A methodology to prevent process piping failures during vapor cloud explosions
Khiavi, Majid Pasbani
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The design and evaluation of offshore structures' piping systems subject to blast events are of significance and require advanced analysis approaches. They are important because during an explosion rupture of a piping and vessel system leads to the leakage or release of hydrocarbons which will likely cause another explosion. Advanced nonlinear analysis in time domain is required in order to agreeably determine the dynamic behavior of the piping and vessels against blast loadings. A linear approach, for example using Caesar II software package, often gives very conservative results. This conservative design approach results in pipes and vessels with high wall thickness. Such pipes and vessels bring more weight to offshore facilities and are not desirable, especially for floating structures. In other words, advanced non-linear time domain analysis is required if weight reduction is a must. This analysis type, broadly, should consider; i. Drag load and blast overpressure, ii. Nonlinear material features for instance thermal and strain-rate dependence, iii. Effects of nonstructural masses and adjacent piping systems; iv. Pipe supports, v. Failure of flanges and piping detail, vi. Effects of operating temperature on material characteristics, vii. Blast direction/Ignition location/Attenuation sensitivity; viii. Shielding effect, i.e. pipes behind large objects such as vessels, and ix. Effects of pipe insulation, e.g. raised pipe diameters. The study, firstly, examines the approach/techniques to describe for such effects with finite element analysis. This paper then uses case studies to demonstrate the methodology that includes advanced simulation techniques for pipe blast behavior. The case studies include a piping system that is simulated from overall to detail modeling. Simulations are carried out using the general-purpose, FEA package, ABAQUS. The goal of the paper is to discuss the challenges and propose the methodology for realistic simulation of response of a piping system in a blast event. The paper is expected to serve as a complimentary example to recommended practice (FABIG Technical Notes and API 2FB 2006).
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