AE06.pdf

Should be silence the inspector can locate the

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should be silence, the inspector can locate the dysfunctional valve. The ultrasound detector is often the only instrument used to check hydraulic systems. It has eliminated the previous step-by-step replacement of valves that took as long as 4 to 8 h per faulty system. The ultrasonic test requires only 15 to 20 min. Its use has reduced the inventory required for components and similarly reduced linear flow equipment costs and operator time. The device is also used to check the integrity of nitrogen pressurized engine shipment containers and in the overhaul of engines. Mechanical Inspection of Compressor Valves Locating dysfunctional valves and valve plates in multivalve cylinders is a straightforward application of ultrasound detection. Cracked or broken valve plates in compressors can be located without the contact probe but the contact probe permits much wider use of ultrasound detectors in machinery maintenance. To pinpoint dysfunctional valves, the inspector places the probe against the valve plate, head or rocker box cover and listens for the pulsed whistling of compression bypass. Many maintenance inspectors become so adept that they can predict which quadrant of a valve plate is leaking before disassembly. The ultrasonic contact probe is used whenever a compressor fails to maintain rated pressure levels. By holding the contact probe at right angles against the valve head, the operator can troubleshoot which valve plate, for example, is cracked within a multivalve head. The diagnosis of valve bypassing is straightforward; the operator needs know only the compressor’s timing sequence to know when there should be periods of silence. The translated rushing sounds of valve bypassing are indications of trouble. Marine Industry Although ultrasound leak test techniques in marine propulsion system applications are the same as those discussed previously, the problems of locating condenser and boiler tube leaks have historically proved vexing enough to warrant special discussion. One major producer of single-plane marine propulsion units reports a 50 percent reduction in time required for leak testing compared with the time required to perform hydrostatic tests. Hydrostatic testing involves preparatory steps such as blanking the flange between low pressure and high pressure turbines. Although two-plane marine propulsion systems require less 206 Acoustic Emission Testing
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preparatory blanking, ultrasound testing during the inspection phase is equally effective and considerably faster. After salinity indicators have revealed a leak in axial flow condenser units, the water boxes are drained and manhole covers at both ends are removed. Next, the steam side of the condenser is isolated, which merely entails securing all lines into and out of the condenser, such as dumps, drains, suctions and exhausts.
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  • Fall '19
  • Acoustic Emission

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