JP5640286B2 - Piping evaluation method - Google Patents

Description

  The present invention relates to a pipe evaluation method.

  Patent Document 1 relates to a method for evaluating a corrosion state in a pipe based on X-ray imaging of the pipe.

JP-A-6-221840

  In order to correctly evaluate the deterioration status of the piping, it is necessary to evaluate the piping status based on the results of the inspection on an appropriate sample while considering the piping status widely.

  An object of the present invention is to provide a pipe evaluation method capable of correctly evaluating the deterioration state of pipes.

The pipe evaluation method of the present invention is a corrosion inspection step for inspecting the corrosion state on the inner surface of a plurality of types of sample pipes based on at least one of visual observation, optical observation, X-ray inspection, and ultrasonic inspection , based on the test results before Symbol corrosion test step, the and the sample tubing and a degradation evaluation step of evaluating the entire related deterioration degree of the evaluated range at least including the deterioration evaluating step, the inspection of the corrosion test step A corrosion amount deriving step for deriving a corrosion amount in the sample pipe based on the result; a minimum wall thickness evaluating step for evaluating a minimum wall thickness of the pipe based on the corrosion amount derived in the corrosion amount deriving step; the plurality of types of for each sample pipe, the Sun showing evaluation results in the minimum thickness evaluation step Deterioration rank corresponding to the degree of degradation with respect to the nominal thickness of Le pipe is determined on the basis of the associate reference value for the deterioration degree to degradation rank as the nominal thickness and the plurality of types of sample pipe and each other information corresponding to Table No. The rank number of the degradation rank is common regardless of the type of the sample pipe, and the criteria for ranking based on the evaluation result in the minimum wall thickness evaluation step is as follows. It includes a reference value related to the degree of deterioration with respect to the nominal thickness, and relates to at least any rank among at least two types of the sample pipes that are different from each other with respect to at least one of the presence or absence of a thread portion, the presence or absence of a resin lining, and the presence or absence of a joint. The reference values are different. In another aspect, the pipe evaluation method of the present invention inspects the corrosion status on the inner surface of a plurality of types of sample pipes based on at least one of visual observation, optical observation, X-ray inspection, and ultrasonic inspection. A corrosion inspection step, and a deterioration evaluation step for evaluating a degree of deterioration related to the entire evaluation target range including at least the sample pipe based on the inspection result in the corrosion inspection step, the deterioration evaluation step comprising: A corrosion amount deriving step for deriving the corrosion amount in the sample pipe based on the inspection result of the corrosion inspection step, and a minimum wall thickness for evaluating the minimum wall thickness of the pipe based on the corrosion amount derived in the corrosion amount deriving step. the thickness evaluation step, for each of the plurality of types of sample pipe, evaluation in the minimum thickness evaluation step A rank determination step of determining the deteriorated rank corresponding to the degree of deterioration indicated by results, the includes a step of deriving the estimated value Y of the useful life for each sample pipe, the number of ranks the deterioration rank, the sample pipe The standard for ranking based on the evaluation result in the minimum wall thickness evaluation step is different between at least two types of sample pipes different from each other, and the estimated value Y of the useful life is The corrosion amount per year based on the maximum corrosion amount derived in the corrosion amount deriving step and the age of the piping equipment is σ, and the minimum thickness indicated by the evaluation result in the minimum wall thickness evaluation step is tm. When the minimum required thickness of the pipe is t0, it is expressed as Y = (tm-t0) / σ * Z using the correction coefficient Z, and the correction coefficient Z is the service life. By assigning a numerical value greater than 0 indicating a degree of influence and smaller than 1 to each of a plurality of factors that are assumed to affect the estimated value Y of N, and subtracting the sum of those numerical values from 1, 0 <Z <When set in the range of 1 and the degree of progress of corrosion is evaluated based on the first numerical value that is larger as the age of the pipe is larger, the analysis result of the water quality analysis that analyzes the quality of the water flowing through the pipe The second numerical value that is larger, and at least two of the third numerical value that is larger when the degree of progress of corrosion is evaluated to be large based on the usage status and installation environment of the piping, is at least 2 of the plurality of factors. Assigned as a numerical value. In still another aspect, the pipe evaluation method of the present invention includes a corrosion inspection step for inspecting a corrosion state on an inner surface of a sample pipe based on an X-ray inspection, and the sample pipe based on an inspection result in the corrosion inspection step. A deterioration evaluation step for evaluating the degree of deterioration with respect to the entire evaluation target range including at least, and the deterioration evaluation step derives the corrosion amount in the sample pipe based on the inspection result of the corrosion inspection step. A minimum thickness evaluation step for evaluating a minimum thickness of the pipe based on the corrosion amount derived in the derivation step, the corrosion amount derived in the corrosion amount derivation step, and the minimum thickness evaluation for each of the plurality of types of sample pipes. A rank determination step for determining a deterioration rank according to the deterioration degree indicated by the evaluation result in the step; The number of ranks of the degradation rank is the same regardless of the type of the sample pipe, and at least two types of the sample pipes having different ranking criteria based on the evaluation result in the minimum wall thickness evaluation step are used. In the corrosion inspection step, an X-ray imaging image including cross sections of both end portions in the radial direction of the sample pipe is shown by X-ray inspection including detection of X-rays passing near the axis of the sample pipe in the corrosion inspection step. Image data is acquired, and in the corrosion amount derivation step, among the pixels included in the X-ray captured image, the reference near the axis of the sample pipe with respect to the brightness value of the pixel at the reference location near the axis of the sample pipe While acquiring the relative magnitude of the brightness value of the pixel at a location different from the location based on the image data Obtained on the basis of the relative size and the nominal wall thickness values of the sample pipe of the brightness value, the corrosion amount in the another portion is derived.

  According to the present invention, the degradation rank is determined based on a standard having a common rank number for each of a plurality of types of sample pipes, the service life is evaluated in consideration of various conditions such as the age of the pipes, and both ends of the pipes are evaluated. By evaluating the thickness based on the X-ray image including the cross section of the part, the pipe is evaluated in consideration of various situations surrounding the sample pipe. As a result, it is possible to evaluate the correct deterioration state while widely considering the piping state.

It is a flowchart which shows each step of the piping evaluation method which concerns on one Embodiment of this invention. It is a front view of piping which shows an example of the joining method of piping. It is a schematic diagram which shows a mode that X-rays are irradiated to piping from an X-ray irradiation apparatus in X-ray inspection. It is a flowchart which shows each step of the method of determining the degradation rank of piping. It is an example of the X-ray imaging of piping. It is a schematic diagram of the X-ray image which shows the formation condition of the scale in piping. It is a table | surface which shows the evaluation result by one Example of the piping evaluation method of this embodiment. It is a table | surface which shows the evaluation result by another Example of the piping evaluation method of this embodiment.

  Hereinafter, an embodiment of the present invention will be described. The piping evaluation method according to the present embodiment relates to a method for evaluating deterioration of piping equipment constructed in office buildings, schools, hotels, amusement facilities, and the like. This method assumes that the evaluation result will be used as a reference when considering equipment maintenance and renovation. Also, based on the evaluation results, existing equipment that cannot be used will be replaced, but those that can be used will be used as they are, thereby reducing the maintenance effort and costs and extending the life of the entire equipment. be able to. The range to be evaluated is the whole or a part of the piping equipment constructed in the facility. This piping evaluation method is implemented along the steps shown in FIG. Hereinafter, a description will be given with reference to FIG.

  First, a preliminary survey will be conducted regarding the scope of evaluation for piping equipment. In the preliminary survey, interviews with facility managers and owners, check of drawings related to the piping system, simple survey of the actual site, etc. are performed (step S1 in FIG. 1; hereinafter, simply referred to as “S1”, etc.). Next, the characteristics of the equipment are grasped (S2). Specifically, the usage, usage status, classification, classification, joining method, etc. of piping are as follows.

  Regarding the use of piping, it is specified whether the piping is a water supply pipe, a hot water supply pipe, a drain pipe, a drain pipe, an air conditioning pipe, a sanitary pipe, or the like. Moreover, regarding the usage status of the piping, it is specified whether or not there is a load due to internal pressure, whether or not the piping is always filled with liquid, and the like. Air conditioning piping, sanitary piping, water supply pipes, hot water supply pipes, and the like are subjected to loads due to internal pressure. On the other hand, drain pipes and drain pipes are not loaded by internal pressure. Regarding the classification of piping, it is specified whether the piping is a steel pipe (carbon steel pipe, etc.), a cast iron pipe, a lining steel pipe, a copper pipe, a stainless steel pipe, or the like. Regarding piping classification, it is specified whether each part of the piping equipment is a main pipe, a standing system pipe, a branch pipe, a branch pipe or the like.

  Moreover, regarding the joining method of piping, what kind of joint is used is specified. FIG. 2 shows an example of a joining method, and straight pipe portions 11 to 15 are connected to each other by joint portions 21 and 22. A portion closer to the end portion than the straight pipe portions 11 to 15 is threaded on the outer surface to constitute a screw portion. For example, screw portions 11 a to 13 a are provided on the end side of the straight pipe portions 11 to 13. The inner surfaces of the end portions of the joint portions 21 and 22 are threaded so as to engage with the screws on the straight pipe portions 11 to 14 side. The straight pipe parts 11 to 14 and the joint part 21 or 22 are connected by fastening the screws to each other. In addition to such a joining method, pipes may be connected to each other using a joint called a mechanical joint that does not require a thread on the outer surface of the straight pipe portion, or may be joined by welding. In these cases, a pipe having no threaded portion is used as the straight pipe portion.

  Next, a sample to be inspected is extracted from each part of the piping (S3). Originally, it is preferable that the entire evaluation range is an inspection target, but this is often impossible due to time and cost. Therefore, in many cases, a plurality of locations are extracted from the evaluation range and used as evaluation samples. When the inspection object is a straight pipe portion, the sample unit is from one end of the straight pipe portion to the other end (range Q in FIG. 2). When the inspection object is a joint, the unit of the sample is one joint. Then, the inspection content is determined for each sample (S4).

  The contents of the inspection are determined as appropriate for the determination of the degradation rank and the estimation of the service life described later. Appropriate inspection conditions for determining the degradation rank and the like vary depending on the type of the target piping, the usage state of the piping, and the like. For example, in the case where the target pipe is a carbon steel pipe, the straight pipe portion of the sample is included as a target for the later-described X-ray inspection or the like regardless of whether the pipe includes a threaded portion. Since the thickness of the threaded portion is smaller than that of the straight tube portion (for example, about half the thickness of the straight tube portion), when corrosion progresses, a hole due to corrosion penetrates the threaded portion before the straight tube portion. Therefore, it is difficult to grasp whether the corrosion portion is the most advanced corrosion portion or the maximum amount of corrosion. Further, when the target pipe is a pipe with resin lining, such as a lining steel pipe, it is suitable to determine the deterioration rank based on the thickness value of the joint portion. This is because when the pipe is provided with a resin lining, the joint portion is more likely to deteriorate than the straight pipe portion. Therefore, in this case, the joint portion is included as a target for an X-ray inspection or the like described later.

Each inspection method has the following characteristics. For this reason, an appropriate inspection method is selected according to the sample classification and usage. As an inspection method of this embodiment, (1) appearance observation,
There are (2) X-ray examination, (3) endoscopy, (4) ultrasonic examination, (5) water quality analysis, (6) macroscopic / microscopic observation, and the like.

(1) Appearance observation In the appearance observation, leakage of fluid from the inside of piping, such as anticorrosive coating and galvanization of pipes, and the state of heat insulating materials, etc. are inspected by visual inspection or a photograph check of the appearance. As long as the external appearance of the pipe can be grasped, external observation is always performed.

(2) X-ray inspection (corrosion inspection step)
The X-ray inspection method is as follows. As shown in FIG. 3, X-rays are irradiated from the X-ray irradiation apparatus 100 toward the sample S. By detecting the transmitted light, a transmission image of the pipe is acquired. Alternatively, the photosensitive film may be exposed to transmitted light and then developed, and the development result may be captured by a scanner. FIG. 3 schematically shows an example of the relationship between transmitted X-rays and imaging results. Each pixel of the captured image obtained by the X-ray inspection corresponds to a transmission X-ray path. Depending on the thickness of the pipe along each path, the intensity of the transmitted X-ray corresponding to the path changes. On the other hand, the pixel value of each pixel in the captured image differs according to the intensity of the transmitted X-ray corresponding to that pixel. Therefore, the captured image is an image according to the thickness of each part of the sample S. For example, it is assumed that X-ray imaging is expressed in gray scale, and the brightness of each pixel indicates the intensity of transmitted X-rays corresponding to that pixel. Specifically, it is assumed that the higher the lightness, the weaker the transmitted X-ray, and the lower the lightness, the stronger the transmitted X-ray. In this case, the high brightness of a certain pixel indicates that the thickness of the pipe along the path corresponding to that pixel is large. Moreover, the low brightness of a certain pixel indicates the opposite. FIG. 5 is an example of X-ray imaging expressed in gray scale.

  Therefore, in the X-ray inspection, the thickness of the pipe is derived by analyzing the acquired image. The analysis is performed by computer analysis of the image data. For example, the computer analysis may be performed on a corrected image obtained by performing image processing for enhancing brightness on an acquired image. A specific method for deriving the thickness in the computer analysis will be described later. The selection criteria for the X-ray examination are as follows. The inspection can basically be selected regardless of the classification of piping (lined steel pipe, copper pipe, etc.) and application. When the outer surface of the pipe is covered with a heat insulating material such as urethane foam, it is often possible to take a picture as it is. When the pipe diameter exceeds the range where imaging can be performed once, the entire image may be acquired by imaging a plurality of times while changing the X-ray irradiation direction. However, when the pipe diameter is large to some extent and the inspection is performed in a state where water is almost filled, the irradiated X-rays are likely to be scattered, which is relatively unsuitable for the main inspection.

(3) Endoscopy (optical observation)
Endoscopic examination is performed by imaging the inside of a sample with an endoscopic camera. The captured image is evaluated by sensory evaluation or computer analysis. The selection criteria for endoscopy are as follows. This inspection can only be performed after draining the pipe because the endoscope is passed through the sample. On the other hand, drainage may be difficult depending on the usage status of the piping, and in such cases it is not suitable for this inspection.

(4) Ultrasonic inspection The method of ultrasonic inspection is as follows. Ultrasonic waves are emitted from the outer surface of the sample into the pipe. By capturing the reflected wave reflected from the inner surface of the pipe, the thickness of the pipe is measured based on the propagation time. There are many thickness measuring instruments using such ultrasonic waves, and any measuring instrument may be used. When the outer surface of the pipe is covered with a heat insulating material or the like, it is often necessary to measure after removing the heat insulating material or the like. The selection criteria for this examination are as follows. When the pipe diameter is large to some extent and the inspection is performed in a state where the water is almost filled inside, the ultrasonic inspection is selected instead of the X-ray inspection as described above. In addition, ultrasonic inspection may not be used depending on the piping material. Furthermore, it is difficult for the ultrasonic inspection to grasp the state of pitting corrosion having a relatively narrow width. This is because, for example, the depth of pitting that is narrower than the resolution of the inspection apparatus cannot be accurately grasped. Moreover, when detecting pitting corrosion with a comparatively wide width, it is necessary to grasp the whole image of pitting corrosion by measuring a plurality of times while shifting the inspection position little by little. As described above, the ultrasonic inspection can locally grasp the situation of the inner surface of the pipe, but it is difficult to grasp the situation in a wide range.

(5) Water quality analysis (water quality analysis step)
In the water quality analysis, the following items related to the quality of water flowing through the pipe are inspected and calculated. (Reference items) dissolved oxygen, pH, electrical conductivity, chloride ion concentration, sulfate ion concentration, acid consumption, total hardness, calcium hardness, ionic silica concentration, turbidity. (Reference items) Iron ion concentration, zinc ion concentration, copper ion concentration, chemical oxygen demand, sulfide ion concentration, ammonium ion concentration, residual chlorine concentration, free carbonic acid concentration, saturation index (Langeria) Index), Mattson ratio. Water quality analysis can be applied to all categories other than drainage pipes.

  The above items are preferably adopted according to the classification and use of the piping. For example, the Langeria index is a corrosive index for any type of piping, such as steel pipes and copper pipes, and therefore, any pipe is preferably employed as an analysis item. On the other hand, the Mattson ratio is mainly used as an indicator of the corrosiveness of the copper pipe, and is therefore used when the inspection target includes a copper pipe.

  Samples for water quality analysis are general tap water, water stored in a water supply source (such as a water supply tank) in a facility to be inspected, and water at the end of a pipe such as a faucet. By comparing these inspection results, it is used as an index for evaluating the deterioration of the pipe. For example, when the steel pipe is included in the inspection object and the concentration of iron ions at the end of the pipe is higher than the water supply source, it is estimated that the pipe material is eluted in the water. However, if the concentration of iron ions in the water supply source is high in the first place, there is a possibility that it does not depend on the elution of the piping material. Further, by comparing the general tap water and the water of the water supply source, it is estimated whether there is a problem with the water supply source itself such as deterioration of the water supply tank.

The need for water quality analysis is high when copper pipes are included in the inspection target. For example, the cause of type I pitting corrosion and type II pitting corrosion can be estimated based on the Mattson ratio, pH, free carbonic acid concentration, and the like. Type I pitting corrosion tends to occur in water supply piping when the pH is relatively low and the concentration of free carbonic acid is high. Type II pitting corrosion tends to occur in hot water supply piping when the Mattson ratio is 1 or less and the pH is less than 7. Further, it is known that moundless pitting occurs even when the Mattson ratio is 1 or more. According to recent research, the moundless pitting corrosion is said to occur when the concentration of ionic silica (SiO ₂ ) is high and the sulfate ion concentration is relatively high. Furthermore, since chloride ions and sulfate ions destroy the protective coating formed on the inner surface of the copper tube, the concentration of these ions is also important.

  As described above, there is a strong correlation between the results of water quality analysis and the occurrence of corrosion. On the other hand, regional characteristics may be seen in water quality. For this reason, when it is known from the past water quality surveys that there are corrosive water quality characteristics in the area where the facility exists, it is preferable to pay attention to the water quality characteristics in the water quality analysis. For example, it is known that in certain areas of Hokkaido, the concentrations of ionic silica and sulfate ions, which are the cause of moundless pitting, tend to be high. Therefore, when the facility to be inspected is in or around the specific area, ionic silica and sulfate ions are added as inspection items for water quality analysis. Then, based on the concentration of ionic silica and the concentration of sulfate ions, whether or not moundless pitting corrosion has occurred is evaluated. It has also been proposed to depend on the relationship between these concentrations and the chloride ion concentration (Reference: “Influence of silica, chloride, and sulfate ions on pitting corrosion of copper” “Materials and Environment” ", 60, 126-128 (2011)). Therefore, in order to evaluate the occurrence of moundless pitting with higher accuracy, it is more preferable to use the concentration of ionic silica, sulfate ions and chloride ions. In this manner, the area and the inspection item may be associated with each other, and based on the association between the inspection item and the area where the facility to be inspected exists, it may be determined whether or not to perform water quality analysis on each inspection item. .

(6) Visual inspection / microscopic inspection (visual observation, optical observation)
In the macroscopic and microscopic inspection, a sample is partially taken out and the inner surface thereof is observed with the naked eye or a microscope. In particular, for copper pipes, microscopic observation is effective because minute corrosion that cannot be grasped with the naked eye may be a major cause of deterioration in piping function. When observing with the naked eye or under a microscope, the surface may be washed with a strong acid such as dilute sulfuric acid in order to remove deposits such as scales on the inner surface of the pipe in advance. This makes it possible to clearly observe pitting and erosion formed under the deposit.

  Next, based on the sample and inspection content determined in S3 and S4, the inspection is performed and the inspection result is analyzed (S5). Next, based on the result of the preliminary investigation in S1 and the analysis result in S5, it is determined whether or not the inspection is sufficient to evaluate the deterioration of the pipe (S6; corrosion inspection determination step). Whether or not the inspection is sufficient to evaluate the deterioration of the pipe mainly depends on the corrosion mode in the pipe grasped by the X-ray inspection in S5 and the tendency of the corrosion indicated by other inspections such as water quality analysis. It is determined based on the comparison of For example, if the result of water quality analysis or the like shows a tendency of corrosion, but no corrosion in the pipe is found by X-ray inspection or the like, the inspection of S5 is considered to be insufficient (S6, unsatisfactory). sufficient). That is, there is a possibility that the number of samples extracted and the extraction method are not sufficient. Therefore, the process returns to step S3 for re-inspection regarding another sample or additional inspection based on a new inspection item. On the other hand, when it is determined that the inspection of S5 is sufficient (S6, sufficient), the steps after S7 are performed.

  A specific example in the case where it is determined that the inspection of S5 is insufficient is as follows. Even if no corrosion is found by X-ray inspection or the like in S5, as a result of water quality analysis, the concentration of a specific component indicating corrosion is high (exceeding a predetermined reference value or above a predetermined reference value). If it is determined that there is an X), it is determined that the X-ray inspection or the like is insufficient (S6). Then, a sample is added and X-ray inspection is performed again, or visual observation / microscopic observation is performed (S3 to S5). For example, as described above, two concentrations of ionic silica and sulfate ions satisfy a predetermined condition suggesting moundless pitting corrosion, or three concentrations of ionic silica, sulfate ions and chloride ions are moundless. If another condition that strongly suggests pitting corrosion is satisfied, whether or not moundless pitting corrosion has occurred by extracting a part of the piping as a sample and observing the inner surface with the naked eye / microscope Check again. Further, even when the sample is already observed with the naked eye, a microscopic observation may be added, or the macroscopic / microscopic observation may be performed again after washing with a strong acid.

  Based on the inspection results of S3 to S6, (a) a deterioration rank indicating the degree of deterioration is determined (S7; deterioration evaluation step), and (b) the service life is estimated (S8; deterioration evaluation step). Hereinafter, determination of the degradation rank and estimation of the service life will be described.

(A) Deterioration rank determination The determination of the deterioration rank will be described. The method shown in FIG. 4 is performed using a predetermined standard based on the results of X-ray examination, ultrasonic examination, or endoscopic examination. Other methods will be described later. First, when determining the rank, it is selected whether to determine based on the thickness of the pipe or the blockage rate (S21). When an inspection for deriving the thickness of the pipe such as an X-ray inspection or an ultrasonic inspection is performed, the thickness is preferentially selected. On the other hand, some samples may not be inspected to derive the thickness of the pipe. In such a case, it is based on the blockage rate. When the rank is determined based on the thickness (S21, “thickness”), whether to determine the rank is selected based on the result of the X-ray inspection or the ultrasonic inspection (S22).

  When based on the X-ray inspection (S22, “X-ray”), first, the thickness reduction rate is derived by image analysis based on the X-ray imaging acquired in S5 of FIG. 1 (S23). As described above, the captured image reflects the thickness of the sample. Therefore, the thickness of a location where the thickness is desired to be derived (hereinafter referred to as a thickness deriving location) is derived based on the brightness of the pixel corresponding to the location. Also, a reference location (hereinafter referred to as a reference location) for deriving the thickness is set. The reference location is set to a location where the thickness is estimated not to decrease at all. That is, the position is set to the highest brightness in the target area.

  The thickness deriving location is set according to the classification and application of the piping. For example, when the pipe is a carbon steel pipe, the straight pipe portion is set regardless of whether or not the sample has a thread portion. Moreover, when piping is a lining steel pipe, a thickness derivation | leading-out location is set to a joint part. This is because they are suitable for estimation of the deterioration rank and the service life as described above. Further, the threaded portion has a tapered shape with a smaller thickness as it approaches the tip. This is because the thickness is not constant and it is difficult to grasp the standard of thickness. Note that it is preferable to set a plurality of thickness derivation locations for each sample. As described above, which part should be set for the thickness derivation location differs depending on the classification and application of the pipe. For this reason, in S4, it is necessary to set inspection conditions so that a thickness derivation location can be appropriately set. For example, as described above, when the sample is a carbon steel pipe, the straight pipe portion must be included in the X-ray inspection target as an inspection condition.

  Moreover, both the thickness deriving location and the reference location are set near the axis of the pipe. For example, it is set within the area indicated by R in FIG. As shown in FIG. 3, the farther away from the axis, the more the path of the transmitted X-ray deviates from the radial direction of the pipe, so that the intensity of the transmitted X-ray and the thickness of the pipe are difficult to correspond.

  Then, the ratio of the brightness value of the pixel corresponding to the thickness deriving location to the brightness value of the pixel corresponding to the reference location is calculated. Thereby, the ratio of the thickness at the thickness deriving location when the thickness at the reference location is set to 1 is obtained. Next, the thickness at the thickness deriving location is derived based on the assumption that the thickness at the reference location is equal to the nominal thickness value of the pipe. That is, the thickness is derived by (thickness of the thickness deriving location) = (nominal thickness value) * (thickness ratio).

  On the other hand, when the ultrasonic inspection is selected in S22 (S22, “ultrasound”), the thickness of the thickness deriving location is directly acquired from the measurement result of the ultrasonic measuring device in S5 (S23).

  Next, the thickness acquired in S23 or S24 is subtracted from the nominal thickness value for each thickness deriving location. This value corresponds to the amount of corrosion at each thickness deriving location (S25). Since one or more thickness deriving locations are set for each sample, one or more corrosion amounts are also acquired for each sample. Hereinafter, the maximum value of the corrosion amount for each sample is referred to as the maximum corrosion amount in the sample. The place where the maximum amount of corrosion in the sample is taken is the place where the progress of corrosion is fastest in the sample. Of the plurality of samples, the sample with the largest maximum corrosion amount in the sample is the sample with the most corrosion.

  However, since the sample is only a part of the entire piping system, the maximum value of the maximum amount of corrosion in the sample in all samples does not match the value of the most corroded portion of the entire piping system. there is a possibility. Therefore, depending on the case, the amount of corrosion at the location where the corrosion is most advanced in the entire piping is statistically estimated. On the other hand, when the number of samples is sufficiently large, the maximum value of the maximum corrosion amount in the sample may be estimated as the actual maximum value of the entire piping system without estimating the maximum value.

  Based on the above, whether or not to use the maximum value estimation is selected (S26). When the estimation of the maximum value is used (S26, Yes), the true maximum value in the piping system is estimated using one of the following two methods.

The first method is as follows. First, when the entire piping system includes sections such as (Category 1) main pipe, (Category 2) system pipe, and (Category 3) branch pipe, the maximum value of the corrosion amount is acquired for each of these sections. Assuming that the maximum value of the corrosion amount for each category is x, the distribution F (x) is assumed to be expressed by the following Equation 1, and the parameters λ and α are set using the MVLUE (Minimum Variance Linear Unbiased Estimate) method. To derive. The recurring period is T, and an estimated value S of the true maximum value is derived from Equation 2. Here, exp represents an exponential function, and ln represents a natural logarithm.
[Formula 1] F (x) = exp [−exp {− (x−λ / α)}]
[Formula 2] S = λ + α * ln (T)

The second method is as follows. In general, as the number of measurements increases, the measured value of the corrosion amount follows a normal distribution. Therefore, even when the actual number of measurements is limited, a confidence interval in which the reliability is a specific value is derived. Thus, the true maximum value of the corrosion amount can be estimated. Specifically, when the population follows a normal distribution with an average μ, _assuming that the average corrosion amount for all thickness deriving locations is m and the square root of its unbiased variance is δ _n−1 , t = (m− μ) * √N / δ _n−1 follows the t distribution f _N−1 (t). N is the number of samples. Thus, if the confidence interval is {−t _a , t _a } (t _a > 0), the average μ of the population satisfies Equation 3 below. Here, when β is a reliability, ∫ {−t _a → t _a } f _N−1 (t) dt = β is satisfied from the definition of the confidence interval. ∫ {a → b} g (t) dt is a definite integral from t = a to t = b (> a) of the function g (t). From the above, for example, S represented by Equation 4 is estimated as the maximum value of the corrosion amount.
[Formula 3] m−δ _n−1 * t _a / √N <μ <m + δ _n−1 * t _a / √N
[Formula 4] S = m + δ _n−1 * t _a / √N

  Next, a deterioration rate is derived for each sample (S28). The deterioration rate is the ratio of the corrosion amount to the nominal thickness value when it is assumed that the corrosion has progressed to the maximum corrosion amount estimated in S27 in each of the straight pipe portion, the thread portion, and the joint portion. Since the nominal wall thickness value differs depending on each part of the straight pipe part, the thread part, and the joint part, the deterioration rate is calculated for each. However, since only the one with the highest deterioration rate is used for determining the deterioration rank and estimating the useful life, only the one with the highest deterioration rate may be calculated.

  On the other hand, if it is determined in S26 that the estimation of the maximum value is not used (S26, No), the ratio of the maximum corrosion amount in the sample to the nominal thickness value is calculated as the deterioration rate for each sample (S29). Since the nominal wall thickness value differs depending on each part of the straight pipe part, the thread part, and the joint part, the deterioration rate is calculated for each. However, as described above, only the one having the largest deterioration rate may be calculated.

  Next, a degradation rank is determined based on the maximum degradation rate calculated in S28 or S29 (S30). At this time, the following Table 1 or Table 2 is used. Tables 1 and 2 are examples of criteria for determining the degradation rank. Tables 1 and 2 are created on the basis of the three viewpoints of whether or not there is a load due to internal pressure in the piping that is subject to deterioration rank determination, the classification of the piping, and whether or not the piping includes a threaded portion. Table 1 is used when there is a load due to internal pressure, and Table 2 is used when there is no load due to internal pressure.

  Table 1 includes columns i through c. First, it is determined whether to use row A or row B or to use row C, depending on whether or not the pipe has a resin lining. When the pipe for which the degradation rank is to be determined is a pipe with a resin lining, the criteria for row C are used. On the other hand, when the pipe is a pipe that has not been subjected to resin lining, it is determined which one of row A and row B is used depending on whether or not a thread portion is provided at the end of the straight pipe portion. . If there is a threaded portion, the row reference is used, and if there is no threaded portion, the row reference is used.

  Symbols a1, a2, b1, b2, c1, and c2 included in each column indicate reference values of deterioration rates. These values satisfy the relationship of a1> a2, b1> b2, and c1> c2. Each column shows the correspondence between the degradation rank included in the leftmost column in Table 1 and the range of the degradation rate. For example, row A is degradation rank A when the degradation rate is a1 or more, degradation rank B when the degradation rate is in the range of a2 or more and less than a1, and the degradation rate is less than a2. Indicates that the rank is degradation rank C. Thus, the deterioration rank is determined as one of A to C depending on which range in the table the deterioration rate based on the measured value falls into. The degree of deterioration decreases in the order of A → B → C.

  The reference for row A is set so that the deterioration rank indicates that the degree of deterioration is high even if the deterioration rate is relatively small compared to the reference for row or row C. For example, a1 <b1, a2 <b2, a1 <c1, a2 <c2 are set. The speed at which the wall thickness decreases is the same regardless of whether it is a threaded part or straight pipe part. Compare the case where the threaded part is provided with the case where the threaded part is not provided. This is because even if the deterioration rate is the same, the former is expected to reach the limit earlier than the latter.

  The criterion for row C is set so that the degradation rank indicates that the degree of degradation is high even if the degradation rate is relatively small compared to the criterion for row C. For example, c1 <b1 and c2 <b2 are set.

  Table 2, like Table 1, shows the correspondence between the degradation rank and the range of the degradation rate. d1, d2, e1, e2, f1, and f2 indicate reference values of deterioration rates, and satisfy the relations of d1> d2, e1> e3, and f1> f2. Since Table 2 is applied in the case of a drain pipe or the like to which no internal pressure is applied, each of columns D to F is intended for a pipe that is not subjected to resin lining. As in the case of row A and row B in Table 1, the criteria for row D and row E are properly used depending on whether or not a screw portion is provided. Therefore, for example, there is a relationship of d1 <e1, d2 <e2. The standard of the F row is used when the diameter of the pipe is relatively large with respect to the E row. For example, the reference for the row is used when the diameter of the pipe is X mm or more, and the reference for the row is used when the diameter of the pipe is less than X mm. For example, there is a relationship of e1 <f1, e2 <f2.

  After determining the deterioration rank as described above, the overall rank is determined according to the deterioration ranks in a plurality of samples (S31). For example, the overall rank may be determined in units of sections such as a main system, a branch pipe, and a branch pipe. In this case, the rank indicating that the deterioration is most advanced among the deterioration ranks of all the samples included in the category is determined as the overall rank. This is because it is necessary to consider the most deteriorated part with the highest priority in the maintenance of the equipment. In addition, the overall rank may be determined for each use of the piping, such as the entire system of the water supply pipe if the evaluation target is a water supply pipe, and the entire system of the hot water supply pipe if the evaluation target is a hot water supply pipe. Whether or not the overall rank, that is, the evaluation of the deterioration status of the piping and the entire system correctly reflects the actual situation depends on whether the inspection and extraction of the sample are sufficient. In the present embodiment, not only corrosion is inspected simply by X-ray inspection or the like, but also whether or not the inspection is sufficient is determined based on water quality analysis (S6 in FIG. 1). If the number of samples and the contents of inspection are insufficient, a sample is added and reinspection is performed, or inspection items are added. Therefore, since sufficient inspection is performed to evaluate the deterioration state of the piping and the entire system, the deterioration state can be appropriately evaluated.

  If it is selected in S21 that the rank is determined based on the blocking rate (S21, “blocking rate”), the blocking rate is derived as follows (S41). The occlusion rate is derived from an image obtained by X-ray examination or endoscopy using sensory evaluation or image analysis. In sensory evaluation, it is visually evaluated how much the scale is clogged in the pipe from the scale generation state in the image. In the image analysis, the computer calculates the ratio of the area of the net region where the scale is formed in the image to the entire region in the tube (the tube region in FIG. 6) when there is no scale. Specifically, for example, the computer displays an image of a cross section of the pipe on the display and receives an input for designating an arbitrary range in the image via an input device such as a pointing device or a keyboard. Thereby, when the user roughly specifies the area where the scale is formed (scale forming area in FIG. 6), the computer recognizes the edge of the scale existing within the range specified by the user, and based on the recognition result, The area of the net area where the scale is formed is calculated. Note that the user may directly specify an edge via a pointing device. Then, the computer calculates the ratio of the net area where the scale is formed to the area of the entire region in the tube.

  Next, a degradation rank is determined based on the derived blockage rate (S42). The degradation rank is determined based on Table 3 showing the correspondence relationship between the range of the blocking rate and the degradation rank. Symbols g1 and g2 included in each column of Table 3 indicate reference values for the blocking rate, and satisfy g1> g2. It should be noted that the deterioration rank criteria may be different from those in Table 3 depending on the classification, usage, usage status, etc. of the pipes. Tables 1 and Tables used when determining based on the deterioration rate This is the same as the case of 2.

  Note that the degradation rank may be determined without being based on either the degradation rate or the blockage rate. For example, when the pipe is a copper pipe, there is often no obvious deterioration feature from an image taken by X-ray inspection or endoscopic inspection. Therefore, in this case, a sample is cut out from the piping system, and the corrosion state of the inner surface is grasped by visual observation / microscopic observation. Also, grasp the cause of piping deterioration. Further, there may be a case where a comprehensive determination is made according to the usage environment of the piping. Regarding the corrosion status, for example, the extent to which patina is generated, the extent to which other corrosion products are generated, the extent to which pitting corrosion and erosion have occurred (depth and number of pitting corrosion, etc.), respectively. Rank. Regarding the usage environment, refer to the history of maintenance management and rank the number of times that water leakage has occurred in piping, the number of years since the start of use of piping equipment, etc., respectively. Then, the ranking result of these rankings is comprehensively determined, and the deterioration rank of the pipe (copper pipe) is determined.

(B) Estimating the service life The service life is usually calculated based on the result of calculating the remaining thickness of the piping and the number of years since the start of use of the piping equipment. Basically, the service life is the minimum remaining wall thickness in each sample divided by the rate of corrosion. The rate of corrosion is a value obtained by dividing the maximum value of the corrosion amount by the number of years elapsed.

  On the other hand, the above calculation method is based on the premise that the amount of corrosion is linear with respect to the elapsed time, and that the start of corrosion is simultaneous with the start of equipment use. However, these assumptions do not always hold. The following factors further contribute to the derivation of an accurate service life. (Factor I) The start of corrosion is not always the same as the start of use of equipment. (Factor II) The mode of corrosion varies depending on the usage status and installation environment of the piping. (Factor III) The degree of corrosion changes depending on physical factors such as changes in water quality. (Factor IV) The measurement accuracy is limited. These are examples of assumed factors.

Therefore, it is considered to introduce a correction coefficient Z (0 <Z <1) for derivation of an accurate service life and calculate the service life based on the following formula 5. Here, Y is the service life, t _{m is the} minimum remaining thickness, t _{0 is the} minimum required thickness, and σ is the amount of corrosion per year. t _m is obtained by subtracting the maximum corrosion amount in the sample or the estimated maximum value from the nominal wall thickness of the pipe. The minimum required thickness is the minimum thickness that can withstand the assumed internal pressure. σ is calculated by dividing the amount of corrosion to date by the age of the equipment.
[Formula 5] Y = (t _m −t ₀ ) / σ * Z

An example of a method for setting the correction coefficient Z is as follows. As shown in Table 4, coefficients x ₁ , x ₂ , x ₃ , and x ₄ (all positive real numbers) are set for each factor that requires correction of the useful life.

These coefficients are set in a range satisfying 0 ≦ x ₁ + x ₂ + x ₃ + x ₄ <1. In this example, four factors are considered. If the assumed factor is different from this, the number of coefficients corresponding to the number of factors is set. By the way, it is considered that how much the above-mentioned factors affect the estimation of the service life depending on the piping situation at the time of estimating the service life. For example, if the age of piping is already long and it is difficult to grasp the start of corrosion at the present time, the influence of factor I should be taken into account when estimating the service life. Therefore, in this case, a relatively large value coefficients _{x 1} (e.g., 0.2) to. Further, based on the results of water quality testing, changes in water quality to be able to infer that promotes the progress of corrosion, a relatively large value coefficients x ₃ factors III (e.g., 0.15) to. In this way, in each factor, the situation that promotes the progress of corrosion is recognized, or the situation is unknown with the information on hand, so it may be better to estimate the service life short considering the worst assumptions . In such a case, a large coefficient corresponding to the factor is set. Then, after setting x _{1 to} x ₄ , a correction coefficient Z is derived based on Equation 6.
[Formula 6] Z = 1− (x ₁ + x ₂ + x ₃ + x ₄ )

Another example of the method for setting the correction coefficient Z is as follows. If it is difficult to guess the cause of corrosion or the relationship between each factor and the degree of corrosion (for example, when the pipe is a copper pipe), set Z according to the number of years elapsed as shown in Table 5. May be. In the table, y ₁ , y ₂ , and y ₃ indicate the number of years, and y ₁ <y ₂ <y ₃ = (general useful life). For example, when the elapsed year is in the range of y ₁ to y ₂ , the correction coefficient Z is set as Z ₀ .

  Since the service life is estimated for each sample, it is important for the evaluation of the entire piping whether or not an adequate number of samples have been inspected. In the present embodiment, as described above, it is determined whether the inspection is sufficient based on the water quality analysis (S6 in FIG. 1). If the number of samples and the contents of inspection are insufficient, a sample is added and reinspection is performed, or inspection items are added. Therefore, since sufficient inspection is performed to evaluate the deterioration state of the piping and the entire system, estimation of the service life based on the inspection result is also sufficiently valuable.

(Example)
Hereinafter, an example where the piping is evaluated based on the above-described embodiment is described with reference to FIGS. 7 and 8. 7 and 8, all the units of the value indicating the size are millimeters, and all of the units of the value indicating the rate (ratio) are percentage.

  FIG. 7 is an example of an evaluation result when the maximum value estimation is not used in S26. Items 1 to 3 are the results of the preliminary survey (S1) and indicate the classification, use, and classification of the piping. Item 4 is an inspection method applied to each sample, and is selected based on items 1 to 3, the use state of piping, and the like (S4). For example, sample 1-2 is a carbon steel pipe and uses X-ray inspection. On the other hand, although the sample 1-1 is a carbon steel pipe, the endoscopic inspection is selected because the space for placing the inspection device cannot be secured. Sample 2-1 is selected for X-ray inspection, but sample 2-2 is ultrasonic because it exceeds the predetermined diameter and must be inspected with water inside. Inspection is selected.

  Items 5 to 10 are the age of the piping facility, the piping diameter, the joining method, and the nominal wall thickness, which were grasped in the preliminary survey (S1). Item 11 is the maximum amount of corrosion in the sample, that is, the maximum amount of corrosion in the sample. The maximum thinning rate of item 12 indicates the ratio of the maximum corrosion amount in the sample to item 8 or 10, that is, the nominal value of the straight pipe portion or the joint portion. In addition, since the sample 1-1 is only subjected to endoscopy, the thinning rate is not calculated. The same applies to items 12-19.

  The remaining thickness of items 13 to 15 is obtained by subtracting item 11 from each of items 8 to 10. As described above, the reason why the maximum corrosion amount in the sample is subtracted from the nominal thickness of each part is that the corrosion of the maximum corrosion amount in the sample is considered to occur regardless of whether it is a straight pipe portion or a screw portion. In other words, when the worst situation is assumed, there is a possibility that the maximum amount of corrosion in the sample may occur at any location. Note that items 13 to 15 include only some of the numerical values in each part. For example, in the case of sample 2-1, only the value related to the joint portion is included. This is because, as described above, when the pipe is a lining steel pipe, the thickness deriving portion is set in the joint portion. In the case of Samples 1-2 and 1-3, the thickness derivation location is set to the straight pipe portion, and only numerical values relating to the straight pipe portion and the screw portion are included.

  Items 16 to 18 are deterioration rates of the respective parts. For example, item 16 is calculated by multiplying item 11 divided by item 8 by 100 (S29). The maximum deterioration rate of item 19 is the maximum of the deterioration rates of the respective parts. Item 20 is the thickness of the deposit adhered to the inner surface of the tube, and is obtained by visual observation based on a captured image obtained by X-ray inspection or endoscopic inspection. The item 21 is obtained by visual observation or image analysis based on a captured image obtained by X-ray inspection or endoscopic inspection (S41). Item 22 is a degradation rank. The deterioration rank is determined based on Table 1 or Table 2 for the samples 1-1 to 2-2 from which the maximum deterioration rate is derived (S30). For example, the sample 1-3 is a water supply pipe, a carbon steel pipe, and has a threaded portion, so that the row A in Table 1 is used. The rank is determined to be A based on which range in row (a) of Table 1 corresponds to the maximum deterioration rate (69.1%). Moreover, since sample 2-2 is a water supply pipe and a vinyl lining pipe, row C in Table 1 is used. The rank is determined to be B based on which range in row C in Table 1 corresponds to the maximum deterioration rate (19.6). Further, for the sample 1-1 for which the maximum deterioration rate has not been derived, the rank is determined based on the blocking rate (S42).

Item 23 is acquired in the preliminary survey (S1). Item 24 is derived based on Equation 6 by referring to Item 5 (Elapsed Years) and others and considering various factors that are expected to affect the estimation of the useful life. The estimated useful life is calculated by Equation 5 based on items 5, 8-11, 13-15, and 24. In Equation 5, t _m is the minimum value among the items 13 to 15, and σ is obtained from the items 5 and 11.

  FIG. 8 is an example of an evaluation result when the maximum value estimation is used in S26. Item 26 is the true maximum value of the amount of corrosion estimated in S27. As described above, the maximum value is calculated for each section of piping. Items 27 to 33 are obtained by the same calculation as items 13 to 19 when item 11 is replaced with item 26. Then, as in the case of FIG. 7, the degradation rank is derived based on the item 33, and the estimated useful life is derived based on the items 27 to 29.

11-15 Straight pipe part 11a-13a Thread part 21 Joint part 100 X-ray irradiation apparatus S Sample

Claims (8)

Corrosion inspection step for inspecting the corrosion state on the inner surface of a plurality of types of sample pipes based on at least one of visual observation, optical observation, X-ray inspection, and ultrasonic inspection,
A deterioration evaluation step for evaluating a deterioration degree related to the entire evaluation target range including at least the sample pipe based on the inspection result in the corrosion inspection step;
The deterioration evaluation step includes
Corrosion amount derivation step for deriving the corrosion amount in the sample pipe based on the inspection result of the corrosion inspection step;
Based on the corrosion amount derived in the corrosion amount deriving step, a minimum wall thickness evaluation step for evaluating the minimum wall thickness of the pipe,
For each of the plurality of types of sample pipes, a deterioration rank corresponding to the degree of deterioration with respect to the nominal thickness of the sample pipe indicated by the evaluation result in the minimum wall thickness evaluation step is a reference value regarding the deterioration rank and the degree of deterioration with respect to the nominal thickness. And a rank determining step for determining based on information corresponding to a table associating the plurality of types of sample pipes with each other ,
The rank number of the degradation rank is common regardless of the type of the sample pipe,
The criteria for ranking based on the evaluation result in the minimum thickness evaluation step includes a reference value for the degree of deterioration with respect to the nominal thickness for each rank, and the presence or absence of a threaded portion, the presence or absence of a resin lining, and the presence or absence of a joint. The pipe evaluation method according to claim 1, wherein the reference value regarding at least one rank is different between at least two types of sample pipes different from each other with respect to at least one of the above .   2. The pipe evaluation method according to claim 1, wherein the ranking classification is different between the sample pipe having a load due to an internal pressure and the sample pipe having no load due to an internal pressure. In the corrosion inspection step, the sample pipe includes a resin-lined pipe and a joint portion that connects the pipe to other pipes,
The criteria for ranking are different between the joint and other pipes,
3. The pipe evaluation according to claim 1, wherein, in the rank determination step, when determining a deterioration rank of the pipe subjected to the resin lining, the pipe evaluation is based on the criteria of the rank classification related to the joint portion. Method. Further comprising a blockage evaluation step for evaluating the degree of blockage due to the scale formed in the sample pipe;
In the case where the rank criteria are the first reference when the deterioration rank is determined based on the evaluation result in the minimum wall thickness evaluation step, and the deterioration rank is determined based on the evaluation result in the blockage evaluation step. And a second standard of
The pipe evaluation method according to any one of claims 1 to 3 , wherein the number of ranks of the deterioration rank is common to the first reference and the second reference. A copper pipe is included in the evaluation target range,
The pipe evaluation method according to any one of claims 1 to 4 , wherein in the water quality analysis of the water flowing through the pipe, the concentration of ionic silica and the concentration of sulfate ions are derived. In the corrosion amount deriving step, a corrosion amount is derived for a portion having a larger nominal thickness of the sample pipe including two portions having different nominal thicknesses,
In the minimum thickness evaluation step, the remaining thickness when assuming that the same amount of corrosion as the maximum corrosion amount derived in the corrosion amount deriving step has occurred with respect to the smaller nominal thickness of the sample pipe The pipe evaluation method according to any one of claims 1 to 5 , wherein a minimum thickness is set. Corrosion inspection step for inspecting the corrosion state on the inner surface of a plurality of types of sample pipes based on at least one of visual observation, optical observation, X-ray inspection, and ultrasonic inspection,
A deterioration evaluation step for evaluating the degree of deterioration of the entire evaluation target range including at least the sample pipe based on the inspection result in the corrosion inspection step,
The deterioration evaluation step includes
Corrosion amount derivation step for deriving the corrosion amount in the sample pipe based on the inspection result of the corrosion inspection step;
Based on the corrosion amount derived in the corrosion amount deriving step, a minimum wall thickness evaluation step for evaluating the minimum wall thickness of the pipe,
For each of the plurality of types of sample pipes, a rank determining step for determining a deterioration rank according to the degree of deterioration indicated by the evaluation result in the minimum wall thickness evaluation step;
Deriving a service life estimate Y for each sample pipe,
The rank number of the degradation rank is common regardless of the type of the sample pipe,
The criteria for ranking based on the evaluation result in the minimum wall thickness evaluation step are different between at least two types of the sample pipes different from each other,
The estimated value Y of the service life is defined as an evaluation result in the minimum wall thickness evaluation step, where σ is a corrosion amount per year based on the maximum corrosion amount derived in the corrosion amount deriving step and the elapsed years of the piping equipment. Is expressed as Y = (t _m −t ₀ ) / σ * Z using the correction coefficient Z, where t _m is the minimum wall thickness and t ₀ is the minimum required pipe thickness.
The correction factor Z is
By assigning a numerical value larger than 0 and indicating a degree of influence to each of a plurality of factors assumed to affect the estimated value Y of the useful life, and subtracting the sum of the numerical values from 1 It is set in the range of 0 <Z <1,
A first numerical value that increases as the age of the pipe increases, a second numerical value that increases as the degree of progress of corrosion is evaluated based on the analysis result of the water quality analysis that analyzes the quality of water flowing in the pipe, and Assigning at least any two of the third numerical values as numerical values related to at least two of the plurality of factors as the degree of progress of corrosion is evaluated based on the usage status and installation environment of the piping. A characteristic pipe evaluation method. A corrosion inspection step for inspecting the corrosion condition on the inner surface of the sample pipe based on the X-ray inspection;
A deterioration evaluation step for evaluating a deterioration degree related to the entire evaluation target range including at least the sample pipe based on the inspection result in the corrosion inspection step;
The deterioration evaluation step includes
Corrosion amount derivation step for deriving the corrosion amount in the sample pipe based on the inspection result of the corrosion inspection step;
Based on the corrosion amount derived in the corrosion amount deriving step, a minimum wall thickness evaluation step for evaluating the minimum wall thickness of the pipe,
For each of the plurality of types of sample piping, including a rank determining step for determining a deterioration rank according to the deterioration degree indicated by the evaluation result in the minimum wall thickness evaluation step,
The rank number of the degradation rank is common regardless of the type of the sample pipe,
The criteria for ranking based on the evaluation result in the minimum wall thickness evaluation step are different between at least two types of the sample pipes different from each other,
In the corrosion inspection step, by X-ray inspection including detection of X-rays passing near the axis of the sample pipe, image data indicating an X-ray captured image including cross sections of both ends in the radial direction of the sample pipe is acquired. ,
In the corrosion amount derivation step,
Among pixels included in the X-ray captured image, the relative value of the brightness value of a pixel at a location different from the reference location near the axis of the sample pipe with respect to the brightness value of the pixel at the reference location near the axis of the sample pipe A specific size is acquired based on the image data, and the amount of corrosion at the other location is derived based on the acquired relative size of the brightness value and the nominal thickness value of the sample pipe. Piping evaluation method characterized by the above.