JP7238836B2 - Steel pipe pass/fail judgment system and pass/fail judgment method, and steel pipe manufacturing method - Google Patents

Description

The present invention relates to a steel pipe pass/fail judgment system and pass/fail judgment method for judging acceptance/rejection of flaws on the outer and inner surfaces of a steel pipe and judging acceptance/rejection of the wall thickness of a steel pipe using ultrasonic flaw detection, and a steel pipe manufacturing method.

Conventionally, ultrasonic flaw detection has been used to inspect the presence or absence of flaws on the outer surface of steel pipes, the presence of flaws on the inner surface of steel pipes, and the strength of thick-walled pipes. Specifically, an ultrasonic inspection is performed by setting thresholds for the depth of flaws and the lower and upper limits for judging wall thickness. It is understood that there is an abnormality in the outer surface, inner surface, and wall thickness of the steel pipe. For this reason, acceptance/rejection of steel pipes is determined through inspection using ultrasonic flaw detection. For example, Patent Document 1 proposes a harmful defect determination method in ultrasonic flaw detection that can easily determine whether or not the defect is a harmful defect by combining the measurement results of vertical flaw detection and the measurement results of oblique flaw detection. .

On the other hand, ultrasonic flaw detection has long been used not only to determine the presence or absence of flaws in steel pipes and the wall thickness, but also as a pass/fail determination method for various metal materials such as round bars and steel strips. For example, Patent Document 2 proposes a pass/fail judgment method in ultrasonic flaw detection of a round bar as a flaw detection target. Further, Patent Document 3 proposes a pass/fail determination method for a steel strip used as a steel plate for cans.

Moreover, ultrasonic flaw detection is used not only for defects in the manufacturing process, but also for determining wall thickness defects in steel pipes due to corrosion and pitting corrosion. For example, in Patent Document 4, regarding a heat transfer tube used in a feed water heater or the like, it is possible to automatically determine whether or not a wall thickness defect that spreads is normal. We are proposing a system that enables wall thickness evaluation by stress evaluation and pitting corrosion evaluation of thick parts.

A steel pipe that is judged to be unacceptable for the depth of flaws on its outer surface or inner surface using ultrasonic flaw detection is then repaired, for example, by grinding the outer surface of the steel pipe if it fails for the depth of flaws on its outer surface. By doing so, ultrasonic flaw detection is used again to determine pass/fail.

Among typical flaws occurring in steel pipes, flaws determined by ultrasonic flaw detection include flaws due to material defects and flaws due to rolling. Most of the flaws due to material defects are angled with respect to the longitudinal direction of the steel pipe, while the flaws due to rolling are parallel to the longitudinal direction. Ultrasonic flaw detection judges linear or point-like flaws with a length of about 10 mm to 100 mm and a depth of about 0.2 mm. It is determined as "flawed".

JP 2003-222617 A JP 2007-271375 A JP 2010-25835 A JP 2009-8587 A

When a steel pipe that has been judged to be unacceptable by inspection using ultrasonic flaw detection is repaired, especially when grinding, the lower limit of wall thickness judgment becomes less than the threshold value due to grinding, and the pass/fail judgment using ultrasonic flaw detection is performed again. In this case, it may be rejected due to poor wall thickness. In this case, steel pipes that have no room for maintenance are to be repaired and re-inspected, and the process of making pass/fail judgments using ultrasonic flaw detection again becomes useless, resulting in a significant drop in steel pipe manufacturing efficiency.

On the other hand, if the lower limit threshold for wall thickness judgment is set in consideration of the room for grinding, there is a risk that even steel pipes that are originally acceptable will be rejected. It is not desirable to set the lower limit threshold for wall thickness determination in consideration of room as a wall thickness determination standard for steel pipes.

Patent Documents 1 to 4 described above describe how to determine the wall thickness of a steel pipe that has been rejected by an inspection using ultrasonic flaw detection, when the steel pipe is to be cleaned, for example, by grinding. do not have.

Therefore, the present invention prevents a steel pipe that has no room for maintenance from being repaired when acquiring information on flaws on the outer surface and inner surface of the steel pipe and the wall thickness of the steel pipe using ultrasonic flaw detection and making pass/fail judgments. To provide a technique that does not reject steel pipes that are originally acceptable.

In order to solve the above problems, the present invention provides the following [1] to [9].

[1] A steel pipe pass/fail judgment system that performs ultrasonic flaw detection to acquire information on flaws on the outer and inner surfaces of a steel pipe and the wall thickness of the steel pipe, and judges the pass/fail of the steel pipe,
a flaw determination unit that determines the presence or absence of flaws on the outer surface and the inner surface of the steel pipe;
a thickness determination unit that determines the thickness of the steel pipe;
a setting unit for setting a criterion for determining the thickness of the thickness determination unit;
has
The setting unit includes, as the determination criteria, a first thickness lower limit value applied when the flaw determination unit determines that there is no flaw, and a first wall thickness lower limit applied when the flaw determination unit determines that there is a flaw. and a second thickness lower limit that is greater than the first thickness lower limit,
A pass/fail determination system for a steel pipe, wherein when ultrasonic flaw detection is performed on the steel pipe, a wall thickness is determined based on different determination criteria depending on the presence or absence of the flaw.

[2] When ultrasonic flaw detection is performed on the steel pipe, the wall thickness determination unit sets the lower limit of the second wall thickness in a predetermined range including a portion determined to have a flaw by the flaw determination unit. The steel pipe pass/fail determination system according to [1], wherein the value is applied.

[3] When the flaw determination unit determines that there is a flaw, and the wall thickness determination unit determines that the wall thickness is equal to or greater than the second wall thickness lower limit value, maintenance of the steel pipe is performed. and if it is determined that the wall thickness is smaller than the lower limit value of the second wall thickness, the steel pipe is scrapped. system.

[4] The setting unit acquires the information on the flaw and changes the setting value of the lower limit value of the second wall thickness according to the depth of the inner surface flaw and the outer surface flaw [1] ] to [3].

[5] A steel pipe pass/fail judgment method for performing ultrasonic flaw detection to acquire information on flaws on the outer and inner surfaces of a steel pipe and the wall thickness of the steel pipe and making a pass/fail judgment for the steel pipe,
As a criterion for determining the thickness of the steel pipe in determining the thickness of the steel pipe, a first lower limit value of the thickness applied when it is determined that there is no flaw, and a first thickness lower limit value applied when it is determined that there is a flaw. A second thickness lower limit value greater than the first thickness lower limit value is set,
A method for judging acceptance/rejection of a steel pipe, wherein when the steel pipe is subjected to ultrasonic flaw detection, a wall thickness is judged according to a different judgment criterion depending on the presence or absence of the flaw.

[6] When ultrasonic flaw detection is performed on the steel pipe, the second wall thickness lower limit is applied in a predetermined range including a portion judged to have a flaw by the flaw judgment unit. The acceptance/rejection determination method for the steel pipe according to [5].

[7] When it is determined that there is a flaw by the ultrasonic flaw detection, and when the wall thickness is determined to be equal to or greater than the second lower limit value of the wall thickness, the steel pipe is repaired and the wall thickness is reduced. The steel pipe acceptance/rejection determination method according to [5] or [6], wherein the steel pipe is scrapped when it is determined that the wall thickness is smaller than the second lower limit value.

[8] Acceptance or rejection of the steel pipe according to any one of [5] to [7], characterized in that the set value of the lower limit value of the second wall thickness is changed according to the depth of the inner surface flaw and the outer surface flaw. judgment system.

[9] A method of manufacturing a steel pipe, wherein the steel pipe is manufactured by applying the steel pipe pass/fail determination method according to any one of [5] to [8] above.

In the present invention, as the criteria for determining the thickness of the steel pipe, the first thickness lower limit value applied when the flaw determination unit determines that there is no flaw, and the first thickness lower limit value applied when the flaw determination unit determines that there is a flaw. A second wall thickness lower limit that is greater than the applied first wall thickness lower limit is set, and when the steel pipe is subjected to ultrasonic flaw detection, the wall thickness is determined according to different criteria depending on the presence or absence of flaws. judgment is made. For this reason, it is possible to prevent a steel pipe with a thick wall that should be repairable from being consumed as a reject decision, and if repair (for example, grinding) is performed, the wall thickness will be rejected. It is possible to save waste by trimming (grinding) such steel pipes and again using ultrasonic flaw detection. Therefore, the steel pipe can be manufactured without deteriorating both accuracy of flaw determination and wall thickness determination and productivity.

1 is a block diagram showing a steel pipe acceptance/rejection determination system according to an embodiment of the present invention; FIG. FIG. 2 is a flow chart showing a steel pipe pass/fail judgment method executed by the steel pipe pass/fail judgment system of FIG. 1 ; FIG. FIG. 3 is a diagram showing an example of an investigation of how much the thickness of a steel pipe is actually reduced by grinding. It is a schematic diagram which shows the example of the applicable range of the lower limit (lower limit B) of the 2nd thickness of thickness. FIG. 10 is a diagram showing an example of determination of no maintenance fee/scrap when the second lower limit value (lower limit value B) of the wall thickness in the present invention is applied.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a steel pipe acceptance/rejection determination system according to an embodiment of the present invention, and FIG. 2 is a flow chart showing a steel pipe acceptance/rejection determination method executed by the system of FIG.

A steel pipe acceptance/rejection determination system 1 includes a flaw determination unit 2 , a wall thickness determination unit 3 , a setting unit 4 , and an output unit 5 . The steel pipe pass/fail determination system 1 performs ultrasonic flaw detection on the steel pipe using an ultrasonic flaw detector 10 to acquire information on flaws on the outer and inner surfaces of the steel pipe and on the wall thickness of the steel pipe.

The flaw determination unit 2 acquires flaw information of the steel pipe from the ultrasonic flaw detector 10 and determines whether or not there is a flaw in the steel pipe. The flaw judging section 2 judges linear or point-like flaws with a length of about 10 mm to 100 mm and a depth of about 0.2 mm or more, and the judgment criterion is a flaw of 5% or more of the thickness. is determined to be "flawed".

The wall thickness determination unit 3 acquires wall thickness information of the steel pipe from the ultrasonic flaw detector 10 and determines whether or not the wall thickness satisfies the determination criteria.

The setting unit 4 uses, as a thickness determination criterion, a first thickness lower limit value (lower limit value A) applied when the flaw determination unit 2 determines that there is no flaw, and a flaw determination unit 2 determines whether there is a flaw. A second thickness lower limit value (lower limit value B) that is greater than the first thickness lower limit value that is applied when it is determined that

The thickness determination unit 3 determines the thickness based on the first thickness lower limit value and the second thickness lower limit value set as the thickness determination criteria in the setting unit 4 .

Specifically, the thickness determination unit 3 acquires the determination information of the flaw determination unit 2, and when the flaw determination unit 2 determines that there is no flaw, the first thickness lower limit value is used as a determination criterion. (Lower limit value A) is used to determine the wall thickness to determine whether the wall thickness is acceptable or unacceptable. On the other hand, when the flaw determination unit 2 determines that there is a flaw, that is, when the flaw determination is unacceptable, the thickness is determined using the second thickness lower limit (lower limit B) as the determination criterion. Then, it is determined whether the steel pipe is subjected to maintenance such as grinding or scrapped. The determination result of the thickness determination unit 3 is output from the output unit 5 .

Next, the acceptance/rejection determination method at this time will be described in detail with reference to FIG.
First, the lower limit values (lower limit values A and B) of the first and second thicknesses are set by the setting unit 4 as criteria for thickness determination (step ST1). Next, ultrasonic flaw detection is performed using the ultrasonic flaw detector 10 to acquire flaws and wall thickness information (step ST2).

Based on the acquired flaw information, the flaw determination unit 2 determines whether or not there is a flaw (step ST3). When it is determined that there is no flaw, the thickness determination section 3 determines whether or not the thickness of the steel pipe is equal to or greater than the first lower limit value (lower limit value A) of the thickness (step ST4). If the thickness is equal to or greater than the lower limit value (lower limit value A) of the first thickness, the output unit 5 outputs a determination result of "accepted". On the other hand, when the thickness is smaller than the lower limit value (lower limit value A) of the first thickness, the output unit 5 outputs a determination result of “fail”. When the flaw determination unit 2 determines that there is a flaw, the thickness determination unit 3 determines whether the thickness of the steel pipe is above the second lower limit value (lower limit value B) of the thickness (step ST5). If the wall thickness is equal to or greater than the second lower limit value (lower limit B) of the wall thickness, it is determined that the steel pipe has a "maintenance allowance" (for example, there is a grinding allowance), and the output section 5 indicates "a maintenance allowance". is output. In this case, the steel pipe is repaired (for example, by grinding), and the ultrasonic flaw detection is performed again. On the other hand, if the wall thickness is smaller than the second wall thickness lower limit value (wall thickness lower limit value B), it is determined that there is no "maintenance allowance" for the steel pipe, and the determination result of "no maintenance allowance" is output from the output unit 5. is output. In this case, the steel pipe is scrapped without any maintenance.

In the present embodiment, the same automatic ultrasonic flaw detector 10 is used for flaw detection and wall thickness measurement of the steel pipe. , may be performed on separate devices.

FIG. 3 shows an example of an investigation of how much the thickness of a steel pipe is actually reduced by grinding treatment in carrying out the above method. It is desirable to set the second wall thickness lower limit (lower limit B) by previously investigating the amount of grinding as shown in FIG. If the lower limit value B is set excessively, even steel pipes with sufficient maintenance allowance must be discarded, which is a factor in lowering production efficiency. For example, in the example of FIG. 3, grinding a portion of a steel pipe having a thickness of 4.68 mm results in a thickness of 4.43 mm, and the amount of thickness reduction due to grinding is 0.25 mm. Therefore, assuming that the 4.68 mm thick portion is within the range of "flawed" and must be ground for maintenance, the thickness of 4.43 mm after grinding is an allowable thickness. The question is whether. For example, if the lower limit of the wall thickness allowed after grinding is 4.5 mm, the second lower limit of the wall thickness (lower limit B) is 4.75 mm, and in the example of FIG. Become.

In this embodiment, when the ultrasonic flaw detection fails, it is determined whether it is appropriate to perform maintenance of the steel pipe, for example, grinding, and then perform ultrasonic flaw detection again. In order to prevent sonic flaw detection from being wasted, two lower limits (first and second lower limits of thickness (lower limits A, B)) are provided as criteria for determining thickness. there is At this time, the lower limit value (lower limit value B) of the second wall thickness may be uniformly set as in the above example, but it is more reliable to prevent the maintenance of the steel pipe and the ultrasonic flaw detection again from being wasted. From the viewpoint of prevention, the setting unit 4 acquires flaw information and changes the set value of the lower limit value (lower limit value B) of the second wall thickness according to the depth of the inner surface flaw and the outer surface flaw. It is desirable to

Ultrasonic flaw detection is preferably performed over almost the entire length of the steel pipe except for the dead zone, which is a section where ultrasonic flaw detection cannot be performed. When it is determined that there is a "flaw", the lower limit value B can be applied within a predetermined range before and after the flaw. For example, as shown in FIG. 4, when 20 mm is defined as one section and it is determined that there is a flaw in the section, the lower limit value B is applied to a section of 20 mm before and after that section. In other words, the applicable range of the lower limit value B, which is the second lower limit value of the thickness, is 60 mm, including the portion with the flaw. On the other hand, the lower limit A, which is the lower limit of the first wall thickness, can be applied to the entire length of the steel pipe for ultrasonic flaw detection.

As described above, in the present embodiment, the first wall thickness lower limit value (lower limit value A) applied when the defect determination unit determines that there is no defect, and A second thickness lower limit value (lower limit value B) that is larger than the first thickness lower limit value applied when the determination unit determines that there is a flaw is set, and different determinations are made depending on the presence or absence of flaws. Judgment of wall thickness is performed according to the standard. Therefore, it is possible to prevent a steel pipe having a wall thickness that should be repairable from being consumed without a maintenance fee. In addition, it is possible to eliminate waste caused by cleaning (grinding) a steel pipe whose wall thickness would be rejected by cleaning (for example, grinding) and using ultrasonic flaw detection again. Therefore, the steel pipe can be manufactured without deteriorating both accuracy of flaw determination and wall thickness determination and productivity.

Next, examples will be described.
Here, for all the steel pipes subjected to ultrasonic flaw detection, the ratio of the steel pipes that were thinner than the lower limits A and B and were judged to be rejected was examined over a period of about one month. The results will be described with reference to Table 1. do. The steel pipe subjected to ultrasonic flaw detection had an outer diameter of 60.3 to 177.8 mmφ and a wall thickness of 4.0 to 40.5 mm.

At this time, if the lower limit of the wall thickness of the required specification is, for example, 6.02 mm, the lower limit of the wall thickness A is set to +0.13 mm of the required specification, that is, 6.15 mm, and the lower limit of the wall thickness is B was set to 6.30 mm by adding 0.15 mm to the lower limit A. FIG. 5 shows an example of a steel pipe judged to be "no maintenance fee/scrap" under these conditions. That is, in the example of FIG. 5, the wall thickness is 6.22 mm with "flaw", which is below the lower limit B of 6.30 mm, so the determination is "no maintenance fee/scrap".

In Table 1, the lower limit value B is set variously, and in the pass/fail judgment by ultrasonic flaw detection of steel pipes, for all steel pipes subjected to ultrasonic flaw detection, among the steel pipes in which flaws were found by ultrasonic flaw detection, shows the percentage of steel pipes below the lower limits A and B of . Here, the value of the lower limit A was unchanged at +0.13 mm, and the value of the lower limit B was changed, and the number of steel pipes below the lower limit B was investigated for one month. In Table 1, the value of the lower limit B is described as an increase from the lower limit A, and is in the range of +0.15 to +0.3.

As shown in Table 1, 1.5% of all the steel pipes subjected to ultrasonic flaw detection are below the conventional lower limit value A. On the other hand, if the percentage of steel pipes below the lower limit B is, for example, 0.15%, compared to before the implementation of the present invention, the operational waste due to maintenance, grinding, and re-implementation of ultrasonic flaw detection of steel pipes is reduced by 1. It can be said that it was possible to save it.

From Table 1, by setting the lower limit B to +0.30 mm, 0.36% of the steel pipes were rejected because they fell below the lower limit B in wall thickness. Compared with the ratio of the steel pipes falling below the lower limit A, it means that 24% of the waste of performing maintenance and performing ultrasonic flaw detection again was able to be saved. However, the larger the value of the lower limit B is, the more the steel pipes, which are supposed to pass after maintenance and grinding, are rejected. In this example, the target value was set at 0.24%. As a result, the target was achieved when the lower limit B was +0.30 mm. For this reason, the lower limit B was set to +0.30 mm as an optimum value. This target value can be appropriately set in consideration of the maintenance and grinding amount to be reduced.

In the present invention, a steel pipe whose wall thickness falls below the lower limit after maintenance (grinding) is determined by determining the lower limit value B before maintenance (grinding). However, as can be seen from FIGS. 3 and 5 described above, since the amount of wall thickness reduction due to grinding has a large fluctuation range, if the lower limit value B is set to a larger value, even a steel pipe with sufficient grinding allowance can be rejected. (Grinding is not possible). For this reason, the optimum thickness determination is to investigate the amount of grinding in detail, and if possible, consider the lower limit of thickness for the steel type and required specifications, and set the lower limit B one by one. be.

Although the embodiments and examples of the present invention have been described above, they should be considered as merely illustrative and not restrictive. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the gist of the present invention.

1 steel pipe pass/fail determination system 2 flaw determination unit 3 wall thickness determination unit 4 setting unit 5 output unit

Claims (9)

A steel pipe pass/fail judgment system for performing ultrasonic flaw detection to acquire information on flaws on the outer and inner surfaces of a steel pipe and the wall thickness of the steel pipe, and making a pass/fail judgment of the steel pipe,
a flaw determination unit that determines the presence or absence of flaws on the outer surface and the inner surface of the steel pipe;
a thickness determination unit that determines the thickness of the steel pipe;
a setting unit for setting a criterion for determining the thickness of the thickness determination unit;
has
The setting unit includes, as the determination criteria, a first thickness lower limit value applied when the flaw determination unit determines that there is no flaw, and a first wall thickness lower limit applied when the flaw determination unit determines that there is a flaw. and a second thickness lower limit that is greater than the first thickness lower limit,
A pass/fail determination system for a steel pipe, wherein when ultrasonic flaw detection is performed on the steel pipe, a wall thickness is determined based on different determination criteria depending on the presence or absence of the flaw. When the steel pipe is subjected to ultrasonic flaw detection, the wall thickness determination unit applies the second wall thickness lower limit to a predetermined range including the portion determined to have a flaw by the flaw determination unit. The acceptance/rejection determination system for steel pipes according to claim 1, characterized in that: When the flaw determination unit determines that there is a flaw and the wall thickness determination unit determines that the wall thickness is equal to or greater than the second lower limit value of the wall thickness, the steel pipe is repaired, 3. The steel pipe acceptance/rejection determination system according to claim 1 or 2, wherein the steel pipe is scrapped when it is determined that the wall thickness is smaller than the lower limit value of the second wall thickness. 1 to 4, wherein the setting unit acquires the information on the flaw and changes the setting value of the lower limit value of the second wall thickness according to the depth of the inner surface flaw and the outer surface flaw. Item 4. The acceptance/rejection determination system for the steel pipe according to any one of Item 3. A steel pipe pass/fail determination method for performing ultrasonic flaw detection to acquire information on flaws on the outer and inner surfaces of a steel pipe and the wall thickness of the steel pipe, and determining pass/fail of the steel pipe,
As a criterion for determining the thickness of the steel pipe in determining the thickness of the steel pipe, a first lower limit value of the thickness applied when it is determined that there is no flaw, and a first thickness lower limit value applied when it is determined that there is a flaw. A second thickness lower limit value greater than the first thickness lower limit value is set,
A method for judging acceptance/rejection of a steel pipe, wherein when the steel pipe is subjected to ultrasonic flaw detection, a wall thickness is judged according to a different judgment criterion depending on the presence or absence of the flaw. The second wall thickness lower limit is applied to a predetermined range including a portion determined to have a flaw by the flaw determination unit when ultrasonic flaw detection is performed on the steel pipe. The acceptance/rejection determination method for the steel pipe according to claim 5. When it is determined that there is a flaw by the ultrasonic flaw detection, and when the wall thickness is determined to be equal to or greater than the second lower limit value of the wall thickness, the steel pipe is repaired, and the wall thickness is reduced to the second wall thickness. 7. The steel pipe acceptance/rejection determination method according to claim 5 or 6, wherein the steel pipe is scrapped when it is determined that the wall thickness is smaller than the lower limit of the wall thickness. 8. The acceptance/rejection determination of the steel pipe according to any one of claims 5 to 7, wherein the set value of the lower limit value of the second wall thickness is changed according to the depth of the inner surface flaw and the outer surface flaw. Method. A method for manufacturing a steel pipe, wherein the steel pipe is manufactured by applying the steel pipe pass/fail determination method according to any one of claims 5 to 8.

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