JP6732485B2 - Ultrasonic flaw detection method for welded joint and ultrasonic flaw detection apparatus - Google Patents

Description

The present invention relates to, for example, an ultrasonic flaw detection method and an apparatus for flaw detection of a welded joint portion of a general structure, and in particular, a tank for storing a gas such as LNG (Liquid Natural Gas). Also, the present invention relates to an ultrasonic flaw detection method and apparatus for flaw detection of a welded joint made of a high nickel alloy as a welding material.

In the situation where the energy demand in the world is increasing, the use of clean energy is drawing attention as a countermeasure to global environmental problems. Under these circumstances, LNG has a smaller amount of CO ₂ emission than petroleum and coal, and the long-term supply stability is high, so that the demand is rapidly increasing. Many LNG tanks for storing this are currently in operation both in Japan and overseas, but LNG tanks are always required to have high safety. Specifically, the inner tank of the LNG tank is made of steel material, and necessary parts are joined by welding joints to secure strength, liquid tightness, and airtightness. Therefore, it is desired to be able to appropriately detect flaws in the welded joint portion in a non-destructive state.

Regarding such a flaw detection method for a welded joint, a technical idea relating to defect inspection of a welded portion by ultrasonic waves as disclosed in Patent Document 1 is disclosed.

In Patent Document 1, ultrasonic waves are applied to the welded portion between the first-side base material and the second-side base material from the side orthogonal to the welding line, and the ultrasonic waves are reflected by this irradiation. Regarding a weld defect inspection apparatus having a configuration for detecting a defect type existing in a weld according to ultrasonic information, it is described that a defect type can be objectively specified.

However, when the welded joint of the inner tank of the LNG tank, particularly the bottom plate portion, is composed of the first side base material, the second side base material, the welded portion between them, and the backing metal provided below the welded portion, The base material and the backing metal are preferably nickel steel, and the welded joint is preferably a high nickel alloy. However, in the high nickel alloy, there are many problems of ultrasonic wave diffusion and attenuation. It does not mention any solution to detection, and it is unclear whether defects can be detected with high accuracy.

JP-A-5-333001

The present invention is intended to solve the above-mentioned problems, and an object thereof is to provide an ultrasonic flaw detection method capable of detecting defects with high accuracy.

In order to solve such a problem, the present invention is an ultrasonic flaw detection method for flaw detection of a welded joint using ultrasonic waves, which is a creeping wave method, a longitudinal wave bevel method, a round trip method, a transverse wave method. It is characterized in that flaw detection is performed by a combination of at least two of the bevel methods.

Further, the present invention may be characterized in that the welded joint is a high nickel alloy. Here, the high nickel alloy refers to a nickel-based alloy having a nickel content of 50% or more and having a high Ni content (for example, 60 to 80%), and has a cryogenic temperature that is an environment in which the LNG tank inner tank is used. It is a material with excellent toughness below.

By doing so, it is possible to detect defects accurately by combining four types of flaw detection methods each having different flaw detection capabilities. Particularly, even in the case of a high nickel alloy having a problem of ultrasonic wave diffusion or attenuation, Defects can be detected with high accuracy.

Further, the present invention may be further characterized in that the flaw detection is performed only from the front side of the welded joint.

This eliminates the need for flaw detection from the back side. For example, in the case of the bottom surface of the LNG tank, in addition to flaw detection from above, there is no need to place the LNG tank on the temporary mount and perform flaw detection from below. In terms of man-hours and equipment, there is a large cost reduction effect.

As another aspect of the present invention, there is provided an ultrasonic flaw detector for flaw detection of a welded joint by ultrasonic waves, the ultrasonic probe transmitting and receiving ultrasonic waves, and a signal from the ultrasonic probe. And an ultrasonic flaw detector for detecting defects by using the ultrasonic wave flaw detector, and as a probe, a creeping wave probe, a longitudinal wave oblique angle probe, and a transverse wave oblique angle probe The feature may be that each target defect is combined.

In this way, regardless of the method, appropriate defects can be detected, and the effect is extremely large.

The flaw detection method for welded joints according to the present invention enables simple and accurate defect detection.

It is a schematic explanatory drawing of the ultrasonic flaw detection method which concerns on one Embodiment of this invention. It is a block diagram of the flaw detector of the ultrasonic flaw detector according to one embodiment of the present invention. It is explanatory drawing of the ultrasonic flaw detection method which concerns on one Embodiment of this invention. It is explanatory drawing of the ultrasonic flaw detection method which concerns on one Embodiment of this invention. It is explanatory drawing of the ultrasonic flaw detection method which concerns on one Embodiment of this invention. FIG. 10 is an explanatory diagram of an ultrasonic flaw detection method using a round trip method according to another aspect of the present invention. It is explanatory drawing of the test piece for verification of the ultrasonic flaw detection method which concerns on one Embodiment of this invention.

Hereinafter, an ultrasonic flaw detection method and an ultrasonic flaw detection device according to an embodiment of the present invention will be described with reference to the drawings. In the following, the range necessary for the explanation for achieving the object of the present invention is schematically shown, and the range necessary for the explanation of the relevant part of the present invention will be mainly explained, and the explanation will be omitted. A known technique is used.

FIG. 1 is a schematic explanatory diagram of an ultrasonic flaw detection method according to an embodiment of the present invention. The welding joint to be subjected to ultrasonic flaw detection includes members 2a and 2b forming the bottom plate of the inner tank of the LNG tank, a welded portion 3 that connects the bottom plate members 2a and 2b, and a backing that supports the lower side of the welded portion 3. It consists of gold 4. As conceptually shown in the same figure, preferably, a gap is provided at the joint between the backing plate 4 and the bottom plate members 2a, 2b, and the welded portion 3 is formed so as to fill the gap.

The bottom plate members 2a and 2b are high-tensile steel plates (for example, 7% Ni-TMPC steel) containing 7% of nickel, which are excellent in low-temperature toughness, and have a thickness of about 8 mm, but are not limited thereto. ..

The backing plate 4 is preferably a thin plate made of the same material as the floor plate members 2a and 2b, but is not limited thereto.

The welded portion 3 is made of a Hastelloy metal-based high nickel alloy having excellent low temperature toughness as a welding member, for example, an alloy containing about 70% nickel and about 20% molybdenum (US-709S manufactured by Kobe Steel, Ltd.). , Welding is performed by the one-side butt welding method with a backing plate. Specifically, a submerged arc welding method with a groove angle of 50 degrees is preferable, but the invention is not limited thereto, and for example, a TIG (Tungsten Inert Gas) welding method or a covered arc welding method may be used.

Next, the ultrasonic flaw detector 1 includes a probe 10 that transmits and receives ultrasonic waves, and a flaw detector 20 that flaw-defects based on the information received by the probe 10.

The probe 10 is installed so as to transmit ultrasonic waves to the welding part 4 and receive its reflection (echo) on one side of the extension direction (welding line L) of the central part of the welding part 4. , A creeping wave probe 10a, a longitudinal wave bevel probe 10b, and a transverse wave bevel probe 10c.

In addition, the probe 10 manually performs a zigzag scan of a scan in a direction parallel to the welding line L which is the center line in the longitudinal direction of the welded joint, a scan in a direction orthogonal to the welding line L, or a zigzag scan of a combination thereof. Or it can be done automatically.

FIG. 2 is a configuration diagram of a flaw detector of the ultrasonic flaw detector according to an embodiment of the present invention. An interface 201 for exchanging information with the probe 10 and flaw detection based on information received by the probe 10 are performed. A flaw detection control unit 202 for performing, a memory 203 for storing information and a program, an input unit 204 for inputting a flaw detection instruction and processing of a flaw detection result, an output unit 205 for outputting a flaw detection result, a flaw detection unit 205 such as a printer, a flaw detection It includes a display unit 206 such as an LED display for displaying a waveform or the like.

Next, an ultrasonic flaw detection method using the ultrasonic flaw detector 1 having such a configuration will be described.

FIG. 3 is an explanatory diagram of the ultrasonic flaw detection method according to the embodiment of the present invention, and particularly relates to the creeping wave probe 10 a of the probe 10. From the creeping probe 10a, ultrasonic waves horizontally propagated on the upper surface of the welded portion 4 are transmitted in a direction orthogonal to the welding line L of the welded portion 4 as shown in FIG. Receive (echo).

FIG. 4 is an explanatory diagram of the ultrasonic flaw detection method according to the embodiment of the present invention, and particularly relates to the longitudinal wave bevel probe 10b of the probe 10. As shown in the figure, the longitudinal wave bevel probe 10b transmits longitudinal ultrasonic waves obliquely downward at a fixed angle (for example, the refraction angle α is 70 degrees to 75 degrees), and is reflected by the defect K (echo). ) Is received.

FIG. 5 is an explanatory diagram of the ultrasonic flaw detection method according to the embodiment of the present invention, and particularly relates to the transverse wave bevel probe 10c of the probe 10. As shown in the figure, the transverse wave oblique probe 10c transmits transverse ultrasonic waves obliquely downward at a fixed angle (for example, the refraction angle α is 65 degrees to 70 degrees), and reflection (echo) at the defect K occurs. Be received.

Here, in the case of a welded joint of a high nickel alloy, it is desirable to use a longitudinal wave bevel method using a longitudinal wave bevel ultrasonic wave, which is less affected by ultrasonic wave diffusion and attenuation. However, the longitudinal wave bevel method alone cannot cover all regions of the welded joint where defects are expected to occur.

Specifically, in the region from the center to the bottom surface of the welded joint, the longitudinal wave bevel method by zigzag scanning of the longitudinal wave bevel probe is suitable.

Further, for this area, as shown in FIG. 6 as another aspect of the present application, the round trip method (RTT method), which is excellent in the vertical defect detection performance, is also effective. Here, the round trip method is a flaw detection method utilizing mode conversion, and is a method of detecting a reflected wave after obliquely incident through the bottom surface. A longitudinal wave bevel probe is used as the probe. Note that, in FIG. 6, the same objects as those described in the above figures are denoted by the same reference numerals and the description thereof will be omitted.

For the area near the surface, the creeping wave method by parallel scanning of the creeping wave probe is effective. According to this, it is possible to detect surface defects, wormholes, and blowholes near the surface.

Next, for the region of the weld groove surface (boundary surface with the base metal), the shear wave oblique angle method by zigzag scanning of the shear wave oblique angle probe is effective. According to this, it is possible to detect poor fusion of the groove surface and insufficient penetration near the back surface of the weld.

This makes it possible to detect possible defects in all areas. Depending on the defects that are expected to occur in the welded portion, it is not necessary to use all of these methods from the viewpoint of cost efficiency, and two or more of them may be used in combination.

The defect detection capability of the welded joint described so far has been verified by artificially manufactured test pieces.

FIG. 7 is an explanatory diagram of a test piece for verification of the ultrasonic flaw detection method according to the embodiment of the present invention. A test piece having a welded joint portion having the following defects was prepared.
a) Flat-bottomed horizontal hole-A model imitating a planar defect such as a crack in a welded portion.
b) Oblique flat bottom hole-a model imitating poor fusion of the groove surface.
c) Round head vertical hole-A model that imitates a worm hole and a blow hole generated from the gap between the back metal and the back metal.
d) Surface angle groove-a model in which a surface defect such as a crack near the weld surface is imitated.
e) Backside corner groove-a model that imperfectly melts on the groove root surface.
f) Surface round head vertical hole-a model that imitates a worm hole and blow hole generated in the second layer welding.

By the test using this test piece, the defect could be detected at a sufficient S/N ratio.
That is, a), c), d) and f) near the surface in the creeping wave method, a) and c) in a deeper region in the longitudinal wave bevel method and the RTT method, and in the transverse wave bevel method, It was possible to detect b) and e).

The present invention is not limited to the above-described embodiments, and various substitutions, replacements, additions, enlargements, reductions, and the like can be made within the scope of an equivalent technical idea.

For example, the present invention can be applied not only to the welding of the bottom plates but also to the welding of the bottom plate and the annular plate, or the welding of general structural parts other than the bottom plate.

Further, as the steel material, 7% nickel steel has been described as an example, but the nickel content is not limited to 7% and may be, for example, 9%. Instead of nickel steel, another steel sheet (for example, austenitic stainless steel) is used. Etc.) can also be applied to welded parts. Furthermore, the invention can be applied not only to the defect in the welded part but also to the defect in the metal part of the non-welded part.

As described above, the present invention can easily and accurately inspect the safety of a welded portion of a large structure such as an LNG tank. Therefore, the present invention is very important in the construction industry, shipbuilding, energy industry, etc. Have availability.

1 Ultrasonic Flaw Detector 2 Bottom Plate 3 Welding Part 4 Backing Plate 10 Probe 10a Creeping Wave Probe 10b Longitudinal Wave Angle Probe 10c Transverse Wave Angle Probe 20 Flaw Detector 201 Interface 202 Flaw Control Unit 203 Memory 204 Input unit 205 Output unit 206 Display unit

Claims (4)

An ultrasonic flaw detection method for flaw detection of a welded joint using an ultrasonic probe that transmits and receives ultrasonic waves , wherein the ultrasonic probe is an upper surface of a welding surface in a direction orthogonal to a welding line. Is a creeping wave probe that emits ultrasonic waves that propagate in a substantially horizontal direction and receives reflection at a defect, longitudinal wave that obliquely downwardly transmits a fixed angle longitudinal wave that transmits reflection at a defect An oblique angle probe, including a transverse wave oblique probe that emits transverse ultrasonic waves obliquely downward at a fixed angle and receives reflection at a defect, wherein the creeping wave probe and the longitudinal wave oblique probe are included. It is possible to combine at least any two or more of the probe and the transverse wave bevel probe for each flaw detection site and/or defect to be detected, so that the creeping wave probe can be used for parallel scanning . Leaping wave method, longitudinal scanning bevel method by scanning including parallel scanning, orthogonal scanning and zigzag scanning of the longitudinal wave bevel probe, reflected wave after obliquely incident using the longitudinal wave bevel probe The ultrasonic wave characterized by performing the flaw detection by an arbitrary combination of a round-trip method for detecting the wave through the bottom surface, parallel scanning of the transverse wave oblique probe, orthogonal scan, and transverse wave oblique method by scanning including zigzag scanning Method of flaw detection. The ultrasonic flaw detection method according to claim 1, wherein the welded joint is a high nickel alloy. The ultrasonic flaw detection method according to claim 1, wherein flaw detection is performed only from the front side of the welded joint. An ultrasonic flaw detector for flaw detection of welded joints by ultrasonic waves,
-An ultrasonic probe that transmits and receives ultrasonic waves,
-Including an ultrasonic flaw detector for detecting the defect using a signal from the ultrasonic probe,
As the ultrasonic probe, a creeping wave probe that transmits ultrasonic waves propagating in a substantially horizontal direction on the upper surface of the welding surface in a direction orthogonal to the welding line and receives reflection at a defect, oblique with a fixed angle Longitudinal wave oblique probe that emits downward longitudinal ultrasonic waves and receives reflection at a defect, transverse wave oblique probe that transmits oblique downward ultrasonic waves at a fixed angle and receives reflection at a defect It is possible to combine any two or more of the creeping wave probe, the longitudinal wave bevel probe, and the transverse wave bevel probe for each flaw detection site and/or defect to be detected. An ultrasonic flaw detector characterized in that it is possible.

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