Risk Assessment of a Deep Sea Pipeline (1996)

Abstract A unique design of subsea gas pipeline has been under consideration for several years. It would traverse the Arabian Sea for 1,100 kilometers with a large part of it at depths over 3,000 meters and temperatures near 2°C. A Probabilistic Risk Analysis has been performed with special attention to the novel technical features of the design, construction and operating environments. The factors considered to date have included: pipe and materials design for internal pressures to 500 bar and external pressures to 430 bar, laydown processes, materials quality and QA/QC, piping stress and strain levels m laydown and spans, route selection, and other factors, The methods used to screen, rank, and quantifying the risks are described. The scenarios involving the principal hazards are deseribed and the risks are quantified. Options for Ml-m risk control and reduction measures are also identified. The results at this stage show relatively low expected values for the principal risks. Assuming effective implementation of the available control measures, the proposed design is calculated to have risk levels lower than the historical average for similar mega-projects. Introduction As a part of an overall risk management approach, an intensive formal risk assessment effort was mounted for the preliminary design phase of the proposed pipeline. The usual engineering design approach uses established codes and standards, supplemented by experience and established analysis routines to provide sufficient margins to assure successful completion and performance. The available codes and standards have limited applicability for the conditions of thus project, making a probabilistic risk analysis appropriate as a source of added insight for recognizing and controlling risks in design, specifications, procurement, and construction. State-of-the-art methods for tin ding, screening, modeling, and quantifying the physical risks were used. The work involved over 85 man-months of direct engineering effort, plus significant supporting efforts horn other organizations participating in a design and technical developmentteam. Prior to starting this work, a preliminary design phase had been completed involving most of the organizations likely to be capable of handling the construction of such a project. The reference design phase included full scale pipe fabrication and testing of pipe design A narrow scan route survey supplementing prior wide scan surveys, was also underway in parallel to the risk study. Ordinary logistic delays, such as delays m transport or unavailabilities of labor, are not included in this paper. Overview of the Risk Assessment Process and Methods The overall structure of the assessment process used is shown in Figure 1. This work was focused primarily, but not exclusively, on the technological risks and uncertainties associated with the novel features of the pipeline and equipment. Bask Design and Environment Information The preliminary design studies were extensively documented. This provided the basic familiarization with the main technological options and challenges of the pipeline, as well as a range of judgments on the best approaches for coping with these challenges, The on going work of the design and testing teams was available as a continuing resource as questions arose.