News - API Tubing and Casing Size Chart: A Complete Reference for OCTG Specifications

Oil and gas well construction depends on tubular products engineered to exact dimensional and mechanical standards. Among the most widely referenced specifications worldwide is API SPEC 5CT, published by the American Petroleum Institute, which governs the dimensions, material grades, and testing requirements for casing and tubing used in upstream operations.

At Royal Steel Group, we supply a full portfolio of API 5CT-compliant casing and tubing across a broad range of sizes, wall thicknesses, and steel grades. Below is a practical reference covering standard dimensions, weight ranges, grade selection, and typical field applications — intended to help procurement teams, drilling engineers, and project managers specify the right OCTG product for their well program.

What Are API Casing and Tubing?

Casing is the structural pipe cemented into a wellbore after drilling. Its primary functions are to prevent borehole collapse, isolate productive and non-productive formations, and provide a pressure-containing barrier for the life of the well.

Tubing is the smaller-diameter pipe run inside the casing through which produced hydrocarbons (or injected fluids) flow to the surface. Unlike casing, tubing is generally not cemented and can be pulled and replaced during workover operations.

Both products fall under the broader category of OCTG (Oil Country Tubular Goods), which also includes drill pipe, pup joints, couplings, and premium connections.

Standard Size Ranges at a Glance

Casing Pipe

Parameter	Standard Range
Outside Diameter (OD)	4½" – 20" (114.30 – 508.00 mm)
Wall Thickness (WT)	5.21 – 16.13 mm
Length Range	R1, R2, R3
Common Grades	H40, J55, K55, N80, L80, P110, Q125

Tubing Pipe

Parameter	Standard Range
Outside Diameter (OD)	1.050" – 4½" (26.67 – 114.30 mm)
Wall Thickness (WT)	2.11 – 16.13 mm
Length Range	R1, R2, R3
Common Grades	H40, J55, K55, N80, L80, C90, T95, P110

OCTG Casing Dimensions and Weight Chart

Common Casing Sizes (OD)

The following nominal sizes are the most frequently specified in conventional well construction:

4½", 5", 5½", 6⅝", 7", 7⅝", 8⅝", 9⅝", 10¾", 11¾", 13⅜", 16", 18⅝", 20"

Typical Wall Thickness Series

5.21 mm · 6.35 mm · 7.72 mm · 9.17 mm · 10.36 mm · and heavier options depending on grade and pressure rating.

Casing by Well Section

Well Section	Typical OD Range	Purpose
Surface Casing	13⅜" – 20"+	Shallow intervals; protects freshwater zones and supports the wellhead
Intermediate Casing	9⅝" – 13⅜"	Seals off problematic zones (shale, salt, lost circulation) in the mid-well section
Production Casing	4½" – 7"	Isolates the reservoir and provides the production conduit for the life of the well

Well Section Typical OD Range Purpose

Surface Casing 13⅜" – 20"+ Shallow intervals; protects freshwater zones and supports the wellhead
Intermediate Casing 9⅝" – 13⅜" Seals off problematic zones (shale, salt, lost circulation) in the mid-well section
Production Casing 4½" – 7" Isolates the reservoir and provides the production conduit for the life of the well

Thread and Connection Types

STC (Short Thread Coupled): Standard for lower-pressure, shallower casing strings.
LTC (Long Thread Coupled): Improved joint integrity for deeper or higher-pressure service.
BTC (Buttress Thread Coupled): Higher tensile capacity and gas-sealing performance; widely used in production and intermediate strings.

Premium connections (e.g., VAM, TMK, Hydril-style) are available for high-pressure/high-temperature (HPHT) and corrosive service where API connections are insufficient.

OCTG Tubing Dimensions and Weight Chart

Common Tubing Sizes

Nominal Size (inches)	OD (mm)
1.050"	26.67
1.315"	33.4
1.660"	42.16
1.900"	48.26
2.375"	60.33
2.875"	73.03
3.500"	88.9
4.000"	101.6
4.500"	114.3

Wall Thickness

Standard API tubing wall thickness ranges from 0.083" (2.11 mm) to 0.400" (10.16 mm). For example, a 2⅞" tubing string is commonly offered in:
0.217" (5.51 mm) — NUE, lower pressure
0.276" (7.01 mm) — standard service
0.308" (7.82 mm) — heavy-duty, higher pressure
Thick-wall tubing exceeding 16 mm can be manufactured to custom specification for deep, high-pressure, or corrosive wells.

Length Ranges (API 5CT)

Range	Feet	Meters
R1	18 – 22 ft	5.49 – 6.71 m
R2	27 – 30 ft	8.23 – 9.14 m
R3	38 – 42 ft	11.58 – 12.80 m

R2 is the most common for onshore operations; R3 reduces the number of connections and is preferred where rig time and connection integrity are priorities.

Thread Types

NU (Non-Upset): Standard external upset not applied; used in lower-pressure service.
EU (External Upset): Reinforced pin end for improved tensile and pressure performance; the most common tubing connection.
Premium Threads (VAM, TMK, etc.): Gas-tight, metal-to-metal sealing for HPHT, gas storage, and corrosive environments.

Tubing by Application

Size Range	Typical Use
1.050" – 2.375"	Low-pressure or low-rate wells; slimhole completions
2.875" – 3.500"	Conventional production wells — the most widely used range
4.000" – 4.500"	High-rate wells, gas lift, and water/CO₂ injection

Steel Grades and Mechanical Properties

The grade designation in API 5CT indicates the minimum yield strength in thousands of psi (e.g., N80 = 80,000 psi minimum yield). Higher grades offer greater tensile and collapse resistance but may be more susceptible to sulfide stress cracking (SSC) in sour service.

Mechanical Property Summary

Standard	Grade	Tensile Strength (MPa)	Yield Strength (MPa)
API SPEC 5CT	J55	≥ 517	379 – 552
	K55	≥ 517	≥ 655
	N80	≥ 689	552 – 758
	L80 (13Cr)	≥ 655	552 – 655
	P110	≥ 862	758 – 965

Chemical Composition (Typical)

Grade	C	Si	Mn	P	S	Cr	Ni	Cu	Mo	V
J55 / K55 (37Mn5)	0.34–0.39	0.20–0.35	1.25–1.50	≤0.020	≤0.015	≤0.15	≤0.20	≤0.20	—	—
N80 (36Mn2V)	0.34–0.38	0.20–0.35	1.45–1.70	≤0.020	≤0.015	≤0.15	—	—	—	0.11–0.16
L80 (13Cr)	0.15–0.22	≤1.00	0.25–1.00	≤0.020	≤0.010	12.0–14.0	≤0.20	≤0.20	—	—
P110 (30CrMo)	0.26–0.35	0.17–0.37	0.40–0.70	≤0.020	≤0.010	0.80–1.10	≤0.20	≤0.20	0.15–0.25	≤0.08

Grade Selection Guidance

J55 / K55: Cost-effective for shallow, low-pressure wells and surface casing.
N80: Versatile mid-strength grade for intermediate and production strings in conventional wells.
L80 (13Cr): Corrosion-resistant martensitic stainless steel; suitable for CO₂ and mildly sour environments.
C90 / T95: Sour-service grades with controlled hardness (≤ 22 HRC) for H₂S-containing wells.
P110 / Q125: High-strength grades for deep, high-pressure wells; require careful SSC assessment in sour conditions.

Key Selection Considerations

Choosing the right casing and tubing is not simply a matter of matching OD and wall thickness. A complete tubular design should integrate the following factors:

Well Depth and Pressure Profile — Determines required collapse, burst, and tensile ratings, which drive grade and weight selection.

Corrosion Environment — CO₂, H₂S, chloride, and elevated temperatures may require 13Cr, super 13Cr, or duplex alloys rather than carbon steel.

Formation and Geomechanics — Shale swelling, salt creep, and abnormal pressure influence casing setting depths and wall thickness.

Connection Type — API round or buttress threads suffice for many wells; premium connections are needed for gas-tight sealing or high-load conditions.

Regulatory and Operator Specifications — Many operators impose additional requirements beyond API 5CT, including supplementary NDE, hardness testing, and drift dimensions.

Royal Steel Group's OCTG Capability

Royal Steel Group manufactures and supplies API 5CT casing and tubing with the following scope:

Full size range: 1.050" through 20" standard, with large-diameter and custom sizes available.

Comprehensive grades: H40, J55, K55, N80, L80, C90, T95, P110, Q125, and 13Cr / super 13Cr corrosion-resistant alloys.

Connection options: STC, LTC, BTC, NU, EU, and premium threaded connections upon request.

Quality assurance: Full-length UT/MT inspection, hydrostatic testing, hardness survey, and third-party inspection (BV, SGS, DNV) available.

Delivery: R1 / R2 / R3 random lengths, with coupling and pup joint supply as a complete package.

Our production is certified to API SPEC 5CT and ISO 9001, with mill test reports (MTRs) provided for every heat and lot.

ROYAL GROUP

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Kangsheng development industry zone,
Wuqing district, Tianjin city, China.

E-mail

admin@royalsteelgroup.com

Phone

Cherry Yang - CEO : +8613652091506
Wendy Wu -Business Director : +8615222747108

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Post time: Aug-13-2026