An Integrated Outflow-Spill Modeling Approach for Risk-Based Valve Placement of Liquid Transmission Pipelines

Weir et al’s work [1] applied the relative effectiveness of outflow reduction to address the Intelligent Block Valve Placement (IVP) for liquid transmission pipelines. In their work, the effectiveness measure for each potential valve placement location is a length-weighted sum of the calculated volume reduction at all points along the pipeline in which the outflow volumes are multiplied by weighting factors that reflect the relative importance of spills in different sensitive areas; In our work, the original approach was enhanced to more quantitatively reflect both the likelihood of line failure and the full consequences of line failure as impacted by additional valve placement considering both block and check valves. This paper presents an IVP approach integrated with a quantitative risk assessment through which block and/or check valve placement schemes are optimized. The process involves a computer analysis in which block and check valves are iteratively selected and placed for each case. The risk reduction associated with each case is determined as the product of failure likelihood and the weighted average cost reduction. Failure likelihood is typically quantified using reliability methods or industry failure statistics, and is not the focus of this paper. The cost reduction focuses on environmental factors, which are represented by the clean-up cost of a spill that impacts both sensitive and non-sensitive areas for each incidence. In modeling consequence, the reduction of outflow potential is quantified by an in-house outflow simulation tool; and the potential spill impact is assessed through a mechanistic in-house VBA extension of ArcGIS, a three-dimensional (3-D) overland-hydrographical spill simulation package. Optimal valve placement design is achieved by balancing the costs associated with environmental risk with the costs associated with installing and maintaining block and check valves. The valves included in the assessment for outflow simulation and cost analysis are check valves and block valves. The automatic valve placement simulation is terminated when the valve installation/maintenance cost outweighs the benefits of placing more valves in the line.