Minimizing Risk on Long Pipelines

Pipelines are prone to leaks, bursts, damage and poor jointing. The longer the pipeline, the greater the risk of downtime to make repairs. The engineer frequently does not relate the standards to the risk. The greater the geometry of the pipeline the bigger the risk. A systems analysis is required to select the correct reliability factors. Pipelines are subject to failures on a scale proportional to length and diameter. Materials, laying and supply also are subject to quality variation. The cost of failures increases with risk. In an attempt to minimize risk of down-times, intermediate storage and isolating valves are required. A 400km long Glass fiber reinforced pipeline in Botswana is used as a case study. It is found in the risk study that length, diameter and laying conditions are in that order the main effects on risk. The optimization spreadsheet was designed showing the relations between the isolation valves intervals and the costs involved. The optimum cost of valves installation was computed by augmenting the cost of completed valve chambers and the cost of water lost over a certain distance. These computations were carried out for each of the four pipe diameters along the line. The least combined cost of valve chamber per kilometer and water lost cost per kilometer were used to define the optimum number of valves required over each section of the specified pipe diameter. This study also addresses the optimization of reliable emergency storage reservoirs near water treatment works. Currently, there are three major centers that are supplied by the North South Carrier pipeline, namely Palapye, Mahalapye and Gaborone. During pipeline failures these centers face shortage of water, when there is no pumping at all because all pump stations are synchronized with the three water works. Pumps run only when there is demand from the treatment plant. When the transportation system shuts down, the treatment successively comes to a halt, cutting supply to the consumers. This is the scenario, which is experienced during the down time — when the system fails. Lack of emergency supply in the system is the main source of this problem. Cost effective and efficient planning, design and construction of system elements like valves and reservoirs can be optimized to curb the down time impacts on the water authorities and the consumers.