Exploring the Greatness of API 20e Nuting ASTM A193 2H Nut in Russia

The ASTM A194 2H heavy hex nut is the nut specified to pair with A193 B7 stud bolts on ASME flanges. It keeps high clamp load without galling and is the default for refinery, pipeline, and pressure-vessel bolting. For the full sealing set, see our flange gaskets and flange products.

What an A194 2H Nut Is

A194 2H is a heavy hex nut made from carbon or alloy steel, hardened and tempered to a controlled hardness band. The heavier section and wider wrench flats give more bearing area and resist rounding under high torque. It is not a general-purpose nut; it is engineered for the bolt loads found in pressure-flange joints.

Matching to the Stud Bolt

• A193 B7 stud + A194 2H nut — the standard refinery and pipeline combination.
• A193 B7M stud + A194 2HM nut — sour-service (NACE) version at lower hardness.
• A320 L7 stud + A194 2H/7 nut — low-temperature service.

Why Heavy Hex, Not Standard Hex

API 20E and the Bolting Specification

Where a project calls out API 20E (Threaded Fasteners for Pressure Equipment), the nut is bought, traced, and tested as part of a qualified bolting system: material certificate, hardness, and coating are controlled. A194 2H meets the nut side of most API 20E bolting lists, but always confirm the exact grade, coating, and stamping the specification requires.

Key Benefits

• Holds high preload and resists loosening under vibration and thermal cycling.
• Wide flats survive high torque without rounding.
• Controlled hardness avoids thread galling when paired with a lubricated B7 stud.
• Full material traceability for inspection and recertification.

Where They Are Used

A194 2H nuts are used wherever A193 B7 studs clamp ASME B16.5 or B16.47 flanges: oil and gas plants, pipelines, petrochemical units, power stations, and pressure vessels. They suit any flange joint that must stay sealed through pressure and temperature swings.

In the Joint

The nut converts torque into bolt tension; the flange carries the clamp load into the flange face, and the gasket between the faces does the sealing. Nut, stud, and gasket must be sized and lubricated as one system.

Handling and Installation

Use a hardened washer where the specification requires one, lubricate the nut face and threads to a known friction factor, and tighten in a star pattern to the target torque in at least two passes. Re-check after the joint reaches operating temperature. Replace nuts that show thread damage or are below the hardness band, and keep the material certificate with the joint record.

Frequently Asked Questions

2H or 2HM for sour service?

Use 2HM (lower hardness) with B7M studs when the line is sour per NACE MR0175/ISO 15156. 2H alone is not accepted for H2S service.

Can I reuse 2H nuts?

Only after inspection and hardness check. Nuts take more wear than studs, so replace them more often, especially after thermal cycles.

Why specify heavy hex?

The thicker section spreads load and resists the nut embedding into the flange or rounding under torque — standard hex nuts fail here.