JPH11271046A - Inspection method for dimension of metal pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inspection method in which judgment information on a reinspection or on a production-process inspection is obtained by a method wherein a metal pipe is divided into a plurality of sections in the length direction, the amplitude of the maximum dimension and the minimum dimension of the respective sections is found, the mean value of the dimensions is found and whether a specific condition is true or not is judged with reference to a predetermined amplitude tolerance, a predetermined amplitude-difference tolerance and a predetermined level tolerance. SOLUTION: A steel pipe 1 is immersed in a water tank 3, and it is turned while it is being conveyed to the transverse direction by conveyance devices 2. An ultrasonic measuring device 4 measures the outside diameter, the inside diameter and the wall thickness of the steel pipe 1. Then, the steel pipe 1 is divided into a plurality of sections in the length direction. The amplitude of the maximum dimension and the minimum dimension of the respective sections is found, and the mean value of the dimensions is found. Then, whether two conditions are true or not is judged out of four conditions, i.e. A) the amplitude of the sections ia larger than an amplitude tolerance, B) the difference between a maximum section amplitude and a minimum section amplitude is larger than an amplitude difference torenace, C) the difference between the section averages of the steel pipe 1 divided into two equal parts is larger than a level tolerance and D) the difference between section averages of the steel pipe 1 divided into three equal sections is larger than the level tolerance, with reference to a predetermined amplitude tolerance, a predetermined amplitude tolerance and a predetermined level tolerance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting dimensions of a metal tube, and more particularly to a steel tube having strict dimensional accuracy and quality control standards.
The present invention relates to a method for inspecting dimensions of high alloy pipes and non-ferrous pipes.

[0002]

2. Description of the Related Art Steel pipes for aerospace, military, nuclear, etc.
High alloy pipes and non-ferrous pipes (titanium, copper and their alloy pipes) require much stricter quality than general applications.

[0003] In the production specifications of these metal tubes, inspection standards for the production process are determined based on customer standards (quality standards), and quality control is performed in accordance with the standards. The above-mentioned high-quality metal pipes are often required to be inspected in their entirety and in their entire length, and in many cases, it is necessary to store detailed measurement conditions and measurement results at the time of inspection.

[0004] In quality inspection of metal tubes, the outer diameter, inner diameter,
Inspection of dimensions such as wall thickness is the most common, and usually defines control limits (upper limit, lower limit) and judges pass / fail. In the case of the above-mentioned high-quality metal tube, the pattern of the dimensional chart may become a problem even within the dimensional control limit. The reason is that even if the dimensions are within the control limits for the application,
This is because there is an empirical fact that if there is any defect in the internal quality or the manufacturing process, it will appear in the dimensional fluctuation.

[0005] In order to manage such a pattern of dimensional fluctuation, a method is generally used in which an inspector visually judges a dimensional chart, and there is an advantage that it can flexibly cope with various inspection standards. Human error is inevitable. Further, the accuracy of the above-mentioned visual judgment data is insufficient for collecting quality data for elucidating the cause of the occurrence from the pattern of the dimensional variation that occurs typically.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for inspecting dimensions by spirally scanning a metal tube, particularly for a high-quality metal tube, to determine the type of dimensional variation abnormality, The purpose of the present invention is to provide information that contributes to the judgment of inspection and the judgment of inspection of the manufacturing process, or to provide data that contributes to quality statistical analysis.

[0007]

FIG. 1 is a schematic diagram showing an example of the configuration of an inspection apparatus using a steel pipe as an example. The steel pipe 1 is, for example,
Seamless steel pipe, hot rolled, cold rolled, cold drawn,
It is one that has gone through steps such as straightening, pickling, and polishing.

In the inspection process, the steel pipe 1 is immersed in a water tank 3 and is rotated by the transport device 2 while being transported in the lateral direction. The detector 4 is a sensor of an ultrasonic dimension measuring device, and measures an outer diameter, an inner diameter, and a wall thickness of the steel pipe 1. The inspection control device 5 makes a pass / fail judgment of the outer diameter, the inner diameter, and the wall thickness based on a normal management standard, and outputs the result to a printer (not shown) and a display (not shown).
Alternatively, information is transmitted to a host computer (not shown).

The absolute value of the outer diameter, the inner diameter, or the wall thickness is checked by the pass / fail judgment of the normal control limit as described above.
However, even when the dimensions are within the control limits, a peculiar pattern appears on the dimension chart, which may be linked to the cause estimation of the manufacturing process.

FIG. 2 is a graph showing main abnormal patterns in a chart of dimensions (outer diameter, inner diameter or thickness).

[0011] Since the steel pipe is scanned in a spiral shape, N in FIG.
o. Nos. 1-3 and No. As shown in the first half of FIG. 4, the width fluctuates in the rotation cycle of the steel pipe 1 with a width corresponding to the difference between the maximum outer diameter and the minimum outer diameter. If the outer diameter or inner diameter is flat, or if the wall thickness is uneven (the wall thickness differs depending on the circumferential part),
The chart fluctuates in a pattern as shown. This pattern having a large amplitude is called, for example, an A type.

In FIG. 2, 4, and 5 have large amplitude portions and small amplitude portions. For example, this is due to the eccentricity of the rolling roll, a defect in the cold working process, and the like, and such a mixed pattern of the amplitudes is called, for example, a B type.

In FIG. Nos. 6 to 9 have different dimensional levels between the first half and the second half. For example, it is considered that this is caused by a defect in the pickling process or the polishing process. There is also a protruding abnormality at the pipe end. Such a case where there is a difference in dimensional level between the first half and the second half is called a C type.

In FIG. In FIG. 10, there is a difference in the dimensional level between the first half, the middle part, and the second half, and a V-shaped pattern is formed. It is considered to be caused by defective jigs and tools in the cold rolling or cold drawing process, defective handling, and the like. Such a V-shaped or (mountain-shaped) pattern is called a D type.

In FIG. No. 1 central part, and No. 1 4
The sharp peak seen at the left edge of the may be due to detector noise or extraneous foreign matter, or a small dent. This abnormal pattern is called, for example, N type. The inventors attempted to categorize these fluctuation patterns, corresponded to the causes thereof, and arranged as follows.

(A) In order to express the fluctuation range of the chart, it is better to represent the fluctuation range of the chart with the range between the maximum value and the minimum value than with the standard deviation, and to match the visual judgment. (b) The type A abnormality may be managed by determining whether the dimensional variation (amplitude) of the outer diameter, the inner diameter, or the thickness is within a predetermined range.

(C) The abnormality of the B type may be determined by dividing the steel pipe into a plurality of sections and determining whether there is a difference in amplitude between sections. (d) Since the abnormality of the C type appears as a gradual change in the average dimension over the entire length of the steel pipe, it is sufficient to compare the dimensional levels in the first half and the second half of the steel pipe.

(E) The abnormalities of the D type are the first half, the center,
What is necessary is just to compare the dimensional level in the latter half. (f) For an N-type abnormality, it may be determined whether or not the moving average in a narrow section width is significantly different from the preceding and following section average levels.

Based on the above findings, the gist of the present invention is as follows. (1) In a method of inspecting dimensions by spirally scanning a metal pipe, the metal pipe is divided into a plurality of sections in the longitudinal direction, and the amplitude of the maximum and minimum dimensions of each section (section amplitude) and the The average value (section average) of the dimensions is obtained, and the authenticity of at least two of the following conditions (A) to (D) is determined for the predetermined amplitude allowable value, amplitude difference allowable value, and level allowable value. Dimension inspection method for metal pipes, characterized by identifying the type of abnormality. (A) The section amplitude of any section is larger than a predetermined amplitude allowable value. (B) The difference between the maximum section amplitude and the minimum section amplitude in any section is larger than a predetermined amplitude difference allowable value. (C) Divide the total length of the metal tube into two equal parts,
The difference between the average of the section averages of the division and the average of the other section averages is larger than a predetermined level allowable value. (D) Divide the total length of the metal tube into three equal parts, and １ ／ of the sum of the average of the section average of the first division and the average of the section average of the third division
And the average of the section averages of the second division are greater than a predetermined level allowable value.

(2) The difference between the moving average of a plurality of continuous dimension values smaller than the number of dimension measurements of the section and the section average of the section relating to the plurality of dimension values is larger than a predetermined noise allowable value. The dimension inspection method for a metal tube according to the above mode (1), wherein the method is determined as noise.

The terms of the section amplitude, section average, and moving average of the present invention will be described below. Although the outer diameter dimension will be mainly described, the same applies to the inner diameter, wall thickness, or other dimensions.

[0022] FIG. 3 is a schematic view showing a method of dividing the total length of the metal tube in the present invention in section C _i. As shown in the figure, the total length of the metal pipe is set to N _P sections C _i (i = 1 to 1).
N _P ).

FIG. 4 is a schematic diagram showing a method of collecting dimensional data according to the present invention. As shown in FIG. 4, for collecting the one section C _i N _C-number of outer diameter data _{D j (j = 1~N C)} .

In FIG. 4, the section amplitude is a certain section C
In _i, the maximum value of the outer diameter data D _j D _max, the minimum value and D _min, as B _i = D _max -D _min, defines a section amplitude B _i. Instead of defining the section amplitude B _i by the difference between D _max and D _min as described above, it is made dimensionless and B _i
= _Dmax / _Dmin .

The section average is the average value of the outer diameter data of the section C _i , and defines the section average (M _i ) as M _i = (1 / N _C ) ΣD _j (in FIG. 4, N _C = shown as the average of eight dimension data).

The moving average is a data sampling section having a width indicated by K as shown by Mref in FIG. 4 (moving average section width. In FIG. 4, the number of data at K is exemplified by 5). an average size of at, D ₁ of the start point of the moving average section width K is C ₁ interval, D _2, ... D _8, then D _1, D ₂ of C ₂ sections, and ..., sequentially moved Go. The moving average section width K (data count) is the width of the section C _i (data count)
Shall be smaller.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION A steel pipe is spirally scanned to measure dimensions, and the section amplitude, section average, and moving average are obtained as described above, and then the following judgment is made.

FIG. 5 is a flowchart showing the abnormality determination method of the present invention. Referring to the flowchart of FIG.
The method of determining the dimension pattern of each step (S1, S2.
).

S1. In accordance with the specification of the metal tube, a predetermined allowable value is found from a constant table.

S2. The outer diameter data is collected, and the section amplitude, the section average value, and the moving average are prepared.

S3 to S4. This is the amplitude abnormality determination step. For a predetermined amplitude allowable value Bmax, B _i >
Bmax, however, i = 1 to N _P, if at least one the section C _i satisfying, this is a determination of the type A. According to this determination method, No. 1 in FIG. The outer diameter patterns 1, 3, 5, and 8 are determined to be Type A abnormalities.

S5-6. This is a determination step in a case where a part having a large amplitude and a part having a small amplitude are mixed. Against predetermined amplitude difference tolerance _{Bdif, Max (B i) -Min} (B i)> Bdif, where a _{i = 1~N P, Max (B} i) is the B _i over the steel pipe total length maximum value, Min (B _i) is, the B _i
(Hereinafter the same), it is determined that the amplitude difference is abnormal. This is a type B determination. According to this determination method, No. 1 in FIG. The outer diameter patterns 2, 4, and 5 are determined to be Type B abnormalities.

S7-8. This is a determination as to whether there is a difference (variation in the outer diameter level) in the average outer diameter between the first half and the second half of the steel pipe.

As shown in FIG. 3, the overall length of the steel pipe is divided two equal, the average M1 of interval average M _i for the first division, the second
The average M2 of interval average M _i of the _{divided, M1 = (1 / N 2} ) ΣM i, _{however, i = 1~N 2 M2 = (} 1 / N 2) ΣM i, however, i = (N ₂ +1) ＮN _P.

[0035] Here, N ₂ is the maximum integer not exceeding N _P / _2, N 2 = denoted as [N _P / 2].

When | M1−M2 |> L2 is satisfied with respect to the predetermined dimension level tolerance L2 of two divisions, it is determined that the dimension level fluctuation of the two divisions is abnormal. This is determined as type C. According to this determination method, No. 1 in FIG. Outer diameter pattern of 6 to 9 is type C
Is determined to be abnormal.

S9-10. This is to determine whether there is a change in the outer diameter level in the first half, center, and second half of the steel pipe.

As shown in FIG. 3, by dividing the total length of the steel pipe 3, etc., the average M1 of the mean value M _i for the first division, on average M2, and the third division of the average value M _i for the second division the average M3 of the mean value _{M i, M1 = (1 /} N 3) ΣM i, (i = 1~N 3) M2 = (1 / N 3) ΣM i, (i = (N 3 +1) ~2N
₃ ) M3 = (1 / N ₃ ) ΣM _i , (i = (2N ₃ +1) 〜3
N ₃ ). Here, N ₃ = a [N _P / 3].

When | ((M1 + M3) / 2) −M2 |> L3 is satisfied with respect to the predetermined outer diameter level tolerance L3 of three divisions, it is determined that the dimensional level fluctuation of the three divisions is abnormal. This is determined as type D. According to this determination method, No. 1 in FIG. The dimension pattern of No. 10 is determined to be Type D abnormality.

Next, a noise determination method will be described.
4, the number of data of moving average size included in the section width K measurements shall less than the number data of the section C _i. For example, in FIG. 4, the number of data in the section is 8, whereas the number of data in the moving average section width is 5. That is, the number of data of the moving average section width for noise determination must be smaller than the number of data in the section.

The moving average value in a certain moving average section is represented by Mref
Then, | M _i −Mref | shown in FIG. 4 is compared with a predetermined noise determination level Lnoise, and if it is larger than this, it is determined that Type N is abnormal (noise determination). According to this determination method, No. 1 in FIG. The dimension patterns 1 and 3 are determined to be type N abnormalities. Further, the moving average section width K is sometimes taken across section C _i and C _{i + 1.} In that case, a large number of data may be compared with the moving average interval average M _i of the section belonging to harvesting.

In the above data collection, when the dimension measurement becomes unstable at the extreme end of the steel pipe, it is desirable to appropriately use only the stable portion as the dimension measurement data.

In the present invention, the section number N _P of the entire length of the steel pipe is determined in consideration of the overall length of the steel pipe, dimensional accuracy, fluctuation behavior, and the like, so that the width of the section is about 50 to 200 mm. Then, since the workability at the time of re-inspection is good, the length 4
For a steel pipe of about 10 to 10 m, it is preferable that N _P = about 10 to 500 sections, and more preferably, 20 to 200 sections.

The number of data collected in one section is limited by the measurement space of the detector, the response speed, the transfer speed of the steel pipe, the rotation speed, etc. However, as much data as possible to detect flat deformation, local dents, etc. It is desirable to collect That is,
For spiral scanning, 4 to 16 data can be collected per round, and it is preferable to measure at a pitch of 5 to 50 mm in the longitudinal direction. It is preferable to collect data at a pitch of 10 to 20 mm.

When the above-described procedure is executed, as shown in FIG. 2, each dimensional abnormal pattern is identified as an abnormal type in the right column, and data processing becomes easy. These anomalies do not necessarily imply rejection of individual metal tube products. Rather, it can be used actively for quality control, and the metal tube identified as abnormal can be re-examined later, or the production process can be inspected as a sign of any abnormality in production. It is desirable to take actions such as repairing. In addition, inspection data can be accumulated, and these abnormality identification data can be statistically processed and used for quality control.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Software for a metal pipe inspection method of the present invention was incorporated in an inspection control device 5 shown in FIG. The steel pipe to be inspected was a stainless steel pipe having an outer diameter of 10.7 mm, a wall thickness of 9.4 mm, and a length of 4.0 m. The dimensional inspection control range of the steel pipe according to the standard was an outer diameter tolerance of ± 0.04 mm. The outer diameter of this steel pipe was inspected by an inspection apparatus shown in FIG.

The steel pipe is fed in the axial direction at 1 cm per rotation. Eight data points are collected per rotation. One section was about 1 cm, and the number of data per section was eight. Therefore, the entire length of the steel pipe was divided into about 400 sections. The moving average section was an average of four data.

In the inspection method of the present invention, the allowable value of the variation (amplitude) of the outer diameter is set to の of the outer diameter tolerance. The permissible level is 1/3 of the outer diameter tolerance in two divisions, and the permissible level in three divisions is 1 of the outer diameter tolerance.
/ 4.

About 400 steel pipes were inspected, and the inspection result by the inspection apparatus of the present invention and the inspection result by visual judgment were compared.

First, the result of the automatic inspection by the inspection method of the present invention and the inspection result by the visual judgment were collated at the same time, and then the visual judgment was again performed on the steel pipe in which both the judgment results did not match.

Table 1 shows the comparison result of the first automatic inspection / visual judgment and the comparison result of the second automatic inspection / visual inspection. As shown in the table, in each abnormal pattern, in the first test, the automatic inspection according to the method of the present invention and the visual judgment inspection did not match well, but the visual reexamination matched well with the automatic inspection, and the inspection according to the present invention. It was found that the method was more accurate than the normal visual judgment.

[0052]

[Table 1]

[0053]

According to the method of the present invention, it is possible to automate a high-quality metal pipe, improve the inspection accuracy, and automatically collect data for quality control. Can be greatly contributed to.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a steel pipe inspection device.

FIG. 2 is a graph showing a pattern of a dimension measurement chart.

FIG. 3 is a schematic view showing a method of dividing the entire length of a metal tube into sections according to the present invention.

FIG. 4 is a schematic diagram showing a method of collecting dimension data according to the present invention.

FIG. 5 is a flowchart illustrating an abnormality determination method according to the present invention.

[Explanation of symbols]

1 steel pipe 2 conveying device 3 water tank 4 detector 5 test controller D dimension data N _P interval number N _C data acquisition number C _i sections B _i interval amplitude D _max the maximum outer diameter D _min minimum outer diameter M _i interval average K moving average Section width Mref Moving average

Claims (2)

[Claims] In a method for inspecting dimensions by spirally scanning a metal tube, the metal tube is divided into a plurality of sections in a longitudinal direction, and amplitudes (section amplitudes) of maximum and minimum dimensions of each section and each of the sections are determined. The average value of the section size (section average) is determined, and the authenticity of at least two of the following conditions (A) to (D) is determined for the predetermined amplitude allowable value, amplitude difference allowable value, and level allowable value. A method for inspecting dimensions of a metal tube, characterized by determining and identifying the type of abnormality. (A) The section amplitude of any section is larger than a predetermined amplitude allowable value. (B) The difference between the maximum section amplitude and the minimum section amplitude in any section is larger than a predetermined amplitude difference allowable value. (C) Divide the total length of the metal tube into two equal parts,
The difference between the average of the section averages of the division and the average of the other section averages is larger than a predetermined level allowable value. (D) Divide the total length of the metal tube into three equal parts, and １ ／ of the sum of the average of the section average of the first division and the average of the section average of the third division
And the average of the section averages of the second division are greater than a predetermined level allowable value. 2. When a difference between a moving average of a plurality of continuous dimension values smaller than the number of dimension measurements of a section and a section average of a section related to the plurality of dimension values is larger than a predetermined noise allowable value. 2. The method according to claim 1, wherein the noise is determined to be noise.