Strength differential effect and influence of strength criterion on burst pressure of thin-walled pipelines

In the framework of the finite deformation theory, the plastic collapse analysis of thin-walled pipes subjected to the internal pressure is conducted on the basis of the unified strength criterion （USC）. An analytical solution of the burst pressure for pipes with capped ends is derived, which includes the strength differential effect and takes the influence of strength criterion on the burst pressure into account. In addition, a USC- based analytical solution of the burst pressure for end-opened pipes under the internal pressure is obtained. By discussion, it is found that for the end-capped pipes, the influence of different yield criteria and the strength differential effect on the burst pressure are significant, while for the end-opened pipes, the burst pressure is independent of the specific form of the strength criterion and strength difference in tension and compression.

Manufacture of Extra-Thin Wall Steel Pipe by LD Cluster Mill

The manufacture of extra-thin wall steel pipe by LD cluster mill through suitable tool design and process design was described in detail.The defects in steel pipe produced during rolling were analysed and some measures were taken to improve them.Five kinds of extra-thin wall steel pipes have been produced successfully,which are as follows:φ18.5mm×0.25 mm,φ15.5mm×0.25 mm,φ11.4mm×0.2mm,φ14- 24mm×0.12 mm,φ21.74mm×0.12 mm.

Development of ToSPACE for Pipe Wall Thinning Management in Nuclear Power Plants

A number of piping components in the secondary system of nuclear power plants are exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), cavitation, flashing, SPE (Solid Particle Erosion), LDIE (Liquid Droplet Impingement Erosion), etc. Those mechanisms may lead to thinning, leak, or rupture of the components. Due to the pipe ruptures caused by wall thinning in Surry unit 2 of USA in 1986 and in Mihama unit 3 of Japan in 1994, the pipe wall thinning management has emerged as one of the most important issues in nuclear power plants. To manage the pipe wall thinning in the secondary system, Korea has used a foreign program since 1996. As using the foreign country’s program for long term, it was necessary to improve from the perspective of the users. Accordingly, KEPCO-E & C has started to develop the 3D-based pipe wall thinning management program (ToSPACE, Total Solution for Piping And Component Engineering management) from eight years ago, and the development was successful. This paper describes the major functions included in ToSPACE program, such as 3D-based DB (Database) buildup, development of FAC and erosion evaluation theories, UT (Ultra-sonic Test) data reliability analysis, field connection with 3D, automatic establishment of long-term inspection plan, etc. ToSPACE program was developed to allow site engineers performing the selection of inspection quantity at each refueling outage, UT data reliability analysis, UT evaluation, determination of next inspection timing, identification of the inspecting and replacing components in 3D drawings, etc., to access easily.

Development of New Methodology for Distinguishing Local Pipe Wall Thinning in Nuclear Power Plants

To manage the wall thinning of carbon steel piping in nuclear power plants, the utility of Korea has performed thickness inspection for some quantity of pipe components during every refueling outage and determined whether repair or replacement after evaluating UT data. Generally used UT thickness data evaluation methods are Band, Blanket, and PTP (Point to Point) methods. Those may not desirable to identify wall thinning on local area caused by erosion. This is because the space between inspecting points of those methods are wide for covering full surface being inspected components. When the evaluation methods are applied to a certain pipe component, unnecessary re-inspection may also be generated even though wall thinning of components does not progress. In those cases, economical loss caused by repeated inspection and problems of maintaining the pipe integrity followed by decreasing the number of newly inspected components may be generated. EPRI (Electric Power Research Institute in USA) has suggested several statistical methods such as FRIEDMAN test method, ANOVA (Analysis of Variance) method, Monte Carlo method, and TPM (Total Point Method) to distinguish whether multiple inspecting components have been thinned or not. This paper presents the NAM (Near Area of Minimum) method developed by KEPCO-E & C for distinguishing whether multiple inspecting components have been thinned or not. In addition, this paper presents the analysis results for multiple inspecting ones over three times based on the NAM method compared with the other methods suggested by EPRI.

A Study on the Cause Analysis for the Wall Thinning and Leakage in Small Bore Piping Downstream of Orifice

A number of components installed in the secondary system of nuclear power plants are exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), Cavitation, Flashing, and LDIE (Liquid Droplet Impingement Erosion). Those aging mechanisms can lead to thinning of the components. In April 2013, one inch small bore piping branched from the main steam line experienced leakage resulting from wall thinning in a 1000 MWe Korean PWR nuclear power plant. During the normal operation, extracted steam from the main steam line goes to condenser through the small bore piping. The leak occurred in the downstream of an orifice. A control valve with vertical flow path was placed in front of the orifice. This paper deals with UT thickness data, SEM images, and numerical simulation results in order to analyze the extent of damage and the cause of leakage in the small bore piping. As a result, it is concluded that the main cause of the small bore pipe wall thinning is liquid droplet impingement erosion. Moreover, it is observed that the leak occurred at the reattachment point of the vortex flow in the downstream side of the orifice.

冲击力下薄壁内衬复合管界面黏结强度效应分析

【目的】研究薄壁内衬复合管在受冲击力作用下的界面黏结强度对层间剥离屈曲的影响。【方法】建立薄壁内衬复合管在弹性阶段的非线性分析模型,对薄壁内衬复合管材模态试验与分析模型的分析结果进行对比,验证有限元分析模型可靠性。通过改变衬层与原基层管壁间的界面黏结强度,研究复合管在冲击力下的动态特征。【结果】研究结果表明,当冲击荷载较小、管道变形处于弹性阶段时,薄壁内衬复合管的损伤大都集中在层间界面处。界面黏结强度对层间剥离屈曲有较大的影响,随着层间界面黏结强度的增加,外基层管与内衬层的最大等效应力差值减少。此外,外基层管和内衬层的变形协调性能力随着黏结强度增加而增大,径向层间位移减小,增加了复合管的整体性和连续性。【结论】研究结果可为薄壁内衬修复管道设计方法及层间界面效应分析提供参考。

基于熔体发泡法泡沫铝填充管力学性能研究

采用熔体发泡法制备闭孔泡沫铝,研究泡沫铝填充密度对铝合金薄壁管的压缩及吸能性能提升作用,对比提升效果,确定最佳密度参数;并在最佳密度的基础上设计三类不同截面的复合结构,研究填充管的截面结构对压缩性能及吸能性能的影响,确定最佳结构参数。采用万能试验机进行准静态压缩试验,并利用有限元模拟结果与试验结果相对比,验证数据准确性。结果表明:填充梯度泡沫铝会增加薄壁管的力学性能,如屈服强度、平均压溃载荷和吸能性能,降低曲线波动性,密度为0.480 5 g/cm3的闭孔泡沫铝表现出最优结果;二次试验中,复合结构能进一步提升薄壁管的力学性能,其中外方管内圆管的复合结构具有最高的屈服强度、平均压溃载荷以及吸能效果。

TA1高频感应焊接头和基体在NaCl溶液中的电化学腐蚀行为

高频感应焊TA1薄壁管的焊接接头和基体在微观结构方面存在差异,电化学腐蚀行为往往是不同的。采用动电位极化技术和电化学阻抗谱(EIS),分析了TA1基体和焊接接头在不同浓度NaCl溶液中的电化学腐蚀行为。实验结果表明,随着氯离子浓度的增加,TA1基体和焊接接头的腐蚀电位呈负偏移,极化电阻逐渐减小,腐蚀速率增大。相比基体,焊接接头的腐蚀电位更高、极化电阻更大、腐蚀速率更低,表明耐腐蚀性能更好。实验可为高频感应焊TA1薄壁管在海水环境中的实际应用提供一定的理论依据。

显微组织对薄壁X65M管线钢落锤试验性能的影响

对厚度为6~9.5 mm的薄壁管线钢低温落锤性能容易出现波动的问题,通过轧制对比实验分析,探究了薄规格X65M管线钢低温落锤性能的控制工艺的影响因素。通过不同低温落锤试验结果样品的显微组织分析和数值化结构研究,发现钢中多边形铁素体晶粒尺寸大小和钢板心部片条状分布的M/A组织对低温落锤性能影响显著。当钢中面积在200μm^(2)以上的晶粒数量较多,平均面积超过260μm^(2),或者M/A组织占比>6%时,钢板低温落锤性能明显恶化。通过连铸过热度控制以及控轧控冷工艺优化,有效细化了晶粒尺寸并减少了M/A组织的形成,实现6~9.5 mm薄壁钢板批量稳定生产8万t以上,可以满足-30℃低温落锤要求,对薄规格管线钢产品的研发和生产具有重要意义。

钛合金薄壁弯管熔模铸造工艺研究

通过对钛合金薄壁弯管的结构进行分析,利用三维软件UG对其进行几何建模,采用ProCAST软件对顶注式、雨淋式和底注式三种浇注方案熔模铸造工艺进行了数值模拟,研究对比其在三种浇注方案下铸件的充型及可能出现缺陷的情况。得出在底注式浇注工艺方案下铸件的整体质量最优的结论,并对其进行了试验验证,获得无疏松和夹杂等缺陷的优质铸件。

泉州海湾大道软土地基处治方案研究

通过泉州海湾大道工程案例,分析项目地质情况、软基路段分布情况、土体参数,从常用的浅层、中层、深层软基处理方法中初选软基处理方案。通过地基处理计算、软基段边坡稳定分析及沉降分析等方法充分比选各方案的技术可行性。在技术可行的基础上,通过施工可行性及工程投资等方面对各方案进行综合比选,选出适应本项目不同深度的最优方案。同时,对存在软基的特殊断面位置进行特殊处理。在控制总沉降的同时,过渡特殊位置的差异沉降,使设计方案能够达到良好的处治效果,满足设计使用要求。

封闭式自熔焊工艺参数对薄壁不锈钢管焊缝成形的影响

采用封闭式机头对12 mm×2 mm的不锈钢洁净管进行全机械化的钨极氩弧焊自熔焊,研究了不同焊接工艺参数对薄壁不锈钢管焊缝成形的影响。通过拉伸、弯曲、无损检测、宏观金相试验验证了薄壁不锈钢管的接头力学性能与组织特征,针对不同焊接位置制定了焊接工艺参数。结果表明,基/峰值电流、占空比、钨极高度和保护气流量是影响焊缝成形的主要因素。回转焊接时,当焊接位置由立向上改变至立向下焊接时,需加大基/峰值电流,以避免焊缝出现外表面塌陷和内表面凹陷。焊接接头微观组织为奥氏体+铁素体,接头抗拉强度接近于母材,弯曲试验中无裂纹产生,探伤试验无气孔、裂纹等缺陷产生,各项性能均满足相关标准要求。

钢管柱外包薄壁装饰清水混凝土施工技术

装饰清水混凝土利用混凝土原色,体现建筑物的品质和格调,沉稳大方,但在空间较大的框架结构的公共建筑中,为保障最大限度地利用空间,柱网尺寸较大,很难实现清水混凝土效果,因此,相关问题催生出了在钢管圆柱外包薄壁清水混凝土的施工做法。文中采用钢管柱外侧设置栓钉、混凝土内配置抗裂钢筋的形式,使混凝土与钢结构完美贴合,同时避免了混凝土裂纹的产生,提升了建筑整体格局,产生了良好的社会效益。

某滑梯喷嘴组件加工工艺研究

针对应急撤离滑梯喷嘴组件采用常规手工钨极氩弧焊易存在变形、烧穿、焊瘤缺陷等问题,通过对喷嘴组件加工工艺分析研究,采用多种加工工艺进行试验筛选,开发了高频脉冲弧焊和真空钎焊等方法,保证了喷嘴组件焊接质量,解决了型号研制的加工瓶颈。同时,通过对几种加工方法进行对比分析,确定了不同产量需求下的加工工艺措施,为滑梯喷嘴组件的高质量制造提供了解决方案。

薄壁大口径PE管材弯曲有限元分析

对加入钢丝网的薄壁大口径PE管,运用有限元法分析其在弯曲过程中出现的内侧失稳起皱、横截面畸变等问题。采用理论分析、数值模拟和实验研究相结合的方法,对薄壁大口径PE管材弯曲进行有限元分析,在分析PE管材弯曲机理和失效形式的基础上,通过实例得出有钢丝网PE管材的弯曲所受应力主要由钢丝网承载,结合弯曲测试,发现加入钢丝网可有效增强管材的刚度、抑制管材弯曲时内侧失稳起皱和横截面畸变等现象的发生,有限元数值模拟结果与实验结果较为一致,说明有限元数值模拟分析的可靠性。

薄壁异形方半管零件充液成形工艺研究

目的为解决薄壁异形方半管零件成形过程中易起皱、破裂、形状冻结性不佳的难题,引入充液成形工艺。为进一步掌握不同工艺参数对零件成形性能的影响,对薄壁异形方半管零件的充液成形过程进行研究。方法以液室压力、压边力、拉深深度、摩擦因数等工艺参数为影响因子,进行正交试验,通过分析不同工艺参数下零件最大减薄率、贴模度、最大回弹量的变化规律,掌握充液成形工艺中不同工艺参数对零件起皱、破裂、形状冻结性的影响。结果零件的破裂和起皱现象受液室压力影响显著,而零件的形状冻结性则受压边力影响较大。在数值模拟中,优化后的最优工艺参数如下:液室压力为15 MPa,压边力为120 kN,拉深深度为110 mm,摩擦因数为0.15。经模拟验证,与优化前相比,在该工艺参数下得到的结果更优,零件最大减薄率降低到11.5%、贴模度提高了0.212 mm、最大回弹量降低了1.955 mm。结论通过模拟分析和现场试验验证可知,采用正交试验得到的最优工艺参数可以完成半管零件的成形,合理的工艺参数能有效抑制零件起皱、破裂、形状冻结性不佳的现象,从而提高半管零件的成形性能。

薄壁内衬复合管衬层径向临界脱层屈曲分析

薄壁内衬复合管受周围环境影响处于复杂受力状态,其衬层受径向力的作用易产生脱层剥离现象,导致内衬层脱层剥离屈曲失效。基于经典的圆柱壳理论,建立薄壁内衬复合管径向力作用下的壳体动力控制方程,推导得到满足复合管径向压力达到临界值时的计算公式和内衬层最小厚度的计算方法,为后续研究应用提供理论基础。利用双线性内聚力关系建立数值分析模型,考虑内衬层厚度对薄壁内衬复合管径向屈曲的影响,将理论结果与数值分析结果对比分析。结合相关算例和试验结果与本文数学分析模型结果对比,进一步验证数学模型的准确性和可靠性。结果表明,复合管径向临界屈曲的数值分析结果、算例和试验结果与理论结果对比,最大误差均在实际应用允许范围内。研究方法可以用于分析径向力下复合管道内衬层的脱层屈曲问题,为进一步研究非开挖管道的内衬修复技术提供理论依据。

TIG电弧辅助激光焊TA2直缝薄壁焊管的组织性能研究

为解决纯钛TA2直缝管在钨极氩弧焊(TIG)高速焊接时出现的咬边、驼峰成形缺陷等问题,提出了TIG在前的电弧辅助激光焊工艺。针对φ19 mm×0.7 mm的TA2直缝焊管,对单TIG自熔焊和TIG电弧辅助激光焊采用不同的热源模式,采用Abaqus软件建立焊接有限元模型,对比分析了这两种焊接过程中的温度循环曲线和焊后残余应力,并对得试验到的TA2薄壁焊管进行了显微组织分析及性能测试。结果表明:模拟所得的两种接头的焊缝轮廓尺寸与实际接头轮廓相近,TIG电弧辅助激光焊接时焊缝中心温度、焊后Von Mises应力低于TIG焊接的。与TIG焊相比,TIG电弧辅助激光焊的焊缝中心及热影响区的显微组织更小,抗拉强度、伸长率基本持平,屈服强度更高。在获得良好焊缝成形的条件下,采用TIG电弧在前的电弧辅助激光焊方法可以获得较高的焊缝质量。

高频感应焊接铝合金薄壁管加热过程数值模拟

以厚度0.26 mm的散热器用铝合金高频焊管为研究对象,通过有限元软件COMSOL Multiphysics对不同参数下焊管加热过程进行模拟,分析了不同焊接参数和线圈与焊管的同心度对焊接质量的影响。结果表明,焊接频率为365 kHz、V形角为6°时,铝合金薄壁管会被全壁厚加热,能够获得较好的焊接质量;较高的频率和较小的V形角可以提高加热效率,但较高的频率会使焊管产生“漏焊”,较小的V形角会导致焊管形成“砂眼”等焊接缺陷;在其它焊接条件一定时,线圈与管材的横向偏差,会改变加热效率,纵向偏差对加热无明显影响。

基于悬臂结构薄壁变截面钢管杆静载变形分析

基于材料力学基本公式推导了变截面钢管杆在静载荷作用下挠度与转角系列计算公式,针对多个不同参数的变截面杆,采用推出公式、有限元法进行计算,两种计算结果吻合很好,验证了公式的正确性。利用推出的公式,定量分析了单位集中力载荷下杆几何参数对挠度的影响。结果表明,推出的公式正确、简洁,为薄壁截面钢管杆体设计提供了理论参考。