ASTM A789 Duplex Stainless Steel Coil Tube — Seamless & Welded
Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., the ASTM A789 duplex stainless steel coil tube is a high-performance tubing solution engineered for demanding applications that require exceptional corrosion resistance, superior mechanical strength, and long-term structural integrity. Available in both seamless and welded configurations, this coil tube delivers the dual-phase microstructure advantage of ferrite-austenite balance, making it the preferred choice for industries where reliability and durability are non-negotiable.
Product Overview
ASTM A789 is the definitive American standard specification covering seamless and welded austenitic and duplex stainless steel tubing. The duplex stainless steel coil tube supplied by Wenzhou Jixing Metal Materials Co., Ltd. is designed to meet the rigorous requirements of this standard, offering a balanced two-phase microstructure (approximately 50% ferrite / 50% austenite) that provides significant advantages over conventional austenitic grades:
- 2–3× higher yield strength compared to standard austenitic stainless steels such as 304 or 316
- Superior resistance to chloride pitting and crevice corrosion, enabled by elevated PREN (Pitting Resistance Equivalent Number) values
- Enhanced resistance to stress corrosion cracking (SCC), particularly in chloride-containing environments
- Outstanding fatigue and wear resistance for extended service life in cyclic loading conditions
- Good weldability and formability, allowing versatile fabrication into complex geometries
Material & Properties
Available Duplex Grades
The coil tube is available in the following widely recognized duplex stainless steel grades under ASTM A789:
| Grade | UNS Designation | PREN (Min.) | Yield Strength (MPa, Min.) | Tensile Strength (MPa, Min.) | Key Characteristics |
|---|---|---|---|---|---|
| 2205 | S32205 | ≥34 | 450 | 550 | Standard duplex; excellent general corrosion resistance |
| 2507 (Super Duplex) | S32750 | ≥40 | 550 | 720 | Super duplex; exceptional chloride and high-temperature resistance |
| 2507 (Super Duplex) | S32760 | ≥40 | 550 | 720 | European super duplex equivalent; wide temperature range |
| 253 (Lean Duplex) | S32500 | ≥37 | 450 | 550 | Cost-effective duplex with enhanced resistance |
Mechanical & Physical Properties (Typical for 2205 / S32205)
| Property | Value |
|---|---|
| Relative Density | 7.8 |
| Specific Heat (25°C) | 0.50 J/(g·°C) |
| Thermal Conductivity (25°C) | 18 W/(m·°C) |
| Modulus of Elasticity | 200 GPa |
| Thermal Expansion Coefficient (25–100°C) | 12.4 µm/(m·°C) |
| Maximum Service Temperature | 300°C (continuous) |
| Minimum Service Temperature | −50°C (with impact testing qualification) |
Chemical Composition (Typical for 2205 / S32205)
| Element | Specification (wt%) |
|---|---|
| C | ≤ 0.030 |
| Si | ≤ 1.00 |
| Mn | ≤ 2.00 |
| P | ≤ 0.030 |
| S | ≤ 0.020 |
| Cr | 22.0 – 23.0 |
| Ni | 4.5 – 6.5 |
| Mo | 3.0 – 3.5 |
| N (Nitrogen) | 0.14 – 0.20 |
Specifications
| Parameter | Specification |
|---|---|
| Governing Standard | ASTM A789 / A789M |
| Product Form | Coil Tube (Coiled Tubing) |
| Manufacturing Method | Seamless & Welded (ERW, TIG/Auto-clad welded) |
| Outer Diameter (OD) | 6.0 mm – 219.1 mm (custom sizes available) |
| Wall Thickness | 0.5 mm – 19.0 mm (custom thicknesses available) |
| Coil Length | Standard: 5 m – 20 m per coil; custom lengths available |
| Surface Finish | Pickled & Passivated (2B), Mill Finish, or Custom (e.g., No. 4 Brushed, Polished) |
| Heat Treatment Condition | Solution Annealed (Pickled & Passivated) |
| Tolerance (OD) | ±0.05 mm (fine tolerance available on request) |
| Tolerance (Wall) | ±10% of nominal |
| End Form | Plain, Beveled, or Custom |
| Packaging | Export-standard coil packaging with protective wrapping |
Manufacturing Process
Wenzhou Jixing Metal Materials Co., Ltd. employs a rigorously controlled manufacturing process to ensure every coil tube meets or exceeds ASTM A789 requirements:
Seamless Coil Tube Production
- Raw Material Selection: High-purity duplex stainless steel billets are sourced from certified mills with verified chemical composition and low interstitial element content (C, N, S).
- Piercing & Hot Rolling: Billets are heated to controlled temperatures and pierced to produce seamless hollow blanks, maintaining uniform microstructure throughout the wall thickness.
- Hot Reduction: The hollow blank is rolled to near-final dimensions on a seamless tube mill, ensuring tight dimensional control.
- Intermediate Annealing: Tubes are annealed to relieve residual stresses and restore ductility for subsequent cold working operations.
- Cold Drawing / Cold Pilgering: Tubes are drawn through precision dies to achieve final OD and wall thickness with fine tolerance control.
- Final Annealing (Solution Heat Treatment): Tubes are solution annealed at 1050°C – 1150°C followed by controlled cooling to establish the optimal ferrite-austenite phase balance.
- Pickling & Passivation: Acid pickling removes surface oxide scale, followed by passivation treatment to form a protective chromium oxide film.
- Coiling: Finished tubes are wound into coils of specified length and diameter, with end protection applied to prevent damage.
Welded Coil Tube Production
- Strip Milling & Cold Rolling: Duplex stainless steel strip is cold-rolled to precise thickness tolerances.
- Forming: The strip is fed through precision roll-forming stations to create the tubular cross-section.
- Welding: A high-quality longitudinal weld is produced using submerged arc welding (SAW) or automatic TIG welding, with tight control of heat input to prevent sensitization and sigma phase formation.
- Post-Weld Heat Treatment (PWHT): Welded tubes undergo solution heat treatment to homogenize the weld zone and restore the desired ferrite-austenite ratio.
- Pickling & Passivation: Surface treatment to remove weld discoloration and establish corrosion protection.
- Coiling: Tubes are coiled to order specifications with protective packaging.
Quality Assurance & Critical Testing
Wenzhou Jixing Metal Materials Co., Ltd. implements a comprehensive quality assurance program with emphasis on three critical duplex stainless steel verification parameters:
1. Ferrite Ratio Verification
The ferrite content of every heat is measured using a portable or laboratory-grade ferrite scope in accordance with ASTM A955 / ASTM E1719. The target range is maintained at 35–65 ferrite number (FN) to ensure:
- Adequate weldability (lower ferrite) while maintaining SCC resistance (higher ferrite)
- Optimal balance between toughness and strength
- Prevention of detrimental phase precipitation
2. PREN (Pitting Resistance Equivalent Number) Verification
PREN is calculated from the certified chemical analysis of each heat using the formula:
PREN = %Cr + 3.3 × %Mo + 16 × %N
For the 2205 grade, PREN ≥ 34 is verified; for super duplex (2507), PREN ≥ 40 is confirmed. This quantitative metric provides a reliable predictor of resistance to localized (pitting and crevice) corrosion in chloride environments.
3. Sigma Phase Detection
Sigma phase (FeCr) is a brittle intermetallic compound that can precipitate in duplex stainless steels when exposed to temperatures in the range of 600°C – 1000°C for extended periods. Its presence severely degrades toughness and ductility. Wenzhou Jixing Metal Materials Co., Ltd. performs:
- Macro-etch testing in accordance with ASTM E388 to detect sigma phase formation on transverse and longitudinal sections
- Microstructural examination via metallographic analysis at 100×–500× magnification
- Charpy impact testing to verify toughness is not compromised by phase precipitation
- Strict control of welding and heat treatment parameters to prevent sigma phase formation
Additional Quality Tests
| Test Method | Standard | Purpose |
|---|---|---|
| Chemical Analysis (Spectrometry) | ASTM E415 | Verify full chemical composition |
| Tensile Testing | ASTM A370 | Confirm yield and tensile strength |
| Hardness Testing | ASTM E92 / E18 | Verify hardness within specification |
| Hydrostatic / Pneumatic Testing | ASTM A530 | Detect internal defects and weld integrity |
| Intergranular Corrosion Testing | ASTM A262 | Verify resistance to sensitization |
| Impact Testing | ASTM A370 | Confirm low-temperature toughness |
| Dimensional Inspection | ASTM A789 | OD, wall thickness, and length compliance |
| Surface Inspection | Visual & MPI | Detect surface imperfections |
Applications
ASTM A789 duplex stainless steel coil tube finds critical use across a wide spectrum of high-performance industries:
Oil & Gas Industry
- Subsea production tubing and wellhead components
- Offshore platform structural piping
- Gas separation and processing equipment
- Flow lines and tie-back systems in sour service (H₂S-containing environments)
Chemical & Petrochemical Processing
- Heat exchanger tubes and condensers
- Reactor internals and agitated vessel components
- Acid and alkali handling piping systems
- Chlor-alkali plant equipment
Marine & Offshore Engineering
- Ballast water systems and seawater piping
- Desalination plant feed water and brine circuits
- Shipbuilding structural and piping components
- Harbor and dock infrastructure
Power Generation
- Flue gas desulfurization (FGD) system components
- Heat recovery steam generators (HRSG)
- Condensate and cooling water systems
Food & Pharmaceutical
- High-sanitation processing equipment
- Hygienic piping systems requiring high strength and corrosion resistance
Mineral Processing & Mining
- Sulfuric acid leaching circuits
- Cyanide processing plant components
- Wear and corrosion-resistant structural applications
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and provides the following certifications for every shipment:
- Mill Test Certificate (MTC / EN 10204 3.1): Full chemical analysis, mechanical test results, and heat treatment records
- EN 10204 3.2 Certificate (Third-Party Inspection): Available upon request with independent surveyor verification
- ISO 9001:2