KR102328306B1 - Method for estimating seam weld penetration depth - Google Patents

Abstract

The present invention provides a method for estimating the penetration depth of a three-ply seam weld: (A) A probability distribution is obtained by assuming that the relationship between the welding width (La) and the penetration depth (P) of the nugget stored in the DB is a bivariate normal distribution. obtaining; (B) obtaining an estimated defective rate curve of P according to La based on a preset acceptance criterion (AC) value of P using the bivariate normal distribution; and (C) comparing the estimated defective rate curve of P according to La and a preset self-quality determination defect rate criterion to obtain a value La that does not exceed the self-quality determination defect rate criterion.
Accordingly, the possibility of field application as a quality inspection of seam welds through a non-destructive inspection method in the manufacture of LNGC cargo holds is very high, and there is an effect that can reduce time and cost.

Description

{Method for estimating seam weld penetration depth}

The present invention relates to a welding process for a ship, and more particularly, to a method for estimating the depth of penetration of a seam weld by performing a welding part daily test as a quality inspection for the production of an LNG cargo hold.

Seam welding accounts for approximately 90% of the manufacturing process of LNGC cargo holds, and has a large and direct impact on productivity. In general, the condition of the equipment is checked through testing before the actual production of LNGC cargo holds. This includes the process of test welding, specimen inspection, cross-section analysis, and report writing. In this process, quality check through periodic cut analysis for inspection of seam welds is usually accompanied, resulting in a lot of time and cost.

As prior art documents that can be referenced in this regard, the following Korean Patent Application Laid-Open No. 2001-0041402 (Prior Document 1), Korean Patent Application Publication No. 0237153 (Prior Document 2), and the like are known.

Prior Document 1 is a method for inspecting a weld seam of a weld joint, the height of the weld seam passing through the weld seam is continuously scanned to detect the disadvantages of the welding, the disadvantages of the weld seam are detected in the area of excess height of the weld seam, and the height of the weld seam It is scanned with a visual distance measuring device. Accordingly, an effect of simply and reliably detecting a disadvantage of welding during deep welding is expected.

Prior Document 2 measures welding voltage E, welding current I, electrode pressing force P, welding speed S, and lap quantity L, and calculates unit lap quantity and heat input per unit plate width dQ/dx based on this, and calculates the material and thickness of the welded object. A standard set value and an allowable range for the measured and calculated values are respectively set and compared, and when it is out of the allowable range, the welding quality is judged to be abnormal.

However, according to the above-mentioned prior literature, seam welding reveals a limitation in reducing the time required for the inspection of the welding quality in the manufacture of an LNGC cargo hold in which the absolute weight is occupied.

Korean Patent Laid-Open Publication No. 2001-0041402 "Method and Apparatus for Inspecting Welding Seams" (Published on: September 10, 1999) Korean Patent Publication No. 0237153 "Welding quality evaluation method" (Published date: May 28, 1997)

It is an object of the present invention to improve the conventional problems as described above, to estimate the penetration depth without direct destructive measurement of the seam weld in the manufacture of LNGC cargo hold and to present a standard related to quality inspection. is to provide

In order to achieve the above object, the present invention in a method for estimating the penetration depth of a three-ply seam weld: (A) the relationship between the welding width (La) and the penetration depth (P) of the nugget stored in the DB is bivariate normal obtaining a probability distribution by assuming a distribution; (B) obtaining an estimated defect rate curve of P according to La based on a preset Acceptance Criteria (AC) value of P using the bivariate normal distribution; and (C) comparing the estimated defective rate curve of P according to La and a preset self-quality determination defect rate criterion to obtain a value La that does not exceed the self-quality determination defect rate criterion.

As a detailed configuration of the present invention, it is characterized in that the cross-section weld width La of the step (A) is in a linear relationship with the overall weld width Lt.

As a detailed configuration of the present invention, the welding width (La) and the penetration depth (P) of the nugget stored in the DB is characterized in that it follows a normal distribution.

As a detailed configuration of the present invention, the step (C) is characterized in that it further comprises the process of selecting the minimum welding width (La) for the estimated penetration depth (P) to satisfy the acceptance criterion (AC).

As described above, according to the present invention, it is possible to reduce time and cost while the possibility for field application is greatly increased by the quality inspection of seam welds through the non-destructive inspection method in the manufacture of LNGC cargo holds.

1 is a data exemplifying a dimension item related to the quality of a seam weld;
Figure 2 is a table statistically processed dimensional information for each joint of the seam weld
3 is a flowchart showing the main algorithm of the method according to the present invention;
Fig. 4 is a chart showing the correlation of major elements of the macro dimension of Fig. 3;
5 is a chart showing a normal distribution state for the macro dimensions of FIG. 3
6 is a chart showing a method for estimating the defect rate with respect to the penetration depth of FIG. 3
7 is a table showing the application of quality standards to the penetration depth of FIG.

Hereinafter, an embodiment of the present invention will be described in detail based on the accompanying drawings.

The present invention proposes a method for estimating the penetration depth of a three-ply seam weld. It is intended for the manufacture of LNGC cargo holds, where the proportion of seam welding is absolutely high, but is not necessarily limited thereto. 1A and 1B exemplify a state of performing triple-seam welding in a state in which three objects to be welded are overlapped.

Hardware resources for implementing the present invention are configured based on a PC for a terminal and a network (intranet, Internet, LAN, etc.) in addition to a DB (server). The server is equipped with a microprocessor, memory, and I/O interface, drives the hardware including DB and communication with the set algorithm, and outputs it on the screen of the PC. The data of the seam welding process is stored, updated, classified in the DB and retrieved through the PC.

On the other hand, LNGC welding part daily test data is collected in the DB, and the data collected by the operation of the server is normalized.

Referring to FIG. 1A, which schematically shows the results of the macro test of FIG. 1B, in the three-ply seam welding of the upper, middle, and lower members, Lt means the maximum welding width of the entire nugget, whereas La is the upper or lower surface of the intermediate member. It means the welding width of the smaller side of the nugget area cut by . The height of the nugget with respect to the upper and lower surfaces of the intermediate member means the penetration depth expressed by the symbol P (or P1, P2).

In FIG. 1C , the joint shapes indicated by symbols A to E indicate the thickness of a three-ply seam weld, for example, A indicates 0.7/0.5/0.7 and E indicates 1.5/1.5/1.5. Such data can be obtained through a known macro test. As the table of FIG. 1c exemplifies the acceptance criteria (AC), in seam welding, the welding widths (La, Lt) and the penetration depth (P) are important factors in relation to the quality determination of the seam welding.

3 is a flowchart showing an example of the main algorithm of the method according to the present invention, including directly or indirectly the main steps (A) (B) (C) of the present invention, which will be described later. In any case, it is estimated by statistically analyzing the macro dimensions in the entire period (the entire period) accumulated in the DB. However, according to the method of the present invention, time and cost can be saved by reducing the frequency of actual cutting analysis.

Step (A) according to the present invention proceeds to the process of obtaining a probability distribution assuming the relationship between the welding width (La) and the penetration depth (P) of the nugget stored in the DB as a bivariate normal distribution. 5A shows the formula for the bivariate normal distribution, where x ₁ and x ₂ are used by replacing the La and P values described above. Figure 5b shows the relationship between the weld width (La) and the penetration depth (P) by schematically showing the cross-sectional and three-dimensional form of Figure 5a, respectively. Based on the acceptance criterion (AC) of the penetration depth (P), the distribution of P according to La and the defect rate can be estimated. For example, when the welding width La is an average of 2.29 mm and a standard deviation of 0.175, the penetration depth P is estimated to be an average of 0.37 mm and a standard deviation of 0.066. As described above, the relationship between the weld width and the penetration depth can be assumed to be a bivariate normal distribution, and the defect rate of the penetration depth with respect to the welding width can be calculated according to the acceptance criterion (AC).

As a detailed configuration of the present invention, it is characterized in that the cross-section weld width La of the step (A) is linearly related to the overall weld width Lt. The weld width of the macro dimension is estimated from one measurement by assuming a linear relationship between La and Lt. Referring to FIG. 4A , when the relationship between La and Lt is expressed by a simple linear regression model, the coefficient of determination (R ² ) is 0.88, indicating a linear relationship. This means that there is no significant difference using any of La and Lt in estimating the P value. In the present invention, the P value is estimated using the La value measured by a known non-destructive method. On the other hand, referring to FIG. 4B , it can be seen that the relationship between La and P cannot be linearly expressed.

As a detailed configuration of the present invention, the welding width (La) and the penetration depth (P) of the nugget stored in the DB is characterized in that it follows a normal distribution. 2A is a distribution diagram of occurrence probability for La, e, and P accumulated through a macro test for a specific joint shape. Since the elements (macro dimensions) accumulated in the DB form a Normal or Gaussian distribution as shown in FIG. 2A, utilization can be expected in the field of quality control of seam welding. When the number of data is sufficient, the actual defective rate and the defective rate estimated through the normal distribution agree very well. According to the current acceptance criteria (AC), most of the defects are due to the lack of the P value, which is the penetration depth. FIG. 2B shows that the distribution diagram and the estimated defective rate can be calculated using the probability density function (PDF) and the probability distribution function (CDF) from the normal distribution of each macro dimension.

Step (B) according to the present invention undergoes a process of obtaining an estimated defective rate curve of P according to La based on a preset acceptance criterion (AC) value of P using the bivariate normal distribution. Measure the weld width (La) instead of the penetration depth (P), which is difficult to measure by methods such as eddy current flaw detection method (ECT), leakage magnetic flux flaw detection method (MFL), and ultrasonic flaw detection method (MPA) Calculate the probability of penetration depth (P) by statistical method using Estimating the defect rate of the penetration depth P contributes to the simplification of inspection standards and flow.

More specifically, it is possible to derive the penetration depth (P) by statistically processing the information of the DB. According to the test comparing the actual defective rate and the estimated defective rate according to the quality acceptance criteria (AC) of the penetration depth (P), which is the main goal, there is no significant difference between the actual defective rate and the estimated defective rate in any joint type. The process proceeds to obtain a value of La that does not exceed the self-quality determination defect rate criterion by comparing the estimated defect rate curve of P according to La and a preset self-quality determination defect rate criterion.

Of course, as the data accumulation progresses, the reliability for statistical processing and quantification of the quality level improves.

As a detailed configuration of the present invention, the step (C) is characterized in that it further comprises the process of selecting the minimum welding width (La) for the estimated penetration depth (P) to satisfy the acceptance criterion (AC). According to the bivariate normal distribution of the DB data shown in FIGS. 6 and 7 , in addition to estimating the P value from the La value, it is easy to calculate the La value corresponding to the P value satisfying AC conversely. Moreover, even if the manager changes the acceptance criteria (AC) of seam weld quality according to the situation of the site, the update information on the weld width and penetration depth is quickly and accurately derived.

As shown in the upper figure of FIG. 6 , the allowable standard (AC) of the penetration depth P can be represented by assuming that the red line is 0.20 mm. Of course, AC is a value that fluctuates depending on the site situation, and the administrator can set it to a value lower or higher. In the lower part of FIG. 6 , assuming that AC is 0.1 mm, 0.15 mm, and 0.2 mm, respectively, the probability (defect rate) that the actual P value is lower than the AC according to the change of the La value is shown. That is, if the value of La is known, the probability that the value of P exceeds/and does not exceed AC can be obtained.

Referring to FIG. 7 , the lower red dotted line indicates a case in which the probability that the value of P estimated from the measured La does not satisfy AC is 1%. Although it is assumed that the quality standard for the defect rate itself is 1%, the same principle can be applied even if the quality standard is different. The case in which the allowable standard (AC) of the penetration depth is applied in three ways: 0.2mm (blue curve), 0.15mm (red curve), and 0.1mm (green curve) will be described.

(1) If La is 2.26mm when AC = 0.2mm, the probability that the actual P value will not exceed 0.2mm is 1% (i.e., 99% pass, 1% fail)

-> If the measured La value is 2.26mm or more, it is judged that the P value exceeds AC and is not defective.

-> If the measured La value is less than 2.26mm, it is judged that the P value does not exceed AC and cut analysis is performed.

(2) When AC = 0.15mm, if La is 2.19mm, the probability that the actual P value will not exceed 0.15mm is 1% (99% pass, 1% fail)

(3) When AC = 0.10mm, if La is 2.12mm, the probability that the actual P value will not exceed 0.10mm is 1% (99% pass, 1% fail)

When the method of the present invention is applied, it is possible to compensate for the disadvantages accompanying the non-destructive inspection of the seam weld, so that the possibility of field application is very high.

The present invention is not limited to the described embodiments, and it is apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the present invention. Accordingly, it should be said that such variations or modifications fall within the scope of the claims of the present invention.

La, Lt: Weld width P: Penetration depth
AC: Acceptance Criteria

Claims (4)

In the method for estimating the penetration depth of a three-ply seam weld:
(A) obtaining a probability distribution assuming the relationship between the welding width (La) and the penetration depth (P) of the nugget stored in the DB as a bivariate normal distribution;
(B) obtaining an estimated defective rate curve of P according to La based on a preset acceptance criterion (AC) value of P using the bivariate normal distribution; and
(C) comparing the estimated defective rate curve of P according to La and a preset self-quality determination defect rate criterion to obtain a La value that does not exceed the self-quality determination defect rate criterion; Seam weld penetration depth estimation, characterized in that it comprises a Way. The method according to claim 1,
Seam weld penetration depth estimation method, characterized in that the cross-section weld width (La) of the step (A) has a linear relationship with the total weld width (Lt). The method according to claim 1,
Welding width (La) and penetration depth (P) of a nugget stored in DB is a seam weld penetration depth estimation method, characterized in that it follows a normal distribution. The method according to claim 1,
The step (C) is a seam weld penetration depth estimation method, characterized in that it further comprises the step of selecting a minimum welding width (La) for the estimated penetration depth (P) to satisfy the acceptance criterion (AC).

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