JP4669134B2 - Flaw detection method for open rack type vaporizer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flaw detection method in an existing apparatus that is large and difficult to disassemble or remove, such as an open rack type vaporizer, and enhances transmitted X-rays at a site to be inspected using X-rays having a focal size of several μm. A method for flaw detection in an existing apparatus , particularly the open rack type vaporizing apparatus , characterized in that an enlarged image is formed on a sensitivity imaging plate, and this is scanned with a laser to form a sharp digital image to obtain an analytical image that can be easily viewed on site. The present invention relates to a flaw detection method .
[0002]
[Prior art]
An open rack type vaporizer (ORV) for vaporizing liquefied natural gas (hereinafter referred to as LNG) is, for example, a single panel having fin tubes with a pair of fins protruding in the diameter direction in the fin direction. A heat exchange panel is formed by providing header tanks at the upper and lower ends, and a plurality of such panels are arranged in a row, and heat is exchanged for seawater as a heat medium from a watering trough disposed above the heat exchange panel. The heat exchange is performed with the LNG that flows down to the panel surface and flows up in the fin tube.
[0003]
As described above, the single tube ORV has a simple structure and is easy to manufacture. However, since the heat medium seawater and the cryogenic LNG exchange heat directly through the single tube wall of the heat exchange panel, That is, there is a problem that ice adhesion occurs and increases on the surface of the heat exchange panel.
[0004]
In addition, in the ORV upflow, the lower header tank is an ultra-low temperature liquid on the lower side of the tank, whereas the upper side of the tank is heated higher than the lower part because it receives heat input from the water spray from the heat source. Thermal stress acts upon the start / stop of the ORV, such as a bowing phenomenon in which a temperature difference occurs between the upper part and the lower part, resulting in a bowing phenomenon.
[0005]
[Problems to be solved by the invention]
When the ORV fin tube was pulled out and the remaining life was diagnosed, a vertical crack was found along the U-shaped groove on the inner surface of the lower end of the fin tube. As a result of thermal stress analysis, it was found that the thermal fatigue crack was based on the thermal deformation of the lower header when the ORV was started and stopped.
[0006]
The occurrence site of the vertical crack is a place where the fin tube is embedded in the header tank and welded, and from the outside, a plurality of metal materials appear to be interlaced.
[0007]
Therefore, the flaw is a crack that cannot be detected by a known flaw detection method such as an ultrasonic CT (Computed Tomography) method and an X-ray CT method that can be performed at an existing position, and is only investigated by the above-described extubation, The remaining life diagnosis of the ORV device could not be performed non-destructively.
[0008]
In the present invention, as in the case of the ORV described above, it is impossible to detect by a known nondestructive flaw detection method, or it is in a position where it is difficult to flawlessly, for example, it is difficult to extubate. It is possible to perform flaw detection / analysis on site, identify the location of occurrence of cracks, etc. Furthermore, these flaw detection / analysis methods can be remotely controlled in existing equipment , especially the ORV example above An object of the present invention is to provide a method for flaw detection in ORV that detects vertical cracks without extubation .
[0009]
[Means for Solving the Problems]
As a result of various examinations on X-rays and analysis methods for the purpose of a flaw detection method that enables non-destructive inspection of a required part of an existing apparatus on site, the inventors have found that the focal spot size is several μm at the existing site. Is it possible to obtain an analytical image that can be easily seen in the field by enlarging the transmitted X-ray of the site to be inspected on the high-sensitivity imaging plate using a line, and scanning this with a sharp digital image? We have found out that this is possible and have completed the present invention.
[0010]
That is, in the present invention, the fin tubes are arranged in the fin direction to form a single panel, and a heat exchange panel is formed by providing header tanks at the upper and lower end portions thereof, and a water spray disposed above the heat exchange panel. This is a flaw detection method in an open rack type vaporizer that exchanges heat with LNG that flows up in the fin tube by allowing the heat medium to flow down from the trough to the heat exchange panel surface, and the fin tube is embedded in the lower header tank. A flaw detection method in an open rack type vaporizer that non-destructively inspects the vertical cracks generated along the U-shaped groove on the inner surface of the welded and welded portion using the following steps (1) to (3) .
(1) A step of irradiating a portion of the welded overlay with microfocus X-rays from the side facing the panel surface of the heat exchange panel .
(2) A step of enlarging an image of the microfocus X-ray that has passed through the welded portion on the imaging plate.
(3) A step of forming a digital image by laser scanning the enlarged imaging plate.
[0011]
Further, according to the present invention, in the method having the above-described configuration, the location where the vertical crack is generated is defined as the total number of start / stop times and low load operation times of the open rack type vaporizer, the header material, the fin tube material, and the fitting of these. Based on the shape and its method, and the generation pattern obtained by the cross-sectional shape of the fin tube, a method for non-destructive inspection specified in advance, when irradiating the welded portion of the microfocus X-ray, and irradiation from the vertical direction, how to perform the three-way radiation that combines the radiation from the slope directions within opposite sides ± 30 ° centered on the vertical direction, is proposed together.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention uses a microfocus X-ray with a focal size of several μm at an existing site of an open rack type vaporizer to form an enlarged image of transmitted X-rays at a site to be inspected on a high-sensitivity imaging plate, and scan this with a laser. An object is to obtain a vertical crack along the U-shaped groove on the inner surface of the lower end of the fin tube as an inspection image that can be visually confirmed by forming a sharp digital image.
[0013]
In the present invention, as the X-ray generation means, a microfocus X-ray generator having a very small focal size of 8 μm or less, preferably 5 to 7 μm is employed. For example, an apparatus having a tube voltage of 50 kV to 100 kV and a tube current of about 0 to 0.25 mA can be employed. When the focal size is 5 μm × 5 μm, an enlarged image of 400 times can be obtained as in the examples described later.
[0014]
Microfocus X-ray irradiation conditions irradiate a point to be inspected from the vertical direction, but the discrimination of scratches such as cracks greatly affects the X-ray irradiation direction. The inventors provided a turning means to the apparatus to set the X-ray irradiation angle to ± 40 degrees from the center (a range in which the angle can be changed), and confirmed the distinguishability of cracks. About ± 30 degrees Since the discriminability of cracks greatly decreases when the above is reached, it has been confirmed that the flaw detectability can be greatly improved, preferably by performing three-way irradiation with the irradiation direction at the center and about ± 20 degrees.
[0015]
In this invention, the X-ray image forming means is not an X-ray film as an X-ray photosensitive plate, but a photosensitive plate using a stimulable phosphor having a sensitivity several tens of times higher than this, a so-called high-sensitivity imaging plate. It is preferable to do. That is, because of the high sensitivity, the irradiation time can be greatly shortened.
[0016]
The method for holding the high-sensitivity X-ray photosensitive plate needs to be able to accurately set the distance from the point to be inspected, and to set the distance between the X-ray focal point position, the defect position of the subject to be inspected, and the photosensitive plate position. The enlargement ratio is determined.
[0017]
In the present invention, as the image analysis means, means for laser scanning a high-sensitivity X-ray photosensitive plate and means for performing image processing on the laser-scanned image to be inspected by the computed radiography (CR) method are adopted. . Any known portable device and method can be employed for the laser scanning means and the CR processing of images.
[0018]
In addition, the scanned image to be inspected may be combined with known digital image processing, CT method, etc. to enlarge and sharpen the image, to make the image two-dimensional or three-dimensional, or to output and save the image data. preferable. Furthermore, it is also preferable to identify a part or a defect in the image together with information from other temperature sensors.
[0019]
By the above image analysis means, it is possible to perform image processing / observation / evaluation in the field after imaging by microfocus X-ray inspection, and it is easy to store / record / reproduce images. That is, the time required for confirmation of imaging by X-ray inspection is shortened, and the work efficiency and the inspection process can be greatly shortened.
[0020]
Conventionally, the present invention assumes a specific condition in which flaw detection of an existing apparatus cannot be carried out on site and nondestructively. For example, it may be impossible to predict whether a defect or the like has occurred at a point to be inspected. Therefore, in order to improve the efficiency of inspection work, various analyzes such as structure, stress, thermal stress, etc. are performed on the object to be inspected in advance by a structural analysis method using a two-dimensional and three-dimensional analysis model method on a computer. It is possible to set a part where a defect or a flaw is predicted in advance and perform a simulation of the X-ray inspection of the part.
[0021]
【Example】
Example 1
As shown in FIG. 1A, for an ORV heat exchange panel having 150 fin tubes 2 per panel that is operating at an LNG operating pressure of 0.8331 MPa, the fin tubes 2 are embedded in the lower header tank 1 and welded. It was inspected whether vertical cracking occurred in the U-shaped groove of the fin on the inner surface of the fin tube 2 at the overlaid position.
[0022]
As for the inspection method, the flaw detection method by microfocus X-ray transmission of the present invention is carried out at the existing site of the heat exchange panel in operation, and the vertical cracks in the U-shaped grooves of the inner surface fins are inspected for each fin tube 2. Presence / absence, defect position, and vertical crack height were measured.
[0023]
L7902 (manufactured by Hamamatsu Photonics) was used as the X-ray generator 4 and operated at a maximum tube voltage of 100 kV, a tube current of 0.1 mA, and a focal size of 5 μm × 5 μm. As the high-sensitivity X-ray photosensitive plate, a high-sensitivity imaging plate 3 manufactured by Fuji Photo Film Co., Ltd. is used. As shown in FIG. 1C, the distance L ₁ between the fin tube 2 center and the X-ray generator 4, the fin tube 2 center, X-ray transmission imaging was performed by appropriately selecting the distance L ₂ from the high-sensitivity imaging plate 3 and setting the geometric magnification ratio to 8 times and the irradiation time to 30 seconds.
[0024]
The X-ray generator 4 is mounted on a manipulator (not shown) that can be remotely controlled. As shown in FIG. 2, the X-ray is irradiated in three directions with the irradiation direction at the center and ± 20 degrees. 3 was exposed. Thereafter, the high-sensitivity imaging plate 3 was scanned with a laser to form a digital image, and further enlarged and sharpened by CR operation, whereby a 200-400 times magnified image could be appropriately obtained on the CRT screen.
[0025]
Furthermore, the operation of the heat exchange panel to be inspected is stopped, disassembled, and the extracted fin tubes are subjected to the ultrasonic CT method, the X-ray CT method, and the high resolution X-ray transmission method of the present invention in the examination room. Each was inspected in detail. After inspecting the fin tube in which the vertical crack was detected by the flaw detection method using X-ray transmission, the entire amount of the fin tube in which the vertical crack was not detected was also inspected.
[0026]
The position of the vertical crack in the fin tube and the height of the vertical crack detected by carrying out the flaw detection method using microfocus X-ray transmission according to the present invention completely coincided with the result of the destructive inspection in the laboratory.
[0027]
Example 2
The vertical crack generated in the U-shaped groove of the tube inner fin detected in Example 1 is a conventionally unknown defect, and the inventors investigated the cause of the occurrence. As a method, calculation of stress concentration factor of inner fin valley bottom by 2D analysis model, investigation of cause of vertical crack by 3D analysis model, especially analysis of temperature distribution of said model, analysis of thermal stress value of model, Further, the occurrence of flaws was simulated in consideration of the fatigue curve of the fin tube material and the history of the number of start and stop times of the ORV.
[0028]
As a result of the simulation, it has been found that this defect is a vertical crack due to low cycle fatigue, and is consistent with the total number of times of start and stop of the machine and frequent low load operation times of 20% or less. Further, the present inventors have found that the locations where the vertical cracks are likely to occur and their forms vary depending on the header and fin tube materials, their fitting shapes and methods, the cross-sectional shape of the fin tubes, and the like, and the occurrence can be patterned.
[0029]
Therefore, when the flaw detection method according to the present invention was performed on the ORV heat exchange panel different from that in Example 1 under the conditions of Example 1, it was possible to specify and carry out the X-ray transmission imaging location as described above. Therefore, the working time could be shortened to 1/2 that of the first embodiment.
[0030]
【The invention's effect】
As shown in the embodiment, the present invention, as shown in the embodiment , a vertical crack along the U-shaped groove on the inner surface of the welded portion of the build-up welded portion of the fin tube and the lower header tank in the open rack type vaporizer that cannot be detected by a known nondestructive flaw detection method, In-situ and non-destructive flaw detection is possible. In addition, flaw detection and analysis can be performed on-site, and the occurrence position of cracks can be specified. Further, a series of flaw detection and analysis can be remotely controlled.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram showing a configuration of an ORV heat exchange panel in the vicinity of a lower header tank used in an embodiment and a microfocus X-ray irradiation method according to the present invention, where A is a heat exchange panel and B is a diagram of FIG. aa arrow view, C is a bb arrow view of A figure.
FIG. 2 is an explanatory view showing the position of the microfocus X-ray irradiation method of the present invention on a high-sensitivity imaging plate, and is an upper surface explanatory view seen from the axial direction of the fin tube.
[Explanation of symbols]
1 Lower header tank 2 Fin tube 3 High sensitivity imaging plate 4 X-ray generator

Claims (3)

A fin tube is arranged in the fin direction to form a single panel, and a heat exchange panel is formed by providing header tanks at the upper and lower ends, and a heat medium is formed from a watering trough disposed above the heat exchange panel. Is a flaw detection method in an open rack type vaporizer that exchanges heat with LNG that flows up in the fin tube by flowing down the heat exchange panel surface, and the fin tube is embedded in the lower header tank and welded Flaw detection method in an open rack type vaporizer that non-destructively inspects vertical cracks that occur along the U-shaped groove on the inner surface of the portion using the following steps (1) to (3) .
(1) A step of irradiating a portion of the welded overlay with microfocus X-rays from the side facing the panel surface of the heat exchange panel .
(2) A step of enlarging an image of the microfocus X-ray that has passed through the welded portion on the imaging plate.
(3) A step of forming a digital image by laser scanning the enlarged imaging plate. The location where vertical cracking occurs depends on the total number of start / stop operations and low load operation times of the open rack type vaporizer, header material and fin tube material, their fitting shape and method, and fin tube cross-sectional shape. The flaw detection method in the open rack type vaporizer according to claim 1, wherein nondestructive inspection is performed by specifying in advance based on the obtained generation pattern . Three directions combining irradiation from the vertical direction of the heat exchange panel and irradiation from an inclination direction within ± 30 degrees on both sides centering on the vertical direction when irradiating the welded part with microfocus X-rays The flaw detection method in the open rack type vaporization apparatus of Claim 1 or 2 which performs irradiation .

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