ASTM A194

About ASTM A194

ASTM A194 is a standard material specification covering carbon, alloy, and stainless steel nuts designed specifically for high-pressure, high-temperature, or extreme environments.

These heavy-duty fasteners are most commonly used in conjunction with ASTM A193 bolts or studs across industries like oil and gas, petrochemical processing, power generation, and chemical plants.

Key Technical Specifications

• Product Style: Typically manufactured according to the American National Standard Heavy Hex Series (ANSI/ASME B18.2.2). They are slightly larger and thicker than standard hex nuts to provide a greater clamping force.

• Size Range: Covers nominal sizes from 1/4 inch to 4 inches (and metric equivalents from M6 to M100).

• Thread Series: Nuts up to 1 inch generally utilize the UNC Series Class 2B fit, while sizes over 1 inch leverage either UNC or 8 UN Series Class 2B fit.

Common Grades and Materials

The standard includes several distinct material grades optimized for specific mechanical properties:

Protective Coatings

To extend the lifespan of carbon and alloy steel grades in corrosive environments, these nuts are frequently modified with specialized surface treatments:

• PTFE Coating: Often applied in bright blue, green, or yellow. It dramatically reduces friction (torque requirement) and prevents chemical galvanic corrosion.

• Hot-Dip Galvanizing & Zinc Plating: Provides standard barrier and sacrificial protection against moisture.

• Phosphate & Cadmium Coating: Offers basic wear protection and consistent torque performance