Drill Collar Sub Assembly Plate

Drill collar sub assembly plates are critical load transfer interfaces within the BHA (Bottom Hole Assembly), especially during high-weight-on-bit operations. These plates are engineered to withstand severe axial and torsional forces without plastic deformation. Advanced metallurgical selection combined with precision controlled forging and subsequent quenching ensure uniform core hardness and superior tensile properties. This structural resilience maintains joint preload and thread engagement, significantly reducing the risk of mechanical backlash, fatigue-induced separation, or stress risers in collar stacks during prolonged drilling. 

Material Grade & Specification

AISI 4130 (or equivalent) Alloy Steel, API 7-1, ASTM A36 (if carbon steel), ASTM A105

Dimensional Tolerances

±0.005 inches (±0.13 mm) for critical dimensions, ±0.001 inches (±0.025 mm) for threads

Surface Finish Requirement

Ra ≤ 1.6 µm (63 µin) for sealing surfaces, Ra ≤ 3.2 µm (125 µin) for non-critical areas

Heat Treatment Specification

Quenching and Tempering (QT) to 28-32 HRC (Hardness) for increased strength and toughness

Concentricity Requirement

≤ 0.002 inches (0.05 mm) for critical concentricity of bore to OD for high performance

Product Description

Drilling operations in HPHT (High Pressure High Temperature) environments impose cyclic thermal and mechanical loads that can induce dimensional drift. Sub assembly plates are machined using sub-micron tolerance control and subjected to multi-axis CNC profiling followed by double-stage stress relief annealing. These processes ensure stability of concentricity, face parallelism, and perpendicularity over extended use. The result is consistent joint interface performance, elimination of face runout deviations, and preserved structural alignment under fluctuating borehole pressures. 

Thread Type & Specification

API 7-1, 2 3/8″ Reg API, 2 7/8″ IF (or per customer request), NPT (if applicable)

Hardness Requirement

28-32 HRC (after heat treatment)

Non-Destructive Testing (NDT) Requirement

Ultrasonic Testing (UT), Magnetic Particle Testing (MT), Dye Penetrant Testing (DPT) as per API standards

Coating/Plating Requirement

Phosphate coating (if required for corrosion resistance), or zinc plating

Certification Standard

API Spec 7-1, ISO 9001:2015, PED (Pressure Equipment Directive)

Technical Advantages

Downhole assemblies are frequently subjected to NDT protocols such as UT, MPI, and EMI, requiring sub assembly components to exhibit consistent magnetic permeability and acoustic impedance characteristics. Material selection for these plates is constrained to homogenous low-permeability alloys (µr ≤ 1.01) with tightly regulated inclusion content and directional grain orientation. Post-machining demagnetization and residual field assessments are conducted to maintain NDT compatibility without distorting signal propagation in proximity to MWD/LWD electronics or EMI-sensitive modules. 

Contact surfaces between the sub assembly plate and adjoining drill collar sections require precise surface flatness and micro-finish characteristics to prevent localized stress concentrations. Face lapping to below 0.8 µm Ra combined with controlled circularity and flatness tolerances ensures optimized load transfer and minimizes the risk of fretting corrosion at the interface. This is critical in reducing micro-movement during high-torque transitions and maintaining static sealing integrity in pressure-tight assemblies. 

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Industry Applications

Deep Well Drilling Assemblies

Supports high axial load transmission in extended-reach wells while maintaining alignment between collars under compressive stresses. 

High-Pressure High-Temperature (HPHT) Wells

Provides structural stability and thermal resistance in environments exceeding 20,000 psi and 400°F during drilling operations. 

Directional and Horizontal Drilling

Maintains geometric alignment in non-vertical wells where lateral forces and torsional vibration induce complex stress profiles on sub-components. 

Measurement While Drilling (MWD) Systems

Integrates with low-permeability tool strings, enabling interference-free operation of magnetic field sensors and telemetry systems. 

Sour Gas Drilling Environments

Fabricated from H2S-resistant alloys to mitigate sulfide stress cracking under hydrogen-induced embrittlement conditions. 

Coiled Tubing Bottom Hole Assemblies

Adapts to dynamic cyclic loading in coiled tubing applications requiring precise alignment and resistance to bending fatigue. 

Threaded Connection Integrity

Drill collar sub assembly plates frequently integrate thread profiles such as NC, IF, or custom API-compliant geometries. Thread zones are machined using calibrated threading cycles with strict flank angle and pitch diameter tolerances, followed by cold rolling or burnishing for enhanced surface hardness. Threaded sections undergo dye penetrant inspection, pitch runout measurement, and controlled thread compound application. 

Each sub assembly plate is manufactured from traceable mill-certified bar stock or forgings with recorded heat numbers and full mechanical test data. Heat treatment batches are mapped and tagged with corresponding MTCs, hardness profiles, and grain flow orientation charts. This traceability supports lifecycle tracking, recall readiness, and compliance with metallurgical audits in drilling asset registries. 

 

Drill Collar Sub Assembly Plate

Having Doubts? Our FAQ

Check all our Frequently Asked Question

How does Frigate ensure face flatness in sub assembly plates under load-bearing conditions?

Frigate uses controlled CNC face milling followed by precision lapping to achieve flatness below 0.8 µm Ra. This reduces the risk of point loading and preserves full-face contact during axial compression. Surface deviation is verified using coordinate metrology under load simulation. Such accuracy prevents micro-movement and fretting at joint interfaces. 

What machining tolerance levels does Frigate maintain for sub assembly plate concentricity and parallelism?

Frigate maintains concentricity within ±0.01 mm and parallelism within ±0.015 mm across the plate diameter. These tight tolerances reduce eccentric torque loads during high-RPM drilling. Precision ensures consistent stress paths between collar sections. Each plate undergoes 3D metrology validation before dispatch. 

 

How does Frigate handle non-magnetic sub assembly plate requirements for MWD compatibility?

Frigate uses low-permeability austenitic alloys with certified µr ≤ 1.01 for EMI-sensitive environments. Material batches are spectrally verified and demagnetized post-machining. Final assemblies are scanned for magnetic anomalies using Gaussmeter mapping. This ensures compatibility with magnetic and gyro-based downhole tools. 

 

What kind of fatigue testing does Frigate apply to validate the plates for long-term downhole service?

Frigate conducts rotary bending fatigue and thermal cycle simulation on prototype plates. Stress thresholds are validated beyond expected downhole axial-torsional loads. Results are benchmarked against fatigue limits of API-compatible joints. Data from testing informs design thresholds for critical applications. 

How does Frigate ensure material traceability across each sub assembly plate delivered?

Each plate is tagged with a unique heat number linked to full MTC, grain flow, and hardness data. Frigate integrates digital traceability into its production system, including UT and MPI test records. Clients receive structured documentation for QA integration. This supports audit readiness and component lifecycle tracking. 

 

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LOCATIONS

Global Sales Office

818, Preakness lane, Coppell, Texas, USA – 75019

Registered Office

10-A, First Floor, V.V Complex, Prakash Nagar, Thiruverumbur, Trichy-620013, Tamil Nadu, India.

Operations Office

9/1, Poonthottam Nagar, Ramanandha Nagar, Saravanampatti, Coimbatore-641035, Tamil Nadu, India. ㅤ

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Drill Collar Sub Assembly Plate

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