PIPE RATING: A NEW APPROACH TO COLLECTION SYSTEM REHABILITATION

The Metropolitan Sewerage District of Buncombe Co., N.C. (MSD) has developed a new program called Pipe Rating. The objectives of the program are to serve as a guide for MSD's rehabilitation efforts under its Capital Improvement Program (CIP) and also as an asset management tool for the collection system. It accomplishes this by objectively rating the structural integrity of individual pipe segments.Pipe Rating begins with a Closed Circuit TV (CCTV) review of each line segment, which is performed as a part of MSD's Preventative Maintenance Program. Each defect noted receives a standardized score in accordance with MSD's Defect Rating Manual. Pipe segments are next coded within the Geographic Information System (GIS) database, where they receive a rating based upon four factors.Rated segments are weighed against one another and ranked accordingly. Pipes with the highest rating (meaning “worst”) are then flagged for further investigation by engineering staff.To date, the program has rated over 1,381,500 LF (262 miles) of pipe, and has flagged 412,500 LF (78 miles) as significant enough to need further investigation. As of June, 2005 MSD has completed two separate rehabilitation contracts based upon the Pipe Rating Program. These contracts totaled 6,839 Linear Feet (LF) of trenchless lining. A third contract totaling approximately 5054 LF is currently in the construction phase, and will also emphasize trenchless rehabilitation.The overall goal of Pipe Rating is to obtain the biggest “bang for the buck” by targeting rehabilitation where it is most needed. Pipe that is structurally sound, even if 75 years old or more, may be left in place; while failing sections are replaced using a variety of methods. These range from single point repairs to the various trenchless rehabilitation options, and up to full-scale dig & replace (D&R) projects.Pipe Rating is a proactive, structural analysis tool developed solely by MSD staff using off-the-shelf software. The program is flexible and can be modeled to serve the priorities of any utility.