High H₂S Collection & Transportation Pipeline — Stainless Steel Coil Tube (Coiltube)
Product Overview
The High H₂S Collection & Transportation Pipeline Coil Tube is a specialized seamless or welded stainless steel coil tube engineered for the most demanding sour gas environments encountered in upstream and midstream petroleum and petrochemical operations. Designed for service conditions where the hydrogen sulfide (H₂S) partial pressure exceeds 0.0003 MPa and chloride ion (Cl⁻) concentrations are elevated, this product addresses the dual metallurgical threats of Sulfide Stress Cracking (SSC), Hydrogen-Induced Cracking (HIC), and Chloride Stress Corrosion Cracking (Cl-SCC) that plague conventional carbon steel and austenitic stainless steel materials.
Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube product is supplied in continuous coil form to facilitate efficient downstream forming, coiling, and installation processes. The product is specifically qualified for use in sour gas gathering, processing, and transportation infrastructure within acidic gas fields, where exposure to aggressive chemical species demands superior resistance to both uniform and localized corrosion mechanisms.
Material & Properties
Primary Material Grades
Two principal material configurations are offered to meet the full spectrum of sour service requirements:
- Duplex and Super Duplex Stainless Steel (Base Material):
- Duplex 2205 (UNS S31803 / S32205): A 22% chromium, 5% nickel, 3% molybdenum duplex stainless steel offering a dual-phase microstructure of austenite and ferrite. Provides yield strength approximately twice that of conventional austenitic grades (304/316L) while maintaining excellent resistance to Cl-SCC and pitting corrosion. Typical minimum yield strength of 450 MPa with elongation ≥ 25%.
- Super Duplex 2507 (UNS S32750 / S32760): A 25% chromium, 7% nickel, 3% molybdenum super duplex grade with an even higher resistance to pitting (PREN ≥ 40) and Cl-SCC. Minimum yield strength of 550 MPa. Recommended for the most aggressive chloride-containing sour environments.
- Inconel 625 Lining (UNS N06625): A nickel-chromium-molybdenum superalloy (Ni ≥ 58%, Cr 20–23%, Mo 8–10%) applied as an overlay or cladding on carbon steel or low-alloy steel substrates. Inconel 625 provides exceptional resistance to H₂S-induced SSC, HIC, and general corrosion even at elevated temperatures (up to 400°C continuous service). The overlay thickness typically ranges from 1.5 mm to 3.0 mm, applied via Thermal Spray (HVOF), TIG weld overlay, or explosion cladding.
Key Mechanical Properties
| Property | Duplex 2205 | Super Duplex 2507 | Inconel 625 (Overlay) |
|---|---|---|---|
| Yield Strength (min.) | 450 MPa | 550 MPa | 310 MPa (overlay) |
| Tensile Strength (min.) | 550 MPa | 620 MPa | 550 MPa (overlay) |
| Elongation (min.) | 25% | 25% | 30% (overlay) |
| Pitting Resistance Equivalent Number (PREN) | ≥ 34 | ≥ 40 | ≥ 30 (base alloy) |
| Maximum Service Temperature | 300°C | 300°C | 400°C |
| H₂S Partial Pressure Limit | Unlimited (per NACE MR0175) | Unlimited (per NACE MR0175) | Unlimited (per NACE MR0175) |
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Coil Tube for Sour Gas Collection & Transportation |
| Material Options | Duplex 2205 (UNS S31803) / Super Duplex 2507 (UNS S32750) / Carbon Steel with Inconel 625 (UNS N06625) Lining |
| Outer Diameter (OD) | Φ21.3 mm – Φ114.3 mm (configurable per project requirement) |
| Wall Thickness | 1.5 mm – 8.0 mm (standard); up to 12.0 mm upon request |
| Coil Length | 15 m – 60 m per coil (adjustable) |
| Coil Weight | Up to 10,000 kg per coil |
| Manufacturing Standard | ASTM A790 / ASTM A791 / ASTM A312 / EN 10217-7 / EN 10216-5 |
| Forming Standard | ASTM A398 / EN 10219-2 (Cold-formed) |
| H₂S Partial Pressure Service | > 0.0003 MPa (Full sour service compliance) |
| Chloride Environment | High Cl⁻ concentration (up to 100,000 ppm in process fluids) |
| Temperature Range | -46°C to +300°C (duplex grades); -46°C to +400°C (Inconel 625 lined) |
| Pressure Rating | Per ASME B31.3 / B31.8 design code (PN16 – PN100 equivalent) |
| Surface Finish | Pickled and Passivated (2A finish) / Mirror polished upon request |
| End Condition | Plain end / Beveled end / Threaded (NPT/BSP) / Coupling ready |
| Coating (External) | Optional: 3PE / FBE / Polyurethane external coating for buried or subsea applications |
Manufacturing Process
The production of this specialized coil tube follows a rigorous multi-stage manufacturing sequence to ensure metallurgical integrity and dimensional accuracy:
- Raw Material Selection & Inspection: Certified ingots or mill products from approved suppliers are subjected to spectroscopic chemical analysis (OES) and mechanical property verification prior to acceptance. All raw materials must carry valid mill test certificates (MTC) compliant with EN 10204 Type 3.1.
- Hot Rolling / Pipe Blank Preparation: Billet or strip stock is hot-rolled to the required dimensions. For seamless variants, hot-forged pipe blanks are prepared for subsequent piercing.
- Cold Forming / Coiling: Flat strip or pre-formed pipe sections are cold-formed into the final coil tube geometry using precision roll-forming equipment. Tight dimensional tolerances (±0.1 mm wall thickness, ±0.5 mm OD) are maintained throughout the forming process.
- Heat Treatment (Solution Annealing): Duplex grades are solution-annealed at 1020–1150°C followed by rapid water quench to achieve the optimal 40–60% austenite/ferrite phase balance. This critical step prevents sigma phase precipitation and ensures full SSC resistance.
- Inconel 625 Overlay Application (if applicable): The Inconel 625 cladding is applied via one of the following methods:
- High-Velocity Oxygen Fuel (HVOF) Thermal Spray: Powder feedstock is sprayed at supersonic velocities, producing dense overlays with excellent metallurgical bond strength (≥ 15 MPa adhesion).
- TIG Weld Overlay: Multi-pass gas tungsten arc welding with ERNiCrMo-3 consumable wire, followed by machining to final overlay thickness.
- Explosion Cladding (Exploting): High-strain-rate bonding of Inconel 625 sheets onto carbon steel substrates, achieving diffusion-bonded interfaces with minimal dilution.
- Pickling & Passivation: All stainless steel surfaces undergo hydrofluoric/nitric acid pickling to remove surface scale, followed by passivation to establish a protective chromium oxide film (≥ 100 nm thickness).
- Final Quality Inspection: Comprehensive testing including ultrasonic testing (UT) for internal defects, magnetic particle inspection (MT) for surface discontinuities, hardness testing (HV 250 max. for NACE compliance), and dimensional verification per ASTM A398.
Applications
Primary Application Domain: Acidic Gas Fields (Sour Gas)
This coil tube product is purpose-engineered for the following sour service applications in petroleum and petrochemical operations:
- Sour Gas Gathering & Collection Pipelines: Transportation of produced gas containing H₂S partial pressures exceeding 0.0003 MPa from wellheads to processing facilities. The coil form enables efficient routing through complex field layouts with minimal welding joints.
- Gas Processing & Sweetening Plants: Internal piping for amine treating units, acid gas regeneration systems, and sulfur recovery facilities where Cl⁻ contamination from corrosion inhibitors or produced water is prevalent.
- Separator & Scrubber Internals: Coil-formed heat exchangers, reflux drums, and separator internals exposed to wet H₂S and chloride-rich condensate.
- Wellhead & Flowline Assemblies: High-pressure flowlines, Christmas tree connections, and blowout preventer (BOP) accessory piping in sour wells.
- Offshore Sour Gas Platforms: Subsea and topside piping systems where space constraints favor coil tube deployment and where Cl⁻ from seawater ingress compounds sour service aggressiveness.
- Refinery Sour Water Systems: Collection and transport of sour water containing dissolved H₂S, HS⁻, and Cl⁻ from distillation and hydrotreating units.
Environmental Conditions Addressed
| Corrosion Mechanism | Trigger Condition | Material Solution |
|---|---|---|
| Sulfide Stress Cracking (SSC) | H₂S partial pressure > 0.0003 MPa, low-hardness carbon steel | 2205/2507 Duplex (hardness ≤ 250 HV) / Inconel 625 overlay |
| Hydrogen-Induced Cracking (HIC) | H₂S + water + steel microstructure imperfections | 2205/2507 Duplex (inherently resistant) / Inconel 625 overlay |
| Chloride Stress Corrosion Cracking (Cl-SCC) | Cl⁻ > 50 ppm + temperature > 60°C + tensile stress | 2205/2507 Duplex (PREN ≥ 34/40) / Inconel 625 overlay |
| Pitting & Crevice Corrosion | Localized Cl⁻ concentration under deposits/biostatic films | 2507 Super Duplex (PREN ≥ 40) / Inconel 625 overlay |
| Hydrogen Embrittlement (HE) | High-strength steels in wet H₂S at low temperature | 2205/2507 Duplex (controlled hardness) / Inconel 625 overlay |
Quality Certifications & Compliance
NACE MR0175 / ISO 15156 Full Compliance
All materials, manufacturing processes, and finished products conform to the NACE International MR0175/ISO 15156 standard — "Materials for Use in H₂S-Containing Environments in Oil and Gas Production — Part 1: Criteria for Selecting Cracking-Resistant Materials." This comprehensive certification covers:
- Section 1 (Criteria for Selecting Cracking-Resistant Materials): Full material selection compliance for sour service, including hardness limits (≤ 250 HV for duplex grades, ≤ 22 HRC for Inconel 625 overlay), chemical composition requirements, and impact testing criteria.
- Section 2 (Criteria for Selecting Cracking-Resistant Materials for Carbon Steel): Applicable where carbon steel substrates are used with Inconel 625 overlay; full compliance with impact energy requirements (27 J at -46°C per ASTM A370).
- Section 3 (Welding and Weld Repair): Weld procedures qualified per NACE MR0175 requirements; all weld consumables certified for sour service compatibility.
- Section 4 (Heat Treatment): Solution annealing procedures documented and verified per standard requirements.
- Section 5 (Other Joining Processes): Braze, adhesive, and mechanical joining methods (if applicable) qualified per standard.
- Section 6 (Materials Not Covered): Non-applicable — all materials used are explicitly covered by NACE MR0175.
Additional Certifications & Standards
- ASTM A790: Standard Specification for Ferritic/Austenitic (Duplex) Stainless Steel Welded Pipes
- ASTM A791: Standard Specification for Ferritic/Austenitic (Duplex) Stainless Steel Seamless Pipes
- AST