RU2611132C1 - Control method for pipeline process modes - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to a control method for process modes in the course of pipeline operation based on processing the data of dispatch control system regarding the actual cycling of operating pressure in the pumped medium.

EFFECT: increased reliability of the pipeline operation due to predicting and detecting the moments of pipeline operation transition to dangerous operating conditions from the point of view of the cyclic damage accumulation leading to the growth of fatigue defects to a certain state.

Description

FIELD OF THE INVENTION

The invention relates to the field of trunk transportation of oil and oil products, and in particular to methods of monitoring technological conditions during the operation of the pipeline based on data processing of the supervisory control system (SDCU) according to the actual cyclic operating pressure of the pumped medium. This invention can be used in sections of pipelines where it is impossible to conduct in-line diagnostics to identify defects, for example pipelines with washers, jumpers, process pipelines.

State of the art

Pipelines intended for the transportation of oil and oil products are exposed to cyclic pressure during operation, which occurs when any pumping equipment is turned on or as a result of a process switch in the process section. One of the factors influencing the growth of fatigue defects is just the cyclic change in working pressure. Currently, the operating pressure regimes of the main pipelines are not monitored and analyzed from the point of view of the danger of fatigue damage accumulation due to the influence of cyclic loads, which are the main reasons for the growth of crack-like defects.

The non-destructive testing of pipelines used today, based on various physical principles, makes it possible to identify existing defects. Those. the consequence is controlled, and not the cause of the formation of defects - the intensity of cyclic loading (for example, RU 2474812 C1, publication date 02/10/2013; RU 2473063 C1, publication date 01/20/2013).

In sections of the pipeline where non-destructive testing is possible, this approach is fully justified. However, for pipeline sections where it is impossible to conduct in-line diagnostics to identify defects, a different approach is needed to ensure trouble-free operation.

There is a method of ensuring a given level of reliability of a product, including non-destructive testing of the product before and during operation and repair of identified defects, in which before operation: performing non-destructive testing by technical means with known characteristics of reliability of control and determine the residual defectiveness of the product from the results obtained, using mechanical methods damage determines the critical dimensions of the defects, according to the known curve of residual defects and certain critical values The size of defects determines the initial probability of product failure, install sensors on the product that provide information on the operating loads on the product during its operation, after the start of operation: the readings of the operational load sensors are periodically recorded and stored in the form of the product’s operating history, periodically real-time operation determine the defect undergrowth and the corresponding change in the position of the residual defective curve at the points of the characteristic dimensions of the defects, if the new probability of failure determined in this way becomes unacceptably high, the operation of the product is stopped and its condition is monitored non-destructively, followed by repair of the identified defects that are unacceptable in operation, and after checking and repairing the detected defects, the new position of the residual curve is determined defects and new reliability characteristics of the product, the change of which is determined during operation using systems of operational load sensors, subsequent operation is carried out until the reliability level drops to unacceptable values (patent RU 2531428 C1, publication date 10/20/2014).

This method allows you to monitor the reliability of the product in real time and includes non-destructive testing of the product before and during operation and repair of identified defects. However, if it is impossible to conduct non-destructive testing, this method is not applicable. As a result, this method does not allow us to justify the need to adjust the operating modes of the pipeline in the direction of decreasing the intensity of the loading cycle if it is impossible to conduct non-destructive testing (in-line diagnostics).

SUMMARY OF THE INVENTION

The problem to which the claimed invention is directed, consists in creating a method for monitoring pipeline operating modes based on data processing of a supervisory control system (CDCS) based on the actual cyclic operating pressure of the pumped medium, based on which a conclusion is drawn on the need to adjust the operating mode in the direction of decreasing intensity cyclicity of working pressure.

The technical result achieved during the implementation of the invention is to increase the reliability of the operation of the pipeline by predicting and identifying the moments when the pipeline is in dangerous operation mode from the point of view of the accumulation of cyclic damage, leading to the growth of fatigue defects to the ultimate state.

The claimed technical result is achieved due to the fact that the method of controlling changes in the technological modes of operation of pipelines is characterized in that they select the estimated period of time, which allows to detect changes in the intensity of the cyclicity of the working pressure; select from the database of the dispatch control system of the pipeline control data on the actual cyclicity of the working pressure for the estimated period of time; convert the data of the actual cyclicity of the working pressure for the estimated period of time by highlighting the cycles of the working pressure and their number; determine the amplitude of the equivalent loading and the given number of cycles of equivalent loading for the estimated period of time; select the initial characteristics of the design defect in the pipe wall in such a way that, with the actual cyclicity of the working pressure, the real increase in the design defect allows you to detect changes in the intensity of the cyclic working pressure; calculate the growth time of the design defect in the pipeline wall from the initial depth to the final, which is a characteristic of the intensity of the loading cycle, with an equivalent pressure amplitude and the given number of cycles for the calculation period of time; carry out real-time assessment of the intensity of the loading cycle according to the data of the supervisory control system by the pressure cycle of each current settlement time period; comparing the intensity of the cyclic loading for each calculated period of time; form reference levels of intensity of the cyclic loading; control the mode of operation of the pipeline by comparing the actual cyclicality with the reference levels of intensity of the cyclic loading and in case of exceeding the actual intensity of the cyclicity of the reference level, adjust the mode of operation in the direction of decreasing the intensity of the cyclicity of the working pressure.

Thus, the control of changes in the actual parameters of the cyclicity of the working pressure according to the SDKU allows you to identify the moment of transition of the pipeline to a dangerous mode of operation from the point of view of accumulation of cyclic damage without the use of additional non-destructive testing.

Information confirming the implementation of the invention

FIG. 1 - FIG. 4 is a diagram of the actual modes of operation of the pipeline for various periods of time; FIG. 5 is a comparative diagram of the intensity of cyclic loading.

The technological mode of operation of the main pipeline for the estimated time period, for example, a month or a quarter, is characterized by the actual cyclic parameters of the operating pressure for this period of time according to SDKU. The operating mode according to the pressure cyclicity is characterized by the number of cycles, the maximum and minimum pressure values in the cycle. The cyclic parameters determine the intensity of the cyclic loading of the pipeline, and as a characteristic of the intensity of the cyclic loading, we can take the growth time of the calculated defect in the pipeline wall from the initial depth to the final one with the actual cyclic operating pressure, which is known for the calculated time period. The next estimated time period is characterized by its cyclic operating pressure parameters.

The method is as follows.

The choice of the estimated time period is made, which makes it possible to identify significant changes in the intensity of the cyclicity of the working pressure and these pressure changes, which should be used to calculate the characteristics of the intensity of the cyclic loading. The recommended minimum time interval is from 1 to 3 months.

Select data from the SDKU database on the actual cyclicality of the working pressure for the estimated period of time.

The data on the actual cyclicity of the working pressure for the calculated period of time is converted into the type of block loading (the cycles of the working pressure and their number are distinguished). The conversion is carried out by the method of full cycles or by the method of "rain" in accordance with GOST 25.101-83 "Calculations and strength tests. "Methods for the schematization of random processes of loading elements of machines and structures and the statistical presentation of the results."

A longitudinal surface semi-elliptic crack is accepted as a design defect, as the most dangerous defect from the point of view of growth under cyclic loading by internal pressure. The initial crack dimensions (length and depth) are selected on the basis of test calculations in such a way that, with the actual cycling of the working pressure, the real growth of the calculated crack allows significant changes in the operating conditions to be detected.

The growth time of the calculated defect in the pipe wall from the initial depth to the final one is calculated with the actual cyclicity of the working pressure, which is a characteristic of the intensity of the cyclic loading. The calculation is performed using the kinetic equation of Paris, which describes the middle section of the kinetic diagram of fatigue failure (KDUR), (VP Kogaev, NA Makhutov, AP Gusenkov. Calculations of machine parts and structures for strength and durability. Reference. M .: Engineering, 1985). The parameters of cyclic crack resistance and the expression of the stress intensity factor of the calculated crack are taken according to the reference data (Karzov G.P., Leonov V.P., Timofeev B.T. Welded pressure vessels. L .: Mashinostroyenie, 1982, 287 pp.).

A real-time assessment of the intensity of cyclic loading is carried out according to the growth time of the design defect in the pipeline wall from the initial depth to the final (the recommended value is 80% of the pipeline wall thickness) for each calculation period of time.

The intensities of the loading cyclicity are compared for each estimated time period.

The reference levels of the intensity of the loading cycle are formed. For example, the recommended values of the intensity of the loading cycle may be less than 15 years (dangerous intensity of the loading cycle), from 15 to 30 years (moderate intensity of the loading cycle), more than 30 years (light intensity of the loading cycle).

The mode of operation of the pipeline is controlled by comparing the actual cyclicality with the reference levels of intensity of the cyclic loading and, if the actual intensity of the cyclic intensity of the reference level is exceeded, the operating mode is adjusted to reduce the intensity of the cyclic loading.

The implementation of the method is confirmed by the following example.

As an example, we consider four pipeline operating modes (pressure cyclicity) according to the SDKU data corresponding to four design time intervals. Data on the actual cyclic operating pressure in each time interval is shown in FIG. 1 - FIG. four.

The outer diameter of the pipeline is 1220 mm, the nominal wall thickness is 9.5 mm. The initial dimensions of the design crack are 30 cm long and 2 mm deep.

After processing each operating pressure mode by the “rain” method, in accordance with the requirements of GOST 25.101-83, the amplitude of the equivalent loading (pressure) and the reduced cyclicity (the number of cycles of equivalent loading for each calculated time interval) are determined.

For the first time interval (Fig. 1), the amplitude of the ring stresses corresponding to the equivalent pressure amplitude is 149.5 MPa. The cyclicity is 412 cycles. The growth time of the design defect in the pipeline wall from the initial depth to the final, which characterizes the intensity of the loading cycle, is 17.4 years.

For the second time interval (Fig. 2), the amplitude of the annular stresses corresponding to the equivalent pressure amplitude is 118.6 MPa. The cyclicity is 498 cycles. The growth time of the design defect in the pipeline wall from the initial depth to the final, which characterizes the intensity of the loading cycle, is 28.8 years.

For the third time interval (Fig. 3), the amplitude of the ring stresses corresponding to the equivalent pressure amplitude is 107.9 MPa. The reduced cycle is 964 cycles. The growth time of the design defect in the pipeline wall from the initial depth to the final, which characterizes the intensity of the loading cycle, is 19.8 years.

For the fourth time interval (Fig. 4), the amplitude of ring stresses corresponding to the equivalent pressure amplitude is 133.1 MPa. The cyclic rate is 494 cycles. The growth time of the design defect in the pipeline wall from the initial depth to the final, which characterizes the intensity of the loading cycle, is 20.6 years.

For comparison, the characteristics of the intensity of the cyclic loading obtained for each calculation interval are plotted on the diagram of the intensity of cyclicity (Fig. 5), which also shows the recommended reference levels of intensity of cyclic loading.

From the diagram (Fig. 5) it can be seen that all values of the intensity of loading cyclicity fell into the region of moderate cyclicity and, therefore, such modes of operation of the pipeline are not dangerous. However, in the first time interval, there is a tendency toward an increase in the intensity of loading cyclicity towards dangerous cyclicity.

Thus, the possibility of comparing the intensity of loading cycles for various design intervals and deciding on a possible adjustment of the operation mode of the pipeline is shown.

Claims (12)

The way to control changes in the technological modes of pipelines, characterized in that: choose the estimated period of time, allowing to identify changes in the intensity of the cyclicity of the working pressure; select from the database of the dispatch control system of the pipeline control data on the actual cyclicity of the working pressure for the estimated period of time; convert the data of the actual cyclicity of the working pressure for the estimated period of time by highlighting the cycles of the working pressure and their number; determine the amplitude of the equivalent loading and the given number of cycles of equivalent loading for the estimated period of time; select the initial characteristics of the design defect in the pipe wall in such a way that, with the actual cyclicity of the working pressure, the real increase in the design defect allows you to detect changes in the intensity of the cyclic working pressure; calculate the growth time of the design defect in the pipeline wall from the initial depth to the final, which is a characteristic of the intensity of the loading cycle, with an equivalent pressure amplitude and the given number of cycles for the calculation period of time; carry out real-time assessment of the intensity of the loading cycle according to the data of the supervisory control system by the pressure cycle of each current settlement time period; comparing the intensity of the cyclic loading for each calculated period of time; form reference levels of intensity of the cyclic loading; control the operating mode of the pipeline by comparing the actual cyclicality with the reference levels of the intensity of the cyclic loading and in case of exceeding the actual intensity of the cyclic reference level adjust the mode of operation in the direction of reducing the intensity of the cyclicity of the working pressure.

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