factor, making it possible to accurately and easily detect the cause of thickness imbalance and take appropriate measures. This not only greatly improves pipe quality, but also eliminates unnecessary inspections and
The present invention has excellent effects in that maintenance can be omitted and labor can be saved, and parts can be replaced at appropriate times, preventing unnecessary parts replacement and reducing parts costs. .

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the manufacturing process of a seamless pipe using a Mansuman mandrel mill to which the method of the present invention is applied; Fig. 2 is a block diagram of a wall thickness measuring device using electromagnetic ultrasonic waves;
Figure 4 is a flowchart 1-1 showing the process of determining factors for uneven thickness in the method of the present invention.
It is an explanatory diagram showing a diagnosis process of uneven thickness caused by Bile No. 1 - One-sided grilling & J. 1... Billet 2... Heating furnace 3... Drilling machine 4
... Mandrel mill 5 ... Reheating furnace 6 ... Stretch reducer 7 ... Cooling bed 10 ... Thickness measuring device 11, ], 2 ... Transmission and reception coils 20
・Arithmetic and control unit 30...Display unit patent Applicant: Sumitomo Metal Industries Co., Ltd. Agent Patent attorney: Noboru Kono Fugei Figure 3, Figure 4 (8) Screen, chopsticks 4, a ('') Shaft length direction ) (to) item

Claims (1)

[Scope of Claims] 1. Measure the wall thickness at multiple locations in the circumferential direction of a seamless pipe manufactured by drilling a billet using a punching machine and stretching and rolling the resulting raw pipe, at each location in the axial direction. Then, based on the measured values, the thickness distribution function in the longitudinal direction of each axis is determined for any two locations in the circumferential direction, a cross-correlation function is derived based on these thickness distribution functions, and a bias is calculated based on the cross-correlation function. A method for diagnosing uneven wall thickness of seamless pipes, which is characterized by determining the wall thickness factor. 2. Measure the wall thickness of each part in the axial direction at multiple locations in the circumferential direction of a seamless pipe manufactured by drilling holes in the billet using a punching machine and stretching and rolling the obtained raw pipe, and calculate the wall thickness at each part in the axial direction. Based on this, the thickness distribution function in the longitudinal direction of each axis is determined for two arbitrary points in the circumferential direction, a cross-correlation function is derived based on these thickness distribution functions, and the peak value of the cross-correlation function within a predetermined region is Judging whether or not it exceeds the established standard value, calculating the average value of the wall thickness in the longitudinal direction of each axis of the above measured values, and calculating the difference between the maximum value and the minimum value in the circumferential direction among the average values. A method for diagnosing a cause of uneven thickness of a seamless pipe, characterized by comparing the cause with another predetermined reference value and determining the cause of uneven thickness based on a judgment as to whether the difference exceeds the reference value.