JP2012077778A - Diagnostic method of lng open rack type vaporizer heat transfer tube panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of diagnosing existence of defects inside a heat transfer tube of an LNG open rack type vaporizer.SOLUTION: In diagnosing the existence of defects inside the LNG open rack type vaporizer, a heat transfer tube base part arranged in the nearest position to an upward hole out of sparge tube gas vent holes formed inside a heat transfer tube header is selected as a photographing start section. A damage on the base part is photographed by a micro focus X-ray, and existence of the damage is checked from an image to check an inside defect condition.

Description

  The present invention relates to a diagnostic method for an LNG open rack vaporizer that vaporizes liquefied natural gas (LNG) by heat exchange in a thermal power plant or the like.

  FIG. 1 is a diagram for explaining a general LNG system in a power plant, and FIG. 2 is a diagram for explaining the structure of an LNG open rack type vaporizer. In the LNG base, as shown in FIG. 1, LNG stored as liquefied gas in the LNG tanks 101 and 102 is gasified by the LNG open rack type vaporizers 200 and 400 and supplied to a gas turbine or a boiler. This LNG open rack type vaporizer 200 has a structure as shown in FIG. It consists of lower headers 221, 222, 223 connected to the lower manifold 210, upper headers 241, 242, 243 connected to the upper manifold 250, and heat transfer tube panels 231, 232, 233 connecting the upper header and the lower header. . A heat transfer tube panel is a general term for a set of heat transfer tubes connected to a pair of upper and lower header portions. The LNG open rack type vaporizer 400 in FIG. 1 has a similar structure although not shown.

  Moreover, troughs 301, 302, and 303 are provided so as to sandwich the upper header, and normal temperature seawater is supplied therefrom. LNG is supplied from the lower manifold, is vaporized through heat exchange with seawater while passing through the lower header, the heat transfer tube, and the upper header, and is sent out as natural gas (NG) from the upper manifold.

  FIG. 3 is a view for explaining the vaporization principle of the LNG open rack type vaporizer. When the seawater overflowing from the troughs 301 and 302 flows along the outside of the heat transfer tube 231, the LNG inside the heat transfer tube is warmed and the LNG is vaporized into NG. For this reason, the heat transfer tube panel 231 of the LNG open rack type vaporizer is exposed to a large thermal stress, and it is seen that the vaporizer member is cracked.

  Conventionally, cracks in internal structures have been detected by X-ray imaging, but linear defects that cannot be detected by normal X-rays may cause defects. For this reason, it is necessary to use a high-resolution microfocus X-ray inspection apparatus, but this has a problem that the focal size is small.

  In general, one heat transfer tube panel is composed of a plurality of heat transfer tubes, and one LNG open rack type vaporizer has several thousand heat transfer tube panels. For this reason, in a microfocus X-ray inspection apparatus with a small focal size that needs to be imaged multiple times to image a single heat transfer tube, an unrealistic number of images is required to investigate the entire LNG open rack vaporizer. Is required.

  Therefore, an object of the present invention is to provide an efficient method for diagnosing internal defects that can be actually implemented using microfocus X-rays.

  The inventor diligently studied the above problems, and identified the cause of the occurrence of internal defects in the LNG open rack type vaporizer, and came to the present invention.

  That is, the present invention is as follows.

A diagnostic method for determining the presence or absence of internal defects in an LNG open rack type vaporizer heat transfer tube panel, including an imaging start site selection step, a microfocus X-ray imaging step, an image formation step, an image analysis step, a damage tracking step, and a residual sparg This includes the step of checking the gas vent hole and the step of judging the internal defect of the heat transfer tube panel. In the part to be imaged step, the part where the sparge pipe root installed closest to the gas spout hole in the heat transfer pipe header is started In addition, in the heat transfer tube panel internal defect determination step, for all the sparge tube degassing holes of the panel, if no flaws are found in the captured images of the heat transfer tube roots installed closest to each, The panel is judged to have no internal defects. This is a diagnostic method for the Punrak vaporizer heat transfer tube panel. Further, the image analysis step includes an internal defect tracking step. When the internal defect is recognized in the image analysis step, and the scratch is extended outside the captured image in the additional imaging necessity determination step, This is a diagnostic method for an LNG open rack type vaporizer heat transfer tube panel that repeats imaging by changing the imaging part along the line.

  The present invention is based on the following internal defect mechanism of the LNG open rack vaporizer discovered by the inventors.

FIG. 4 is a diagram for explaining an image of thermal shock stress due to LNG ejected from a sparge pipe vent hole. In FIG. 4, LNG supplied from the lower manifold 210 is ejected from the sparge pipe degassing hole 291 a of the sparge pipe 281 in the lower header 221, and is accumulated in each heat transfer pipe of the heat transfer pipe panel 231 after filling the lower header. Go. When the LNG open rack type vaporizer is operating steadily, the liquid level of the LNG inside the heat transfer tube 231 is stable, but when the LNG open rack type vaporizer is started, the LNG ejected from 291a is transferred. The vicinity of the weld A at the base of the heat tube 2311 is rapidly cooled to apply stress.

The inventor has discovered that the thermal shock stress imparted by the LNG ejected from the sparge tube degassing hole 291a of the sparge tube 281 is a main cause of internal defects in the heat transfer tube panel of the LNG open rack type vaporizer. Furthermore, from this discovery, the welded part at the base of the panel tube near the sparge tube vent hole is photographed in detail with microfocus X-rays. If there is no damage here, it is determined that there is no internal defect. Was invented a diagnostic method of tracking the stalk and specifying its size.

According to the present invention, it is possible to efficiently diagnose the presence or absence of a linear defect that cannot be detected by ordinary X-rays.

LNG open rack carburetor at power plant Structure of LNG open rack type vaporizer LNG vaporization principle Thermal shock due to LNG ejected from the sparge pipe vent hole? Image of Flow of LNG open rack type vaporizer panel diagnostic method Microfocus X-ray photography in the vicinity of the sparge tube vent hole

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified.

  FIG. 5 is a flow of this diagnostic method. This flow is intended for diagnosis of a single heat transfer tube panel. Since there are a plurality of panels in the entire LNG open rack type vaporizer, the total number of panels is diagnosed.

  In the imaging start part selection step (S01), an imaging start position is selected. Specifically, the welded portion of the heat transfer tube located closest to the sparge tube vent hole facing upward is selected. In FIG. 4, the welded portion A of the heat transfer tube 2311 is selected. This is because, as mentioned above, this part has the severest thermal shock stress.

  In the microfocus X-ray imaging step (S02), imaging with microfocus X-rays is performed.

FIG. 6 is a diagram for explaining a microfocus X-ray imaging form in the vicinity of a sparge tube degassing hole. Photographing is performed by combining the seven angles shown in FIG. For shooting, the shooting location is sandwiched between the microfocus line source 401 and the imaging plate 402, and shooting is performed in the positional relationship shown in FIG. Specifically, the welded portion A at the base of the heat transfer tube 241 is horizontally oriented at three angles (FIG. 6 (a) is a side view, FIG. 6 (b) is a top view), and the center of the lower header 221 is centered. Three angles from the bottom to the top so as to pass (FIG. 6 (b)), and the welded portion A of the target heat transfer tube 231a is one angle from the bottom (FIG. 6 (c)). This makes it possible to diagnose the heat transfer tube weak spot with a small number of 7 angles at the maximum.

  In this embodiment, the imaging plate 402 is used, but a normal film may be used.

  In the image forming step (S03), an image is formed. In the case of an imaging plate, an image is formed on a computer using dedicated software. In the case of a normal film, the image is formed by development.

  In the image analysis step (S04), the presence or absence of a flaw is visually confirmed from the formed image. If there are no scratches. The process proceeds to the remaining sparge pipe degassing hole confirmation step (S08). If there is a scratch, the process proceeds to the internal defect tracking step (S05).

  In the internal defect tracking step (S05), it is confirmed whether or not the found scratch extends so as to protrude from the captured image. In this case, the size of the scratch is specified and recorded in the image (S06), and the process proceeds to the remaining sparge tube degassing hole confirmation step (S08). On the other hand, if the scratch extends so as to protrude from the image, the shooting location is changed and the shooting is repeated so as to track the scratch (S07).

  FIG. 8 is an image diagram showing the tracking of a flaw in step S07. Move the part so as to cover the direction in which the scratch extends, and repeat this until the end of the scratch can be shot.

  In the remaining sparge pipe degassing hole confirmation step (S08), it is determined whether or not a sparge pipe degassing hole that has not been photographed remains on the panel. In the present invention, the drain hole facing the lower part is excluded. This is because there is no weld at the root of the heat transfer tube in the direction of the LNG to be ejected. In the LNG open rack type vaporizer in the present embodiment, a plurality of sparge pipe vent holes exist in one sparge.

  In the heat transfer tube internal defect determination step (S09), the presence or absence of a heat transfer tube internal defect is determined based on whether or not a flaw has been found from the image of the vicinity of the sparging gas vent hole that is to be imaged on the panel. If no flaw is found, it is determined that “the flaw is not present on the panel” (S10). If there is a flaw, the flaw data recorded in S06 is called (S11), and this diagnosis is concluded.

101, 102 LNG tank 102 LNG tank (separate system)
200, 400 LNG open rack type vaporizer 210 Lower manifolds 221, 222, 223 Lower headers 231, 232, 233 Heat transfer tubes 231 a Heat transfer tubes 241, 242, 243 Upper header 261 Heat transfer tube panel 270 Upper manifold 281 Sparge tube 291 Sparge tube gas Holes 301, 302, 303 Trough 401 Microfocus source 402 Imaging plate

Claims (2)

A diagnostic method for determining the presence or absence of internal defects in an LNG open rack carburetor heat transfer tube, which includes an imaging start site selection step, a microfocus X-ray imaging step, an image formation step, an image analysis step, an internal defect tracking step, and a residual sparge tube gas. In the step of selecting the object to be imaged, including a step for checking a hole and a step for determining a defect inside the heat transfer tube, the root of the heat transfer tube installed closest to the upward hole among the sparge tube degassing holes provided inside the heat transfer tube header is photographed. As a starting site,
In the heat transfer tube internal defect determination step, if no scratches are found in the respective captured images of the heat transfer tube roots installed closest to each of the upward sparge tube vent holes of the panel, Method for diagnosing LNG open rack type carburetor heat transfer tube, characterized in that there is no internal defect The image analysis step further includes an internal defect tracking step,
When a scratch is recognized in the image analysis step,
In the additional shooting necessity determination step,
If the scratch extends outside the captured image,
2. The diagnostic method for an LNG open rack type vaporizer heat transfer tube according to claim 1, wherein the imaging region is changed along the wound and the imaging is repeated.