Failure Rate Library
A failure rate library provides a structured way to manage equipment reliability information that can support safety instrumented system design and ongoing lifecycle decisions. Within Safety Lifecycle Manager (SLM), Prior Use Certificates (PUCs) can hold manually entered failure-rate information as well as in-service failure rates calculated from operational event data.
This creates a connection between the reliability assumptions used for equipment and the experience accumulated while instruments and devices are operating in the field. Instead of treating failure-rate information as an isolated design input, organisations can maintain model-specific records and build evidence from actual service history.
This guide explains how the SLM Failure Rate Library uses Prior Use Certificates, how failure-rate information is populated, how PUCs are associated with devices, and how operational experience can contribute to prior-use qualification.
What Is a Failure Rate Library?
A failure rate library is a structured repository for reliability information associated with equipment or model types. Within SLM, this capability is centred on Prior Use Certificates (PUCs), which can be created for instrumentation model types used by instruments and devices.
PUCs exist at the enterprise level and can be managed through the Global and Operate & Maintain modules. They are separated according to equipment use, including Input PUCs, Output PUCs and Logic Solver PUCs. This distinction is important because the same certificate cannot simply be shared between different instrument kinds.
SLM can maintain manually entered failure-rate values for a PUC while also calculating in-service failure rates using operational event information. This allows engineering reference data and accumulated operating experience to coexist within the same model record.
For safety instrumented systems, maintaining reliable lifecycle information is particularly important because equipment assumptions do not end when a system enters service. The Safety Instrumented System guide provides additional context on how SIS information fits into the broader functional safety lifecycle.
Creating and Managing Prior Use Certificates
A Prior Use Certificate represents an instrumentation model type against which reliability and usage information can be maintained. When a new PUC is created in SLM, the model number is entered and the record is saved before its remaining configuration and reliability information is populated.
Where organisations need to establish or update larger libraries, PUC records can also be imported through the SLM Adapters module. This provides an alternative to editing each certificate individually when multiple records or fields need to be maintained.
Each PUC must correspond to the appropriate instrument category. SLM separates certificates into Input, Output and Logic Solver PUCs so that model information can be associated with the correct type of instrument or device.
This structure helps prevent reliability information from being applied without regard to the equipment’s function. It also provides the basis for associating operational event information with the appropriate model type later in the lifecycle.
How Cascading PUC Fields Classify Equipment
Correct classification is fundamental to the way SLM associates Prior Use Certificates with instruments and devices. PUC records therefore use cascading fields in which the options available in one field depend on selections made previously.
For an Input PUC, for example, selecting a function such as Transmitter and then a process measurement such as Pressure produces the relevant Input Type options. Selecting another process measurement, such as Flow, produces a different set of applicable options.
The available values can be configured by administrators through the IO Type Codes reference table in the System module. These options correspond with the related data fields used for inputs, outputs, logic solvers and devices.
This classification is more than an administrative convenience. The selected fields allow SLM to attribute PUCs to appropriate instruments and devices and subsequently accumulate relevant device-event information back against those model records.
Failure Rate Library Data and Failure-Rate Sources
The failure rate library can contain both manually entered reliability information and failure rates derived from operating experience. These sources serve different purposes and should be understood separately.
For manually maintained information, a PUC can record up to three externally sourced failure rates together with a manufacturer’s failure rate for the model type. SLM also provides a Default Design Failure Rate for Enterprise field. According to the demonstrated SLM workflow, this value is used as the design-basis failure-rate source within SIL calculation functionality.
The value selected for that design basis can come from one of the recorded external sources or another appropriate rate entered by the user. This enables the organisation to retain supporting reliability references while identifying the particular value being used for its design basis.
In-service failure rates operate differently. They are calculated from event data captured through the Operate & Maintain workflow and therefore will not initially contain accumulated operational information for a newly created PUC.
This distinction between assumed or externally sourced data and actual operating experience is valuable for lifecycle reliability management. IEC 61511 addresses the specification, design, installation, operation and maintenance of safety instrumented systems as part of a lifecycle approach. The IEC 61511-1 publication provides the authoritative standard context for these SIS lifecycle requirements.
Associating Prior Use Certificates with Devices
A PUC cannot automatically be selected for every instrument simply because it exists in the enterprise library. Device association is controlled by the site’s usage configuration for the certificate.
Before a PUC becomes available for an instrument or device at a particular site, that site must first be configured as an allowable location for use of the PUC. Once site usage is enabled and the appropriate instrument type and manufacturer selections are made, the corresponding PUC can become available for selection.
Devices associated with the certificate are then displayed within the Model Usage information for that PUC. This establishes the relationship needed for SLM to connect model information with the equipment using that model.
The relationship is particularly important when operational history is being collected. The related Logging Events workflow explains the event-recording side of the Operate & Maintain process, while Service Status Change Event covers another part of the operational data that can contribute to equipment history.
Using In-Service Data to Build Prior Use Evidence
One of the principal benefits of connecting PUCs with devices is the ability to build reliability evidence from operating experience. SLM can track device events and service information associated with the model type and use this information when calculating in-service failure rates.
The PUC view can provide usage information including accumulated hours in service, overall calculated failure rates and failure rates according to severity of service. This gives users operational information that can contribute to decisions concerning the suitability and qualification of a particular model type.
The distinction between externally sourced reliability information and actual prior-use experience is important. A published or manufacturer failure rate represents one source of evidence, whereas accumulated operating history reflects experience with equipment being used within the organisation’s own operational environment.
The separate How to Gather Prior Use Failure Rate Data guide provides further detail on the workflow for accumulating this operational reliability information.
Device Usage Approval and Prior Use Qualification
SLM allows additional usage information to be maintained for a Prior Use Certificate. This can include the severity of services for which a model type is considered acceptable, its certification status and basis, and qualification information relating to areas such as equipment usage, standards compliance and personnel training.
An important distinction in the demonstrated workflow is that certification status and site usage are not the same control. SLM can permit a PUC to be associated with instruments or devices when its site usage configuration allows it, even when the model type has not yet been marked as certified for use.
This means the decision over whether a model should be used remains with the organisation and its users rather than being automatically determined by the software’s certification-status field. It can also allow service hours to begin accumulating while a model type is still developing the evidence needed to support its qualification.
That makes governance important. Qualification status, operational evidence and engineering approval should be understood in their appropriate context rather than treating the existence of a PUC as proof that a device is automatically suitable for every safety application.
Why Failure Rate Data Matters During SIS Operation and Maintenance
Reliability assumptions influence decisions throughout the SIS lifecycle. During design, failure-rate data may contribute to quantitative assessments and calculations. Once equipment enters service, organisations also have an opportunity to compare those assumptions with evidence generated through actual operation.
A structured failure rate library helps maintain that relationship by keeping model information, reference failure rates, device associations, service experience and qualification information connected rather than distributed across unrelated records.
For organisations managing substantial installed equipment populations, this can improve traceability when engineers need to understand which models are in use, where they are permitted, what operating experience has been accumulated and what reliability information is available to support lifecycle decisions.
Other Operate & Maintain workflows complement this process. Tier 3 Metrics provides another perspective on operational performance information, while Configuring Test Groups addresses the organisation of testing activities within the module.
Managing Failure Rate Information with Safety Lifecycle Manager
Safety Lifecycle Manager provides a structured environment for maintaining the Prior Use Certificates described in this guide. The workflow brings together model classification, externally sourced reliability information, enterprise design-basis values, site usage, device associations and operational event information.
The broader MSS Safety Systems solution supports the management of safety-system information across the lifecycle. Within the Operate & Maintain workflow demonstrated here, the Failure Rate Library provides a way to connect equipment reliability assumptions with information accumulated from devices operating in service.
This approach does not replace the engineering judgement required to determine whether equipment is suitable for a particular safety application. Instead, it gives engineers and functional safety teams a structured record from which reliability evidence, usage history and qualification information can be reviewed and maintained.
