Reliability Analysis of a Safety Critical System

Client: AkzoNobel

AkzoNobel had designed and built a chlorine production facility in Germany and wished to be assured that, in the event of an incident on site leading to a possible release, the facility would be able to safely and reliably dispose of all chlorine that had already been produced.

In 2012 Egerton Consulting was invited to carry out a reliability analysis of the electrical power system that was proposed at that time. However, the design was subsequently revised and our client asked us to update their analysis of the power system and also to assess the reliability of three other functions, all of which were important in terms of demonstrating the value of the protection systems that had been developed.

We worked closely with our client to understand the systems being analysed, the equipment that comprised those systems and the planned operating and maintenance strategies. In order to achieve this Egerton Consulting visited AkzoNobel’s offices in The Netherlands during which our reliability specialists liaised with the client’s process and electrical engineers to:

1. Gain a detailed appreciation of the design and proposed mode of operation of the various systems – this allowed us to identify those combinations of equipment required to work for the system to function adequately.
2. Establish appropriate failure rates and repair times for critical items – these were collated from a variety of sources including the expert judgement of our client’s engineers.
3. Construct fault trees for each of the scenarios being considered and calculate the frequency or probability of failure for each of the proposed scenarios.
4. Identify and carry out appropriate sensitivity studies to investigate the effect on system reliability of changing the frequency of equipment proof testing.

The above analysis provided assurance that the frequency and downtimes of the electrical power supply would meet the stringent targets that had been set whilst highlighting those components for which prompt repair in the event of failure would be most important. However, the analysis also highlighted a need for more frequent proof testing for certain components than had previously been proposed. As a result AkzoNobel amended their proof testing strategy for those critical items in line with Egerton Consulting’s recommendations.

More information about the facility can be found here