SIL Solver® Frequently Asked Questions

1. Are there any special software requirements for SIL Solver?

No. SIL Solver® was developed using Microsoft Foxpro and does not require any additional software beyond Microsoft Windows (see 2). SIL Solver® installs in a user-designated directory and operates independently of other software. It does require administrative rights to the installation computer. SIL Solver® uses Crystal Reports as the print interface, so the computer registry must be accessed to register the license for Crystal Reports. If SIL Solver® is installed without administrative rights, the software will install and will operate normally from a user standpoint, but the reports will not print and error messages will be displayed to the user when the print function is used. After installation, the user must have read, write, and modify rights to the SIL Solver® folders.

2. What versions of Windows does SIL Solver support?

SIL Solver 5.53 and higher has been tested and successfully installed on Windows 98, Windows Me, Windows NT, Windows 2000, Windows XP, Windows 7, Mac Snow Leopard and Mac Lion. Both Mac OS requires Parallels.  SIL Solver has not been tested on Windows Vista.

3. Are there any special hardware requirements for SIL Solver?

At least 64MB of available memory is recommended.

4. Does SIL Solver support mirrored drives?

No. While the majority of SIL Solver® features will function normally, the rename and delete features do not work properly when SIL Solver® operates using a mirrored drive. SIL Solver® must be provided with a physical address for the program and data files.

5. Can the user designate where SIL Solver is installed?

Yes. During installation, the user can select either the default location or another location. The folder specified during installation establishes where SIL Solver® program files are located. This folder location cannot be changed without re-installation. Projects created in SIL Solver® are stored as folders in the default directory C:/silsolver_projects. The user can change this default directory by selecting Options Project Files Location on the project screen (main screen) in SIL Solver®. The function and project reports are generated by Crystal Reports, which uses templates that are located in c:/SILSolver_CR_Dbf. This template location may not be changed by the user. The user must have read, write, and modify rights to the SIL Solver® program directory, the project files location (default – C:/silsolver_projects_, and c:/SILSolver_CR_Dbf.

6. Does SIL Solver support a multi-user installation?

No. Version 5.53 only allows a single user to access the project folders at any one time.

7. How much data is in the device database?

There are currently over 150 devices in the SIL Solver® database. The database has grown through the years and users with active licenses receive the new device data with program updates. Users may also add their own devices and failure rate data.

8. Where does the data come from?

The data is based on a variety of sources. The data accounts for typical process application impact, covering the full boundary of the device. Each data sheet contains a listing of the data sources that were reviewed during the data selection process. The database is a compilation of failure rate data from various industry published databases, end-user data, and manufacturer data.

9. How does SIL Solver® do the calculations?

SIL Solver® is an advisory software package intended for use in the verification of the Integrity Level (IL) of Protective Instrumented Functions (PIF) commonly encountered in the process industries. SIL Solver® utilizes reliability block diagrams with fault tree equations to calculate the probability to fail on demand (PFDAVG) and the MTTFspurious of the protective instrumented function (PIF). SIL Solver® uses globally recognized standards and methodologies to analyze components, subsystems, and PIFs, such as:
ANSI/ISA 84.00.01-2004 (IEC 61511)
ISA TR84.00.02
IEC 61511
IEC 61508

SIL Solver® is capable of analyzing PIF with multiple input and output elements, tested at different intervals, including partial stroke testing of valves, and includes a device failure rate database.

10. What are the report features?

Crystal Reports is used as the backplane for report construction. There are currently seven reports: 1) documentation, 2) safety function summary, 3) safety function details, 4) safety function data, 5) device data sheet, 6) logic solver data sheet, and 7) support system data sheet. Custom reports can be constructed.

11. Has the data been accepted by regulatory authorities?

SIL Solver data has been used to support submissions to regulatory authorities of various governments across the world. For example, it has been used to demonstrate to OSHA that SISs were designed sufficiently to prevent event recurrence, to EPA as part of consent decree response, and to HSE for safety case submission.

12. What voting architectures are available?

SIL Solver is structured to allow rapid modeling of instrumented functions in an easy to use interface. SIL Solver provides 1oo1, 1oo2, 1oo3, 2oo2, 2oo3, and 3oo3 in both diagnostic and non-diagnostic configurations. SIL Solver limits the selected voting architectures to reduce potential systematic error.

Some process requirements specifications will include voting architectures that are 2ooN, where N can be a large number, e.g., 2oo9, 2oo16, and 2oo50. While the IPS logic may be implemented in this manner, these architectures are misleading from a verification standpoint, because they often indicate more fault tolerance than is actually provided by the installation. For example, a 2oo9 architecture requires that 8 devices fail dangerously before a hazardous event occurs; 2oo16 requires 15 failures, and 2oo50 requires 48 failures.  It is unlikely that 9, 16 or 50 devices would be installed if all were measuring the same process condition and addressing the same process hazard.

2ooN architectures with large N values typically indicate applications where the unacceptable process condition can occur in multiple distinct locations, e.g., a hot spot on the vessel wall. What appears to be a redundant architecture is actually a simplification of what could be a more complex voting scheme. For example, in the case of a plugged flow reactor, it may be that 2oo3 voting sensors are used in each of three reactor zones, leading to an overall 2oo9 voting scheme. The verification of the risk reduction should be based on the voting architecture that detects the hazardous event. In the case of 2ooN architectures, the voting architecture is usually 2oo2 or 2oo3 at best.

13. What percentage of functions can be modeled?

Beginning users can model more than 90% of the safety functions associated with refining and petrochemical applications. Power users can increase this percentage significantly by breaking the function down into subsystems for modeling. FaultTree can also be used to independently model very complex portions of a function.  SIL Solver provides fields for manual entry of the resulting input or action results to yield the overall performance.

14. What limits the test interval selection?

SIL Solver provides pre-built test intervals for user selection. The test intervals are daily, weekly, monthly, 3 months, 6 months, 12 months, 18 months, 2 years, 3 years, 4 years, 5 years, 6 years, and 7 years. The default data is limited to 7 years, because there is insufficient evidence that the assumed failure rates are valid when the equipment undergoes such infrequent proof testing. Of course, the user can build custom datasheets and enter any test interval desired, whether a whole number or fraction.

The user should choose the test interval, which provides the most cost effective maintenance scheduling meeting the PFDAVG and has been proven through experience to be sufficient to maintain the equipment in the “as good as new” condition. In general, the test interval is constrained by production schedules which provide off-line access to equipment. Opportunities for inspection, preventive maintenance, and proof testing should be identified by process engineering and operations personnel in the process requirements specification.