ASTM A350 LF2 Flange for Low Temperature

ASTM A350 LF2 flanges are produced from forged or ring-rolled carbon steel and heat treated to meet the mechanical and notch-toughness requirements of ASTM A350/A350M. Unlike a general carbon steel flange specification that is selected mainly around strength and pressure service, ASTM A350/A350M requires impact toughness to be verified for low-temperature service, helping control brittle-fracture risk as metal temperature decreases.

LF2 is one of the principal carbon steel grades within ASTM A350/A350M and is supplied in defined material classes according to the required mechanical and impact properties. In a complete flange specification, ASTM A350/A350M defines the material and toughness requirements, while flange size, pressure Class, dimensions, facing and drilling are established separately by standards such as ASME B16.5 or ASME B16.47.

ASTM A333 Grade 6 pipe and ASTM A420 WPL6 fittings are commonly specified alongside A350 LF2 components in low-temperature carbon steel piping systems. They should be treated as complementary product specifications rather than automatic material equivalents, with the final combination determined by the piping code, design temperature and project specification.

ASTM A350 LF2 Flange Range

Standards Scope

ASTM A350 covers several grades of carbon and low-alloy steel forged or ring-rolled flanges, forged fittings and valves intended primarily for low-temperature service and requiring notch toughness testing. They are made to specified dimensions, or to dimensional standards, such as the ASME and API Specifications referenced in Section 2. Although this specification covers some piping components machined from rolled bar and seamless tubular materials, it does not cover raw material produced in these product forms.

Product furnished in ASTM A350/ ASME SA350 shall conform to the requirements of Specification A961/A961M, including any supplementary requirements that are indicated in the purchase order. Failure to comply with A961/A961M will be considered nonconformance with A350. And in case of conflict between ASTM A350 and A961/A961M, this specification shall prevail.

ASTM A350 Flange Datasheet

Chemical Composition

Mechanical Properties

Tension Tests Requirements—The material shall conform to requirements for tensile properties in below table.

Heat Analysis and Product Analysis

A chemical heat analysis and product analysis in accordance with Specification A961/A961M shall be made and conform to the requirements as to chemical composition prescribed in this table. Leaded steels shall not be permitted. Product analysis

ASTM A350/A350M Impact Test Requirements

Impact testing is a defining requirement of ASTM A350/A350M because the specification is intended for piping components requiring verified notch toughness at low temperature. Test temperature and minimum absorbed-energy requirements depend on the grade, material class, specimen size and applicable purchase requirements.

Test Specimens by 10mm x 10mm

Impact test values: Charpy V-Notch Energy Requirements for specimens 10mm by 10mm.

ASTM A350 LF2 Class vs Flange Pressure Class

ASTM A350 LF2 Class 1 or Class 2 identifies the material-property classification under ASTM A350/A350M. ASME Class 150, 300, 600 and other pressure classes identify the flange pressure-temperature rating and dimensional system. The two designations control different parts of the purchase specification and should not be used interchangeably.

Referenced Documents

ASTM Standards:

• A788/A788M Specification for Steel Forgings, General Requirements
• A961/A961M Specification for Common Requirements for Steel Flanges, Forged Fittings, Valves, and Parts for Piping Applications

ASME Standards:

• B 16.5 Steel Pipe Flanges and Flanged Fittings
• B 16.9 Factory-Made Wrought Steel Butt-Welding Fittings
• B 16.10 Face-to-Face and End-to-End Dimensions of Ferrous Valves
• B 16.11 Forged Steel Fittings, Socket-Welding and Threaded
• B 16.30 Unfired Pressure Vessel Flange Dimensions
• B 16.34 Valves-Flanged, Threaded, and Welding End
• B 16.47 Large Diameter Steel Flanges
• ASME Boiler and Pressure Vessel Code

AWS Standards:

• A 5.1 Mild Steel Covered Arc-Welding Electrodes
• A 5.5 Low-Alloy Steel Covered Arc-Welding Electrodes

API Standards:

• 600 Steel Gate Valves with Flanged or Butt-Welding Ends
• 602 Compact Design Carbon Steel Gate Valves for Refinery Use
• 605 Large Diameter Carbon Steel Flanges

Manufacture - Melting and Forging

Melting Process - The steel shall be produced by any of the following primary processes: open-hearth, basic oxygen, electric-furnace, or vacuum-induction melting (VIM). The primary melting may incorporate separate degassing or refining, and may be followed by secondary melting using electroslag remelting (ESR), or vacuum-arc remelting (VAR).

Discard - A sufficient discard shall be made to secure freedom from injurious piping and undue segregation.

Forging Process

Material for forgings shall consist of ingots, or forged, rolled, or strand cast blooms, billets, slabs, or bars.

Heat Treatment

After hot working and before reheating for heat treatment, the forging shall be allowed to cool substantially below the transformation range.

Forgings grades except Grade LF787, should be heat treated in normalized, or normalized and tempered, or quenched and tempered. By manufacturer's option, material that performed in quenched and tempered could be normalized prior to the austenitize/quenched operation.

No limitation on size is intended beyond the ability of the manufacturer to obtain the specified requirements. However, Class 3 of Grade LF787 is only available in the quenched-and-precipitation heat treated condition.

Hydro-static Test

Forgings manufactured under ASTM A350/ ASME SA350 shall be performed with a hydro-static test compatible with the rating of the finished item. Such tests shall be conducted by the manufacturer only when Supplementary Requirement S57 of Specification A961/A961M is specified.

ASTM A350 LF2 Flange Selection

Selecting an ASTM A350 LF2 flange requires more than specifying the material grade. The flange standard, material class, pressure class, piping dimensions and low-temperature design condition need to be confirmed together.

1. Define the Material Requirement

Specify ASTM A350/A350M LF2 and the required material class. LF2 Class 1 or Class 2 identifies the applicable material-property and toughness requirements of the forging.

2. Select the Flange Standard and Size

Use ASME B16.5 for applicable flanges through NPS 24, with Class 2500 limited to NPS 12. For large-diameter flanges from NPS 26 through NPS 60, specify ASME B16.47 Series A or Series B as required.

3. Confirm the Connection Configuration

Define the flange type, pressure Class, facing and bore configuration. For weld neck flanges, the bore and welding end need to match the connected pipe dimensions or schedule.

4. Confirm the Low-Temperature Condition

Provide the project design temperature and required impact-test condition. These inputs determine whether the specified LF2 material class and toughness requirements are appropriate for the intended service.

5. Define Inspection and Documentation

State the required material certificate, heat-treatment records, mechanical-property results, impact-test records and any project-specific inspection documentation needed for release.

Two Designations That Should Not Be Confused

ASTM A350 LF2 Class 1 or Class 2 refers to the material classification of the forging.

ASME Class 150, 300, 600 and other pressure classes refer to the flange pressure-temperature rating and dimensional system.

They control different parts of the flange specification and should be stated independently.

Before Sending an RFQ

A complete inquiry should identify the ASTM A350/A350M edition, LF2 material class, dimensional standard, NPS, flange pressure Class, flange type, facing, bore or pipe schedule, minimum design temperature, quantity, and required inspection documentation.

FAQ

Q: What makes ASTM A350 LF2 suitable for low-temperature flange service?

A: ASTM A350/A350M requires notch-toughness testing in addition to chemical and mechanical property control. This provides direct verification of the forging material's impact performance for the specified low-temperature condition.

Q: Is ASTM A350 LF2 Class 1 the same as ASME Class 150?

A: No. LF2 Class 1 is a material classification under ASTM A350/A350M, while ASME Class 150 is a flange pressure-rating and dimensional designation. Both may appear on the same purchase specification but control different requirements.

Q: Does ASTM A350/A350M define the dimensions of an LF2 flange?

A: No. ASTM A350/A350M defines the material and forging requirements. Flange dimensions, facing, drilling and pressure Class are specified separately by standards such as ASME B16.5 or ASME B16.47.

Q: What information should be included in an ASTM A350 LF2 flange RFQ?

A: State the ASTM A350/A350M edition, LF2 material class, flange standard, NPS, flange pressure Class, flange type, facing, bore or pipe schedule where applicable, minimum design temperature, quantity, and required impact-test and inspection documentation.

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