Flow measurement doesn't happen in a vacuum. Whether you're measuring crude oil at a custody transfer point, monitoring hazardous gas in a chemical plant, or billing customers for water usage, regulations and standards dictate how your flow metre must perform.
This guide maps the major standards landscape and helps you determine which certifications and compliance requirements apply to your specific application.
Why Flow Meter Standards Matter
Standards exist to solve three problems:
- Safety: Hazardous area classification (ATEX, IECEx) prevents explosions
- Accuracy: Custody transfer standards (MID, OIML) protect financial interests
- Reliability: Maintenance and diagnostics standards (ISO, API) ensure measurement integrity
Meeting the right standard is often a legal requirement, not optional. Non-compliance can result in failed audits, rejected custody transfers, or worse—operational shutdown.
Major Flow Meter Standards: Overview
1. ISO 5167: Differential Pressure Flow Measurement
Scope: Orifice plates, venturi tubes, flow nozzles, and related DP devices.
When it applies: Mandatory for most process industries (refining, chemicals, power generation) when using differential pressure flowmeters. Often specified in engineering specifications as "designed to ISO 5167."
Key requirements: Specifies discharge coefficients, expansibility factors, installation upstream/downstream lengths, and calculation methodology for DP flow.
Your action: Read our ISO 5167 Detailed Guide
2. ATEX 2014/34/EU: Hazardous Area Equipment
Scope: Equipment used in explosive atmospheres (gases, vapours, dusts).
When it applies: Mandatory in the EU, UK, and EEA if your process contains or may contain explosive atmospheres. North Sea oil platforms, chemical plants, refineries, flour mills, grain silos, and coal handling facilities all require ATEX certification.
Key requirements: Zone classification (0/1/2 for gas, 20/21/22 for dust), equipment category (1/2/3), protection concept (intrinsic safety, flameproof, increased safety, non-sparking), temperature class.
Cost impact: ATEX-certified flow metres typically cost 20–40% more than standard versions.
Your action: Read our ATEX Flow Meters Detailed Guide
3. IEC 61508/61511: Safety Instrumented Systems
Scope: Safety Integrity Level (SIL) ratings for safety-critical measurement and control systems.
When it applies: Any application where a measurement failure could result in loss of life, environmental damage, or major financial loss (process safety, nuclear, offshore drilling, hazardous chemical operations).
Key requirements: SIL 1/2/3 ratings based on probability of failure on demand (PFD). Mandates proof test intervals, redundancy architectures (1oo1, 1oo2, 2oo3), and documentation of failure rates.
Your action: Read our SIL Rated Flow Meters Detailed Guide
4. MID 2014/32/EU & OIML R117: Custody Transfer Metering
Scope: Measuring instruments for fiscal and custody transfer applications (energy billing, fuel dispensing, water metering).
When it applies: Mandatory in the EU and many international markets whenever measurement results are used to determine payment or settle commercial disputes. Water bills, district heating charges, fuel delivery, and clinical drug dispensing all require MID.
Key requirements: Accuracy classes (0.3%, 0.5%, 1.0%), type approval, initial verification, periodic reverification, traceability to national standards.
Your action: Read our MID & Custody Transfer Detailed Guide
5. API MPMS: Petroleum Measurement Standards
Scope: Petroleum industry measurement and sampling procedures, including flow measurement, temperature, density, and custody transfer.
When it applies: Oil and gas upstream, midstream, and downstream operations. Often specified in contracts for crude oil, refined products, and natural gas transactions.
Key requirements: Defines acceptable technologies, calibration intervals, meter selection criteria, and procedures for settling allocation disputes.
Note: API MPMS Chapter 5 (Metering Stations) often mandates Coriolis metres for custody transfer instead of DP devices due to superior accuracy and multi-phase capability.
6. NACE/ISO 14972: Corrosion Monitoring in Pipelines
Scope: Materials and inspection for corrosion-prone applications (sour service, H2S-bearing, CO2-bearing streams).
When it applies: Sour service oil and gas (H2S-bearing), CO2 pipelines, and subsea operations.
Impact on flow metres: Restricts material selection; stainless steel material certification required. Some technologies (Coriolis) may need special certifications.
7. EN 60068: Environmental Testing
Scope: Test procedures for electronic equipment exposed to temperature, vibration, humidity, and shock.
When it applies: All industrial flow metres; specifies how manufacturers test equipment reliability.
Your benefit: When you see "EN 60068 tested," you can trust the metre will survive harsh field conditions.
Standards Mapping: Which Applies to Your Application?
| Application / Industry | Primary Standard | Secondary Standards | Certification Cost Impact |
|---|---|---|---|
| Oil & Gas Custody Transfer | API MPMS + MID (EU) | ISO 5167 (if DP used) | High (±0.2% accuracy mandatory) |
| Hazardous Area (Oil Platform, Refinery) | ATEX 2014/34/EU | IEC 61511 (if SIL required) | High (+20–40%) |
| Chemical Plant (Non-Hazardous) | ISO 5167 or ISO EN 19739 | ISO 13407 (if liquid hazardous) | Medium |
| Water & Wastewater Utility | MID (EU) / AWWA (US) | EN 14615 (water quality) | Medium (±0.5%–1.0%) |
| District Heating / Cooling | MID 2014/32/EU | EN 1434 (heat metering) | Medium |
| Food & Beverage Processing | ISO 22000 (HACCP) | ISO 5167 (DP), ISO 8316 (flow) | Medium |
| Pharmaceutical Manufacturing | FDA 21 CFR Part 11 | ISO 9001, ISO 14644 | High (data integrity, traceability) |
| Power Generation (Nuclear) | IEC 61508/61511 (SIL) | ASME BPV Code | Very High (redundancy required) |
| Hydrogen / Renewable Energy | ISO/IEC 62282 (H2 safety) | ISO 5167 (generic DP) | Medium (emerging standards) |
Key Questions to Determine Your Standards Obligations
1. Does Your Process Involve Explosive Atmospheres?
If YES: You need ATEX certification (EU/UK) or IECEx (international). Exceptions: inert gas, safe practices that prevent explosive concentrations.
If NO: Continue to question 2.
2. Is Measurement Result Used to Settle Payment?
If YES: You need MID (EU) or equivalent custody transfer certification. This includes fuel delivery, water billing, district heating, clinical dispensing.
If NO: Continue to question 3.
3. Is a Measurement Failure Safety-Critical?
If YES: You likely need IEC 61508/61511 SIL rating. This includes nuclear safety systems, pressure relief interlock monitoring, blowdown protection.
If NO: Continue to question 4.
4. What is Your Industry Sector?
Oil & Gas: API MPMS (upstream/midstream); ISO 5167 (DP flows); potentially ATEX or SIL.
Chemical / Pharmaceutical: ISO 5167 (DP); ISO 9001 (quality); potentially ATEX or FDA 21 CFR Part 11.
Water / Utilities: MID (EU) or AWWA (US); ISO 14615.
Power Generation: ASME BPV Code; IEC 61508 (SIL) for safety systems.
Food & Beverage: ISO 22000 (HACCP); ISO 5167 (DP); potentially ISO 8316.
Certification Process: What to Expect
ATEX Certification (Typical Timeline: 4–6 months)
- Manufacturer prepares technical dossier (design, materials, testing)
- Notified Body (third-party lab) reviews dossier
- Type testing: explosibility, temperature classification, surface temperature limits
- EC Type-Examination Certificate issued
- Manufacturer declares conformity and affixes CE + ATEX mark
MID Certification (Typical Timeline: 3–4 months)
- Manufacturer obtains type approval from Notified Body
- Accuracy testing at independent test facility (typically 0.3%, 0.5%, or 1.0% class)
- Initial verification (first unit off production line tested)
- Periodic reverification every 2–5 years depending on accuracy class and use
IEC 61508/61511 SIL Certification (Typical Timeline: 6–12 months)
- Functional safety assessment by independent third party
- Failure Rate Data (from manufacturer or equivalent component history)
- Safety Manual documentation and proof test procedures
- SIL rating certificate (SIL 1, SIL 2, or SIL 3)
Common Compliance Mistakes to Avoid
Mistake 1: Assuming ATEX Isn't Required
Many engineers neglect ATEX in "controlled" environments. However, the directive applies to ANY location where explosive atmospheres could exist, even occasionally (maintenance, process deviations, emergency scenarios). When in doubt, conduct a Zone Classification study.
Mistake 2: Specifying Generic DP Metres for Custody Transfer
Differential pressure flow measurement can achieve high accuracy, but only if you specify ISO 5167 compliance AND rigorous calibration. Many custody transfer disputes arise from DP metres that lack traceability. Use MID-certified metres instead.
Mistake 3: Buying SIL Equipment Without Understanding Redundancy
A SIL-2-rated transmitter doesn't automatically make your system SIL 2. Your architecture (redundancy, voting logic, proof test intervals) determines actual SIL capability. Document your safety case.
Mistake 4: Ignoring Material Certifications
Sour service (NACE/ISO 14972) and corrosive applications require specific material certifications. A standard stainless steel metre may fail catastrophically. Verify material traceability.
Getting Started: Next Steps
1. Determine your regulatory obligations: Use the questions in Section 4 to identify which standards apply.
2. Read the detailed guides: We provide in-depth coverage of ATEX, SIL, MID, and ISO 5167 separately. Start with the one most relevant to your project.
3. Consult with a Notified Body or certification body: If certification is required, reach out early. They can advise on tests, timelines, and costs before you commit to a design.
4. Select your flow metre: Once you know your standards, use our selector tool to compare certified metres from leading manufacturers.
Standards By Detailed Page
We've prepared deep-dive guides for each major standard: