JP2013122411A - Pipe creep life evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pipe creep life evaluation method capable of performing life evaluation with high accuracy by estimating the degree of progress of a creep damage from the amount of change in outer diameter by accurately specifying a swelling place in a pipe covering a wide range.SOLUTION: A life evaluation method of a pipe (1) relating to this invention includes the steps of: preliminarily and tentatively calculating a relation between the life consumption rate and the swelling amount of the pipe, and calculating an allowable swelling amount Rs by applying the current life consumption rate to the relation with the swelling amount that is preliminarily and tentatively calculated (step S103); converting the allowable swelling amount into an allowable outer diameter Ls (step S104); specifying a swelling range (3) by using a first gauge (2) having an inner diameter corresponding to the allowable outer diameter (step S105); specifying the maximum swelling point (6) by using a second gauge (5) having a larger inner diameter (step S107); and calculating a life consumption rate by calculating the maximum swelling rate from an outer diameter measured at the maximum swelling point (step S109).

Description

  The present invention relates to a pipe life evaluation method for performing life evaluation by calculating a life consumption rate of a pipe based on an outer diameter change amount due to aging in a pipe used for a heat transfer pipe such as a boiler pipe. Related to the field.

  Piping used for boiler tubes and the like of thermal power plants is manufactured from a metal material such as 9-12 chrome steel (Tue STBA28, Tue SUS410J3, etc.). Pipes made of this type of material are subject to creep damage due to the generation of steam oxidation scale inside the pipe as it deteriorates over time.

  Boiler piping has a design life with a sufficient margin, but facilities such as thermal power plants are aging and are expected to be used for as long as possible beyond their design life. Is the actual situation. Under such circumstances, research has been conducted on methods for estimating the remaining life of piping. For example, in Patent Document 1, there is a technique for estimating a stress increase due to a change in the outer diameter or thickness of a pipe accompanying the progress of creep damage and a temperature change accompanying scale generation, and performing a life evaluation based on a creep rupture diagram obtained in advance. It is disclosed. Patent Document 2 discloses a method for evaluating the life based on the amount of deformation accompanying the progress of creep damage in the bent portion of the pipe.

Japanese Patent No. 3171285 JP 2009-180610 A

  In this type of piping, when the scale generated on the inner surface peels off or rises, the heat transfer is locally inhibited at that portion, and the temperature rises. As a result, creep damage may be locally accelerated in a part of the piping. Materials used for piping include a tempered martensite structure, and it is known that when such materials are subjected to local thermal processing, the strength rapidly decreases. Therefore, in the life evaluation of piping, it is important for safety to estimate the life based on the location where damage is most advanced.

  However, in a large-scale facility such as a boiler, when a pipe is used over a wide range as a heat transfer rod, it is difficult to specify a site where damage is locally progressing in this way. Therefore, even when performing life evaluation based on the measurement result of the outer diameter of the piping as in Patent Documents 1 and 2, it is possible to visually determine the location where the bulge amount will be the largest, The current situation depends on general measuring instruments, and the accuracy of the evaluation results cannot be said to be sufficient.

  In particular, the high-strength steels such as the above-mentioned fire STBA28 and fire SUS410J3 have a slight change in the outer diameter at the time of creep damage. Therefore, with the conventional evaluation method, it is difficult to consider the progress of local damage, and accurate evaluation is difficult.

  Moreover, when measuring the bending part which is the measurement object in Patent Document 2 with a general caliper, a measurement error is large and high life evaluation accuracy cannot be expected.

  The present invention has been made in view of the above-mentioned problems, and by accurately identifying the maximum bulge location in a wide range of pipes, the progress of creep damage is estimated from the amount of change in outer diameter, and the life evaluation is performed accurately. The purpose is to provide a method for evaluating the service life of piping.

  In order to solve the above problems, the pipe life evaluation method according to the present invention is a pipe life evaluation method for performing life evaluation of the pipe by calculating a life consumption rate based on an outer diameter change amount of the pipe. The allowable swell rate calculating step for obtaining the allowable swell rate by preliminarily obtaining the relationship between the life consumption rate and the bulging amount in advance and applying the allowable lifetime consumption rate of the pipe to the relationship in advance. And an allowable outer diameter calculating step for calculating an allowable outer diameter from the calculated allowable bulging rate, and a first gauge having an inner diameter corresponding to the calculated allowable outer diameter along the extending direction of the pipe. A bulging range specifying step for specifying a bulging range in which the outer diameter bulges beyond the allowable outer diameter by moving while covering the outer diameter, and a second gauge having a larger inner diameter than the first gauge. An outer diameter cover along the extending direction of the pipe A maximum bulging point identifying step for identifying the largest bulging point having the largest bulging amount in the identified bulging range, and an outside of the pipe at the identified maximum bulging point. The maximum bulging point outer diameter measuring step for measuring the diameter, the maximum bulging rate is calculated from the measured maximum bulging outer diameter, and the lifetime consumption rate is calculated by applying the calculated maximum bulging rate to the relationship. A lifetime consumption rate calculating step.

  According to the present invention, by moving the first gauge having an inner diameter corresponding to the allowable outer diameter calculated from the current life consumption rate along the pipe, the locally expanded range can be identified with a simple operation. can do. Further, by moving the second gauge having an inner diameter larger than that of the first gauge along the pipe, the maximum bulging point having the largest bulging amount in the bulging range can be easily specified. In the present invention, by calculating the life consumption rate based on the outer diameter measured at the maximum bulging point specified in this way, the life evaluation can be performed with a simple operation with high accuracy.

  Preferably, in the maximum bulge point specifying step, the maximum bulge point may be specified by gradually increasing the inner diameter of the second gauge. According to this, by gradually increasing the inner diameter of the second gauge, the maximum bulging point can be easily simplified while gradually narrowing the bulging range in which the outer diameter is larger than the allowable outer diameter. Can be identified efficiently.

  The first and second gauges may be formed in a semicircular shape so that the inner peripheral surface is in contact with the outer peripheral surface of the pipe. According to this, by sliding the gauge along the outer peripheral surface of the pipe, it is possible to easily detect the bulging point locally generated in a part on the outer periphery, so the maximum bulging point can be more accurately detected. Can be specified.

  In the maximum bulge outer diameter measurement step, the measurement may be performed by bringing a planar measurement unit into contact with both sides of the outer diameter of the pipe at the specified maximum bulge point. Since the stability is increased by bringing the measuring part into contact with the flat surface in this way, the measurement result varies by the measurer compared to the case where the measuring part is in line contact with the outer diameter of the pipe as in a general caliper. Errors due to individual differences such as can be reduced. As a result, a more accurate life evaluation can be performed.

  According to the present invention, by moving the first gauge having an inner diameter corresponding to the allowable outer diameter calculated from the allowable lifetime consumption rate at the present time along the pipe, the locally expanded range can be easily operated. Can be specified. Further, by moving the second gauge having an inner diameter larger than that of the first gauge along the pipe, the maximum bulging point having the largest bulging amount in the bulging range can be easily specified. In the present invention, by calculating the life consumption rate based on the outer diameter measured at the maximum bulging point specified in this way, the life evaluation can be performed with a simple operation with high accuracy.

It is a graph which shows an example of the relationship between the lifetime consumption rate calculated | required experimentally, and the swelling rate. It is a flowchart which shows the specific procedure which enforces the lifetime evaluation method which concerns on this invention. It is the top view and side view which show the structure of a dedicated gauge in the lifetime evaluation method of piping which concerns on this invention. It is a schematic diagram which shows the usage example of the exclusive gauge shown in FIG. It is the schematic diagram which showed notionally several dedicated gauges designed so that an internal diameter may increase in steps. It is a schematic diagram which shows a mode that a bulging range and the maximum bulging point are specified using an exclusive gauge. It is a schematic diagram which shows a contact part in the case of measuring the outer diameter in the maximum bulging point using a digital caliper.

  Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this example are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.

  The pipe life evaluation method according to the present invention performs life evaluation using the characteristic that the outer diameter changes as the creep damage progresses due to aging of the pipe. Therefore, as a premise for carrying out the present invention, it is necessary to obtain a relationship between the lifetime consumption rate and the bulging amount on a trial (experimental) basis in advance. This relationship is prepared in advance for each piping specification (for example, material and dimensions).

  FIG. 1 is a graph showing an example of the relationship between the lifetime consumption rate and the bulging rate obtained experimentally. The horizontal axis represents the life consumption rate (%), and this life consumption rate represents the life (typically the life time period) defined in advance as the specification as 100%. The vertical axis indicates the bulging rate, and this bulging rate indicates the rate of change with respect to a pre-specified outer diameter (that is, the initial outer diameter when not in use).

  As shown in FIG. 1, the bulge rate of the piping increases as the creep damage progresses and the life consumption rate increases. In particular, when the lifetime consumption rate is in the second half, the degree of increase in the bulging rate tends to accelerate. Strictly speaking, the behavior of the bulging rate with respect to the lifetime consumption rate differs depending on specifications such as materials and dimensions, but the general tendency is common.

  Next, a specific procedure for carrying out the life evaluation method according to the present invention will be described after preparing the relationship between the life consumption rate and the bulging amount shown in FIG. FIG. 2 is a flowchart showing a specific procedure for carrying out the life evaluation method according to the present invention.

  First, the worker who is the main body that implements this method selects a portion where the life evaluation should be performed among the pipes to be evaluated (step S101). The pipe to be evaluated is assumed to be a pipe used as a heat transfer pipe in a boiler, for example, but this type of pipe is often constructed over a wide range in a large-scale facility such as a thermal power plant. When performing life evaluation based on the amount of change in outer diameter, it is important to identify the part of the pipe that is installed over a wide range that is most likely to be damaged by creep and where the amount of change in outer diameter will be large. It is.

  Although it is difficult to accurately identify the point where the outer diameter change amount is maximum, based on the design conditions of the piping to be evaluated, past usage status, future usage schedule status, etc. It is relatively easy to roughly specify a range in which a portion where the outer diameter change amount is maximum is included. In step S101, a range suitable for carrying out the life evaluation is selected based on the specifications and usage conditions of the piping.

Subsequently, for the pipe to be evaluated, a lifetime consumption rate allowable at the present time is calculated (step S102). The calculation of the allowable lifetime consumption rate at this moment is based on the following formula: current lifetime consumption rate Tc = (current operation period) / (current operation time + future operation time) Operating time) x 100 (1)
Calculated by

  In the above equation (1), the allowable lifetime consumption rate Tc is calculated taking into consideration only the “current operation period”, but environmental requirements such as temperature and humidity during the operation of the piping, etc. It is preferable to calculate in consideration of various parameters related to the operation status because accuracy is further improved.

  Subsequently, an allowable bulging rate Rs corresponding to the current allowable lifetime consumption rate Tc calculated in step S102 is obtained (step S103). Step S103 is an example of the “allowable swell rate calculating step” according to the present invention. The relationship between the life consumption rate and the swell amount shown in FIG. 1 is prepared for the pipe to be evaluated, and the current time calculated in step S102 is prepared. The allowable bulge amount corresponding to the allowable life consumption rate is obtained. Thereby, the allowable bulging rate corresponding to the lifetime consumption rate Tc allowable at the present time can be accurately estimated based on the test result. Specifically, the allowable bulging rate (Rs) corresponding to the arrow (Tc) shown on the horizontal axis of FIG.

Subsequently, an allowable outer diameter Ls corresponding to the allowable bulge rate Rs obtained in step S103 is calculated (step S104). In general, the bulge rate of piping is calculated by using the initial outer diameter (outer diameter when not in use) and the current outer diameter. Diameter x 100 (2)
It is represented by Step S104 is an example of the “allowable outer diameter calculating step” according to the present invention. By substituting the allowable bulge rate Rs obtained in step S103 and the initial outer diameter of the pipe to be evaluated into (2), the allowable bulge is obtained. An allowable outer diameter Ls corresponding to the output rate Rs is calculated (allowable outer diameter calculating step). This allowable outer diameter Ls is an estimate of the outer diameter L that would have changed from the initial outer diameter at the present time as an allowable value based on the test results of FIG. It is.

  In the actual piping, since the local bulge has occurred as described in the background art, there is a portion bulged larger than the allowable outer diameter Ls estimated in this way. Therefore, the following process is characterized in that the life evaluation can be performed with higher accuracy by specifying a portion bulging larger than the allowable outer diameter Ls.

  Step S105 is an example of the “bulging range specifying step” according to the present invention, and a range (from the allowable outer diameter Ls using the dedicated gauge 2 which is an example of the “first gauge” according to the present invention ( Hereinafter, this is referred to as “bulging range 3”. FIG. 3 is a plan view (a) and a side view (b) showing the configuration of the dedicated gauge 2 used in step S105, and FIG. 4 is a schematic diagram showing an example of use of the dedicated gauge 2.

  The dedicated gauge 2 has a substantially U shape made of tool steel, and when the outer diameter of the pipe 1 is covered from the outside as shown in FIG. 4, the inner peripheral surface 4 becomes the outer diameter of the pipe. It is comprised so that it may contact | abut over a semicircle along. The semicircular inner peripheral surface 4 of the dedicated gauge 2 is set so that its diameter becomes the allowable outer diameter Ls calculated in step S104. As shown in FIG. 4, the dedicated gauge 2 configured in this way is covered from the outside with respect to the outer diameter of the pipe 1 to be evaluated, along the extending direction of the pipe 1 (see the arrow in FIG. 4). The bulging range 3 in which the outer diameter bulges beyond the allowable outer diameter Ls is specified.

  Note that the dedicated gauge 2 shown in FIG. 3 has a semicircular contact surface (inner peripheral surface 4) with respect to the outer diameter of the pipe 1. It is good to investigate evenly whether there is a bulging range on the outer periphery of 1. Further, since the inner peripheral surface 4 of the dedicated gauge 2 is in contact with the outer periphery of the pipe 1, tool steel (more preferably, surface hardening such as water quenching) is performed so that the inner diameter does not change due to friction. It is good that it is made).

  Returning to FIG. 2 again, it is determined whether or not the bulging range 3 has been found as a result of investigating the pipe 1 to be evaluated using the dedicated gauge 2 in this way (step S106). If the bulging range 3 is not found here (step S106: NO), there is no portion that bulges locally beyond the allowable outer diameter Ls, and it is sufficient to perform a life evaluation based on the allowable outer diameter Ls. . Therefore, the process proceeds to step S109, which will be described later, and the lifetime consumption rate is calculated using the allowable outer diameter Ls (a specific method for calculating the lifetime consumption rate will be described later).

  On the other hand, when the bulging range 3 is found (step S106: YES), the maximum bulging point 6 is specified from the bulging range 3 using the dedicated gauge 5 having a larger inner diameter (step S107). That is, step S107 is an example of the “maximum bulging point specifying step” according to the present invention. The dedicated gauge 5 used here is basically the same type as the dedicated gauge 2 used in step S104, but differs in that the inner peripheral surface 4 that contacts the outer diameter of the pipe 1 is set large. . A portion having an outer diameter larger than the permissible outer diameter Ls by moving such a dedicated gauge 5 along the extension of the pipe 1 while covering the outer diameter of the pipe 1 again as shown in FIG. Can be specified (limited).

  A plurality of dedicated gauges 5 designed in step S107 are prepared so that the inner diameter increases stepwise. FIG. 5 conceptually shows a plurality of dedicated gauges 5 designed so that the inner diameter increases stepwise. Each dedicated gauge 5 is provided with each dedicated gauge 5 whose inner diameter increases step by step, including the smallest dedicated gauge 2 whose inner diameter is the allowable outer diameter Ls used in step S105.

  Here, the increase amount of the inner diameter in the plurality of dedicated gauges 5 may be constant or indefinite, but considering that the typical outer diameter of the pipe 1 to be evaluated is 20-70 mm, it is 0.1 mm. From experience, it is preferable to prepare a plurality of dedicated gauges whose inner diameter increases in steps. 5, a dedicated gauge 5a having the smallest inner diameter La, a dedicated gauge 5b having the next smallest inner diameter Lb (= La + a), and a dedicated gauge 5x having the largest inner diameter Lx (= La + n × a) are prepared. Each of the inner diameters is different by a certain amount a. In order to specify the maximum bulging point 6 with high accuracy, it is preferable to set the interval a for increasing the inner diameter as small as possible. However, since the number of dedicated gauges 5 to be prepared increases accordingly, It may be set appropriately in consideration of the time and effort.

  In the present embodiment, the case where the dedicated gauges 2 and 5 having different inner diameters are prepared separately will be described as an example, but instead of these, an integrated dedicated gauge whose inner diameter is configured to be variable in stages is described. It goes without saying that a gauge may be prepared.

  FIG. 6 schematically shows how the bulging range 3 and the maximum bulging point 6 are specified in steps S105 and S107. First, when the dedicated gauge 2 is moved along the pipe 1 in step S105, the dedicated gauge 2 can pass through a region where the outer diameter is equal to or smaller than the allowable outer diameter Ls, but a region larger than the allowable outer diameter Ls (that is, a bulging range). 3) cannot pass. The bulging range 3 is specified by performing this operation on the pipe 1 to be evaluated.

  Subsequently, in step S <b> 107, among the dedicated gauges 5 whose inner diameter is set to be gradually increased, the dedicated gauge 5 b having an inner diameter next to the allowable outer diameter Ls is moved along the pipe 1. Thereby, the range which has an outer diameter larger than the internal diameter of the said exclusive gauge 5b can be narrowed down from the bulging range 3 specified by step S105. Then, by carrying out the same operation using the dedicated gauge 5c having the next smallest inner diameter, it is possible to further narrow the range where the bulge amount is large. By repeating such an operation using a plurality of dedicated gauges 5 prepared, it is possible to finally identify the maximum bulging point 6 having the maximum outer diameter.

  Returning to FIG. 2 again, in step S108, the outer diameter Lmax of the pipe 1 is measured at the specified maximum bulging point 6. That is, step S108 is an example of the “maximum bulging point outer diameter measuring step” according to the present invention. Here, the measurement of the outer diameter Lmax has a large measurement error with a simple vernier caliper that is generally commercially available. Therefore, the measurement can be performed with high accuracy using a digital caliper, a micrometer, or a non-contact type laser displacement meter. Preferably it is done.

  For example, when the outer diameter Lmax is measured using a digital caliper, as shown in FIG. 7, the contact portion 8 of the digital caliper 7 to the pipe 1 may be formed in a planar shape. As a result, the surface of the tubular pipe is brought into surface contact, so that the stability is increased compared to the case of line contact like a general caliper, and the outer diameter can be measured with higher accuracy. In addition, it is preferable that the planar shape portion has a large area as much as possible from the viewpoint of increasing the stability, but if the area becomes large, it becomes difficult to accurately contact the outer diameter surface with the contact portion in the curved portion of the pipe, etc. It is good to adjust appropriately.

  In step S109, the lifetime consumption rate is calculated using the outer diameter Lmax at the maximum bulging point 6 measured in this way. That is, step S109 is an example of a “lifetime consumption rate calculating step” according to the present invention. Specifically, the outer diameter Lmax at the maximum bulging point 6 is substituted into the above equation (2) to calculate the bulging rate. And the lifetime consumption rate corresponding to this bulging rate is obtained by applying to the correlation shown in FIG.

  In addition, when the bulging range is not found in step S106 (step S106: NO), the corresponding life consumption rate is obtained by applying the bulging rate calculated in step S103 to the relationship shown in FIG.

  As described above, according to the life evaluation method of the pipe 1 according to the present embodiment, the dedicated gauge 2 having an inner diameter corresponding to the allowable outer diameter Ls calculated from the allowable lifetime consumption rate Tc along the pipe 1 is provided. Thus, the bulging range 3 can be specified with a simple operation. Further, by moving a dedicated gauge (second gauge) 5 having an inner diameter larger than that of the dedicated gauge (first gauge) 2 along the pipe 1, the maximum bulge having the largest bulge amount in the bulging range 3. Point 6 can also be easily identified. In the present invention, by calculating the life consumption rate based on the outer diameter Lmax measured at the maximum bulging point 6 specified as described above, the life evaluation can be performed with a simple operation with high accuracy.

  INDUSTRIAL APPLICABILITY The present invention is used in a pipe life evaluation method for performing life evaluation by calculating a life consumption rate of a pipe based on an outer diameter change amount due to aging in a pipe used for a heat transfer pipe such as a boiler pipe. Is possible.

1 Piping 2 Dedicated gauge (first gauge)
3 Swelling range 4 Inner peripheral surface 5 Dedicated gauge (second gauge)
6 Maximum bulging point 7 Digital caliper 8 Contact area

Claims (4)

A pipe life evaluation method for performing life evaluation of the pipe by calculating a life consumption rate based on an outer diameter change amount of the pipe,
A preliminarily obtained relationship between the life consumption rate and the bulging amount on a trial basis, and an allowable bulging rate calculating step for obtaining an allowable bulging rate by applying the current life consuming rate of the pipe to the relationship;
An allowable outer diameter calculating step of calculating an allowable outer diameter from the obtained allowable bulging rate;
By moving the first gauge having an inner diameter corresponding to the calculated allowable outer diameter while covering the outer diameter along the extending direction of the pipe, the outer diameter bulges beyond the allowable outer diameter. A bulging range specifying step for specifying a bulging range;
By moving a second gauge having an inner diameter larger than that of the first gauge while covering the outer diameter along the extending direction of the pipe, the maximum bulge amount having the largest bulge amount in the specified bulge range is obtained. A maximum bulging point identifying step for identifying a starting point;
A maximum bulge point outer diameter measuring step of measuring an outer diameter of the pipe at the specified maximum bulge point;
A life consumption rate calculation step of calculating a maximum bulge rate from the measured maximum bulge outer diameter and calculating the lifetime consumption rate by applying the calculated maximum bulge rate to the relationship. Pipe life evaluation method.   2. The pipe life evaluation method according to claim 1, wherein the maximum bulge point specifying step specifies a maximum bulge point by gradually increasing an inner diameter of the second gauge. 3.   The pipe life evaluation method according to claim 1 or 2, wherein the first and second gauges are formed in a semicircular shape so that an inner peripheral surface thereof is in contact with an outer peripheral surface of the pipe. .   4. The measurement according to claim 1, wherein the maximum bulging outer diameter measuring step performs measurement by bringing a planar measuring portion into contact with both sides of the outer diameter of the pipe at the specified maximum bulging point. 5. The pipe life evaluation method according to any one of the above.

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