Microstructure and toughness of thick-gauge pipeline steel joint via double-sided friction stir welding combined with preheating

Fusion welding easily causes microstructural coarsening in the heat-affected zone(HAZ) of a thick-gauge pipeline steel joint. This is most significant in the inter-critically coarse-grained HAZ(ICCGHAZ), which considerably deteriorates the toughness of the joint. In the present work, 11-mm thick pipeline steel was joined by preheating and double-sided friction stir welding(FSW). A comparative study on the microstructure and toughness in the ICCGHAZs for FSW and gas metal arc welding(GMAW) was performed. The toughness in the ICCGHAZ for FSW was improved significantly than that in the ICCGHAZ for GMAW. Generally, the nugget zone(NZ) has a coarse microstructure in the FSW steel joint formed at the highest peak temperature. However, in the current study, the microstructure in the one-pass NZ was remarkably refined owing to the static recrystallization of ferrite. An excellent toughness was achieved in the NZ of the pipeline steel joint that employed FSW.

Experimental research on the contact force of the bi-directional pig in oil and gas pipeline

The migration process of the pig in oil and gas pipeline is a complex dynamic problem.During the pigging operation,the variation of friction force caused by the nonlinear contact between the sealing disc and the pipe wall is the key factor affecting the dynamic characteristics of the pig motion.At present,the existed pigging models for predicting pigging behavior regard friction as an invariant constant.Experimental research indicates that the friction force of the pig varies with the contact force and the lubrication conditions.Therefore,the assumption that the friction force is constant cannot reflect the friction dynamic characteristics of the pig during pigging,and will also affect the accuracy of the pigging model.Exploring the variation of friction force of pig under different conditions is the basis of establishing the transient dynamic model of a pig.As a result,in this paper,a method of direct measurement of contact force between the pig and the pipeline is presented,the contact force,the friction force,as well as the friction coefficient of the pig are obtained from the experiment.Research results in this paper can help to establish a more accurate dynamic model of pig.

Standard friction prediction model of long-distance hot oil pipelines

We developed a predictive model for the pipeline friction in the 520-730 m^3/h transmission range using the multi-layerperceptron-back-propagation(MLP-BP)method and analyzing the unit friction data after the pigging of a hot oil pipeline.In view of the shortcomings of the MLP-BP model,two optimization methods,the genetic algorithm(GA)and mind evolutionary algorithm(MEA),were used to optimize the MLP-BP model.The research results were applied to the standard friction prediction of three sections of a hot oil pipeline.After the GA and MEA optimizations,the average errors of the three sections were 0.0041 MPa for the GA and 0.0012 MPa for the MEA,and the mean-square errors were 0.083 and 0.067,respectively.The MEA-BP model prediction results were characterized by high precision and small dispersion.The MEABP prediction model was applied to the analysis of the wax formation 60 and 90 days after pigging.The analysis results showed that the model can effectively guide pipe pigging and optimization.There was little sample data for the individual transmission and oil temperature steps because the model was based on actual production data modeling and analysis,which may have affected the accuracy and adaptability of the model.

Global buckling behavior of submarine unburied pipelines under thermal stress

Buckling of submarine pipelines under thermal stress is one of the most important problems to be considered in pipeline design. And pipeline with initial imperfections will easily undergo failure due to global buckling under thermal stress and internal pressure. Therefore, it is vitally important to study the global buckling of the submarine pipeline with initial imperfections. On the basis of the characteristics of the initial imperfections, the global lateral buckling of submarine pipelines was analyzed. Based on the deduced analytical solutions for the global lateral buckling, effects of temperature difference and properties of foundation soil on pipeline buckling were analyzed. The results show that the snap buckling is predominantly governed by the amplitude value of initial imperfection; the triggering temperature difference of Mode I for pipelines with initial imperfections is higher than that of Mode I1; a pipeline with a larger friction coefficient is safer than that with a smaller one; pipelines with larger initial imperfections are safer than those with smaller ones.

Frequency-dependent friction in pipelines

A comprehensive study of modeling the frequency-dependent friction in a pipeline during pressure transients following a sudden cut-off of the flow is presented. A new method using genetic algorithms（GAs） for parameter identification of the weighting function coefficients of the frequency-dependent friction model is described. The number of weighting terms required in the friction model is obtained. Comparisons between simulation results and experimental data of transient pressure pulsations close to the valve in horizontal upstream and downstream pipelines are carried out respectively.The validity of the parameter identification method for weighting function coefficients and the calculation method for the number of weighting terms in the friction model is confirmed.

Friction coupling vibration characteristics analysis of aviation hydraulic pipelines considering multi factors

As the power transmission system of an aircraft,a hydraulic pipeline system is equivalent to the " blood vessel" of the aircraft. With the development of aircraft hydraulic system to high pressure,high speed and high power ratio,the fluid-structure interaction vibration mechanism of hydraulic pipeline is more complex and the influence of friction coupling on vibration cannot be ignored. The fluid-structure interaction of hydraulic pipeline will lead to system vibration,lower reliability of system operation and even pipeline rupture. Taking a hydraulic pipeline of C919 aircraft wingtip as the research object,a 14-equation model of fluid-structure interaction vibration considering friction coupling effect is established in this paper. The effects of friction and fluid parameters on the pipeline fluid-structure interaction vibration characteristics are studied and verified by experiments. The research results will provide theoretical guidance for the analysis of the pipeline fluid-structure interaction vibration and have important theoretical significance and great engineering value for promoting the localization process of large aircraft.

Model inference using the Akaike information criterion for turbulent flow of non-Newtonian crude oils in pipelines

The friction factor is a crucial parameter in calculating frictional pressure losses. However, it is a decisive challenge to estimate, especially for turbulent flow of non-Newtonian fluids in pipes. The objective of this paper is to examine the validity of friction factor correla- tions adopting a new informative-based approach, the Akaike information criterion （AIC） along with the coeffi- cient of determination （R2）. Over a wide range of measured data, the results show that each model is accurate when it is examined against a specific dataset while the E1-Emam et al. （Oil Gas J 101：74-83, 2003） model proves its supe- riority. In addition to its simple and explicit form, it covers a wide range of flow behavior indices and generalized Reynolds numbers. It is also shown that the traditional belief that a high R2 means a better model may be mis- leading. AIC overcomes the shortcomings of R2 as a trade between the complexity of the model and its accuracy not only to find a best approximating model but also to develop statistical inference based on the data. The authors present AIC to initiate an innovative strategy to help alleviate several challenges faced by the professionals in the oil and gas industry. Finally, a detailed discussion and models＇ ranking according to AIC and R2 is presented showing the numerous advantages of AIC.Keywords Friction factor - Pipeline Information theory Non-Newtonian Turbulent

Friction Characteristics at the Pipe-Soil Interface

-In order to analyze the stability of pipelines on the sea bed, the friction characteristics at the pipe-soil interface were examined by means of special direct shear tests. High density polythene was used as the surface of the pipe, which is a widely-utilized material for the outer cover of the pipe to prevent sea water corrosion. Sands of different gradings were tested. The reconstituted soft clay taken from the Bohai area was consolidated to different degrees of consolidation by the vacuum preloading technique, and tested.

Truss-type maintenance devices and corresponding pipeline lifting control strategies

For new submarine pipeline maintenance lifting equipment,a specialized analysis model is constructed in this study.A pipeline can be divided into the lifted portion and the touch-down portion that lies on the seabed,and each of these portions can be analyzed separately by converting the continuity conditions at the touch-down points to boundary conditions.The typical two-point sequence secant iterative technique is used to obtain the unknown lifted length and determine pipeline lifting confgurations.The BVP4C module in MATLAB software is used to solve this multiple-point boundary value problem issued from frst-order diferential equations.Also,the triple-point lifting mode of truncated maintenance and the two-point lifting mode of online maintenance are discussed.When the lifted heights at truss positions are shown,the lifting deformation,lifting forces,bending moment distribution,and axial force distribution can be analyzed using a dedicated analysis program.Numerical results can then be used to design a lifting strategy to protect the pipeline.

纯氢与掺氢天然气管道摩阻系数预测

纯氢与掺氢天然气管道是实现氢气长距离、大规模输送的最佳方式之一,其中摩阻系数是气体管道水力计算的关键参数,现有的经验公式不能满足预测掺氢天然气的摩阻系数要求。为改进传统的摩阻系数计算公式在纯氢与掺氢天然气管道系统的适用性,搭建了纯氢和掺氢天然气管输调压综合实验平台,开展纯氢和不同比例的掺氢天然气管输流动实验,根据实验采集的流量、温度、压力和管道的长度、管径等参数计算管道的摩阻系数,同时建立了摩阻系数与雷诺数、粗糙度之间的关系,并修正了传统摩阻系数公式,最后利用湖南省巴陵—长岭纯氢气管道的实际运行数据进行了验证。研究结果表明:①由于氢气与天然气物性差异较大,掺氢比会影响流动摩阻系数,相同条件下掺氢比越大摩阻系数越小;②传统摩阻系数计算公式存在30%左右的误差,创新提出的适用于纯氢和掺氢天然气的3段式摩阻系数经验公式,相对误差最大11.84%,能够有效降低误差;③与巴陵—长岭纯氢气管道实际的运行数据相比,修正后摩阻系数预测公式的平均误差为0.62%,该公式可以满足实际工程的误差要求。结论认为,得到的纯氢与掺氢天然气管道摩阻系数修正公式可应用于纯氢与掺氢天然气管道工程设计,具有重要的工程应用价值和前景。

油田注水系统仿真模型参数修正方法研究

油田注水管网经过多年运行后,管道内壁由于腐蚀、结垢等原因致使其摩阻系数与原始数据不一致,导致管网平差计算和系统仿真模拟结果超出工程允许范围。由于经济原因和施工难度,不可能对整个管网节点进行压力和流量测试从而反演求解出各管段真实的摩阻系数。为此,以管网各管段摩阻系数为研究对象,以管网有限个压力测试点为已知参量,建立管网摩阻系数反演模型和测压点分布模型,利用改进的人工蜂群算法对反演模型进行最优化求解,计算结果在工程误差允许范围。

大屯锡矿尾砂膏体环管管输数值模拟研究

膏体管输沿程阻力是影响管道设计与采场充填质量的关键因素之一,采用Fluent建立与实际环管实验系统一样的管道输送的几何模型,分析得到不同管线沿程阻力损失之间的关系以及膏体配比参数对沿程阻力损失的影响规律。研究表明:膏体在管道中弯管处的速度和压力都发生急剧的变化,弯管外侧压力和速度明显大于弯管内侧,有着明显的梯度。在水平管段速度和压力在管道径向上存在明显的梯度,呈结构流的特点,分为柱塞流动区和边界层区域。在膏体管道输送中管道内膏体的速度和压力均存在着边界效应,随着流速的增大,管输阻力增大;随着膏体质量浓度增加,沿程管道阻力损失变大;随着屈服应力与塑性黏度的增加,沿程阻力损失也增大,获得了不同物料组成、管道内径、管流流速下水平段膏体压力损失,为大屯锡矿最终输送泵、充填管道选型提供了依据。

有压管道瞬变流的非恒定摩阻模型改进

有压管道流动系统运行中经常发生水锤现象,极易导致爆管甚至人员伤亡,因此准确预测有压管道内的水锤现象对于保证系统安全运行具有重要意义。在有压管道内的水锤模拟中,以ZIELKE摩阻模型为代表的基于加权函数的非恒定摩阻模型能够描述有压管道瞬变流中的摩阻效应,但存在计算效率低下的问题。为提高计算效率,该研究提出了“先分段,后整体”的两阶段最小二乘拟合方法,建立了包含19个指数项的近似加权函数,并与已有近似加权函数进行对比,同时开展关阀水锤试验,对比了建立的摩阻模型与已有模型的计算效率和精度。结果表明,该研究建立的近似加权函数能够很好地拟合ZIELKE加权函数,其与ZIELKE加权函数的相对百分比误差近似为0;且其适用范围更宽,能够对无量纲时间在t∈[10-9,∞)范围内的非恒定流进行有效模拟。在计算精度方面,建立的模型与ZIELKE模型在阀门和中点处水头的最大相对百分比误差较小,分别为0.17%和0.15%,与URBANOWICZ模型的表现基本相同;在计算效率方面,建立的模型能够使ZIELKE模型计算效率提升约90%,能够使URBANOWICZ模型计算效率提升约30%。该研究建立的模型在适用范围、计算精度和计算效率方面具有较好的综合表现,能够在保证较宽适用范围和较高计算精度的前提下,提升计算效率。研究可为有压管道瞬变流的准确高效模拟提供理论支撑与参考。

低压干燥条件下热湿氧协同输送管道摩擦阻力特性

青藏高原低压缺氧干燥的特殊气候条件使建筑室内有加湿增氧的需求,而现有研究未考虑低压和加湿增氧导致空气组分变化对管道摩擦阻力特性的影响。本文以输送热湿氧直管道为对象,研究了大气压力、入口流速、湿氧浓度、管径、壁面粗糙度等因素对摩擦阻力的影响。结果表明:当管道仅送热时,5 km海拔下管道单位管长摩擦阻力约为常压下的62%;当热湿氧协同输送时,供氧浓度升高可使管道单位管长摩擦阻力增大约8.4%,而增大相对湿度对单位管长摩擦阻力影响较小,仅减小2%;单位管长摩擦阻力随入口流速的增大而增大,最大可增大约16倍;在壁面粗糙度较小时(K=0.03~0.20 mm),处于水力光滑区,阻力不随粗糙度的增大而变化;当进入混合摩擦区(K>0.40 mm)时,阻力开始随粗糙度的增大而增大,最大可增大约45%。最后给出了低压条件下热湿氧协同输送管道在不同工况下的摩擦阻力推荐值。

考虑流体作用的清管器翻越凹陷通过性研究

针对清管器在经过含凹陷管段时的通过性研究鲜有涉及。为此,以ø168管道清管器为研究对象,分别建立其翻越凹陷管道的三维准静态和流固耦合仿真模型并进行对比,进一步再分别基于驱动皮碗接触摩擦力学和清管器动力学特性参数的变化规律,对清管器翻越管道凹陷过程的通过性进行定量分析。研究结果表明:清管器驱动皮碗在通过管道凹陷段时,运行速度不稳定可能会降低相应管段检测的准确率;清管器翻越凹陷过程的速度变化敏感性随过盈量的增加而增大;为提高清管器对于含凹陷管道的通过性能,ø168清管器皮碗过盈量应小于4%,密封皮碗夹持率应在55%~65%之间,皮碗结构分界面相对位置应不小于2%。研究结论可为清管器优化设计及工程应用提供理论指导。

海上油田钻屑远距离传输摩阻计算研究

在缺少现场数据验证的情况下,对已开发的钻屑远距离传输技术在现场应用过程中发现的能耗较高、部分工况易发生堵塞等问题,针对摩阻开展浆体摩阻理论计算、OLGA软件计算、FLUENT单相流及多相流计算、混凝土摩阻计算、流变原理计算等5种计算并对不同计算结果进行对比分析,结果发现,浆体摩阻理论计算法与流变原理计算法的计算结果接近且数值最大;FLUENT单相流和多相流的计算结果接近且数值偏小;混凝土摩阻计算法在25℃时计算结果居中,OLGA软件计算在20℃及30℃时计算结果居中,该结论为钻屑远距离传输提供了理论支持与技术参考。

Prediction of M–A Constituents and Impact Toughness in Stir Zone of X80 Pipeline Steel Friction Stir Welds

This study explored a strategy for predicting the proportion of martensite–austenite(M–A)constituents and impact toughness of stir zone(SZ)on X80 pipeline steel joints welded by friction stir welding(FSW).It is found that the welding forces,including the traverse force(F_(x)),the lateral force(F_(y))and the plunge force(F_(z)),are the key variables related to the change of welding parameters and influence remarkably the characteristics of M–A constituents and impact toughness of SZ.The impact toughness of SZ is commonly lower than that of the base material due to the formation of lath bainite and coarsening of austenite.The characteristics of M–A constituents in SZ are sensitive to the variation of welding parameters and respond well to the change of welding forces.The proportion of small island M–A constituents increases with the decrease in rotational speed and the increase in Fz.The increase in the amount of island M–A constituents is beneficial to improve the impact toughness of SZ.Based on the above findings,a machine learning(ML)model for predicting the M–A constituents and impact toughness is constructed using the force features as the input data set.The force data-driven ML model can predict the M–A constituents and impact toughness precisely and exhibits higher accuracy than ML built with welding parameters.It is believed that the high accuracy is achieved because the force features include more details of FSW process,such as the heat generation,material flow,plastic deformation,and so on,which govern the microstructural evolution of SZ during FSW.

长输供热管道经济比摩阻的影响因素分析

为推动大面积清洁供暖,分布式燃煤、燃气锅炉房逐步被热电联产所取代。与热电联产配套的长输供热管道成为常见的一种供热设备。长输供热管道比摩阻的选取,在项目建设运行经济性上起到重要的作用。以呼和浩特市某一长输供热管道工程项目为例,采用单因素分析法,探究了不同工程参数对经济比摩阻的影响。计算结果显示该工程的实际最佳经济比摩阻为22.8 Pa/m。以实际工程为例,详细分析了经济比摩阻的优化过程,同时分析了各因素对经济比摩阻的影响程度,供热温差对经济比摩阻的影响最大,供热负荷次之,供热年限最小。因此在设计经济比摩阻时,应着重考虑工程项目的供热温差。

辅热搅拌摩擦焊X80钢接头组织演变与韧性

【目的】利用搅拌摩擦焊接技术可高质量完成钢铁材料的焊接,但昂贵的搅拌头磨损严重,焊前辅助加热是减轻搅拌头磨损的有效方式。【方法】文中利用控温辅热垫板将X80管线钢焊缝预热至150℃和270℃后采用搅拌摩擦焊接技术进行焊接,并对辅热搅拌摩擦焊接X80管线钢的接头温度变化、组织特征和冲击韧性展开详细研究。【结果】常温和150℃辅热下焊接接头组织相近,主要为板条贝氏体和少量粒状贝氏体,冲击韧性略微升高,270℃辅热下接头组织主要为粗大的粒状贝氏体,冲击韧性下降。在较低的辅热温度下,辅热软化材料使焊接主要热输入搅拌头摩擦产热降低,环境温度升高带来的影响较小,峰值温度降低进而晶粒细化;在较高的辅热温度下,环境温度升高的影响大于搅拌头产热减小的影响,所以峰值温度升高进而晶粒粗化。【结论】焊接时采用较低的辅热温度可获得良好的焊接效果。

中低浓度煤矸石浆液管道输送参数分析

煤矸石是进行煤矿采动空间注浆的重要材料,在粉碎制浆以后管道输送过程中,面临淤积堵管、摩阻损失以及管道承压安全性等问题,影响注浆效率。结合注浆实践,对中低浓度煤矸石浆液(质量浓度小于50%)的基本性质、流体类型以及管道输浆的流态、临界流速、摩阻损失和耐压能力等参数进行了系统研究。通过测试分析,发现中低浓度煤矸石浆液流体类型为牛顿体,管道输浆流态一般处于紊流的水力光滑区-混合摩擦区;演算了不同浆液浓度(体积浓度0.16~0.22、固相粒度(0.15~1.18mm))条件下临界流速(费祥俊公式与WASP公式对照),取值为1.2~1.9m/s(管道内径D=76mm);输浆摩阻损失本质上取决于比摩阻R(水力坡降),最敏感因子是管径(R∝D^(~5))。针对母杜柴登管道输浆实际,认为其堵管风险低,管道承压满足安全性要求,比摩阻理论值与实测值吻合;同时,鉴于目前比摩阻偏高,建议调整管道内径,由当前76mm提升至88mm及以上,比摩阻可下降一半以上。研究可用于指导中低浓度煤矸石浆液管道输送设计,为管道输浆的安全与高效提供理论依据。