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Help CenterSteel Pipe & Tube & OCTG Oil Pipe，Gr.B、X42、X52、J55、N80、L80、P110、X42/X52/X60/X70/X80
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1. Product Definition & Main Categories
Oil special steel pipes are collectively called OCTG (Oil Country Tubular Goods), which are core seamless pressure-bearing steel pipes for oil & gas exploration, drilling, well completion, oil production and long-distance pipeline transportation. They withstand complex downhole loads including high temperature, high pressure, H₂S/CO₂ corrosion, tension, collapse and torsion. Products comply with international API standards and corresponding Chinese GB national standards, divided into four core categories: Casing, Tubing, Drill Pipe and Line Pipe.
2. Core Applicable Standards
Casing & Tubing (Downhole OCTG)International Standard: API Spec 5CT (11th Edition), ISO 11960; Equivalent Chinese Standard: GB/T 19830Thread Gauge Standard: API Spec 5B
Long-distance Oil & Gas Line PipeInternational Standard: API Spec 5L, ISO 3183; Chinese Standard: GB/T 9711Two quality grades: PSL1 (General Grade), PSL2 (Strict Low-temperature Crack Resistance Grade)
Drill Pipe: API Spec 5DP
Corrosion-resistant Sour Service Pipe: ISO 13680, NACE MR0175 (H₂S Anti-corrosion Standard)
3. Four Core Products: Function, Size & Steel Grades
3.1 Casing
Run into borehole and cemented permanently to stabilize wellbore, prevent formation collapse, isolate formation fluid, protect underground fresh water and install blowout preventers. Divided into 4 casing strings by running sequence:
Conductor Casing: Wellhead surface protection to avoid shallow washout
Surface Casing: Isolate freshwater layers, support wellhead BOP
Intermediate Casing: Seal high-pressure circulation loss & corrosive zones
Production Casing: Main outer pipe for hydrocarbon production through reservoir
Common Steel Grades (Strength Ascending)
H40, J55, K55 (Shallow Wells); N80-1/N80Q, L80-1/9Cr/13Cr (Medium-deep Wells, Corrosion Resistance); C90, T95 (Sour Gas Wells); P110, Q125 (Deep & Ultra-deep High-pressure Wells)
Main Outer Diameter Sizes
4-1/2", 5-1/2", 7", 9-5/8", 10-3/4", 13-3/8", 20"
Thread Connections
SC Short Round Thread: Low cost, fast running for shallow low-pressure wells
LC Long Round Thread: Higher connection strength & sealing performance, widely used for conventional wells
BTC Buttress Thread: Excellent collapse & tension resistance, standard for deep high-pressure wells
Premium Gas-tight Thread: Zero leakage for ultra-deep & sour gas wells
3.2 Tubing
Suspended inside casing, retrievable and replaceable. It serves as dedicated channel to lift crude oil, natural gas & formation water to surface; also applied for fracturing, acidizing, chemical injection and downhole pump matching.
Common Steel Grades
J55, N80, L80, P110; L80-13Cr stainless steel tubing for corrosive fields
OD Sizes
1.05", 1.315", 1.66", 2-3/8", 2-7/8", 3-1/2", 4"
Pipe End Upset Types
NU Non-upset Tubing, EU External Upset Tubing, IJ Integral Joint Tubing (Ultra-high Tensile Strength)
3.3 Drill Pipe
Circulation channel during drilling, transmits torque to drive drill bit for rock breaking, delivers drilling fluid and carries cuttings to surface. Subject to combined tension, compression, torsion and abrasion loads.Steel Grades: E75, X95, G105, S135; Standard API 5DP; Single length 8–9.6m, with upset tool joint & hardbanding.
3.4 Line Pipe (API 5L)
Onshore & subsea long-distance pipeline for produced crude oil, natural gas and condensate, including seamless line pipe, LSAW submerged arc welded pipe and ERW high-frequency electric resistance welded pipe.
Main Steel Grades
Gr.B, X42(L245), X52(L360), X60, X65, X70, X80; X100 for ultra-high pressure trunk lines
Anti-corrosion Coatings
3LPE, FBE Fusion Bonded Epoxy, 3LPP Subsea Heavy-duty Coating
OD Range
60.3mm–762mm, Wall Thickness 3–120mm
4. Manufacturing Process & Core Advantages
Forming Technology: All downhole OCTG adopt hot rolling seamless process; line pipes include seamless, LSAW and ERW welded types
Key Performance:
High Collapse Resistance: Resist external formation rock pressure without indentation & deformation
High Tensile Strength: Prevent pipe string falling & rupture in deep wells
H₂S/CO₂ Corrosion Resistance: L80 13Cr, C90, T95 for sour oil & gas fields
Pressure Tight Sealing: Special thread + metal seal, no leakage under downhole high pressure
Low-temperature Toughness: PSL2 line pipe & low-temperature grades resist impact cracking at -40℃
Surface Treatment: Pipe end thread phosphating/copper plating for rust prevention; pipe body black/grey epoxy coating; 3-layer polyethylene heavy anti-corrosion for subsea pipelines
5. Connection Methods
Round Thread & Coupling Connection: General for casing & tubing (SC/LC)
BTC Buttress Thread Connection: Deep high-pressure casing
Premium Special Gas-tight Connection: Sour gas & ultra-deep high-temperature wells
Butt Welding for Line Pipe: Long-distance trunk pipelines
Flange Connection: Station equipment & valve jointing
6. Complete Matching Accessories
Couplings, Thread Protectors, Sub, Reducer Joint, Centralizer, End Caps, Thread Compound, Matching fishing tools
7. Application Scenarios
Onshore conventional shallow, medium-deep and ultra-deep oil wells
Sour oil & gas fields with hydrogen sulfide & carbon dioxide
Shale oil & tight gas fracturing wells
Offshore platforms & subsea gathering pipelines
Geothermal wells, CO₂ flooding injection strings
Urban natural gas pipeline network, refinery process pipelines
8. API Mandatory Factory Inspection Items
Dimensional Tolerance Full Inspection: OD, wall thickness, length, thread dimension
Mechanical Test: Tensile, Yield Strength, Hardness, Charpy Impact Toughness
NDT Non-destructive Test: UT Ultrasonic, MT Magnetic Particle, ET Eddy Current for internal crack & lamination detection
Hydrostatic Burst Test: Hold pressure per standard without leakage or bulging
Thread Stand-off, Thread Height & Taper Gauge Inspection
Spectrum Chemical Composition Analysis, strict control of harmful S & P impurities
9. Advantages & Disadvantages
Advantages
Seamless base body, far higher pressure & deformation resistance than welded pipes, high underground safety factor
Complete steel grade system, full selection coverage from shallow wells to 10,000m ultra-deep wells & corrosive fields
Standardized threads, universal interchangeable fittings for global oilfields
Adaptable to extreme downhole conditions of high temperature, high pressure and severe corrosion, long service life
Complete supporting products, one-stop tubular supply covering drilling, production and surface transportation
Disadvantages
Complex production process for seamless OCTG, higher cost than galvanized steel pipe & ordinary welded pipe
Extremely high precision requirement for thread machining; poor processing easily causes downhole leakage & thread jump-out accidents
Sour service corrosion-resistant alloy steel (13Cr) has much higher procurement cost than carbon steel OCTG
10. Procurement & Acceptance Identification Tips
Check API Monogram Certificate, Material Test Report, Hydrostatic & NDT Inspection Report, verify steel grade & standard edition
Outer wall clearly marked with steel grade, OD, wall thickness, length, heat number & API logo
Uniform copper plating/phosphating on thread surface, no burrs or collision damage; matched original couplings
Verify wall thickness tolerance, tensile & yield strength data, distinguish PSL1/PSL2 line pipe grades
NACE anti-sulfide inspection report must be provided for sour well orders
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