A safety study of the pipeline and upstream process has identified that it is feasible to generate a high pressure in the system upstream of the liquid-gas separator vessel V01.

The project team has decided to implement the SIL 3 capable high pressure protection system (HIPPS) upstream of the liquid-gas separator vessel V01 as a change to the project. 

A fault tree study for the over pressure scenario has been completed and the target PFDavg for the HIPPS SIF has been selected as PFDavg = 0.0002.

The pipeline safety study has identified the process safety time for the hazard scenario as 20 seconds and propose time for the SIF be 70% of the time.

For the purpose of the assignment assume the diameter of the pipeline is 300mm.

Assuming a low demand mode of operation, you are required to carryout market research to identify components that comply with IEC 61508 and using the component safety manual obtain the data necessary data for you to develop the architecture for the SIF.

Base the design go the SIF on the following type of equipment:

Sensor sub system: Based on pressure Transmitter with smart functionality with diagnostics

Logic solver sub system: Solid data with diagnostics

Final element sub system: Quarter Turn valve with spring return actuator (air fail closed) and electrical solenoid, no diagnostics.

For each of the components selected state:

- The IEC 61508 device type

- Safe failure fraction

- Dangerous detected and undetected failure rates

- Required hardware fault tolerance for SIL 3 capable system based on the appropriate IEC 61508-2 hardware fault tolerance tables

- The estimated response time of the device

Assume the estimated response time for valve is 25mm.

 

a) Propose a hardware architecture that you assume will meet SIL 3 target in terms of hardware fault tolerance, systematic capability and achieve the target PFDavg of 0.0002 and draw a system block diagram of the SIF clearly identufying each of the components in the SIF, to which sub system it has been allocated and the interconnections between the components.

 

b) Calculate the overall response time for the SIF architecture and compare it to propose overall SIF response time of 70% of the process safety time, and state if the response time is achieved.

 

c) For your chosen SIF architecture, using the data from your market research of your chosen components, calculate the probability of failure on demand average (PFDavg) for each of the sub systems and for the overall SIF, ensure that you account for common cause failures with the SIF architecture.

 

d) Compare the calculated PFDavg to the target PFDavg of 0.0002. State if the following targets have been achieved for the SIF:

- PFDavg

hardware fault tolerance for SIL 3 capability

- Systematic capability for SIL 3 capability 

- SIF response time