SIS design and engineering

The objective of this subclause is to provide guidance in the design of the SIS. Each SIF has its own SIL. A component of a SIS, for example, a logic solver, may be used by several SIFs with different SILs. 

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The objective of the requirements of this ciause is to design one or muitipie SiS to provide the safety instrumented function(s) and meet the specified safety integrity ievei(s). 

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Clause 11 SIS design and engineering Standard discusses designing one or multiple SlSs to provide SIF and meet SIL requirements. 

SIS DESIGN AND ENGINEERING (lEC 61511 CLAUSE 11) Requirements for functional specification... 

Fig. 2, Box 4 SIS design and engineering To design the SIS to meet the requirements for safety instrumented functions and safety integrity 11 and 12.4 sis safety requirements Software safety requirements Design of the SIS in conformance with the sis safety requirements planning for the SIS integration test...

It is usually the best practice to work through design calculations in the units in which the result is to be presented but, if working in SI units is preferred, data can be converted to SI units, the calculation made, and the result converted to whatever units are required. Conversion factors to the SI system from most of the scientific and engineering units used in chemical engineering design are given in Appendix D. 

The SIS is normally designed to fail-safe on loss of power and takes action only when the process demands that it do so. These demands often occur when safe operating limits are exceeded due to BPCS failures. Therefore, the SIS is designed and managed to be independent of the BPCS in terms of its hardware and software and its user interfaces, such as operator, maintenance, and engineering interfaces. 

As the United States moves toward acceptance of the International System of Units, or the so-called SI units, it is particularly important for the design engineer to be able to think in both the SI units and the U.S. customary units. From an international viewpoint, the United States is the last major country to accept SI, but it will be many years before the U.S. conversion will be sufficiently complete for the design engineer, who must deal with the general public, to think and write solely in SI units. For this reason, a mixture of SI and U.S. customary units will be found in this text. 

In the 4 phase (2013-2017) and 5 phase(2018-2021), the engineering scale demonstration facihty( 10,000 Nm /h) will be designed and constructed in partnership with the industry. In the first half of 2019, the facilify will be coupled to the VHTR system. After a completion of the safefy check for the coupling system between the VHTR and the engineering scale SI facility, a full power hydrogen generation test by the VHTR will be conducted finally in 2020. 

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