FEATURE PROCESS SAFETY HOW SAFE DO YOU NEED TO BE?
Selecting measurement instruments that can offer maximum protection against potentially dangerous or catastrophic failures can play a major role in helping to minimise the risk of injury or loss of life in industrial applications. One way to do this is to select SIL-rated instruments. In this article, David Bowers, product manager Pressure and Process Flow for ABB Measurement and Analytics in the UK, explains more about SIL, its impact on process safety and the important factors to consider when specifying equipment for a SIL application
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David Bowers, product manager Pressure and Process Flow for ABB Measurement and Analytics in the UK
oday’s industrial processes rely heavily on the determination and
implementation of safety systems and requirements to identify potential risks and maintain a safe place for operators to work. Where measurement instruments are concerned, devices need to be evaluated and checked to ensure they can offer maximum protection in the event of a potentially hazardous situation. This is where SIL comes in. Defined by IEC 61508, the SIL (Safety
While SIL is commonplace in the petrochemical industry, there is no reason why it should not be applied across other industries as a matter of best practice
Integrity Levels) methodology was created as a way of evaluating and quantifying the effectiveness of a safety system and the probability of failure on demand (PFD) within hazardous processes handling dangerous fluids and chemicals. SIL ratings range from SIL1 to SIL4, with the lowest number corresponding to a lower chance of a system failure. As the SIL rating increases, so too does the cost of maintaining an instrument to be SIL compatible, reflecting the seriousness and impact of a potential failure. When dealing with SIL, it is important
to understand and distinguish between the different requirements relating to SIL-approved instruments and SIL- rated applications.
Instruments themselves are not given
a SIL rating; the rating instead applies to the process the instruments are being used in. Any instrument that is going to be measuring a dangerous parameter in a hazardous environment has to be approved and be suitable for operation within a SIL location. Individual safety instrumented functions (SIF) and safety instrumented systems (SIS) within a process can obtain SIL ratings, but instruments can only be perceived as being compatible with a particular SIL-rated application. Instrument providers supplying any
measuring device for use in a SIL rated application must undertake rigorous qualification and testing to ensure it is safe and will not fail in place. Furthermore, the device must be able to perform self-verification checks. Self- verification can check the instrument’s current operational status and can even predict future faults. In most cases, test data can be downloaded directly to produce verification and service reports that can then be evaluated. If instruments are not continuously checked, recalibrated and maintained, then all safety measures are effectively rendered invalid, underlining the importance of having a comprehensive
maintenance programme in place. The performance of the instrument
also needs to be tested and guaranteed fully operational before it is sent to site. For instance, the coil resistance of a MagMeter or the oscillating tubes of a Coriolis flowmeter need to perform with the highest level of accuracy possible. When it comes to SIL rated sites, the
entire site needs to be SIL approved to avoid a catastrophic disaster. In addition, operators need to be concerned with any instrument that might fail in place. To counter this worry, all SIL rated sites must have a second device as back-up in case the primary instrument breaks down or ceases to work, which can prove costly. Any back-up device needs to be different from the primary device in order to reduce the chance of total failure across a particular range of instruments. Typically, a back-up instrument may come from a different manufacturer; or in the case of SIL3 applications, in a redundant configuration. Given the importance of safety in
modern industrial applications, it is perhaps worrying that SIL is not a more common legal requirement within general industry. Granted most industries are not as dangerous or hazardous as the petrochemical industry, but why wouldn’t operators in the food and beverage sector want to know if a measuring device was accurate or in fact was not working at all? There is no reason why stricter safety measures should not be applied across the board as a matter of best practice. In a perfect world, it would be ideal if SIL
become standard practise, with no alternatives on offer. With a larger take up, SIL compatible instruments would become the norm, which in turn would drive down the cost, ultimately helping all industries to be safer and more efficient. To find out how ABB can help
you assess your SIL requirements and make your process safer, visit
http://bit.ly/ABB-SIL, email
enquiries.mp.uk@
gb.abb.com or call 01642 372115, ref. ‘SIL’.
ABB
www.abb.com
16 WINTER 2018 | INDUSTRIAL COMPLIANCE / INDUSTRIALCOMPLIANCE
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