1. Three methods of operating block valves can be considered: locally, remotely and automatically.
2. The appropriate method shall be determined from a study of the likely effects of a leak and acceptable released volumes, based on the total time in which a leak can be detected, located and isolated.
3. The closure time of the valves shall not create unacceptably high surge pressures.
4. Automatic valves can be activated by detection of low pressure, increased flow, rate of loss of pressure or a combination of these, or a signal from a leak detection system.
5. Low pressure detection shall not be used if the control system is designed to maintain the pipeline pressure.
6. Automatic valves shall be fail-safe.
7. Onshore : For pipelines transporting toxic category B fluids and category C and D fluids, the installation of remotely operated sectionalising block valve is recommended to further reduce the extent of a leak.
8. The emergency shutdown valves should be automatically actuated when an emergency shutdown condition occurs at the plant or facility.
9. Offshore : The emergency shutdown valves should be automatically actuated when an emergency shutdown condition occurs on the platform.
