本文選題：管道凹坑 + 輪廓擬合　； 參考：《西南石油大學(xué)》2015年碩士論文

【摘要】：石油和天然氣作為可被大量發(fā)掘利用的能源,早已成為國家工業(yè)體系的血液,為社會各行各業(yè)的發(fā)展提供了力量。管道運(yùn)輸以其合理利用地下空間、密閉輸送、經(jīng)濟(jì)環(huán)保等優(yōu)勢,逐步成為石油和天然氣的主流運(yùn)輸方式。管道運(yùn)輸?shù)陌踩珕栴}直接關(guān)系到能源安全和生命財產(chǎn)安全,需要引起足夠的重視。凹坑是管壁受外部擠壓或碰撞而產(chǎn)生徑向位移形成的缺陷,屬于管道機(jī)械損傷的一種,它引起的應(yīng)力和應(yīng)變集中對管道的安全運(yùn)行造成了極大地威脅,因此需要對凹坑缺陷進(jìn)行合理的評價,及時維修和替換損傷嚴(yán)重的管段。本文針對凹坑缺陷的應(yīng)變評估進(jìn)行了以下幾方面的研究： 首先,整理和歸納了油氣管道上凹坑缺陷的分類原則、常見類型、檢測方式和現(xiàn)有的評估標(biāo)準(zhǔn),介紹了ASMEB31.8中凹坑缺陷應(yīng)變評估的具體方法。 其次,在對管道凹坑缺陷的材料非線性和幾何非線性等分析基礎(chǔ)上,建立了平滑型凹坑和曲折型凹坑的有限元模型,得到兩種凹坑缺陷的應(yīng)變分布規(guī)律,以及凹坑缺陷在內(nèi)壓作用下發(fā)生回彈的應(yīng)變變化規(guī)律。 然后,針對現(xiàn)有的應(yīng)變評估標(biāo)準(zhǔn)做了一系列的改進(jìn)研究。第一,在內(nèi)檢測數(shù)據(jù)到應(yīng)變求解的過程中,缺少噪聲消除和輪廓擬合的相關(guān)方法。本文提出了采用四階B-樣條最小二乘擬合算法將檢測數(shù)據(jù)進(jìn)行噪聲消除和輪廓擬合,建立了從含有噪聲的檢測數(shù)據(jù)到應(yīng)變求解的輪廓描述模型。第二,提出采用弧長法計算薄膜應(yīng)變,同時,考慮管道圓柱殼體的幾何特點(diǎn),改進(jìn)了標(biāo)準(zhǔn)中等效應(yīng)變的計算方法。將改進(jìn)的凹坑缺陷應(yīng)變計算結(jié)果、標(biāo)準(zhǔn)計算結(jié)果和有限元結(jié)果對比,結(jié)果顯示改進(jìn)的應(yīng)變計算模型大大提高了計算精度。第三,采用斷裂力學(xué)和損傷力學(xué)的相關(guān)理論,建立了管道凹坑缺陷韌性損傷模型,分析了兩種凹坑類型不同區(qū)域的損傷程度、管規(guī)格對凹坑損傷的影響以及不同內(nèi)壓下的凹坑缺陷損傷程度,得出不同內(nèi)壓下臨界失效應(yīng)變的擬合關(guān)系式,為應(yīng)變評估時許可應(yīng)變的擬定提供依據(jù)。 最后,在凹坑缺陷應(yīng)變計算模型和韌性失效損傷模型的基礎(chǔ)上,提出了包含在線檢測、缺陷輪廓描述、應(yīng)變求解和許可應(yīng)變選取的基于應(yīng)變的凹坑缺陷評估流程,并且針對約束型和非約束型凹坑分別采用不同的應(yīng)變標(biāo)準(zhǔn)。對蘭成渝管線廣元至江油段檢測到的凹坑缺陷進(jìn)行應(yīng)變評估,工程評估結(jié)果顯示該流程能夠滿足工程實(shí)際且具有較高的可操作性,同時評估結(jié)果能夠?yàn)榘才砰_挖維修順序提供指導(dǎo)。
[Abstract]:Oil and natural gas as a large number of energy can be exploited, has become the blood of the national industrial system, for the development of various sectors of society to provide power. Pipeline transportation has gradually become the mainstream transportation mode of oil and natural gas due to its advantages of rational use of underground space, airtight transportation, economic and environmental protection, etc. The safety of pipeline transportation is directly related to the safety of energy and life and property. Pit is the defect of radial displacement caused by external extrusion or collision of pipe wall. It belongs to one kind of pipeline mechanical damage. The concentration of stress and strain caused by it poses a great threat to the safe operation of pipeline. Therefore, it is necessary to evaluate the defect of pit and repair and replace the damaged section in time. In this paper, the strain assessment of pit defects is studied in the following aspects: Firstly, the classification principles, common types, detection methods and existing evaluation standards of pit defects on oil and gas pipelines are summarized and the concrete methods for evaluating pit defects strain in ASMEB31.8 are introduced. Secondly, based on the analysis of material nonlinearity and geometric nonlinearity, the finite element models of smooth and zigzag concave are established, and the strain distribution laws of two kinds of pitches are obtained. And the strain variation law of rebound under the action of internal pressure of pit defect. Then, a series of improved researches are made on the existing strain assessment criteria. First, there is a lack of relevant methods for noise elimination and contour fitting in the process from the inner detection data to the strain solution. In this paper, a fourth-order B-spline least square fitting algorithm is proposed to remove the noise and fit the contour of the detected data, and a contour description model from the noise detection data to the strain solution is established. Secondly, an arc length method is proposed to calculate the strain of thin film. At the same time, the calculation method of standard medium effect variation is improved taking into account the geometric characteristics of cylindrical shell. The results of improved pit defect strain calculation, standard calculation and finite element analysis show that the improved strain calculation model greatly improves the accuracy of the calculation. Thirdly, based on the theory of fracture mechanics and damage mechanics, the ductile damage model of pipe pit defects is established, and the damage degree in different regions of two types of pits is analyzed. The influence of pipe specification on pit damage and the degree of defect damage under different internal pressure are obtained. The fitting formula of critical failure strain under different internal pressure is obtained, which provides a basis for the determination of allowable strain in strain assessment. Finally, based on the calculation model of pit defect strain and the model of ductile failure damage, an evaluation process based on strain is proposed, which includes on-line detection, description of defect profile, strain solution and selection of allowable strain. Different strain standards are adopted for constrained and unconstrained pits. The strain assessment of the pit defects detected in the Guangyuan to Jiangyou section of the Lancheng Chongqing pipeline shows that the process can meet the practical needs of the project and has a high maneuverability. At the same time, the evaluation results can provide guidance for the order of excavation and maintenance.
【學(xué)位授予單位】：西南石油大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TE973

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