Inconel 625/825 Seamless Coil Tubing for Subsea Wellhead Control Lines
Product Overview
The Inconel 625/825 Seamless Coil Tubing manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a premium-grade corrosion-resistant tubing solution purpose-engineered for deepwater subsea wellhead control line applications. This product addresses the extreme dual-corrosion environment encountered in subsea oil and gas operations, where tubing is simultaneously exposed to aggressive wellbore fluids (containing H₂S, CO₂, chlorides, and hydrocarbons) and cold, oxygenated seawater from the external ocean environment.
Compliant with the stringent API 17D standard for tubing and pipe for wellhead and tree accessories, this coil tubing provides exceptional resistance to stress corrosion cracking (SCC), pitting, crevice corrosion, and general uniform corrosion in the most demanding offshore conditions. The coiled configuration enables efficient, continuous deployment in subsea control line runs, minimizing weld joints and reducing potential failure points in critical well control systems.
Material & Properties
Inconel 625 (UNS N06625)
- Composition: Nickel-Chromium-Molybdenum alloy with additions of niobium (Nb) for enhanced strength and weldability
- Nickel Content: ≥58% (balance)
- Chromium Content: 20.0–23.0%
- Molybdenum Content: 8.0–9.0%
- Niobium Content: 4.0–5.5%
- Excellent resistance to oxidizing and reducing acids, chlorinated environments, and seawater at elevated temperatures
- High tensile strength at temperatures ranging from cryogenic to 980°C (1,800°F)
- Superior weldability without risk of sensitization, maintaining full corrosion resistance in the heat-affected zone
Inconel 825 (UNS N08825)
- Composition: Nickel-Iron-Chromium alloy with controlled additions of molybdenum, copper, and titanium
- Nickel Content: 41.0–47.0%
- Chromium Content: 24.0–26.0%
- Molybdenum Content: 2.65–3.10%
- Copper Content: 2.65–3.10%
- Exceptional resistance to sulfuric acid, hydrochloric acid, and wet H₂S environments
- Outstanding resistance to chloride-induced stress corrosion cracking
- Optimal performance in mixed wellbore fluid environments containing both acidic and chlorinated media
Specifications
| Parameter | Specification |
|---|---|
| Product Type | Seamless Coil Tubing (Coiltube) |
| Material Grades | Inconel 625 (UNS N06625) / Inconel 825 (UNS N08825) |
| Manufacturing Standard | API 17D / ASTM B734 / ASTM B751 |
| Outer Diameter (OD) | 15.88 mm (5/8") to 168.3 mm (6-5/8") |
| Wall Thickness | 1.24 mm (0.049") to 18.0 mm (0.710") |
| Coil Length | Up to 5,000 m (16,404 ft) continuous length |
| Coil Inner Diameter | 600 mm (23.6") to 1,500 mm (59.1") |
| Surface Finish | Pickle & Polish / Industrial / Bright Annealed |
| Maximum Operating Pressure | Up to 105 MPa (15,225 psi) (per API 17D rating) |
| Operating Temperature Range | −196°C (−321°F) to +980°C (+1,796°F) |
| Corrosion Resistance | Dual protection: wellbore fluid + seawater environments |
| H₂S Resistance | Compliant with NACE MR0175 / ISO 15156 |
| Heat Treatment Condition | Solution Annealed (1120°C ± 25°C / 2,048°F ± 45°F) |
| End Preparation | Plain / Threaded & Coupled (per API 17D) |
| Application Category | Deepwater Subsea Facilities – Wellhead Control Lines |
Manufacturing Process
Step 1: Raw Material Selection & Verification
Premium-grade Inconel 625 or 825 bar stock is sourced from certified suppliers with full traceability documentation. Each heat lot undergoes spectroscopic analysis to verify chemical composition compliance with ASTM and API specifications prior to processing.
Step 2: Hot Piercing & Extrusion
The solid bar stock is heated to the appropriate forging temperature and pierced through a mandrel to form a hollow tube blank. The material is subsequently hot-extruded to achieve the target outer diameter and wall thickness with tight dimensional tolerances.
Step 3: Cold Drawing & Sizing
The hot-worked tube is cold-drawn through precision dies to achieve final dimensions within API 17D tolerances. This process enhances mechanical properties, improves surface finish, and ensures consistent wall thickness throughout the coil length.
Step 4: Heat Treatment (Solution Annealing)
The tubing is solution-annealed at 1,120°C ± 25°C (2,048°F ± 45°F) followed by controlled water quenching. This eliminates residual stresses, dissolves carbide precipitates, and restores full corrosion resistance and ductility in the final product.
Step 5: Surface Treatment & Pickle & Polish
Acid pickling removes oxide scale and surface contaminants, followed by mechanical or electrolytic polishing to achieve a smooth, clean surface finish. This is critical for minimizing crevice corrosion initiation sites in subsea environments.
Step 6: Coil Winding & Packaging
The finished tubing is wound into coils on precision-mandrel equipment, ensuring uniform curvature and avoiding any kinking or deformation. Coils are packaged with protective wrapping and wooden or steel cradles for safe ocean-going transportation.
Step 7: Quality Inspection & Testing
Each coil undergoes comprehensive inspection including dimensional verification, hydrostatic testing, ultrasonic testing (UT) for internal defects, and surface inspection for imperfections. Certificates of compliance and material test reports (MTRs) are issued per API 17D requirements.
Applications
Primary Application: Subsea Wellhead Control Lines
This product is specifically engineered for the following deepwater subsea facility applications:
- Subsea Wellhead Control Lines: Transporting control fluids (hydraulic fluid, nitrogen, and chemical injection fluids) from the surface or umbilical spools to the subsea wellhead assembly and Christmas tree
- Well Control Fluid Circulation: Carrying high-pressure control media for actuating subsea valves, chokes, and safety devices at depths exceeding 1,500 m (4,921 ft)
- Chemical Injection Lines: Delivering corrosion inhibitors, scale inhibitors, and biocides to the wellbore through subsea manifolds
- Nitrogen Blanketing Lines: Providing inert gas supply for wellhead pressure maintenance and safety isolation
- Subsea Umbilical Inner Tubing: Serving as the inner tubing within subsea umbilical assemblies connecting surface facilities to subsea wells
Dual-Corrosion Environment Challenge
The defining challenge in subsea wellhead control line applications is the simultaneous exposure to two aggressive corrosion environments: internal wellbore fluids containing dissolved H₂S, CO₂, chlorides, and hydrocarbons at elevated pressures and temperatures, combined with external seawater exposure through any micro-defects or during installation and maintenance. Inconel 625 and 825 seamless coil tubing provides unmatched dual-corrosion resistance, ensuring long-term integrity in this uniquely demanding service condition.
Additional Suitable Applications:
- Deepwater subsea production manifolds
- Subsea tieback lines and flowlines
- Offshore platform hydraulic control systems
- Chemical processing lines in marine environments
- Oil and gas extraction equipment in sour service conditions
Quality Certifications & Compliance
Standards Compliance:
- API 17D: Tubing and Pipe for Wellhead and Tree Accessories – Full compliance for subsea well control applications
- ASTM B734: Standard Specification for Nickel-Chromium-Iron-Molybdenum-Columbium (Niobium) Alloy Seamless Tubing (Inconel 625)
- ASTM B751: Standard Specification for Nickel-Chromium-Iron Alloy Seamless Tubing (Inconel 825)
- NACE MR0175 / ISO 15156: Materials for use in H₂S-containing environments in oil and gas production
- ISO 9001:2015: Quality Management System certification
- ASME Section IX: Welding procedure qualification for Inconel alloys
Testing & Certification Documentation:
- Mill Test Reports (MTRs) with full chemical and mechanical property data for each heat lot
- Hydrostatic test certificates confirming pressure integrity
- Ultrasonic testing (UT) reports for internal defect verification
- Positive Material Identification (PMI) verification via XRF spectroscopy
- Third-party inspection (TPI) available per client requirements
- Traceability documentation linking each coil to its raw material heat number
Unique Selling Points
- API 17D Certified for Subsea Service: One of the limited manufacturers producing Inconel 625/825 coil tubing fully compliant with API 17D requirements for wellhead and tree accessories
- Dual-Corrosion Engineered: Specifically designed to withstand simultaneous attack from aggressive wellbore fluids internally and corrosive seawater externally
- Ultra-Long Continuous Lengths: Available in coil lengths up to 5,000 m (16,404 ft), minimizing the number of field welds required and reducing potential failure points in critical well control systems
- Superior Weldability: Inconel 625 and 825 maintain full corrosion resistance in the heat-affected zone after welding, eliminating the need for post-weld heat treatment in the field
- Proven Deepwater Track Record: Successfully deployed in multiple deepwater subsea installations worldwide, including ultra-deepwater projects exceeding 2,000 m (6,562 ft) water depth
- Full Traceability & Documentation: Complete material traceability from raw material through final product, with comprehensive test documentation meeting the highest offshore industry standards
Technical Support & Customization
Wenzhou Jixing Metal Materials Co., Ltd. provides comprehensive technical support for project-specific requirements including custom OD/wall thickness combinations, special end preparations, surface treatments, and packaging configurations tailored to offshore logistics constraints. Engineering consultation is available for material selection optimization based on specific wellbore fluid chemistry, water depth, and expected service life requirements.