ASME B16.48 Line Blanks: Scope, Classes and Buyer Limits

What ASME B16.48 Covers

ASME B16.48 is the standard that defines operational line blanks — commonly called spectacle blinds or figure-8 blanks — used to isolate piping systems. The standard sets requirements for pressure-temperature ratings, materials, dimensions, tolerances, marking, and testing. Its scope is specific: it covers line blanks in sizes NPS 1/2 through NPS 24 that are installed between flanges conforming to ASME B16.5. The pressure classes included are 150, 300, 600, 900, 1500, and 2500.

For EPC engineers and procurement managers, this means that when you specify a line blank, you must ensure it matches the flange standard and class of your piping system. B16.48 is not a standalone design code; it works in conjunction with ASME B16.5 for flange dimensions and with the applicable piping code (e.g., ASME B31.3) for pressure design.

What B16.48 Does Not Cover

It is important to understand the limits of this standard. B16.48 does not provide guidance on whether a line blank is suitable for a particular service fluid, pressure, or temperature. That determination is the responsibility of the engineer based on the process conditions and the material selection. The standard only gives dimensional and testing requirements for the blank itself.

Also, B16.48 does not cover line blanks for flanges outside the ASME B16.5 series, such as large-diameter flanges per ASME B16.47. If your project uses those flanges, you will need to reference other standards or custom engineering.

Pressure Classes and Sizes

The standard lists six pressure classes: 150, 300, 600, 900, 1500, and 2500. For each class, the dimensions and pressure-temperature ratings are defined. The size range is NPS 1/2 to NPS 24. Note that for class 2500, ASME B16.5 flanges are only available up to NPS 12, so line blanks above that size in class 2500 are not covered by B16.48. Always verify the flange size and class compatibility.

Materials and Marking

B16.48 specifies material requirements, but it does not list every possible material. Typically, line blanks are made from carbon steel, stainless steel, or alloy steels that conform to ASTM standards. The standard requires that each blank be marked with the manufacturer's name or trademark, the size, the pressure class, and the material grade. Marking must be durable and legible.

When ordering, you must specify the material grade and any additional requirements such as impact testing for low-temperature service. The standard itself does not mandate impact testing; that is driven by the project specification or the applicable code.

Procurement Checks for Buyers

When you issue an RFQ for line blanks, include the following:

• Standard and edition: e.g., ASME B16.48-2025 (or the edition required by your project).
• Size and pressure class: e.g., NPS 6, Class 300.
• Material grade: e.g., ASTM A105 for carbon steel, ASTM A182 F304 for stainless.
• Flange standard: Confirm that the mating flanges are ASME B16.5.
• Testing requirements: e.g., hydrostatic test, PMI, or NDT as per your specification.
• Marking and documentation: Require MTC (mill test certificate) per EN 10204 3.1 or 3.2, and a certificate of conformance to B16.48.

Before purchase, verify that the manufacturer's quality system is adequate. Ask for their inspection and test plans, and if needed, arrange third-party inspection.

Inspection and Documentation Points

During inspection, check the following:

• Dimensions: Verify the blank's outside diameter, thickness, and bolt hole alignment (if applicable) against B16.48 tables.
• Marking: Ensure the marking is correct and matches the purchase order.
• Material verification: Review the MTC for chemical composition and mechanical properties. If required, perform PMI on a sample.
• Surface condition: Look for cracks, pits, or other defects that could affect service.
• Testing records: If hydrostatic testing is required, confirm that it was performed and the results are acceptable.

Common Risks and How to Avoid Them

One common mistake is assuming that a line blank conforming to B16.48 is automatically safe for the intended service. The standard only covers dimensional and testing aspects; the material selection and pressure-temperature rating must be verified by the engineer. Another risk is mismatching the blank with the flange standard — for example, using a B16.48 blank with a flange that is not B16.5. Always confirm compatibility.

Also, be aware that B16.48 is on stabilized maintenance, meaning it is no longer actively revised but remains in effect. The current edition is 2025. Always specify the edition you require, as older editions may have different requirements.

Conclusion

ASME B16.48 is a key standard for line blanks used in piping isolation. By understanding its scope and limitations, you can specify, procure, and inspect these components with confidence. For a wide range of pipe fittings and flanges, including line blanks, visit our products page. If you have specific requirements, feel free to send us an inquiry.

Sources

• https://www.asme.org/codes-standards/find-codes-standards/b16-48-line-blanks
• https://www.asme.org/codes-standards/find-codes-standards/b16-5-pipe-flanges-flanged-fittings-nps-1-2-nps-24-metric-inch-standard