08 May 2011
As an interested but unschooled outsider, I confess to finding the topic of SIL, or Safety Integrity Level(s), to use the proper name, rather complex and hard to grasp. I was therefore very fortunate recently to meet with Mr Marc Van den Bosch. As a Sales Engineer in Flowserve’s Flow Control Division he knows a thing or two about safety in process facilities and he was both patient and kind enough to explain more about the topic.
He started by explaining that important criteria for the rating of final control elements in safety systems are design, dimensioning, production quality assurance, the outcome of in-practice endurance tests and the long-term field experiences made with the particular equipment. Appropriate testing and statistical analysis of the field experience make possible a reliable assessment of the fail-safety and the regulator's qualification as safety-relevant system in plants with a certain IEC 61508 safety integrity level (SIL). Additional benefits the operator can reap from the use of high-quality devices are higher plant availability, longer inspection intervals and better product quality.
Mr Marc Van den Bosch, Flowserve.
“Today’s businesses are all too aware of the importance of running process facilities safely and cleanly,” noted Mr Van den Bosch. “That is why we as suppliers are seeing increased interest from the marketplace in products with certification such as SIL and TA Luft.”
Mr Van den Bosch continued by explaining how clients can make risk assessments of their process facilities. “The client has to determine to possible consequences of an incident. So what might happen if for example a control valve were to fail? Would the plant continue to run safely or could the problem potentially escalate and lead to an explosion? That information can be used to create a risk assessment and thereby determine the appropriate SIL for each specific piece of equipment.”
He added: “Safety-relevant equipment and components are to be considered along the entire train of measurement and control (sensors, signal processing, actuators/regulators). All components must work trouble-free over the entire operating period. Failures always have plant safety consequences and may lead to a more or less grave disturbance of the production process. Appropriate selection and proper design of all devices, equipment and systems on the basis of reliable process data are of crucial importance in the prevention of dangerous operational conditions. This explains the interest in SIL from industries such as chemicals, petrochemicals, etc.” Using this information, the plant owner can select appropriate products from his suppliers. This means that the products themselves also need to be analysed and certified, confirmed Mr Van den Bosch. “If I speak for Flowserve, we use our extensive reference database which tracks our equipment such as valves which is installed world-wide. We record data such as their reliability, the maintenance history, etc, and use that to obtain certificates of product worthiness for specific applications.”
To ensure transparency, all SIL3/SIL4 certificates that relate to our control valves are provided by third-parties. “This helps to establish a high level of confidence amongst buyers,” he said.
Now obviously I am no expert on SIL, so any over-simplification of this topic is my fault, and not Mr Van den Bosch’s. But the message, I hope, is clear: SIL can be a very useful tool when it comes to ensuring safety in process facilities. But for more information, I am sure your local Flowserve representative would be more than willing to assist.
NB: special thanks to Mr A. Muschet, Flowserve Austria GmbH, for his comments ‘industrial valves’ 2004.