Drill Pipe Guide: Oil Rig & Water Well Sizes, Threads, and Weight

What People Mean by “Oil Rig Pipe”

On an oil rig, “pipe” can refer to multiple tubular products: drill pipe, casing, tubing, or surface line pipe. When drilling, the rotating tubular that connects the surface to the bit is drill pipe—a central part of the drill string. Casing and tubing are installed in the wellbore and generally stay there; drill pipe is made up and broken out repeatedly and must survive high torque, tension, bending, and cyclic fatigue.

This guide focuses on drill pipe (including common configurations used in water-well drilling such as mud rotary, air rotary, and DTH/rotary programs).

What Drill Pipe Is Made Of

A drill pipe “joint” typically consists of a pipe body plus two heavy-walled ends called tool joints. Tool joints are welded to the pipe body and provide robust threaded connections for repeated make-up and break-out.

• Pipe body: the long tube section (often ~27–30 ft for Range 2)
• Tool joints: heavy ends that carry the threads and torque
• Pin: male threaded end
• Box: female threaded end
• Rotary-shouldered connection: tapered threads plus a shoulder that seals and transmits torque

Because tool joints add significant metal, two strings with the same tube OD can have meaningfully different “real” weights depending on connection style and upset geometry. The most reliable approach is to treat pipe body and connection mass as separate when precision matters.

How Drill Pipe Is Specified (The 6 Specs You Actually Need)

A typical designation like “3-1/2 inch, 13.3#, X-95, NC38, Range 2” encodes the drill pipe’s dimensions, strength, and connection standard. These are the specifications you need for selection, compatibility, and logistics.

1. Tube OD (outside diameter), such as 2-3/8", 2-7/8", 3-1/2", 4", 4-1/2", 5", 5-1/2", 6-5/8"
2. Nominal weight (lb/ft), used for identification and many planning calculations
3. Wall thickness and ID (inside diameter), which drive hydraulics and pipe-body strength
4. Grade (yield strength family), such as E-75, X-95, G-105, S-135
5. Length range, typically Range 1 (18–22 ft), Range 2 (27–30 ft), Range 3 (38–45 ft)
6. Connection / thread type, such as NC, IF, FH, or REG (plus legacy variants)

For most decision-making, OD + grade + connection control compatibility and mechanical limits, while ID controls hydraulics and performance in mud or air systems.

Drill Pipe Sizes and Weights (Practical Reference)

The table below provides a compact reference for common drill pipe OD sizes and typical nominal weights, plain-end weights, IDs, and wall thicknesses. Use ID for hydraulic decisions, and use nominal/with-connection weight for logistics and string-weight estimates when you don’t have manufacturer joint weights.

Practical rule: when you need a quick estimate without manufacturer joint data, use nominal weight × joint length for a planning number, then add BHA components. For crane lifts and transport, always use the most conservative (heavier) published weight for the exact connection and length range.

Water Well Drill Pipe vs Oilfield Drill Pipe

Water-well drilling spans multiple methods (mud rotary, air rotary, DTH hammer). Many sizes overlap with oilfield drill pipe, but the decision drivers shift.

Oil & gas (deep/high-load)

• Higher sustained torque and tension; more fatigue exposure
• Stronger emphasis on standardization, inspection, and traceability
• Connections frequently standardized around common rotary-shouldered families

Water well / environmental / geothermal

• Thread compatibility with existing subs/hammer/bit systems often dominates selection
• Common sizes include 2-3/8" through 4-1/2" depending on rig class and depth
• Joint lengths and connection styles can vary more widely by supplier and region

In practical terms, water-well drill pipe selection is frequently compatibility-first, while oilfield programs are often load-cycle and standards-first.

Drill Pipe Threading: NC, IF, FH, and REG

Most drill pipe tool joints use rotary-shouldered connections: tapered threads help stabbing and alignment, and a shoulder provides the primary seal and transmits torque. Connection “families” matter because they determine what can mate safely, what gauges you need, and what accessories are available.

Common connection families

• NC (Numbered Connections): widely used “numbered” rotary-shouldered ecosystem
• IF (Internal Flush): designed to reduce internal restriction through the connection
• FH (Full Hole): intended to preserve larger internal flow area through the connection
• REG (Regular): often encountered to match legacy or established inventories

Selection logic: choose IF/FH when you’re prioritizing hydraulics and minimizing restriction, choose NC when you want broad compatibility and common tooling, and choose REG when you must match existing stock. The correct choice ultimately depends on your rig’s torque/pullback capability and the rest of your tool string.

Interchangeability warning

Some connections can partially mate but are not truly interchangeable. If threads “make up” but feel wrong, leak, or show shoulder mismatch, stop and verify with the correct gauges. A near-match can be unsafe for torque and tension service.

How to Identify an Unknown Drill Pipe Thread (Field Workflow)

When you inherit pipe or mix suppliers, thread identification becomes the fastest way to avoid downtime. Use this workflow to get from “unknown pin/box” to a confirmed connection family and size.

1. Check markings on the tool joint (connection type, size, grade are often stamped).
2. Measure tool joint OD/ID and compare to known inventory dimensions.
3. Use a pitch gauge to estimate TPI and note taper behavior.
4. Confirm with the proper thread gauges whenever the pipe will see meaningful torque/tension service.
5. If you suspect a “mates-but-wrong” scenario, do not force makeup—validate compatibility first.

Operational takeaway: the cost of gauging is usually trivial compared to the cost of galling, leaks, connection failure, or a stuck string event.

Weight of Drill Pipe: Definitions, Formulas, and Examples

“Weight of drill pipe” can mean pipe-body weight, nominal weight, or an average joint weight including tool joints. Always confirm which definition you’re using before you compare quotes or calculate hookload.

Three weight concepts you should keep separate

• Plain-end weight (lb/ft): pipe body only (excludes connection mass)
• Nominal weight (lb/ft): standard naming convention used for identification and planning
• Joint weight (lb/joint): the value that best fits lifting, shipping, and detailed string inventory

Quick geometry-based pipe-body weight formula

If you know OD and ID (inches), estimate pipe-body weight per foot (steel) with: Weight (lb/ft) ≈ 2.673 × (OD² − ID²)

Worked example (2-3/8" with ~1.815" ID)

OD² − ID² ≈ 2.35, so weight ≈ 2.673 × 2.35 ≈ 6.27 lb/ft, which aligns with typical plain-end values in reference tables.

From lb/ft to weight per joint and string weight

• Weight per joint (air) ≈ (lb/ft) × (joint length in ft)
• String weight (air) ≈ sum of all joints + BHA component weights
• In fluid, buoyancy reduces effective hookload; do not use buoyed weight for lifting/transport

For safe handling: use air weight and conservative published joint weights. For drilling mechanics: compute buoyed hookload using an appropriate buoyancy factor for the fluid system.

How to Choose the Right Drill Pipe (Selection Checklist)

Use this checklist to converge on a drill pipe program that matches your rig limits, drilling method, and connection ecosystem.

Step 1: Start with constraints

• Rig torque capability (rotary/top drive)
• Max hookload / pullback and mast limits
• Target depth, dogleg severity, and expected fatigue exposure
• Hole size, hydraulics (ID), and drilling fluid/air program
• Required thread compatibility with existing subs/BHA

Step 2: Pick OD and wall (hydraulics vs strength)

Smaller OD strings are common on smaller rigs and shallower programs; larger OD strings increase stiffness and torque capacity but add weight and cost. If hydraulics are limiting (pressure losses, air volume), prioritize ID continuity and connection style.

Step 3: Pick grade (strength family)

Higher grade increases yield strength but does not automatically solve fatigue or operating-practice issues. Choose grade based on tension/torque requirements, depth, and inspection discipline.

Step 4: Standardize connections

The fastest way to reduce downtime is to standardize on a single compatible connection family and verify inventory with proper gauges. Mixed threads are a predictable failure mode in both oilfield and water-well operations.

Handling and Maintenance to Prevent Failures

Most drill pipe problems trace back to thread and shoulder damage, contamination, improper makeup torque, or skipped inspections. These issues show up as galling, leaks, weak makeup, washouts, fatigue cracks, and connection failures.

• Use thread protectors for storage and transport
• Keep threads clean; use appropriate compound and handling practices
• Make up connections to correct torque with calibrated equipment
• Inspect regularly to catch washouts, cracks, and excessive wear early

The operating conclusion: disciplined handling and inspection produces the biggest reliability gains—often more than changing grade or upsizing pipe.