CN113158489B - Equivalent load-based method for calculating wall thickness of anti-explosion pipeline - Google Patents
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Abstract
The invention discloses a method for calculating the wall thickness of an anti-explosion pipeline based on equivalent load, which comprises the steps of firstly calculating the detonation pressure of mixed gas in the pipeline when the most dangerous condition is considered according to the type of combustible gas in the pipeline and the type of oxidizing gas possibly mixed in, namely the mixing ratio of the combustible gas and the oxidizing gas in the pipeline is the stoichiometric ratio, taking k times of the detonation pressure as equivalent static pressure, then preliminarily calculating the wall thickness of the pipeline according to a formula, and then rounding upwards to obtain the final wall thickness of the pipeline. The method of the invention fully considers the service installation conditions of the pipeline and different possible explosion scenes in the pipeline, can meet the design requirements of the pipeline more pertinently, ensures that the designed pipeline has more proper wall thickness while meeting the anti-explosion performance, thereby having better economy, and the method is convenient and rapid to implement and has low requirement on the professional degree of personnel.
Description
Technical Field
The invention relates to the field of pipeline explosion prediction, in particular to a method for calculating the wall thickness of an anti-explosion pipeline based on equivalent load.
Background
In the fields of national defense, chemical engineering, nuclear power, public safety and the like, the requirement of anti-explosion performance needs to be met when certain cylindrical shell structures or pipelines are designed, namely, an internal explosion structure cannot lose efficacy, and the design requirement of intrinsic safety is met. One key in the design of an anti-knock container or pipe is the calculation and determination of wall thickness, and at present, there are two main types of methods. One is a theoretical or empirical method, such as an equivalent single degree of freedom method. The basic idea of the method is to calculate the equivalent static pressure of the explosive load, and then calculate the wall thickness according to the design method of the conventional container, but the method is mainly suitable for the situation that the explosive is TNT, and for the common combustible gas pipeline, different explosion scenes such as deflagration, detonation and deflagration-to-detonation possibly occur in the pipeline, and the equivalent static pressures corresponding to the different explosion scenes are different, which is not considered by the current method. The second type is a numerical simulation method, which needs to perform elastoplastic finite element kinetic analysis on the designed pipeline, judges whether the structure can resist corresponding explosion load according to the analysis result, and if not, increases the wall thickness for repeated analysis. The method has high requirements on the professional level of implementers, the numerical analysis result is influenced by the selection of a constitutive model, the size of a grid and the like, the model needs to be verified before specific implementation, the implementation period is long, and the difficulty is high.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the method for calculating the wall thickness of the anti-explosion pipeline based on the equivalent load, the method can meet the pipeline design requirement in a more targeted manner, and the calculation is quick and convenient.
The purpose of the invention is realized by the following technical scheme:
a method for calculating the wall thickness of an anti-explosion pipeline based on equivalent load specifically comprises the following steps:
(1) according to the type of combustible gas in the pipeline and the type of oxidizing gas possibly mixed in, considering the most dangerous situation, namely when the mixing ratio of the combustible gas and the oxidizing gas in the pipeline is stoichiometric ratio, calculating the detonation pressure p of the mixed gas in the pipeline for detonation CJ ；
(2) Taking detonation pressure p CJ K times as the equivalent static pressure p eq I.e. by
p eq ＝k·p CJ
Wherein k has different values in different scenes;
(3) preliminarily calculating the wall thickness delta of the pipeline according to the following formula
(4) The preliminarily calculated pipeline wall thickness delta is superposed with the pipeline corrosion allowance, and the upward value is obtained according to the national standard of pipeline design to obtain the final pipeline wall thickness delta n 。
Further, the detonation pressure p CJ Obtained by the following two methods:
(1) calculated by the following theoretical formula
In the formula, Q is energy released by chemical reaction of unit mass of mixed gas in the pipeline and is calculated according to the combustion heat of the reaction gas; gamma is the adiabatic index of the detonation product and can be obtained by calculation according to the type and volume percentage of the gas of the detonation product, and the value range of gamma is 1.1-1.4;
is the average molar mass of the initial mixed gas in the pipeline; r is an ideal gas constant; t is the temperature of the mixed gas in the pipeline, and can be obtained by inquiring the operating process parameters of the pipeline or taking the ambient temperature.
(2) Calculated using the program CEARUN.
Further, the values of k are as follows:
when two ends of the designed pipeline are connected with other pipelines or openings and only bear the steady detonation load of the gas, k is 0.70;
when two ends of the designed pipeline are connected with other pipelines or openings and gas deflagration to detonation is possible, k is 5.25;
when one end of the designed pipeline is closed and only bears the detonation load of the steady gas, k is 1.68;
when one end of the designed pipeline is closed and the gas detonation to detonation is possible, k is 12.6.
The invention has the following beneficial effects:
(1) the method fully considers the service installation conditions of the pipeline and different possible explosion scenes in the pipeline, correspondingly provides different equivalent static pressure calculation scaling coefficients, can more pointedly meet the pipeline design requirements, enables the designed pipeline to meet the anti-explosion performance and have more proper wall thickness, and thus has better economy;
(2) the wall thickness design is mainly calculated according to a formula, the steps are clear, the parameters are clear, and compared with a numerical simulation method, the wall thickness design method is convenient and quick to implement and has low requirement on the professional degree of personnel.
Drawings
FIG. 1 is a flow chart of a method for calculating the wall thickness of an anti-detonation pipeline based on equivalent load according to the invention;
FIG. 2 is a schematic diagram of the calculation of detonation pressure using the procedure CEARUN in the example.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments, and the objects and effects of the present invention will become more apparent, it being understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.
As shown in FIG. 1, the method for calculating the wall thickness of the anti-explosion pipeline based on the equivalent load specifically comprises the following four parts.
1. Specifying the design requirements and basic parameters of a pipeline
According to the design requirements of the pipeline, the type of gas in the pipeline is determined, and the designed inner diameter D of the pipeline is obtained i Acquiring the running pressure p of the pipeline, and inquiring allowable stress [ sigma ] of the material according to the material of the pipeline]And yield strength σ y In general, [ sigma ]]＝σ y And/n and n are safety factors.
2. Calculating the detonation pressure of gas in the pipeline
According to the type of combustible gas in the pipeline and the type of oxidizing gas (such as air and oxygen) possibly mixed in, considering the most dangerous situation, namely the mixing ratio of the combustible gas and the oxidizing gas in the pipeline is stoichiometric ratio, calculating the detonation pressure p of the mixed gas in the pipeline for detonation CJ Specifically, the following two methods can be used for calculation:
theoretical formula method
Calculating the detonation pressure p of the mixed gas in the pipeline by adopting the following formula CJ ：
In the formula, Q is the energy released by the chemical reaction of the mixed gas in unit mass in the pipeline and can be calculated according to the combustion heat of the reaction gas; gamma is the adiabatic index of detonation product (gas), and can be calculated according to the type and volume percentage of the detonation product gas, and the value range of common gas is as follows: 1.1-1.4;
is the average molar mass of the initial mixed gas in the pipeline; r is an ideal gas constant; t is the temperature of the mixed gas in the pipeline, and can be obtained by inquiring the operating process parameters of the pipeline or taking the ambient temperature.
② calculation by using the procedure CEARUN
The CEARUN program can provide a more accurate calculation result of the detonation pressure of the gas, is simple and convenient to operate, has a webpage version user operation interface, and can be widely used by field researchers, and the specific website is as follows: https:// cearun. The detonation pressure p can be calculated and obtained by inputting the types and volume percentages of the mixed gas, the initial pressure, the temperature and other parameters of the gas according to the program specification CJ 。
3. Calculating equivalent static pressure of pipeline design
Defining the equivalent static pressure as: the plastic deformation of the pipeline under the action of the pressure is consistent with the plastic deformation of the pipeline caused by the corresponding gas explosion scene, and the size of the plastic deformation is equal to k times of the gas explosion pressure, namely:
p eq ＝k·p CJ
the k value is determined according to the following principle:
firstly, two ends of a designed pipeline are connected with other pipelines or openings through flanges, and only bear the stable detonation load of gas:
in the scene, the detonation wave cannot be axially reflected in the designed pipeline, and k is 0.70.
And two ends of the designed pipeline are connected with other pipelines or openings through flanges, and gas Deflagration to Detonation (DDT) may occur:
in the scene, the maximum dynamic pressure in the pipeline is generated by DDT, the pressure of the initial detonation wave can be superposed, and the k value is 5.25.
Thirdly, one end of the designed pipeline is connected with a flange blind plate or closed and only bears the detonation load of the steady gas:
in this scenario, the detonation wave may be reflected during the axial propagation in the pipe, and a larger dynamic pressure is formed, where k is 1.68.
One end of the pipeline is connected with a flange blind plate or closed, and gas detonation can be generated:
considering the most dangerous situation under the scene, namely the DDT of the gas in the pipeline and the axial reflection of the detonation wave occur simultaneously, and the initial detonation wave pressure is superposed, and then the k value is 12.6.
4. Calculating and determining nominal wall thickness of pipe
According to the equivalent static pressure, selecting a proper pressure vessel design criterion (such as an elastic failure criterion, a plastic failure criterion, a blasting failure criterion and the like), and calculating the wall thickness delta of the pipeline:
if p eq ＜0.4[σ]Then, the pipe wall thickness δ is generally calculated according to the elastic failure design criteria and the pitch diameter formula:
if p eq ≥0.4[σ]Then, the pipe wall thickness δ can be calculated according to the plastic failure criterion and the Rahmere formula:
according to the calculated wall thickness delta, the corrosion allowance of the pipeline is superposed and the final nominal thickness delta of the pipeline is determined by rounding upwards n 。
A specific example is given below to further illustrate the calculation and results of the method of the present invention.
The inner diameter of a certain pipeline is 40mm, the material is 6061-T6 aluminum alloy, the internal gas is ethylene and oxygen mixed according to the stoichiometric ratio, the initial pressure of the gas is 180kPa, and the ambient temperature is 300K. The pipeline is installed under the condition that one end of the pipeline is connected with other pipelines through flanges, and the other end of the pipeline is sealed through a polyester membrane. The design requires that the pipeline can bear the steady-state detonation load of the mixed gas of the ethylene and the oxygen in the pipeline so as to carry out related experimental research. The wall thickness of the anti-explosion pipeline is designed according to the invention as follows:
step 1: specifying the design requirements and basic parameters of a pipeline
The type of gas in the pipeline is ethylene (C) according to the design requirement of the pipeline 2 H 4 ) And oxygen (O) 2 ) Design inner diameter D of pipe i Inquiring 6061-T6 material mechanical property parameters and yield strength sigma of the pipe when the pipe operating pressure p is 180kPa at 40mm y 240MPa, taking a safety factor of 1.5, and allowable stress [ sigma ]]＝σ y /1.5＝160MPa。
Step 2: calculating the detonation pressure of gas in the pipeline
The interior of the pipe is itself a stoichiometric mixture of ethylene (C) 2 H 4 ) And oxygen (O) 2 ) Namely, under the most dangerous condition, the gas temperature is 300K at the ambient temperature, the initial pressure is 180kPa, and the gas detonation pressure is calculated by adopting the following two methods:
theoretical formula method
The chemical reaction equation for ethylene and oxygen is:
C 2 H 4 +3O 2 ＝2CO 2 +2H 2 O
the energy released by the reaction of this combustible mixed gas was found to be 987.14kJ/kg, and the adiabatic index γ of the detonation product (reaction product) was found to be 1.14. Average molar mass of the starting gas
The gas detonation pressure is calculated according to the formula as:
② calculation by using the procedure CEARUN
Opening a webpage https:// cearun.grc.nasa.gov/index.html, selecting the problem type as 'det' (solving the gas detonation pressure), the input gas temperature as 300K, the initial pressure as 180kPa, and selecting the comburent as ethylene C 2 H 4 The oxide is oxygen O 2 Setting the molar mixing ratio of the two as 1: and 3, calculating by clicking, wherein the detonation pressure solved by the program is 6.10MPa, as shown in FIG. 2.
And step 3: calculating equivalent static pressure of pipeline design
The pipeline is installed under the condition that one end of the pipeline is connected with other pipelines through flanges, and the other end of the pipeline is sealed through a polyester membrane. The polyester film sheet can be rapidly broken under the action of detonation waves, detonation wave reflection cannot be caused, namely the pipeline installation condition is processed according to openings at two ends, the design requirement is that the pipeline only needs to bear gas steady-state detonation load, according to the specification of the invention, k takes a value of 0.70, the gas detonation pressure (6.10MPa) calculated by a CEARUN program is selected as a reference, and the design equivalent static pressure of the pipeline is calculated as follows:
p eq ＝k·p CJ ＝0.70×6.10＝4.27MPa
and 4, step 4: calculating and determining nominal wall thickness of pipe
The design equivalent static pressure p of the pipeline eq And if the allowable stress of the material is less than 0.4 times, calculating the wall thickness of the pipeline according to the elastic failure criterion as follows:
inquiring the national standard of GB/T4436-.
A gas detonation loading experiment is carried out on the pipeline, and the result shows that the pipeline does not generate plastic deformation and meets the corresponding design requirement.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and although the invention has been described in detail with reference to the foregoing examples, it will be apparent to those skilled in the art that various changes in the form and details of the embodiments may be made and equivalents may be substituted for elements thereof. All modifications, equivalents and the like which come within the spirit and principle of the invention are intended to be included within the scope of the invention.
Claims (1)
1. A method for calculating the wall thickness of an anti-explosion pipeline based on equivalent load is characterized by comprising the following steps:
(1) according to the type of combustible gas in the pipeline and the type of oxidizing gas possibly mixed in, considering the most dangerous situation, namely when the mixing ratio of the combustible gas and the oxidizing gas in the pipeline is stoichiometric ratio, calculating the detonation pressure p of the mixed gas in the pipeline for detonation CJ ；
(2) Taking detonation pressure p CJ K times as the equivalent static pressure p eq I.e. by
p eq ＝k·p CJ
Wherein k has different values in different scenes;
(3) preliminary calculation of the pipe wall thickness δ according to the following equation
Wherein D is i Designing an inner diameter for the pipeline; [ sigma ] A]Allowable stress of the pipeline material; sigma y Is the yield strength of the pipe material;
(4) the preliminarily calculated pipeline wall thickness delta is superposed with the pipeline corrosion allowance, and the upward value is obtained according to the national standard of pipeline design to obtain the final pipeline wall thickness delta n ；
Said detonation pressure p CJ Obtained by the following two methods:
(1) calculated by the following theoretical formula
In the formula, Q is energy released by chemical reaction of unit mass of mixed gas in the pipeline and is calculated according to the combustion heat of the reaction gas; gamma is the adiabatic index of the detonation product and can be obtained by calculation according to the type and volume percentage of the gas of the detonation product, and the value range of gamma is 1.1-1.4;
is the average molar mass of the initial mixed gas in the pipeline; r is an ideal gas constant; t is the temperature of the mixed gas in the pipeline, and can be obtained by inquiring the operating process parameters of the pipeline or taking the ambient temperature; p is the pipeline operating pressure;
(2) calculating by using a program CEARUN;
the k values are as follows:
when two ends of the designed pipeline are connected with other pipelines or openings and only bear the steady detonation load of the gas, k is 0.70;
when two ends of the designed pipeline are connected with other pipelines or openings and gas deflagration to detonation is possible, k is 5.25;
when one end of the designed pipeline is closed and only bears the detonation load of the steady gas, k is 1.68;
when one end of the designed pipeline is closed and gas deflagration to detonation is possible, k is 12.6.
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| CN108318654A (en) * | 2017-12-29 | 2018-07-24 | 中国人民解放军陆军工程大学 | Destructor detonation thermodynamic state verification method for simulating the experiment of centrifuge high G-value |
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Application publication date: 20210723 Assignee: Qingdao Zhongchuang Zhihui Electronic Technology Co.,Ltd. Assignor: CHINA University OF PETROLEUM (EAST CHINA) Contract record no.: X2022980024511 Denomination of invention: A Calculation Method of Anti explosion Pipe Wall Thickness Based on Equivalent Load Granted publication date: 20220826 License type: Common License Record date: 20221227 |