National Academies Press: OpenBook

Maintenance Planning for Rail Asset Management—Current Practices (2020)

Chapter: Chapter 5 - Case Examples

« Previous: Chapter 4 - Evaluation of Survey Results
Page 29
Suggested Citation:"Chapter 5 - Case Examples." National Academies of Sciences, Engineering, and Medicine. 2020. Maintenance Planning for Rail Asset Management—Current Practices. Washington, DC: The National Academies Press. doi: 10.17226/26012.
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Page 29
Page 30
Suggested Citation:"Chapter 5 - Case Examples." National Academies of Sciences, Engineering, and Medicine. 2020. Maintenance Planning for Rail Asset Management—Current Practices. Washington, DC: The National Academies Press. doi: 10.17226/26012.
×
Page 30
Page 31
Suggested Citation:"Chapter 5 - Case Examples." National Academies of Sciences, Engineering, and Medicine. 2020. Maintenance Planning for Rail Asset Management—Current Practices. Washington, DC: The National Academies Press. doi: 10.17226/26012.
×
Page 31

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29 Three transit agencies were selected for follow-up case examples. Although a broad range of issues were discussed with these agencies, a common focus was the presence of a relatively large number of broken rails, as discussed earlier in this report. Of the three agencies, one (Minneapolis Metro Transit) reported a large number of broken rails with a very small cor- responding number of detected defects. The other two agencies, CTA and WMATA, reported significant numbers of detected defects and relatively large numbers of broken rails. Thus, another focus of the case examples was the reasons that the broken rails were detected not by UT testing, but rather by either track circuits or visual inspection. The case examples are presented separately for each participating transit agency. 5.1 Washington Metropolitan Area Transit Authority1 WMATA ultrasonically tests three times per year: twice with its own rail-bound vehicle (WMATA’s own track geometry car on which a UT unit is mounted) and once with a con- tractor as a check/fail-safe. WMATA continues to upgrade its database, but the agency is familiar with risk-based UT scheduling and plans to implement it once the quality of the data improves. WMATA reported 18 broken rails in 2019 and detected via UT 80 defects in 2018 and 133 defects in 2019. This increase in detected defects between 2018 and 2019 was attribut- able to several factors. The first factor was the use of a more precise UT technology, which has the ability to detect defects as small as 5% and 10% of the rail head area. The second was the inclusion of NHT defects that were not initially confirmed by hand testing but that were found by the UT unit. The third was the inclusion of non-testable rail (NTA). The 2019 data include 28 of these types of defects that the 2018 data do not include (the 2018 data total also omits two such defects). It should also be noted that the NHT and NTA defect types are not acted upon until they are further verified. Rail grinding is typically implemented to redesignate NTA rail from defect status by allowing it to be hand tested and cleared of any defect. However, WMATA’s data set does not account for the quantity of non-testable rail redesignated as such, but rather maintains the initial defect count. WMATA had one derailment in January 2018; the derailment stemmed from a defect at the base of the rail that was not reliably detectable by UT. The defect propagated rapidly, so the rail deteriorated quickly before the next UT test. C H A P T E R 5 Case Examples 1 WMATA-supplied data are considered sensitive and must be used only for the purposes of TCRP Project J-7/Topic SE-07.

30 Maintenance Planning for Rail Asset Management—Current Practices In analyzing its broken rail defects, WMATA found that most were not reliably detectable by conventional UT. Among them were a major cause category of defects initiating from rail base corrosion, usually in the form of a corrosion-initiated base defect, not detectable by UT. Other broken rails were attributed to gauge corner defects hidden under RCF. RCF does not allow the UT signals to penetrate below its layer and detect a defect underneath. Freight railroads experience this problem as well, which often results in a “no test” that then requires retesting, often using hand testing. The problem is addressed through grinding off the RCF layer to allow for more effective testing. Note, WMATA has investigated the application of eddy current test- ing to better identify RCF conditions as well and is planning a pilot program to evaluate if eddy current testing will better identify RCF conditions and reduce rail failures. Thermite weld problems were the third problem area identified for rail breaks, which can also be hard to find by UT. Specifically, bad thermite welds, which are not very detectable by rail, bound UT equipment due to lack of fusion in the base. Training on thermite welding is being emphasized and a team dedicated to hand testing (UT) welds has been developed to detect bad welds. WMATA also has had problems with rail head surface defects, which also lead to some rail breaks. In such cases, the rail-bound UT cannot receive good confirmation of defects due to interference from surface defects. WMATA has issued new directives and prepared new train- ing on rail head surface defects for track inspectors together with improved reporting. This is an area of focus. 5.2 Minneapolis Metro Transit Minneapolis’s Metro Transit ultrasonically tests once per year, using a testing contractor. Scheduling is a problem because of the agency’s small size. Metro Transit usually gives the contractor a wide testing time window, and the contractor tells the agency a few weeks in advance when he or she is in the area and can conduct testing. Metro Transit would like to increase testing to twice per year for peace of mind. However, given its very low defect rate (zero detected defects in 2018 and 2019, and two so far in 2020) and low annual MGT, the agency cannot justify the additional testing at this time. Metro Transit noted that the defects detected so far in 2020 have included a bolt hole crack at an insulated joint and a split web in embedded track. Metro Transit reported nine broken rails in one year (2019), but the agency noted that was an unusual occurrence. That winter season was particularly bad and extended, with temperatures reaching the –30s (°F). As a result of the extreme cold, the nine broken rails were pull-aparts, primarily at welds in embedded track or at crossings. There was also reported batter at these welds, but no evidence of internal defects and thus no reason for the ultrasonic tests to detect them. The agency noted that track circuits are limited and did not find these defects: rather, the broken rails were found by visual inspection. If a broken rail is found, immediate action is taken either by application of joint bars or by replacement of the rail with a plug—that is, if the pull-apart coincides with a power rail or is located where the public can access it. Otherwise, the pull-apart is left in place in the embedded track, because the embedded track secures the rail. The track is slow ordered as necessary until remedial action can be taken. Corrective action is usually scheduled as track time and resources become available, and perhaps as weather conditions improve.

Case Examples 31 5.3 Chicago Transit Authority CTA currently ultrasonically tests once per year, with around 80 to 120 defects found (84 in 2018 and 120 in 2019). CTA’s follow-up maintenance occurs after the ultrasonic test, which is usually conducted overnight. After the data are analyzed, a hand ultrasonic test crew, accom- panied by the local roadmaster, is sent out the next morning. If the crew confirms the presence of a defect, the roadmaster can order appropriate remedial action immediately. CTA employs three major types of remedial action: (a) removal of the defect, (b) installation of joint bars, and (c) application of slow orders. In the latter two cases, the defects remain in place; when the next test occurs, they are again reported as defects. Thus, some of the annual defects are “repeats,” such as those where joints bars were installed and the defects left in the track. However, they are still counted as new defects for each test. The reported defects also included a significant number of engine burn fractures, which are located under surface rail head engine burns. CTA reported 22 broken rails in 2019. Most of these were not associated with a UT detected defect, but rather were found through visual inspection or track circuits. These broken rails included • Cold weather breaks (no correlation with thermite welds), • Breaks that initiated from rail base corrosion, and • Detail fracture on the field side of the rail head, initiating from weld used for attaching bond wires near insulated joints (for running rail negative return). The latter condition, which has caused a significant number of broken rails, was also the cause of CTA’s one reported derailment. (Fortunately the derailment occurred at a low speed near a station.) What makes detail fracture very difficult to detect through ultrasonic testing is its location on the field side of the rail head. Conventional UT configuration does not include a probe that tests to the field side of the rail head, because most railroads and transits do not have this type of weld or weld-initiated defect. As a result, a transit such as CTA does not have the ability to implement additional test probes at that location. CTA has start installing joint bars to prevent large breakouts at such defect sites, such as that which caused the derailment. In fact, CTA reported that the presence of such a joint bar prevented a recent fracture from becoming a derailment. Like most rail transit systems, CTA indicated that rail wear is the primary reason for rail replacement, not a primary cause of an excessive number of defects.

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The occurrence of rail defects, broken rails, and broken rail derailments is consistent with the rate of development found in other studies that look at larger populations of rail defects. Likewise, the larger and more heavily used transit systems develop increased levels of defects, which is again consistent with what is seen in the railroad industry at large.

The TRB Transit Cooperative Research Program'sTCRP Synthesis 151: Maintenance Planning for Rail Asset Management—Current Practices presents the results of a survey and the analysis of the response data in an effort to synthesize current practices.

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