JP2005196748A - Pipe material design method, manufacturing method of pipe, pipe, and pipeline - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pipe material design method capable of cost reduction while securing safety, a manufacturing method of a pipe using the pipe material design method, and a pipe and a pipeline manufactured by the manufacturing method. <P>SOLUTION: The pipe material design method has a pipe condition setting process for setting the diameter D and thickness t of a pipe, and required compression local buckling strain ε<SB>req</SB>; a strain hardening characteristic acquiring process for finding a strain hardening characteristic in the vicinity of the buckling point of the pipe which should satisfy conditions set in the pipe condition setting process; and a process for setting the strain hardening characteristic as a condition which the stress-strain curve of the pipe should satisfy. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a pipe material design method, a pipe manufacturing method, a pipe, and a pipeline used in a gas / oil pipeline.

Construction of gas pipelines and oil pipelines has been promoted as the basis of energy supply. In recent years, gas fields have often been developed far away from consumption areas, especially against the backdrop of increasing demand for natural gas. For this reason, pipelines tend to have long distances, and the trend toward larger diameters and higher pressures is increasing for mass transport.
FIG. 13 shows a flowchart of pipeline construction focusing on such pipeline design.
Conventional pipeline designs are roughly classified into (1) system design and (2) structural design.
In the system design, the pipe type, pipe diameter, pipe thickness, and operating pressure are temporarily set so that the operation cost and construction cost of the pipeline are minimized, assuming the transport amount and transport distance representing the project scale. .
The structural design takes into account the ground displacement, etc. that occurs during an earthquake based on the laying alignment that is the shape of the pipeline that is assumed at the time of laying based on the strength and shape of the pipe temporarily set in the system design and the topography of the laying location. Structural analysis, allowable stress verification, allowable strain verification, and local buckling verification.

  If the pipe specifications temporarily set in the system design do not satisfy these check conditions, the system design is returned to the system design again to reset the pipe specifications. Then, when the checking conditions are satisfied, the specifications of the pipe are determined based on the provisionally set specifications in the system design, and the pipe manufacturing is ordered from the steel company. The steel company that has received the order manufactures and delivers the line pipe according to the order specification of the pipeline company.

  Local buckling verification means that the pipe under the conditions temporarily set in the system design has sufficient local buckling performance to withstand the maximum compressive strain and maximum bending strain assumed under the condition where the pipeline is laid. It is to check whether it is equipped. Specifically, the local buckling strain of the designed pipe is obtained, and it is determined whether or not this local buckling strain is larger than the maximum strain generated in the pipeline.

By the way, the method for obtaining the local buckling strain of the designed pipe was as follows.
The compression local buckling strain of a pipe is generally expressed as: compression local buckling strain = coefficient (tube thickness / tube diameter) ^index . And the coefficient and the index in the above relational expression are plotted as shown in FIG. 14 by plotting the actual compressed local buckling experimental data, and a curve is drawn so as to envelope the lower limit of the experimental data, and this lower limit envelope curve is fitted. So ask.

Table 1 shows the local buckling strain estimation formula obtained based on the above-described actual tube buckling experiment.

The local buckling strain estimation formula defined in the current design standard shown in Table 1 is X65 (US API (American
Based on the experimental data of the following pipes (strength grade according to Petroleum Institute) standard. This is why the application range in FIG. 13 is limited to a line pipe of X65 or less.
In addition to the one shown in Table 1, as a local buckling strain estimation formula, there is ε = 35 (t / D) (%) shown in the high pressure gas conduit seismic design guideline of the Japan Gas Association (non-patent document) 1).

Since the local buckling strain estimation formula has been obtained based on the actual tube buckling experiment in this way, in the local buckling verification, the compression local buckling strain is obtained based on this estimation formula, and this is the maximum strain. It is judged whether it is larger. If it is smaller than the maximum strain, the condition is reset by returning to the system design. As a method of resetting at this time, the local buckling strain of the pipe is increased by increasing the tube thickness because there is a relationship of compression local buckling strain = coefficient (tube thickness / tube diameter) ^index. ing.

The above is for a line pipe of X65 or less for which the local buckling strain estimation formula has been acquired,
When adopting a steel grade of X70 or higher for which no local buckling strain estimation formula exists in the pipeline, as shown in FIG. 15, a sample tube is produced as a prototype, and a local buckling experiment is performed. Get distortion. Then, it is determined whether or not the acquired local buckling strain of the pipe is larger than the maximum strain. In this case as well, if it is small, a sample tube with an increased tube thickness is manufactured again and checked in the same manner as in the case of X65 or less.
"High-pressure gas pipe seismic design guideline (revised version)", published by the Japan Gas Association, March 2000, page 39

As described above, in conventional pipeline design, local buckling verification is performed based on empirical formulas, and if it is determined that local buckling verification is not possible, local buckling strain is increased by increasing the tube thickness. Increasing. For this reason, there are the following problems.
(1) Problems caused by performing local buckling verification based on empirical formulas As mentioned above, the current buckling formula for pipes below X65 is based on buckling strain = coefficient ( (Thickness / Tube Diameter) ^Index , where “Coefficient” and “Index” are values on the safe side obtained by buckling experiments on actual pipes. Moreover, as can be seen from Table 1 and FIG. 14, there are large variations in the experimental results and the equations themselves.
In this way, there is a large variation in the experimental results themselves, and the local buckling check was performed using the buckling strain estimation formula based on the safety side experimental values to determine the local buckling strain. There is a high possibility that an acceptable judgment will not be made due to too much judgment on the safe side.
In this case, although it is originally acceptable, it is not possible, and a safety specification is required, so that there is a problem of over-spec and high cost.

(2) The problem of increasing local buckling strain by increasing the tube thickness Recent new pipelines tend to be longer distances, and the tendency to increase diameter and pressure for mass transportation It is coming. In such a new pipeline, it has been demanded that a high-strength steel pipe is used to withstand a high internal pressure with a thin pipe thickness even with a large diameter. This is because by reducing the pipe thickness, the welding costs and pipe transportation costs at the site are reduced, and the total cost of construction and operation of the pipeline can be reduced.
For this reason, a high-strength pipe is required, but the yield ratio (Y / T: ratio of tensile strength T to yield stress Y) tends to increase as the strength of the steel pipe for pipelines increases. It is in.

On the other hand, assuming that the tube diameter and the tube thickness are the same, the higher the yield ratio, the lower the local buckling strain. Therefore, the higher the strength of the pipe, the lower the local buckling strain.
For this reason, it is necessary to increase the local buckling strain of the pipe, but if measures were taken to increase the pipe thickness in order to meet this need, the pipe thickness should be reduced by using a high-strength pipe. This is contrary to the attempt to reduce the total cost of pipeline construction and operation.

As described above, in the conventional pipeline design method, the local buckling check is not appropriate, and as the means for increasing the local buckling strain is only by increasing the tube thickness, the cost of the pipeline is increased. I was invited.
Such a situation is not limited to pipelines, but can also be applied to building materials using steel pipes.
The above is for pipes of X65 or less with a buckling strain estimation formula, but for pipes of X70 or more without a buckling strain estimation formula, it is necessary to make a prototype of the actual pipe, and it takes time and effort. The point of increasing the tube thickness to increase the bending strain is the same, and there is a problem similar to the case of pipes of X65 or less.
Further, in the structural design of the pipeline, in addition to the compression local buckling strain of the pipe, a bending local buckling strain is required. As described above, the basic equation is required for the compression local buckling strain, but the basic equation is not required for the bending local buckling strain. Therefore, it depends on the experimental value of the actual pipe as in the case of the pipe of X70 or higher, and has the same problem as described for the pipe of X70 or higher.

The present invention has been made to solve such a problem, and an object of the present invention is to obtain a pipe material design method capable of reducing costs while ensuring safety.
Another object of the present invention is to obtain a pipe and a pipeline manufactured by the pipe manufacturing method using the pipe material design method, and further by the pipe manufacturing method.

  In the conventional pipeline design, local buckling strain is estimated by an estimation equation based on the pipe diameter and pipe thickness set in the system design, and if this estimated value is smaller than the required value, the pipe thickness is increased. It is. However, in this method, the estimation formula itself is an empirical formula and does not necessarily satisfy both economic efficiency and safety. As long as the local buckling estimation value using the estimation formula based on this experimental value is used as a reference, However, it is not always possible to design a pipe that satisfies both economic efficiency and safety.

  Therefore, the inventor estimates the local buckling strain required for the pipe, such as estimating the local buckling strain of the pipe by giving the pipe diameter and pipe thickness designed for the system, and by system design etc. In addition to the required pipe diameter and pipe thickness, the required local buckling strain is also given in advance, and the required local buckling strain is given in advance, such as designing the pipe material to satisfy this condition. In addition, we have learned that it is effective to utilize new parameters that have not been noticed in conventional structural design. As a result of further studies, the present invention has been completed by finding that the strain hardening characteristics of the pipe greatly influence the local buckling behavior of the pipe as a new parameter. Here, the strain hardening property is a parameter indicating the degree of increase in strain with respect to an increase in stress or the degree of increase in stress with respect to an increase in strain, for example, based on the slope of the tangent line of the stress-strain curve at the buckling point, or This is given as a stress relationship between a plurality of points obtained by combining buckling points and auxiliary points in a stress strain curve.

(1) The pipe material design method according to the present invention is set in a pipe condition setting step for setting a pipe diameter D, a pipe thickness t, and a required compression local buckling strain ε _req of the pipe, and a pipe condition setting step. A strain hardening characteristic obtaining step for obtaining a strain hardening characteristic in the vicinity of the buckling point of the pipe that should satisfy the condition; and a step for setting the strain hardening characteristic to be a condition that the stress strain curve of the pipe should satisfy.
Here, “in the vicinity of the buckling point” refers to a plurality of points obtained by using a virtual buckling point and auxiliary points provided in the vicinity of the buckling point in order to calculate the tangential coefficient E _Tcr as described later. This is intended to include the partial stress relationship between points in the “strain hardening characteristics” referred to herein.

(2) A pipe condition setting step for temporarily determining the diameter D, the pipe thickness t, and the transport pressure of the pipe used in the pipeline based on at least the transport amount and transport distance of the pressurized fluid transported in the pipeline. The pipeline is structurally designed in consideration of the linearity laid on the pipe having the tentatively determined diameter and pipe thickness, and when the transportation pressure, ground displacement and / or external force is applied to the structurally designed pipeline, the pipe A maximum compression axial strain calculating step for obtaining a maximum compression axial strain generated in the step, a required compression local buckling strain setting step for setting a required compression local buckling strain ε _req based on the maximum compression axial strain, the diameter D, a strain hardening characteristic acquisition step of obtaining the strain hardening property in the buckling point near the pipe should satisfy all the conditions of the pipe thickness t, and required compression local buckling strain epsilon _req, the stress-strain of the strain hardening characteristics the pipe Those having the steps of a condition to be satisfied.

  When the pipeline is subjected to bending deformation, it is necessary to provide the pipeline with safety against bending local buckling. However, an analytical solution for calculating the bending local buckling strain of the pipe is not required. Therefore, the relationship (ratio) between the compression local buckling strain and the bending local buckling strain of the pipe is obtained quantitatively by finite element analysis, etc., and the required bending local buckling strain is requested using this quantitative ratio. By converting into a compression local buckling strain and using the above-mentioned means based on this required compression local buckling strain, the material design of the pipe can be designed when the pipeline is subjected to bending deformation as follows. FIG. 7 shows the compression local buckling strain and the bending local buckling strain of the pipe obtained by finite element analysis and plotted on the same coordinates. In this example, the ratio D / t of the pipe diameter D and the pipe thickness t is 50 and 60, and the yield ratio (Y / T) (the ratio of the tensile strength T to the yield stress Y) is 0.80, 0.85, 0.90, This is an example of analysis for 0.93. From FIG. 7, it can be seen that the compression local buckling strain and the bending local buckling strain have a 1: 2 relationship when evaluated on the safe side.

(3) The pipe material design method when the pipeline is subjected to bending deformation includes the pipe diameter setting step, pipe thickness t, pipe condition setting step for setting the required bending local buckling strain of the pipe, and bending local buckling. A local buckling strain converting step of converting the required bending local buckling strain into a required compressing local buckling strain ε _req from the quantitative relationship between the strain and the compressive local buckling strain, the diameter D, the tube thickness t and the required A strain hardening characteristic acquisition step for obtaining a strain hardening characteristic in the vicinity of the buckling point of the pipe that should satisfy all the conditions of the compression local buckling strain ε _{req, and} a condition that the stress strain curve of the pipe should satisfy the strain hardening characteristic And a process.

(4) A pipe condition setting step for temporarily determining a diameter D, a pipe thickness t, and a transport pressure of the pipe used in the pipeline based on at least a transport amount and a transport distance of the pressurized fluid transported by the pipeline; The pipeline is structurally designed in consideration of the linearity laid on the pipe having the tentatively determined diameter and pipe thickness, and when the transportation pressure, ground displacement and / or external force is applied to the structurally designed pipeline, the pipe The maximum bending strain calculation step for obtaining the maximum bending strain generated in the step, the required bending local buckling strain is set based on the maximum bending strain, and further, from the quantitative relationship between the bending local buckling strain and the compression local buckling strain The local buckling strain conversion step for converting the required bending local buckling strain into the required compression local buckling strain ε _req and all the conditions of the diameter D, the tube thickness t, and the required compressing local buckling strain ε _req should be satisfied. Pipe buckling point A strain hardening characteristic acquisition step of obtaining the strain hardening property in the near, the steps of the condition to be satisfied with the strain hardening property stress-strain curve of the pipe, and has a.

(5) Further, the strain hardening characteristics in the above (1) to (4) are obtained when the virtual buckling point on the stress strain coordinate corresponding to the required compression local buckling strain ε _req is assumed. It is characterized by being given on the basis of the slope of the tangent line of the stress-strain curve at the buckling point.

(6) When the strain hardening characteristics in the above (1) to (5) are H and a virtual buckling point corresponding to the required compression local buckling strain ε _req is assumed in the stress strain coordinates, The strain hardening characteristic H satisfies the following equation, where E _Treq is the slope of the tangent line of the stress-strain curve at the buckling point.

Here, the expression (1.1) of the above (6) will be described.
There is the following formula (1.2) as a basic formula that represents the buckling strain of a pipe that receives compressive force.

In equation (1.2), ε _cr is the compression local buckling strain, ν is the Poisson's ratio, t is the pipe thickness, and D is the pipe diameter. In addition, E _scr represents the slope of a line connecting the origin and the buckling point (hereinafter referred to as “secant modulus”) in FIG. 8 showing the continuous hardening type stress strain curve, and E _Tcr is the buckling point. The slope of the stress-strain curve (hereinafter referred to as “tangent coefficient”) is shown.
In equation (1.2), the following equation (1.3) is obtained by substituting 0.5 as the Poisson's ratio ν for plastic deformation.

The following equation (1.4) is obtained by squaring both sides of equation (1.3) and solving for E _Tcr .

If the stress corresponding to ε _cr on the stress-strain curve is σ _cr , then E _scr = σ _cr / ε _cr (see FIG. 8), so equation (1.4) is expressed as:

Here, the value of the requested local buckling strain input as the required value because the local buckling strain epsilon _cr more values, referred to as requesting local buckling strain epsilon _req to distinguish a local buckling strain epsilon _cr . When the required local buckling strain ε _req is used, the required tangential coefficient is the minimum value that satisfies the required conditions. Therefore, when these conditions are added to the equation (1.5), E _Treq as a condition to be satisfied by the stress-strain curve is expressed by the following equation (1.6).

In equation (1.6), σ _req is the stress at the point corresponding to ε _req on the stress-strain curve. The right side of equation (1.6) includes σ _req which is a dependent variable of ε _req . Therefore, if the right side is arranged as a function of the provisional value and the required value, and the dependent variable σ _req and the tangent coefficient E _req as the required value are arranged on the left side, Equation (1.7) is obtained, which is shown in (6) above. is there.

In the above description, 0.5 is substituted for Poisson's ratio ν in equation (1.2) and the constant in equation (1.3) is set to 4/3, but a numerical value other than 0.5 is substituted for Poisson's ratio ν for various reasons. In this case, the constant 4/3 in equation (1.3) varies. Therefore, the expression (1.3) can be generally expressed as the following expression (1.8) with A as a constant. Similarly, the constant 9/16 in (1.7), (2.1), (4.1), (5.9) can be replaced with 1 / A ² and the constant 9/32 in (3.9) is 1. Can be replaced with / (2A ² ).

(7) According to another pipe material design method of the present invention, the strain hardening characteristics in the above (1) to (4) are virtual on the stress strain coordinates corresponding to the required compression local buckling strain ε _req. Assuming a buckling point and one or more auxiliary points at a position where the strain value is away from the buckling point, using the virtual buckling point and the one or more auxiliary points, It is characterized by being given as a partial stress relationship.
By giving the strain hardening characteristics as a partial stress relationship between a plurality of points, it becomes easy to determine whether, for example, a pipe manufactured by an existing manufacturing method satisfies the strain hardening characteristics required. In other words, since the stress-strain relationship of pipes manufactured by the existing manufacturing method is given as a point sequence, by giving the required strain hardening characteristics as a partial stress relationship between multiple points, existing data and Can be easily compared, and the above determination can be easily performed.

(8) Further, the partial stress relationship between a plurality of points in (7) satisfies the following expression.

Here, the equation (2.1) in the above (8) will be described.
An assumed continuous-curing stress-strain curve is shown in FIG. In FIG. 9, the horizontal axis represents the compression axial strain of the pipe, and the vertical axis represents the compression axial stress. Ε _cr on the horizontal axis is the required compression local buckling strain, and ε ₂ is the strain at the auxiliary point 2 set at an arbitrary interval on the right side of ε _cr . The points on the stress-strain curve corresponding to ε _cr and ε ₂ on the horizontal axis are called buckling point C and auxiliary point 2, respectively. The stresses at the buckling point C and the auxiliary point 2 are expressed as σ _cr and σ ₂ , respectively. The secant coefficient E _Scr is represented by the slope of the line segment connecting the coordinate origin and the buckling point C. Assuming that the stress relationship between the buckling point C and the auxiliary point 2 is a linear relationship, the tangent coefficient and secant coefficient are expressed as follows.

The local buckling strain of the pipe is given by the following equation (2.4) as described above.

Substituting (2.2) and (2.3) into (2.4) and rearranging gives the following (2.5).

Here, as in the case of (6) described above, the required local buckling strain is expressed as ε _req in order to distinguish the required local buckling strain input as the required value from the local buckling strain ε _cr . Further, when the stress corresponding to the required local buckling strain ε _req on the stress strain curve is σ _{req and} the right side of the equation (2.5) is arranged as a function of the provisional value and the required value, the following equation (2.6) is obtained.

Since the equation (2.6) shows the minimum value, as a result, the partial stress relationship between a plurality of points as a condition to be satisfied by the stress-strain diagram of the pipe becomes the following equation (2.7), which is the above ( It is the same as formula 2.1).

(9) Further, another pipe material design method according to the present invention is characterized in that the partial stress relationship between a plurality of points satisfies the following (3.1) in the above (7). .

Here, the formula (3.1) of the above (9) will be described.
An assumed continuous hardening type stress-strain curve is shown in FIG. The horizontal axis of FIG. 10 represents the compression axial strain of the pipe, and the vertical axis represents the compression axial stress. Ε _cr on the horizontal axis is a compression local buckling strain, and ε ₁ and ε ₂ are strains of auxiliary points 1 and 2 set at arbitrary intervals on the left and right of ε _cr . Note that the interval between ε _cr and ε _{1 and} the interval between ε _cr and ε ₂ are equal.
Points on the stress-strain curve corresponding to ε _cr , ε ₁ and ε ₂ on the horizontal axis are referred to as buckling point C, auxiliary point 1 and auxiliary point 2, respectively. The stresses on the vertical axis corresponding to the buckling point C, auxiliary point 1 and auxiliary point 2 are denoted as σ _cr , σ ₁ and σ ₂ , respectively. Furthermore, point A represents the midpoint of points 1 and C, and point B represents the midpoint of points C and 2. The strains on the horizontal axis corresponding to the points _A and _B are expressed as ε _A and ε _B, and the respective values are average values of ε ₁ and ε _cr and ε _cr and ε ₂ . The stresses on the vertical axis corresponding to ε _A and ε _B are σ _A and σ _B , respectively. These relationships are expressed by the following equations (3.2) to (3.5).

The tangent coefficient E _Tcr and secant coefficient E _{cr at the buckling} point (C point) are expressed by the following equations.

By squaring both sides of equation (1.2) and substituting equations (3.6) and (3.7), equation (3.8) is obtained.

Here, as in the case of (6) described above, the required local buckling strain ε _cr is expressed as the required local buckling strain ε _req to distinguish the required local buckling strain input as the required value from the local buckling strain ε _cr . Further, the stress corresponding to the required local buckling strain ε _req on the stress strain curve is σ _req . Since equation (3.8) shows the minimum value, the partial stress relationship between multiple points that the stress-strain curve of the pipe should satisfy is the following equation (3.9), which is the above equation (3.1) and Are the same.

(10) Further, another pipe material design method according to the present invention is characterized in that, in the above (7), the partial stress relationship between a plurality of points satisfies the following expression (4.1). is there.

The equation (4.1) will be described.
When the entire stress-strain curve is represented by a single power function, the following equation (4.2) is obtained.
σ = Aε ⁿ --------------------------------------- (4.2)
Here, σ is stress, ε is strain, A is a coefficient, and n is a strain hardening index.
When the stress-strain relationship of the pipe is expressed by the power hardening law as shown in the equation (4.2), the tangential coefficient E _T and the secant coefficient E _S are respectively expressed as the following equations.

Therefore, the root number of the basic equation (1.3) expressing the buckling strain of the pipe is expressed as follows.

Substituting equation (4.6) into equation (1.2) gives the buckling strain as

When the stress-strain relationship is expressed by the above (4.2), if the stress-strain relationship is plotted on the logarithmic axis as shown in FIG. 11 and ε ₂ (auxiliary point 2) is provided on the right side of the point ε _cr , The curing index n is calculated by the following formula.

Here, the stress-strain relationship is a monotonically increasing function, and in the case of local buckling in the plastic region considered in this specification, the stress relationship between the two points on the right side of the above equation is expressed by the following equation (4.9): It becomes like this.

In addition, in a logarithmic function, x is a positive number and can be approximated by the following equation (4.10) for a minute amount x close to 0.

Substituting (4.11) into (4.8),

Here, as in the case of (6) described above, the required local buckling strain ε _cr is expressed as the required local buckling strain ε _req to distinguish the required local buckling strain input as the required value from the local buckling strain ε _cr . Further, the stress corresponding to the required local buckling strain ε _req on the stress strain curve is σ _req . Since (4.14) shows the lowest value, the partial stress relationship between multiple points that should be satisfied by the pipe stress-strain curve is as follows. (4.15) Are the same.

(11) Further, another pipe material design method according to the present invention is characterized in that, in the above (7), the partial stress relationship between a plurality of points satisfies the following expression (5.1). is there.

Here, the equation (5.1) in the above (11) will be described.
FIG. 12 shows an assumed continuous hardening type stress strain curve. In FIG. 12, the horizontal axis represents the compression axial strain of the pipe, and the vertical axis represents the compression axial stress.
When the stress-strain relationship is expressed by a power function, the point on the stress-strain curve corresponding to ε _cr , ε _1, and ε ₂ on the horizontal axis (on the strain axis) is equivalent to the case where the stress-strain relationship is expressed by the linear relationship described above. When the stress is the buckling point C (σ _cr ), the auxiliary point 1 (σ ₁ ), and the auxiliary point 2 (σ ₂ ), the following relationship is obtained.

The strain hardening index adopts an approximate expression as in the case of two-point display, and is expressed by the following expression.

Here, as in the case of (6) described above, the required local buckling strain ε _cr is expressed as the required local buckling strain ε _req to distinguish the required local buckling strain input as the required value from the local buckling strain ε _cr . Further, the stress corresponding to the required local buckling strain ε _req on the stress strain curve is σ _req . Since (5.8) shows the lowest value, the partial stress relationship between multiple points to be satisfied by the pipe stress-strain curve is as follows: (5.9) Are the same.

(12) Further, in the pipe material design method according to the present invention, in the above (1) to (11), in addition to the strain hardening characteristics, the yield stress range and the tensile stress determined by the material standard or required conditions The range is a condition that the stress-strain curve of the pipe should satisfy.
As described above, when selecting a pipe that satisfies the design condition from pipes manufactured by the existing manufacturing method by using the yield stress range and the tensile stress range as a condition, before examining the strain hardening characteristics, Since it is possible to narrow down by the yield stress range and the tensile stress range, it is easy to select a pipe. In addition, when a pipe is newly manufactured based on the material design, the manufacturing method can be narrowed down by using the yield stress range and the tensile stress range as conditions.

(13) In the above (1) to (12), when the strain hardening characteristic acquired in the strain hardening characteristic acquisition step is set as the condition that the stress strain curve of the pipe should satisfy, the stress strain curve that satisfies the condition Judgment process for determining whether or not a pipe having the mechanical properties shown in FIG. 6 can be manufactured, and when it is determined that the pipe can be manufactured in the determination process, the diameter or thickness of the pipe set or provisionally determined is adopted. However, when it is determined that the production is impossible, the process is performed again from the pipe condition setting step.

(14) In addition, when the determination step in the above (13) is manufactured by an existing manufacturing method, and when the existing manufacturing method is not suitable, the chemical component design and / or process of the material And a determination on a manufacturing method whose design has been changed.

(15) Further, in the above (1) to (14), in addition to the strain hardening characteristics, it is a condition that the stress strain curve of the pipe should satisfy the continuous hardening type.

(16) Further, the pipe manufacturing method according to the present invention includes a material design process for designing a pipe material by the pipe material design method according to any one of (1) to (14), and the material design process. And a step of performing chemical component design and / or process design of the material based on the conditions to be satisfied by the stress-strain curve of the pipe obtained by the above.

(17) Moreover, the pipe which concerns on this invention was manufactured according to the manufacturing method of the pipe of the said (16) description, It is characterized by the above-mentioned.

(18) Further, a pipeline according to the present invention is characterized by being configured by connecting the pipes described in the above (17).

In the present invention, the local buckling strain required in addition to the pipe diameter and pipe thickness is also given in advance, and the material design of the pipe that satisfies this condition is made, so both economy and safety are achieved. The material design of the pipe to be filled becomes possible.
By using this pipe material design method, a pipe manufacturing method that satisfies both economic efficiency and safety can be realized.
Furthermore, the pipe manufactured by this manufacturing method and the pipeline constituted by connecting the pipe satisfy economic efficiency and safety.

[Embodiment 1]
FIG. 1 is a flowchart for explaining a pipe material design method according to an embodiment of the present invention. In the present embodiment, as shown in FIG. 1, the diameter of the pipe used in the pipeline is based on at least the transport amount and transport distance of the pressurized fluid transported in the pipeline determined by the project scale (S1). D. Pipe condition setting step (S3) for tentatively determining the pipe thickness t and the transport pressure, and the pipeline is structurally designed in consideration of the laying line in the pipe having the tentatively determined diameter and pipe thickness. A maximum compression axial strain calculating step (S5) for obtaining a maximum compression axial strain generated in the pipe when the transport pressure, ground displacement and / or external force is applied to the pipeline, and a required compression based on the maximum compression axial strain the required compression local buckling strain setting step of setting local buckling strain ε _req (S7), the diameter D, pipe thickness t, and required compression local buckling strain epsilon pipes should meet all the conditions of the _req buckling point near The strain hardening characteristic acquisition step (S9) for obtaining the strain hardening characteristic in the step, the step (S11) of using the strain hardening characteristic as a condition of the stress strain curve of the pipe, and the strain hardening characteristic acquired in the strain hardening characteristic acquisition step. A determination step (S13) for determining whether or not a pipe having the mechanical properties indicated by the stress-strain curve that satisfies the conditions when the conditions of the stress-strain curve of the pipe are satisfied can be manufactured.
Hereinafter, each step will be described in detail.

<Pipe condition setting process>
Based on the transport amount and transport distance of the pressurized fluid transported by the pipeline, the pipe diameter D, the tube thickness t, and the transport pressure are provisionally determined to minimize the operation cost and the construction cost.
The operating cost is a function of the operating pressure P and the pipe diameter D, and the operating pressure is a function of the transport amount Q, the pipe diameter D, and the transport distance L. The tube diameter D is a function of the transport amount Q, the operating pressure P, and the transport distance L.
The construction cost is a function of the pipe diameter D, the pipe thickness t, and the material grade TS (yield strength), and the pipe thickness t is a function of the transport pressure P and the material grade TS.
Therefore, it is necessary to determine the diameter D, the tube thickness t, and the transport pressure so that the parameters related to each other are adjusted to obtain the lowest cost.
In this example, outer diameter D = 610.0mm, tube thickness t = 12.2mm, material grade TS: API
5L X80 and design internal pressure = 10MPa. API 5L X80 has the standard minimum yield point (YSmin) of 551 MPa, allowable tensile strength width of TSmin = 620 MPa, and TSmax = 827 MPa.

<Maximum compression shaft strain calculation process>
In this example, the case where the strain hardening characteristic for not bending local buckling is calculated with respect to the lateral flow of the ground is taken as an example.
Fig. 2 shows the ground displacement distribution to be considered when lateral flow occurs. The figure also shows the general concept of an embedded pipeline that is deformed by lateral flow. The ground displacement distribution due to the lateral flow can be expressed by the lateral flow width W and the maximum displacement δ _max . In actual seismic design, it is difficult to estimate the liquefaction width W. Therefore, here, W is used as a variable, and the required strain is calculated after calculating the maximum bending strain in the pipeline. Determine curing properties. In this trial calculation example, δ _{max is set} to 2.0 m.

  The pipeline shown in Fig. 2 is modeled as a shell element based on the conditions of pipe diameter D, pipe thickness t, material grade TS, and transport pressure P temporarily determined in the pipe condition setting process, and maximum compression bending is performed by a finite element analysis program. Calculate strain and maximum tensile bending strain. The spring characteristics of the ground were set based on the gas pipe liquefaction seismic design guidelines (2003). At this stage, the stress-strain curve of the material is provisionally determined so as to satisfy the standard minimum yield stress (SMYS) and the standard minimum yield strength (SMTS) specified by the API standard.

  Of the results calculated by the finite element analysis program, the maximum compressive bending strain (positive sign) and the maximum tensile bending strain (negative sign) of the pipeline are shown in FIG. As shown in FIG. 3, the maximum bending strain generated in the pipeline has a maximum value when the lateral flow width W is 30 m. The maximum compressive bending strain, which is important for examining local buckling, is also maximized when W is 30 m, and the value is about 2%. Since the bending local buckling strain and the compression local buckling strain have a quantitative relationship that 1/2 of the compression bending strain becomes the compression local strain (see FIG. 7), the maximum compression axial strain in this case is about 1%.

<Required compression local buckling strain setting process>
Once the maximum compression axial strain is calculated, the required compression local buckling strain is then determined. The required buckling strain is determined not less than the maximum compression axial strain and taking into account a predetermined safety factor. In this example, the required buckling strain is set to 1%, which is substantially the same as the maximum compression axial strain (S7).

<Strain hardening characteristic acquisition process>
In the present embodiment, as means for acquiring the strain hardening characteristics, there is a virtual buckling point on the stress strain coordinate corresponding to the required compression local buckling strain ε _req and a position where the strain value is away from the buckling point. When one auxiliary point is assumed, a virtual buckling point and the one auxiliary point are used to give a partial stress relationship between a plurality of points. Specifically, the strain hardening property is given based on the above-described formula (2.1).

Ε _req on the left side of the above formula: 0.010, 0.015 (Auxiliary point 2 is set to 1.5% by adding 0.5% to the required buckling strain of 1.0%), t: 12.2 mm, D: 610.0 mm Then

<Process in which strain hardening characteristic is a condition of stress strain curve of pipe>
Since the strain hardening property H = σ ₂ / σ _req ≧ 1.07, if the ratio of the stress at 1% strain to the stress at 1.5% strain is 1.07 or more in the stress strain curve, the outer diameter is 610.0 mm and the tube thickness is 12.2 mm. The compressive local buckling strain of the pipe is over 1%.

<Judgment process>
FIG. 4 is a flowchart for explaining the determination process. Hereinafter, the determination process will be described with reference to FIG. The material grade set in the pipe condition setting step (S3) is API 5L X80, and the pipe to be manufactured is API 5L X80 standard minimum yield point (YSmin) 551 MPa, allowable tensile strength width TSmin = 620 MPa, TSmax = 827 MPa, and the strain hardening characteristic H ≧ 1.07 must be satisfied. Therefore, candidate manufacturing methods A, B, C, D, E, and F are selected from the conventional manufacturing results (S51), and the required buckling strain ε _req (1.0%) is obtained from each stress strain curve. Read stress σ _1.0% and stress σ _1.5% corresponding to strain (1.5%), and calculate H _(1.0-1.5) . Table 1 shows the value of H _(1.0-1.5) obtained for each manufacturing method.

Based on Table 1, it is determined whether or not there is a manufacturing method in which the obtained value of H _(1.0-1.5) is greater than the strain hardening characteristic H (S53). When there is a desired manufacturing method, the local buckling strain of a pipe having an outer diameter of 610.0 mm and a pipe thickness of 12.2 mm can be set to 1% or more by selecting the manufacturing method. In this example, as shown in Table 1, it cannot be manufactured by the manufacturing methods A, B, D, and F, and can be manufactured by the manufacturing methods C and E. When a plurality of manufacturing methods can be selected as described above, a more optimal method, for example, a method capable of improving manufacturing stability, reducing manufacturing cost, or improving buckling resistance can be selected. In this case, the method C having a large H value is selected so that the local buckling strain becomes larger (S55), and the process proceeds to S15 in FIG. According to the manufacturing method C selected at this time, a pipe satisfying the required compression local strain required for the lateral flow is obtained, and the safety is satisfied. Moreover, the tube thickness t at this time is determined in consideration of the cost in the pipe condition setting step, and is excellent in economic efficiency.

In the determination of S53, when H _(1.0-1.5) is smaller than the strain hardening property H for all existing manufacturing methods, the manufacturing conditions (rolling temperature, It is examined whether or not the required strain hardening property H is satisfied by adjusting the cooling temperature or adjusting the chemical composition (S57). If the value of H _(1.0-1.5) can be made larger than the required strain hardening characteristic H by adjusting the manufacturing conditions, etc., the manufacturing method is selected and the process proceeds to S15 in FIG.

  As a method for adjusting the manufacturing conditions in S57, steel having no yield shelf and large local buckling strain is composed of a two-phase structure of ferrite and a hard phase (such as bainatonite and martensite). The strain hardening characteristics can be changed by changing the structure of the hard phase and the hard phase fraction by changing the start temperature and / or the cooling rate, and further the cooling stop temperature. As an example of the chemical component adjustment method, the structure of the hard phase and the hard phase fraction can also be changed by changing the amount of carbon (C) or manganese (Mn), for example.

  If the existing manufacturing method does not satisfy the conditions for the strain hardening characteristics H, and if the conditions for the strain hardening characteristics H are not satisfied even if the manufacturing conditions are adjusted or the chemical components are adjusted, it is determined that the manufacturing is impossible. Then, returning to the pipe condition setting step (S3) again, the specifications of the pipe are reset and the same processing is repeated.

  When it is determined in the determination step (S13) that the manufacture is possible, the determined manufacturing method and pipe specifications are presented to the orderer for confirmation (S15). If the orderer confirms and understands the specifications of the pipe, the orderer places an order with the manufacturer, and the manufacturer who has received the order manufactures in compliance with the determined manufacturing method (S17). The manufactured pipe is delivered to the orderer, the pipeline is constructed (S19), and the operation is started after construction (S21).

[Embodiment 2]
The present embodiment relates to a material design method for preventing local buckling against a strike-slip fault. Since the processing flow of the present embodiment is basically the same as that of the first embodiment, overlapping portions will be described briefly and different portions will be described in detail.
<Pipe condition setting process>
As in the first embodiment, assuming the transport amount and transport distance of the pressurized fluid transported by the pipeline, the pipe diameter D, the pipe thickness t, and the transport pressure are assumed to minimize the operation cost and the construction cost. Decide.
The pipe specifications provisionally determined in the present embodiment are the same as those in the first embodiment, the outer diameter D = 610.0 mm, the tube thickness t = 12.2 mm, the material grade TS: API
5L X80 and design internal pressure = 10MPa. API 5L X80 has the standard minimum yield point (YSmin) of 551 MPa, allowable tensile strength width of TSmin = 620 MPa, and TSmax = 827 MPa.

<Maximum compression shaft strain calculation process>
This embodiment relates to a strike-slip fault, and FIG. 5 shows a general concept of an embedded pipeline deformed by a strike-slip fault. In this trial calculation example, the maximum displacement amount δ _max was set to 2.0 m as in the embodiment, and the ground spring characteristics were set in the same manner as in the first embodiment.
Among the results calculated by the finite element analysis program, the maximum compression bending strain (positive sign) and the maximum tensile bending strain (negative sign) of the pipeline are shown in FIG. As shown in Fig. 6, the maximum bending strain that occurs in the pipeline is about 5m away from the fault plane, and the maximum compressive bending strain that is important for examining local buckling is about 2.4%. It is. Since 1/2 of the compression bending strain is the compression local strain, the maximum compression axial strain is about 1.2%.

<Required compression local buckling strain setting process>
Once the maximum compression axial strain is calculated, the required compression local buckling strain is then determined. In this example, considering the safety factor of 1.25, the required local buckling strain ε _req was determined to be 1.5%.

<Strain hardening characteristic acquisition process>
Also in the present embodiment, the strain hardening characteristics are obtained based on the formula (2.1) as in the first embodiment. As with the first embodiment, the auxiliary point was set to 2.0% by adding 0.5% to the required buckling strain (1.5%). When calculating with the necessary numerical values in (2.1), it is as follows.

<Process in which strain hardening characteristic is a condition of stress strain curve of pipe>
Since H = σ ₂ / σ _req ≧ 1.11, in the stress-strain curve, if the ratio of the stress at 1.5% strain to the stress at 2.0% strain is 1.11 or more, the pipe of outer diameter 610.0mm and pipe thickness 12.2mm The compression local buckling strain is 1.5% or more.

<Judgment process>
The pipe to be manufactured must satisfy the strain hardening characteristic H ≧ 1.11 while satisfying the standard minimum yield point (YSmin) of 551 MPa of material grade API 5L X80, allowable width of tensile strength TSmin = 620 MPa, TSmax = 827 MPa. There is. As in the first embodiment, candidate manufacturing methods A, B, C, D, E, and F are selected from the conventional manufacturing results, and the required buckling strain ε _req (1.5%) is selected from each stress strain curve. Read the corresponding buckling stress σ _req and the stress (σ ₂ ) corresponding to the reference strain (2.0%), and calculate H _(1.5-2.0) . Table 2 shows the value of H _(1.5-2.0) obtained for each manufacturing method.

As shown in Table 3, if there is a manufacturing method in which the obtained H _(1.5-2.0) value is larger than the strain hardening characteristic H, the outer diameter 610.0 mm, the tube can be selected by selecting the manufacturing method. The local buckling strain of a pipe having a thickness of 12.2 mm can be 1.5% or more. As shown in Table 2, it cannot be manufactured by the manufacturing methods A, B, D, E, and F, and can be manufactured by the manufacturing method C. According to this manufacturing method C, a pipe that satisfies the required compression local strain required for the strike-slip fault is obtained, which satisfies safety. Moreover, the tube thickness t at this time is determined in consideration of the cost in the pipe condition setting step, and is excellent in economic efficiency.
The subsequent processing is the same as in the first embodiment.

As described above, according to the first and second embodiments, it is possible to adopt as much as possible the pipe thickness determined in consideration of the cost in the pipe condition setting process, which satisfies safety and is excellent in economy. Pipe material design can be realized.
In addition, in the case of the material which becomes the continuous hardening type stress-strain curve exemplified in the first and second embodiments, there is an effect that the required buckling strain can be arbitrarily designated. In other words, in the case of a material that has a yield-shelf-type stress-strain curve, the required buckling strain must be specified as a value after the strain-hardening region, whereas the material that has a continuous-curing-type stress-strain curve In this case, the material design can be simplified because any value can be designated without such restrictions.

  Moreover, in this Embodiment, the concept of the material design which was not able to be known in the conventional pipeline company side as shown to the required compression local buckling strain setting process (S7)-determination process (S13) of FIG. 1 was presented. This makes it possible to request pipes from the pipeline company that can make construction costs more advantageous to the manufacturer. The production of line pipes becomes possible.

In the first and second embodiments, the bending local buckling strain is obtained from the quantitative relationship between the bending local buckling strain and the compression local buckling strain by giving the bending local buckling strain as a required condition in the pipe condition setting step. However, when the compression local buckling strain is given as a requirement, only the conversion step is eliminated, and the other steps are the same as in the first embodiment. 2 is possible.
In the first and second embodiments, the example in which the strain hardening characteristic is given as a partial stress relationship between a plurality of points is shown. However, the present invention is not limited to this, and the required compression local buckling. When a virtual buckling point on the stress-strain coordinate corresponding to the strain ε _req is assumed, it can be given as the slope of the tangent line of the stress-strain curve at the virtual buckling point or based on the slope. .

  Further, in the first and second embodiments, the example in which the material grade (material standard) is used as the condition to be satisfied of the pipe in the pipe condition setting step is shown, but the present invention is not limited to this, and the pipe The requirements of the line company or the like (YS, TS range, etc.) may be used as a condition to be satisfied by the pipe in the pipe condition setting step.

In the first and second embodiments, as shown in the flowchart of FIG. 1, the pipe condition setting step (S1, S3) and the maximum compression axial strain calculation step (S5) based on the transport amount and transport distance are performed in the pipeline. An example is given in which a steel company performs the required compression local buckling strain setting step (S7) to the determination step (S13). However, the pipe condition setting process (S1, S3) and the maximum compression axial strain calculation process (S5) based on the transport amount and transport distance may be performed by a steel company or a consulting company other than the pipeline company. In addition, the requested compression local buckling strain setting step (S7) to the determination step (S13) may be performed by, for example, a pipeline company or a consulting company other than the steel company.
In this way, who can perform each step shown in the flowchart of FIG. 1 can be freely selected according to the business situation.

It is a flowchart explaining Embodiment 1 of this invention. It is explanatory drawing of the lateral flow distribution of the ground in Embodiment 1 of this invention. It is a graph which shows the finite element analysis result which concerns on Embodiment 1 of this invention. It is a flowchart explaining the determination process in Embodiment 1 of this invention. It is explanatory drawing of the strike-slip fault of the ground in Embodiment 2 of this invention. It is a graph which shows the finite element analysis result which concerns on Embodiment 2 of this invention. It is explanatory drawing explaining the relationship between the compression local buckling distortion of a pipe, and a bending local buckling distortion. It is explanatory drawing of the concept of the local buckling in a continuous hardening type stress-strain curve. It is explanatory drawing of the stress relationship between the several points on the stress strain coordinate in this invention (the 1). It is explanatory drawing of the stress relationship between the several points on the stress strain coordinate in this invention (the 2). It is explanatory drawing of the stress relationship between the several points on the stress-strain coordinate in this invention (the 3). It is explanatory drawing of the stress relationship between the several points on the stress strain coordinate in this invention (the 4). It is a flowchart explaining the flow of a process of general gas pipeline construction (the 1). It is explanatory drawing of the relationship between the experimental data regarding local buckling distortion, and a design formula. It is a flowchart explaining the flow of a process of general gas pipeline construction (the 2).

Claims (18)

A pipe condition setting step for setting a pipe diameter D, a pipe thickness t, and a required compression local buckling strain ε _req of the pipe;
A strain hardening property acquisition step for obtaining a strain hardening property in the vicinity of the buckling point of the pipe that should satisfy the conditions set in the pipe condition setting step;
And a step of making the strain hardening characteristic a condition that the stress-strain curve of the pipe should satisfy. A pipe condition setting step for tentatively determining the diameter D, the pipe thickness t and the transport pressure of the pipe used in the pipeline based on at least the transport amount and transport distance of the pressurized fluid transported in the pipeline;
The pipeline is structurally designed in consideration of the laying line on the pipe having the tentatively determined diameter and pipe thickness, and when the transport pressure, ground displacement and / or external force is applied to the structurally designed pipeline, A maximum compression shaft strain calculating step for obtaining a maximum compression shaft strain to be generated;
A required compression local buckling strain setting step for setting a required compression local buckling strain ε _req based on the maximum compression axial strain;
A strain hardening property obtaining step for obtaining a strain hardening property in the vicinity of the buckling point of the pipe that should satisfy all the conditions of the diameter D, the tube thickness t, and the required compression local buckling strain ε _req ;
And a step of making the strain hardening characteristic a condition that the stress-strain curve of the pipe should satisfy. A pipe condition setting step for setting a pipe diameter D, a pipe thickness t, and a required bending local buckling strain of the pipe;
From the quantitative relationship between the bending local buckling strain and the compression local buckling strain, the local buckling strain converting step of converting the required bending local buckling strain into the required compressing local buckling strain ε _req ,
A strain hardening property obtaining step for obtaining a strain hardening property in the vicinity of the buckling point of the pipe that should satisfy all the conditions of the diameter D, the tube thickness t, and the required compression local buckling strain ε _req ;
And a step of making the strain hardening characteristic a condition that the stress-strain curve of the pipe should satisfy. A pipe condition setting step for tentatively determining the diameter D, the pipe thickness t and the transport pressure of the pipe used in the pipeline based on at least the transport amount and transport distance of the pressurized fluid transported in the pipeline;
The pipeline is structurally designed in consideration of the laying line on the pipe having the tentatively determined diameter and pipe thickness, and when the transport pressure, ground displacement and / or external force is applied to the structurally designed pipeline, A maximum bending strain calculation step for obtaining the maximum bending strain to be generated;
The required bending local buckling strain is set based on the maximum bending strain, and the required bending local buckling strain is determined from the quantitative relationship between the bending local buckling strain and the compression local buckling strain. a local buckling strain conversion step to convert to _req ;
A strain hardening property obtaining step for obtaining a strain hardening property in the vicinity of the buckling point of the pipe that should satisfy all the conditions of the diameter D, the tube thickness t, and the required compression local buckling strain ε _req ;
And a step of making the strain hardening characteristic a condition that the stress-strain curve of the pipe should satisfy. The strain hardening characteristic is based on the tangential slope of the stress strain curve at the virtual buckling point, assuming a virtual buckling point corresponding to the required compression local buckling strain ε _req in the stress strain coordinates. The pipe material design method according to any one of claims 1 to 4, wherein the pipe material design method is provided. Assuming that the strain hardening characteristic is H and a virtual buckling point corresponding to the required compression local buckling strain ε _req is assumed in the stress strain coordinates, the slope of the tangent line of the stress strain curve at the virtual buckling point is represented by E _Treq. The material design method for a pipe according to any one of claims 1 to 5, wherein the strain hardening characteristic H satisfies the following formula.

The strain hardening characteristics are assumed when a virtual buckling point on the stress strain coordinate corresponding to the required compression local buckling strain ε _req and one or more auxiliary points at a position where the strain value is separated from the buckling point are assumed. 5. The pipe according to claim 1, wherein the stress is given as a partial stress relationship between a plurality of points using the virtual buckling point and the one or more auxiliary points. Material design method. The pipe material design method according to claim 7, wherein a partial stress relationship between a plurality of points satisfies the following expression.

The pipe material design method according to claim 7, wherein a partial stress relationship between a plurality of points satisfies the following expression.

The pipe material design method according to claim 7, wherein a partial stress relationship between a plurality of points satisfies the following expression.

The pipe material design method according to claim 7, wherein a partial stress relationship between a plurality of points satisfies the following expression.

The pipe according to any one of claims 1 to 11, wherein a stress-strain curve of the pipe satisfies a yield stress range and a tensile stress range determined by a material standard or a required condition in addition to the strain hardening characteristics. Material design method. When the strain hardening characteristic acquired in the strain hardening characteristic acquisition step is the condition that the stress strain curve of the pipe should satisfy, it is determined whether or not a pipe having the mechanical properties indicated by the stress strain curve that satisfies the condition can be manufactured. A determination process;
If it is determined that the manufacture is possible in the determination step, the set or provisionally determined diameter and thickness of the pipe are adopted, and if it is determined that the manufacture is impossible, the process is repeated from the pipe condition setting step. The pipe material design method according to any one of claims 1 to 12. The determination step includes a determination for a case of manufacturing by an existing manufacturing method, and a determination of a manufacturing method in which the chemical composition design and / or process design of a material is changed when there is no suitable existing manufacturing method. The pipe material design method according to claim 13, further comprising: The pipe material design method according to any one of claims 1 to 14, wherein in addition to the strain hardening characteristics, the stress hardening curve of the pipe is to satisfy the condition of being a continuous hardening type. A material design process for designing a pipe material by the pipe material design method according to any one of claims 1 to 15,
And a step of performing chemical component design and / or process design of the material based on a condition to be satisfied by a stress-strain curve of the pipe obtained by the material design step. A pipe manufactured according to the method for manufacturing a pipe according to claim 16. A pipeline constructed by connecting the pipes according to claim 17.

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