Equipment sizing, risk assessment

Engineering design, chemical reactivity hazard management, 23 Equipment design, documentation, 105 Equipment sizing, risk assessment, 95 Existing management systems, chemical... 

Crawley and Grant (1997) have developed a risk assessment tool for new offshore installations. They have examined typical leak frequencies of equipment items and the ignition probability of these leaks in four pressure bands. With this information it was possible to define leak size and frequency for any piece of equipment and the ignited leak frequency. In off-shore installations gas separation vessels were found to have ten times higher ignited event frequency than oil pumps. 

Accidental fires interact with their environment, should this be pipework, equipment and structures in process plants in petrochemical industry, or facilities on offshore oil and gas installations. For plant design and risk assessment, cautious best estimates and uncertainty ranges are required for a number of combustion parameters. These include release rates, flame size and shape, heat output, thermal radiation to its environment, and the heating-up of structures, pipework and items of equipment. The estimate can result in the assessment of time to loss of functionality of these structures and pressurized equipment. 

The user enters the (legislative) requirements and his wishes concerning the equipment in the URS (see Sect. 21.5.2 for a URS based on risk assessment). Then he tries to find a supplier who can supply a machine or installation that meets the URS. After the URS the FRS has to be drafted. The FRS results from the translation of the wishes of the user (what should it be able to do ) to the functionality and design of a device or installation (how are the requirements met ). The functional requirements describe what the equipment should be able to do and how it should look, such as the size or the materials to be used. Sometimes technical requirements are laid down in a separate document, the TRS. On the basis of these specifications a vendor may then, if necessary, design the machine or installation. The more carefully the user prepares the URS and FRS, the better the quality of next steps are. 

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