MSS SP-44 Flange: Dimensions, Pressure Ratings & Material Guide (2026 Edition)

When specifying large-diameter pipeline flanges, engineers often find themselves navigating three overlapping standards: MSS SP‑44, ASME B16.47, and ASME B16.5. Knowing which standard applies - and why - is essential for correct specification and procurement.

This guide provides a complete, practice‑oriented overview of MSS SP‑44 steel pipeline flanges, based on the latest ANSI/MSS SP‑44‑2026 edition, with insights drawn from more than 12 years of manufacturing stainless steel flanges.

What Does MSS SP Stand For?

 

MSS stands for Manufacturers Standardization Society of the Valve and Fittings Industry, Inc. - a U.S.-based standards development organization focused on valves, fittings, flanges, and pipe supports. SP stands for Standard Practice, which is MSS's designation for its published technical documents. Therefore, MSS SP-44 refers to Standard Practice No. 44, which specifically governs steel pipeline flanges.

Definition & Scope

MSS SP-44 is a standard practice that defines requirements for steel pipeline flanges used in high-pressure, large-diameter pipeline applications. It covers pressure-temperature ratings, materials, dimensions, tolerances, marking, and testing. The current edition is ANSI/MSS SP-44-2026, published by the Manufacturers Standardization Society and approved as an American National Standard.

The standard was established approximately 50 years ago in response to industry demand for pipeline flanges in sizes larger than those covered by ASME B16.5 - particularly for use with high-strength, thin-wall carbon steel line pipe, which requires special considerations at the welding end of the flange.

Size range: NPS 12 to NPS 60 (DN 300 to DN 1500), in two-number intervals 

Pressure classes: Class 150, 300, 400, 600, and 900

Flange types: Weld Neck, Blind, Slip On, Lap Joint 

For NPS 10 and smaller, dimensional requirements refer to ASME B16.5

This is one of the most frequently asked questions about MSS SP-44, and the answer is straightforward: MSS SP-44 is technically equivalent to ASME B16.47 Series A.

When ASME published B16.47 - the standard for large-diameter steel flanges - it adopted MSS SP-44 as the technical basis for Series A. The two documents share the same dimensional data, pressure-temperature ratings, and material requirements for sizes NPS 12 to NPS 60. In practice, specifying 'ASME B16.47 Series A' and 'MSS SP-44' refers to the same flange.

 

Important note: Series A (MSS SP-44) and Series B flanges are NOT interchangeable above NPS 26 - bolt hole count, outside diameter, and flange thickness all differ. Always confirm which series your piping specification requires before ordering.
 

MSS SP-44 covers the following flange types. Weld neck flanges must be forged steel; blind flanges may be made from either forged steel or steel plate.

MSS SP-44 addresses five pressure classes. Ratings are based on material grade and service temperature; the values below represent the baseline pressure ratings at 38°C (100°F) for Grade F42 as a reference point.

Note: Pressure ratings decrease as temperature increases. When MSS SP-44 flanges are mated with valves and used at temperatures between 100°F and 450°F (38°C–232°C), the valve's pressure rating will be lower than the flange rating. Always verify the limiting component in the assembly.

MSS SP-44 covers nominal pipe sizes (NPS) from 12 to 60 in two-number intervals. The corresponding DN values are listed below. For NPS 10 and smaller, dimensional and tolerance requirements are provided by reference to ASME B16.5.

Note: NPS 22 flange dimensions are only available in MSS SP-44 - this is the sole source for NPS 22 above NPS 24 coverage.
 

Key dimensional parameters specified in MSS SP-44 include outside diameter, flange thickness (C dimension), raised face diameter and height, bolt circle diameter (PCD), number and diameter of bolt holes, and weld end bevel dimensions for weld neck flanges.

For detailed dimension tables by class and size (including bolt hole count, PCD, and flange thickness for each NPS/Class combination), contact CNCJ to request our complete MSS SP-44 dimension reference sheet.
 

All materials used in the manufacture of MSS SP-44 flanges must be fully killed steel - steel that has been completely deoxidized before casting. This ensures high chemical homogeneity and eliminates gas porosity, which is critical for the integrity of high-pressure pipeline joints.

MSS SP-44 defines material grades by minimum yield strength (in ksi), from F36 to F80:

About Grade F52

F52 is one of the most widely specified grades for oil and gas transmission pipelines. With a minimum yield strength of 359 MPa (52 ksi) and good weldability, it provides the right balance of strength and field fabrication performance. F52 is directly compatible with API 5L Grade X52 line pipe - making it the natural flange choice when the pipeline pipe body is X52.

Weld Compatibility

MSS SP-44 flanges are suitable for field welding to pipe, fittings, and other flanges manufactured to the following specifications: ASTM A105, A53, A106, A350, A381, A516, A537, A694, A707, and API 5L.

Carbon Equivalent (CE) Requirement 

Based on ladle analysis, the maximum carbon content is 0.30% and the carbon equivalent (CE) shall not exceed 0.48% without prior purchaser approval. If CE exceeds 0.45%, the actual CE value must be stamped on the flange.

The following chemical composition limits apply to all MSS SP-44 flange materials (based on ladle analysis), per ANSI/MSS SP-44-2026:

Note (2026 update): The combined Cu+Ni+Cr+Mo limit has been removed from Table 1 in the 2026 edition, harmonizing with current ASME B16 practice.

Hardness & Impact Testing

Maximum hardness: HBW 235 for all grades.

Impact testing is not required for Grade F42 and lower grades. For Grade F42 and above, one set of three specimens per steel heat shall be tested at a maximum temperature of -45°C (-50°F). The minimum average impact value is 27 J (20 ft-lb); the minimum individual specimen value is 20 J (15 ft-lb).

Proper heat treatment is essential for MSS SP-44 flanges to achieve the required balance of strength, toughness, and weldability - particularly for higher-strength grades used in demanding pipeline service.

• Grade F42 and higher: Normalized, normalized and tempered, quenched and tempered, or precipitation treated and aged. 
• Grade F36 in Class 400 and higher: Annealed, normalized, normalized and tempered, or quenched and tempered. Minimum tempering temperature: 540°C (1,000°F). 
• Hydrostatic testing of individual flanges is not required, but joint hydrostatic testing may be performed at up to 1.5× the 38°C (100°F) pressure rating. 

Because MSS SP-44 and ASME B16.47 Series A are technically equivalent, the real decision engineers face is Series A (SP-44) versus Series B. These two series have the same pressure classes but different dimensional standards - and they are not interchangeable above NPS 26.

Selection guidance: If your piping specification references API standards or oilfield equipment, Series B is likely required. For general pipeline, water treatment, power generation, and chemical plant applications, Series A (MSS SP-44) is typically the correct choice. Always confirm with the applicable piping code (e.g., ASME B31.4, B31.8) or project specification.

Oil & Gas Transmission Pipelines

The primary application. Cross-country oil and gas pipelines require large-diameter, high-strength flanges at pump stations, valve stations, and tie-in points. F52 and F60 grades are most commonly specified.

Large-Diameter Water Pipelines

Municipal water transmission mains and water treatment plant interconnecting piping often specify MSS SP-44 Class 150 flanges for sizes NPS 24 and above.

Power Generation

Main steam and feedwater piping in power plants requires large, high-integrity flanged connections, where MSS SP-44 Class 600 or 900 flanges are commonly applied.

Chemical & Petrochemical Plants

Large-diameter process piping connecting columns, reactors, and heat exchangers in refinery and chemical plant service.

Mining & Slurry Pipelines

High-wear slurry transport pipelines benefit from the higher-strength grades (F56–F70) available under MSS SP-44.

The current edition, ANSI/MSS SP-44-2026, was published in early 2026 and supersedes the 2019 edition. The 2026 revision consists primarily of editorial clarifications to requirements established in the 2016 and 2019 editions. Key changes include:

Source: ANSI Blog, blog.ansi.org, February 2026

Section 2 'Definitions' was added in accordance with MSS requirements, with all subsequent sections renumbered.

ASTM A515/A515M plate material was added to the weld compatibility list - expanding material options for blind flange fabrication. 

The combined Cu+Ni+Cr+Mo limit was removed from Tables 1 and E1 - harmonizing with current ASME B16 practice. 

Metric conversions and tolerance on hydrostatic testing allowance were harmonized with ASME B16 standards. 

Test location requirements were clarified for greater consistency.

If you are working with older project specifications that reference MSS SP-44-2016 or 2019, the dimensional and pressure-rating data remain unchanged. The 2026 updates are editorial in nature and do not affect procurement or fabrication decisions for standard applications.

As a China-based stainless steel flange manufacturer with over 12 years of production experience, Zhejiang Chengjiu Pipeline Co., Ltd. (CNCJ) produces MSS SP-44 flanges for global pipeline projects. Unlike trading companies, we manufacture in-house with full control over material traceability, dimensional inspection, and heat treatment processes.

Whether you need a single flange for replacement or bulk supply for a pipeline project, contact our technical team with your NPS, pressure class, material grade, and quantity. We provide material test certificates (MTC) to EN 10204 3.1 as standard.   sale@cncjflange.com

References & Sources

ANSI/MSS SP-44-2026: Steel Pipeline Flanges. Manufacturers Standardization Society (MSS).

ANSI Blog: 'ANSI/MSS SP-44-2026: Steel Pipeline Flanges.' blog.ansi.org, February 2026.

ASME B16.47-2017: Large Diameter Steel Flanges. American Society of Mechanical Engineers.

ASME B16.5-2017: Pipe Flanges and Flanged Fittings. American Society of Mechanical Engineers.