RU2654154C2 - Method of determining the residual life of the pipelines - Google Patents

Abstract

FIELD: pipes.

SUBSTANCE: invention relates to the diagnosis of pipelines to assess their residual life. Initial data for determining the residual life are relative deformations obtained from extensometers, and the pressure values inside the pipeline, obtained from the pressure sensors. Method of determining the residual life of the pipelines is, that in the pipeline identify a zone with a potentially depleted resource, in this zone define a place, extensometers and a pressure sensor are installed, on the basis of which is continuously calculated he residual life.

EFFECT: method of determining the residual life of the pipeline can be used to determine the residual life of the pipeline in pressure pipelines of round cross-section.

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Description

The invention relates to the diagnosis of pipelines and can be used to assess the residual resource of pipelines during operation.

A known method for determining the residual metal resource of pipes of the main pipeline intended for reuse (RF patent No. 2226681, CL G01N 3/00, from 08.19.2002). This method includes non-destructive testing, sample preparation, mechanical testing and determination of residual life. In this case, the pipes are distributed into a batch of one steel grade, of the same diameter and wall thickness, they are selected from the batch of pipes with maximum diameters, non-destructive methods are selected from them to control the pipe with the maximum average values of hardness and coercive force for the manufacture of samples and mechanical testing of two equal groups of samples , one of which is preliminarily subjected to heat treatment, and the residual life of achieving standard values of the mechanical properties of the metal of the pipes is determined by calculation.

The main disadvantage of this method is the indirect nature of the determination of the residual resource and the associated significant errors.

A known method for determining the residual resource of pipelines (RF patent No. 2413195, class G01N 3/00, dated 20.07.2009), related to ensuring the safe operation of pipelines for long-term operation in the oil and gas industry. Samples indicating the pipeline resource are cut from the controlled area. Samples are cut from the least exposed sections of the pipeline, with half of the samples being annealed and the other half left in the initial state. Both parts of the samples - the initial (annealed) and unannealed - are subjected to tests (static and fatigue) and a comparative analysis is carried out, and the residual resource is determined by the results of the tests by the formula.

The disadvantages of this method is the high complexity and destructive method for determining the residual resource of pipelines.

A known method for diagnosing the technical condition of the main pipeline (RF patent No. 2423644, class. F17D 5/06, 09/23/2009). The method relates to pipeline transport and can be used to predict the appearance of a dangerous condition of the main pipeline, for example, when the main pipeline crosses roads or at intersections of several pipelines. A method for diagnosing the technical condition of the main pipeline consists in monitoring the magnitude of the stress-strain state of the pipeline using a linear strain gauge, and using the acoustic emission sensor, monitoring the level of acoustic emission from developing pipeline defects. The magnitude of the stress-strain state of the pipeline and the level of acoustic emission from developing defects in the pipeline are measured simultaneously with the subsequent determination of the value of the correlation coefficient between the measured values and if the correlation coefficient exceeds a predetermined threshold value, the threat of a dangerous state of the main pipeline is diagnosed.

The disadvantage of this method is the low accuracy of predicting the residual resource of the main pipeline.

The purpose of the invention is to reduce the complexity and increase the accuracy of determining the time before the destruction of the pipeline.

The goal is achieved by identifying a zone with a potentially reduced resource in the pipeline, in this zone the installation location of the pressure sensor and four extensometer sockets is determined, based on the readings of which the residual resource of the pipeline cross section is continuously calculated.

The initial data for determining the residual life are the relative deformations obtained from extensometers and the pressure values inside the pipeline obtained from the pressure sensor.

The calculation of the residual resource of the pipeline is as follows.

For each of the four extensometer sockets installed in the studied section, the system of equations is solved:

where ε ₀ is the relative strain measured by an extensometer directed along the axis of the pipe;

ε ₉₀ is the relative deformation measured by an extensometer directed tangentially to the diameter of the pipe;

ε ₄₅ - relative deformation measured by an extensometer in the direction of 45 ° to the axis of the pipe;

ε _t is the relative deformation of the pipe in the circumferential direction;

ε _z is the relative deformation of the pipe in the axial direction;

ε _r is the relative deformation of the pipe in the radial direction;

γ is the relative torsional strain of the pipe.

In this system, the values ε ₀ , ε ₉₀ and ε ₄₅ are known, which are measured by extensometers. Having solved this system, the values of the relative strains ε _z , ε _t and γ on the outer surface of the pipe (with radius R) are calculated for four points of this surface. Thus, as a result, 12 values of relative strains are calculated, namely ε _z1,2,3,4 , ε _t1,2,3,4 and γ _1,2,3,4, where indices 1-4 indicate the point number, in which deformation value is obtained. Moreover, we introduce the notation in such a way that points 1 and 3 are opposite to each other, respectively, points 2 and 4 are also opposite to each other.

Next is the distribution of deformations along the outer and inner surfaces of the pipe from the following equations:

where μ is the Poisson's ratio;

E - Young's modulus, MPa;

p - overpressure in the pipe, MPa;

r is the inner radius of the pipe, mm;

R is the outer radius of the pipe, mm;

ϕ is the angular coordinate, rad;

ε _e (R, ϕ) is the equivalent relative deformation for the outer surface of the pipe;

ε _e (r, ϕ) is the equivalent relative deformation for the inner surface of the pipe.

For the positive direction of the angular coordinate, the direction from point 2 to point 1 is taken along the shortest path. Moreover, ϕ = 0 at point 2.

Then, the equivalent relative deformation is calculated for the outer and inner surfaces of the pipe:

To calculate according to the above functions (12) and (13), it is necessary to determine n points of the outer and inner cross-sectional surfaces of the studied pipeline. Based on the results of previous calculation cycles, for each of these points, local maxima and minima of the equivalent relative strain ε _{max, j} and ε _{min, j are found} , where j = 1 ... n. Then, the characteristics of the local loading cycle at each of the points are calculated:

where ε _max is the local maximum in time of the equivalent relative deformation;

ε _min is a local minimum in time of equivalent relative deformation.

Then, the equivalent relative deformation of the cycle ε _ets for each point is found:

where σ _-1 is the endurance limit in a symmetric cycle, MPa;

σ ₀ - endurance limit during a pulsating cycle, MPa.

The number of cycles N _ez for each point of the inner and outer surface that can withstand a portion of the pipeline for a given type of loading is determined from the Morrow-Manson equation:

Here:

- ε _ƒ - fatigue viscosity (the value of the amplitude of plastic deformation at which failure (failure) will occur during one half-cycle of loading, provided there are no elastic deformations)

-ψ is the relative narrowing of the material at break;

- σ _ƒ - fatigue strength (the value of the stress amplitude at which failure (failure) will occur during one loading half-cycle provided that there are no plastic deformations)

- b - exponent of fatigue strength (Baskvin exponent)

- c - fatigue viscosity exponent

Next, we calculate the accumulated damage at each point:

- величина накопленных повреждений, определяемая в ходе текущего цикла расчета;Where

- the amount of accumulated damage determined during the current cycle of calculation;

- величина накопленных повреждений, определенная в ходе предыдущего цикла расчета.

- the amount of accumulated damage determined during the previous calculation cycle.

From the calculated values of the accumulated damage for each of the individual points of the inner and outer surfaces of the pipeline in this section there is a maximum:

The value of the consumed resource in hours for the studied pipeline in this section is determined according to the expression:

where T _service.norm - standard pipeline service life, h.

The value of the residual resource is determined according to the expression:

An example embodiment of the invention.

A section of a pipeline with a length of 4.5 m of circular cross section and a diameter of D _y = 100 mm (R = 57 mm, r = 50 mm) is given. Characteristics of the pipe material (steel 20):

E = 212000 MPa;

μ = 0.33;

σ _-1 = 193 MPa;

σ ₀ = 320 MPa;

ψ = 0.5;

σ _in = 412MPa.

In the middle section of the pipeline, four extensometer sockets and one pressure sensor are installed. At the initial moment of time, all relative strains are equal to zero.

In the middle section of the pipeline under study, a load is applied that varies cyclically from 0 to 9450 N, which creates a bending force, which corresponds to a deflection of the pipeline in the middle part by 0-25 mm, respectively. In this case, 2 × 10 ⁸ loading cycles of the pipeline are considered.

In this case, the values of the relative deformation recorded by the extensometer outlet at maximum deflection correspond to:

The pressure in the pipeline was 0.5 MPa.

For sockets No. 1 and No. 2 after substituting the values ε ₀ , ε ₄₅ and ε ₉₀ from (1) - (3) we obtain:

and its solution:

ε _z = 7.0 · 10 ^-4 ;

ε _t = -3.5⋅10 ^-6 ;

γ = -6.23⋅10 ^-7 .

For sockets No. 3 and No. 4, the system of equations will look as follows:

and its solution:

ε _z = -7.0 · 10 ^-4 ;

ε _t = 3.5 x 10 ^-6 ;

γ = 3.77 × 10 ^-7 .

As a result of solving the above systems of equations, we obtained a set of relative strains ε _z , ε _t and γ from 12 quantities:

Substituting these values in (4) - (11), we obtain the following system of equations:

.

.

Next are equivalent relative deformations for the outer and inner surfaces of the pipe according to (12) - (13):

;

;

On the outer and inner surface of the cross section of the studied pipeline, we select 8 points (n = 8), which are 45 degrees apart (or π / 4). Since the first calculation cycle is considered, for all points ε _{min, j} = 0, a ε _{max, j} is equal to the value of the function ε _e (R, ϕ) for the outer surface and ε _e (r, ϕ) for the inner surface. These values are equal to:

Thus, when substituting these values in (14) - (15), we obtain the following results:

For the Morrow-Manson equation, the coefficients according to (18) - (21) are equal to:

The number of cycles N _ets for each considered point of the pipeline, calculated according to (17), is:

Accumulated damage, according to (22), at each point is:

As can be seen from these data, the maximum value of accumulated damage is observed at point No. 6 and is for one loading half-cycle:

.

.

The magnitude of resources spent hours on (24), given that the standard service life of 25 years (GOST 27751-2014), ie 25⋅8760 = 219 000 hours, and the number of half cycles of _{the CPU} load N is equal to ⁸ 4⋅10:

The residual resource T _ost according to (25) is:

219000 h - 152950 h = 66050 h or 7.5 years.

Thus, the proposed method allows you to more fully use the resource of the pipeline without the risk of failure.

Claims (19)

A method for determining the residual life of a pipeline, in which the initial data for determining the spent life are relative deformations and pressure values inside the pipeline, characterized in that a zone with a potentially reduced resource is detected in the pipeline, the location of the pressure sensor and extensometers is determined in this zone, based on the readings which continuously calculates the residual resource according to the expression: T _ost = T _service.norm -T, where T _service.norm - the standard service life of the pipeline; T is the value of the consumed resource in a given section of the pipeline, which is determined according to the expression:

- accumulated damage:

- the amount of accumulated damage determined during the current cycle of calculation;

- the amount of accumulated damage determined during the previous cycle of calculation; N _ez - the number of cycles that a pipeline section can withstand for a given type of loading is determined from the Morrow-Manson equation:

Where

- fatigue viscosity (the value of the amplitude of plastic deformation at which failure (failure) will occur during one half-cycle of loading, provided that there are no elastic deformations)

ψ is the relative narrowing of the material at break;

- fatigue strength (the value of the stress amplitude at which failure (failure) will occur during one half-cycle of loading, provided there are no plastic deformations)

b - exponent of fatigue strength (Baskvin exponent)

s - exponent of fatigue viscosity