Crack-opening-area analyses for circumferential through-wall cracks in pipes—Part II: model validations

This is the second paper in a series of three papers generated from a recent study on crack-opening-area analysis of circumferentially cracked pipes for leak-before-break applications. This paper (Part II—Model Validations) focuses on the evaluation of current analytical models, discussed in the first paper (Part I—Analytical Models) as well as finite element models for conducting crack-opening-area analyses of pipes with circumferential through-wall cracks. The evaluation was performed by direct comparisons of the predicted results with the test data from full-scale pipe fracture experiments. The results from 25 full-scale pipe fracture experiments, conducted in the Degraded Piping Program, the International Piping Integrity Research Group Program and the Short Cracks in Piping and Piping Welds Program, were used to verify the analytical models. The main objective was the evaluation of engineering analysis procedures (estimation methods) as well as the ability of the finite element method to predict crack-opening displacements and shapes in pipes with circumferential through-wall cracks. Statistics were developed to quantify the accuracy of the current predictive models. A wide variety of pipe fracture tests involving cracks in base metals, weld metals and bimetallic weld metals were analyzed. Pipes containing both simple through-wall cracks and complex cracks were evaluated.     

Crack-opening-area analyses for circumferential through-wall cracks in pipes—Part I: analytical models

Leak-before-break (LBB) analyses for circumferentially cracked pipes are currently being conducted in the nuclear industry to justify elimination of pipe whip restraints and jet impingement shields which are present because of the expected dynamic effects from pipe rupture. The application of the LBB methodology requires calculation of leak rates. The leak rates depend on the crack-opening area of the through-wall crack in the pipe. In addition to LBB analyses which assume a hypothetical flaw size, there is also interest in the integrity of actual leaking cracks corresponding to current leakage detection requirements in NRC Regulatory Guide 1.45, or for assessing temporary repair of Class 2 and 3 pipes that have leaks, as are being evaluated in ASME Section XI. The objectives of this study were to review, evaluate, and refine current predictive models for performing crack-opening-area analyses of circumferentially cracked pipes. A three-phase effort was undertaken to accomplish this goal. It is described here in a series of three papers generated from this study. In this first paper (Part I — Analytical models), a comprehensive review is performed to determine the current state-of-the-art in predicting crack-opening displacements for circumferentially cracked pipes under pure bending, pure tension, and combined bending and tension loads. Henceforth, new and improved analytical models and some preliminary results are presented for cases where current methods are inadequate or there are no available methods. Also, based on this review, a number of appropriate predictive models are identified for a systematic evaluation of their accuracy. The results of their evaluations will be presented and examined in the forthcoming companion papers (Part II — Model validations [1] and Part III — Off-center cracks, restraint of bending, thickness transition, and weld residual stresses) [2].     

KI–T estimation for embedded flaws in pipes – Part II: Circumferentially oriented cracks

This paper, in parallel to the investigation on axially embedded cracks reported in the companion paper, presents a numerical study on the linear-elastic K_I and T-stress values over the front of elliptical cracks circumferentially embedded in the wall of a pipe/cylindrical structure, under a uniform pressure applied on the inner surface of the pipe. The numerical procedure employs the interaction-integral approach to compute the linear-elastic stress-intensity factor (SIF) K_I and T-stress values for embedded cracks with practical sizes at different locations in the wall of the pipe. The parametric study covers a wide range of geometric parameters for embedded cracks in the pipe, including: the wall thickness to the inner radius ratio (t/R_i), the crack depth over the wall thickness ratio (a/t), the crack aspect ratio (a/c) and the ratio of the distance from the centerline of the crack to the outer surface of the pipe over the pipe wall thickness (e_M/t). The parametric investigation identifies a significant effect of the remaining ligament length on both the T-stress and K_I values at the crack-front location (denoted by point O) nearest to the outer surface of the pipe and at the crack-front location (denoted by point I) nearest to the inner surface of the pipe. The numerical investigation establishes the database to derive approximate functions from a nonlinear curve-fitting procedure to predict the T-stress and K_I values at three critical front locations of the circumferentially embedded crack in a pipe: points O, I and M. The proposed T-stress and K_I functions utilize a combined second-order polynomial and a power-law expression, which presents a close agreement with the T-stress and K_I values computed from the very detailed finite element models. The comparison between the circumferentially embedded crack and the axially embedded crack indicates that both the T-stress and K_I values at crack-front points O and I in a circumferential crack equal approximately 50% the T-stress and K_I values at the corresponding front locations in an axial crack with the same crack depth ratio, the same crack aspect ratio and the same pipe wall thickness to the inner radius ratio.     

普京,天然气,乌克兰

由于乌克兰本身地缘政治上的敏感性、历史文化宗教形成的国家认同的分裂,俄罗斯对于乌克兰难以割舍骨肉关系和错综复杂的利益和乌克兰西部绝不放弃的＂欧洲之梦＂的追求。乌克兰的局势急速变化,既血腥又富有戏剧性令人目不暇接。季莫申科和亚努科维奇在政治上是一对老冤家。季莫申科是十年前的乌克兰＂橙色革命＂（类似于这一次的街头动乱,但没有这一次死伤700多人那么血腥）的英雄,在此后2005年的选举中亲西方的尤先科胜出,而亲俄罗斯的亚努科维奇则以微弱的劣势落败。     

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<正>哥本哈根气候大会已经在喧嚣中落幕了,虽然本次会议具体成果了了,但在这场"盛宴"中聚集而发的应对气候变化的危机意识正在全世界扩散。大力发展新能源,积极应对气候变化,成为一种新思想。中国是一个先知先觉的国家。为履行减排承诺,同时契合国内保增长、扩内需、调结构,加快培育新的经济增长点的需要,新能源正在成为引领中国经济增长和可持续发展的新引擎。     

热,动,冷联产节能,节电的浅析

热、动、冷联产是利用能源的有效手段之一。东风制药厂的实践证明了热、动、冷联产不仅技术可行,而且具有明显的经济效益和节能节电效果,从而促进了能源利用结构的改变。     

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供、管、用、节四统一的能源管理体制哈尔滨制氧机厂张东学１新形势下能源管理必须加强在改革的年代，在搞市场经济的大气候下，在搞活企业、扩大企业的经营自主权的时候，企业的能源管理工作该如何搞，企业的能源管理人员和管理机构该如何设置，企业的能源管理工作是该加...     

高硅铝合金中Si,Fe,Cu,Mn快速测定

在高硅铝合金试样的溶解中,最常用的方法是氢氧化钠水溶溶样法。这种方法手续繁冗、时间较长。影响了生产的进度: 我们经过反复试验,找出了一种新方法——硝酸、氢氧酸溶样法。该方法操作简单,易于掌握,分析一个样品约需二十分钟。1 方法要点 试样用硝酸和氢氟酸溶解,用尿素来分解氮化物,加入过量的硼酸使过量的氢氟酸转化为氟硼酸,以免侵蚀玻璃,影响测定。     

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目前我国小型锅炉通用的引风机,其转速为2900转/分者较多,这种固定高转速,靠风门调整风量的运行方式,确实是弊多利少,很值得研讨。首先是耗电量太高。大家知道轴功率是与转速的三次方成正比,也就是转速增加1/8,而功率就增加1/2,以一台2吨/时锅炉为例,理论计算引风机轴功率只有1—2KW,而实际则