3-1/2 in NC38 Heavy Weight Drill Pipe for BHA Transition

Description

Goldenman 3-1/2 in NC38 Heavy Weight Drill Pipe is designed for installation between conventional drill pipe and drill collars in a bottom-hole assembly.

The thick-wall body, enlarged center upset and heavy-duty tool joints provide greater weight and stiffness than standard drill pipe while maintaining more flexibility than a drill collar. This helps create a smoother stiffness transition within the drillstring and supports weight-on-bit, directional control and fatigue management in demanding drilling operations.

The standard reference configuration has an 88.9 mm body outside diameter, an NC38 rotary shouldered connection and a 127 mm tool joint outside diameter.

Conventional, spiral and project-specific configurations are available with optional hardbanding, internal coating, stress-relief features and customer-specified dimensional requirements.

Goldenman supplies Heavy Weight Drill Pipe under the applicable API Spec 7-1 product scope, with NC38 connections manufactured and inspected according to applicable API 7-2 requirements.

Product Short Description

The Goldenman 3-1/2 in NC38 HWDP provides additional drillstring weight and a controlled transition between standard drill pipe and drill collars.

Its reinforced body, center upset and heavy-duty tool joints are suitable for vertical, directional and extended-reach drilling. Final bore, weight, length, hardbanding and connection features can be configured according to the bottom-hole assembly and operating requirements.

Product Highlights

• Manufactured to applicable API Spec 7-1 requirements
• 3-1/2 in / 88.9 mm nominal body OD
• NC38 box-up and pin-down connections
• 127 mm reference tool joint OD
• Thick-wall body for increased drillstring weight
• Enlarged center upset for wear protection and stiffness control
• Conventional, spiral and integral configurations available
• Optional tool joint and center-upset hardbanding
• Optional stress-relief features
• API 7-2 connection dimensional and gauging requirements
• Box and pin thread protection
• Full-length bore drift inspection
• Material traceability and heat-treatment records
• UT, MPI and dimensional inspection options
• Connection and thread-gauge reports available
• Custom internal bore, length and wear-pad configuration

What Is Heavy Weight Drill Pipe?

Heavy Weight Drill Pipe is a rotary drillstem component normally positioned between standard drill pipe and drill collars.

Its body is thicker and heavier than conventional drill pipe, but it remains more flexible than a drill collar.

This intermediate stiffness helps the drillstring transition from the relatively flexible drill pipe section to the more rigid bottom-hole assembly.

HWDP can perform several functions:

• Add weight to the lower drillstring
• Transfer drilling torque
• Transmit axial drilling load
• Carry drilling fluid through the internal bore
• Reduce abrupt stiffness changes
• Support directional drilling assemblies
• Improve drillstring stability
• Provide wear-resistant contact areas
• Reduce concentrated bending stress near the BHA transition

The number and position of HWDP joints should be determined by the drilling program and bottom-hole assembly design.

API 7-1 HWDP vs API 5DP Drill Pipe

Heavy Weight Drill Pipe and standard drill pipe are separate products.

Comparison	API 7-1 Heavy Weight Drill Pipe	API 5DP Drill Pipe
Main position	Lower drillstring and BHA transition	Main drillstring
Primary function	Adds weight and controls stiffness transition	Transmits torque and circulating fluid over the drillstring length
Body construction	Thick-wall body with center upset or wear area	Standard drill pipe body with end upsets
Typical structure	Integral or welded HWDP assembly	Pipe body with welded tool joints
Applicable product standard	API Spec 7-1	API Spec 5DP
Connection requirements	API 7-2 rotary shouldered connection requirements	API 5DP tool joint and applicable connection requirements
Common procurement basis	OD, bore, center upset, tool joint and BHA requirement	OD, nominal weight, wall thickness, grade and length range

Steel grades such as E75, X95, G105 and S135 are commonly associated with API 5DP drill pipe and should not be used as the primary material-classification table for this API 7-1 HWDP page.

3-1/2 in NC38 Reference Specifications

Parameter	Available Reference Specification
Product name	Heavy Weight Drill Pipe
Applicable standard	API Spec 7-1, applicable current edition
Connection standard	Applicable API Spec 7-2 requirements
Nominal size	3-1/2 in
Pipe body OD	88.9 mm
Available pipe body ID	57.4 mm or 57.2 mm reference configurations
Center upset OD	101.6 mm
End upset OD	98.4 mm
Rotary shouldered connection	NC38
Tool joint OD	127 mm
Available tool joint ID	52.4 mm or 57.2 mm reference configurations
Hardband bevel diameter	116.3 mm
Reference mass	Approximately 282 or 312 kg per joint, depending on configuration
Connection orientation	Box up, pin down
Main material	4145H alloy steel or approved project-specific material
Structure	Conventional, spiral, integral or welded configuration
Length	According to approved manufacturing drawing
Hardbanding	Optional
Internal coating	Optional
Stress-relief features	Optional
Thread protection	Pin and box protectors
Certification	Applicable API certificate
Inspection	According to API and purchase-order requirements

The two listed bore and weight options must be confirmed against the current Goldenman manufacturing drawing before order placement.

Reference weight depends on the final bore, length, tool joint, center-upset geometry and hardbanding configuration.

Main Structural Sections

Heavy-Wall Pipe Body

The central pipe body provides axial strength, torque transmission and drilling-fluid circulation.

Compared with conventional drill pipe, the HWDP body has a smaller internal bore relative to its outside diameter, producing greater mass and bending stiffness.

The selected bore affects:

• Joint weight
• Hydraulic flow area
• Pressure loss
• Torsional capacity
• Tensile capacity
• Drift diameter
• Compatibility with internal tools

The final ID should therefore be selected from both mechanical and hydraulic requirements.

Center Upset

The enlarged center upset is a defining feature of conventional HWDP.

It helps:

• Protect the main pipe body from direct borehole contact
• Provide an additional wear area
• Increase weight near the center of the joint
• Control bending behaviour
• Provide a location for optional hardbanding
• Improve handling and inspection identification

The center-upset profile and OD must be confirmed when matching existing HWDP or calculating annular clearance.

Tool Joints

The pin and box tool joints transmit drilling torque and connect the HWDP to adjacent drillstem components.

The 3-1/2 in model uses an NC38 rotary shouldered connection.

Connection inspection should cover:

• Thread form
• Pitch diameter
• Taper
• Lead
• Stand-off
• Seal shoulder
• Pin nose
• Box counterbore
• Tool joint OD and ID
• Bevel diameter
• Surface condition

The connection must match the NC38 components installed above and below the HWDP.

Conventional, Spiral and Integral HWDP

Conventional HWDP

Conventional HWDP normally uses a smooth heavy-wall body with an enlarged center upset.

It is suitable for:

• Standard BHA transition sections
• Vertical drilling
• Directional drilling
• General weight-on-bit support
• Replacement of conventional NC38 HWDP

Optional hardbanding can be applied to the tool joints and center upset.

Spiral Heavy Weight Drill Pipe

Spiral HWDP uses raised spiral wear features along selected parts of the body.

The spiral profile may help:

• Reduce continuous wall contact
• Provide additional wear protection
• Support cuttings movement around the pipe
• Reduce differential-sticking exposure in selected conditions
• Improve performance in deviated and horizontal sections

The spiral OD, blade profile, number of spirals and hardbanding arrangement must be confirmed through the final drawing.

Integral HWDP

Integral HWDP is manufactured from one machined piece rather than welding separate tool joints to a tube.

It may be selected where the project requires:

• Continuous material construction
• Removal of tool-joint weld interfaces
• Project-specific fatigue performance
• High-load or critical BHA applications
• Special dimensional configurations

Integral and welded HWDP should not be assumed to have identical weight, fatigue response or repair procedures.

How to Select the Correct 3-1/2 NC38 HWDP

1. Verify Connection Compatibility

Confirm that the components directly above and below the HWDP use compatible NC38 connections.

The purchase specification should state:

• Box-up and pin-down orientation
• NC38 connection
• Tool joint OD
• Tool joint ID
• Shoulder dimensions
• Required stress-relief features
• Required surface treatment
• Make-up torque basis

Do not identify compatibility using only the historical description “3-1/2 IF.” The actual NC38 dimensions and gauges should be used.

2. Select the Internal Bore

The existing page lists 52.4 mm and 57.2 mm reference tool joint ID options.

A smaller bore may provide more metal cross-sectional area but increases hydraulic restriction.

A larger bore may improve hydraulic flow but changes:

• Joint weight
• Torsional performance
• Tensile capacity
• Drift diameter
• Connection balance
• Compatibility with internal equipment

Goldenman should confirm mechanical ratings for the selected configuration before quotation.

3. Confirm the Required Joint Weight

Do not select HWDP only by nominal outside diameter.

Required weight depends on:

• Desired weight on bit
• Number of HWDP joints
• Drill collar configuration
• Hole inclination
• Buoyancy factor
• BHA neutral point
• Rig hook-load limitations
• Dynamic drilling loads

Reference mass must be confirmed from the final drawing rather than copied from a general product table.

4. Define the Center-Upset Configuration

Provide:

• Smooth or spiral body preference
• Center-upset OD
• Center-upset length
• Wear-pad requirement
• Hardbanding requirement
• Maximum allowable BHA OD
• Hole and casing clearance

An oversized center upset may create clearance or fishing limitations in a restricted wellbore.

5. Define Hardbanding Requirements

Hardbanding can be applied to:

• Pin tool joint
• Box tool joint
• Center upset
• Spiral wear areas

The purchase order should define:

• Hardbanding material or approved equivalent
• Application location
• Band width and thickness
• Flush or raised profile
• Casing-friendly requirement
• Repair and reapplication requirements

Hardbanding should be selected for both tool-joint wear resistance and compatibility with casing or open-hole contact conditions.

HWDP Position in the Bottom-Hole Assembly

A typical drillstring transition may include:

1. Standard drill pipe
2. Heavy Weight Drill Pipe
3. Drill collars
4. Stabilizers and directional tools
5. Mud motor or rotary steerable system
6. Bit

The HWDP section provides an intermediate stiffness transition between drill pipe and drill collars.

The required quantity depends on the actual BHA and drilling program. It should not be selected using a fixed number of joints for every well.

Engineering inputs may include:

• Hole size
• Hole inclination
• Dogleg severity
• Bit weight requirement
• Drill collar OD and ID
• Drill pipe dimensions
• Rotary speed
• Drilling torque
• Expected buckling
• Fatigue exposure
• Directional assembly design

NC38 Connection and Stress-Relief Features

NC38 is a rotary shouldered connection used to transmit torque and axial load through the seal shoulder and threaded connection.

Optional connection stress-relief features may be specified to reduce local fatigue concentration at critical connection areas.

Possible options include:

• Pin stress-relief groove
• Box bore-back
• Cold-worked thread roots where specified
• Phosphate or copper-based thread surface treatment
• Customer-specified connection treatment

These options must be stated in the purchase agreement and shown on the approved drawing.

Make-up torque must be determined from the final connection dimensions, material properties, surface treatment and operating requirements.

Hardbanding and Wear Protection

HWDP operates near the lower drillstring where contact loads and lateral movement can be severe.

Wear protection may include:

• Tool joint hardbanding
• Center-upset hardbanding
• Spiral wear pads
• Replaceable or repairable wear surfaces
• Customer-approved casing-friendly hardband material

During inspection, pay particular attention to:

• Tool joint OD loss
• Center-upset wear
• Hardband cracking
• Spalling
• Uneven wear
• Heat-affected-zone condition
• Reapplication history

Hardbanding repairs should follow an approved welding and heat-control procedure.

Internal Coating

An optional internal coating may be applied to improve corrosion protection and hydraulic surface condition.

Selection should consider:

• Drilling-fluid chemistry
• Chloride concentration
• Temperature
• Abrasive solids
• Chemical-cleaning procedures
• Required drift diameter
• Coating repairability

The coating thickness must be considered when confirming the final drift and hydraulic bore.

Replacement and Interchangeability

A replacement 3-1/2 NC38 HWDP should not be ordered using only the nominal size and connection.

Provide:

• Existing manufacturer
• Original part number
• Nominal body OD
• Body ID
• Center-upset OD and length
• End-upset dimensions
• Tool joint OD
• Tool joint ID
• Bevel diameter
• Overall length
• Joint weight
• Hardbanding position
• Stress-relief features
• Connection inspection requirements
• Existing drawing or photographs

Two 3-1/2 NC38 HWDP joints may connect together but still have different weight, stiffness, hydraulic bore and wear geometry.

Manufacturing and Quality Control

Goldenman manufacturing and quality-control procedures can include:

• Raw material certificate verification
• Heat-number traceability
• Chemical and mechanical property review
• Heat-treatment control
• Ultrasonic examination of bar or tube material
• Weld inspection for welded assemblies
• Magnetic-particle inspection of critical areas
• Dimensional inspection
• Body OD and ID inspection
• Center-upset dimensional inspection
• Full-length bore drift inspection
• Straightness inspection
• Tool joint dimensional inspection
• NC38 thread gauging
• Seal-shoulder inspection
• Hardness testing
• Hardbanding inspection
• Internal coating inspection
• Product marking verification
• Final document review

The exact inspection plan depends on whether the product is integral or welded and on the agreed API and customer requirements.

Product Identification and Traceability

Product marking can include:

• Manufacturer name or identifying mark
• API 7-1 identification
• Product traceability number
• Nominal size
• Connection type
• Serial or heat number
• Additional customer-required marking

Marking location and method should not damage critical threaded or highly stressed areas.

Available Documentation

The project documentation package can include:

• API certificate
• Certificate of Conformity
• Approved product datasheet
• Dimensional drawing
• Material certificates
• Heat-treatment records
• Mechanical test reports
• Ultrasonic inspection report
• Magnetic-particle inspection report
• Weld inspection report where applicable
• Hardness report
• Dimensional inspection report
• Bore drift inspection record
• NC38 thread-gauge report
• Hardbanding inspection report
• Internal coating report
• Product traceability list
• Packing list
• Third-party inspection report

Frequently Asked Questions

Is Heavy Weight Drill Pipe manufactured to API 5DP or API 7-1?

Heavy Weight Drill Pipe used as a bottom-hole assembly component is covered by API Spec 7-1.

API Spec 5DP applies to conventional drill pipe bodies, tool joints and drill pipe assemblies. Thick-wall drill pipe manufactured under API 5DP should not automatically be described as API 7-1 HWDP.

What is the difference between HWDP and drill collar?

HWDP is heavier and stiffer than conventional drill pipe but generally more flexible than a drill collar.

It is commonly positioned between drill pipe and drill collars to create a more gradual stiffness transition while adding drillstring weight.

Can 3-1/2 NC38 HWDP connect directly to 3-1/2 IF equipment?

NC38 has historically been associated with some 3-1/2 IF terminology, but replacement compatibility should be confirmed using the current NC38 dimensional and gauging requirements.

Connection names alone should not replace inspection of the thread, shoulder and bore dimensions.

Why does the page list two different internal bores and weights?

The existing product data includes two reference 3-1/2 NC38 configurations with different body or tool joint bores and approximate weights.

The final selection must be confirmed from the required hydraulic bore, mechanical properties, overall length and approved manufacturing drawing.

How should the correct HWDP weight be selected?

The required joint weight and quantity should be determined from the BHA design, required weight on bit, drill collar configuration, inclination and buckling analysis.

Nominal size alone does not determine the correct number of HWDP joints.

Should conventional or spiral HWDP be selected?

Conventional HWDP is suitable for general BHA transition and weight-control service.

Spiral HWDP may be preferred in deviated or horizontal sections where additional wear protection and reduced continuous wall contact are required. Final selection depends on hole geometry, clearance and sticking risk.

Can one hardbanding material be used for every drilling application?

No.

Hardbanding should be selected according to open-hole wear, casing contact, drilling environment and repair requirements. The purchase specification should identify whether casing-friendly performance is required.

What information is required for a replacement NC38 HWDP?

Provide the existing body OD and ID, center-upset dimensions, tool joint OD and ID, overall length, weight, hardbanding, connection features and original drawing or part number.

Matching NC38 threads alone does not confirm complete interchangeability.

What inspections are most important for used HWDP?

Critical inspection areas include the NC38 connections, seal shoulders, tool joint OD, center upset, hardbanding, pipe body, weld areas and internal bore.

Inspection scope should reflect operating hours, dogleg exposure, over-torque events and previous repairs.

Can stress-relief grooves be added to the NC38 connection?

Stress-relief features can be supplied when specified in the purchase agreement and when they conform to the approved connection design.

They should not be machined into existing HWDP without an engineering and remaining-strength review.

Information Required for Quotation

Please provide:

• Required quantity
• Nominal size: 3-1/2 in
• Required connection: NC38
• Conventional, spiral or integral design
• Required overall length
• Required body ID
• Required tool joint ID
• Required joint weight
• Center-upset dimensions
• Tool joint OD
• Hardbanding material
• Hardbanding locations
• Internal coating requirement
• Stress-relief groove requirement
• Bore-back requirement
• Thread surface-treatment requirement
• Required mechanical properties
• Drilling-fluid conditions
• Operating temperature
• H₂S conditions where applicable
• NDE requirements
• API certificate requirement
• Third-party inspection requirement
• Required documentation
• Destination country
• Required delivery schedule

For replacement orders, also provide the existing product drawing, markings, part number and clear photographs.

Request a Technical Quotation

Goldenman supplies API 7-1 Heavy Weight Drill Pipe for vertical, directional, extended-reach and bottom-hole assembly applications.

The 3-1/2 in model is available with NC38 connections, conventional or spiral configurations, project-specific bore options, hardbanding and inspection documentation.

Send your required length, bore, weight, center-upset dimensions, hardbanding and inspection requirements to:

Email: info@goldenman.com

Goldenman will review the BHA and replacement requirements and prepare the dimensional drawing, technical datasheet and commercial quotation.