Process and Machinery Safety
Many installations feature safety instrumented systems (SIS) providing a level of risk reduction and claim to be SIL compliant as per BS EN / IEC 61511. These systems have been designed to bring the process to safe conditions in the event of mal-operation. This safe operation is through the design and implementation of safety instrumented function (SIF) loops and other means of inherently failsafe design.
Many safety instrumented functions are operating in low demand mode, where the final elements such as valves are effectively dormant until needed to act. The only way to ensure that the SIF loop will operate correctly in the event of a trip is via periodic proof testing; a sometimes-overlooked aspect of the safety lifecycle. Without maintaining a proof test and inspection regime an installed SIS cannot be claimed to maintain SIL compliance.
Proof testing differs to normal testing, as a SIF proof test must be designed to reveal otherwise unrevealed faults that prevent the SIS from operating in accordance with the safety requirements specification. The goal is to exercise every active device in the SIF loop. This may be a subset or repeat of many of the steps that should have occurred during the original validation testing.
Inspec Solutions have TÜV certified Functional Safety engineers who understand the importance of regular SIF proof testing in order to maintain the original design integrity levels, and as such we offer a comprehensive testing service to ensure regulatory compliance.
Starting with all available documentation, we review the “As-built” (or As-Validated) documents to baseline the operation. This includes numerous different documents, but typically we start with:
- Piping & Instrumentation Diagrams
- Cause and Effects Diagrams
- Wiring Schematics
- General Arrangements
- Safety Requirements Specifications
- Proof Test Procedures
Where conflicts occur between documents (usually when they have not been well controlled through the systems lifetime, especially in legacy systems), we ensure to understand and document the discrepancies before commencing testing.
After establishing the documentation status, we carry out a physical SIS inspection, in order to anticipate in advance of failures:
- Inspect for obvious damage or signs of corrosion/degradation
- Check equipment tags / SIF identification
- Check software and/or firmware revisions match document records
- Check for wiring, cable or termination issues
- Check for poorly supported pipework/cabling
- Cabinet security from unauthorised access
- Signs of moisture/water ingress
- Leaks from piping or gaskets
The above list is not exhaustive, and the original equipment supplier installation/operation/maintenance manuals will be used to provide further information to understand operation.
At the end of the inspection phase, the “As-Is” status of the equipment is recorded before any test or rectification of problems takes place. This ensures that causes of problems are captured prior to problems being fixed.
Following the initial inspection, SIF proof testing is commenced. Testing is preferably completed offline, when the equipment is not in-service protecting against a real hazard, although online testing can be carried out in a closely controlled and monitored manner.
The result of the testing is fully documented so that the records can be used for regulatory compliance, future improvement where appropriate and elimination of potentially dangerous failures.
Typically, the testing report contains;
- Document name, unique number, issue date, author and revision information
- A list of documentation that was reviewed before the tests were undertaken
- Information on the document audience, detailing who is intended to use the procedure and perform each task
- Any special tools, equipment, or access requirements for the test
- Instruction & fields to record tags, SIF loop identifier, software and firmware, where applicable
- Specific instructions to record the current condition of each active SIF device
- Detail of the hazard and consequences of failure, with mitigating measures for on-line tests
- Detailed step-by-step task instructions for the test sequence
- Pass / Fail criteria per step, with comments
- Space to record the post-test condition of each device
- Space to record the tester name, signature and date(s) of the test
Inspec Solutions SIF Proof Testing service is designed to ensure that your systems maintain compliance and operations whilst removing the distractions from your maintenance personnel.
“Following a recent HSE audit Wavin have gone above and beyond the remit of the audit, committing to Functional Safety at every level of the business.
Inspec Solutions have supported Wavin every step of the way with HAZOP, LOPA & SIL verification services in an exemplary manner, advising and executing the work in a highly professional and quality way. Their support has been invaluable in our continued drive for the safety of our hazardous processes.”
Chris Earl – Site Operations Manager – Clayware and Balbriggan – Wavin