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using an induced noise. The inspection tool provided a calculated minimum average remaining wall thickness of 7.3 mm, which was a 25% wall loss from the pipe’s original thickness of 9.7 mm. IMPLEMENTATION To calculate the hoop stresses developed on the pipe, Ahammed and Melchers (1994) approach to calculate vertical loads (live and dead load) was used in the calculation of the circumferential (hoop) stress, in addition to Rajani et al. (2000) approach to calculate internal pressure and frost loads. Given that no geotechnical information and pipe installation methods were available, some practical assumptions and values were considered. Utilizing an optimization algorithm, the best-fit pit depth curve of the twophase model corresponding to the 2018 inspection is shown in Figure 1. Once the condition state was established at the time of inspection (2018), an MCS was utilized to run 5,000 samples to address uncertainties in the pipe

Figure 1. Corrosion model.

residual strength calculation for each future year, in combination with the predicted future wall loss based on the bestfit 2-phase pit depth model. The remaining economic life was determined to be 30 years (2048) and the remaining service life was 39 years (2057), corresponding to the cumulative probability of 90%. This assumes no environmental changes occur during the pipe lifespan that could impact corrosion rates and/or cycling loads acting on the pipe.

CONCLUSIONS Providing reliable infrastructure is a paramount objective for any municipality. Responding to aging infrastructure is costly, especially when pre-planning was not performed. To properly plan renewal programs, a variety of fieldbased condition assessment tools, utilized in conjunction with engineering statistical methods, can allow pipe owners to understand their CI pipe inventocontinued overleaf…



Scott McLeod, Aerzen Canada Sales Manager +1 450 424 3966 ext.226

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June 2019  |  13

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Environmental Science & Engineering Magazine | June 2019