In order to assess the safety of an oil pipeline, a HAZOP (Hazard & Operability) analysis was carried out in accordance with the following standards:
- “Petroleum and natural gas industries – Offshore production installations – Guideline on tools and techniques for hazard identification and risk assessment” Std. ISO 17776;
- IEC 61882: “Hazard and Operability studies – Application guide.
Once the safety instrumented functions (SIF) have been identified, their SIL classification (SIL Allocation) has been identified in accordance with the following standards:
- IEC – 61508 Functional safety of electrical / electronic / programmable electronic safety-related system;
- IEC – 61511 Functional Safety – Safety Instrumented System for the Process Industry sector.
Once the SIL level was assigned, it was verified that the design achieved could reach the assigned SIL level.
Failure on Demand testing must take into account the reliability characteristics of the loop, including test intervals, its architecture, and level of diagnostics.
The probability of failure on demand results from the combination of the contributions of the three subsystems: sensor, logic and final element.
The analyzed pipeline connects a refinery to the port, where crude oil is received and finished products are shipped by sea. The oil pipeline has a length of about 20 km and along its path there are motorized shut-off valves equipped with limit switches which determine the automatic blocking of the transfer. In the arrival and departure stations, pressure control systems in majority logic (2oo3) are installed which, in the event of deviation from normal operating conditions (high and / or low pressure), cause the booster pumps to stop.
Since an adequate communication system is required to operate the motorized valves in the chambers, it has been redundant. In case of lack of signal, the system is expected to stop immediately (Pumping stop).
Software used: Exilentia (EXIDA)