Tubular String Fishing Tool — Box Tap

A box tap is a specialized tool designed for thread-milling fishing operations on the outer wall of tubular fish.

01 Structure

Long cylindrical integral structure, composed of a sub and a body (which has fishing threads on its inner conical surface). The box tap is made of high-strength alloy steel forgings. To facilitate threading, cutting grooves are opened on the fishing threads. The upper sub is equipped with clockwise/counterclockwise thread indicator grooves, and fishing threads are provided on the inner conical surface of the body.

02 Fishing Principle

The box tap is machined from high-strength alloy steel forgings and finished by heat treatment. Its fishing threads are available in two types: (serrated) and triangular. The taper of the thread section is 1:16.

The fishing principle of the box tap is to perform threading by pressing on the exterior of the fish top. Specifically, the fishing threads are pressed to engage with the outer wall of the fish for threading — this threading relies on press-fit engagement, with no cutting involved.

03 Fishing Operation

When the tool is lowered to 1-2 cm above the fish top, start circulating pump flushing, then gradually lower the tool to the fish top and monitor pump pressure changes:

• If the pump pressure rises suddenly and the suspended weight drops, it indicates the fish top has entered the box tap, and threading/fishing can proceed.
• If the suspended weight drops gradually but the pump pressure remains unchanged, the fish top has not entered the box tap. Lift the drill string, rotate the tubular string, and re-align with the fish bore until both the suspended weight and pump pressure change significantly (i.e., the fish top enters the bore) — only then can pressure be applied for threading and fishing.

For fish with a small outer diameter at the top (where pump pressure shows no obvious change), a guide shoe structure shall be used to avoid threading position errors and potential accidents.

Note: During fishing operations, do not force the fish top abruptly, to prevent damage to the fish top or fishing threads. Special attention shall be paid to analyzing and confirming the threading position, to avoid serious consequences.

Contact :Jessie Zhou

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Email: energy@landrilltools.com