Common Standards Used for Integral Flanges (ASME, API, EN)

Integral flanges are typically specified under ASME, API, or EN standards, depending on the pressure class, application environment, and regional compliance requirements. In practice, ASME standards dominate general industrial and piping systems, API standards apply to high-pressure and oil & gas service, and EN standards are widely used in European projects and EPC-driven specifications. Selecting the correct standard directly affects pressure ratings, dimensional compatibility, inspection scope, and long-term system reliability.

Understanding how these standards apply to an integral flange is essential for engineers, procurement teams, and project managers involved in custom piping systems.

What standards are commonly used for integral flanges?

Integral flanges are not always listed as a standalone product category in standards, but their dimensions, pressure ratings, materials, and testing requirements are governed by established flange and pressure equipment standards.

The most commonly referenced standards include:

• ASME B16 series (especially B16.5 and B16.47)

• API standards such as API 6A for high-pressure service

• EN standards such as EN 1092-1 for European flange systems

Each standard serves different operating conditions and industries.

ASME standards for integral flanges

ASME B16.5 – The most widely used reference

ASME B16.5 is the most frequently applied standard when specifying an integral flange for industrial piping systems.

It defines:

• Nominal pipe sizes (½” to 24”)

• Pressure classes (150 to 2500)

• Dimensional tolerances

• Facing types

• Material groupings

Although ASME B16.5 does not explicitly label products as “integral flanges,” integral flange designs are commonly machined or forged to comply with B16.5 dimensional and pressure requirements, particularly when welded directly to pipes or pressure components.

Typical applications

• Petrochemical piping

• Power plants

• General industrial pipelines

• Custom fabricated piping assemblies

ASME B16.47 – Large-diameter considerations

For integral flanges exceeding 24 inches, ASME B16.47 may be referenced for dimensional guidance. While integral flanges are often custom-made, alignment with B16.47 dimensions ensures compatibility with standard mating flanges.

Why ASME standards are preferred for integral flanges

ASME standards are favored because they:

• Are globally recognized

• Provide clear pressure–temperature ratings

• Simplify compatibility with standard valves and fittings

• Are widely accepted by EPC contractors and inspectors

For many projects, specifying an integral flange manufactured in accordance with ASME B16.5 reduces technical and commercial risk.

API standards for integral flanges in oil & gas service

API 6A – High-pressure and critical service

API 6A is commonly applied when integral flanges are used in high-pressure, high-integrity oil and gas systems, such as:

• Wellhead equipment

• Christmas trees

• High-pressure flowlines

• HPHT applications

API 6A governs:

• Pressure ratings beyond typical ASME classes

• Material traceability

• Enhanced testing and inspection

• Product-level certification requirements

An integral flange built to API 6A requirements typically undergoes stricter quality control than standard industrial flanges.

When should API standards be specified?

API standards are preferred when:

• Operating pressures exceed conventional ASME limits

• Sour service or H₂S resistance is required

• The project is governed by upstream oil & gas specifications

• Full material traceability and certification are mandatory

In these cases, an integral flange designed under API rules provides higher confidence in structural integrity and sealing performance.

EN standards for integral flanges

EN 1092-1 – European flange standard

EN 1092-1 is the primary European standard for steel flanges, covering:

• PN pressure ratings (PN6 to PN400)

• Metric dimensions

• Material designations under EN systems

Integral flanges supplied for European projects are often custom machined to match EN 1092-1 flange dimensions, ensuring compatibility with valves, fittings, and piping supplied by EU-based manufacturers.

Key differences between EN and ASME standards

Understanding these differences is critical when an integral flange must interface with mixed-standard systems.

ASME vs API vs EN – Technical Comparison for Flange Selection

How do standards affect material selection for integral flanges?

Material requirements are closely tied to the governing standard.

• ASME-based integral flanges commonly use ASTM A105, A182 F316, or alloy steels

• API-based designs may require enhanced impact testing, sour service compliance, or special alloy grades

• EN-based projects specify materials according to EN 10222 or similar standards

In all cases, material certification and traceability must align with the referenced standard, particularly for pressure-retaining components.

Are integral flanges fully standardized products?

Integral flanges are often custom-manufactured rather than mass-produced, even when built to ASME, API, or EN requirements.

Standards typically define:

• Dimensional envelopes

• Pressure ratings

• Material groups

• Inspection criteria

However, the final geometry of an integral flange is usually engineered to match a specific system, especially when welded directly to pipes, vessels, or manifolds.

This makes standard compliance even more important, as it ensures the custom component integrates safely into standardized piping systems.

How to specify the correct standard for an integral flange

When preparing a technical specification or RFQ, the following should be clearly stated:

• Applicable standard (ASME, API, or EN)

• Pressure class or PN rating

• Design temperature

• Material grade and heat treatment

• Testing and inspection requirements

• Dimensional compatibility with mating components

Clear standard selection reduces engineering revisions, manufacturing delays, and inspection disputes.

Choosing the right standard improves long-term performance

Selecting the appropriate standard for an integral flange is not just a documentation step—it directly impacts safety, compatibility, and lifecycle cost.

• ASME standards suit most industrial and process piping

• API standards are essential for high-pressure oil & gas systems

• EN standards ensure compliance with European projects and regulations

For engineered piping systems, aligning the integral flange design with the correct standard ensures reliability from fabrication through long-term operation.