CN103136701A - Method for quantitatively evaluating pipe condensation probability of crude oil pipeline - Google Patents

Abstract

The invention discloses a method for quantitatively evaluating the pipe condensation probability of a crude oil pipeline, and relates to the technical field of pipeline systems. The method comprises the following steps of: 1) automatically extracting and analyzing the safety influence factor; 2) counting a data distribution rule of the influence factor; 3) calculating certainty shutdown and restart-up pressure; 4) setting an evaluation frequency and randomly sampling parameters; 5) calculating uncertainty shutdown and restart-up pressure; 6) counting a calculation frequency of restart-up failure; 7) obtaining a calculation result (the pipe condensation probability of the pipeline); 8) judging whether ineffectiveness judgment can be accepted; 9) if the ineffectiveness judgment cannot be accepted, adjusting a flowing guarantee scheme, turning to the step 2) of counting the data distribution rule of the influence factor, and if the ineffectiveness judgment can be accepted, submitting the flowing guarantee scheme. By the method, the crude oil pipeline flowing safety can be evaluated; and technical support can be supplied to safety and high-efficiency running of the pipeline.

Description

The solidifying pipe of crude oil pipeline probability method for quantitatively evaluating

Technical field

The present invention is the solidifying pipe of a kind of crude oil pipeline probability method for quantitatively evaluating, relates to the piping system technical field.

Background technology

One of final ultimate limit state of wax-containing oil pipe is exactly the solidifying tubulose attitude of knowing, and this is to need in conduit running to be avoided as possible, and the production loss that brings is also maximum.Generally, the main cause that this ultimate limit state occurs is after pipeline plan, especially accident stopping transportation, the solidifying pipe that start-up course unsuccessfully causes.Judge that at present common practice that whether pipeline coagulates pipe is the current inlet temperature according to pipeline, according to the surrounding enviroment situation, considers that in given shutdown time, whether crude oil temperature is greater than its condensation point.Though this way is simple and easy to use, science is not strong.At first, the method is not considered the uncertainty of conduit running technological parameter, and for example ground temperature is actual fluctuates; Secondly, the index of simply using condensation point is science not, and whether required pressure is obviously more objective greater than the maximum allowable operating pressure of pipeline when starting.

Summary of the invention

The objective of the invention is to invent a kind of based on the certainty and uncertainty method reliably, the solidifying pipe of crude oil pipeline probability method for quantitatively evaluating accurately.

The pipeline actual production is in service, its throughput rate, out-station temperature, steady-state operation overall heat transfer coefficient, buried depth of pipeline, buried depth of pipeline place ground temperature, soil thermal conductivity etc. all have uncertainty, evaluation has been considered the uncertainty of these factors take the actual production form as the basis.Estimate the automatic extraction and analysis of involved calculating parameter and completed by software, as throughput rate, pressure, inlet temperature, out-station temperature etc., and the accuracy of these data is checked.

The solidifying pipe of the crude oil pipeline that the present invention proposes method for quantitatively evaluating, mainly flow process is as shown in Figure 1:

1) robotization of safety effects factor is extracted and is analyzed;

2) the data distributivity rule of influence factor statistics;

3) determinacy stopping transportation restart pressure calculates;

4) estimate the setting of number of times and the grab sample of parameter;

5) calculating of uncertain stopping transportation restart pressure;

6) the statistics pipeline is restarted the calculation times of failure;

7) the drawing of result of calculation (the solidifying pipe of pipeline probability);

8) whether satisfy and to accept the judgement of losing efficacy;

9) if do not satisfy, after adjusting the flow assurance scheme, turn 2) the data distributivity rule statistics of influence factor;

If satisfy, submit the flow assurance overall plan to.

The pipeline actual production is in service, its throughput rate, out-station temperature, steady-state operation overall heat transfer coefficient, buried depth of pipeline, buried depth of pipeline place ground temperature, soil thermal conductivity etc. all have uncertainty, evaluation has been considered the uncertainty of these factors take the actual production form as the basis.Estimate the automatic extraction and analysis of involved calculating parameter and completed by software, as throughput rate, pressure, inlet temperature, out-station temperature etc., and the accuracy of these data is checked.Solidifying pipe definition of probability is as follows:

For a given ultimate limit state, probability analysis comprises the model of broad sense random load S and the random drag R of broad sense.Corresponding limit state function can be expressed as following form in general manner:

g(x)＝R-S (1)

Obviously, indicate inefficacy as g (x)＜0.

The definition failure probability is as follows:

$P_f=\underset{g\left(x\right)\≤0}{\∫}{f}_x\left(x\right)\mathrm{dx}---\left(2\right)$

In formula, x is the stochastic variable vector; f _x(x) be joint probability density function.

Restart problem for the crude oil pipeline stopping transportation, definition load S is the minimum starting pressure of pipeline, and getting drag R is pipeline maximum allowable operating pressure (MAOP), and Pf is solidifying pipe probability.

Described data distributivity probability statistics and check are:

According to ISO 16708, the production run data of quantitative evaluation pipeline collection are carried out uncertainty and value analysis.To manage in defeated process the pipeline flow data regularity of distribution as example, chosen the data on flows of three months flowmeter statistics for certain east pipeline.Result is as follows:

The statistical law of table 1 pipeline throughput rate data

The result of table 1 shows, the kurtosis of throughput rate data is close to 3, and deviation is close to 0, can think the Normal Distribution rule.The uncertainty analysis process of other mobile Safety Influence Factors as above.

Described determinacy stopping transportation restart pressure calculates:

As mentioned before, this evaluation method is estimated framework based on secondary, and first order framework is not in the situation that consider the fluctuation of production run situation, for satisfying on-the-spot demand, with the security of the existing production and operation condition of Deterministic Methods assessment, if dangerous, will take the flow assurance measure according to result.The determinacy operating mode is generally on-the-spot given production data.

The setting of described evaluation number of times and the grab sample of parameter are:

After having completed the deterministic parsing in system one-level framework, just can carry out large-scale probability sampling, the sampling number of times is defaulted as 10000 times, generates corresponding numerical value by its regularity of distribution function during the every sub-sampling of production run parameter, but must set the bound of production run parameter.What reason was the generation of regularity of distribution function is the numerical value that meets the mathematical distribution rule, but must not have physical significance.In the situation that there is no the production scene appointment, the bound of system default is as follows, and throughput rate is between 3 times of variances of its average plus-minus, and temperature out of the station is between 0 ℃-90 ℃, and ground temperature is between-20 ℃-50 ℃.

Described uncertain stopping transportation restart pressure calculates and starts frequency of failure calculating:

It is evaluation number of times according to having set that uncertain stopping transportation restart pressure calculates, and whether each estimates production run parameter that number of times generates and analyze solidifying pipe and occur.As start unsuccessfully and to occur to be recorded as 1, do not occur to record 0.After completing, evaluation can record the number of times that total stopping transportation is restarted failure.

Described interpretation of result is:

Solidifying tube failure probability P f based on calculating is defined as pipeline shutdown with (1-Pf) and restarts safety indexes (SRSI).Under constant condition of pipeline shutdown time, the SRSI graded index is larger, and the possibility of pipeline shutdown failure is less restarting just, and the safe coefficient of pipeline restart procedure is just higher; Otherwise the possibility that pipeline is restarted failure is just larger, according to evaluation result, to the security of operation proposition safeguard of pipeline.

The defeated technology Calculation of evaluation procedure pipe

Waterpower, heating power during normal the conveying calculate

(1) normally moving the axial temperature drop of hot oil pipeline calculates

Stablizing under transport condition, between the temperature drop rate that in hot oil pipeline, oil flows and the coefficient of heat conductivity of conduit running parameter (out-station temperature, throughput rate etc.), caliber, buried depth of pipeline and surrounding medium thereof, temperature, heating station, length and crude oil property (specific heat capacity, density, viscosity etc.) etc. are closely related.In pipe, oil stream can be similar to Л e й б e н з о Н formula along the journey Temperature Distribution and describe:

T _L＝(T ₀+b)+(T _R-T ₀-b)e ^-aL (3)

In formula, a=K π D/Gc, b=ig/c _pa； G is the mass rate of oil product, kg/s; C _pBe the specific heat capacity of crude oil, J/ (kg ℃); D is outer diameter tube, m; L is the distance apart from heating station, m; K is the pipeline overall heat transfer coefficient, W/ (m ²℃); T _RBe heating station departures oil temperature, ℃; T _LBe the oil temperature of distance heating station distance for the L place, ℃; T ₀Be ambient temperature, buried pipeline is got the natural ground temperature in tube hub buried depth place, ℃.

(2) frictional resistance of hot oil pipeline calculates

The pressure gradient that fluid flows in horizontal pipe is:

$i=\mathrm{\λ}\frac{\mathrm{\ρ}{V}^2}{2D}=4f\frac{\mathrm{\ρ}{V}^2}{2D}---\left(4\right)$

In formula, i is pressure gradient, Pa/m; V is the mean flow rate of pipeline inner fluid, m/s; ρ is the density of fluid, kg/m ³D is round tube inside diameter, m; λ is the darcy coefficient of friction resistance; F is the peaceful coefficient of friction resistance of model.

The calculating of stopping transportation temperature drop

In the evaluation procedure of initial set probability, according to evaluation requirements, can take Lumped-Capacity method or two kinds of solutions of numerical method to the stopping transportation temperature drop, Lumped-Capacity method has computing velocity and the relatively conservative characteristics of result, and numerical solution calculates accurately, but computing velocity is slower.

(1) Lumped-Capacity method

After hot oil pipeline shutdown, apart from starting point any distance l place, in stopping transportation t managed after the time, the calculating formula of oil temperature is as follows:

$T=T_0+(T_R-T_0)\exp (-\frac{\mathrm{K\π}{D}_{\mathrm{out}}l}{{\mathrm{Gc}}_y}-\mathrm{bt})---\left(5\right)$

$b=\frac{\mathrm{KD}}{\frac{D_1^2}{4}{c}_y{\mathrm{\ρ}}_y+\frac{(D_2^2-D_1^2)}{4}{c}_g{\mathrm{\ρ}}_g}---\left(6\right)$

In formula, T is apart from pipeline starting point l place, the oil temperature of stopping transportation t after the time, ℃; T ₀Be ambient temperature (being the ground temperature at buried depth place to buried pipeline), ℃; T _RBe the oil temperature at beginning pipeline starting point place during stopping transportation, ℃; Overall heat transfer coefficient when K is the pipeline steady-state operation, W/ (m ℃); D _outBe pipe external diameter, m; G is the pipeline throughput rate, kg/s; L is that calculation level is apart from the distance of pipeline starting point, m; T is shutdown time, s; B is coefficient, s ^-1, value is determined by formula (2-30); D ₁, D ₂Be respectively pipe diameter and external diameter, m; c _y, c _gBe respectively the specific heat capacity of crude oil and steel pipe, kJ/ (kg ℃); ρ _y, ρ _gBe respectively specific heat capacity and the density of steel pipe, kg/m ³

(2) numerical solution

Temperature drop process after pipe inner wax crude oil shutdown is a three-dimensional unsteady heat transfer problem of following phase transformation, natural convection and moving boundary.According to the difference of heat transfer type, after stopping transportation, the heat transfer of the interior crude oil of pipe can be divided into three phases again: free convection heat transfer stage, natural convection and heat conduction co-controlling stage and pure heat conduction stage.

Based on the complicacy of temperature drop process after the waxy crude oil stopping transportation, introduce following hypothesis in this model and realize simplifying:

1) introducing equivalent heat conductivity processes the Natural Convection Problem of liquid crude oil as Heat Conduction Problems;

2) in the process of stopping transportation temperature drop, along with reducing the wax crystalline substance, oil temperature separates out gradually, form solidifying oil reservoir, due to the complicacy of engineering problem, suppose that growth and the pipeline of solidifying oil reservoir is concentric;

3) utilize the specific heat capacity variation with temperature to describe the wax partial crystallization and go out to discharge latent heat to the impact of stopping transportation temperature drop process;

4) in the subordinate phase of stopping transportation temperature drop, the concept of quoting stagnant point is divided into natural convection district and thermal conductive zone with pipe interior.

Be a pure Heat Conduction Problems by above supposition with stopping transportation temperature drop problem reduction.

In pipe, the heat transfer equation of crude oil is:

$\mathrm{\ρC}\frac{\∂T}{\∂\mathrm{\τ}}=\frac{1}{r}\frac{\∂}{\∂r}\left({\mathrm{\λ}}_{e}r\frac{\∂T}{\∂r}\right)---\left(7\right)$

Wherein:

${\mathrm{\λ}}_e=\frac{-{\mathrm{\α}}_1(T_L-T_w)}{{\left(\frac{\∂T}{\∂r}\right)}_w}---\left(8\right)$

During program was calculated, during higher than stagnant point, coefficient of heat conductivity adopted following formula to calculate when oil temperature, and oil temperature is chosen the coefficient of heat conductivity of crude oil during lower than stagnant point.

$\mathrm{\&lambda;}=\left\{\begin{array}{cc}{\mathrm{\&lambda;}}_e& t>T_{\mathrm{zl}}\\ {\mathrm{\&lambda;}}_o& t<T_{\mathrm{zl}}\end{array}\right.---\left(9\right)$

The heat transfer equation of wax deposition layer, tube wall and anticorrosive coat

${\mathrm{\&rho;}}_n{C}_n\frac{\&PartialD;T_n}{\&PartialD;\mathrm{\&tau;}}=\frac{1}{r}\frac{\&PartialD;}{\&PartialD;r}\left({\mathrm{\&lambda;}}_{n}r\frac{\&PartialD;T_n}{\&PartialD;r}\right)---\left(10\right)$

In formula, n=1,2,3 represent respectively wax deposition layer, tube wall and anticorrosive coat.

The thermal conduction of soil equation

${\mathrm{\&rho;}}_s{C}_s\frac{\&PartialD;T_s}{\&PartialD;\mathrm{\&tau;}}=\frac{1}{r}\frac{\&PartialD;}{\&PartialD;r}\left({\mathrm{\&lambda;}}_{s}r\frac{\&PartialD;T_s}{\&PartialD;r}\right)---\left(11\right)$

The periphery of soil Domain is First Boundary Condition: temperature is the natural ground temperature at buried depth of pipeline place.

Correlation Criteria is satisfied in the heat transfer of wax deposition layer, tube wall, anticorrosive coat and soil, that is:

$T_k{|}_{r=R_k}=T_{k+1}{|}_{r=R_k}$ k＝1，2，3

${\mathrm{\&lambda;}}_3\frac{\&PartialD;T_3}{\&PartialD;r}{|}_{r=R_3}={\mathrm{\&lambda;}}_s\frac{\&PartialD;T_s}{\&PartialD;r}{|}_{r=R_3}$

The stopping transportation restart pressure calculates

Adopt Liu Tian to help model and calculate starting pressure, in model, starting pressure is divided into three parts: liquid is by the static inertial force that accelerates to toggle speed, the friction force between liquid and tube wall and destroy the thixotropic additional force of non-newtonian fluid structure.Suppose to start throughput rate and remain unchanged, the maximal value of the starting pressure of derivation is:

$P_{\max }=\frac{4\mathrm{Q\&rho;a}}{\mathrm{\&pi;}{d}^2}+\frac{4{\mathrm{\&tau;}}_{\&infin;}L}{d}+\frac{4a({\mathrm{\&tau;}}_0-{\mathrm{\&tau;}}_{\&infin;})}{\mathrm{dB}}(1-e^{-\frac{\mathrm{BL}}{a_s}})---\left(12\right)$

Tube wall shear rate and the relation that starts throughput rate Newtonian fluid stable-state flow formula approximate representation:

In formula: τ ₀, τ _∞, B: oil transportation temperature down cut speed is The time initial shearing stress, balance shear stress and thixotropy index, L is duct length, a _sBe pressure-wave emission speed.

First, formula (12) the right is the inertia pressure drop, makes crude oil produce acceleration, by the static toggle speed that reaches; Second is the pressure drop of balance frictional resistance, the viscous friction drag when overcoming mobile the shearing between fluid and tube wall; The 3rd is the thixotropy pressure drop, is used for destroying near the structure of the crude oil of tube wall.

The present invention can whether solidifying pipe be quantitatively described to pipeline, and the suggestion of proposition reliability is optimized in security and the operation of pipeline.The present invention has considered the uncertainty of influence factor first in solidifying pipe probability assessment; Determined concrete acceptable failure probability index first in solidifying pipe probability assessment; Thixotropy of Crude Oil model, pressure wave transmission speed have been considered in the computation process of solidifying pipe probability.The present invention can instruct the crude oil pipeline safety evaluatio that flows, and provides technical support to safe, the efficient operation of pipeline.

Description of drawings

The solidifying pipe of Fig. 1 crude oil pipeline probability quantitative evaluation process flow diagram

Embodiment

Embodiment. the solidifying pipe of crude oil pipeline probability method for quantitatively evaluating by the method that this example proposes, has carried out the evaluation of solidifying pipe probability to domestic certain crude oil pipeline as shown in Figure 1, draws the conclusion that is adapted to produced on-site.

The statistical study of field data

In the evaluation of solidifying pipe probability, when thinking pipeline throughput rate, out-station temperature, steady-state operation, overall heat transfer coefficient, wax deposition thickness, buried depth of pipeline, the buried depth of pipeline place gentle soil thermal conductivity in ground etc. all have uncertainty, this pipeline data that Field Research obtains in February, 09 are carried out automatic statistical analysis, the results are shown in Table 2 and table 3.

The Safety Influence Factors uncertainty analysis of flowing of certain crude oil pipeline of table 2

The uncertain value of the mobile Safety Influence Factors of certain crude oil pipeline of table 3

Solidifying pipe probability calculation result and analysis

Solidifying pipe probability when (1) stopping transportation reaches the longest permission shutdown time

The longest permission shutdown time of target pipeline according to stipulating in the conduit running rules has carried out solidifying pipe probability calculation.The longest permission shutdown time of this pipeline in different months of rules regulation sees Table 4.

Different months of table 4 the longest permission shutdown time

Based on conduit running parameter during in May, 2008～2009 year April, calculate the solidifying pipe probability between this pipeline 6 stations, the results are shown in Table 5.

The solidifying pipe probability calculation result of pipeline when table 5 stopping transportation reaches the longest permission shutdown time

By table 5, in conjunction with estimating basic data as can be known, with respect to commingled crude (29 ℃ of condensation points), No. 2 former crude oil fluidities relatively poor (32 ℃ of condensation points) of carrying of through-station, carry the inlet temperature of initial station-No. 1 through-station of this crude oil, No. 1-No. 2 through-station pipeline sections generally at 34～35 ℃, higher 2～3 ℃ than condensation point of crude oil.Therefore-No. 1 through-station in initial station is in November, and No. 1-No. 2 through-station is bigger than normal at the solidifying pipe probability in February and November.And the inlet temperature between all the other stations of conveying commingled crude is higher 4～5 ℃ than condensation point of crude oil generally at 33～34 ℃, and therefore, solidifying pipe probability is lower, can suitably reduce inlet temperature again.

(2) the fixing solidifying pipe probability under shutdown time

Calculate the solidifying pipe probability under stopping transportation 24h condition, the results are shown in Table 6.

The solidifying pipe of pipeline probability under table 6 stopping transportation 24h

As shown in Table 6, at first stop-No. 1 through-station pipeline section is in November, No. 1-No. 2 through-station pipeline sections February and November solidifying pipe probability higher.

(3) the solidifying pipe probability under different shutdown times

Choose ground temperature and carry out computational analysis minimum February.Solidifying pipe probability calculation between the different shutdown time conditions of target pipeline lower 6 stations be the results are shown in Table 7.

Solidifying pipe probability calculation result under table 7 different shutdown time conditions in February

Can be found out by result in table 7, along with the increase of shutdown time, between each station solidifying pipe probability gather way and inconsistent, therefore the solidifying manage-style between each station is distinguished by inches to some extent.

(4) the solidifying pipe probability under different inlet temperatures

Calculate respectively February at 1 ℃, 2 ℃, the solidifying pipe probability of 24h after stopping transportation under 3 ℃ of conditions that enter the station and under the actual fed operating mode more than condensation point more than condensation point more than condensation point, see Table 8.

Solidifying pipe probability under the different inlet temperature conditions of table 8

As shown in Table 8, when between each station during all according to same index regulation inlet temperature, for example, when entering the station, the solidifying pipe probability at each station is also incomplete same according to " condensation point+3 ℃ ".To same pipeline (region is identical) under the same time, even result is like this, for the pipeline of carrying different crude oils, in Various Seasonal, this difference can be larger, therefore, searching determines that than " condensation point+3 ℃ " index that more reasonably enters the station or inlet temperature mobile Safety Assessment System is expected to address this problem comprehensively according to being possible.Result based on above-mentioned evaluation draws can instruct produced on-site and procedure making, can find out thus the significance of carrying out the quantitatively evaluating safety that flows.

Claims (8)

1. a crude oil pipeline coagulates pipe probability method for quantitatively evaluating, it is characterized in that its main flow process is:

1) robotization of safety effects factor is extracted and is analyzed;

2) the data distributivity rule of influence factor statistics;

3) determinacy stopping transportation restart pressure calculates;

4) estimate the setting of number of times and the grab sample of parameter;

5) calculating of uncertain stopping transportation restart pressure;

6) the statistics pipeline is restarted the calculation times of failure;

7) pipeline solidifying pipe probability calculation result draws;

8) whether satisfy and to accept the judgement of losing efficacy;

9) if do not satisfy, after adjusting the flow assurance scheme, turn 2) the data distributivity rule statistics of influence factor;

If satisfy, submit the flow assurance overall plan to.

2. crude oil pipeline according to claim 1 coagulates pipe probability method for quantitatively evaluating, it is characterized in that the solidifying pipe of described pipeline probability is:

For a given ultimate limit state, probability analysis comprises the model of broad sense random load S and the random drag R of broad sense; Corresponding limit state function can be expressed as following form in general manner:

g(x)＝R-S (1)

Obviously, indicate inefficacy as g (x)＜0;

The definition failure probability is as follows:

$P_f=\underset{g\left(x\right)\&le;0}{\&Integral;}{f}_x\left(x\right)\mathrm{dx}---\left(2\right)$

In formula, x is the stochastic variable vector; f _x(x) be joint probability density function;

Restart problem for the crude oil pipeline stopping transportation, definition load S is the minimum starting pressure of pipeline, and getting drag R is pipeline maximum allowable operating pressure (MAOP), and Pf is solidifying pipe probability.

3. crude oil pipeline according to claim 1 coagulates pipe probability method for quantitatively evaluating, it is characterized in that described data distributivity probability statistics and check are:

According to ISO 16708, the production run data of quantitative evaluation pipeline collection are carried out uncertainty and value analysis.

4. crude oil pipeline according to claim 1 coagulates pipe probability method for quantitatively evaluating, it is characterized in that described determinacy stopping transportation restart pressure calculating is:

This evaluation method is estimated framework based on secondary, first order framework in the situation that do not consider production run situation fluctuation, is to satisfy on-the-spot demand, with the security of the existing production and operation condition of Deterministic Methods assessment, if dangerous, will take the flow assurance measure according to result; The determinacy operating mode is on-the-spot given production data.

5. crude oil pipeline according to claim 1 coagulates pipe probability method for quantitatively evaluating, it is characterized in that the setting of described evaluation number of times and the grab sample of parameter are:

After having completed the deterministic parsing in system one-level framework, just can carry out large-scale probability sampling, the sampling number of times is defaulted as 10000 times, generates corresponding numerical value by its regularity of distribution function during the every sub-sampling of production run parameter, but must set the bound of production run parameter; In the situation that there is no the production scene appointment, the bound of system default is as follows, and throughput rate is between 3 times of variances of its average plus-minus, and temperature out of the station is between 0 ℃-90 ℃, and ground temperature is between-20 ℃-50 ℃.

6. crude oil pipeline according to claim 1 coagulates pipe probability method for quantitatively evaluating, it is characterized in that described uncertain stopping transportation restart pressure calculates and the calculating of the startup frequency of failure is:

Whether uncertain stopping transportation restart pressure calculates is to analyze solidifying pipe according to the production run parameter that the evaluation number of times of having set and each evaluation number of times generate to occur; As start unsuccessfully and to occur to be recorded as 1, do not occur to record 0; After completing, evaluation can record the number of times that total stopping transportation is restarted failure.

7. crude oil pipeline according to claim 1 coagulates pipe probability method for quantitatively evaluating, it is characterized in that described interpretation of result is:

Solidifying tube failure probability P f based on calculating is defined as pipeline shutdown with (1-Pf) and restarts safety indexes (SRSI); Under constant condition of pipeline shutdown time, the SRSI graded index is larger, and the possibility of pipeline shutdown failure is less restarting just, and the safe coefficient of pipeline restart procedure is just higher; Otherwise the possibility that pipeline is restarted failure is just larger, according to evaluation result, to the security of operation proposition safeguard of pipeline.

8. crude oil pipeline according to claim 1 coagulates pipe probability method for quantitatively evaluating, it is characterized in that the defeated technology Calculation of evaluation procedure pipe is:

Waterpower, heating power during normal the conveying calculate

(1) normally moving the axial temperature drop of hot oil pipeline calculates

Stablizing under transport condition, between the temperature drop rate that in hot oil pipeline, oil flows and the coefficient of heat conductivity of conduit running parameter, caliber, buried depth of pipeline and surrounding medium thereof, temperature, heating station, length and crude oil property are closely related; In pipe, oil stream can be similar to Л e й б e н з о Н formula along the journey Temperature Distribution and describe:

T _L＝(T ₀+b)+(T _R-T ₀-b)e ^-aL (3)

In formula, a=K π D/Gc, b=ig/c _pa； G is the mass rate of oil product, kg/s; C _pBe the specific heat capacity of crude oil, J/ (kg ℃); D is outer diameter tube, m; L is the distance apart from heating station, m; K is the pipeline overall heat transfer coefficient, W/ (m ²℃); T _RBe heating station departures oil temperature, ℃; T _LBe the oil temperature of distance heating station distance for the L place, ℃; T0 is ambient temperature, and buried pipeline is got the natural ground temperature in tube hub buried depth place, ℃;

(2) frictional resistance of hot oil pipeline calculates

The pressure gradient that fluid flows in horizontal pipe is:

$i=\mathrm{\&lambda;}\frac{\mathrm{\&rho;}{V}^2}{2D}=4f\frac{\mathrm{\&rho;}{V}^2}{2D}---\left(4\right)$

In formula, i is pressure gradient, Pa/m; V is the mean flow rate of pipeline inner fluid, m/s; ρ is the density of fluid, kg/m ³D is round tube inside diameter, m; λ is the darcy coefficient of friction resistance; F is the peaceful coefficient of friction resistance of model;

The calculating of stopping transportation temperature drop

In the evaluation procedure of initial set probability, according to evaluation requirements, can take Lumped-Capacity method or two kinds of solutions of numerical method to the stopping transportation temperature drop, Lumped-Capacity method has computing velocity and the relatively conservative characteristics of result, and numerical solution calculates accurately, but computing velocity is slower;

(1) Lumped-Capacity method

After hot oil pipeline shutdown, apart from starting point any distance l place, in stopping transportation t managed after the time, the calculating formula of oil temperature is as follows:

$T=T_0+(T_R-T_0)\exp (-\frac{\mathrm{K\&pi;}{D}_{\mathrm{out}}l}{{\mathrm{Gc}}_y}-\mathrm{bt})---\left(5\right)$

$b=\frac{\mathrm{KD}}{\frac{D_1^2}{4}{c}_y{\mathrm{\&rho;}}_y+\frac{(D_2^2-D_1^2)}{4}{c}_g{\mathrm{\&rho;}}_g}---\left(6\right)$

In formula, T is apart from pipeline starting point l place, the oil temperature of stopping transportation t after the time, ℃; T ₀Be ambient temperature, ℃; T _RBe the oil temperature at beginning pipeline starting point place during stopping transportation, ℃; Overall heat transfer coefficient when K is the pipeline steady-state operation, W/ (m ℃); D _outBe pipe external diameter, m; G is the pipeline throughput rate, kg/s; L is that calculation level is apart from the distance of pipeline starting point, m; T is shutdown time, s; B is coefficient, s ^-1, value is determined by formula (2-30); D ₁, D ₂Be respectively pipe diameter and external diameter, m; c _y, c _gBe respectively the specific heat capacity of crude oil and steel pipe, kJ/ (kg ℃); ρ _y, ρ _gBe respectively specific heat capacity and the density of steel pipe, kg/m ³

(2) numerical solution

Temperature drop process after pipe inner wax crude oil shutdown is a three-dimensional unsteady heat transfer problem of following phase transformation, natural convection and moving boundary; According to the difference of heat transfer type, after stopping transportation, the heat transfer of the interior crude oil of pipe can be divided into three phases again: free convection heat transfer stage, natural convection and heat conduction co-controlling stage and pure heat conduction stage;

Based on the complicacy of temperature drop process after the waxy crude oil stopping transportation, introduce following hypothesis in this model and realize simplifying:

1) introducing equivalent heat conductivity processes the Natural Convection Problem of liquid crude oil as Heat Conduction Problems;

2) in the process of stopping transportation temperature drop, along with reducing the wax crystalline substance, oil temperature separates out gradually, form solidifying oil reservoir, due to the complicacy of engineering problem, suppose that growth and the pipeline of solidifying oil reservoir is concentric;

3) utilize the specific heat capacity variation with temperature to describe the wax partial crystallization and go out to discharge latent heat to the impact of stopping transportation temperature drop process;

4) in the subordinate phase of stopping transportation temperature drop, the concept of quoting stagnant point is divided into natural convection district and thermal conductive zone with pipe interior;

Be a pure Heat Conduction Problems by above supposition with stopping transportation temperature drop problem reduction;

In pipe, the heat transfer equation of crude oil is:

$\mathrm{\&rho;C}\frac{\&PartialD;T}{\&PartialD;\mathrm{\&tau;}}=\frac{1}{r}\frac{\&PartialD;}{\&PartialD;r}\left({\mathrm{\&lambda;}}_{e}r\frac{\&PartialD;T}{\&PartialD;r}\right)---\left(7\right)$

Wherein:

${\mathrm{\&lambda;}}_e=\frac{-{\mathrm{\&alpha;}}_1(T_L-T_w)}{{\left(\frac{\&PartialD;T}{\&PartialD;r}\right)}_w}---\left(8\right)$

During program was calculated, during higher than stagnant point, coefficient of heat conductivity adopted following formula to calculate when oil temperature, and oil temperature is chosen the coefficient of heat conductivity of crude oil during lower than stagnant point;

$\mathrm{\&lambda;}=\left\{\begin{array}{cc}{\mathrm{\&lambda;}}_e& t>T_{\mathrm{zl}}\\ {\mathrm{\&lambda;}}_o& t<T_{\mathrm{zl}}\end{array}\right.---\left(9\right)$

The heat transfer equation of wax deposition layer, tube wall and anticorrosive coat

${\mathrm{\&rho;}}_n{C}_n\frac{\&PartialD;T_n}{\&PartialD;\mathrm{\&tau;}}=\frac{1}{r}\frac{\&PartialD;}{\&PartialD;r}\left({\mathrm{\&lambda;}}_{n}r\frac{\&PartialD;T_n}{\&PartialD;r}\right)---\left(10\right)$

In formula, n=1,2,3 represent respectively wax deposition layer, tube wall and anticorrosive coat;

The thermal conduction of soil equation

${\mathrm{\&rho;}}_s{C}_s\frac{\&PartialD;T_s}{\&PartialD;\mathrm{\&tau;}}=\frac{1}{r}\frac{\&PartialD;}{\&PartialD;r}\left({\mathrm{\&lambda;}}_{s}r\frac{\&PartialD;T_s}{\&PartialD;r}\right)---\left(11\right)$

The periphery of soil Domain is First Boundary Condition: temperature is the natural ground temperature at buried depth of pipeline place; Correlation Criteria is satisfied in the heat transfer of wax deposition layer, tube wall, anticorrosive coat and soil, that is:

$T_k{|}_{r=R_k}=T_{k+1}{|}_{r=R_k}$ k＝1，2，3

${\mathrm{\&lambda;}}_3\frac{\&PartialD;T_3}{\&PartialD;r}{|}_{r=R_3}={\mathrm{\&lambda;}}_s\frac{\&PartialD;T_s}{\&PartialD;r}{|}_{r=R_3}$

The stopping transportation restart pressure calculates

Adopt Liu Tian to help model and calculate starting pressure, in model, starting pressure is divided into three parts: liquid is by the static inertial force that accelerates to toggle speed, the friction force between liquid and tube wall and destroy the thixotropic additional force of non-newtonian fluid structure; Suppose to start throughput rate and remain unchanged, the maximal value of the starting pressure of derivation is:

$P_{\max }=\frac{4\mathrm{Q\&rho;a}}{\mathrm{\&pi;}{d}^2}+\frac{4{\mathrm{\&tau;}}_{\&infin;}L}{d}+\frac{4a({\mathrm{\&tau;}}_0-{\mathrm{\&tau;}}_{\&infin;})}{\mathrm{dB}}(1-e^{-\frac{\mathrm{BL}}{a_s}})---\left(12\right)$

Tube wall shear rate and the relation that starts throughput rate Newtonian fluid stable-state flow formula approximate representation:

In formula: τ ₀, τ _∞, B: oil transportation temperature down cut speed is

The time initial shearing stress, balance shear stress and thixotropy index, L is duct length, a _sBe pressure-wave emission speed;

First, formula (12) the right is the inertia pressure drop, makes crude oil produce acceleration, by the static toggle speed that reaches; Second is the pressure drop of balance frictional resistance, the viscous friction drag when overcoming mobile the shearing between fluid and tube wall; The 3rd is the thixotropy pressure drop, is used for destroying near the structure of the crude oil of tube wall.

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