A label "ISO/PN compliant" that passes in Europe can slow down a project in North America. Here, the framework remains ASME (pressures/temperatures, ends) and API (specifications by type + testing). ISO is mainly used for testing methods (e.g., ISO 5208, ISO 15848) when the client requests it or to harmonize practices. The good reflex:  take ASME as the backbone, then add API or ISO without creating contradictions.

1 - The three families: Roles and scopes

ASME (American Society of Mechanical Engineers) - The pressure/temperature & ends foundation

ASME B16.34 defines the pressure/temperature ratings by class (Class 150/300/600/900/1500/2500), by material (group of carbon steel, stainless steel, alloys), and imposes requirements for minimum thicknesses, design, and testing.

The ends refer to other ASME standards:

• B16.5 (flanges NPS ½ to 24),

• B16.47 (flanges beyond NPS 24),

• B16.25 (BW welded ends),

• B16.11 (SW fittings) and B1.20.1 (NPT threads).

  
  

In North America, we talk about NPS/Class rather than DN/PN. ASME B16.34 remains the safeguard to check that the valve holds the announced conditions.

API (American Petroleum Institute) - Specifications by type & testing

• API 600 : gate valves made of cast steel, flanged bonnet (refining).

• API 602 : compact gate/globe/check (small diameters, forged).

• API 608 : ball valves metal, threaded ends, flanged, welded.

• API 609 : butterfly valves Lug/Wafer types (cat. A/B).

• API 598 : leak testing body/seating and acceptance criteria by valve type.

• API 607 / API 6FA :  fire-safe tests (in practice 607 for soft-seated quarter-turn; 6FA more “general fire”).

• API 641 : fugitive emissions (quarter-turn packing).
  
  

🛢️ In oil & gas/refining, API is the mother tongue.

ISO (International Organization for Standardization) - International testing methods

• ISO 5208 : leak testing methodology with classes A to G (A being the strictest).

• ISO 15848 : fugitive emissions (Tightness/Endurance Classes).
  
  

🌐 ISO is useful for aligning global suppliers. However, one must ensure to specify the class and not overlay it with the API 598 standard without a defined hierarchy.

2 - How to specify in a Canadian tender

Petrochemicals / Refining

To specify : ASME B16.34 (class + material) + API by type (600/602/608/609) + API 598.
Add: API 607 if the valve has soft seats &API 641 or ISO 15848 if the project requires certified performance on fugitive emissions.

This facilitates the QA/QC (Quality Assurance / Quality Control) audit and maintenance of installations.

Water / Communities

To specify : ASME B16.34 (class + material) + ISO 5208 (please indicate leak class) or API 598.

This allows for technical adequacy without over-specifying. Adding heavier standards when not necessary inflates costs without adding value in standard applications (water, steam, air, common processes).

Steam & utilities (High pressure + High temperature)

To specify : ASME B16.34 → design and mechanical resistance standard. It provides the pressure/temperature curves by material : this indicates if a valve in A105, F316, etc., can hold X bar at Y °C.
To specify : API 598 or ISO 5208 → these are the leak testing standards (hydrotest, leak tests). One must choose a protocol (one or the other), but not double unnecessarily.
Key point : seats & packing compatible (PTFE filled, PEEK, metal-metal) according to T/ΔP (temperature and pressure differential) and cycling. Example: PTFE = good for moderate utilities, but not stable at 250 °C; metal-metal = robust in HP/HT but more expensive.

💡Good reflex : always ASME B16.34 first (class, material, ends), then API 598 or ISO 5208 (not both without hierarchy), and, if needed, API 607/641 or ISO 15848 as supplements.

3 - Frequent errors

1. Mixing Class and PN in the same line

✔︎ Choose a main reference (NPS/Class in Canada/USA). Provide an indicative PN↔Class table (reading), but size exclusively using ASME B16.34.

2. Stacking API 598 & ISO 5208

✔︎ One testing protocol for leak testing. If ISO 5208, specify the class. If API 598, no need to add ISO 5208 unless project requirements, but with a clear hierarchy.

3. Forget local maintenance

✔︎ Check the standard footprints (e.g. ISO 5211 for actuator mounting bases), seat/packing kits, and the local availability in North America of parts. This point saves weeks of downtime.

4 - Decision method based on 5 criteria

1. Safety/Compliance : ASME B16.34 (class, material) vs actual P/T curves.

2. Performance : API 598 or ISO 5208 (class), supplements API 607 / API 641 / ISO 15848 if required.

3. Process compatibility : fluid, T, P, corrosion/abrasion, cycling.

4. Maintenance : standardization, ISO 5211, kits, North America network.

5. Total cost & timeline : purchase + energy (losses/leaks) + MRO + supplier delays.

Purchase = acquisition price of the valve.
Energy = overconsumption due to losses or leaks.
MRO = Maintenance, Repair, and Operation: everything that touches the operational lifecycle of the valve, costs related to maintenance, repair, spare parts, maintenance labor, production downtime…
Supplier delays = the delivery time of parts and equipment.

What VAMECA does:
We transform your technical criteria into a simple choice sheet with two options compared (A/B).
Each option highlights the impact on cost, delivery time, and lists the required documents: MTR (Material Test Report - Material Certificates), WPS/PQR (Welding Procedure Specification / Procedure Qualification Record - Welding Procedures), test reports, CSA/UL/FM/Ex certifications for classified areas.

Result: you save time, avoid unnecessary over-specifications, and secure your compliance from the start.

☎︎ Contact Vameca today to simplify your choices and accelerate your projects.

5) PN ↔ Class Table

* Indicative ≠ calculation basis. Always refer back to the P/T curves of ASME B16.34 and the material actually supplied. The equivalence between American pressure classes (ASME/ANSI) and European PN (Pressure Nominal) is not exact, as the two references do not use the same calculation bases (pressure/temperature, materials, safety coefficients). ⚠️

6 - Reception FAQ

Can we size in ASME and accept according to API?
Yes. It is the recommended practice: use ASME B16.34 for sizing (pressure/temperature, material) and API 598 for acceptance after testing (or ISO 5208 if requested and well defined).

What to do if an existing site is in PN and the new section in Class?
Set NPS/Class as the main reference. Provide an indicative PN ↔ Class table to facilitate matching, but always validate according to ASME B16.34 (pressure/temperature curves + material).

Is an “API Monogram” required?
The monogram applies only to manufacturers. As a distributor/integrator, the important thing is to provide the documents required by the client:  MTR, API 598/ISO 5208 test reports, certificates and complete traceability.

Conclusion

In North America, the most reliable path is to use ASME B16.34 as the design reference, to rely on API 598 for acceptance testing, and to resort to ISO only when a specific testing protocol is required. It is essential to avoid mixing PN and Class on the same piping line and to define a single clear testing protocol. This approach ensures compliant purchases, unambiguous receptions, and controlled local maintenance.