HK1086879B - Method and system for monitoring the performance of a pipe containing a pressurised fluid - Google Patents

Description

The present invention relates to a method for monitoring the behaviour of a pipeline containing a fluid under pressure and to a system for implementing this method.

The present invention is part of the general framework of the management of pipeline aging, particularly in reinforced or prestressed concrete containing a pressurized fluid whose outer face is accessible (either in a tunnel or through a clearance).

These reinforced or pre-stressed concrete pipes are fitted with steel rods which are liable to corrosion and which in time will result in a decrease in their cross-section.

Document DE 35 31 975 A1 describes a system and procedure for monitoring the wall thickness of a pipe.

A major concern for operators of pressure fluid conveying systems is to control the risk of rupture of pipes containing these pressurised fluids.

This is achieved by a process according to claim 1 to monitor the behaviour of reinforced concrete piping containing a pressurised fluid, with at least one running area and one single area.

In a particular complete form of the invention, the monitoring process also includes dynamic monitoring of the pipework, to provide information on the proper vibration modes and frequencies of the pipework, which is then also used, together with the information on circumferential dilatations, for the calculation of the effective stiffness and the measured residual steel section.

The process according to the invention may also include: a process for predicting the time evolution of an A's(t>ti) estimator of the residual steel section, this prediction being made on the basis of a model of corrosion and mechanical behaviour of the piping,a comparison between the measured residual steel section (As(ti) and the A's(ti) estimator of the residual steel section, and an update of the corrosion model, when the difference between the said measured residual steel section Asti) and said residual steel section estimator A's(ti) is greater than a predetermined precision.

In an advantageous version of the invention, the prediction process is designed to incorporate information from an external source into the corrosion model update phase.

The monitoring procedure according to the invention may also include a comparison of the measured As (ti) of the residual steel section with a mechanical strength limit criterion (CL) as follows: either an information to be issued for the immediate replacement of a section of said pipe corresponding to the monitored areas, where this measured value As(ti) is below the said mechanical strength limit criterion (CL),or a calculation of a residual service life D(ti) of said pipe.

The method of the invention may also include a comparison of the measured As (ti) of the residual steel section with an alarm criterion (CA) associated with the mechanical strength of the said pipework, as follows: either a provision of comfort and subsequent replacement information for a section of said pipeline corresponding to the monitored areas, where this measured value As(ti) is below that alert criterion (CA),or a calculation of a service life before alarm Da(ti) of said pipeline.

Following another aspect of the invention, a system according to claim 7 is proposed to monitor the behaviour of a pipeline containing a pressurised fluid, this pipeline having at least one common zone and single zones.

In a particular embodiment of the invention, this system also includes a dynamic piping monitoring device to provide information on the proper vibration modes and frequencies of the piping, and this information on the proper vibration modes and frequencies is also exploited by the means for calculating the effective rigidity and residual steel section of the piping.

The system according to the invention may also include: means of predicting the time evolution of an A's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's's

The static monitoring device may include means of measuring longitudinal deformations of a section of pipe and means of measuring circumferential deformations of that section.

The dynamic monitoring device includes seismometric means for measuring the movement speeds at a predetermined number of points on the pipe.

The system of the invention may also include means for pre-processing raw data provided by the static monitoring device and the dynamic monitoring device, these means of pre-processing being arranged to calculate average distortion over a given period and average operating phase proper frequencies.

The present invention combines techniques for continuous monitoring of the in-use performance of this type of piping and predictive modelling of its ageing in order to control the risk of rupture of these pipes and to optimize their replacement periods.

The long-term behaviour of the individual zones (e.g. right-handedness of support blocks, elbows, reducing cones, etc.) of this type of piping must be differentiated from the long-term behaviour of the common zone, as shown in Table 1. - What?

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	x (autres modes de vibration)	XX (Mode I de vibration)

The process according to the invention is as follows in its complete version: to instrument a limited number of pre-defined singular zones (supports, elbows, etc.) by means of a static monitoring system; and to supplement this system by instrumenting a section of pipeline comprising common zones and singular zones by means of a dynamic monitoring system.

However, it should be noted that the process of the invention can only operate on the basis of static monitoring.

A significant contribution of the process and system according to the invention in its complete version is linked to the combination of two types of monitoring (static and dynamic) whose originality is to be able to continuously monitor the mechanical behavior of the current area and that of the individual areas.

The second contribution of the process and system of the invention is the development of a solution combining monitoring methods (surveillance of circumferential and longitudinal deformations, monitoring of proper modes and frequencies) of a pipe section and pre-processing of the measured data, which makes it possible to determine indirectly the residual steel section of the instrumented section.

The third contribution is based on the use of monitoring data in a model for predicting the corrosion kinetics of metal parts of pipes, which enriches the modelling to converge towards a prediction of service life which minimises uncertainty and enables the right maintenance actions to be initiated at the right time.

In conclusion, these three contributions make it possible to optimise the replacement times of instrumented pipes while controlling the risk of rupture of these structures.

The method of monitoring according to the invention enables: continuously and indirectly determine the residual steel section present in reinforced concrete piping;compare the measured values with estimators from validated physical models;value the monitoring data in a predictive tool to predict the long-term evolution of the residual steel section by minimising sources of uncertainty;compare the measured values with mechanical strength criteria;define a comprehensive strategy for managing a pipeline network using only a limited number of individual sections;engage in appropriate maintenance actions to reduce the pipeline deterioration in terms of time and cost and to minimise the costs associated with maintenance;minimize the risks of pipeline accidents;activate the monitoring and monitoring of the public by providing intelligent and continuous assistance.

Other advantages and features of the invention will be apparent from the detailed description of a not restrictive method of implementation and the attached drawings on which: Figure 1 illustrates the principle of operation of the process of the invention;Figure 2 is a schematic description of a static monitoring device;Figure 3 illustrates the pressure behaviour of a pipeline for which the solution can be implemented (in the case of a reinforced concrete pipe);Figure 4 illustrates the various steps of the pre-processing of the basic data to arrive at the value of the residual steel section (illustrated for the case of static monitoring); andFigure 5 illustrates an actualisation procedure implemented in the process of the invention.

The combination of the continuous monitoring techniques and the predictive tool constitutes the intelligent monitoring device (IMD) of the system of the invention.

Pre-processing of the data from the continuous monitoring is necessary to retain only a limited number of data (pipe rigidity K (ti) and its residual steel section As (ti)) summarising the measurements taken over a defined period.

The predictive tool is based on physical laws (modelling of corrosion and mechanical piping behaviour) which allow calculation of an estimator of the residual steel section A's(ti) and its evolution over time A's(t > ti.

The residual steel section obtained by the monitoring system As(ti) is then compared at regular intervals with its estimator A's(ti). If the difference between these two values is greater than a pre-set precision E, the value of the measured residual steel section As(ti) is used to update the corrosion model. This update procedure allows the residual steel section A's(ti) estimator and its evolution over time A's(t > ti to be recalculated. The predictive tool is designed so that information from a source other than static corrosion monitoring (dynamic tests, laboratory tests, visual inspections, failure numbers, etc.) can be incorporated into the model update phase.

Once the desired precision is achieved, the value of the residual steel section measured As ((ti) is compared with a mechanical strength limit criterion CL. If the measured value is below the criterion, an immediate replacement of the instrumented section of pipe may, for example, be decided.

If the measured value of the residual steel section As(ti) is above the limit criterion, the residual service life of the pipe D(ti) is determined by the evolution of the residual steel section calculated by the predictive tool.

The next step is to compare the value of the residual steel section measured As(ti) with an AC alarm criterion associated with mechanical strength.

If the measured value of the residual steel section As (ti) is above the alarm criterion, the operating time before the alarm Da (ti) is determined by the evolution of the residual steel section calculated by the predictive tool.

The following is a detailed description of a form of implementation of the system according to the invention.

The static monitoring system is implemented on a limited number of pre-defined single zones, the purpose of which is to monitor the long-term evolution of longitudinal and circumferential deformations of pipes in single zones.

In order to ensure the reliability of this static monitoring, two types of sensors should be considered: for example, a combination of standard extensometry sensors (inductive sensors) and fiber optic sensors measuring on bases of different lengths may be possible.

Longitudinal deformations are mainly used in the event of accidental stresses (earthquakes, overpressures) to check the mechanical strength of pipes (risk of rupture).

The dynamic monitoring device exploits the natural vibration of pressure pipes. It is designed to measure the travel speeds at a defined number of points using seismometers. The purpose of the dynamic monitoring device is to determine the proper vibration patterns of the pipes (modal deformation) and the associated frequencies.

Depending on the frequency of measurement, the volume of raw data collected by the monitoring device becomes large and it is necessary to pre-process these data at regular intervals in order to extract a limited number of values to quantify the residual steel section.

This pre-treatment consists of calculating from the raw data (deformations, pressure, eigenfrequencies, modal deformations): average deformation over a given period (e.g. before, during and after a pressure cycle); average operating phase proper frequencies; rigidity K of the pipe section over a given period, as shown in Figures 3 and 4; corresponding residual steel section As.

The diagram in Figure 4 illustrates the various stages of pre-treatment in the case of static monitoring.The laws defining the relations between deformation and rigidity and between rigidity and residual steel section are intrinsic features of instrumented piping.

A diagram similar to that in Figure 4 is developed for dynamic monitoring. In this case, the laws used allow the relationship between a clean frequency, the loss of rigidity of the area concerned (this depends on the associated vibration mode) and the residual steel section to be defined. These laws are also intrinsic to instrumented piping and depend strongly on the on-board conditions of the piping.

The various steps of the pre-processing of the basic data allow the residual steel section value to be obtained, as illustrated in Figure 4 for static monitoring.

The next step is to compare at regular intervals the residual steel section obtained by the monitoring system As (ti) with its estimator A's (ti). If the difference between these two values is greater than a pre-set precision, the value of the measured residual steel section As (ti) is used to update the corrosion model.

This update is based, inter alia, on a Bayesian approach which allows the predictive model to be more accurate when field data are available.

The update procedure allows the residual steel section estimator A's(ti) and its evolution over time A's(t > ti to be recalculated.

The predictive tool is designed to allow the incorporation of information from sources other than static or dynamic monitoring (laboratory tests, visual inspections, number of failures, etc.) into the corrosion model update phase.

Once the desired precision is achieved, the value of the residual steel section measured As ((ti) is compared with a mechanical strength limit criterion CL. If the measured value is below the criterion, an immediate replacement of the instrumented section of pipe may, for example, be decided.

The next step is to compare the value of the residual steel section measured As(ti) with an AC alarm criterion associated with mechanical strength.

If the measured value of the residual steel section As(ti) is higher than the limit criterion, the residual service life of the pipe shall be determined by the evolution of the residual steel section calculated by the predictive tool as follows, with reference to Figure 5: $D\left(t_i\right)=t\left(A_s,=,\mathrm{CL}\right)-t_i$

If the measured value of the residual steel section As(ti) is higher than the alarm criterion, the operating time before alarm Da(ti) is determined using the evolution of the residual steel section calculated by the predictive tool as follows: $D_a\left(t_i\right)=t\left(A_s,=,\mathrm{CA}\right)-t_i$

When the measured value of the residual steel section As ((ti) is above the alarm criterion, the maintenance action would be, for example, to do nothing and the piping would be left as it is.

Of course, the invention is not limited to the examples just described and many modifications can be made to these examples without going beyond the scope of the invention.

Claims (12)

1. A method for monitoring the performance of a pipe containing a pressurized fluid, made of reinforced concrete, this pipe comprising at least one continuous run zone and singularity zones, said method comprising:

   - a monitoring, said static monitoring, of a predetermined number of singularity zones and/or continuous run zones, in order to provide circumferential expansion information, and

   - a calculation of the effective stiffness K(ti) of the pipe and its residual steel cross-section As(ti) using said circumferential expansion information and predetermined laws defining the relationships between said circumferential expansion and the stiffness and between the stiffness and the residual cross-section, said laws being the intrinsic characteristics of said pipe
2. The method according to claim 1, characterized in that it also comprises a dynamic monitoring of the pipe in order to provide information relating to the vibration eigen modes and frequencies of said pipe, and in that this information relating to eigen modes and frequencies is also used to calculate the stiffness K(ti) and the measured residual steel cross-section As(ti) of the pipe.
3. The method according to one of claims 1 or 2, characterized in that it also comprises:

   - a process of predicting the temporal evolution A's(t>ti) of an estimator A's(ti) of the residual steel cross-section, this prediction being made on the basis of a model of the corrosion and the mechanical performance of the pipe,

   - a comparison between the measured residual steel cross-section (As(ti) and the estimator A's(ti) of the residual steel cross-section, and

   - an updating of the corrosion model, when the difference between said measured residual steel cross-section As(ti) and said estimator of the residual steel cross-section A's(ti) is greater than a predetermined precision.
4. The method according to claim 3, characterized in that the prediction process is organized so as to integrate, in the phase of updating the corrosion model, information coming from an external source.
5. The ethod according to one of claims 3 or 4, characterized in that it also comprises a comparison of the measured value As(ti) of the residual steel cross-section with a limit criterion of mechanical strength (CL), this comparison being followed by:

   - either a transmission of information for immediate replacement of a section of said pipe corresponding to the monitored zones, when this measured value As(ti) is less than said limit criterion for mechanical strength (CL),

   - or a calculation of the remaining service life D(ti) of said pipe.
6. The method according to claim 5, characterized in that it also comprises a comparison of the measured value As(ti) of the residual steel cross-section with an alarm criterion (CA) associated with the mechanical strength of said pipe, this comparison being followed by:

   - either a transmission of information for reinforcement and subsequent replacement of a section of said pipe corresponding to the monitored zones, when this measured value As(ti) is less than said alarm criterion (CA),

   - or a calculation of operating time before the alarm Da(ti) of said pipe actuates.
7. A system for monitoring the performance of a pipe containing a pressurized fluid, made of reinforced concrete, this pipe comprising at least one continuous run zone and singularity zones, the system comprising:

   - a device for monitoring, said static monitoring, of a predetermined number of singularity zones and/or continuous run zones in order to provide circumferential expansion information, and

   - means configured for calculating the effective stiffness K(ti) of the pipe and its residual steel cross-section As(ti) using said circumferential expansion information and predetermined laws defining the relationships between said circumferential expansion and the stiffness and between the stiffness and the residual cross-section, said laws being the intrinsic characteristics of said pipe
8. The system according to claim 7, characterized in that it also comprises a device for dynamic monitoring of the pipe in order to provide information on eigen vibration modes and frequencies of said pipe, this information on eigen modes and frequencies being used by the means for calculation of the effective stiffness K(ti) and of the measured residual steel cross-section As(ti).
9. The system according to one of claims 7 or 8, characterized in that it also comprises:

   - means for predicting the temporal evolution A's(t>ti) of an estimator A's(ti) of the residual steel cross-section, this prediction being made on the basis of a model of the corrosion and the mechanical performance of the pipe,

   - means for comparing the measured residual steel cross-section (As(ti) and the estimator A's(ti) of the residual steel cross-section, and

   - means for updating the corrosion model, when the difference between said measured residual steel cross-section As(ti) and said estimator of the residual steel cross-section A's (ti) is greater than a predetermined precision.
10. The system according to one of claims 7 to 9, characterized in that the static monitoring device comprises means for measuring longitudinal deformations of a section of the pipe and means for measuring circumferential deformations of said section.
11. The system according to claim 8 and one of claims 9 or 10, characterized in that the dynamic monitoring device comprises seismometry means for measuring displacement speeds at a predetermined number of points on the pipe.
12. The system according to one of claims 7 to 11, characterized in that it also comprises means for pre-processing raw data provided by the static and/or dynamic monitoring device, these pre-processing means being designed to calculate an average deformation over a given period and average eigen frequencies in the operating phase.