OCTG Casing and Tubing

API Casing Chart: Complete Guide to API Casing Sizes, Weights, Grades and Specifications

Lincoln Lau — Mon, 08 Jun 2026 03:02:25 +0000

In oil and gas well construction, API casing refers to steel pipe manufactured according to American Petroleum Institute standards and used to support the wellbore, isolate formations, and ensure safe drilling and production operations. Because casing selection involves multiple technical factors, engineers, buyers, and field personnel often refer to an api casing chart to quickly compare key data across different casing options. A typical oilfield casing chart summarizes essential information such as outside diameter, nominal weight, wall thickness, steel grade, drift size, burst pressure, collapse pressure, and connection details.

What Is an API Casing Chart — octgcasing.com

What Is an API Casing Chart?

An API casing chart is a standardized reference table published under API Specification 5CT (ISO 11960) that lists the complete dimensional, mechanical, and weight data for every casing and tubing size, wall thickness, and grade recognized by the American Petroleum Institute. It is the single most important reference document used across the OCTG supply chain — from well design to final field installation.

Every row in an API casing chart defines a specific pipe configuration by its key dimensions: the outside diameter (OD), wall thickness, and the resulting unit weight in lb/ft or kg/m. But the chart goes far beyond these basics — it also specifies tolerances and quality parameters that ensure every joint of casing arriving on a rig floor is fit for purpose in a high-pressure downhole environment.

Engineers, procurement teams, and field crews rely on the API casing chart at every stage of a well’s life. During design, it provides the data needed to run casing string calculations for burst, collapse, and tensile loads. During procurement, it standardizes what buyer and supplier agree on. And on location, it gives rig crews the drift diameter and coupling dimensions they need to confirm the pipe is ready to run.

Dimensions covered in an API casing chart

Outside Diameter (OD) Wall Thickness Drift Diameter Unit Weight Ovality Straightness Pipe Length End Bevel Coupling OD & Length

Well Design

Burst, collapse & tensile calculations

Casing Selection

Grade and size specification

Procurement

Standard specs for buyer & supplier

Engineering Calculations

Hook load, string weight, torque

Field Operations

Drift check, tally & running verification

Request a Quote Need a specific size, grade, or connection? Send us your requirements — we’ll respond within 24 hours.

API Casing Size and Weight Selector | Inch & Metric Dimensions

API Casing Dimensions

API Casing Size and Weight Selector

Choose a casing size label and weight label to view matching outside diameter, nominal mass, wall thickness, inside diameter, drift diameter, plain-end mass, and thread values in inch or metric units.

Matching Result

No size and weight selected.

Inquiry List

0 itemsAdd one or more casing specifications before sending an RFQ.

Send RFQ Email

API Casing Size Chart Lookup

This API casing selector uses size label and weight label data from a casing pipe dimensions and weight chart for API round thread and buttress thread products. The selector helps buyers compare inch and metric casing dimensions before requesting a quotation.

The displayed values include outside diameter, nominal linear mass, wall thickness, inside diameter, drift diameter, plain-end mass, round thread values, and buttress thread values. Blank cells indicate that the source chart does not list a value for that casing specification.

How to use this casing selector

Select Inch or Metric according to the unit system required for your casing inquiry.
Choose a Size label, then choose an available Weight label from the filtered list.
Review the matching result and add one or more casing specifications to the inquiry list.
Use the RFQ email button to send the selected API casing specifications to info@balingpipe.com.

Download API Casing Size Table
save and use you at anytime for your casing pipe

API Tubing Size Selector | Standard Tubing Dimensions and Masses

API Tubing Dimensions

API Tubing Size Selector

Choose the OD and PPF to view matching standard tubing dimensions, metric masses, wall thickness, inside diameter, and API tubing connection mass gain or loss data.

Matching Result

No OD and PPF selected.

Inquiry List

0 itemsAdd one or more tubing specifications before sending an RFQ.

Send RFQ Email

Download API Tubing Size Table
save and use you at anytime for your tubing pipe

API Casing Grade Chart

Grade	Typical Application	Yield Strength MPa	Tensile Strength MPa	Hardness Requirement	Heat Treatment
H40	Shallow wells, low-load wells	276–552	≥414	—	Hot rolled
J55	Shallow wells, conventional wells	379–552	≥517	≤207 HB	Normalized
K55	Medium-shallow wells, wells requiring higher tensile strength	379–552	≥655	≤207 HB	Normalized
M65	Sour wells, low-strength sour-service conditions	448–586	≥586	≤22 HRC	Quenched and tempered
N80-1	Deep wells, conventional high-load wells	552–758	≥689	≤241 HB	Normalized
N80-Q	Deep wells, wells requiring higher toughness	552–758	≥689	≤241 HB	Quenched and tempered
L80-1	Sour wells, anti-sulfur wells	552–655	≥655	≤23 HRC	Quenched and tempered
L80-9Cr	CO₂ corrosion wells	552–655	≥655	≤23 HRC	Quenched and tempered
L80-13Cr	CO₂ corrosion wells, mild to moderate corrosive wells	552–655	≥655	≤23 HRC	Quenched and tempered
C90-1	High-pressure sour wells	621–724	≥689	≤25.4 HRC	Quenched and tempered
T95-1	High-temperature, high-pressure sour wells	655–758	≥724	≤25.4 HRC	Quenched and tempered
P110	Ultra-deep wells, high-load wells	758–965	≥862	—	Quenched and tempered
Q125	Ultra-deep wells, ultra-high-pressure wells	862–1034	≥931	≤321 HB	Quenched and tempered

How to Use an API Casing Chart for Casing Selection

Selecting the right oil casing pipe requires more than matching the nominal outside diameter. An API casing chart helps engineers compare casing size, weight, wall thickness, inside diameter, drift size, and pipe body dimensions, then match these values with well depth, pressure, load conditions, corrosion environment, and required mechanical performance. The following steps explain how to use an API casing chart for casing selection.

How to Use an API Casing Chart — 12-Step Selection Guide — octgcasing.com

Confirm the Well Depth and Casing Section

Start by identifying the well depth and which casing section is being installed — surface, intermediate, production, or liner. Deeper wells require higher strength, heavier wall thickness, and better collapse resistance because external pressure and axial loads increase with depth.

For each casing string, define the setting depth, hole size, previous casing size, cementing requirements, and the required internal clearance for drilling or production tools.

Determine the Required Casing Size

Use the casing chart to select the nominal outside diameter — such as 7″, 9-5/8″, 13-3/8″, or 20″ casing. The selected OD must fit the wellbore design, allow proper cement clearance, and provide enough inside diameter for tools, completion equipment, tubing, packers, or production flow.

Don’t select by OD alone — the same OD may have several weight options, each with a different wall thickness, ID, and drift size.

Compare Nominal Weight and Wall Thickness

After selecting the OD, compare the available nominal weights in the casing chart, usually shown in lb/ft. A higher nominal weight normally means a thicker wall, smaller inside diameter, and higher pipe body strength.

A heavier casing weight may improve burst, collapse, and tensile performance — but it also reduces internal clearance and increases total string weight. The selected weight must balance mechanical strength, drift requirement, running conditions, and cost.

Check Inside Diameter and Drift Size

The inside diameter shows the available internal bore. The drift diameter is the minimum guaranteed diameter that a standard drift mandrel can pass through.

Always compare the drift size with the maximum outside diameter of tools that must pass through — drill bits, logging tools, perforating guns, packers, plugs, tubing, and completion assemblies. The drift size should be larger than the maximum tool OD with enough clearance.

If the drift size is too small, the casing may meet strength requirements but still fail operationally — downhole tools cannot pass through safely.

Evaluate Burst Pressure Requirement

Burst pressure is the internal pressure capacity of the casing. It becomes critical when the pressure inside the casing is higher than the external formation or annulus pressure.

Calculate the maximum expected internal pressure during drilling, testing, stimulation, production, or well control conditions. Then compare it with the pipe body burst rating for the selected OD, weight, and grade.

If the burst rating is insufficient, select a heavier weight, thicker wall, or higher-strength grade.

Evaluate Collapse Pressure Requirement

Collapse pressure is the casing’s resistance to external pressure. It is especially important in deep wells, depleted formations, high-mud-weight wells, and cementing operations.

Calculate the maximum external pressure and minimum internal pressure that the casing may experience. Then compare with the collapse rating of the selected size, weight, and grade.

If collapse resistance is too low, choose a heavier wall, higher grade, or a casing design with improved collapse performance.

Check Axial Load and Tensile Capacity

Casing must support its own weight plus additional loads from running, cementing, pressure testing, thermal effects, bending, drag, and possible overpull. The deeper the well, the more important tensile capacity becomes.

Use the casing weight from the chart to estimate total string weight. Then compare the expected axial load with the pipe body yield strength and connection strength. The selected grade and connection type must provide adequate tensile capacity with the required safety factor.

Select the Proper API Grade

Casing grade determines the material strength and directly affects burst, collapse, and tensile performance. Common API casing grades include J55, K55, N80, L80, P110, and Q125.

For shallow or low-pressure wells, lower grades may be sufficient. For deep, high-pressure, or high-load wells, higher grades are needed.

Grade selection must also consider corrosion and sour service conditions — in H₂S, CO₂, or high-chloride environments, material compatibility may matter more than simply choosing the highest strength grade.

Consider the Corrosion Environment

Before finalizing casing selection, evaluate the corrosion environment — H₂S, CO₂, chlorides, water cut, oxygen exposure, temperature, and expected well life.

For corrosive wells, consider sour-service grades (L80, C90, T95), corrosion-resistant alloys (13Cr, Super 13Cr, duplex), coating, inhibitor programs, or additional corrosion allowance.

A casing that is mechanically strong may not be suitable if it cannot withstand the actual downhole chemical environment.

Verify Connection and Thread Type

The casing chart lists pipe body dimensions, but the final selection must also include the connection type — STC, LTC, BTC, or premium connections.

The connection must meet the same design requirements as the pipe body: tension, compression, internal pressure, external pressure, sealing performance, torque capacity, and running conditions.

For high-pressure gas wells, horizontal wells, or severe service wells, premium connections with metal-to-metal seals are often required.

Compare All Design Parameters Together

Final casing selection should be based on the combined result of all key parameters — well depth, formation pressure, burst requirement, collapse requirement, axial load, corrosion environment, OD and wall thickness, nominal weight, API grade, ID and drift size, connection type, and cementing and running requirements.

The best casing is not always the heaviest or highest grade — it is the one that satisfies pressure, load, corrosion, drift, and operational requirements with the proper safety margin and reasonable cost.

Finalize the Casing Selection

Once the candidate casing size, weight, and grade meet the required burst, collapse, tensile, drift, and corrosion criteria, confirm the selection against API 5CT specifications, project design standards, and manufacturer performance data.

The API casing chart should be used as the starting point for dimensional selection, while burst, collapse, tensile, and connection performance should be verified using approved engineering data before procurement or field use.

Check API Casing and Tubing Size with BSCO

When selecting oilfield casing, accurately understanding its dimensions, weight, steel grade, thread type, and applicable operating conditions is crucial for ensuring the safe and efficient progress of oil and gas projects. The API Casing Chart allows you to quickly compare casing parameters across different specifications, providing a reference for design, procurement, and cost control.

If you are still unsure which casing specification is best suited for your project, please contact BSCO. With extensive industry experience and professional technical support, BSCO can provide you with suitable oilfield casing size recommendations, specification selection solutions, and price consultations based on your well conditions, project needs, and budget, helping you reduce your project procurement burden and more efficiently complete budget planning and material preparation.

Frequently Asked Questions (FAQs)

What information is included in an API casing chart?

Conductor Casing: Technical Guide for OCTG Casing and Tubing Buyers

Lincoln Lau — Wed, 03 Jun 2026 08:25:41 +0000

Conductor casing is the first and largest casing string installed in a well, isolating loose surface formations and providing structural support for subsequent casing strings. BSCO explains conductor casing functions, drilling use, installation, sizes, specs, diagrams, and applications.

What Is Conductor Casing?

What Is Conductor Casing — octgcasing.com

Definition of Conductor Casing

Conductor casing is the outermost, shallowest string in a well, set before main drilling begins. Distinct from offshore drive pipe, it is typically low-carbon steel line pipe (API 5L X56, BTC) or heavy-wall OCTG.

Conductor casing position in a typical well

Casing Program Order — octgcasing.com

Where It Sits in the Casing Program

The well conductor casing is always the first string installed — the starting point of a casing program that builds inward: conductor → surface → intermediate → production casing, with tubing run inside the innermost string.

Casing program installation sequence

Function and Purpose of Conductor Casing

Conductor Casing Primary Functions — octgcasing.com

Primary Functions of Conductor Casing

Prevent Borehole Collapse

Stabilizes shallow unconsolidated formations — sand, gravel, and weak soil — that would otherwise cave into the borehole and block drilling progress before deeper casing can be set.

Support the Wellhead & BOP Stack

Provides the structural foundation for the wellhead assembly and blowout preventer (BOP) stack — the critical surface equipment that controls well pressure throughout drilling and completion.

Protect Freshwater Aquifers

Isolates shallow freshwater-bearing zones from drilling fluids and wellbore contaminants, ensuring compliance with environmental regulations and safeguarding groundwater resources.

Enable Drilling Fluid Returns

Acts as a conduit for drilling returns — mud and cuttings — to flow back to the surface in a controlled manner, especially on land wells where the conductor provides the initial return flow path before the surface casing is in place.

Contain Shallow Gas Kicks

Provides the first line of defense against unexpected shallow gas influx, allowing the diverter system to be installed and enabling the rig crew to safely redirect gas away from the rig floor during initial drilling operations.

Why It Is the First Casing String Run

It is run first because conductor casing creates the well’s structural foundation and acts as an initial safety barrier before deeper drilling begins. Onshore, it is typically set at 50–500 ft (15–150 m), while offshore wells often require greater depths.

Conductor Casing in Drilling and Well Construction

Conductor Casing During Spudding and Drilling — octgcasing.com

Role During Spudding

The spud is the very first moment a drill bit touches the ground — and the conductor casing in drilling operations is what makes it possible. Already set in place, the conductor gives the bit a stable, guided entry into the formation and keeps the shallow borehole from caving in before surface casing can be run.

Conductor Is Set First Driven or drilled and cemented to 60–150 ft before the rig is fully rigged up — this is the anchor for everything that follows.
Drill Bit Enters Inside the Conductor When spudding begins, the bit drills downward through the conductor bore, which acts as a guide sleeve to keep the hole straight and on-target.
Borehole Stays Open The conductor walls hold back loose sand and gravel, preventing collapse and allowing mud circulation to start from the very first meter.
Wellhead Lands on Top The wellhead housing is installed on the conductor, creating the surface control point for all subsequent casing strings and pressure equipment.

Spudding through conductor casing

Interaction with Drilling Fluids and Returns

During top-hole drilling, the conductor casing is the only barrier between the wellbore and the surrounding formation. It channels drilling mud and cuttings back to the surface in a controlled loop — and on higher-risk wells, it is where the diverter system connects to redirect flow if shallow gas is encountered.

Mud Circulation Loop Drilling mud is pumped down through the drill string, exits the bit, and returns upward through the annulus between the drill pipe and conductor wall — carrying rock cuttings to surface.

Hydrostatic Pressure Control The mud column inside the conductor applies hydrostatic pressure on the formation face, preventing fluid influx from shallow permeable zones while the top-hole section is drilled.

Cuttings Transport to Surface The conductor annulus must be sized to allow sufficient fluid velocity for efficient cuttings transport. Too large a gap slows velocity; too narrow restricts flow and increases pump pressure.

Diverter System Tie-In On offshore rigs and high-risk land wells, a diverter is installed on top of the conductor. If shallow gas enters the wellbore, the diverter seals around the drill pipe and routes the gas overboard or to a safe flare — protecting the rig crew.

Mud circulation through conductor

Installation Methods of Conductor Casing

Conductor Casing Installation Methods — octgcasing.com

Driving / Pile-Driving

Onshore Firm Soil / Clay Shallow — 40–150 ft

The simplest and fastest installation method. A diesel or hydraulic pile hammer sits on top of the conductor pipe and drives it into the ground with repeated blows — much like driving a fence post, but at industrial scale. No drilling or cementing is required, making this the most cost-effective option for shallow wells in firm soil.

The hammer strikes a drive head that distributes the impact evenly across the pipe’s top edge. Blow count per foot is monitored to confirm the conductor reaches competent formation and achieves adequate bearing capacity to support the wellhead and BOP.

EquipmentDiesel or hydraulic pile hammer
CementingNot required
SpeedFast — often completed in hours
Best ForOnshore wells, firm or stiff soil

Drilling and Cementing

Onshore & Offshore Any Formation 60–500+ ft

The most widely used method across both onshore and offshore operations. A hole is drilled to the target setting depth using a smaller pilot bit or large-diameter hole opener, then the conductor casing is lowered in and cemented in place — creating a permanent bond between the pipe and the surrounding formation.

Cementing can be done in two ways. Top-up cementing is simpler: cement is pumped down the annulus from the surface and allowed to fill upward. Inner-string cementing uses a small-diameter stinger run inside the casing to pump cement through the shoe and up the annulus — giving better control of placement, especially on deeper conductors where top-up cement may not reach the shoe evenly.

EquipmentDrill bit + cement unit
CementingRequired — top-up or inner string
SpeedModerate — 1–2 days typical
Best ForMost well types; any formation

Jetting (Offshore / Soft Seabed)

Offshore / Deepwater Soft Sediment 50–300 ft below mudline

In deepwater and soft-seabed locations, jetting conductor casing is the standard method where pile-driving is impractical. High-pressure drilling mud is pumped down through the drill string and out jet nozzles at the casing shoe, washing away soft sediment and allowing the conductor to sink under its own weight and the weight of the drill string above it.

Once the conductor reaches the target penetration depth, the pumps are stopped and the surrounding sediment reconsolidates around the pipe, providing friction-based support. In some cases, cement is pumped afterward to improve the bond. This method is standard for deepwater subsea wells where the seabed consists of soft clay and silt.

EquipmentMud pumps + jet shoe
CementingOptional — often not needed
SpeedModerate — depends on seabed hardness
Best ForDeepwater subsea wells, soft clay seabed

Installation method comparison

Factor	Pile-Driving	Drill & Cement	Jetting
Environment	Onshore	Onshore & offshore	Offshore / deepwater
Formation Type	Firm soil, clay, packed gravel	Any — soft to hard	Soft seabed sediment (clay, silt)
Cement Required	No	Yes — top-up or inner string	Optional
Typical Depth	40–150 ft	60–500+ ft	50–300 ft below mudline
Speed	Fastest (hours)	Moderate (1–2 days)	Moderate (variable)
Relative Cost	Lowest	Moderate	High (deepwater spread)

Conductor Casing Size, Diameter, ID, Depth and Length

Common Outside Diameters

Nominal OD	Typical Wall (in)	Approx. ID (in)	Common Grade	Typical Use
20″	0.500 – 0.750	18.5 – 19.0	API 5L X52 / B	Onshore deep wells
24″	0.500 – 1.000	22.0 – 23.0	API 5L X52 / B	Onshore / shallow offshore
26″	0.625 – 1.000	24.0 – 24.75	API 5L X52	Offshore platforms
30″	0.750 – 1.250	27.5 – 28.5	API 5L X56 / X65	Offshore structural
36″	1.000 – 1.500	33.0 – 34.0	API 5L X65 / X70	Deepwater subsea

Wall Thickness and Inside Diameter (ID)

Conductor Casing Size & Weight Calculator — octgcasing.com

Quick Calculator

Nominal OD

Wall Thickness

Calculated Specifications

Weight

—

lb/ft

Weight

—

kg/m

Approx. ID

—

inches

Nominal OD

—

Wall Thickness

—

Common Grade

—

Typical Use

—

Formula: W (lb/ft) = 10.6906 × (OD − WT) × WT | W (kg/m) = W (lb/ft) × 1.4882

Request a Quote Pre-filled with your selected specs — opens your email client.

Typical Setting Depth and Length

Typical conductor casing setting depth is 50–300 ft onshore and about 200–500 ft below mudline offshore, depending on soil strength and well design. Pipe is commonly supplied in R3 length, about 34–48 ft (10.36–14.63 m) per joint.

Specifications and Common Sizes of Conductor Casing Pipe

Material Standards

API 5L conductor casing is commonly supplied as seamless or welded line pipe in PSL1

API 5L Grade	Typical Chemical Composition, PSL1 Max. (%)	Minimum Yield Strength	Minimum Tensile Strength	Typical Cost Level
Grade B	C ≤0.28, Mn ≤1.20, P ≤0.030, S ≤0.030	241–245 MPa	414–415 MPa	Low
X42	C ≤0.28, Mn ≤1.30, P ≤0.030, S ≤0.030	290 MPa	414–415 MPa	Low–Medium
X52	C ≤0.28, Mn ≤1.40, P ≤0.030, S ≤0.030	359–360 MPa	455–460 MPa	Medium
X56	C ≤0.28, Mn ≤1.40, P ≤0.030, S ≤0.030	386–390 MPa	490 MPa	Medium–High
X60	C ≤0.28, Mn ≤1.40, P ≤0.030, S ≤0.030	414–415 MPa	517–520 MPa	High
X65	C ≤0.28, Mn ≤1.40, P ≤0.030, S ≤0.030	448–450 MPa	531–535 MPa	High–Very High

Connections: Welded vs. Threaded

Connection Type	Best For	Advantages	Limitations	Cost Level
Welded / Plain End	Large-diameter conductor casing, offshore wells, driven installation, and projects requiring high structural support	Good structural continuity, no coupling protrusion on the outside diameter, suitable for large OD and heavy-load conditions; material cost is usually lower	Field welding takes longer and requires qualified welders, WPS/PQR, and NDT inspection; weather and site conditions can affect installation	Lower pipe cost, medium–high installation cost
Threaded / Coupled or Special Connector	Onshore wells, HDD projects, shallow wells, no-hot-work environments, or projects requiring shorter rig time	Fast make-up, no field welding required, and more controllable connection quality; special threaded connectors can also be used for conductor driving	Connector or coupling cost is higher, and the outside diameter may increase; standard threaded & coupled connections may be limited by coupling strength or potential leak paths	Higher pipe/connector cost, lower installation time

For large-diameter, offshore, driven or high-structural-load conductor casing, choose welded plain-end pipe or engineered welded-on connectors. For projects prioritizing fast installation, no hot work, repeatable makeup, or limited welding access, choose threaded or special connector conductor casing.

Conductor Casing Size Specifications — octgcasing.com

Size-Specific Specifications

Common conductor casing sizes range from 20″ to 36″ OD. Each size serves a different well type and operating environment. Click any card to send an inquiry with that specification pre-filled.

20″ OD (508 mm)

Onshore Deep Wells

The smallest common conductor size. Used on onshore wells in stable formations where a compact casing program allows a smaller starting diameter. Suitable for wells that begin with a 17-1/2″ surface hole section.

Wall Thickness0.500″ – 0.750″
Weight Range104 – 154 lb/ft
Approx. ID18.5″ – 19.0″
Common GradeAPI 5L X52 / B

Click to Inquire

24″ OD (610 mm)

Onshore / Shallow Offshore

The most versatile conductor size, widely used across onshore and shallow-water offshore wells. Pairs with a 17-1/2″ hole and accepts 20″ or 18-5/8″ surface casing inside, offering flexibility for a range of well designs.

Wall Thickness0.500″ – 1.000″
Weight Range126 – 246 lb/ft
Approx. ID22.0″ – 23.0″
Common GradeAPI 5L X52 / B

Click to Inquire

26″ OD (660 mm)

Offshore Platforms

Common on fixed offshore platforms and jack-up rigs. Provides the clearance needed for 20″ surface casing below, and the wall thickness to handle wave loading and platform structural stresses in shallow to mid-water depths.

Wall Thickness0.625″ – 1.000″
Weight Range170 – 267 lb/ft
Approx. ID24.0″ – 24.75″
Common GradeAPI 5L X52

Click to Inquire

30″ OD (762 mm)

Offshore Structural

A heavy-duty offshore conductor designed to serve as both a well conduit and structural member on platform wells. Higher-grade steels (X56/X65) are specified to resist the combined loads of wave action, current forces, and the weight of the casing strings hung below.

Wall Thickness0.750″ – 1.250″
Weight Range234 – 385 lb/ft
Approx. ID27.5″ – 28.5″
Common GradeAPI 5L X56 / X65

Click to Inquire

36″ OD (914 mm)

Deepwater Subsea

The largest standard conductor, used on deepwater subsea wells where the conductor is jetted into the seabed and must support a tall subsea wellhead stack. The heaviest wall thicknesses (up to 1.500″) and highest grades (X65/X70) provide the axial capacity to support all inner strings in deep water.

Wall Thickness1.000″ – 1.500″
Weight Range374 – 553 lb/ft
Approx. ID33.0″ – 34.0″
Common GradeAPI 5L X65 / X70

Click to Inquire

Conductor Casing vs. Surface Casing

30 Inch Conductor Casing with BTC End

Attribute	Conductor Casing	Surface Casing
Position	Outermost / first string	Inside conductor
Typical OD	20″ – 36″	9-5/8″ – 20″
Setting Depth	50 – 500 ft (onshore)	500 – 2,500 ft
Primary Function	Structural support, surface stability	Aquifer isolation, BOP anchor
Common Standard	API 5L line pipe	API 5CT OCTG
Installation	Driven / drilled+cemented / jetted	Drilled and cemented

Buyer Summary

Conductor casing is the foundation of every well. BSCO is a China-based supplier with 20+ years of experience. Explore our 20″, 30″, and 36″ casing or contact us for the latest price.

Frequently Asked Questions (FAQs)

What is conductor casing in a well?

OCTG Comprehensive Guide: Definition, Classification and Application of Oil Casing Products-2026

Lincoln Lau — Sun, 24 May 2026 07:57:22 +0000

OCTG, short for Oil Country Tubular Goods, refers to the family of steel tubular products used in the drilling, completion, and production of oil and gas wells. By definition, OCTG encompasses three primary product categories — casing, tubing, and drill pipe — each serving a critical function in maintaining well integrity and enabling hydrocarbon extraction. With the global OCTG market valued at over USD 28 billion and projected to grow steadily alongside rising energy demand, understanding these products is essential for procurement professionals and engineers alike. In this guide, we’ll break down the meaning of OCTG, explore each product type in detail, and provide practical selection criteria for your next project.

What Is OCTG?

OCTG’s full English name and standard definition

The acronym OCTG stands for Oil Country Tubular Goods — a term deeply rooted in the petroleum industry’s heritage. Breaking it down word by word reveals exactly what these products are:

What is OCTG? — octgcasing.com

Oil Country Tubular Goods

The environment

Oil Country

“O · C” in OCTG

Historically refers to oil-producing regions and, by extension, the oilfield environment where these products operate. It signals that these tubulars are purpose-built for the demanding conditions found in drilling and production operations.

The shape

Tubular

“T” in OCTG

Describes the cylindrical, hollow shape of the products. Unlike flat-rolled steel or structural beams, OCTG products are seamless or welded tubes engineered to withstand extreme downhole pressures and temperatures.

The category

Goods

“G” in OCTG

Simply denotes manufactured products or commodities, emphasizing that OCTG is a tradeable product category within the broader steel supply chain — bought, sold, and specified to international standards.

In terms of industry standards, the American Petroleum Institute (API) provides the most widely recognized framework for OCTG classification. API Specification 5CT (Casing and Tubing) defines the technical requirements — including steel grades, mechanical properties, dimensions, and threading specifications — for casing and tubing used in oil and gas wells. Meanwhile, API Specification 5DP covers drill pipe standards separately.
On the international level, the ISO 11960 standard mirrors much of API 5CT’s content and serves as the global reference for OCTG manufacturing and quality assurance. Together, these standards ensure that every OCTG product — whether manufactured in China, the United States, or Europe — meets a uniform set of performance and safety benchmarks critical to well integrity.

The Role of OCTG in Oil and Gas — octgcasing.com

The Role of OCTG in the Oil & Gas Industry

OCTG products form the structural backbone of every oil and gas well. From the moment a drill bit penetrates the surface to the final years of production, casing, tubing, and drill pipe work together to ensure well integrity, pressure containment, and safe hydrocarbon flow. Without reliable OCTG, modern drilling and production operations simply could not function.

Drilling Phase

Drill pipe transmits rotational torque and drilling fluid to the bit, while casing strings are set at progressive depths to stabilize the borehole and isolate geological formations. Each casing size is selected to withstand the collapse pressures and tensile loads encountered at that interval.

Completion Phase

Once drilling reaches total depth, production casing and tubing are run and cemented in place. Tubing serves as the primary conduit through which hydrocarbons travel to the surface, engineered to handle corrosive fluids, high temperatures, and sustained internal pressure.

Production Phase

Throughout the productive life of a well — often spanning decades — OCTG must resist ongoing corrosion, erosion, and cyclic loading. Casing maintains zonal isolation to protect freshwater aquifers, while tubing withstands the chemical aggression of produced fluids containing H₂S and CO₂.

The demands placed on OCTG vary significantly depending on the operating environment. Key application scenarios in the oil and gas sector include:

Onshore Drilling Offshore Platforms Shale Gas & Tight Oil Deepwater & Ultra-Deepwater High-Temperature / High-Pressure (HPHT) Sour-Service Environments (H₂S)

Each of these environments imposes distinct mechanical and metallurgical requirements — from the high collapse resistance needed in deepwater wells to the stringent sour-service grades demanded in H₂S-rich reservoirs. Selecting the right OCTG grade, wall thickness, and connection type is critical to well safety, operational efficiency, and long-term asset value. As exploration pushes into more challenging frontiers, the role of high-performance OCTG in the oil and gas industry continues to grow.

OCTG vs Regular Steel Pipe — octgcasing.com

OCTG vs. Regular Steel Pipe — What’s the Difference?

At first glance, OCTG casing and tubing may look similar to standard carbon steel pipe used in plumbing or structural applications. However, the two are engineered for fundamentally different purposes. OCTG products must survive extreme downhole environments — high pressures, corrosive gases, elevated temperatures, and massive mechanical loads — where a failure can mean a costly blowout or environmental disaster. This demands a far higher level of material quality, dimensional precision, and connection integrity than ordinary pipe.

Feature	Regular Steel Pipe	OCTG (Casing & Tubing)
Primary Use	Water, gas distribution, structural support, fencing	Oil & gas well construction — drilling, completion, production
Material Grades	Basic carbon steel (A53, A106)	API 5CT grades (J55, K55, N80, L80, P110, Q125) with strict chemical limits on C, Mn, S, P
Yield Strength	Typically 30–35 ksi	55–125+ ksi, engineered for collapse, burst, and tensile loads
Pressure Rating	Low–moderate; rated for surface pressures	High-pressure rated; must withstand thousands of psi downhole
Connections	Plain end, beveled, or standard NPT threads	API buttress (BTC), short/long round threads (STC/LTC), or premium gas-tight connections
Wall Tolerance	Standard commercial tolerances	Tight OD/ID tolerances per API 5CT; drift-tested to guarantee tool passage
Testing & Inspection	Basic hydrostatic test	Hydrostatic, ultrasonic, electromagnetic, and full-body NDT; heat & lot traceability
Corrosion Resistance	Not rated for H₂S or CO₂ service	Sour-service grades (L80, C90, T95) per NACE MR0175 / ISO 15156
Standards	ASTM A53 / A106	API 5CT, API 5B, ISO 11960

Material & Metallurgy

OCTG steels undergo controlled heat treatment — quench and temper or normalizing — to achieve precise yield and tensile ranges. Harmful elements like sulfur and phosphorus are held to much tighter limits than in commercial pipe, ensuring consistent impact toughness at low temperatures.

Pressure Performance

Every OCTG product is designed against three load cases — burst (internal pressure), collapse (external pressure), and tension (hanging weight). Regular pipe is rated only for low-pressure surface use, making it unsuitable for any downhole application.

Threaded Connections

OCTG threads are precision-machined to API 5B or proprietary premium specifications, providing gas-tight metal-to-metal seals. Standard pipe threads (NPT) rely on tape or compound and cannot maintain integrity under the torque, vibration, and pressure cycling found in wells.

In short, OCTG is not simply a heavier or thicker version of ordinary steel pipe. It is a precision-engineered, rigorously tested product category with material, dimensional, and connection requirements that exist specifically to ensure well integrity and operational safety in the oil and gas industry.

OCTG — octgcasing.com

Three Core OCTG Pipe Products

Every oil and gas well relies on three types of OCTG pipe — each serving a distinct structural and functional role from the surface to total depth. Understanding how casing, tubing, and drill pipe work together is essential for specifying the right products for any well program.

Simplified well cross-section — OCTG product positions

Casing

OCTG Casing Pipe

Casing is the structural backbone of the well. Multiple strings — conductor, surface, intermediate, and production casing — are run at progressively smaller diameters and cemented in place to stabilize the borehole, prevent formation collapse, isolate water-bearing zones, and contain well pressure.

OD Range4-1/2″ – 20″
Common GradesJ55, K55, N80, L80, P110
ConnectionsSTC, LTC, BTC, Premium
StandardAPI 5CT / ISO 11960

Tubing

Oil Well Tubing

Tubing is the conduit through which oil and gas flow from the producing formation to the surface. Suspended inside the production casing by a packer, tubing must resist corrosion from produced fluids (H₂S, CO₂, brine), withstand high temperatures, and maintain gas-tight seal integrity throughout the well’s productive life.

OD Range1.050″ – 4-1/2″
Common GradesJ55, L80, N80, P110
ConnectionsEUE, NUE, Premium
StandardAPI 5CT / ISO 11960

Drill Pipe

OCTG Drill String Component

Drill pipe transmits rotational torque from the surface rig to the drill bit and channels drilling fluid (mud) downhole to cool the bit and carry cuttings to surface. Unlike casing and tubing — which remain permanently in the well — drill pipe is retrievable and reused across multiple wells.

OD Range2-3/8″ – 6-5/8″
Common GradesE75, X95, G105, S135
ConnectionsAPI IF, FH, NC, XT
StandardAPI 5DP / ISO 11961

How to Choose the Right OCTG Products — octgcasing.com

Procurement GuideHow to Choose the Right OCTG Products

Selecting the correct OCTG casing and tubing involves more than picking a size. Well depth, formation chemistry, pressure regime, and connection requirements all influence which steel casing pipe and oil well casing grades will perform safely over the life of the well. This guide walks through the five key decisions every buyer should evaluate.

Select the Steel Grade Based on Well Depth & Formation Conditions

Different well depths impose different mechanical loads — collapse pressure from surrounding formations, burst pressure from internal fluids, and tensile stress from the hanging weight of the string itself. The deeper and more complex the well, the higher the steel grade required.

Well Depth	Typical Conditions	Recommended Grades
Shallow (< 6,000 ft)	Low pressure, stable formations	J55K55
Medium (6,000–12,000 ft)	Moderate pressure, possible salt zones	N80L80
Deep (12,000–18,000 ft)	High pressure, high temperature (HPHT)	P110Q125
Ultra-deep (> 18,000 ft)	Extreme loads, complex geology	Q125140 ksi+

Choose the Right Material Based on Corrosion Environment

Produced fluids often contain corrosive agents — hydrogen sulfide (H₂S), carbon dioxide (CO₂), chlorides, and brine — that can cause sulfide stress cracking, pitting, or general wall loss. Matching the material to the corrosion environment is critical for well integrity and service life.

Standard

Carbon Steel

Suitable for sweet (non-sour) wells with low CO₂ and no H₂S. Cost-effective for most onshore conventional wells. Grades: J55, N80, P110.

Sour Service

Alloy Steel

Required when H₂S is present. Hardness-controlled grades (L80, C90, T95) per NACE MR0175 resist sulfide stress cracking in sour environments.

Severe Corrosion

CRA (Corrosion-Resistant Alloy)

For high-CO₂, high-chloride, or combined sour/acidic conditions. 13Cr, Super 13Cr, duplex (22Cr/25Cr), and nickel alloys offer superior resistance.

Specify the Thread Connection Type

The connection is often the weakest link in the string. Choosing the right thread profile ensures leak-free performance under the expected combination of pressure, tension, bending, and thermal cycling in the well.

Connection Type	Seal Mechanism	Best Suited For
STC / LTC	Thread compound seal	Low-pressure conventional wells; cost-sensitive projects
BTC (Buttress)	Thread-form interference	Higher collapse loads; intermediate and production casing
Premium / Proprietary	Metal-to-metal seal	Gas-tight applications; HPHT, offshore, sour service, ERD wells
EUE / NUE	Thread compound seal	Standard tubing connections; EUE for higher-pressure wells

Verify Supplier Certifications & Quality System

A reliable OCTG supplier should hold recognized industry certifications that demonstrate manufacturing capability, quality control, and traceability. Always verify these credentials before placing an order — substandard pipe can compromise well integrity and safety.

API 5CT License — manufacturer is certified to produce OCTG to API specification
API 5B License — threading and gauging meet API standards
ISO 9001 — quality management system in place
ISO 14001 — environmental management compliance
API Q1 / ISO/TS 29001 — petroleum-specific quality management
Heat & lot traceability — full MTR (Mill Test Report) documentation per heat

Evaluate Supply Experience, Lead Time & Inspection

Beyond product quality, practical supply-chain factors often determine whether a project stays on schedule. Assess these operational capabilities when shortlisting OCTG suppliers.

Track Record

Project Experience

Has the supplier delivered to similar well programs — same region, same grades, same volumes? Ask for reference projects and end-user approvals from major operators.

Logistics

Lead Time & Stock

Confirm standard lead times for made-to-order versus ex-stock availability. A supplier with strategic inventory in key sizes (e.g. 9-5/8″, 7″, 5-1/2″ casing) can respond faster to urgent well requirements.

Quality Assurance

Third-Party Inspection (TPI)

Reputable suppliers welcome independent inspection by agencies such as SGS, Bureau Veritas, or TÜV. Ensure the supplier can provide TPI reports covering dimensional checks, NDT, hydrostatic testing, and material verification.

Documentation

Mill Test Reports & Certificates

Every shipment should include EN 10204 3.1 / 3.2 inspection certificates, full MTRs with chemical and mechanical results, and marking/stenciling that matches the paperwork and API requirements.

OCTG Pipe Loading Protection Methods-Step by Step

OCTG pipe loading protection usually means preventing thread, body, coating, and end damage while casing/tubing/drill pipe is loaded onto trucks, trailers, containers, barges, or pipe racks. OCTG handling is typically governed by API RP 5C1 for care/use, transportation, storage, handling, and reconditioning of casing and tubing, while API Spec 5CT covers casing/tubing requirements and thread protection references

Thread protection

Use correctly fitted pin and box thread protectors on every joint before loading. A thread protector is a cap or insert used to protect threads and seals during handling, transportation, and storage.
For premium connections and premium grade, keep protectors installed until inspection/running preparation.

Pipe body protection

Use timber, rubber-lined, or polymer dunnage between pipe and steel surfaces. Avoid metal-to-metal contact with trailer beds, forklifts, chains, or rack beams.

Layer separation&Chocking and restraint

Use properly spaced separators between each layer. Pipes should not rub, roll, or impact each other during loading or transit.Use pipe chocks, wedges, stanchions, side stakes, and suitable tie-downs. Do not over-tighten chains or straps to the point of denting, ovalizing, or damaging coated pipe.

Lifting method

Use wide web slings, padded hooks, or approved pipe-handling equipment. Avoid bare forks, wire ropes, chains, or hooks directly contacting the pipe body or threads.

End impact protection

For higher-risk moves, add bumper rings or end protectors, especially for premium connections or coated pipe. Class-rated heavy thread protectors are commonly used for axial and angular impact protection.

Inspection before release

Before dispatch, check: protector tightness, pipe count, heat/lot markings, coating condition, body dents, thread-end damage, banding/tie-down condition, and load stability.

Summary — Choose a Reliable OCTG Supplier — octgcasing.com

SummaryWhy Choosing a Reliable OCTG Supplier Matters

Oil Country Tubular Goods are the most critical steel products in any oil and gas well. From surface to total depth, the right combination of OCTG casing, tubing, and drill pipe determines whether a well operates safely, efficiently, and profitably for decades — or fails prematurely.

OCTG Defined

OCTG — Oil Country Tubular Goods — is the purpose-built family of steel pipe products engineered exclusively for the demanding downhole conditions of drilling and production operations.

Three Core Products

Every well program specifies three types of OCTG pipe — casing to stabilize the borehole, tubing to transport hydrocarbons, and drill pipe to transmit torque and circulate fluid.

Quality Is Non-Negotiable

Grade selection, corrosion resistance, threaded connections, and supplier certifications must all align with well conditions. Substandard OCTG pipe risks blowouts, leaks, and costly remediation.

BSCO

Partner with BSCO — Your Trusted OCTG Supplier from China

When it comes to sourcing high-quality OCTG casing and tubing, BSCO stands out as a proven supplier with deep expertise in oil country tubular goods. Based in China, BSCO supplies a comprehensive range of OCTG pipe products — from standard J55 casing for shallow wells to premium P110 and Q125 grades for HPHT and deepwater applications — all manufactured under strict API-licensed quality control.

With a track record of delivering to oilfield projects across the Middle East, Southeast Asia, Africa, and South America, BSCO combines competitive pricing with the quality assurance international operators expect — including full Mill Test Reports, third-party inspection support from SGS or Bureau Veritas, and reliable on-time delivery.

API 5CT Licensed API 5B Certified ISO 9001 Third-Party Inspection Full MTR Traceability

Recommended casing grade by well depth

Shallow < 6,000 ft

K55

Low-pressure conventional wells

View K55 Casing

Medium 6,000–12,000 ft

N80

Moderate pressure, salt zones

View N80 Casing

Deep 12,000–18,000 ft

P110