Condition Assessment Priorities for City of Houston

Over the last few years, The City of Houston has experienced failures of various large diameter water lines. Some of the most notable have involved 36-, 42-, 48-, and 60-inch Prestressed Concrete Pipe (PCCP), and 24-, 30- and 36-inch Cast Iron Pipe. Because of these failures, the City is concerned with the long-term performance and structural integrity of other large diameter water lines. The City requested Lockwood, Andrews & Newnam, Inc., (LAN) to prioritize the water infrastructure for evaluation under a Condition Assessment program. LAN's task is to prioritize existing lines based on the likelihood that they may have distress and the risk if a failure or water outage were to occur. The four pipe lines above were all constructed of prestressed concrete cylinder pipe (PCCP) between 1960 and 1996, however, each failed for distinctly different reasons. The causes of failure of these lines ranged from problems associated with hydrogen embrittlement of prestressing wire, internal corrosion to structural damage caused by transient surges, and failure of lead caulking of cast iron pipe joints. A list of criteria is organized into a GIS database in order to determine the theoretical condition of each pipe line. Physical assessment of the lines is to be scheduled based on criteria including: 1) Age, 2) Pipe Material, 3) Critical nature of line (Facilities served; schools, hospitals, industry, etc.), 4) Cathodic protection system, 5) Leak history, 6) Operational history, 7) Review of construction inspection records, and 8) Adjacent construction projects. This paper describes the criteria used by the City of Houston to prioritize their Condition Assessment program and some of the issues and constraints faced to fully inspect existing pipe lines.