7/27/2019 _0142-1123(91)90472-b] -- Bore Inspection and Life Evaluation of Vintage Steam Turbinegenerator Rotors- Jhansal

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steels and sintered mixes of high-speed steel/low-alloy steel is providing a basisfor understanding failure mechanisms in rolling contact fatigue, and the role ofporosity. Steels used include T15, En24 and M50. Graphs, photomicrographs. 2 refs.

Bore inspect ion and l i fe eva luat ion of v intage steam turbine /g enera torrotors. Jhansale, H.R. and McCann, D.R.AS TM J. Test . Eva / . Nov. 1990 18 (6), 446-453The approaches and methodology used for bore inspection and life evaluation/exten-sion of vintage steam turbine spindles and generator rotors for continued serviceare described. The non-destructive inspections, including visual, magnetic particleand ultrasonic, together with flaw sizing procedures, are described. Life evaluationand extension approaches include conventional and finite-element stress and thermalanalyses, state-of-the-art material evaluation studies, and fatigue-, cree p- andfracture-mechanics-based techniques. Based on the experience of these ongoingstudies on over 250 spindles and rotors (manufactured by Allis-Chalmers, GeneralElectric and Westinghouse), two essential recommendations are made. Firstly, it isbest to evaluate each vintage spindle/rotor on a case-by-case basi s instead of ahistorical and generic bas is. Secondly, most of the vintage spindles/rotors cancontinue to be used safely and with a high degree of reliability with proper periodicinspections and evaluations and life extension measures as needed . Graphs,photomicrographs. 8 refs.Imaging short fa t igue cracks with the ge l e lect rode. Baxter , W.J .AS TM J. Test . Eva l . Nov. 1990 18 (6), 430-438A new non-destructive inspection too l is described for tracking and recording crackgrowth in test coupons and structural components. The current state of developmentof this device, the gel electrode, is reviewed. This hand-held inspection probe canimage surface fatigue cracks in Fe (e.g., 1008, 1065 carbon steels), Ti, magnesium(e.g., EK30) and AI (e.g., 6061-T6) alloys. Fatigue cracks only approximately 10 2 mmlong can be detected, a sensitivity that surpasses that of commercially availabletechniques by a factor of 100. Images of short fatigue cracks are shown for each ofthe above alloy systems. The examples are selected to illustrate the good visibilityand repeatability o f the images, as is required to moni tor crack growth. Includedare quantitative measurements of the growth kinetics of a short (10 I-1 ram) crackin a prototype component. Graphs, photomicrographs. 9 refs.

Fatigue crack characterization by ultrasonic inspection. Rehbein, D.K.,Thompson, R.B. and Buck, O.AS TM J. Test . Eva /. Nov. 1990 18 (6), 421-429The experimental configuration of the ultrasonic measurements is such that a fatiguecrack is illuminated by a longitudinal wave incident perpendicular to the crack faceand focussed in the plane of the crack. The longitudinal wave is partially transmittedby the closure zone and picked up by another focussed receiver transducer. Bychanging the angular orientation of this receiver, longitudinal or transverse polarizedwaves diffracted in the closure zone can be detected. By spectral analysis, translationof the sample with respect to the detection system and rotation of the receiver,one can monit or the frequency, spatial and angular dependences of the cracktransmissivity. These data are described by a spring model, which replaces thetopological description of the closure region and provide the spatial distribution ofthe average diameter, d, and the average separation, C, of the contacts. From thiscontact topology and the flow pressure (three times the ultimate tensile strength)of the material (e.g ., 2024-T651 AI), the residual stress field in the wake of thecrack is deduced. Thes e results agree well with X-ray diffraction measurements.Furthermore, the shielding stress intensity factor is estimated using these resultsfo r a number of fatigue cracks grown under a variety of loading conditions. Ifshielding is taken into account the effects of load excursions on fatigue crackpropagation can be estimated with reasonable accuracy. 20 refs.Probability, con fidence an d samp le size in fat igue testing. Parida, N.,Das, S.K., Gope, P.C., Mohanty, O.NA S T M J . T e s t . E va L Nov. 1990 18 (6), 385-389The sample size necessary for a statistically significant life test has been determined.and a comparison of actual and predicted lives has bee n made for a desiredprobability of survival wi th a given confidence level, statistical error, and coefficientof variation at different stress levels. This approach has been used for cases wheredata follo w a log-nor mal distribution. On the basis of this approximation, it ispossible to estimate the lower tolerance limit using a mini mum number of samples.It has also been concluded that, whatever the sample size, the estimate alwaysresults in some error, Ro, which mainly depends on the confidence level, theprobability of survival and the stress level, and that, beyond a specified samplesize, the estimation of fatigue life is independent o f sample size. The test materialwas a low-alloy steel. Graphs. 5 refs.

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