CN106404260A - Early warning method based on axial monitoring stress of pipeline - Google Patents

Abstract

The invention relates to an early warning method based on the axial monitoring stress of a pipeline, and belongs to the technical field of stress monitoring for long oil gas transmission pipeline. The early warning method comprises that a pipeline axial stress calculating model is established according to time nodes when stress monitoring measures are taken; a pipeline axial stress calculating model when the stress monitoring measures are taken is established; a calculation model between the pipeline axial additional stress and an axial stress monitoring value after the stress monitoring measures are taken is established; a calculation model between the pipeline axial stress and the axial stress monitoring value after the stress monitoring measures are taken is established; a relation of allowed axial additional stress of the pipeline is established; a stress early warning level model based on the axial monitoring stress is established; and according to the stress early warning level model, the stress early warning level of the pipeline is determined. According to the early warning method, the working efficiency is improved, and the possibility that stress early warming makes mistakes due to insufficient recognition of the pipeline stress is reduced.

Description

A kind of method for early warning based on pipeline axial direction monitor stress

Technical field

The present invention relates to a kind of method for early warning based on pipeline axial direction monitor stress, belong to long oil and gas pipeline stress monitoring Technical field.

Background technology

In the construction and planning of long oil and gas pipeline, because of resource market distribution and the factor such as landform, local plan limit System, oil and gas pipes go inevitably through active fault, slopes, goaf, weak soil etc. it may happen that the location of surface displacement. The pipeline in these locations, in addition to ring pressure-bearing, axially also suffers from additional stress because surface displacement causes so that pipeline Stress is in the hole.Currently for it may happen that the pipeline in surface displacement location, adopt stress monitoring measure, so that real more When grasp pipeline stress state, take counter-measure in time.Vibrating string extensometer is because its sensor construction is simple, output signal It is easy to computer disposal, be connected firmly the advantages of be applied to long term monitoring, be widely used in the stress monitoring of long oil and gas pipeline In measure.

During the stress state of assessment buried pipeline, it is typically based on axial stress and axial stress and the circumference stress of pipeline The equivalent stress of combination is evaluated.For buried straight pipeline, piping displacement deformation is main to affect pipeline axial stress, its Impact very little to pipeline circumference stress is negligible, and pipeline circumference stress is only relevant with conduit running pressure.Therefore right When surface displacement segment pipe takes long-term stress monitoring measure, general only arrangement vibrating string extensometer in pipeline axial direction, monitoring The axial stress situation of change of pipeline, with reference to the stress state of the factor evaluation pipeline such as operating pressure.According to pipeline axially Stress evaluation pipe stress state the method judging stress warning level, the referred to as pre- police based on pipeline axial direction monitor stress Method.This monitoring measure method is simple, good economy performance, is easy to apply.

But, because not thorough to the understanding of pipe stress intension in enforcement, easily by pipeline axial stress monitor value with Pipeline axial stress (or axial additional stress) is obscured, and exists simultaneously and takes pipeline axial stress during stress monitoring measure to arrange Do not meet reality, early warning value method to set up unreasonable the problems such as, lead to pipe stress state and the judgement of warning level easily to go out Existing deviation, causes the pipe stress safe condition dangerous situation such as early warning or pipe stress precarious position not early warning by mistake, has a strong impact on Pipe safety and emergency disposal.This is the ess-strain monitoring of Pipeline Crossing Program multiple surface displacement location and warning aspect urgently solves Technical problem certainly.

Content of the invention

In order to solve series of problems present in current pipeline axial stress monitoring and stress early warning, the purpose of the present invention It is to provide a kind of method for early warning based on pipeline axial direction monitor stress.

The purpose of the present invention is achieved through the following technical solutions：

A kind of method for early warning based on pipeline axial direction monitor stress, comprises the following steps：

Step 1, the timing node according to taking stress monitoring measure sets up pipeline axial stress computation model, and it is：

σ_L=σ_L,1+Δσ_L

In formula：σ_LFor taking the pipeline axial stress after stress monitoring measure；σ_L,1For taking pipe during stress monitoring measure Road axial stress；Δσ_LFor taking the pipeline axial direction additional stress after stress monitoring measure；

Step 2, sets up the pipeline axial stress computation model taken during stress monitoring measure, it is：

In formula：μ is Poisson's ratio；α is the linear expansion coefficient of tubing；E is the elastic modelling quantity of tubing；P₁For taking monitoring measure When operating pressure；D is internal diameter of the pipeline；T is pipeline wall thickness；T₀Tube wall temperature when backfilling for descending pipelines into ditch；T₁For taking monitoring Tube wall temperature during measure；

Step 3, sets up between pipeline axial direction additional stress and axial stress monitor value after taking stress monitoring measure Computation model, it is：

In formula：σ_L,MFor pipeline axial stress monitor value；P₂Conduit running pressure for the axial stress monitor value corresponding moment Power；

Step 4, the computation model according to step 1～step 3, set up the pipeline axle after taking stress monitoring measure Computation model between stress and axial stress monitor value, it is：

Step 5, sets up the relational expression that pipeline axially allows additional stress, it is：

In formula：σ_sYield strength for tubing；

Step 6, pipeline according to step 5 axially allows the relational expression of additional stress, sets up and is axially supervised based on pipeline Survey the stress warning level model of stress, it is：

In formula：β is that pipeline axial direction additional stress accounts for the percentage ratio that pipeline axially allows additional stress；

Step 7, using the stress warning level model based on pipeline axial direction monitor stress described in step 6, according to model In pipe parameter, axial stress Monitoring Data and conduit running parameter, calculate the stress state of pipeline, judge the stress of pipeline Warning level.

Further, the relational expression of pipeline axial direction monitor stress permissible value is：

Further, the stress monitoring measure is taken to be：Pipeline selects monitoring cross section, if selecting along monitoring cross section circumference Dry position, as stress monitoring point, is opened each monitoring point anticorrosive coat and is polished smooth tube wall；Respectively should in outer surface of tube wall Power monitoring point along the axial arranged vibrating string extensometer of pipeline, after the vibrating string extensometer of all stress monitoring points deploys, Reset vibrating string extensometer reading, and be calculated as taking the moment of stress monitoring measure this moment, start recording pipeline axially should Force data.

Further, pipe stress warning level is：

When β is between 30% and 60%, for blue early warning；

When β is between 60% and 90%, for blue early warning；

When β is more than 90%, it is red early warning.

The present invention has the beneficial effect that：

The method for early warning based on pipeline axial direction monitor stress that the present invention provides, by setting up simple computation model, makes Pipe design personnel, according to relevant parameters such as pipe parameter, axial stress Monitoring Data and conduit running data, just can calculate The pipe stress state in a certain moment and corresponding warning level, improve work efficiency, reduce and recognize not because of pipe stress Foot causes the probability of stress prediction errors.The present invention implements simple, carries out only needing to during stress monitoring axial arranged in pipeline Vibrating string extensometer, and it is increased without temperature compensation means, you can carry out long-term pipe stress and monitor and assess pipe stress State and warning level；The computation model simultaneously providing, has the advantages that highly versatile, convenient and swift, accuracy are high, Yi Beiguang Big conduit running management personnel and designer grasp, and can be widely applied to pipe stress monitoring field.

Specific embodiment

In order that the objects, technical solutions and advantages of the present invention become more apparent, with reference to embodiments, to the present invention It is further elaborated.It should be appreciated that specific embodiment described herein, only in order to explain the present invention, is not used to limit Determine the present invention.

Pipeline axial stress is decomposed, by theory of mechanics, analyze each axial stress component stress and strain it Between corresponding relation, study reflection in strain gauge for each axial stress component.Multiple surface displacement section buried pipeline axially should Power generally comprises the intrinsic pressure axial Poisson stress σ causing_P, pipeline axial stress σ that causes of temperature change_TCause with piping displacement Axial stress σ_D.Pipeline axial direction monitor stress only reflects the change of pipeline axial stress strain, each axial stress component performance As follows：

(1) the intrinsic pressure axial Poisson stress σ causing_P.Under intrinsic pressure effect, occur while pipeline circumferential expansion axially to receive Contracting, because pipeline is axially subject to the effect of contraction of the soil body to limit the axial deformation of pipeline, axially produces Poisson stress σ in pipeline_P, Axial deformation is 0；Because of deformation and the tunnel synchronization of strain gauge, therefore pipeline axial strain meter cannot measure the intrinsic pressure axial direction causing pool Loose stress σ_P.

(2) pipeline axial stress σ that temperature change causes_T.When conduit running temperature is different with initial temperature, pipeline axle To expanding with heat and contract with cold, the axial deformation of pipeline because of soil body constrained, axially produce axial stress σ in pipeline_T；Axially should Become that meter temperature is identical with tube wall, the vibratory string of strain gauge occurs expanding with heat and contract with cold and showing the change of frequency of vibration of synchronization, and then Produce temperature change and cause stress σ in strain gauge_T1；Strain gauge vibratory string is identical with the linear expansion coefficient of tubing, therefore σ_T=σ_T1, therefore Vibrating string extensometer can reflect pipeline axial stress σ that temperature change causes_T.

(3) axial stress σ that piping displacement causes_D.When pipeline is subjected to displacement deformation, pipeline axially produces strain, axle To strain gauge and pipeline axial deformation synchronization and deflection is equal, therefore pipeline axial strain meter can be measured piping displacement and cause Axial strain so that can get corresponding axial stress σ_D.

By above-mentioned analysis, pipeline axial stress monitor value be not exclusively equal to reality pipeline axial stress (or Pipeline axial direction additional stress).

Embodiment 1

The present invention provides a kind of method for early warning based on pipeline axial direction monitor stress, comprises the following steps：

Step 1, the timing node according to taking stress monitoring measure sets up pipeline axial stress computation model, and it is：

σ_L=σ_L,1+Δσ_L

In formula：σ_LFor taking the pipeline axial stress (MPa) after stress monitoring measure；σ_L,1For taking stress monitoring measure When pipeline axial stress (MPa)；Δσ_LFor taking pipeline axial direction additional stress (MPa) after stress monitoring measure；

Step 2, from theory of mechanics, sets up the pipeline axial stress computation model taken during stress monitoring measure, its For：

In formula：μ is Poisson's ratio, takes 0.3；α is the linear expansion coefficient of tubing, typically takes 1.2 × 10^-5℃^-1；E is tubing Elastic modelling quantity (MPa)；P₁For taking the operating pressure (MPa) during monitoring measure；D is internal diameter of the pipeline (mm)；T is pipeline wall thickness (mm)；T₀Tube wall temperature (DEG C) when backfilling for descending pipelines into ditch；T₁For taking the tube wall temperature (DEG C) during monitoring measure；

Step 3, from theory of mechanics, sets up the pipeline axial direction additional stress after taking stress monitoring measure and axially should Computation model between power monitor value, it is：

In formula：σ_L,MFor pipeline axial stress monitor value (MPa)；P₂Pipeline fortune for the axial stress monitor value corresponding moment Row pressure (MPa)；

Step 4, the computation model according to step 1～step 3, set up the pipeline axle after taking stress monitoring measure Computation model between stress and axial stress monitor value, it is：

Step 5, the axial stress of buried pipeline and equivalent stress all should meet code requirement.

Equivalent stress requires：Reference《Code for design of gas transmission pipeline engineering》(GB50251-2015), equivalent stress should be less than 0.9 times of SMYS, as follows：

σ_e=| σ_h-σ_L|≤0.9σ_s

In formula, σ_hFor pipeline circumference stress (MPa),σ_sYield strength (MPa) for tubing；

Can be obtained according to the computation model in above formula and step 1, step 2：

Axial stress requires：Reference《Gas Transmission and Distribution Piping Systems》 (ASME B31.8-2014), axial stress should be less than 0.9 times of SMYS, as follows：

|σ_L|≤0.9σ_s

Can be obtained according to the computation model in above formula and step 1, step 2：

Thus, obtain the relational expression that pipeline axially allows additional stress, it is：

In formula：σ_sYield strength (MPa) for tubing；

Step 6, pipeline according to step 5 axially allows the relational expression of additional stress, sets up and is axially supervised based on pipeline Survey the stress warning level model of stress, it is：

In formula：β is that pipeline axial direction additional stress accounts for the percentage ratio that pipeline axially allows additional stress；

Step 7, using the stress warning level model based on pipeline axial direction monitor stress described in step 6, according to model In pipe parameter, axial stress Monitoring Data and conduit running parameter, calculate the stress state of pipeline, judge the stress of pipeline Warning level.

According to the calculating taken in step 4 between the pipeline axial stress after stress monitoring measure and axial stress monitor value In model and step 5, pipeline axially allows the relational expression of additional stress, obtains the relational expression of pipeline axial direction monitor stress permissible value For：

The present invention is applied to buried straight pipeline and has compared with strong constraint and the less buried bend pipe of angle.

Below with D1219mm/15.3mm wall thickness/X80 steel-grade pipeline, pipe laying with elastic bending section axial stress at certain surface displacement The calculating process of the present embodiment to be described as a example monitoring：

1) pipe parameter, as shown in table 1：

Table 1

2) after taking stress monitoring measure, the Monitoring Data in a certain moment shows, monitoring cross section is in pressured state, greatest axis It is -113.61MPa to compression stress.

3) the stress warning level of pipeline：

Assume that pipe stress warning level setting principle is：Axially allow to add when pipeline axial direction additional stress reaches pipeline Stress 30% when, for blue early warning level；Axially allow the 60% of additional stress when pipeline axial direction additional stress reaches pipeline When, it is yellow early warning level；When pipeline axial direction additional stress reaches the 90% of pipeline axial direction permission additional stress, pre- for redness Alert level.

Judge stress warning level according to based on the stress warning level model of pipeline axial direction monitor stress.Wherein：Poisson Take 0.3 than μ；The linear expansion coefficient α of steel takes 1.2 × 10^-5℃^-1；Elastic modulus E=2.1 × 10 of steel⁵MPa；T is pipeline Wall thickness, mm；D is internal diameter of the pipeline, mm；Tube wall temperature T during descending pipelines into ditch backfill₀=21.8 DEG C；Take fortune during monitoring measure Row pressure P₁=8.38MPa；Take tube wall temperature T during monitoring measure₁=9.8 DEG C；The operation pressure in moment is calculated after stress monitoring Power P₂=7.81MPa；Tubing yield strength σ_s=555MPa；Monitoring cross section maximum axial stress in compression sigma_L,M=-113.61MPa.

First determine whether

Choose formula and calculate

With reference to pipe stress warning level setting principle, pipe stress is in blue early warning level.

The method for early warning based on pipeline axial direction monitor stress that the present embodiment provides, by setting up simple mathematical calculation mould Type, according to relevant parameters such as pipe parameter, Monitoring Pinpelines data and service datas, just can easily calculate pipe stress early warning Rank, improves work efficiency, decrease conduit running management personnel and designer to pipe stress understanding deficiency cause pre- The probability of alert erroneous judgement.The monitoring measure of axial temperature difference stress is comprised in heretofore described axial stress Monitoring Data.This The computation model that invention provides, has the advantages that highly versatile, to calculate quick, easy to use, accuracy high, easily by vast pipe Road operational management personnel, pipe stress monitoring personnel and pipe design personnel grasp, and can be widely applied to pipe stress monitoring neck Domain.

The foregoing is only the preferred embodiments of the present invention, be not limited to the present invention, for the skill of this area For art personnel, the present invention can have various modifications and variations.All within the spirit and principles in the present invention, made any repair Change, equivalent, improvement etc., should be included within the scope of the present invention.

Claims (2)

1. a kind of method for early warning based on pipeline axial direction monitor stress is it is characterised in that comprise the following steps：

Step 1, the timing node according to taking stress monitoring measure sets up pipeline axial stress computation model, and it is：

σ_L=σ_L,1+Δσ_L

In formula：σ_LFor taking the pipeline axial stress after stress monitoring measure；σ_L,1For taking pipeline axle during stress monitoring measure To stress；Δσ_LFor taking the pipeline axial direction additional stress after stress monitoring measure；

Step 2, sets up the pipeline axial stress computation model taken during stress monitoring measure, it is：

${\mathrm{\σ}}_{L,1}=\mathrm{\μ}\frac{P_{1}d}{2t}+\mathrm{\α}E(T_0-T_1)$

In formula：μ is Poisson's ratio；α is the linear expansion coefficient of tubing；E is the elastic modelling quantity of tubing；P₁For taking during monitoring measure Operating pressure；D is internal diameter of the pipeline；T is pipeline wall thickness；T₀Tube wall temperature when backfilling for descending pipelines into ditch；T₁For taking monitoring measure When tube wall temperature；

Step 3, sets up the calculating between pipeline axial direction additional stress and axial stress monitor value after taking stress monitoring measure Model, it is：

${\mathrm{\Δ\σ}}_L={\mathrm{\σ}}_{L,M}+\mathrm{\μ}\frac{(P_2-P_1)d}{2t}$

In formula：σ_L,MFor pipeline axial stress monitor value；P₂Conduit running pressure for the axial stress monitor value corresponding moment；

Step 4, the computation model according to step 1～step 3, set up the pipeline after taking stress monitoring measure and axially should Computation model between power and axial stress monitor value, it is：

${\mathrm{\σ}}_L={\mathrm{\σ}}_{L,M}+\mathrm{\μ}\frac{P_{2}d}{2t}+\mathrm{\α}E(T_0-T_1)$

Step 5, sets up the relational expression that pipeline axially allows additional stress, it is：

$-0.9{\mathrm{\σ}}_s-\mathrm{\μ}\frac{P_{1}d}{2t}+\frac{P_{2}d}{2t}-\mathrm{\α}E(T_0-T_1)\≤{\mathrm{\Δ\σ}}_L\≤0.9{\mathrm{\σ}}_s-\mathrm{\μ}\frac{P_{1}d}{2t}-\mathrm{\α}E(T_0-T_1)$

In formula：σ_sYield strength for tubing；

Step 6, pipeline according to step 5 axially allows the relational expression of additional stress, and setting up should based on pipeline axial direction monitoring The stress warning level model of power, it is：

$\mathrm{\&beta;}=\left\{\begin{array}{cc}\frac{{\mathrm{\&sigma;}}_{L,M}+\mathrm{\&mu;}\frac{(P_2-P_1)d}{2t}}{0.9{\mathrm{\&sigma;}}_s-\mathrm{\&mu;}\frac{P_{1}d}{2t}-\mathrm{\&alpha;}E(T_0-T_1)}\&times;100\%& {\mathrm{\&sigma;}}_{L,M}+\mathrm{\&mu;}\frac{(P_2-P_1)d}{2t}\&GreaterEqual;0\\ \frac{{\mathrm{\&sigma;}}_{L,M}+\mathrm{\&mu;}\frac{(P_2-P_1)d}{2t}}{-0.9{\mathrm{\&sigma;}}_s-\mathrm{\&mu;}\frac{P_{1}d}{2t}+\frac{P_{2}d}{2t}-\mathrm{\&alpha;}E(T_0-T_1)}\&times;100\%& {\mathrm{\&sigma;}}_{L,M}+\mathrm{\&mu;}\frac{(P_2-P_1)d}{2t}<0\end{array}\right.$

In formula：β is that pipeline axial direction additional stress accounts for the percentage ratio that pipeline axially allows additional stress；

Step 7, using the stress warning level model based on pipeline axial direction monitor stress described in step 6, according in model Pipe parameter, axial stress Monitoring Data and conduit running parameter, calculate the stress state of pipeline, judge the stress early warning of pipeline Rank.

2. a kind of method for early warning based on pipeline axial direction monitor stress according to claim 1 is it is characterised in that pipeline axle Relational expression to monitor stress permissible value is：

$-0.9{\mathrm{\&sigma;}}_s+(1-\mathrm{\&mu;})\frac{P_{2}d}{2t}-\mathrm{\&alpha;}E(T_0-T_1)\&le;{\mathrm{\&sigma;}}_{L,M}\&le;0.9{\mathrm{\&sigma;}}_s-\mathrm{\&mu;}\frac{P_{2}d}{2t}-\mathrm{\&alpha;}E(T_0-T_1).$