NAMUR NE 130

Reliability of Field Devices in Functional Safety Applications

NAMUR NE 130 specifies how operators should collect, analyze and use field device failure data for Prior Use justification in functional safety applications. It complements IEC 61511's Route 2H (Prior Use route) for proving SIL capability.

Organisme: NAMUR
Family: Process Instrumentation
Première publication: 2014
Dernière révision: 2014
Prochaine révision: Stable
Statut: current
Accès: Free to NAMUR members; otherwise paid (~€50 from NAMUR.eu)

Structure du document

NAMUR NE 130

Reliability of field devices in functional safety applications

Single recommendation. Defines minimum statistical population (typically 5000 device-years or 100 devices over 10 years), failure data collection requirements, statistical confidence levels, and the documentation needed for Prior Use justification.

Concepts clés

Prior Use: IEC 61511 Route 2H. A device qualifies for use in a SIS without IEC 61508 certification IF the operator can demonstrate sufficient operating experience with documented failure data. NE 130 specifies what 'sufficient' means quantitatively.
Population requirement: NE 130 typically requires 5000 device-years OR 100 devices over 10 years to establish credible MTBF / failure rate statistics for a given device type in a given application context.
Failure classification: Each observed failure must be classified : safe vs dangerous, detected vs undetected, attributable to the device vs to the installation. Misclassification invalidates the statistics.
Operational profile match: Prior Use evidence is only valid for the same operational profile. A pressure transmitter qualified in Zone 1 ambient -20/+50°C cannot be Prior Use'd into a -40/+80°C environment without additional justification.
Confidence level: NE 130 recommends 70% lower confidence bound on the MTBF estimate. Higher confidence (90%) for SIL 3 applications. The point estimate is biased optimistic; confidence bounds give a more honest reliability number.

Notes & guidance

Why Prior Use matters

A typical refinery has 5000-20000 field instruments. Replacing all of them with IEC 61508-certified equivalents to deploy a SIS would be financially impossible. IEC 61511 anticipated this : Route 2H allows an operator to keep using legacy instrumentation in a SIS IF they can prove its reliability empirically rather than by analytical certification.

But “we’ve had a pressure transmitter installed for 20 years and never had a problem” is not evidence. NE 130 turns hand-waving into rigor by specifying :

What data to collect (failures, operating hours, environmental context)
How long (5000 device-years OR equivalent)
How to classify failures (safe/dangerous, detected/undetected)
How to compute confidence-bounded MTBF
What documentation survives an audit (FSA Stage 3 reviewer or competent authority)

Statistical population requirements

For a given device type + application context, NE 130 recommends:

Target	Minimum data	Equivalent
SIL 1	~1000 device-years	~50 devices × 20 years
SIL 2	~5000 device-years	~250 devices × 20 years, or 500 × 10 years
SIL 3	~25000 device-years	Usually requires aggregated industry data, not single site

This is why SIL 3 via Prior Use is rare — single sites cannot accumulate 25k device-years of comparable installations. SIL 2 via Prior Use is achievable in mature plants. SIL 1 is essentially always possible.

Operational profile drift

A key NE 130 requirement is that Prior Use evidence applies only within the operational profile of the original installation. If the new application differs in :

Ambient temperature range
Process medium (different chemistry, vibrations, viscosity)
Mounting orientation
Maintenance regime
Process pressure / temperature swing range

…then the Prior Use claim is only partially valid and needs supplementary justification (e.g., supplementary lab testing, or FMEDA for differing aspects).

This is why a transmitter qualified by Prior Use in tank level service can’t be silently moved to slurry flow service. The operator must reassess.

Practical implementation

Asset register with installation date, environmental context, application type, tagged failures
Failure capture process : maintenance work orders explicitly tag “this work order is a failure / not a failure”
Periodic review (annual) : compile statistics by device family + application
Documentation : Prior Use Justification document for each device family used in SIS, kept up-to-date and reviewed at FSA Stage 3

Modern CMMS systems (SAP PM, IBM Maximo, Aveva ERM) can be configured to support this but most installations need explicit workflow adjustments.

How the future Asset Management app will help

The planned Asset Management app (assets.industryhub.cloud, planned 2026) is being designed around NE 130 from day one:

Failure tagging built into the work-order workflow
Auto-computed MTBF with confidence bounds per device family + application
Operational profile audit (alerts when a device is moved to differing service)
Prior Use Justification report generation per FSA Stage 3 requirements

For now, the FIT ↔ MTBF calculator in our Tools section gives you the basic conversion math.

Industries concernées

Process industries with mature asset registries (oil & gas, chemical, pharma)
Plants with large installed base of legacy field instrumentation
Operators implementing IEC 61511 Edition 2 (which requires Prior Use justification)