ISO 7005-1 Steel Flanges: Series Selection and Scope

Understanding ISO 7005-1:2011

ISO 7005-1:2011, titled "Pipe flanges – Part 1: Steel flanges for industrial and general service piping systems," is a base specification that establishes requirements for steel pipe flanges used in general-purpose and industrial piping systems. It is applicable across a wide range of industries, including chemical processing, power generation, and petroleum and natural gas facilities. The standard covers flanges intended for systems handling various fluids such as steam, pressurized water, chemicals, oil, gas, and related products. Example installations include steam power plants, oil refineries, loading terminals, natural gas processing plants (including LNG facilities), offshore oil and gas production platforms, and chemical plants.

One of the key aspects of ISO 7005-1 is that it places the responsibility for selecting the flange series on the purchaser. This means that when specifying flanges to ISO 7005-1, the buyer must clearly define which series (PN or Class) is required, along with other critical parameters.

Flange Series: PN vs. Class

ISO 7005-1 references two distinct flange series: the PN series and the Class series. These series are based on different pressure designation systems and are not automatically interchangeable. The PN series uses pressure ratings in bars (e.g., PN 10, PN 16, PN 25, PN 40), while the Class series uses rating class designations such as 150, 300, 600, etc., which are commonly associated with ASME B16.5.

The standard defines terms such as "flange nominal size (PN series)" and "flange nominal size (class series)" to distinguish between the two systems. It also defines "flange rating designation (PN series)" and "flange rating designation (class series)" to clarify the pressure rating terminology.

Because the series selection is left to the purchaser, it is essential to specify the correct series in your procurement documents. Failure to do so can result in mismatched flanges, leading to leaks, safety hazards, and costly delays.

ISO 7005-1 vs. ASME B16.5

ASME B16.5 is a separate flange system with its own rating classes, dimensions, materials, tolerances, marking, and testing requirements. It covers pipe flanges and flanged fittings from NPS 1/2 through NPS 24, with rating classes 150, 300, 400, 600, 900, 1500, and 2500 (the latter limited to NPS 1/2 through NPS 12). ASME B16.5 provides requirements in both metric and U.S. customary units, with bolt diameters and hole dimensions expressed in inch units.

While ISO 7005-1 references ASME B16.5 as a source for the Class series, it is crucial to understand that flanges manufactured to ISO 7005-1 and those manufactured to ASME B16.5 are not automatically interchangeable. Even if the nominal size and pressure rating appear similar, differences in dimensions, facing, drilling, and tolerances may exist. Therefore, you must confirm the exact flange series, nominal size system, pressure designation, facing, drilling, and the specific edition of the standard being used.

Procurement Checks for ISO 7005-1 Flanges

When sourcing flanges to ISO 7005-1, consider the following checklist to ensure compliance and avoid costly errors:

• Flange Series: Clearly specify whether you require PN series or Class series flanges. If Class series is needed, confirm that the flanges meet the relevant ASME B16.5 requirements.
• Nominal Size System: Indicate whether you are using metric (DN) or NPS (nominal pipe size) designations. ISO 7005-1 covers both, but the correct system must be stated.
• Pressure Rating: Provide the exact pressure rating (e.g., PN 16 or Class 150) and ensure it matches the design conditions of your piping system.
• Facing and Surface Finish: Specify the flange facing type (e.g., flat face, raised face, ring joint) and the required surface finish (e.g., serrated, smooth).
• Drilling: Confirm the bolt hole pattern and dimensions, including the number of holes, bolt circle diameter, and hole size.
• Material Specification: State the material grade and applicable standard (e.g., ASTM A105 for carbon steel, ASTM A182 for alloy/stainless steel).
• Edition of Standard: Indicate the exact edition of ISO 7005-1 (e.g., ISO 7005-1:2011) and any referenced standards (e.g., EN 1092-1, ASME B16.5).
• Marking and Testing: Verify that the flanges are marked in accordance with the standard and that required testing (e.g., hydrostatic, dimensional) is performed.

RFQ Inputs for ISO 7005-1 Flanges

When preparing a request for quotation (RFQ), include the following information to ensure accurate pricing and delivery:

• Flange type (e.g., weld neck, slip-on, blind, socket weld, threaded)
• Nominal size (DN or NPS)
• Pressure rating (PN or Class)
• Facing type and surface finish
• Material grade and standard
• Quantity
• Required certifications (e.g., EN 10204 3.1 or 3.2 material test certificates)
• Any additional testing or inspection requirements

Inspection and Documentation Points

During inspection, verify that the flanges meet the specified requirements:

• Dimensional Inspection: Check critical dimensions such as outside diameter, thickness, bolt circle, and hub dimensions against the standard.
• Material Verification: Review material test certificates to confirm chemical composition and mechanical properties.
• Marking: Ensure each flange is marked with the manufacturer's name or trademark, material grade, size, pressure rating, and heat number.
• Visual Inspection: Look for surface defects, cracks, or other imperfections that could affect performance.
• Testing: If required, witness hydrostatic testing or other non-destructive examinations.

Common Risks and How to Mitigate Them

• Interchangeability Assumption: Assuming ISO 7005-1 flanges are interchangeable with ASME B16.5 flanges without verification can lead to joint failure. Always confirm the exact series and dimensions.
• Incomplete Specifications: Failing to specify the flange series or edition can result in receiving the wrong product. Use a detailed RFQ and purchase order.
• Material Mismatch: Ensure the material grade is suitable for the service conditions (temperature, pressure, corrosion).
• Documentation Gaps: Insufficient documentation can delay project approvals. Require full material test certificates and inspection reports.

Conclusion

ISO 7005-1:2011 is a comprehensive base specification for steel flanges in industrial and general service piping. Its scope is broad, covering major industries, but it places the onus on the purchaser to select the appropriate flange series. By understanding the differences between PN and Class series, and between ISO 7005-1 and ASME B16.5, you can make informed procurement decisions. Always verify the specific requirements with your supplier and ensure all documentation is in order.

For more information on flanges and other piping components, visit our products page or contact us for expert assistance.

Sources

• https://www.iso.org/standard/42467.html
• https://www.antpedia.com/standard/6239892-1.html
• https://www.asme.org/codes-standards/find-codes-standards/b16-5-pipe-flanges-flanged-fittings-nps-1-2-nps-24-metric-inch-standard