AISI 4130 Pipe Fittings & Flanges

AISI 4130, also known as 25CrMo4 or UNS G41300, is a low alloy steel that contains chromium and molybdenum as its main strengthening elements. This alloy is widely recognized for its excellent balance of strength, toughness, weldability, and fatigue resistance. Because of these superior properties, AISI 4130 pipe fittings and flanges are extensively used in high-pressure systems, critical piping networks, and structural applications across industries such as oil and gas, aerospace, petrochemicals, and power generation.

Unlike conventional carbon steels, AISI 4130 delivers higher mechanical strength while maintaining good ductility and machinability. This makes it a cost-effective and reliable alternative to higher-alloy steels and nickel-based alloys, particularly in demanding service conditions.

Chemical Composition of AISI 4130

The chemical composition of AISI 4130 is carefully balanced to achieve an ideal combination of mechanical strength and toughness. It contains between 0.28 to 0.33 percent carbon, which provides hardness and strength without making the alloy brittle. Manganese is present in the range of 0.40 to 0.60 percent, improving hardenability and strength. Silicon, ranging between 0.15 to 0.35 percent, enhances oxidation resistance and improves the steel’s toughness. Phosphorus and sulfur are controlled at a maximum of 0.035 percent and 0.025 percent respectively to ensure superior ductility and prevent brittleness.

Molybdenum is present between 0.15 to 0.25 percent, offering improved corrosion resistance, elevated temperature strength, and resistance to pitting. Nickel is kept to a maximum of 0.50 percent, primarily to refine toughness. Chromium, which ranges from 0.80 to 1.10 percent, significantly enhances hardness, corrosion resistance, and strength. The balance of the alloy is iron, making up approximately 97 to 98 percent of the material.

Mechanical Properties of AISI 4130

The mechanical properties of AISI 4130 make it suitable for challenging environments. It has a density of about 7.85 grams per cubic centimeter and a melting point of approximately 1432 degrees Celsius. The alloy exhibits a tensile strength of around 560 megapascals, which ensures the ability to withstand high levels of stress without failure. Its yield strength, measured at 0.2 percent offset, is about 460 megapascals, allowing it to maintain shape and integrity under load.

One of the standout properties of AISI 4130 is its ductility, as it provides an elongation of around 21 percent. This combination of tensile strength, yield strength, and elongation ensures that the material can perform reliably under dynamic and high-pressure conditions while resisting brittle failure.

Equivalent Grades of AISI 4130

AISI 4130 is an internationally recognized grade and is available under several equivalent standards. In the European standard system, it is known as 25CrMo4, while in Germany it is designated as Werkstoff Number 1.7218. In the Unified Numbering System, it is identified as UNS G41300. The Japanese standard recognizes it as JIS G4105, and in British standards, it corresponds to BS 970. These equivalent grades ensure that AISI 4130 can be sourced and applied across global industries without issues of compatibility.

Types of AISI 4130 Pipe Fittings and Flanges

AISI 4130 pipe fittings are available in a complete range of buttweld and forged configurations. The most common fittings include elbows in 45, 90, and 180 degrees for changing the direction of flow; equal and reducing tees for branching pipelines; concentric and eccentric reducers for joining different pipe diameters; and caps or stub ends for sealing or connecting with flanges. Forged fittings such as couplings, unions, nipples, plugs, and crosses are also manufactured for high-pressure applications and smaller-diameter piping systems.

The flanges manufactured from AISI 4130 are equally versatile and are available in weld neck, slip-on, blind, socket weld, threaded, lap joint, and ring type joint (RTJ) varieties. Weld neck flanges are best suited for high-pressure and high-temperature conditions, while slip-on flanges are economical and easier to install for lower-pressure systems. Blind flanges are used to terminate pipelines or isolate sections, and socket weld flanges are often used for small-diameter, high-pressure pipelines. Threaded flanges offer connections without welding, lap joint flanges are ideal where frequent disassembly is required, and RTJ flanges provide leak-proof sealing in critical conditions.

Applications of AISI 4130 Fittings and Flanges

The unique combination of strength, toughness, and weldability makes AISI 4130 highly suitable for several industries. In the oil and gas sector, it is used for wellhead components, refinery piping, and high-pressure pipeline systems. In aerospace, it finds applications in aircraft engine mounts, landing gear structures, and other load-bearing parts. Power generation plants use AISI 4130 fittings and flanges in steam piping, turbines, and high-temperature systems. The petrochemical industry relies on it for chemical processing equipment, while the automotive sector employs it in roll cages, suspension parts, and high-performance frames. Offshore and marine applications also benefit from its ability to withstand dynamic stress and moderate corrosion.

Why Choose AISI 4130 Pipe Fittings & Flanges?

Choosing AISI 4130 fittings and flanges means selecting a material that is strong, durable, and versatile enough to perform under extreme service conditions. It is highly weldable, machinable, and heat-treatable, which makes it easy to fabricate into custom designs. Its recognition under international equivalent standards ensures worldwide availability and compatibility. Moreover, it offers a balance of performance and cost-effectiveness, making it one of the most widely used alloy steels for industrial piping and flanges.

Conclusion

AISI 4130 pipe fittings and flanges are engineered for reliability in high-pressure, high-stress, and corrosive environments. With excellent mechanical properties, controlled chemical composition, and compliance with global standards, AISI 4130 remains a preferred material across industries such as oil and gas, aerospace, power generation, petrochemicals, and marine. For projects that demand durability, strength, and performance at a competitive price point, AISI 4130 is an ideal choice.