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Basic Knowledge of OCTG Pipe – Royal Steel Group

Octg Pipes are crucial oil tubular goods, with the static application in oil and gas well drilling, oil and gas well completion and oil and gas well servicing. The major types comprise drill pipes, casings and production tubing. Drill pipes make power transmission to drilling and they are connected to drill collars and drill bits. Casings ensure the stability of the wellbore during drilling as well as following completion and workover to allow for normal well operation. Production tubing plays a vital role as the primary conduit through which downhole oil and gas resources flow to the surface.

As the key to ensure long term oil well operation, casings are under complex underground composite stress which is including tension, compression, bending, torsion, etc, so the steel quality is demanded in high degree. Production decline or even permanent abandonment of oil wells can be caused directly by casing damage. The grades of conventional casing steel are J55, K55, N80, L80, C90, T95, P110, Q125 and V150 based on steel strength. The choice of steel grade is governed by well depth and downhole conditions. Moreover, casing exposed to corrosive environment has to have good corrosion resistance and casing used in complicated geological formation should have good collapse resistance.

Core Professional Terminology

API Pipes: Abbreviation for American Petroleum Institute, which formulates mainstream industry standards for petroleum tubular products.

OCTG Tubing: Short for Oil Country Tubular Goods, referring to dedicated petroleum tubular products, covering finished casings, drill pipes, drill collars, couplings and short joints.

Oil Tubing: Special tubing for downhole operations including oil/gas production, water injection, acidizing and fracturing.

Casing: Large-diameter steel pipes run into drilled boreholes to line well walls and prevent collapse.

Drill Pipe: Key tubular tool for borehole drilling and power transmission.

Line Pipe: Special steel pipes for long-distance oil and gas transportation.

Coupling: Internal-threaded cylindrical fittings for connecting two threaded pipes.

Coupling Material: Special steel materials for manufacturing pipe couplings.

API Threads: Standard threads specified by API 5B, including tubing round thread, casing short/long round thread, casing buttress thread and line pipe thread.

Premium Connection: Non-API special threads with superior sealing and connecting performance.

Failure: Loss of original service function of pipes under working conditions, mainly manifested as extrusion, slippage, rupture, leakage, corrosion, bonding and wear.

Industry Applicable Standards

API Standards: API 5CT (8th Edition) – Casing and Tubing Specification; API 5D (5th Edition) – Drill Pipe Specification; API 5L (44th Edition) – Line Pipe Specification; API 5B – Thread Machining, Measurement and Inspection Specification.

Chinese National Standards: GB/T 9711.1-1997 (Grade A line pipe delivery technical conditions); GB/T 9711.2-1999 (Grade B line pipe delivery technical conditions); GB/T 9711.3-2005 (Grade C line pipe delivery technical conditions).

Oil Tubing

1 Classification

Oil tubing is divided into three types: Non-Upset (NU) tubing (threaded pipe ends without wall thickening, matched with couplings), External Upset (EU) tubing (externally thickened pipe ends before threading and coupling assembly), and integral joint tubing (integral threaded connection without couplings, with matched internal and external thickened threads at both ends).

2 Core Functions

Oil and gas production: Delivers downhole oil and gas to the surface after well drilling and cementing;

Water injection: Supplements downhole pressure by water injection for insufficient formation pressure;

Steam injection: Applies insulated tubing to inject steam for heavy oil thermal recovery;

Acidizing and fracturing: Transmits working media to oil-gas layers to improve well productivity in later development stages.

3 Steel Grades and Performance Differences

Conventional tubing steel grades include H40, J55, N80, L80, C90, T95 and P110.

N80: Split into N80-1 and N80Q with identical tensile properties. N80-1 adopts hot rolling or normalizing delivery, exempt from impact and non-destructive testing; N80Q requires quenching and tempering heat treatment, with mandatory impact test and non-destructive testing complying with API 5CT.

L80: Includes L80-1, L80-9Cr and L80-13Cr. All share consistent mechanical properties and delivery status. L80-1 is for conventional wells; 9Cr and 13Cr types feature high corrosion resistance, high production difficulty and cost, specially applied in severely corrosive wells.

C90 & T95: Both have two subtypes (Type 1 and Type 2), namely C90-1, C90-2, T95-1 and T95-2.

4 Conventional Steel Grade & Delivery Status

J55 (37Mn5): Flat tubing – hot rolled (replace normalizing); upset tubing – full-length normalizing after thickening

N80-1 (36Mn2V): Flat tubing – hot rolled (replace normalizing); upset tubing – full-length normalizing after thickening

N80Q (30Mn5): Full-length quenching and tempering

L80-1 (30Mn5): Full-length quenching and tempering

P110 (25CrMnMo): Full-length quenching and tempering

Couplings: J55 (37Mn5, online hot rolling normalizing); N80/L80-1 (28MnTiB, full-length tempering); P110 (25CrMnMo, full-length tempering)

Casing

Casing is a disposable consumable steel pipe for wellbore support, accounting for over 70% of total oil well tubular consumption. Multiple casing layers are deployed according to well depth and geological conditions, fixed by cementing after running downhole and non-reusable. It is classified into conductor casing, surface casing, technical casing and production casing.

1 Conductor Casing

Mainly used for offshore and desert drilling to isolate seawater and sand, ensuring drilling continuity. Common specifications: Φ762mm (30in) ×25.4mm, Φ762mm (30in) ×19.06mm.

2 Surface Casing

Applied in primary drilling to seal loose surface strata and prevent well wall collapse. Running depth ranges 80–1500m based on stratum conditions. With low internal and external pressure load, it mainly adopts K55 and N80 steel grades. Common specifications: 508mm (20in), 406.4mm (16in), 339.73mm (13-3/8in), 273.05mm (10-3/4in), 244.48mm (9-5/9in).

3 Technical Casing

Used for sealing complex geological layers (collapsing layers, oil/gas/water layers, leakage layers, salt beds) to ensure smooth drilling of deep and complex wells. It requires high mechanical strength and sealing performance, with mainstream steel grades N80 and P110; ultra-deep wells adopt Q125 and high-end non-API V150 steel grades. Common specifications: 339.73mm, 273.05mm, 244.48mm, 219.08mm, 193.68mm, 177.8mm.

4 Production Casing

The innermost and deepest casing layer, used to seal target oil-gas reservoirs and upper exposed strata. It bears the harshest downhole working conditions with the highest requirements for mechanical properties and tightness. Applicable steel grades include K55, N80, P110, Q125 and V150. Common specifications: 177.8mm, 168.28mm, 139.7mm, 127mm, 114.3mm.a

Drill Pipe Series

Drilling tool pipes consist of square drill pipes, standard drill pipes, weighted drill pipes and drill collars, serving as the core downhole power and circulation channel. They bear alternating tension, compression, torsion and bending loads, as well as high-pressure mud scouring and corrosion during operation.

1 Square Drill Pipe

Mainly quadrilateral (hexagonal type optional), with conventional lengths of 12–14.5m. Common specifications: 63.5mm, 88.9mm, 107.95mm, 133.35mm, 152.4mm.

2 Standard Drill Pipe

The main drilling component, continuously lengthened with drilling depth. Common specifications: 60.3mm, 73.03mm, 88.9mm, 114.3mm, 127mm, 139.7mm.

3 Weighted Drill Pipe

Transition component between standard drill pipe and drill collar, optimizing pipe stress status and increasing bit pressure. Main specifications: 88.9mm, 127mm.

4 Drill Collar

Thick-walled high-rigidity pipe at the bottom of drill strings, providing bit rock-breaking pressure and straight-hole guiding. Common specifications: 158.75mm, 177.85mm, 203.2mm, 228.6mm.

seamless steel pipe application

Line Pipe

Line pipes are special steel pipes for transporting crude oil, refined oil, natural gas and water, including welded and seamless types (welded pipes are more widely used).

1 Classification & Specifications

Divided into main pipelines, branch pipelines and urban pipe networks. Main pipelines: diameter 406–1219mm, wall thickness 10–25mm, steel grades X42–X80; branch and urban pipelines: diameter 114–700mm, wall thickness 6–20mm, steel grades X42–X80.

2 Standards & Product Levels

Compliant with API 5L and Chinese GB/T 9711 series national standards. Product Specification Levels are divided into PSL1 and PSL2. PSL2 has stricter requirements on chemical composition, tensile performance, impact energy and non-destructive testing than PSL1.

3 Steel Grades & Testing Requirements

Steel grades (from low to high): A25, A, B, X42, X46, X52, X60, X65, X70, X80. All line pipes require full-piece hydraulic testing (non-destructive testing cannot replace hydraulic testing). PSL1 exempts from non-destructive testing, while PSL2 requires piece-by-piece non-destructive testing.

Line Pipe

Line pipes are special steel pipes for transporting crude oil, refined oil, natural gas and water, including welded and seamless types (welded pipes are more widely used).

1 Classification & Specifications

Divided into main pipelines, branch pipelines and urban pipe networks. Main pipelines: diameter 406–1219mm, wall thickness 10–25mm, steel grades X42–X80; branch and urban pipelines: diameter 114–700mm, wall thickness 6–20mm, steel grades X42–X80.

2 Standards & Product Levels

Compliant with API 5L and Chinese GB/T 9711 series national standards. Product Specification Levels are divided into PSL1 and PSL2. PSL2 has stricter requirements on chemical composition, tensile performance, impact energy and non-destructive testing than PSL1.

3 Steel Grades & Testing Requirements

Steel grades (from low to high): A25, A, B, X42, X46, X52, X60, X65, X70, X80. All line pipes require full-piece hydraulic testing (non-destructive testing cannot replace hydraulic testing). PSL1 exempts from non-destructive testing, while PSL2 requires piece-by-piece non-destructive testing.

Premium Connection

Conventional API threads have obvious limitations in harsh working conditions: API round threads have good sealing but only 60%–80% pipe-body tensile strength, failing deep-well service; API buttress threads have high tensile strength but poor sealing, unable to adapt to high-pressure gas wells. Meanwhile, standard thread grease only works below 95℃, restricting high-temperature well application.
Premium Connection (special premium thread) is an upgraded non-API threaded structure with comprehensive performance
advantages:

1. Excellent metal elastic sealing performance, joint sealing capacity matches pipe-body yield pressure limit;

2. Connection strength reaches or exceeds pipe-body strength, completely solving thread slippage problems;

3. Optimized material and surface treatment avoid thread sticking failure;

4. Rational structural design improves joint stress distribution and stress corrosion resistance;

5. Optimized shoulder structure simplifies on-site threading operation.

At present, more than 100 patented Premium Connection types have been globally developed for high-standard deep wells, high-pressure gas wells and high-temperature corrosive wells.

Advantages of Royal Steel Group

Royal Steel Group is a professional, integrated oilfield tubing manufacturer and global supplier, offering a full range of casing, tubing, drill pipe, and line pipe. Our core strengths include:

Comprehensive Product Range and Grades

Royal Group supply all API-compliant tubing, covering the full range of steel grades from J55 to V150, as well as 9Cr/13Cr corrosion-resistant tubing. We offer standard API threads and custom-made high-grade fittings suitable for deep wells, high-pressure wells, and corrosive wells, and support custom wall thicknesses, coatings, and fittings.

Strict End-to-End Quality Control

All production stages are controlled by an ISO 9001 certified system. Every tube undergoes dimensional inspection, hydrostatic testing, mechanical property testing, full-length non-destructive testing, and thread precision inspection, meeting API and PSL1/PSL2 standards to reduce downhole operational risks.

Stable Production and Ample Inventory

Royal Group own rolling, forging, and threading production lines ensure stable batch deliveries and short lead times. Ample stock of standard specifications ensures we can meet the needs of urgent orders and large-scale energy projects, and provide consistently qualified heat treatment services.

One-stop technical and customization services

Royal Group engineering team can advise on grades and thread matching based on well conditions. Value-added services include anti-corrosion coatings, custom markings, matching fittings, and complete export certification documentation.

Efficient global supply chain

Royal Group partner with major global carriers to serve customers in Southeast Asia, the Middle East, North America, and other oil-producing regions. Direct factory sales reduce intermediary costs, resulting in competitive pricing and timely delivery.

Extensive project experience and after-sales support

Royal Group have supplied products to numerous offshore oilfields, thermal recovery fields, and complex deep well projects. Our professional international team provides rapid technical response and long-term after-sales support to oilfield contractors worldwide.

ROYAL GROUP

Address

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

E-mail

admin@royalsteelgroup.com

Phone

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

Hours

Monday-Sunday: 24-hour Service

Post time: Jul-13-2026
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