Standards and Design Practices
The ever-increasing flow rates in combination with the environmental constraints initiated the widespread and rapid acceptance in the last decades of HIPPS as the ultimate protection system.
The International Electrotechnical Commission (IEC) has introduced the IEC 61508 and the IEC 61511 standards in 1998 and 2003. These are performance based, non-prescriptive, standards which provide a detailed framework and a life-cycle approach for the design, implementation and management of safety systems applicable to a variety of sectors with different levels of risk definition. These standards also apply to HIPPS.
The IEC 61508 mainly focuses on electrical/electronic/programmable safety-related systems. However it also provides a framework for safety-related systems based on other technologies including mechanical systems. The IEC 61511 is added by the IEC specifically for designers, integrators and users of safety instrumented systems and covers the other parts of the safety loop (sensors and final elements) in more detail.
The basis for the design of your safety instrumented system is the required Safety Integrity Level (SIL). The SIL is obtained during the risk analysis of a plant or process and represents the required risk reduction. The SIS shall meet the requirements of the applicable SIL which ranges from 1 to 4. The IEC standards define the requirements for each SIL for the lifecycle of the equipment, including design and maintenance. The SIL also defines a required probability of failure on demand (PFD) for the complete loop and architectural constraints for the loop and its different elements.
The requirements of the HIPPS should not be simplified to a PFD level only, the qualitative requirements and architectural constraints form an integral part of the requirements to an instrumented protection system such as HIPPS.
The European standard EN12186 (formerly the DIN G491) and more specific the EN14382 (formerly DIN 3381) has been used for the past decades in (mechanically) instrumented overpressure protection systems. These standards prescribe the requirements for the over-pressure protection systems, and their components, in gas plants. Not only the response time and accuracy of the loop but also safety factors for over-sizing of the actuator of the final element are dictated by these standards. Independent design verification and testing to prove compliance to the EN14382 standard is mandatory. Therefore the users often refer to this standard for HIPPS design.
Read more about this topic: High-integrity Pressure Protection System
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