Two 24 inch underground High Integrity Pressure Protection System (HIPPS) protecting the equipment and piping upstream of a compressor station in the Netherlands.
This compressor station at the Dutch coast is supplying gas to the United Kingdom at high pressures of approximately 130 bars. In case of a shut-down or failure of the compressor the high downstream pressure could reach the lower rated equipment and piping at the inlet of the compressor. This could cause damage and significant danger to people therefore a SIL3 rated safety instrumented system (SIS) is installed. This HIPPS closes the final elements (valve and actuator) to protect the equipment and piping upstream of the compressor from over-pressure.
The large quantities of gas transported require an inlet piping of 36 inch (DN900) class 900 (PN150). After detailed discussions between the client, the engineering contractor (EPC) and the Mokveld Functional Safety Engineers a solution with 2 parallel 24 inch (DN600) class 900 lines was selected. This design is an optimum in maintainability, availability and total cost of ownership without compromising the required safety level. The high capacity of the Mokveld axial flow valves minimises the pressure loss and thus reduces cost of compression.
Closing within 2 seconds
Since the upstream volume between the compressor and the battery limit is small, a response within 2 seconds is required. Standard valves would close in 1-2 seconds per inch size and thus in minimum 24 seconds. It was considered that increasing the speed of standard valves would have a negative effect on the failure rate of these valves and therefore the reliability of the complete system would be jeopardised.
Therefore the Mokveld axial HIPPS was selected.
For this application an electronic system (in preference to the mechanical version) was selected due to the long distance between the final elements and the sensors. Mokveld supplied the full loop comprising two parallel streams of each two final elements, three pressure transmitters mounted on a high integrity manifold block and a solid state hard-wired Voting Logic performing the 2oo3 voting of the pressure transmitter signals.
The failure data of the Mokveld final elements are field proven failure data of final elements closing within 2 seconds, independent of size. Therefore the Mokveld final elements made it possible to design a SIL3 Safety Instrumented System for a 24 inch or even 36 inch size.
The Mokveld functional safety engineers (FSE) have supported the client during the FEED, basic engineering and detailed engineering and commissioning. A continuous support will be give during the life-cycle of the system by Mokveld FSE after-sales engineers.
In order to ensure you continue to benefit from valves that offer high capacity and safety as standard, we offer a range of modernisation services. For more information about our modernisation services, please contact your Mokveld support office or representative.