What is SIL? Understanding Its Importance in Butterfly Valve Safety

There are huge safety risks that come with using the wrong type of butterfly valve for the temperature and pressure level of your application. Poorly installed butterfly valves can also cause problems. However, even when using a properly installed butterfly valve within its design limits of pressure and temperature, there can be valve failures that result in dangerous leaks. Of course, there are industry standards designed to regulate the market and ensure the valves you’re using are up to code. To minimize safety risks using butterfly valves, you want to look into the SIL rating of your butterfly valves and of the other parts in your processing system. The SIL of a valve or other part in your system is a measure of “Safety Integrity Levels” based on international standards. In this post, we’ll look at what SIL is all about and the role it plays in keeping your facility running smoothly and safely.

Safety Integrity Levels (SIL) and Butterfly Valves

To reduce industrial accidents, valves include safety functions. For example, when the pressure gets too high, your processing system can have a safety valve that opens. When the temperature of the material being processed gets too high, you can have an inlet steam valve that automatically closes. The performance of a valve’s safety features is measured in terms of the Probability of Failure on Demand (PFD). Through this calculation, you get a SIL level as an indication of system reliability and integrity, and it’s measured on a scale of 1 to 4 (4 being the safest and most unlikely to fail).

At SIL-1, there’s a 0.01 to 0.1 percent chance of failure on demand. At SIL-2, the odds decrease to a 0.01 to 0.001 percent probability. SIL-3 rated valves, which are considered the best value for the safety level and cost, have only a 0.0001 to 0.001 percent chance of failing. SIL-4 offers the highest safety level, with a failure probability of 0.00001 to 0.0001 percent. While it’s technically safer, it costs a lot more to put in place compared to SIL-3 valves, which are still unquestionably safe. It may seem these failures on demand probabilities are “one in a million.” However, given the frequency of operation butterfly valves endure in systems like energy generation and water processing, narrowing the odds of failure as much as possible is of the utmost importance.

Which SIL Level is Right for You?

The safety features in place, and thus the SIL ratings that result, are ultimately determined by a valve’s end-user. Therefore, it’s up to the plant owner must determine an acceptable risk level based on their budget. Safety functions aren’t cheap, so costs increase when higher SIL levels are achieved. Some plant owners have to meet specific SIL requirements per their insurance company’s policy. When it comes to butterfly valves, many companies accept a SIL 2 rating. When you get a package deal on a butterfly valve with the safety functions included, it can be a great value, costing you little to nothing more than achieving a SIL-2 rating on your own.

To determine the SIL of the various parts that make up your processing plant, you must form a Hazard and Operability Study (HAZOP) team. The team must analyze each part of the processing system and question its integrity and potential risks. Murphy’s Law is a great rule of thumb: what can go wrong, will go wrong. Once potential risks are identified, the team must assess whether any actions are necessary to remedy these risks. If action is needed, the HAZOP team should identify safety functions capable of preventing dangerous incidents, as well as stop-gaps that can mitigate the effects of an accident. 

Next, operations personnel, design engineers and instrumentation engineers can perform corrections as needed to improve safety levels. Once actions have been taken and new safety functions are in place, a new analysis must be made. New SIL ratings must be determined for the updated system. 

Butterfly Safety – In Conclusion

SIL is meant to help plant owners protect their business and the safety of their staff by measuring the probability of failure. Selecting the right SIL for your application is ultimately a risk management task. Each part that makes up a processing system has its own SIL rating, and the SIL level of each safety function in your system doesn’t need to be the same. Butterfly valves play a huge role in the safety level of the system as a whole because they control flow within the system. We recommend you stick to butterfly valves that are SIL–3 or higher SIr, and Value Valve can handle the safety features for you. With a SIL-3 Butterfly Valve Value Package, you can ensure long-lasting use of your valve and prevent safety hazards in the most critical applications.