Super Duplex Stainless Steel (SDSS) Coil Tube for Deepwater Umbilical Cable
Product Overview
The Super Duplex Stainless Steel Coil Tube (SDSS Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a high-performance, corrosion-resistant metallic tubing specifically engineered for use in deepwater subsea umbilical cable systems. Designed to meet the rigorous demands of offshore oil and gas production environments, this product represents a state-of-the-art solution for conveying hydraulic fluids, chemical agents, and control signals at depths exceeding 3,000 meters. The coil tube is fabricated in continuous coil form to facilitate downstream manufacturing processes including drawing, sizing, and mandrel insertion into umbilical cable assemblies.
Industry Context: Deepwater umbilical cables are multifunctional bundles that integrate hydraulic lines, electrical conductors, and chemical injection lines, serving as the critical control interface between surface facilities and subsea production systems. The metallic tubing components within these cables must withstand extreme hydrostatic pressure, aggressive chloride-rich seawater environments, cyclic loading, and prolonged exposure to sour service conditions (H2S/CO2).
Material & Properties
Alloy Grade
The coil tube is manufactured from Super Duplex Stainless Steel conforming to UNS S32750 / S32760 (equivalent to EN 1.4501, N08904, or 2507 designation). This alloy features a balanced microstructure of austenite (γ) and ferrite (α) phases, typically in a 40:60 to 50:50 ratio, providing an exceptional combination of mechanical strength and corrosion resistance.
Chemical Composition (wt%)
| Element | Minimum | Maximum |
|---|
| C (Carbon) | — | 0.030 |
| Si (Silicon) | — | 0.30 |
| Mn (Manganese) | — | 1.50 |
| P (Phosphorus) | — | 0.030 |
| S (Sulfur) | — | 0.020 |
| Cr (Chromium) | 22.0 | 25.0 |
| Mo (Molybdenum) | 3.0 | 4.0 |
| N (Nitrogen) | 0.24 | 0.32 |
| W (Tungsten) | 0.50 | 1.50 |
| Ni (Nickel) | 6.0 | 8.0 |
Mechanical Properties
| Property | Specification |
|---|
| Yield Strength (0.2% offset) | ≥ 550 MPa |
| Tensile Strength (UTS) | ≥ 720 MPa |
| Elongation (at fracture) | ≥ 15% |
| Pitting Resistance Equivalent Number (PREN) | ≥ 38 (typically 38–42) |
| Impact Energy (at −40°C, Charpy V-notch) | ≥ 40 J |
| Hardness (HBW) | 240–320 |
| Operating Temperature Range | −50°C to +300°C |
Corrosion Resistance Characteristics
- Chloride Stress Corrosion Cracking (Cl-SCC): Superior resistance compared to austenitic grades (e.g., 316L, 321) and conventional duplex grades (e.g., 2205), enabling reliable service in hot chloride environments.
- Pitting and Crevice Corrosion: High PREN value provides excellent resistance to localized corrosion in seawater and brine environments.
- Sour Service Resistance: Suitable for NACE MR0175 / ISO 15156 compliance for environments containing H2S and CO2.
- Erosion-Corrosion: Enhanced resistance to flow-accelerated corrosion at high fluid velocities typical in umbilical hydraulic lines.
- Resistance to Sulfide Stress Cracking (SSC): Suitable for use in sour service without requiring additional hardening controls beyond standard SDSS specifications.
Specifications
| Parameter | Specification / Range |
|---|
| Product Form | Coil Tube (Continuous Coil) |
| Outside Diameter (OD) | 6.00 mm – 25.00 mm (customizable) |
| Wall Thickness (WT) | 0.80 mm – 2.50 mm (customizable) |
| Tolerance on OD | ± 0.05 mm |
| Tolerance on Wall Thickness | ± 0.03 mm |
| Surface Finish | Pickled & Polished (2B) or Bright Annealed (BA); internal surface Ra ≤ 0.4 μm available |
| Coil Weight | 300 kg – 1,500 kg (per coil) |
| Core Diameter | 200 mm – 400 mm (configurable) |
| Manufacturing Standard | ASTM A790 / ASTM A790M (for welded); ASTM A778 / A778M (for seamless) |
| Material Standard | UNS S32750 / S32760; EN 10217-7; EN 10216-5 |
| Applicable Umbilical Standard | API 17J; DNV-RP-F201; NORSOK M-710 |
| Maximum Working Pressure (MWP) | Up to 450 bar (design-dependent) |
| Deepwater Depth Rating | Up to 3,000+ meters |
| End Preparation | Flush cut, beveled, or threaded (per customer specification) |
| Heat Treatment | Solution annealed at 1020–1120°C, followed by rapid water quench |
Manufacturing Process
Process Flow
- Raw Material Procurement & Ingot Casting: High-purity super duplex stainless steel ingots are produced via Vacuum Arc Remelting (VAR) or Electro-Slag Remelting (ESR) to ensure tight control over chemical composition and minimize inclusions.
- Billet Homogenization & Hot Rolling: Ingots are reheated to 1150–1200°C and hot rolled into seamless tube blanks or flat strip for subsequent forming.
- Tube Forming (Seamless or Welded):
- Seamless Route: Hot piercing followed by cold drawing or rotary piercing to achieve desired OD and wall thickness.
- Welded Route: Precision cold-rolled strip is formed into a tube and welded using Pulse Inert Gas Welding (PIGW) or Submerged Arc Welding (SAW) with matched SDSS filler metal.
- Cold Working & Sizing: Multi-stage cold drawing through tungsten carbide dies to achieve final dimensions with tight tolerances. This process enhances mechanical properties through strain hardening while maintaining ductility.
- Solution Annealing: Tubes are heated to 1020–1120°C in a protective atmosphere (argon or nitrogen) and rapidly quenched to dissolve intermetallic phases (σ-phase, χ-phase) and restore full corrosion resistance.
- Pickling & Passivation: Surface oxides are removed via controlled acid pickling (nitric/hydrofluoric acid blend), followed by passivation to establish a stable chromium oxide passive film.
- Coiling: Finished tubes are wound onto precision cores at controlled tension to produce uniform coils suitable for downstream processing.
- Quality Inspection & Non-Destructive Testing (NDT): Comprehensive inspection regime applied at each critical stage.
Key Process Controls
- σ-Phase Avoidance: Critical for SDSS; processing temperatures and cooling rates are rigorously controlled to prevent formation of intermetallic σ-phase (Cr-rich) which severely degrades toughness and corrosion resistance.
- Grain Size Control: Maintained at ASTM No. 4–8 for optimal combination of strength and formability.
- Weld Integrity: For welded tubes, weld penetration and lack of undercut are verified through radiographic testing (RT) or ultrasonic testing (UT).
- Dimensional Accuracy: Automated in-line measurement systems monitor OD, wall thickness, and roundness at speeds exceeding 50 m/min.
Applications
Primary Application: Deepwater Umbilical Cables
The SDSS coil tube serves as the primary metallic tubing component in deepwater umbilical cable assemblies, performing the following functions:
- Hydraulic Control Lines: Conveying high-pressure hydraulic fluid (up to 450 bar) to actuate subsea control modules (SCMs), valves, and actuators on the seabed.
- Chemical Injection Lines: Transporting corrosion inhibitors, scale inhibitors, hydrate inhibitors, and biocides to subsea production equipment.
- Gas Injection Lines: Delivering nitrogen or natural gas for pigging, flow assurance, and hydrate prevention.
- Flow-Through Lines: Providing conduit for hydrocarbon production flow or multiphase sampling.
Secondary Applications
- Subsea Christmas trees and manifolds
- Deepwater subsea completion systems
- Offshore wellhead equipment and tree components
- Subsea flow control devices and valves
- Marine and naval applications (propulsion shafts, piping systems)
- Desalination plant heat exchangers and piping
- Chemical processing equipment in aggressive chloride environments
- Offshore platform structural and process piping
Quality Certifications & Testing
Third-Party Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- API Q1 / API Q2 — Quality Management Systems for Oil and Gas Equipment/Supplies/Services
- DNV-GL Certification — Type Approval for subsea umbilical components
- LR (Lloyd's Register) Approval — Materials certification
- NORSOK M-710 — Qualification of materials for use in offshore petroleum installations
- NACE MR0175 / ISO 15156 — Materials resistant to sulfide stress cracking
In-Process and Final Testing Regime
| Test Method | Standard | Acceptance Criteria |
|---|
| Chemical Analysis (Spectrographic) | ASTM E415 / ASTM E135 | Within specified composition range |
| Tensile Testing | ASTM A370 | YS ≥ 550 MPa; UTS ≥ 720 MPa; Elongation ≥ 15% |
| Impact Testing (Charpy V-Notch) | ASTM A490 | ≥ 40 J at −40°C |
| Hardness Testing | ASTM E10 (HBW) | 240–320 HBW |
| Intergranular Corrosion Test | ASTM A923 Practice E | No intergranular attack |
| Pitting Corrosion Test | ASTM G48 (ASTM A262 Practice B) | No pitting at 42% NaCl, 60°C, 24h |
| Crevice Corrosion Test | ASTM G110 | Pass (no crevice corrosion) |
| Stress Corrosion Cracking (SCC) | ASTM G44 / ASTM G110 | No cracking |
| Hydrostatic Pressure Test | ASTM A530 | No leakage at 1.5× MWP for minimum 60 seconds |
| Visual & Dimensional Inspection | ASTM A790M | Within specified tolerances |
| Magnetic Particle Inspection (MPI) | ASTM E709 | No surface or near-surface defects |
| Eddy Current Testing (ECT) | ASTM E309 | No internal or surface defects |
| Positive Material Identification (PMI) | ASTM E1601 (XRF) | Confirmed alloy grade |
| Phase Analysis (Ferrite Content) | ASTM E1245 (Magnetic Method) | 40–60% ferrite |
| Intermetallic Phase Examination | ASTM A923 / Metallographic | Free of σ-phase, χ-phase, and Laves phase |
Traceability and Documentation
- Full heat traceability from raw material ingot to finished coil
- Mill