Knowing Your Drill Pipe

By Andrew Farr

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Maxi rig HDD contractors have numerous drill pipe options to consider during a purchase, involving eight key factors. These include the size of the mid-body tube, wall thickness (or "weight per foot"), steel grade, connection size and type, the choice between new vs. used pipe, the manufacturer or source of the pipe, availability or delivery time, and hard band options.

It is essential to examine each of these aspects in detail as they significantly influence your buying decision.

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1. Size of the Mid-Body Tube:
Various reference tables and resources provide data about tube properties based on diameter, wall thickness, and steel grade. A crucial yet often overlooked factor is Torsional Stiffness, especially vital for pilot holes in extended reach HDD projects. For example, a 6-5/8 in., 27.70 lbs/ft, S-135 drill pipe with .362-in wall thickness shows 59% less "twist" compared to a 5 in., 19.50 lbs/ft, S-135 pipe with the same wall thickness. This characteristic becomes essential when maintaining the "high side" or clock-face position of the mud motor and drill bit at the end of a 5,000-ft string.

2. Wall Thickness:
Generally, thicker walls mean stronger pipes. Interestingly, a 5-in., 25.60 lbs/ft, S-135 pipe with a .500-in. wall thickness is stronger in torsion and tension than a 5-1/2 in., 21.90 lbs/ft, S-135 pipe with a .361-in. wall thickness, though the latter has better torsional stiffness.

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3. Grade of Steel:
Most contractors and engineering firms prefer S-135 grade drill pipes for maxi rig HDD projects due to modern steel chemistries enhancing their toughness through heat treating. The aim is for the pipe to "leak-before-break" during a failure. Other steel grades like G-105, with a minimum yield strength of 105,000 psi, are primarily used in oil and gas drilling applications where H2S may be present.

4. Connections Size and Type:
Most HDD contractors opt for widely used API style connections such as 4-1/2-in. IF, 5-1/2-in. Full Hole, and 6-5/8-in. Full Hole, along with their Double Shoulder versions. The double shoulder increases strength by around 30% and helps prevent over-torque during downhole make-up.

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5. New vs. Used:
When deciding between new or used pipes, consider the remaining useful life of the used pipe when compared to a new pipe. For instance, a new 6-5/8-in., 27.70 lbs/ft S-135 pipe with 8-1/2-in. OD tool joints must pass a minimum OD of 8-in. to meet Premium Class or DS1-CAT5 criteria. You can calculate the value of the used pipe based on its remaining life before falling below these standards. Evaluate the "useable tong space," as loss of space to Hard Banding could limit its usability with rig vises or jaw dies.

Hard Banding on both Pin and Box tool joints should not interfere with usable tong space, ensuring they meet your rig requirements. For instance, a 6-in. useable tong space may be insufficient for a rig with 14 in. between vise dies.

6. Pipe Source, aka Manufacturer:
Examine the quality control standards of new pipe manufacturers or inspection standards for used pipe. Modern manufacturing has enhanced the length of the upset on the tube at weld neck areas, which increases field reliability and reduces failure chances.

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7. Availability or Delivery Time:
Plan your purchases to get better selection and availability or timely delivery of new pipes. Rushing to purchase in-stock pipes could limit your options regarding hard banding and other features.

8. Hard Band Options:
Hard banding can prolong the life of drill pipes during rock crossings. Discuss with your vendor the available types and placements for optimal benefits.

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Resources from your drill pipe vendor or manufacturer can help in making these decisions. T.H. Hill's inspection criteria are industry standards ranging from Double White Band, API Premium Class, up to DS1-CAT5. Not all two-white-band pipes meet Premium Class or DS1-CAT5 criteria; these may only indicate the minimum 80% Remaining Body Wall (RBW) criteria. Your vendor or manufacturer should provide reference material and inspection reports to assist in choosing the right pipe for your application.

Jay Miller is president and owner of JT Miller Inc., based in Conroe, Texas.

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What Is A Drill Pipe? | Drill Pipe Thread, Grade & Types

Drill Pipe

Drilling is the first phase of creating a wellbore, followed by casing, which lines the wellbore with an outer tube, and lastly, tubing, which transports oil and gas to the surface.

Drilling uses drill pipes to rotate the drill bit, allowing it to penetrate soil and rock to access mineral deposits. Casing involves using a steel pipe, cemented in place, preventing wellbore collapse. Tubing is used in the production phase to move fluids to the surface.

Oil Country Tubular Goods (OCTG) is the collective term for pipes with end connections classified as either casing or tubing.

Drill Pipe

A drill pipe consists of hollow steel tubes that rotate the drill bit while drilling fluid aids the process. Threaded tool joints on both ends of the pipe ensure high torque resistance and durability during rotation.

Since drilling rigs vary in size, standard drill pipes come in different specifications to match these variations.

Parts of a Drill Pipe

• Pipe Body
• Tool Joints: These can be either box (female) or pin (male) end connections

OCTG Standards

The API (American Petroleum Institute) and ISO (International Organization for Standardization) set industry standards for oil and gas operations and testing procedures.

Technical Specifications:

• API Specification 5B: Threading, Gauging, and Inspection of Casing, Tubing, and Line Pipe Threads
• API Specification 7-2: Threading and Gauging of Rotary Shouldered Connections
• API Specification 5CT: Casing and Tubing
• API Specification 5DP: Specification for Drill Pipe
• ISO 11960: Petroleum and Natural Gas Industries — Steel Pipes for use as Casing or Tubing for Wells

Pipe Body

Casing and Tubing Grades

Pipe bodies are classified by grades according to API 5CT and ISO 11960:

Casing and Tubing Grades

1 – Low strength

2 – Suitable for environments with high H2S (hydrogen sulfide)

3 – High strength but lacks corrosion resistance

4 – Higher strength but also lacks corrosion resistance

Steel Grade Definition

Drill pipes are made with varying chemical compositions and properties. They are classified through steel grade, calculated from required tensile and yield strength. Yield strength is the minimum pressure before deformation, and tensile strength is the maximum stress before breaking.

Types of Drill Pipe Steel Grades:

1. E – lowest yield strength per unit area at 75,000 psi
2. X – 95,000 psi
3. G – 105,000 psi
4. S – highest yield strength at 150,000 psi for deeper wells

Steel grades are designated by the letter and minimum yield strength. Grades X-95, G-105, and S-135 are high strength, suitable for deeper wells.

API grades chart:

API Drill Pipe Grade

Minimum Yield Strength (psi)

E

75,000

X

95,000

G

105,000

S

135,000

As drilling requirements evolve, manufacturers have created proprietary steel grades for newer design standards and harsher conditions, such as for critical service, sour service, thermal, or low temperature service.

Steel Grade Identification

Identifications for drill pipe grades are marked on the tool joint or base pin with the following format:

Manufacturer Symbol / Month Welded / Year Welded / Pipe Manufacturer / Drill Pipe Grade

Sample: AA 12 95 N E

Sizes

Length

Drill pipe lengths are classified as:

R1 – 18 to 22 ft

R2 – 27-31 ft

R3 – 38 to 45 ft

Longer pipes like R3 can endure more wear as they carry greater loads than shorter ones.

Outer Diameter

Drill pipe outer diameter ranges from 2 3/8" to 6 5/8".

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Drill pipes come in different weld types. Choosing the right weld depends on tube billet quality and structural requirements.

Seamless

A seamless drill pipe is formed by pushing or pulling steel over a mandrel, eliminating visible seams. These pipes are favored for their uniform structure and high-pressure tolerance.

ERW

ERW (Electronic Resistance Welded) drill pipes result from cold-formed steel edges welded using high-frequency energy. Their surface is easier to maintain.

SAW

Submerged Arc Welding (SAW) joins bent steel plates, making the pipe uniform, compact, and ductile, ideal for pressure vessels.

Tool Joints

Connections at each pipe's ends join two pipes to form a string. High-tension efficiency connections will break the pipe body but not the joint under maximum string tension.

Drill Pipe Specification with Upset and Tool Joint Chart

Parts of a Thread

• Load flank: the surfaces that support the string and contact tightly made-up sections
• Stabbing Flank: surfaces that guide the pin
• Crest: high points of the thread
• Root: low points of the thread

Different thread profiles offer various performance benefits, such as increased load resistance from an optimal gap between stabbing flanks.

Types of Threads

There are two connection types:

• API: Following API Spec 5B standards, including round and buttress threads, single shoulder connectors like Regular, Internal Flush (IF), Full Hole (FH), and Numeric Connection (NC).

• Premium: Superior to API standards, proprietary connections available in various sizes, either threaded, coupled, or integral, with double shoulders for more torque.

Sample of Performance Comparison

Drill Pipe Premium Tensile, Grades, and Mechanical Specification Chart

Round threads feature v-shaped threads with rounded crests and roots, offering good liquid sealability but weak tensile resistance, supporting less than 80% of the pipe body's resistance.

Buttress threads resemble trapezoids with different stabbing and load angles, providing better tension resistance but poor liquid sealability.

Thread Characteristics

NEW DRILL PIPE — TORSIONAL DATA

Connections are classified by:

• Thread profile: Thread shape and part design
• Metal seal: High-pressure contact area on the thread
• Shoulder: Box area contacting the pin tip
• OD: Outer diameter
• Taper: Diameter change rate with length

Drill Pipe Specifications

Product Specification Levels

Advances in OCTG led to Product Specification Levels (PSL) for better pipe classification:

PSL 1 follows API/ISO standards.

PSL 2 and PSL 3 address newer requirements beyond API/ISO, differing in chemical composition, mechanical properties, manufacturing, repair, and traceability certification.

Drill Pipe Product Designation

Oil and gas industry standard designation ensures common understanding of a drill pipe's mass and dimensions.

Sample Designation: 9 5/8" 40# N80 BTC R3

Where:

9 5/8" specifies the outside diameter in inches

40 is the weight in lbs/ft

N80 – steel grade

BTC R3– connection type

Product designation helps buyers match pipes to design requirements.

Specification Sheets

Specification sheets contain:

• Total Size and Weight
• Grade
• Range
• Tool Joint
• Pipe Body Capacity, Tensile Strength, Wall Thickness
• Tubular Assembly Weight, Length (including pins)
• Connection Type

Used Pipe Classification

API defines classes to validate used drill pipes:

1. Class 1 – New, unused drill pipes
2. Premium – Reused pipes with remaining wall thickness ≥ 80% of spec value
3. Class 2 – Remaining wall thickness ≥ 80% of spec value
4. Class 3 – Remaining wall thickness ≥ 70% of spec value

Inspectors measure wall thickness and recalculate max tension capacity to determine if used pipes are qualified for future use.

Drill Pipe HS Codes

Knowing HS (Harmonized System) codes helps with customs during drill pipe import/export. The 6-digit HS code classifies products worldwide.

Drill pipes fall under Chapter 73: Iron or Steel Articles, Heading 04 for Seamless Tubes, Pipes, and Hollow Profiles from Iron (excluding cast iron) or Steel.

Example subheadings for line pipes:

10 – Iron

11 – Stainless Steel

21 – Drill Pipe

22 – Casing, tubing, and drill pipe for oil or gas

A complete sample HS code is 73041120, for stainless steel blanks for tubes and pipes.

Reference HS codes for further details.

If you are looking for more details, kindly visit Oil Drill Pipe.

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