Super Duplex Stainless Steel Coil Tubes for Deep-Sea Umbilical Cables
Product Overview
The Super Duplex Stainless Steel (SDSS) Coil Tube, developed and manufactured by Wenzhou Jixing Metal Materials Co., Ltd., represents a cutting-edge advancement in offshore engineering materials designed specifically for deep-sea umbilical cable applications. Umbilical cables serve as critical lifelines in subsea oil and gas production systems, transmitting hydraulic fluid, electrical power, and chemical injection fluids between surface facilities and subsea wellheads. Operating at depths exceeding 3,000 meters, these cables endure extreme hydrostatic pressures, aggressive chloride-rich environments, and continuous mechanical fatigue. Traditional materials such as conventional 316L austenitic stainless steel or carbon steel with corrosion-resistant alloys (CRA) cladding often fall short in terms of long-term structural integrity and resistance to chloride-induced stress corrosion cracking (SCC).
Wenzhou Jixing Metal Materials Co., Ltd. has pioneered the development of SDSS coil tubes that combine exceptional mechanical strength, outstanding corrosion resistance, and superior weldability — all packaged in a coil form that facilitates efficient downstream processing into umbilical cable armor and pressure tubing. This product addresses the growing demands of the deepwater and ultra-deepwater offshore energy sector, where reliability and lifecycle cost are paramount.
Material & Properties
The coil tubes are fabricated from Super Duplex Stainless Steel, conforming to UNS S32750 / S32760 (ASTM A928 / EN 10217-7) specifications. The metallurgical composition and resulting properties are engineered to deliver performance far exceeding conventional duplex grades such as 2205 (UNS S31803).
Chemical Composition (Typical, wt%)
| Element | Specification |
|---|---|
| C (Carbon) | ≤ 0.030 |
| Si (Silicon) | ≤ 1.00 |
| Mn (Manganese) | ≤ 2.00 |
| P (Phosphorus) | ≤ 0.035 |
| S (Sulfur) | ≤ 0.030 |
| Cr (Chromium) | 27.0 – 30.0 |
| Ni (Nickel) | 6.0 – 8.0 |
| Mo (Molybdenum) | 3.0 – 5.0 |
| N (Nitrogen) | 0.20 – 0.30 |
| Cu (Copper) | 0.5 – 1.0 |
| Ti (Titanium) | 0.5 – 1.0 |
Mechanical Properties
| Property | Minimum Value | Test Temperature |
|---|---|---|
| Tensile Strength (UTS) | ≥ 830 MPa (120 ksi) | Room Temperature |
| Yield Strength (0.2% Offset) | ≥ 550 MPa (80 ksi) | Room Temperature |
| Elongation at Break | ≥ 15% | Room Temperature |
| Impact Energy (Charpy V-Notch) | ≥ 70 J | −40°C (−40°F) |
| Hardness (HBW) | ≤ 350 | Room Temperature |
Corrosion Resistance
- Pitting Resistance Equivalent Number (PREN): ≥ 42, calculated as PREN = %Cr + 3.3×%Mo + 16×%N, indicating exceptional resistance to localized corrosion in chloride environments.
- Stress Corrosion Cracking (SCC) Resistance: Superior to 316L and 2205 duplex stainless steels in saturated chloride solutions at elevated temperatures up to 60°C.
- Sulphuric Acid Resistance: Maintains integrity in dilute sulphuric acid environments commonly encountered in sour well conditions.
- Crevice Corrosion Resistance: Enhanced by the high nitrogen content and balanced Cr/Mo/N alloying system.
Specifications
| Parameter | Specification |
|---|---|
| Product Designation | SDSS Coil Tube (Coiltube) |
| Material Grade | UNS S32750 / S32760 (Super Duplex) |
| Applicable Standards | ASTM A928 / A928M, EN 10217-7, NACE MR0175/ISO 15156, API 5CT (reference) |
| Outer Diameter (OD) | 12.7 mm – 76.2 mm (0.5" – 3") |
| Wall Thickness | 0.8 mm – 10.0 mm (as per requirement) |
| Coil Weight | Typically 1,500 – 5,000 kg per coil |
| Surface Finish | Pickled & Passivated (P&P), or polished as specified |
| Delivery Condition | Hot-rolled & Cold-drawn annealed (solution heat treated) |
| Heat Treatment | Solution annealing at 1050–1100°C followed by water quench |
| Maximum Operating Temperature | ≤ 300°C (572°F) |
| Minimum Design Temperature | −50°C (−58°F) with adequate impact toughness |
| Maximum Design Pressure | Up to 200 MPa (2,900 psi) depending on geometry |
| Coating Options | Polymer coating (e.g., PTFE, HDPE) for internal hydraulic tubing |
| Traceability | Full heat-number traceability with mill test certificates (MTC) |
Manufacturing Process
The production of Super Duplex Stainless Steel Coil Tubes for deep-sea umbilical applications follows a rigorous, multi-stage manufacturing protocol designed to ensure metallurgical integrity, dimensional accuracy, and consistent mechanical performance:
- Raw Material Selection & Melting: Vacuum Arc Remelting (VAR) or Electro-Slag Remelting (ESR) of high-purity SDSS billets to ensure homogeneity, low interstitial content (C, N, S), and freedom from segregation defects. The nitrogen level is precisely controlled to achieve the target PREN value.
- Hot Rolling & Piercing: Billets are reheated to 1,100–1,200°C and hot-rolled into seamless tubes via the Mannesmann piercing or plug-rolling method. The rolling schedule is optimized to achieve a balanced α (ferrite) / γ (austenite) phase ratio of approximately 45–55% / 55–45%.
- Solution Heat Treatment: Hot-rolled tubes undergo solution annealing at 1,050–1,100°C with rapid water quenching to dissolve intermetallic phases (σ, χ, Laves) and restore full ductility and corrosion resistance.
- Pickling & Passivation: Tubes are acid pickled (nitric/hydrofluoric acid blend) to remove oxide scale, followed by passivation to establish a stable chromium oxide passive film on the surface.
- Cold Drawing / Cold Rolling: Tubes are cold-drawn through precision dies to achieve target outer diameter and wall thickness tolerances (typically ±0.1 mm). Multi-pass drawing schedules are employed for larger reductions. Intermediate annealing may be required to prevent work hardening.
- Final Annealing: Cold-worked tubes are solution annealed again at 1,050–1,100°C to relieve residual stresses and restore the optimal microstructure. This step is critical for ensuring SCC resistance in the final product.
- Coiling & Packaging: Tubes are coiled onto precision mandrels with controlled winding tension to prevent deformation. Each coil is wrapped in protective packaging (VCI paper, PE film) and secured for transport.
- Non-Destructive Testing (NDT): Every coil undergoes comprehensive inspection including:
- Eddy Current Testing (ECT) for surface and near-surface defects
- Hydrostatic Pressure Testing at 1.5× maximum service pressure (typically 100–300 MPa)
- Ultrasonic Testing (UT) for internal wall thickness and laminations
- Magnetic Particle Inspection (MPI) where applicable
Key Metallurgical Controls
- Phase Balance Monitoring: Ferrite/austenite ratio is verified via magnetic permeability measurements and metallographic examination per ASTM A955.
- Intermetallic Phase Suppression: The rapid quench rate and controlled cooling prevent precipitation of detrimental σ-phase, particularly critical in the weld heat-affected zone (HAZ).
- Grain Size Control: Austenite grain size maintained at ASTM No. 6–8 for optimal toughness and fatigue performance.
Applications
Super Duplex Stainless Steel Coil Tubes from Wenzhou Jixing Metal Materials Co., Ltd. are purpose-engineered for the following demanding applications:
Primary Application: Deep-Sea Umbilical Cables
- Hydraulic Pressure Tubing: Internal fluid lines within umbilical cables carrying hydraulic control fluids to subsea control modules (SCMs) and remotely operated vehicles (ROVs). The high yield strength allows thinner walls, reducing overall umbilical weight and cost.
- Chemical Injection Lines: Carrying corrosion inhibitors, scale inhibitors, and biocides into subsea production systems. The SDSS material resists degradation from aggressive chemical formulations.
- Wet Gas / Multiphase Flow Lines: Transporting produced fluids in subsea tree connections where H₂S, CO₂, and chloride concentrations are elevated.
Secondary Applications
- Offshore platform piping systems in sour service (H₂S-containing environments)
- Subsea production tubing and casing in deepwater wells
- Marine heat exchangers and condensers in offshore platforms
- Desalination plant piping and brine handling systems
- Pulp and paper industry equipment (digesters, bleaching systems)
- Oil refinery heat exchangers and distillation columns
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that all SDSS coil tube products meet international standards and industry-specific requirements:
Management System Certifications
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health and Safety Management Systems
- ISO 3834-2 — Quality Requirements for Welding of Steel and Nickel Alloys
Product-Specific Certifications & Compliance
- NACE MR0175 / ISO 15156 — Materials for use in H₂S-containing environments in oil and gas production (SDSS qualifies under multiple material categories)
- API 5CT — Casing and Tubing for Petroleum and Natural Gas Industries (applicable reference)
- DNV-GL / Bureau Veritas — Type approval for offshore umbilical components
- ASTM A928 / A928M — Standard Specification for Seamless and Welded Austenitic-Stainless-Steel and Duplex Stainless Steel Tubes for High-Pressure Boilers and Similar Applications
- EN 10217-7 — Tubes for Pressure Purposes — Non-Heat Resistant Steels (Duplex Stainless Steel)
- ASME Section VIII — Pressure Vessel Code compliance for material usage
Testing & Inspection Protocols
- Chemical analysis per ASTM E1019 (Spark-OES) and ASTM E415 (Hydrogen Determination)
- Mechanical testing per ASTM A370 (Tensile), ASTM A490 (Impact), ASTM E18 (Hardness)
- Corrosion testing per ASTM G48 (Pitting & Crevice), ASTM G36 (SCC), ASTM G150 (Intergranular Corrosion)
- Dimensional inspection per ASTM A751 (Sampling for Steel Products)
- Full heat-number traceability with EN 10204 Type 3.1 Mill Test Certificates (MTC)
Unique Selling Points
The SDSS Coil Tubes from W