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Process Documentation
Heavy Weight Drill Pipe
Heavy Weight Drill Pipe (HWDP) — Friction-Welded & Integral Types, API Spec 7-1 Order Basis
heavy weight drill pipe handles the stress concentration that ordinary drill pipe can’t withstand in the collar-to-pipe transition. China Welong was founded in 2001 and supplies HWDP in friction-welded and integral configurations, with the responsible manufacturer identified in the quotation, across the listed 3-1/2” to 6-5/8” OD range; applicable API Spec 7-1 requirements are confirmed in the quotation. Full size range, inspection trail, and logistics terms follow below – no hard sales here.
- Third-party inspection Available for the selected order
- FOB / CIF / DDP / DDU Buyer-selectable Incoterms
- Sea / Air / Rail Multimodal export logistics
3-1/2″–6-5/8″
OD size range, 15 dimensional variants
2 types
Friction Welded & Integral construction
API Spec 7-1
Requirements confirmed per order
Drill String Fatigue at the Collar-to-Pipe Transition, How Heavy Weight Drill Pipe Solves It
01
The heavy weight drill pipe (hwdp) was born from the fact that the drill string fail at points where stiffness changes dramatically – specifically the transition between a rigid drill collar and flexible drill pipe. Existing drillstring failure literature provides numbers for that risk. A well-known 2002 study (Vaisberg, Oil & Gas Science and Technology, IFP Énergies Nouvelles – cited 112 times since) estimates that fatigue-associated failure occurs on about 14% of rigs studied at that time. The paper puts non-productive time at about $106,000 per occurrence (as a 2002 dollar figure not updated for inflation or current rates, nor a claim that we’re making about our own product). The only reason we cited the 2002 work is that it validates that this failure mode costs something significant, which is what HWDP aims to avoid in the first place.
The root cause is a mismatch in stiffness. A drill collar is a thick, stiff bar, and standard drill pipe is a thinner, limber pipe. Run them together and bend stresses concentrate on the collars, causing the nearest pipe joints to fail first. hwdp bridges the gap – it’s an intermediate weight section with a wall about 2-3 times thicker than standard drill pipe, but the same outer dimensions, making it drop into the string with no special handling. Its thicker wall and increased length of the tool joint gradualize the stiffness change over several joints rather than a single abrupt transition, and a wear pad at the center manage the wall-to-wall contact that can abrade the tube body.
02
The number of HWDP joints is determined from the BHA design, hole profile, and fatigue loading; specify the transition section for an engineering check.
There’s nothing particularly esoteric about any of this; it’s a routine consideration in any substantial drill pipe program run miles into the ground – a regular vertical or highly angled directional drilling program. The overall engineering goal is to achieve a gradual transition – a soft slope, not a cliff face – in stiffness between the hard drill collar portion of the string and the standard drill pipe and drill collars connected to it above.
Welong Heavy Weight Drill Pipe Range, Sizes, Types & Selection Reference
Welong supplies heavy-weight drill pipe in two versions and identifies the responsible manufacturer in the quotation, sized to sit alongside our standard drill pipe range. Friction Welded hwdp attaches a heat-treated alloy-steel tube to separately forged tool joints by inertia/friction welding-this is the most common, lowest-cost construction for standard drilling programs. integral HWDP is machined from a single trepanned bar of alloy steel and is built without a weld interface at all-this is the construction specifiers reach for on higher-torque or directional programs where a weld line is one more thing to inspect. Both styles feature the same outer diameter as the equivalent drill pipe size so rig crews handle HWDP with the same elevators, slips, and tongs already on the floor. Each joint is fitted with a center wear pad and longer tool joints than standard drill pipe bodies and the thread and shoulder detail are designed to endure thousands of make-ups and break-outs during the drilling process without any compromise in service life. Skimping on that tool-joint length is a real risk, because the extra material is exactly what lets a joint be re-cut and put back in service instead of scrapped after just 1 year of hard use. Where drilling torque runs high, the longer tool-joints add material that can be re-cut before a joint is retired.
A note on completeness: Certain hwdp programs may also call for a spiral-groove design (grooved center section designed to mitigate differential sticking and hole drag on extended-reach wells). Welong’s current confirmed product offerings are limited to Friction welded and integral construction. Need a spiral configuration HWDP for extended-reach or horizontal applications? Please reach out to our engineering team to verify our current capabilities.
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Dimensional Specifications
The following table lists all the dimensions for the complete heavy weight drill pipe specifications reference for the current Welong product range (sometimes called the heavy weight drill pipe weight chart, although it lists dimensions instead of weight-per-foot; see the note beneath the table for a source of weight data):
| Size (in) | O.D. (in) | I.D. (in) | Tool Joint O.D. (in) | Tool Joint I.D. (in) | Connection | Max Elevator Dia. (in) | Central Upset Dia. (in) | Min Drift Dia. (in) |
|---|---|---|---|---|---|---|---|---|
| 3-1/2 | 3-1/2 | 2-1/4 | 4-3/4 | 2-1/4 | NC38 | 3-7/8 | 4 | – |
| 3-1/2 | 3-1/2 | 2-1/16 | 4-7/8 – 5 | 2-1/16 | NC38 | 3-7/8 | 4 | 1-13/16 |
| 4 | 4 | 2-1/2 | 5-1/4 | 2-1/2 | NC40 | 4-3/16 | 4-1/2 | 2-1/4 |
| 4 | 4 | 2-9/16 | 5-1/4 | 2-9/16 | NC40 | 4-3/16 | 4-1/2 | 2-5/16 |
| 4-1/2 | 4-1/2 | 2-11/16 | 6-1/4 | 2-11/16 | NC46 | 4-11/16 | 5 | 2-7/16 |
| 4-1/2 | 4-1/2 | 2-3/4 | 6-1/4 | 2-3/4 | NC46 | 4-11/16 | 5 | 2-1/2 |
| 4-1/2 | 4-1/2 | 2-13/16 | 6-1/4 | 2-13/16 | NC46 | 4-11/16 | 5 | 2-9/16 |
| 5 | 5 | 3 | 6-5/8 | 3 | NC50 | 5-1/8 | 5-1/2 | 2-3/4 |
Dimensions are ordering references and must be confirmed against the selected supplier drawing and product specification. This table show pipe body and tool-joint dimensions and connections. Detailed mechanical property sheets -tensile yield, torsional yield, and minimum make-up torque by size-are available upon request. It’s best to send you a copy of the full-sheet document for your precise size than to try and squeeze an approximation into a table format.
Dimensional Specifications
| Size (in) | O.D. (in) | I.D. (in) | Tool Joint O.D. (in) | Tool Joint I.D. (in) | Connection | Max Elevator Dia. (in) | Central Upset Dia. (in) | Min Drift Dia. (in) |
|---|---|---|---|---|---|---|---|---|
| 5-1/2 | 5-1/2 | 3-1/4 | 7-1/4 – 7-1/2 | 3-1/4 | 5-1/2 FH | 5-11/16 | 6 | 3 |
| 5-1/2 | 5-1/2 | 3-3/8 | 7-1/4 – 7-1/2 | 3-3/8 | 5-1/2 FH | 5-11/16 | 6 | 3-1/8 |
| 5-1/2 | 5-1/2 | 3-7/8 | 7-1/4 – 7-1/2 | 3-7/8 | 5-1/2 FH | 5-11/16 | 6 | 3-5/8 |
| 5-1/2 | 5-1/2 | 4 | 7-1/4 – 7-1/2 | 4 | 5-1/2 FH | 5-11/16 | 6 | 3-3/4 |
| 6-5/8 | 6-5/8 | 4 | 8 – 8-1/2 | 4 | 6-5/8 FH | 6-15/16 | 7-1/8 | 3-3/4 |
| 6-5/8 | 6-5/8 | 4-1/2 | 8 – 8-1/2 | 4-1/2 | 6-5/8 FH | 6-15/16 | 7-1/8 | 4-1/4 |
| 6-5/8 | 6-5/8 | 5 | 8 – 8-1/2 | 5 | 6-5/8 FH | 6-15/16 | 7-1/8 | 4-3/4 |
Dimensions are ordering references and must be confirmed against the selected supplier drawing and product specification. This table show pipe body and tool-joint dimensions and connections. Detailed mechanical property sheets -tensile yield, torsional yield, and minimum make-up torque by size-are available upon request. It’s best to send you a copy of the full-sheet document for your precise size than to try and squeeze an approximation into a table format.
Selection Reference, Size, Connection & BHA Position
| OD Range | Connection Family | Elevator Dia. | BHA Position |
|---|---|---|---|
| 3-1/2″–4″ | NC38 / NC40 | 3-7/8″–4-3/16″ | Slimhole and workover strings, transition to 3-1/2″–4″ drill pipe |
| 4-1/2″–5″ | NC46 / NC50 | 4-11/16″–5-1/8″ | Most common land-rig transition zone, 4-1/2″ and 5″ drill pipe programs |
| 5-1/2″ | 5-1/2″ FH | 5-11/16″ | Higher-torque directional programs, 5″ and 5-1/2″ drill pipe |
| 6-5/8″ | 6-5/8″ FH | 6-15/16″ | Large-diameter, high-torque strings and offshore/deepwater programs |
hwdp is often placed in between the drill collars and the standard drill pipe within the bottom-hole assembly. applications are grouped into three broad categories: Vertical drilling-the hwdp functions as a compressive member with added weight on bit and transitional fatigue-resistant qualities, and may also supplement some of the collar count; Directional and horizontal drilling-here, the added weight and relative flexibility can both support weight-on-bit and assist in directional control without the rigidity of a full string of collars; and Remedial operations (milling, under-reaming, and hole opening)-the added weight drive the tool with minimal addition to string rigidity.
Heavy Weight Drill Pipe vs Drill Collar, Choosing the Right Transition Component
This isn’t an apples-to-apples comparison of “which is better”-hwdp and drill collars serve different functions in the same assembly and most bottom-hole assemblies include both. This comparison focuses on clear differentiators rather than an overly simplistic “High/Medium/Low” ranking.
| Criterion | Drill Collar | Heavy Weight Drill Pipe |
|---|---|---|
| Construction | Solid bar stock, machined | Tube — Friction Welded or Integral (machined bar) |
| Wall thickness vs. std. drill pipe | Substantially thicker (solid-bar equivalent) | ~2–3× standard drill pipe wall thickness |
| External dimensions | Larger OD than adjacent drill pipe (custom handling) | Same OD as equivalent drill pipe (no special handling) |
| Bending stiffness | High — rigid, minimal flex | Intermediate — flexes more than a collar, less than plain pipe |
| Primary function | Weight-on-bit, string stiffness/stabilization | Fatigue-resistant transition + supplemental weight-on-bit |
| Reference count in transition zone | Varies by hole size and program | 15–30 joints between collars and drill pipe (field-documented range) |
HWDP
API Spec 7-1 Design Basis, Material Traceability & Order-Specific Inspection
API Spec 7-1
Requirements confirmed per order
Third-Party Inspection
Confirmed for the selected order
Inspection Scope
Confirmed for the selected order
For the selected heavy-weight drill pipe, confirm the applicable API Spec 7-1 requirements and supplier evidence in the quotation. Confirm the applicable supplier documentation for the selected connection.
There’s one thing that few suppliers will point out: the API spec 7-1 itself doesn’t define sour-service (H2S) specifications. If your program involves drilling in sour service environments, then you’ll need NACE MR0175/ISO 15156 compliant drill pipe and hwdps – an upgrade option some manufacturers offer, and that warrants a separate conversation from basic API 7-1 compliance. Don’t assume “API compliant” is good enough to meet NACE MR0175/ISO 15156 requirements.
Manufacturing documentation can be reviewed for the selected HWDP configuration.
Welong Quality & Inspection Team
Inspection requirements are confirmed for the selected heavy-weight drill pipe order. Third-party inspection by SGS, DNV, or another qualified provider can be arranged when requested, with its scope and records stated in the quotation.
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From Factory to Wellsite, Procurement, Logistics & After-Sales Support
As a drill pipe international supplier, Welong delivers heavy weight drill pipe to clients in Europe, the Middle East, Russia, South America, and the United States. Shipment is offered under any Incoterm that aligns with your logistical framework-including FOB, CIF, DDP, or DDU. Transit methods include sea, air, or rail, contingent on your timelines and destination. Landed costs are determined on a per-country basis, factoring in current trade policies, maritime shipping rates, port expenses, and duties, publishing one flat figure would be a real risk, because a number that’s accurate for one destination can be wrong by a wide margin for another. To obtain a precise quotation for your specific market, we encourage you to request a price for your specific order and allow us to discuss all components of the landed cost with you.
Pricing for customized heavy weight drill pipe depends on several factors we’ll walk through when you submit an RFQ, rather than disclosing a fixed rate: dimensions and connection type, Friction welded or integral construction, quantity and delivery timeframe, hardbanding and coating alternatives, and the Incoterm you select. Contact us for a price quotation based on your application criteria.
For the selected HWDP order, the quotation identifies the responsible manufacturer, applicable API Spec 7-1 dimensional requirements, in-process and final inspection scope, and non-standard connection or hardbanding requirements. Third-party inspection can be arranged when requested.
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Heavy Weight Drill Pipe (HWDP) Engineering Tools
HWDP Size & Connection Selector
Select the drill pipe size you’re transitioning from — this tool shows every Welong HWDP dimensional variant available in that OD, shown from the current ordering table and subject to quotation confirmation.
Access Tool →Friction Welded or Integral — Which HWDP Construction Fits?
Three questions about your program. No email required — this is a starting point for the conversation, not a substitute for reviewing your well plan with our engineering team.
Access Tool →Transition-Zone HWDP Joint Count — Starting Estimate
Select your well profile for a starting-point HWDP joint count, anchored to the 15–30 joint range documented in published field practice. This is a planning reference, not a substitute for your drilling engineer’s string design.
Access Tool →Frequently Asked Questions
Heavy weight drill pipe (HWDP) sits between the drill collars and standard drill pipe in a bottom hole assembly. It provides a fatigue-resistant transition that absorbs the stiffness change between the two, supplies supplemental weight-on-bit, and in directional and horizontal wells, adds weight while keeping more flexibility than a full drill collar string.
A drill collar is solid bar stock, machined to a larger OD than the adjacent drill pipe, and provides most of the string’s stiffness and weight-on-bit. HWDP is a tube, roughly 2–3× the wall thickness of standard drill pipe, built to the same external dimensions as equivalent drill pipe, so it requires no special handling tools. HWDP is more flexible than a collar and less flexible than plain drill pipe; that intermediate stiffness is the entire point.
Field practice generally runs 15 to 30 joints of HWDP between the drill collars and the standard drill pipe, though the exact count depends on hole size, well trajectory, and program-specific engineering. A documented 2006 field case used 30 joints of HWDP alongside 500 joints of standard drill pipe.
Welong’s current heavy weight drill pipe range covers 3-1/2″ through 6-5/8″ OD across 15 dimensional variants, in NC38, NC40, NC46, NC50, 5-1/2″ FH, and 6-5/8″ FH connections. That table is the full HWDP specs and HWDP sizes reference; request the mechanical property sheet for tensile and torsional yield by size.
Friction Welded HWDP, a heat-treated tube with separately forged tool joints joined by inertia/friction welding, covers most standard drilling programs at a lower cost. Integral HWDP, machined from a single bar with no weld interface, is often specified for higher-torque or directional programs where eliminating the weld line reduces one inspection variable. Tell us your connection torque and well profile and we’ll confirm which construction fits.
For the selected HWDP, confirm the applicable API Spec 7-1 requirements, responsible manufacturer and supplier documentation in the quotation.
No, API Spec 7-1 does not itself define a sour-service requirement. Sour-service HWDP is qualified separately against NACE MR0175/ISO 15156 and offered as a named upgrade grade. If your program is in a sour-service environment, raise it with us directly rather than assuming standard API 7-1 compliance covers it.
FOB, CIF, DDP, and DDU, by sea, air, or rail depending on your timeline and destination. Landed cost depends on destination country and current trade policy, so we quote it per shipment rather than publish a single figure.
Procurement & Capability
Heavy Weight Drill Pipe Capability Review
China Welong reviews the buyer drawing, product specification and inspection scope before quotation.
This review is scoped to the Heavy Weight Drill Pipe configurations set out in the specification table on this page — 8 documented rows covering Size (in), O.D. (in), I.D. (in) and Tool Joint O.D. (in).
24 hEngineer-reviewed quotation on business days
2001Founded in 2001
30+30+ engineers on staff
5 yrStamped serial traceability
Quotation Scope and Commercial Terms
Pricing is prepared against the selected product configuration, material route, inspection scope and shipment terms.
- Quotes are returned within 24 hours on business days, reviewed by an engineer.
- T/T or L/C by wire transfer.
- We ship EXW, FOB, CFR or CIF; other Incoterms on request.
- We work from 2D drawings and 3D CAD models (AutoCAD, Pro/ENGINEER, SolidWorks; .dwg and .igs).
Production Planning
Production timing is confirmed with the quotation after quantity, process route and finishing scope are reviewed.
- We hold agreed items in stock and ship against your release to shorten delivery. Feasibility is confirmed at drawing review.
- Manufacturing at Xi'an, Shaanxi and at Jiyuan, Henan.
- 0.01 mm machining precision.
- Material standards to ISO, BS, ASTM, ASME, DIN, JIS and GB.
- Orders ship in standard export wooden cases, or the packing you specify.
Order Review and Responsibility
The responsible manufacturer, inspection scope and document package are identified for the selected item.
- Every quotation states whether the item is made in our own works or by an approved supplier we developed and supervise.
- We develop, audit and supervise the mills and workshops that make your parts: material mills are re-audited every two years and approved by Welong before they run your order.
- Forgings from 0.2 to 50 tons.
Specification and Inspection Evidence
The specification table on this page is the technical basis for this review: its numeric rows define what we quote, manufacture and inspect against.
- Each piece carries a stamped serial number and stays traceable for five years to its chemical composition, mechanical properties and measurement report, with the test coupon retained.
- An EN 10204-3.1B material certificate with chemical composition and mechanical properties, a dimensional measurement report, and UT and MT reports ships with your order.
- Inspection is by coordinate measuring machine, ultrasonic, magnetic particle and X-ray.
Request a Product Review
Send the drawing, product specification and inspection requirements for a quotation review.
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