Oil and gas production handbook - Process Control and ...

should be handled. On the left of the chart we have possible emergency events; on
top we find possible shutdown actions. On an oil and gas facility the primary
response is to isolate and depressurize In this case the typical action would be to
close the inlet and outlet Sectioning valves (EV 0153 20, EV 0108 20 and EV 0102
20 in the diagram), and open the blowdown valve (EV 0114 20). This will isolate the
malfunctioning unit and reduce pressure by flaring of the gas.
These actions are handled by the Emergency Shutdown System and Process
Shutdown System.
System requirements are set by official laws and regulations and industry standards
such as IEC 61508/61511. which set certification requirements for process safety
systems and set criteria for the safety integrity level (SIL) of each loop.
Events are classified on a scale, e.-g. 1 to 5 plus and Abandon Platform level. On this
scale, the lowest level, APS menas a complete shutdown and evacuation of the
facility. The next levels (ESD1, ESD2) define emergency complete shutdown. The
upper levels (i.e. PSD 3, PSD 4, PSD 5), represent single equipment or process
section shutdowns. A split between APS/ESD and PSD is done in large installations
because most signals are PSD and could be handled with less strict requirements.
The main requirements concern availability and diagnostics both on the system itself
and connected equipment. The prime requirement is on demand failure, or the
system’s ability to react with a minimum probability, to an undesirable event with a
certain time with. The second criteria is not to cause actions due to a spurious event
or malfunction.
Smaller ESD systems, e.g on wellhead platforms can be hydraulic or nonprogrammable..
5.1.3 Control and Safety configuration
Piping and Instrumentation Diagrams (P&ID) show the process, additional
information is needed for the specification of the Process Control and Safety
Systems.
The illustration shows one typical format common format for the Norwegian
offshore industry: The Njård Separator 1 and 2 Systems Control Diagram (SCD.
Essentially, the P&ID mechanical information has been removed, and control loops
and safety interlocks drawn in with references to typical loops.
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