Flange Materials

FLANGE MATERIALS

Forged steel flanges are made from forgings produced to a forgings material specification. Forging material specifications are written by the American Society for Testing and Materials (ASTM), the Manufacturer’s Standardization Society (MSS) and the American Petroleum Institute (API). ASTM specifications are for materials only and are the primary specifications designated by end users for piping applications. MSS and API include dimensional and marking requirements in addition to requirements for chemistry, physical properties and heat treatment of the steel. This section covers only the material properties and therefore, a brief description of the materials is listed below with the chemistry, physical properties and heat treatment condition specified in Table 1.

ASTM MATERIALS
A105 — titled Standard Specification for forgings, carbon steel and piping components — the specification for the materials used for the majority of forged steel flanges in the petrochemical industry. This material is used for ambient and high temperature applications in all pressure classes and may be provided in any of the heat treatment conditions listed below. A105 has no separate classes or grades within it.	A350 — titled Standard Specification for forgings, carbon and low-alloy steel, requiring notch toughness testing for piping components — the specification primarily used for low temperature applications in all pressure classes and must be provided in a heat treated condition other than "as forged" as listed below. A350 has several grades and classes, but the most commonly used are Grade LF2 and Grade LF6, Classes 1 and 2.

A694 — titled Standard Specification for forgings, carbon and alloy steel, pipe flanges, fittings, valves and parts for high pressure transmission service — the ASTM specification used for high strength applications. Yield strengths provide the grade separations for this specification. Grade F42, for example, must have a minimum yield of 42,000 PSI and Grade F60 must have a minimum yield of 60,000 PSI. Forgings to this specification must be provided in a heat treated condition other than "as forged" as listed in Table 2.	A707 — titled Standard Specification for flanges, forged, carbon and alloy steel for low-temperature service — the specification used for high strength, low temperature applications. Chemistry is the basis for grade separations and yield strengths provide the class separations for each grade. The most typically used grades and classes are L3 Classes 2 and 3, and L5 Class 3. This material, like A694, is more commonly used in large diameter flanges.

MSS MATERIALS

MSS SP44 — titled Steel Pipe Line Flanges is the specification written for flanges with diameters of 12" through 60" in pressure classes 150, 300, 400 and 900. As indicated by the title, these flanges are usually ordered for pipeline applications and have a distinct single taper hub. Material grades are determined by yield strength and, like A694 of ASTM, are designated as F36 through F70. Chemistry is limited to a Carbon content of 0.35% max. and, using Barlow’s formula, a carbon equivalency of 0.48%. Barlow’s formula is shown in Table 1.

API MATERIALS

API specification 6A designates materials to be used for wellhead equipment applications.

The significant difference between API 6A and other material specifications is that while API specifies the yield strength of the materials to be used, it also requires the flange manufacturer to write their own internal material specification in order to produce flanges that have the chemical and physical properties required by the API specification. API 6A also designates a unique set of pressure classes and diameters for flanges which are not covered in this web site.

In addition to the criteria listed above, flanges may be made to spec for use of cast iron, copper, aluminum, brass, nickel or any number of other materials which may be forged or cast into a shape that will permit the machining of a flange.

Supplementary specifications, such as NACE MR0175 from the National Association of Corrosion Engineers, are frequently included by end users as a means of imposing limitations beyond that of the material specification. In either case, it is the responsibility of the purchaser to inform the manufacturer of the requirement.