Internal Bore: Diameter 50-200 mm (standard range)

Component Specifications

Definition

The internal bore is a critical cylindrical passage machined through the length of the Kelly Bar, designed to allow the flow of drilling fluid (mud) from the surface to the drill bit. It maintains precise dimensional tolerances to ensure efficient fluid dynamics, structural support under torsional and axial loads, and compatibility with mating components in rotary drilling systems.

Working Principle

The internal bore operates by providing a sealed conduit for high-pressure drilling fluid transmission, which cools the drill bit, removes cuttings, and stabilizes the borehole. Its smooth, concentric geometry minimizes fluid friction and pressure loss while maintaining the bar's torsional rigidity during rotation.

Materials

High-strength alloy steel (e.g., AISI 4140 or 4340), heat-treated to 28-32 HRC, with optional internal coatings (hard chrome plating or tungsten carbide) for wear and corrosion resistance.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Diameter	50-200 mm (standard range)
Tolerance	H7/h6 (ISO)
Straightness	≤ 0.1 mm/m
Surface Finish	Ra ≤ 1.6 μm
Pressure Rating	Up to 35 MPa

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 286-2, DIN 7154, API RP 7G

Engineering Analysis

Risks & Mitigation

Bore wall erosion from abrasive fluids
Misalignment causing seal failure
Fatigue cracking under cyclic loads

FMEA Triads

Trigger: Abrasive particle accumulation in drilling fluid
Failure: Progressive bore wall erosion leading to leaks
Mitigation: Implement fluid filtration systems and use wear-resistant coatings

Trigger: Improper machining tolerances
Failure: Seal incompatibility and fluid leakage
Mitigation: Adhere to ISO H7/h6 tolerance standards and conduct dimensional inspections

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Geometric tolerances per ISO 1101, diameter tolerance H7/h6

Test Method

Ultrasonic testing for wall thickness, pressure testing per API RP 7G

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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CNFX does not score or rank suppliers. Buyers must verify all claims and documents with the legal manufacturer before ordering.

Manufacturers of Internal Bore

Manufacturer profiles associated with Internal Bore.

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review

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Frequently Asked Questions

What is the primary function of the internal bore in a Kelly Bar?

It transmits drilling fluid to the drill bit while providing structural integrity under operational loads.

How does bore diameter affect drilling performance?

Larger diameters reduce fluid pressure loss but may compromise torsional strength; optimal sizing balances flow efficiency with mechanical requirements.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Internal Bore