Use of Tools for Operation and Maintenance of SIS

The Maintenance of SIS (Safety Instrumented System) could become a very challenger activity if some considerations were not made in the project life cycle. The maintenance team should be focused in two activities; The Preventive Maintenance, which includes the periodic test or predictive activities and  On Demand Maintenance, which includes all emergencies for the process operation, but the project mistakes have some influence in the maintenance job.

The activities related with Preventive Maintenance are affected by projects that are not considered indication of standards such as IEC 61511 or some mistakes on SRS (Safety Requirement Specification).

The IEC 61511-2 is described on item 11.8, Maintenance or testing design requirements:  “If the SIS is to be tested while the process is running, the design should not require the disconnection of wires, applying jumpers or forcing software registers since using these techniques may jeopardize the integrity of the SIS. The system design should provide technical and procedural requirements of the SIS in order to accomplish full system testing of sensors, logic solver and final elements safely”. The typical solution used is to plan a Maintenance by-pass procedure and manage by alarms on the operator stations. Unfortunately in some cases  it is necessary to execute physical jumpers or forces in the safety controllers, both actions degraded the safety of the layer SIS and they are very difficult to be managed.  

The SRS could describe a periodic proof test interval that is not compatible with the process operation generally because they are very complex for the operation or the procedure of test could  cause disturbances on process. The most critical elements to be tested are the final elements; there are many solutions for by-pass or partial test (like partial stroke test in valves). Usually the definition of the final elements happens after the emission of the SRS and the Hazard Analysis (example:  HAZOP, ALARP, LOPA, etc.). The proof test, when not well planned, could create conflicts between the operation team and the maintenance, the typical solution for these cases are related in the Hazard Analysis executed during the operation, unfortunately the solutions could be expensive, not applicable in operation or generate a complex procedure difficult to be managed. 

There are many tools to support the management of safety life cycle for maintenance. The correct use of tools like “Device Asset Management”, “By-pass management”, “Systems alarm management” and “SIF Management” could reduce exposition to risk.   The tools aren’t self-managed, it is necessary to create a team or a personnel responsible for managing the KPI’s for safety, safety culture, training and qualification of the team is the base for collect results from the tools.

The article presents some situations where functional descriptions of the tools were not planned during the project can create risks during the maintenance of SIS.