Method for measuring thickness of thermal insulation material for liquefaction gas tank

Abstract

To provide a method for measuring the thickness of a thermal insulation material, that allows accurate, simple and continuous measurement of the thickness of a thermal insulation material composed of resin foam provided on an outer surface of a tank steel plate of a liquefaction gas tank, without impairing the function of the thermal insulation material.SOLUTION: In a method for measuring the thickness of a thermal insulation material provided on an outer surface of a tank steel plate of a liquefaction gas tank, the thermal insulation material contains resin foam, and the thickness of the resin foam is measured using a metal detector of an electromagnetic wave radar type.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the thickness of an insulating material for a liquefied gas tank, and more particularly to a method for measuring the thickness of an insulating material provided on the outer surface of a steel tank plate of a liquefied gas tank. [Background technology]

[0002] Conventionally, known cryogenic liquefied gas tanks include liquefied natural gas tanks, liquefied ammonia tanks, liquefied hydrogen tanks, and liquefied carbon dioxide tanks. For example, LNG carriers that transport or use liquefied natural gas (hereinafter sometimes referred to as LNG) as fuel are equipped with LNG tanks that store cryogenically low-temperature LNG at temperatures as low as -163°C. Standards for LNG tanks are set by the International Maritime Organization (IMO), and among these are Type A LNG tanks with complete secondary barriers, Type B with partial secondary barriers, and Type C LNG tanks, which are pressure vessels that do not require secondary barriers, as self-supporting tank types.

[0003] The Type C LNG tank is generally installed on small ships and is made of steel that can withstand the internal pressure of LNG. Because LNG is at extremely low temperatures as described above, the outer surface of the Type C LNG tank is provided with a number of insulating boards made of, for example, resin foam.

[0004] However, conventional insulation boards have the problem of being prone to cracking and peeling, because steel LNG tanks shrink significantly due to the cryogenic LNG inside, and the insulation boards cannot keep up with the shrinking steel. On the other hand, if a large number of insulation panels are provided on the outer surface of an LNG tank, there is a problem in that the insulating effect is reduced due to the fixing parts between the LNG tank and the insulation panels and the joint parts of the insulation panels.

[0005] In order to solve these problems, the present applicant has proposed in Patent Document 1 (JP 2020-186790 A) an insulating material for liquefied natural gas tanks that is provided on the outer surface of the tank steel plate of a liquefied natural gas tank, the insulating material including a resin foam and characterized in that the insulating material has a density gradient in which the density of the resin foam decreases from the tank steel plate side toward the outside.

[0006] On the other hand, to provide sufficient insulation to the LNG tank and maintain low construction costs, it is necessary to accurately measure the thickness of the resin foam insulation. One known technique for measuring the thickness of the resin foam after construction involves inserting a stainless steel taper gauge into the LNG tank steel plate until it reaches the outer surface, reading the scale on the taper gauge, and measuring the thickness of the resin foam. However, this conventional method has the following problems. (1) A through hole is formed where the taper gauge is removed, impairing the function of the insulation material. (2) For thicknesses of 100 mm to 800 mm, it is difficult to accurately measure thickness using only commercially available taper gauges, whose measurement range (scale length) is a maximum of about 150 mm. (3) It is practically difficult to insert a commercially available taper gauge or a spoke with markings at thicknesses of 100 mm to 800 mm perpendicularly into the outer surface of an LNG tank steel plate. Therefore, the conventional technology has a problem in that it is not possible to accurately measure the thickness of a resin foam having a thickness of 100 mm to 800 mm.

[0007] Furthermore, Patent Document 2 (JP 2019-78719 A) discloses a technique for checking the thickness of the urethane by adhesively fixing a pin of a known height to an object before installing insulation, and then spraying urethane until the tip of the pin is hidden. However, because this method assumes that the object is flat, it is difficult to adhesively fix a pin perpendicularly to a curved surface such as the outer surface of an LNG tank steel plate, making it impossible to accurately measure the thickness of the resin foam, resulting in a discrepancy between the designed thickness of the resin foam and its actual thickness. Furthermore, paragraph 0033 of the specification of Patent Document 2 states that "plate portion 11 of urethane thickness indicator pin 1 is provided with metal plate 13, such as an aluminum plate, which reacts to film thickness measuring instrument 4, so that after forming urethane insulation layer 3, film thickness measuring instrument 4 is used to electronically measure and confirm the thickness of urethane insulation layer 3." However, referring to paragraph 0011 of the specification of Patent Document 2, plate portion 11 on which metal plate 13 is provided is described as having a circular shape with an outer diameter R1 of, for example, about 20 mm to 25 mm, and such a small size cannot be detected by the metal detector exemplified in paragraph 0022 below of the present specification. On the other hand, ultrasonic thickness gauges, which are common thickness measuring devices, identify the countless voids that exist inside the 100mm to 800mm thick urethane as cracks, and the ultrasonic waves disappear partway through the 100mm to 800mm thick urethane and do not reach the tank's steel plate, so the ultrasonic gauge cannot pick up the reflected sound, making it impossible to measure the thickness.

[0008] Meanwhile, the present applicant has proposed a method for measuring the thickness of insulation provided on the outer surface of a steel tank plate of a liquefied natural gas tank, the insulation including a resin foam, and the thickness of the resin foam is measured using a pulse induction metal detector (Patent Document 3). However, the measurement method disclosed in Patent Document 3 is limited to measuring the thickness at one point at a time, and measuring at multiple points is problematic in that it is time-consuming. Therefore, there is a need in the industry for a method for measuring the thickness of a resin foam that enables continuous measurement in the curved surface direction of an LNG tank. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2020-186790 [Patent Document 2] Japanese Patent Application Publication No. 2019-78719 [Patent Document 3] Japanese Patent Publication No. 2022-154845 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a method for measuring the thickness of insulation for a liquefied gas tank, which can accurately, simply, and continuously measure the thickness of insulation made of a resin foam provided on the outer surface of the tank steel plate of a liquefied gas tank without impairing the function of the insulation. [Means for solving the problem]

[0011] As a result of extensive research, the inventors have discovered that the above-mentioned problems can be solved by measuring the thickness of the insulating material using a metal detector, and have thus completed the present invention. That is, the present invention is as follows.

[0012] 1. A method for measuring the thickness of the insulation material provided on the outer surface of the tank steel plate of a liquefied gas tank, The heat insulating material includes a resin foam, The thickness of the resin foam is measured using an electromagnetic wave radar metal detector. A method for measuring the thickness of an insulating material for a liquefied gas tank. 2. The measurement method according to 1 above, wherein the resin foam is selected from polyurethane foam, foamed rubber insulation, and phenol foam. 3. The measuring method according to 1 or 2 above, wherein the thickness of the heat insulating material is within the range of 100 mm to 800 mm. 4. The measurement method according to any one of 1 to 3 above, wherein the liquefied gas tank is fixed to a ship. 5. A method for providing heat insulating material on the outer surface of a steel tank plate of a liquefied gas tank, The heat insulating material includes a resin foam having a thickness in the range of 100 mm to 800 mm, the resin foam is provided by spraying the resin foam onto the outer surface of the tank steel plate multiple times; The thickness of the resin foam formed after each spraying is measured using an electromagnetic wave radar metal detector. A method for providing a heat insulating material on the outer surface of a tank steel plate of a liquefied gas tank. [Effects of the Invention]

[0013] The measurement method of the present invention uses an electromagnetic radar metal detector to measure the thickness of insulation for liquefied gas tanks, eliminating the need to form through-holes in the resin foam provided on the outer surface of the steel tank plate of the liquefied gas tank as in the past, eliminating the possibility of errors in the measured thickness of the resin foam depending on the measurer, and not requiring skilled measurement techniques. Therefore, the measurement method of the present invention makes it possible to accurately and easily measure the thickness of insulation made of resin foam provided on the outer surface of the steel tank plate of a liquefied gas tank without impairing the functionality of the insulation. Furthermore, while the pulse induction metal detector described in Patent Document 3, for example, measures the thickness of insulation on the order of centimeters, an electromagnetic radar metal detector can measure this on the order of millimeters, thereby improving measurement accuracy. Furthermore, an electromagnetic radar metal detector can measure the thickness continuously along the curved surface of the LNG tank and along the surface of the insulation, eliminating the need to perform single-point measurements at multiple locations as in the past, and significantly improving work efficiency. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram illustrating a liquefied gas tank that can be applied to the present invention. FIG. [Figure 2]FIG. 2 is a diagram illustrating measurement points of polyurethane foam in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be further described with reference to the drawings. The liquefied gas tank in the present invention is not particularly limited, but examples thereof include a liquefied natural gas tank, a liquefied ammonia tank, a liquefied hydrogen tank, a liquefied carbon dioxide tank, etc. Hereinafter, a liquefied natural gas tank will be described as an embodiment of the present invention, but the present invention is not limited to the following embodiment. FIG. 1 is a diagram illustrating a liquefied natural gas tank, particularly a Type C liquefied natural gas tank, installed on a ship and applicable to the present invention, in which FIG. 1(a) is a longitudinal side view of the liquefied natural gas tank, and FIG. 1(b) is a diametric front view of the liquefied natural gas tank.

[0016] In FIG. 1, a liquefied gas tank 10, which is a Type C liquefied natural gas tank (LNG tank), includes a cylindrical pressure vessel 12, which is supported by a frame 14. Generally, Type C LNG tanks have a capacity of 30 to 10,000 m 3 The pressure vessel 12 has a capacity of 1000 mbar, and the number of tanks may be one or more. The pressure vessel 12 is made of steel plates such as aluminum, stainless steel, or nickel steel.

[0017] As an example of the thermal expansion and contraction characteristics of the steel plate in the pressure vessel 12, when LNG at extremely low temperatures of -163°C is stored in a pressure vessel made of stainless steel, the stainless steel thermally contracts by approximately 3 mm per meter.

[0018] Therefore, the LNG tank is provided with insulation on the steel plates of the pressure vessel 12. The heat insulating material in the present invention is preferably a resin foam, more preferably a resin foam selected from polyurethane foam, foamed rubber heat insulating material, and phenol foam, and particularly preferably a two-component polyurethane foam, from the viewpoint of good followability to the thermal shrinkage of the steel plate and excellent workability. Below, an example in which the heat insulating material is polyurethane foam will be described.

[0019] The thickness of the polyurethane foam after application in the present invention is preferably 100 mm to 800 mm, more preferably 300 mm to 500 mm, and particularly preferably 350 mm to 450 mm. The density of the polyurethane foam is, for example, 35 kg / m 3 ~80kg / m 3 The density referred to in the present invention is generally measured in accordance with JIS K 7222 "Foamed plastics and rubber - Determination of apparent density."

[0020] The application of polyurethane foam can be carried out by spraying the polyurethane foam onto the outer surface of the steel tank plate of an LNG tank, for example. A known technique can be used for spraying the polyurethane foam. For example, the polyurethane foam can be a two-component type, and the two components are agitated and sprayed while controlling the pressure and temperature. The polyurethane foam may be sprayed multiple times until a predetermined thickness is achieved. For example, if the thickness of the polyurethane foam is set to 400 mm, the predetermined thickness (400 mm) can be achieved by spraying the polyurethane foam to a thickness of about 25 mm per spray and repeating this spraying multiple times.

[0021] In the present invention, the thickness of the polyurethane foam thus formed is measured using an electromagnetic wave radar type metal detector.

[0022] Electromagnetic radar metal detectors emit electromagnetic waves from an antenna toward the tank steel plate, receive the electromagnetic waves reflected from the tank steel plate with a receiving antenna, and calculate the thickness of the polyurethane foam from the time it takes for the electromagnetic waves to return. For example, by clarifying the correlation between the time it takes for the electromagnetic waves to return and the thickness of the polyurethane foam through preliminary experiments, the thickness of the polyurethane foam can be calculated from the time it takes for the electromagnetic waves to return. This correlation can be determined by adjusting the dielectric constant of the electromagnetic radar metal detector at any point on the polyurethane foam and equating the measurements obtained by the metal detector with those obtained using a pointing rod. Furthermore, for actual measurements, it is preferable to use a combination of an electromagnetic radar metal detector and a mobile device. Examples of such a mobile device include a device that can continuously move along the curved surface of the LNG tank and the surface of the insulation. Typically, an electromagnetic radar metal detector is combined with wheels, and the wheels are moved along the surface of the polyurethane foam to continuously measure the time it takes for the electromagnetic waves to return, thereby measuring the thickness of the polyurethane foam. Those skilled in the art can appropriately set the conditions for measuring the thickness of the polyurethane foam depending on the type of electromagnetic radar metal detector.

[0023] The electromagnetic wave radar metal detector used in the present invention can be a commercially available one, such as the GP8000 manufactured by Proceq, or the ADSPIRE01 manufactured by Keisoku Gijutsu Service Co., Ltd. [Example]

[0024] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples.

[0025] Example 1 First, a stainless steel mock-up tank with a diameter of 1.6 m and a longitudinal length of 4 m, as shown in Figure 1, was prepared. Next, two-component polyurethane foam was sprayed onto the entire surface of the mock-up tank. The density of the polyurethane foam was 60 kg / m for the 100 mm thick insulation material extending from the surface of the mock-up tank to the outer 100 mm. 3 The insulation material with a thickness of 300 mm from 100 mm to 400 mm is 40 kg / m 3 It was decided. The thickness of the polyurethane foam was measured at measurement points 1 to 3 shown in Figure 2. In Figure 2, measurement point 1 is the front side surface of the tank in the longitudinal direction, measurement point 2 is the front surface of the tank in the diameter direction (mirror part of the tank) (the surface is curved), and measurement point 3 is the back side surface of the tank in the longitudinal direction, opposite measurement point 1. A commercially available electromagnetic wave radar metal detector was used as the metal detector. In the actual measurements, the electromagnetic wave radar metal detector was combined with a moving means. The moving means can be a means that can move continuously along the curved surface of the LNG tank and the surface of the insulation material. Specifically, the electromagnetic wave radar metal detector was combined with wheels, and the wheels were moved along the surface of the polyurethane foam, and the time until the electromagnetic waves returned was continuously measured.

[0026] The thickness of the polyurethane foam in the measurement ranges AB (approximately 20 m in length of the tank body) and C-C' (tank head section) shown in Figure 2 was continuously measured using an electromagnetic radar metal detector.

[0027] Next, the actual thickness of the polyurethane foam at any three of the measurement points A, B, and C-C' (reference numbers 1, 2, and 3) was measured using a gauge after exposing the cross section of the polyurethane foam, and the measured values ​​were compared with the metal detector measurements. The results are shown in Table 1, and it was confirmed that there was no discrepancy with the measurements using the gauge (pointing rod).

[0028] [Table 1]

[0029] The results in Table 1 show that, according to the measurement method of the present invention, by measuring the thickness of the insulation using an electromagnetic radar metal detector, there is no need to form through holes in the resin foam provided on the outer surface of the tank steel plate of a liquefied gas tank as in the conventional method, and the thickness of the insulation provided on the outer surface of the tank steel plate of a liquefied gas tank can be measured accurately, easily, and continuously without impairing the function of the insulation.

[0030] Example 2 Next, we investigated a method of providing heat insulating material on the outer surface of the steel tank plate of the liquefied natural gas tank. First, as a comparative example, two-component polyurethane foam was sprayed onto the entire surface of a mock-up tank as shown in Figure 1. The density of the polyurethane foam was 60 kg / m for the 100 mm thick insulation material extending from the surface of the mock-up tank to the outer 100 mm. 3 The insulation material with a thickness of 300 mm from 100 mm to 400 mm is 40 kg / m 3 The total target thickness was set at 400mm and the spraying work was carried out. The thickness was not measured during the spraying work, but the actual thickness of the polyurethane foam was measured only after the spraying was completed by exposing the cross section of the polyurethane foam and using a gauge. It was confirmed that the thickness of the formed insulation was 430mm, which was 30mm more than the target thickness. Next, as an example, spray application was carried out using polyurethane foam in the same manner as in the comparative example, except that, as in Example 1, continuous thickness measurements were taken every 100 mm using an electromagnetic radar metal detector, and after spraying up to about 400 mm was completed, continuous thickness measurements were taken using the electromagnetic radar metal detector, and measurements were taken at the same locations as in Table 1 above. The sprayed product was then dismantled and the thickness of the exposed cross section was actually measured. There was no discrepancy between the measurements taken by the electromagnetic radar metal detector and the actual thickness measurements, confirming that the thickness of the polyurethane foam formed was just right and had reached the target thickness of 400 mm. From the above, it was found that when the insulating material is a resin foam with a thickness in the range of 100 mm to 800 mm, the resin foam can be sprayed onto the outer surface of the tank steel plate multiple times, and the thickness of the resin foam formed after each spraying is measured using an electromagnetic radar metal detector, thereby making it possible to form insulating material of the desired thickness on the outer surface of the tank steel plate of a liquefied gas tank. [Explanation of symbols]

[0031] 1, 2, 3 measurement points 10 Liquefied gas tank 12 Pressure vessels 14 Mounting stand

Claims

1. A method for measuring the thickness of a heat insulating material provided on the outer surface of a steel plate of a liquefied gas tank, comprising: The heat insulating material includes a resin foam, The thickness of the resin foam is measured using an electromagnetic wave radar metal detector. A method for measuring the thickness of an insulating material for a liquefied gas tank.

2. 2. The method according to claim 1, wherein the resin foam is selected from the group consisting of polyurethane foam, foamed rubber insulation, and phenolic foam.

3. 2. The measuring method according to claim 1, wherein the thickness of the heat insulating material is in the range of 100 mm to 800 mm.

4. 2. The method of claim 1, wherein the liquefied gas tank is fixed to a ship.

5. A method for providing a heat insulating material on the outer surface of a tank steel plate of a liquefied gas tank, comprising: The heat insulating material includes a resin foam having a thickness in the range of 100 mm to 800 mm, the resin foam is provided by spraying the resin foam onto the outer surface of the tank steel plate multiple times; The thickness of the resin foam formed after each spraying is measured using an electromagnetic wave radar metal detector. A method for providing a heat insulating material on the outer surface of a tank steel plate of a liquefied gas tank.

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