In horizontal directional drilling (HDD), every tool in the drill string has a specific function. One essential but often overlooked component is the blind sub. Despite its simple design, a blind sub plays a critical role in specialized HDD drilling applications.

What Is a Blind Sub in HDD?

A blind sub in HDD drilling is a short drill string component that is internally closed, meaning it has no internal fluid passage. Unlike standard subs or drill pipes, drilling fluid cannot flow through a blind sub.

However, a blind sub is fully capable of transmitting:

  • Torque
  • Thrust and pullback forces
  • Mechanical loads within the HDD drill string

Why Use a Blind Sub in HDD Drilling?

Blind subs are used when fluid circulation must be blocked intentionally. Common reasons include:

  • Isolating drilling fluid from HDD tools
  • Creating a closed drill string section
  • Controlling pressure in specific HDD setups

In many HDD operations, blind subs are installed directly behind the reamer to block drilling fluid flow past the reamer.

Typical Applications of Blind Subs

Blind subs are commonly used in:

  • Pilot drilling operations
  • HDD tooling setups
  • Specialized test runs
  • Custom HDD drill string configurations

Design and Strength

A high-quality blind sub for HDD is manufactured from high-strength alloy steel and designed to withstand:

  • High torsional loads
  • Axial compression and tension
  • Harsh downhole drilling conditions

All connections are compatible with standard HDD drill string threads, allowing easy integration into existing tooling.

Blind Sub vs Standard Sub

Feature Blind Sub Standard Sub
Internal bore No Yes
Fluid circulation Blocked Allowed
Mechanical load transfer Yes Yes
Typical application Isolation & protection Flow & connection

Conclusion

A blind sub in horizontal directional drilling is a vital component for advanced drilling configurations. By transmitting mechanical forces while blocking fluid flow, blind subs enable safe, precise, and adaptable HDD operations.

At HDD Drilling Tools B.V., we design and manufacture blind subs that meet the highest standards for strength, durability, and compatibility with modern HDD systems.