Causes of Etiwanda Pipeline Mortar Lining Failure

Staff from the Metropolitan Water District (MWD) visually inspected 5.3 miles of the 144 inch diameter Etiwanda Pipeline to evaluate the condition of the internal mortar lining. The inspection showed that large portions of the lining are either failing or have failed. Approximately 35% of the total length of the pipeline has either missing or delaminated mortar. MWD conducted an exhaustive literature search to see if other utilities have experienced this type of failure. MWD also reviewed the construction history, soil conditions, backfill and design criteria in order to determine the cause of the failure. After the investigation the significant factors that contributed to the failure are believed to be: 1. The pipe was designed for a higher stress than historically recommended by AWWA standards or traditionally used by MWD. The higher allowable stresses will cause the liner to crack more and have larger cracks than on typical mortar lined steel pipelines. 2. The fact Etiwanda Pipeline is a 12 foot diameter pipe also results in increased crack size in the mortar lining. The large diameter also results in increased length of the arch and this makes the mortar more likely to fail. 3. The Etiwanda Pipeline functions as a penstock for the Etiwanda Power Plant. Pressure fluctuations caused by the Etiwanda Power Plant are preventing the cracks from autogenous healing. The inability of the lining to heal is causing the lining to delaminate from the steel pipe wall. This eventually causes the lining to fail due to the effects of gravity. 4. It is possible that a differential pressure may develop between the water inside the pipe and the water behind the lining In view of this failure it is suggested that tests be performed to determine the stress limitation as the pipe diameter changes. Until those tests are completed the stresses in mortar lined pipe should be limited to 18 ksi. In addition, if a pipeline is to be subjected to fluctuating levels of stress the pipe lining must be chosen carefully. The best choice for the lining would be a flexible lining. Mortar lining without reinforcing should not be used and mortar lining with welded wire fabric should not be used without additional testing verifying its viability.