Fieldbus-based Safety Instrumented Systems (SISs) came a step closer to reality last month when the Fieldbus Foundation conducted an end-user demonstration at Shell Global Solutions facility in Amsterdam, following earlier demonstrations at a BP facility in Germany and a Chevron facility in Houston. The Amsterdam meeting marked the latest stage in the Safety Instrumented Function (SIF) program first initiated by the Foundations board in October 2002.
The overall system concept received TÜV approval at the end of 2003 and the resultant SIS protocol specifications were granted Type Approval to SIL3 in line with IEC 61508 by TÜV Rheinland in December 2005.
In essence, the protocol extends Foundation fieldbus technology to provide a comprehensive solution for SIFs and enables manufacturers to build Foundation fieldbus devices in compliance with IEC 61508. Agencies such as TÜV will then certify the devices as being in compliance and hence as being suitable for use in safety systems. End-users will therefore be able to meet the requirements of IEC 61511 when buying devices from multiple suppliers, rather than being restricted to devices designed specifically for proprietary SIS platforms from a particular vendor. Some thirty companies including major users, vendors and certification agencies have participated in the project.
A key feature of the development process has been an extensive program of laboratory testing during which prototype device suppliers independently implemented the specifications and the test team separately developed test cases and prepared expected test results. The result, says director of technology development David Glanzer, has been to verify that the protocol meets the needs of industrial end users. TÜV Type Approval will help meet the growing worldwide demand for commercial, standards-based, safety instrumented system products incorporating Foundation fieldbus technology, he told representatives of the press at the Amsterdam meeting. End users can now adopt the powerful diagnostics available with Foundation fieldbus and, at the same time, maintain the protection in a SIL3 environment. No changes were required to our existing H1 protocol to add the SIS protocol extensions, clearly indicating the value of the comprehensive, forward-thinking design of Foundation technology.
End-user driven
End users have been the prime movers behind the SIS development, seeing in it the potential to reduce their reliance on proprietary safety platforms and increase their ability to access open, interoperable technologies. One of the leading advocates of the approach is Saudi Aramco whose Process Instrumentation Division engineering specialist, Patrick Flanders, sees it as allowing closer integration of the complete emergency shutdown loop, thus reducing installation cost and improving the capabilities of field devices by communicating self-diagnostic information directly to the safety logic solver. At Saudi Aramco, we see this as a breakthrough in the advancement of SIS design, he said.
Using a DCS controlled demonstration rig with graphic panels showing the safety devices and functions and an operator interface for asset management diagnostic information, in PRM and in the DCS, Shells Audun Gjerde was able successfully to demonstrate a total of 12 safety-related functions involving multiple vendors devices and including high- and low-level trips, manual trips, voting and validation functions and partial stroke testing.
Extended up time
According to Gjerde, once the technology is commercially available, We will be able to run for longer without shutting down the plant for testing purposes, or save on the cost of adding a second or third device.
When will all this be available? The consensus seems to be that it will be sometime in 2011 before vendors have gone through the necessary approval cycles and are able to offer complete product lines.
