The last preparatory step is to pressurize the

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The last preparatory step is to pressurize the condenser (through the steam side) to about 14 kPa (2 lb f ·in. –2 gage) maximum by using the ship’s air system. A pressure gage control valve and relief valve are temporarily installed to regulate pressure within the condenser. Using a 25 mm (1 in.) air hose, it takes about 15 min to achieve satisfactory pressure within an about 27 m 3 (950 ft 3 ) condenser at a gage pressure of 14 kPa (2 lb f ·in. –2 ). Pressure and Vacuum Leak Testing Welding Ships and Large Chambers A portable ultrasonic system to detect and pinpoint leaks has been used to inspect air pressure and venting systems at a major shipbuilding yard. Used on virtually a daily basis during the progress of ship building and repair, several techniques of ultrasound detection for leak testing have been developed. In the 1900s, leak test techniques familiar to inspectors of ships and large closed chambers included bubble testing. Another technique was to evacuate the structure and then move a candle along the course of all welded seams and penetrations. The flame’s flickering indicated a leak. The hazard of the candle test was demonstrated by the fire in a nuclear plant, which destroyed the signal cables to the control room. Ultrasound leak testing has proved to be an effective means of inspecting large welded fabrications. One continuing application is inspecting the integrity of watertight compartments, skegs, rudders, tanks and other structures during shipbuilding and repair. Other similar applications have included the inspection of combustion chambers during the construction of an electric generating plant. Enclosures as large as 6400 m 3 (225 000 ft 3 ) have been tested by using the following procedures. The initial test phase consists of pressurizing the enclosure to 3 to 15 kPa (0.5 to 2.0 lb f ·in. –2 gage) and, in the case of skegs and rudders, to 70 kPa (10 lb f ·in. –2 gage). Obviously, on smaller fabrication (such as small shipboard compartments), if the gage indicates constant pressure for 10 min, there is no need for further inspection. However, when the gage indicates pressure reduction or when the enclosure is so large as to preclude accurate pressure determination, then the ultrasound testing commences. Typically, the rubber extension is placed over the airborne directional probe and the inspector surveys all weldments. In the case of shipboard use, particular attention is applied to cable piping and ventilation penetrations. Field experience has shown that in compartments pressurized to 14 kPa (2 lb f ·in. –2 gage), the ultrasound detector can pinpoint a leak smaller than 0.1 mm (0.004 in.) diameter from a distance of 0.6 m (2 ft) even through 25 mm (1 in.) thick fiberglass insulation. The ultrasonic unit’s standard earphones are normally worn during these tests because of the likely presence of high ambient audible noise levels. Ambient ultrasonic energy such as that released by pneumatic tools can easily be discounted by the operator by noting its direction.
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  • Fall '19
  • Acoustic Emission

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