Global optimization of design and construction cost for a pipeline with surge protection devices

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Global optimization of design and construction cost for a pipeline with surge protection devices

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Summary (English): Water hammer is a result of a fluid velocity change such as valve closure, pump startup and shut-down, pump failure, etc. It can result in extremely high and extremely low pressures along the pipeline or pipe network. Water hammer has been responsible for catastrophic failures and lengthy commissioning/ execution delays in major pipeline projects in Saudi Arabia in the past few years. Several unfortunate incidents of project delays and major pipeline failures during erection /commissioning of the projects forced some major responsible authorities in Saudi Arabia (names are kept confidential) to make it mandatory for any company bidding for a pipeline project to seek a professional consultancy to make sure that transient events are accounted for in the design of the pipeline and pipeline protection devices. High pressures resulting form water hammer can exceed the pipe pressure rating and result in pipe failures. However, water hammer induced low pressures are more dangerous. Low pressure may result in low intensity but widespread leaks by damaging pipe joints. Most pipe joints can withstand fairly high positive pressures but may not be able to withstand even small negative pressure. Such joints are highly susceptible for leakage when they are subject to high negative pressures. Once these leaks are present, they can lead to intrusion of polluted water into the pipeline. Thus, the use of water hammer control methods/ devices is mandatory in all major projects. Hydraulic optimization of transient protection devices has been a fairly recent trend in hydraulic research. Transient considerations in pipeline design are often fundamental, not incidental in determining the ultimate system cost. Any optimized design which fails to properly account for water hammer effects is likely to be, at best suboptimal and, at worst, completely inadequate. This proposal suggests a global cost optimization procedure for the design and construction of a pipeline system. The design takes into account the expected transient flow conditions induced by normal pipeline operation. The optimization technique considers pipe diameter, material and wall thickness. It also considers protection devices types, sizes and locations. The overall cost of the pipeline is to be estimated using actual real-world bids for capital cost, operational cost and maintenance cost for the pipe and protection components. It is intended to use as many practical pipe/device trial parameter values as possible so that those satisfying both steady-state and transient flow constraints are kept for comparison and those violating constraints are ignored. Two real-world pipeline systems will be designed using the suggested global optimization approach. The overall cost of the achieved design will be compared to the overall cost of the traditional design eventually considered for each of the two cases.

This research project will focus on a global cost optimization of design and construction of a pipeline with water hammer protection devices. A careful examination of the literature reveals that this “global” optimization has not been done before as it requires a great deal of effort and dedication. The term “global” refers to considering all the possible variables associated with the design of the pipeline (with water hammer control devices) in the optimization process. These variables are: pipe material, pipe diameter, pipe wall thickness, protection devices parameters (type, number, size and location). Furthermore, the optimization process will not only include initial (capital) cost, but it will also include, operational and maintenance costs. The most recent literate relevant to optimization assumes the pipe dimensions to be readily known and optimization is performed on the protection devices only. Thus, the novelty of this research is evident and the reason that global optimization was avoided in the literature is that it requires a great deal of resources and efforts. The optimization in this research will be performed using real world pipeline projects under construction and includes the following: 1. Collecting data and assessing the size of the search space: Obtain the actual capital cost, operational cost and maintenance cost for the pipe and its components (valves, protection devices, etc.). This cost should be obtained for the different sizes of protection devices and for the different pipe parameters: pipe material, pipe size and pipe wall thickness. The cost information should be obtained from actual bids for major pipeline projects in the Kingdom. 2. Use Surge Software to Search for Optimum Design: Use a suitable software package (Surge 2010 from KYpipe or equivalent) to perform a comprehensive analysis to search for the optimum solution using different water hammer protection strategies. All the variables mentioned in (1) above should be involved in the trial process in search for a global optimum cost for the pipeline design and construction. 3. Perform Comparison Between the Global and Traditional Optimization Techniques: Analyze the results by comparing the obtained global optimum cost with the actual cost of the real-world project which was designed using traditional methods. It is expected to find a remarkable difference between the results of the global optimization and the traditional methods to design and construct a pipeline. Hopefully, once the results are obtained as planned this can convince the decision makers to follow this suggested new strategy of global optimization which can make a great impact on the many ongoing and planned projects in the Kingdom.

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