Verification of Quantitative Assessment of Wall Thickness Reduction in Sewers Due to Corrosion Using AI and Robots

NTT Docomo Solutions, Inc.

Kyoto Prefectural Basin Sewerage Office

Tmsuk Co., Ltd.

NTT Docomo Solutions, Inc. (Headquarters: Minato-ku, Tokyo), in collaboration with the Kyoto Prefectural Basin Sewerage Office (Location: Nagaokakyo City, Kyoto Prefecture) and Tmsuk Co., Ltd. (Headquarters: Kyoto City, Kyoto Prefecture), conducted a survey and verification from April to December 2025 aimed at advancing the inspection work for basin sewerage pipelines within Kyoto Prefecture (hereinafter, this verification). In this verification, data from inside a sewer pipe was acquired using a multi-legged robot for sewer pipe travel developed by Tmsuk, equipped with LiDAR. An AI developed by NTT Docomo Solutions (patent pending) was applied to this data, which estimates the pipe wall shape at the time of its new installation and performs a differential analysis with the current pipe wall shape. As a result, in a partial section of the sewer pipe targeted in this verification, we succeeded in quantitatively grasping and visualizing the depth and extent of wall thickness reduction due to corrosion deterioration. Furthermore, using past pipe inspection data held by Kyoto Prefecture, we analyzed the applicability of existing deterioration prediction models to the sewerage field. The results showed that the analysis partially aligned with trends that sewer managers had empirically sensed, such as sections prone to deterioration and the factors causing it.

The standard service life of sewers is considered to be 50 years. Of the approximately 500,000 km of sewer pipelines nationwide, about 7% had exceeded their service life as of 2022, and this proportion is expected to reach about 42% by 2043. *1 The inspection and renewal of these sewer pipelines have become a financial and technical challenge for local governments. Additionally, in response to a series of road cave-ins caused by aging sewers in recent years, the Ministry of Land, Infrastructure, Transport and Tourism is proceeding with revisions to sewer inspection guidelines, considering increases in the targets and frequency of inspections and surveys, and the addition of quantitative evaluation items. As the targets and frequency of inspections and surveys increase due to these guideline revisions, sewer managers are required to appropriately judge the priority order for repairs and other measures for a large number of pipelines. However, with conventional visual and image-based inspections, while the presence of corrosion and surface conditions such as cracks can be confirmed, it is difficult to quantitatively grasp the depth and extent of corrosion, making it challenging to determine the urgency and priority of repairs.

Against this backdrop, NTT Docomo Solutions, the Kyoto Prefectural Basin Sewerage Office, and Tmsuk conducted this verification.

【Overview and Achievements of This Verification】

■ Implementation Period

April 2025 - December 2025

■ Purpose

Quantitative evaluation of wall thickness reduction and prediction of pipeline deterioration for basin sewers in Kyoto Prefecture.

■ Roles of the Three Parties

NTT Docomo Solutions	Consideration of technology to achieve quantitative assessment of wall thickness reduction using AI and data analysis techniques, implementation of deterioration prediction and cause analysis using accumulated inspection data, planning and execution of this verification.
Kyoto Prefectural Basin Sewerage Office	Selection of target pipelines utilizing knowledge accumulated from managing wide-area main pipelines, provision of verification fields and accumulated inspection data, evaluation of the verification results.
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