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/locate/ndteintNDT&E International 37 (2004) 111118Rail flaw detection: overview and needs for future developmentsRobin Clark*Sperry Rail, Inc., Danbury, CT, USAReceived 10 February 2003; accepted 20 June 2003AbstractRail Flaw Detection has an important part to play in ensuring the safety of the worlds railroads. Recent accidents caused by broken rails have focused attention on the technologies that enable the detection of flaws in railroad rail. This paper reviews the technologies currently employed, along with examples of recent field applications. Some of the ongoing advancements and options for the future are also discussed. q 2003 Elsevier Ltd. All rights reserved.Keywords: Rail inspection; Ultrasonic testing; Electromagnetic testing; Fatigue defects; Roller searchunit1. IntroductionRail Flaw Detection (RFD) is very much in the spotlight at present. If we look at rail testing today we see a very different picture than that presented five years ago. This sector of the industry has undergone many changes in all parts of the world. The Hatfield accident of October 2000 has played a major role in this. That is a terrible statement to make, but how often does that happen? It took a tragedy for people to understand the real value of rail testing.This paper will discuss the rail testing industry from the early days to what we see today. The progress of the work being performed for Railtrack (now Network Rail) will be presented along with some thoughts for the future.2. Rail testing: from the early daysRail Testing really became a serious entity in the late 1920s when Dr Elmer Sperry, driven by the needs of the US railroad industry, developed the induction method for testing railroad rail 1. Over the years this technique was refined in the US and then in the 1950s ultrasonic testing emerged and started to become the mainstay of rail testing globally. This is still true today, even as more companies have entered the rail-testing arena. Some exceptions toE-mail address: r.p.clarkaston.ac.uk (R. Clark).* Present address: School of Engineering and Applied Science, Aston University, Birmingham, UK.this have been Sperry in the US, where the idea of complementary testing techniques has been developed, and in Russia where there are still many cars that use the magnetic induction technique only. The report prepared by the Transportation Technology Center, Inc. (TTCI) for the Office of the Rail Regulator in October 2000 provides much useful background on the global rail testing industry today 2.The basic physical principles of the two majortechniques are as follows. In the case of ultrasonics, we are sending a beam of ultrasonic energy into the rail and looking for the return of reflected or scattered energy using a collection of transducers. The amplitude of any reflections together with when they occur in time can tell us about the integrity of the rail. Since defects are not totally predictable, we send in energy at several differentincident angles in order to ensure that we maximize our chances of finding any detrimental features 3. The refracted angles generally used are 0, 37 or 45 and 708. Inaddition, transducers are also positionedtolookacrossthe rail headfor longitudinaldefects such asvertical split heads and shear defects (Fig. 1a). The induction technique is based on the physics of electromag- netic induction. An high amperage current is injected into the rail via brushes that make contact with the rail head. In effect the rail becomes part of an electrical circuit. If the current encounters a defect, the current will travel around the defect (Fig. 1b). This distortion of the current flow is detected via a block of sensors that detect disturbances of the magnetic field associated with the current flow 4.0963-8695/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.ndteint.2003.06.002R. Clark / NDT&E International 37 (2004) 111118112Fig. 1. (a) Ultrasonic roller search unit; (b) inductionprinciples.3. Response to an accident115On March 18, 2001, the westbound California Zephyr, an Amtrak service from Chicago to the San Francisco Bay Area derailed in rural Iowa. The causea broken rail. One person was killed and 96 were injured. A detector car had been over the track a few weeks before the accident. A defect had been found and the railroad concerned had replaced the rail as determined by the Federal Railroad Administration (FRA) regulations. The problem was that the replacement rail used also had a defect in it. Within one week from the accident, the US rail testing companies had been mobilized to provide a manual testing capability to test the replacement rail on every subdivision of the railroad concerned. This incident was the first major use of manual rail testing on the North American freight railroads. The initial report related to this accident was published by the National Transportation Safety Board (NTSB) in March 2002 5.Following the preparation of a procedure 6 and adequate test trials on a 0.4 km test track in Danbury, CT, up to six Roller Search Unit (RSU) based portable rail detectors or walking sticks were put to work by Sperry. Other contractors contributed equipment and personnel as well. Subsequently, a more controlled schedule has been developed in co-operation with the railroad concerned and they now have a number of rail testersworkingyear round on a regional basis. The Portable Rail Detector (PRD) is shown in Fig. 2. The PRD makes use of thesame RSU as that employed on the test cars operating across North America. As the PRD is moved across therail surface, nine transducers operating at 2.25 MHz are simultaneously inspecting the volume of the rail.Toensure adequate coupling, a water tank isfittedtothe PRD and a copper tube directs the water flow 1 cm or soFig. 2. Portable rail detector (North America).in front of the moving RSU. Although water usage is not excessive, the tank may need filling once or twice in a typical 8-h day. The display is in the form of an A-scan on a conventional ultrasonic test instrument. The NTSB report recommended that the replacement rail testing should continue. Recommendation R-02-5 to the FRA states railroads should conduct ultrasonic or other appropriate inspections to ensure that rail used to replace defective segments of existing rail is free from internal defects. An extension of this process would be to incorporate ultrasonic rail testing stations at rail recycling plants similar to those employed at new rail production plants.The response to Hatfield, although it evolved over a longer time period, saw the development of a PRD for the UK rail system (Fig. 3). This unit has recently started to become a more common feature on the UK rail network. Ergonomically, the unit is more attractive and lighter than the first model. The electronics package has been developed to enable flexibility and use with different ultrasonic testing instruments. The main unchanged feature though, is that of the RSU. The next logical stepR. Clark / NDT&E International 37 (2004) 111118113Fig. 3. Portable rail detector (Europe).is to develop a method of data storage that allows a complete record of the testing work performed to be available for post test review and archive. At present the testing record is a filled out report based on the technicians interpretation of what is seen on the instrument screen and visually on the rail.The RSU is a more appropriate front end unit than the alternative slider probe arrangement, whether considering manual inspection or high speed inspection. The main benefits are the robustness, ability to conform to the rail geometry and most importantly a reliable and efficient transfer of energy into the rail being inspected. These features have encouraged the majority of the ultrasonic rail testing companies around the world to employ this technology. In the PRD case, the RSU houses nine ultrasonic transducers at three different angles, the aim being to fill the rail with as much energy as possible at the optimum incident angles.The unit has been developed with Railtracks support to particularly address the detection of gauge corner cracking (rolling contact fatigue) that contributed to the Hatfield accident 7.4. Existing technologyFig. 4 shows the most recent technology to be deployed on the US railroads. The system brings together the complementary ultrasonic and induction testing techniques on a hi-rail platform. This provides the railroad with a high quality test and increased flexibility of deployment. In the past, induction has only really been possible on a railbound vehicle because of the size of the plant needed to generate the high currents injected into the rails. With developments in power supply technology, the production of a hi-rail based vehicle has proven feasible 8. To date, seven of these cars have been built and released since January 2001. They operate at speeds of up to 32 km/h, although with the stop and confirm testing requirements in North America, there is always an operational trade-off between going forward faster and the risk of longer reversing moves when a confirmation is required.In addition to the above mentioned features, the vehicles have also seen the transition from a strip chart based display to a B-scan based display. The B-scan is a more intuitive representation of the ultrasonic interactions within the rail and is easier for the operator to interpret. Within the B-scan based system, algorithms work to reduce the data presented for interpretation. Data overload for the operator can be a significant problem with rail testing, but on the flip side, mathematics is not always good at dealing with the unusual features encountered on the railroad. There has to be a balance. Gates are employed throughout the rail cross- section and the data is analyzed based on algorithms developed from both lab and field tests, and many years of testing experience. Both the ultrasonic and induction data are presented on the same display in the correct alignment. Much of the work done in the US is focused on the heavy haul railroad environment. Although the train speeds are less, the rail conditions encountered on the close to 200,000 miles of track that make up the North American railroads are much more severe than on most of the passenger biased railroads of Europe. Thoughts on the challenges to the rail testing engineerhavepreviously beenpresentedandtheyFig. 4. Hi-rail ultrasonic/induction vehicle.R. Clark / NDT&E International 37 (2004) 111118114continue to form the driving force for the development work that is performed all over the world 9. The International Heavy Haul Association (IHHA) has acknowledged the demanding environment of the heavy haul railroads and they have collected together much of that wisdom in a book published in 2001 and launched at the IHHA meeting in Brisbane, Australia in that year 10.The International Railway Union (UIC) also has an ongoing initiative that is looking at rail testing globally under the title Rail Defect Management. A few documents have been released so far 11,12 and a good overview was given by Lundgren et al. 13 at the Brisbane IHHA meeting. The reason for mentioning these initiatives is to highlight the global interest in rail testing today and to start to set the scene for the discussion of new technology that follows.In North America, by far the most common and problematical defects are transverse defects, weld defects and vertical split head defects. These defects constitute around 55% of the yearly detected defects by Sperry. They also constitute 75% of the notified failures received. A notified failure is an instance where a rail has broken and the company has been informed of the occurrence. In many cases an investigation will be performed to try and identify the cause of the failure. The possible causes are manyeach situation presenting a source of further learning. On many occasions the defect may be classified as undetectable at the time of test because it may have been too small or the surface condition of the rail may have presented additional noise that may have masked the defect. Also, the cause of the broken rail may have been something such as a wheel flat. In these instances a latent defect likely to be found at the next test may become a catastrophe when subjected to the impact of a train wheel with flats.The hi-rail ultrasonic/induction equipment has been carefully monitored as it has entered service. To date the positives have far outweighed the negatives. Being more sophisticated in its totality, the early days saw many teething troubles from generators to test carriage manipu- lation. The engineers had many challenges presented to them. Now, though the problems seem to be bottoming out as the trucks and the design have stabilized. One railroad has analyzed the performance of the vehicles as part of a Six Sigma Quality Project. The cars have been put on the demanding coal territory of Appalachiamountains, curves, severely worn rail and very variable weather conditions. The analysis has shown that since the introduc- tion of the new vehicles, the instances of rail head defect rail failures have dropped significantly (an over 50% reduction). The test vehicles have been finding more defects and at an earlier point in the defects growth cycle. This helps to emphasize the power of the complementary techniques on a tough to test territory 14. The system has also resulted in fewer stops to do manual verification and a 60% increase in testing speed in most cases. An analysis of the defects detected on one of the main North American freightrailroads over the course of a year showed that 20% of the defects marked indicated only with induction. This helps reinforce the value of complementary techniques.5. Work for Railtrack (now Network Rail)In the latter half of 2001, Sperry was awarded a contract by Railtrack to build and operate an ultrasonic test vehicle on the UK rail network. To that end, 2002 saw much activity aimed at achieving that target. The instrumented carriage (UTU2) was fitted out in Derby in the UK and commis- sioned at the Old Dalby test track in late 2002 (Fig. 5).The ultrasonic test system build and mechanical design and build work for the deployment of the RSUs were performed in the US. The test system is B-scan based and much the same as that used on the hi-rail ultrasonic/induc- tion cars. The mechanical design proved to be a challenge. Conscious of the need to comply with the vehicle acceptance rules in the UK and the tighter clearance demands, the design has been developed from that used on a high-speed vehicle already operating in Europe, most specifically in Sweden, Norway and Germany. The RSU housing has been redesigned to meet the clearance requirements. A model of one quadrant of the RSU deployment arrangement mounted under the vehicle is shown in Fig. 6.The B-scan display is similar to that shown in Fig. 7 without the windows for the induction data. These windows were removed and the ultrasonic display was re-configured to make use of the available space. For ease of training and use the software has been developed in a Windows environment. The vertical dimension of each window relates to the vertical position of the indication source in the rail. The horizontal dimension of each window relates to the longitudinal position of the indication in the rail.The third part of the vehicle work has been the opportunity to design a new calibration rail for Railtrack. Drawing on experience and the requirements/suggestions of other railroads, a new design has been produced for Railtrack. The rails have been installed in the Old DalbyFig. 5. Network Rail test vehicle.R. Clark / NDT&E International 37 (2004) 111118115Fig. 6. Mechanical arrangement on UTU2.test track and have been used in the commissioning work. It is hoped that the design will be adopted by other railroads such that the rail testing community can work towards some form of international standard.The next step in the UK will be the introduction of a new all ultrasonic hi-rail vehicle similar to one recently developed for use in Germany. This vehicle uses the same B-scan based test system and a carriage derived from that used for the hi-rail ultrasonic/induction vehicle in the USA (Fig. 8). Again the stringent vehicle acceptance criteria have dictated the design steps taken. This carriage has room for both ultrasonic RSUs and eddy current sensors.6. Technology developmentRail testing has never seen large amounts of develop- ment funding. It seems that it is only when an accident occurs that money becomes more readily available. When this occurs though, it is perhaps even more important that we demand careful use of that money and co-ordinateFig. 7. B-Scan display.Fig. 8. European ultrasonic hi-rail vehicle.the development efforts in a coherent fashion. We often jump on the new is obviously better bandwagon without thinking. Yes it is good to invite new ideas and people to the table, but we must always be careful that they do truly have something to offer. Also, there is often a tendency to forget the people who have made rail testing their life. These people work for companies that have invested time and money in moving the industry forward when the need for improvements has appeared less of a priority. Different countries have different approaches to development, but the accident scenario I have just described seems commonin the majority of cases.The majority of the technology development in the US is currently performed by the rail testing service suppliers. The railroad challenge has recently received a higher profile in the wider arena 15,16, but many of the new investigators are in the early stages of projects. One of the main problems that few researchers grasp at the outset is how the industry works. The variables that have to be dealt with are more demanding than they realize and the path from the lab to the field is difficult. Rail does not particularly lend itself to being used in exhaustive trials ahead of the service implementation, so developments often reach the field with much work still to be done. The Rail Defect Test Facility (RDTF) at the TTCI in Pueblo, CO is an attempt to help reduce this hurdle.9钢轨探伤：概述和未来发展的需要Robin Clark *斯佩里铁路公司，丹伯里，CT，美国2003 年 2 月 10 日收到；2003 年 6 月 20 日接受摘要钢轨探伤在保证世界铁路安全方面发挥着重要作用。最近由破碎钢轨引起的事故集中在能够检测铁路钢轨缺陷的技术上。本文回顾了目前采用的技术，以及最近的现场应用的例子。一些正在进行的进步和未来的选择也进行了讨论。Q 2003 爱思唯尔有限公司保留所有权利。关键词：钢轨检测；超声波检测；电磁检测；疲劳缺陷；滚轮搜索单元1、引言钢轨探伤是目前备受关注的热点问题。如果我们看看今天的铁路测试，我们看到的景象与五年前的情况截然不同。这个行业在世界各地都发生了许多变化。2000 年 10 月的哈特菲尔德事故在其中起了重要作用。这是一个可怕的声明，但这种情况多久发生一次？人们很难理解铁路测试的真正价值。本文将讨论铁路测试行业从早期到我们今天看到的。正在进行的工作正在进行的Railtrack（现在网络铁路）将提出一些想法，为未来。2、轨道测试：从早期开始在 20 世纪 20 年代末，当 Elmer Sperry 博士在美国铁路行业的需求下，开发了用于测试铁路钢轨的感应法（1）时，铁路测试真正成为一个严肃的实体。多年来，这种技术在美国得到了细化，然后在 20 世纪 50 年代出现了超声波测试，并开始成为全球铁路测试的主流。尽管更多的公司已经进入铁路测试领域，但这一点仍然适用。一些例外的是斯佩里在美国，那里的“互补测试技术”的想法已经开发，在俄罗斯，仍然有许多汽车只使用磁感应技术。运输技术中心（TTCI）为 2000 年 10 月铁路调度员办公室准备的报告为当今全球铁路测试行业提供了许多有用的背景（2）。这两项主要技术的基本物理原理如下。在超声波的情况下，我们将一束超声波能量送入轨道，并利用传感器的集合来寻找反射或散射能量的返回。随着时间的推移，任何反射的振幅都能告诉我们轨道的完整性。由于缺陷不是完全可预测的，所以我们发送能量在几个不同的入射角，以确保我们最大限度地发现任何不利特征的机会3 。通常使用的折射角是 0, 37 或 45 和 708。此外，换能器也被定位为感应技术是以电磁感应物理为基础的。通过与轨道头接触的刷子将高电流电流注入钢轨。实际上，轨道成了电路的一部分。如果电流遇到缺陷，电流将绕缺陷（图 1b）移动。电流流动的这种“失真”是通过检测与电流相关的磁场干扰的传感器块来检测的 4 。3、对事故的反应2001 年 3 月 18 日，加利福尼亚西风西行，一个从芝加哥到旧金山湾地区的美铁服务在爱荷华农村脱轨。断裂的铁轨。一人死亡，96 人受伤。事故发生前几周，一辆探测器车在轨道上行驶。已经发现了一个缺陷，有关铁路已取代铁路由联邦铁路局（FRA）条例确定。问题在于，使用的更换钢轨也有缺陷。在事故发生后的一周内，美国铁路测试公司被动员起来，提供一种手动测试能力来测试相关铁路的每一个细分轨道上的更换钢轨。这一事件是北美货运铁路首次使用手动轨道测试。2002 年 3 月，美国国家运输安全委员会（NTSB）公布了与这起事故有关的初步报告。在准备一个程序（6）和在 CT 丹伯里的 0.4 公里测试轨道上进行充分的试验试验后， 斯佩里将六个滚轮搜索单元（RSU）为基础的便携式轨道检测器或“拐杖”投入使用。其他承包商也提供了设备和人员。随后，与相关铁路合作制定了更为严格的进度计划，并在区域性基础上每年都有一些铁路测试员全年工作。便携式轨道检测器（PRD）如图 2 所示。PRD 使用与在北美国运行的测试车相同的 RSU。当 PRD 在轨道表面上移动时，在 2.25 MHz 工作的九个换能器同时检查轨道的体积。为了确保足够的耦合，在 PRD 上安装水箱，铜管引导移动 RSU 前面 1 厘米左右的水流。虽然水的使用不过量，但在典型的 8 小时内，水箱可能需要一次或两次加注。显示器是在常规超声测试仪器上的 A 扫描形式。NTSB 报告建议继续更换钢轨测试。建议 FRA 国家铁路的 R02-5 应进行超声波或其他适当的检查，以确保用于更换现有钢轨缺陷段的钢轨没有内部缺陷。这一过程的扩展是将类似于在新的铁路生产厂雇用的铁路回收站的超声波轨道测试站结合起来。对哈特菲尔德的响应，虽然它在较长的时间段内发展，但是看到了英国铁路系统的PRD 的发展（图 3）。这个单元最近开始成为英国铁路网的一个更普遍的特征。人体工程学，该单位比第一个模型更具吸引力和更轻。电子封装已开发，以使灵活性和使用不同的超声波测试仪器。然而，主要不变的特征是 RSU。下一步的逻辑步骤是开发一种数据存储的方法，该方法允许完成测试工作的完整记录，用于测试后的审查和存档。目前，测试记录是基于技术人员对仪表屏幕上所见和在轨道上视觉上的解释而填写的报告。RSU 是一个更合适的前端单元比替代滑块探头配置，无论是考虑人工检查或高速检查。主要优点是坚固性，符合轨道几何的能力，最重要的是可靠可靠地将能量转移到被检查的钢轨。这些特点鼓励了世界各地的大多数超声波测试公司采用这项技术。在 PRD 的情况下，RSU 在三个不同的角度容纳九个超声换能器，其目的是在尽可能多的能量下以最佳入射角填充轨道。该单位已开发与 Railtrack 的支持，特别是解决检测角拐角裂纹（滚动接触疲劳）促成了哈特菲尔德事故 7 。4、现有技术图 4 显示了在美国铁路上部署的最新技术。该系统将互补超声和感应测试技术结合在一个高轨平台上。这为铁路提供了高质量的测试和增强的部署灵活性。在过去，感应仅在有轨车辆上才可能发生，因为产生大电流注入轨道所需的设备的大小。随着电源技术的发展，高轨车辆的生产已经证明是可行的8。迄今为止，自 2001 年 1 月以来，其中七辆汽车已经建成并投放市场。它们的运行速度高达 32 公里/小时，尽管在北美洲有“停止和确认”测试要求，但在需要确认的情况下，在前进速度和较长倒车的风险之间总是存在
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