What Is ASTM A194 Grade 2H and Why Is It Used with High Strength Industrial Bolting?

ASTM A194 Grade 2H is a standard specification for heavy hex carbon steel nuts intended for use with high strength bolting in high pressure and high temperature service. It's one of the most widely used nut grades in industrial piping, pressure vessels, and structural bolting applications.

What It Is

• Material: Carbon steel, through hardened by quenching and tempering
• Standard: Governed by ASTM A194/A194M, which covers various grades of nuts for bolting applications
• Hardness: Typically Rockwell C24–38 (or Brinell equivalent), giving it significant strength compared to non heat treated nuts
• Proof load capacity: Designed to match or exceed the strength of the bolts/studs it's paired with, particularly high strength studs like ASTM A193 Grade B7

Key Properties

Why It's Used with High Strength Bolting

1. Matched Strength: High strength studs like A193 B7 develop significant tensile strength through heat treatment. A194 2H nuts are heat treated to match this strength, preventing the nut from stripping, deforming, or failing before the bolt does.
2. Resistance to Galling and Thread Damage: The hardness of 2H nuts makes them more resistant to galling under high torque, which is common when achieving proper preload on high strength bolted joints.
3. High Pressure/High Temperature Service: Because of its strength and dimensional stability, Grade 2H is a standard choice in Flanged pipe connections and Valves
4. Reliability Under Preload: Bolted joints in critical service need to maintain clamping force over time. A softer or lower strength nut could yield or lose torque retention, leading to leaks or joint failure. 2H's hardness ensures it holds preload reliably.
5. Widely Interchangeable Standard: Because A194 2H is so common, it simplifies procurement and interchangeability across projects, since it's specified by many engineering codes as a default nut grade for B7 studs.