Detection of hydrothermal aging in Cured-In-Place Pipes (CIPP) based on microwave system

Pipe rehabilitation by means of trenchless techniques has been performed for more than 40 years already. Cured-in-place pipe (CIPP) is a trenchless method to repair damaged pipelines by inserting a new liner of polymer composite inside the existing host pipe. Since these liners are exposed to water at different temperature after installation for a long time, the purpose of a study was to investigate the effect of hydrothermal aging on CIPP samples and how this effect can be assessed by means of nondestructive testing. The hydrothermal aging was performed by immersion of liner samples in double-distilled water at 65°C. The effect of aging on the samples was determined by comparison of reference information (optical microscopy images and weight) with nondestructive testing parameters using microwaves. For nondestructive material testing, microwaves have been applied in the frequency range between 0.3 and 300 GHz. Microwave based methods have the advantage of no directcoupling between the probe and the object under test being required, such that the evaluation can be performed remotely from a standoff distance. The microwaves used in this study were in the frequency range of 75 - 100 GHz. For this a vector network analyzer (VNA) with frequency-modulated continuous wave (FMCW) radar was used to enable an accurate and broadband measurement. The effect of water-induced aging appeared as a change in the received microwave amplitude, which results from a change in permittivity of the material being inspected. The results of the weight measurement proved the water absorption in the samples. Moreover, the effects of water absorption were visible in the optic microscopic images as cracks and de-bonding between fibers and matrix. Getting those results combined does result in an approach on how to hopefully assess CIPP liners in service in the future.