Sonic/Ultrasonic Testing Provides Reliable Condition Assessment

P restressed cONcrete cylinder pipe (PccP) is a complex composite structure. For such pipe to function properly, all structural elements must perform as intended. Failure of any element—such as a reduction in concrete core strength, delamination between composite layers, and microcracking or core cracking—indicates the pipe section isn’t functioning as intended and structural integrity is compromised. sonic/ultrasonic testing can be used to evaluate these elements. Many factors alone or in combination can shorten PccP service life, including „ defective manufacturing materials or methods „ Aggressive ground and groundwater environments „ Operational parameters that exceed pipe design „ Improper design „ Improper installation sonic/ultrasonic testing also can monitor the PccP aging process. this allows personnel to estimate a pipe’s remaining useful service life and effectively manage the pipeline. How Sonic/UltraSonic teSting workS Measurements are made by creating an acoustic stress wave in the sonic/ultrasonic frequency band with an impact and measuring the transmission velocity of compressional and shear waves and resonance (impact echo) from the pipe’s exterior surface or from delaminations within the pipe. transmission velocity values determine the concrete’s elastic deformational characteristics, an empirically determined calculated strength value, and a direct measurement of the core concrete’s condition. the reflected signals resonate at a frequency related to the radial thickness and compressional wave velocity of the concrete core and coating. Because the average thickness of the pipe wall is known, the average strength of the concrete pipe core and the presence of delamination can be determined from the measured resonant frequency and wave attenuation. such testing provides information to determine if a pipe is functioning as designed or the pipe is deteriorating. signs of deterioration include wire breaks, loss of prestressing, overloading, or coating deterioration. wire Breaks. tests on an out-of-service 60-in.-diameter PccP demonstrated the effectiveness of sonic/ultrasonic measurements in detecting cut or broken prestressing wires. With cuts in 11, five, and six wires in different locations, sonic/ultrasonic measurements were made along a continuous line of coverage across all three wire-cut locations. As shown in the photo at bottom right, the mortar coating on both sides of the cut wires was well bonded to the prestressing wires. sonic/ultrasonic test results indicated loss of full-thickness resonant frequencies for data acquired directly over cut wires. Measurements in areas where wires weren’t cut showed no change in velocity or resonant frequency data, indicating the effect of the broken wires was confined to cut-wire areas. these measurements were repeated annually for six years with no significant changes in velocity values or resonant frequency, indicating the mortar coating and adjacent uncut wires were keeping the prestress wires in tension, outside the wire cut areas. test results were confirmed in the field. An electromagnetic and sonic/ ultrasonic survey inspection conducted on a 66-in. PccP indicated broken sonic/ultrasonic Testing Provides reliable Condition assessment http://dx.doi.org/10.5991/OPF.2013.39.0044