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Help CenterSteel Pipe & Tube & OCTG Oil Country Tubular Goods，API 5CT, API 5B, API 5DP, API 5L, GB/T 19683, SY/T 6194
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1. Product Overview
The full name of oil pipes is Oil Country Tubular Goods (abbreviated as OCTG). They are core pressure-bearing steel pipes covering the whole process of oil and gas exploration, drilling, well completion and gathering & transportation. They fall into four major categories: casing & tubing, drill pipes and pipeline line pipes for oil & gas transmission. All products comply with international standards of American Petroleum Institute (API) as well as domestic GB national standards and SY/T industrial standards. They are applicable to all working conditions including onshore & offshore wells, shallow & deep wells, sulfur-containing corrosive wells and high-pressure oil & gas fields, featuring high strength, superior collapse resistance, internal pressure resistance, tolerance to hydrogen sulfide and carbon dioxide corrosion, and reliable thread sealing performance.
2. Detailed Introduction of Four Major Product Categories
2.1 Casing Pipe
2.1.1 Core Application
Run into wellbore for cementing operation to permanently support well walls, prevent stratum collapse, isolate oil, water and gas formations, and cut off formation high pressure. As disposable consumable pipes, casing accounts for over 70% of oil well consumables. Classified by running depth: conductor casing, surface casing, intermediate casing, production casing and liner.
2.1.2 Standard Specifications
Nominal outer diameter: 114.3mm (4-1/2") ~ 508mm (20")
Wall thickness: 5.0mm ~ 15.9mm
Standard fixed length: 5.5m ~ 22.23m; customized short or extended lengths available
Theoretical weight formula: (OD - WT) × WT × 0.02466 = weight per meter (kg/m)
2.1.3 Common Steel Grades (API 5CT)
Conventional wells: H40, J55, K55
Medium-deep wells: N80, L80
Deep & high-pressure wells: C90, T95, C95, P110
Ultra-deep wells: Q125, V140, V150
Sulfur-containing corrosive wells: L80, 13Cr, Super 13Cr, nickel alloy casing
2.1.4 Thread Types
STC (Short Thread & Coupling): Cost-effective for shallow low-pressure wells
LTC (Long Thread & Coupling): For medium-shallow wells with better sealing performance than STC
BTC (Buttress Thread & Coupling): Applied in medium-deep wells, high torque, excellent collapse and internal pressure resistance
Premium Thread with Metal-to-Metal Seal: VAM TOP, BGT and other types, dedicated for high-pressure gas wells and sulfur-containing wells with zero leakage risk
2.1.5 Executive Standards
API SPEC 5CT (pipe body), API SPEC 5B (thread gauges), SY/T 6194, GB/T 19683
2.2 Tubing Pipe
2.2.1 Core Application
Suspended inside casing to serve as fluid channel for oil & gas lifting, water injection, polymer injection, fracturing and acidizing operations. It can be pulled out and reused repeatedly and acts as the core channel for hydrocarbon production.
2.2.2 Standard Specifications
Outer diameter: 48.36mm (1.9") ~ 114.3mm (4-1/2")
Wall thickness: 4.83mm ~ 9.52mm
Standard length: 6.0m ~ 12.5m
2.2.3 Structural Classification
NU (Non-Upset Tubing): No pipe end thickening, widely used in shallow wells
EU (External Upset Tubing): Outer wall thickened at both ends for improved thread strength, mainstream choice for medium-deep wells
Integral Joint Tubing: No separate coupling, designed for slim hole wells
2.2.4 Matching Steel Grades
N80, L80, C90, T95, P110; 13Cr stainless steel tubing is adopted for corrosive working conditions.
2.3 Drill Pipe
2.3.1 Application
Connect drill bit with surface equipment to transmit rotary torque and circulate drilling mud. Subject to combined alternating loads including tension, compression, torsion and bending.
2.3.2 Specifications & Steel Grades
Outer diameter ranges from 60.3mm to 168.3mm, standard length 8.5m ~ 9.5m. Standard steel grades: E75, X95, G105, S135 (high-strength grade for deep wells). Both ends are equipped with thickened wear-resistant tool joints, complying with API 5DP standard.
2.4 API 5L Line Pipe for Oil & Gas Transmission
2.4.1 Application
Oil & gas field gathering pipelines, long-distance trunk lines, subsea pipelines and process pipelines for refineries, used for transporting crude oil, natural gas and refined oil products.
2.4.2 Specifications & Steel Grades
Outer diameter: 2 inch ~ 48 inch (DN50 ~ DN1200), wall thickness 3mm ~ 40mm. Common steel grades: Gr.B, X42, X52, X60, X65, X70, X80. Customized sulfur-resistant line pipes are available for low-temperature and hydrogen-induced cracking resistant service.
2.4.3 Manufacturing Processes
Seamless line pipe, LSAW (Longitudinal Submerged Arc Welded), ERW (Electric Resistance Welded), SSAW (Spiral Submerged Arc Welded). Supporting anti-corrosion coatings: 3PE, FBE, 2PP.
3. Main Manufacturing Processes
3.1 Seamless OCTG (Mainstream Product for OCTG)
Process flow: Steel billet heating → piercing → continuous hot rolling → sizing & straightening → heat treatment (normalizing / quenching & tempering) → non-destructive testing → threading & coupling machining → phosphating & copper plating to prevent thread galling → thread grease protection → finished product inspection.Advantages: Weld-free structure, uniform pressure bearing performance, superior collapse resistance and hydrogen sulfide cracking resistance. Preferred material for deep wells and sulfur-containing wells.
3.2 Welded OCTG (HFW/ERW)
Process flow: Steel strip forming → high-frequency resistance welding → full weld heat treatment → non-destructive inspection & sizing. Mainly applied to shallow low-pressure casing and line pipes with lower cost.
4. Core Performance Advantages
High strength & pressure bearing capacity: Different steel grades match corresponding yield strength. P110 grade features minimum yield strength of 758MPa to withstand formation high pressure and internal pressure in ultra-deep wells.
Excellent collapse resistance: Casing adopts special thickened wall design to resist surrounding rock extrusion and avoid wellbore deformation.
Complete anti-corrosion system
Carbon steel: For fresh water and conventional oil & gas wells without sulfur
L80 & 13Cr series: For oil & gas wells containing H₂S and CO₂, resistant to stress corrosion cracking
Nickel-based alloy: For high-corrosion, high-temperature ultra-deep wells
High sealing performance of threads: Dual protection of standard threads and premium metal sealing connections to eliminate leakage in high-pressure gas wells. Coupling copper plating avoids thread galling.
High dimensional precision: Strict OD and wall thickness tolerances per API standards, stable inner diameter for smooth running and pulling operations.
100% full-process non-destructive testing: UT ultrasonic testing, ET eddy current testing, hydrostatic pressure test and MT magnetic particle inspection to screen all internal defects before delivery.
5. Surface Anti-Corrosion Treatment Solutions
External anti-corrosion coating: 3PE three-layer polyethylene, FBE fusion bonded epoxy, epoxy zinc-rich primer, coal tar enamel coating for buried pipelines to resist soil corrosion.
Internal anti-corrosion coating: Internal epoxy coating, chrome/copper lining to reduce flow resistance, prevent scaling and slow down medium corrosion.
Thread protection: Coupling phosphating and copper plating; special sealing lubricant coated on threads to prevent rust and abrasion during transportation and well running.
6. Factory Inspection Items (100% Full Inspection)
Mechanical property tests: Tensile test, impact test, hardness test, flattening test
Non-destructive testing: UT ultrasonic inspection, ET eddy current inspection, MT magnetic particle inspection
Hydrostatic burst test: Hold pressure per standard without leakage or deformation
Thread inspection: Full inspection with special API gauges to meet sealing and torque requirements
Chemical composition analysis of raw material: Strict control of harmful impurities S and P to meet sulfur resistance standards
Dimensional & appearance inspection: Outer diameter, wall thickness, length and straightness measured pipe by pipe
7. Marking, Packing & Delivery
Pipe marking: Steel stamp and spray printing including applicable standard, steel grade, OD & WT, length, heat batch number, manufacturer logo and API certification number.
Packing: Small-diameter pipes bundled with steel strips; large-diameter pipes packed as single pieces. Plastic thread protectors installed on both pipe ends to shield threads.
Delivery lead time: Standard spot goods shipped within 5-7 working days; customized special steel grades and premium threads take 10-18 working days. Goods loaded at Tianjin Port or Qingdao Port for export.
Supporting documents: Original material test certificate, API certification, NDT inspection report, hydrostatic test report, commodity inspection certificate.
8. Applicable Industries & Scenarios
Onshore & offshore oil and gas wells, shale oil & gas exploitation, geothermal wells, water injection development oilfields, long-distance natural gas pipeline network, refinery process pipelines, coalbed methane development, heavy oil thermal recovery wells.
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