316L Stainless Steel Coil Tube for Amine Regeneration Tower Reboiler
Product Overview
This high-performance stainless steel coil tube is specifically engineered for deployment in amine regeneration tower reboilers within natural gas processing facilities. Designed to withstand the aggressive chemical environment created by Monoethanolamine (MEA) and N-Methyldiethanolamine (DEA) solutions operating at temperatures ranging from 120°C to 150°C, this coil tube system addresses the critical challenge of acid gas (CO₂/H₂S) loading and the corrosive effects of amine degradation products. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this product represents a reliable solution for sour gas treatment applications in the petrochemical and natural gas processing industries.
The coil tube configuration provides maximum heat transfer surface area within a compact footprint, making it ideal for reboiler duty where efficient thermal energy exchange is paramount. The seamless construction eliminates weld seams that could serve as initiation sites for localized corrosion in the presence of amine degradation byproducts such as heat-stable salts (HSS), carbamate polymers, and iron sulfide particulates.
Material & Properties
Base Alloy: ASTM A312/A213 Type 316L (UNS S31603)
Type 316L is the super-low carbon variant of the 316 austenitic stainless steel family, specifically selected for its superior resistance to intergranular corrosion and pitting attack in chloride-containing, acidic environments. The low carbon content (≤0.03%) ensures that the alloy maintains its mechanical and corrosion resistance properties even after exposure to the elevated temperatures encountered during amine regeneration.
Chemical Composition (wt%)
| Element | Specification | Minimum | Maximum |
|---|---|---|---|
| Carbon (C) | Super-low carbon grade | — | 0.030 |
| Manganese (Mn) | — | — | 2.00 |
| Silicon (Si) | — | — | 1.00 |
| Chromium (Cr) | Primary passivation element | 16.00 | 18.00 |
| Nickel (Ni) | Austenite stabilizer | 10.00 | 14.00 |
| Molybdenum (Mo) | Pitting & crevice corrosion resistance | 2.00 | 3.00 |
| Nitrogen (N) | — | — | 0.10 |
| Phosphorus (P) | — | — | 0.045 |
| Sulfur (S) | — | — | 0.030 |
Mechanical Properties
| Property | Specification | Value |
|---|---|---|
| Tensile Strength (Rm) | ASTM A213 / A312 | ≥ 485 MPa (70 ksi) |
| Yield Strength (Rp0.2) | 0.2% offset | ≥ 170 MPa (25 ksi) |
| Elongation (A) | 50 mm gauge length | ≥ 35% |
| Density | — | 8.0 g/cm³ |
| Thermal Conductivity | At 100°C | ~16.3 W/(m·K) |
| Thermal Expansion Coefficient | 100°C | ~17.5 × 10⁻⁶ /°C |
| Service Temperature Range | Designed for | −40°C to 300°C |
Corrosion Resistance Characteristics
- Molybdenum enrichment (2.0–3.0%) provides enhanced resistance to pitting and crevice corrosion in chloride-rich amine solutions
- Low carbon content (≤0.03%) prevents chromium carbide precipitation at weld boundaries, maintaining intergranular corrosion resistance during heat exposure
- Passive oxide film (Cr₂O₃) self-repairs in aerated environments, providing long-term protection against acid gas attack
- Resistance to amine degradation products including heat-stable salts (HSS), organic acids, and polymeric degradation compounds
- Susceptibility note: While 316L provides excellent general corrosion resistance, prolonged exposure to highly concentrated heat-stable salts at temperatures above 150°C may require monitoring for crevice corrosion at coil supports and connection points
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Type | Coil Tube (盘管) | — |
| Material Grade | 316L Stainless Steel (UNS S31603) | ASTM A312 / A213 |
| Tube Construction | Seamless (无縫管) | ASTM A213 TP316L |
| Tube Diameter Range | 1/2" – 3" (OD) | ASTM A53 / ASME B36.19M |
| Wall Thickness Range | Schedule 40 – Schedule 80 | ASME B36.19M |
| Coil Diameter | Custom (typically 600 mm – 2400 mm) | Per project specification |
| Coil Length | Custom (typically 10 m – 100 m per coil) | Per project specification |
| Surface Finish | Mill finish / Pickled & Passivated | ASTM A967 |
| Operating Temperature | 120°C – 150°C | Process design parameter |
| Operating Pressure | Up to 4.0 MPa (design) | ASME Section VIII |
| Service Fluid | MEA / DEA amine solution with CO₂/H₂S loading | — |
| End Connections | Threaded (NPT/BSP) / Flanged / Socket-welded | ASME B16.5 / B16.11 |
| Heat Treatment | Solution annealed (1050–1150°C) + water quench | ASTM A312 |
Manufacturing Process
- Raw Material Selection: High-purity 316L seamless tubes are procured from certified mills with full traceability documentation. Incoming material undergoes spectroscopic verification (PMI) to confirm chemical composition compliance with ASTM A312/A213 requirements.
- Dimensional Inspection: Tubes are measured for outer diameter (OD), wall thickness (WT), and straightness tolerance. Ultrasonic testing (UT) is performed to detect internal defects, inclusions, or laminations.
- Coil Forming (Bending): Cold bending is executed using precision CNC coil winding equipment to achieve the specified coil diameter and pitch. The bending process is controlled to prevent excessive work hardening, maintaining the material's ductility and corrosion resistance. Minimum bend radius is maintained at ≥ 5× OD to avoid ovalization and stress concentration.
- Post-Forming Stress Relief: Following coil formation, a controlled stress relief anneal is performed to eliminate residual stresses introduced during bending, ensuring dimensional stability during thermal cycling in service.
- Surface Treatment: The coil tube undergoes pickling and passivation treatment per ASTM A967 to remove oxide scale, mill residue, and any surface contamination. A protective passive chromium oxide film is established to maximize corrosion resistance.
- End Preparation: Tube ends are cut square, deburred, and prepared for the specified connection type (threading, welding, or flanging). End connections are fabricated per applicable ASME standards.
- Final Quality Assurance: Completed coil tubes undergo hydrostatic pressure testing (typically 1.5× design pressure), visual inspection, and dimensional verification. Non-destructive testing (NDT) may include dye penetrant testing (PT) at weld connections.
Applications
Primary Application: Amine Regeneration Tower Reboiler
The coil tube is installed within the reboiler of an amine regeneration (stripping) tower in a natural gas sweetening plant. Hot process water or steam transfers thermal energy through the coil tube walls to the amine solution, regenerating the spent solvent by driving off absorbed acid gases (CO₂ and H₂S).
Operating Environment Details
- Primary Solvents: Monoethanolamine (MEA, C₂H₇NO) and N-Methyldiethanolamine (DEA, C₅H₁₃NO₂)
- Absorbed Species: Carbon dioxide (CO₂) and hydrogen sulfide (H₂S) at varying loading ratios (typically 0.3–0.5 mol acid gas/mol amine)
- Operating Temperature: 120°C – 150°C (reboiler duty cycle)
- Corrosive Agents: Heat-stable salts (HSS), formic acid, acetic acid, polymeric degradation products, iron sulfide (FeS) particulates, and chlorides from upstream contamination
Secondary Applications
- Natural gas dehydration and acid gas removal systems
- Refinery sour water stripper reboilers
- Ammonia stripping unit heat exchangers
- Biochemical processing equipment handling amine-based media
Quality Certifications
Standards Compliance
- ASTM A312: Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipe, Tube, and Hollow Shapes
- ASTM A213: Standard Specification for Seamless Austenitic Chromium-Chromium-Nickel Alloy Heat-Transfer, Heat-Distributor, and Exchanger Tubing
- ASME B36.19M: Welded and Seamless Wrought Steel Pipe (dimensional reference)
- ASTM A967: Chemical Passivation of Stainless Steel Parts
- ASME Section VIII: Pressure Vessel Code (design and fabrication)
- ISO 9001:2015: Quality Management System certification
- EN 10216-5: Tubes for heat exchangers and heat distributors (European equivalent)
Testing & Certification Documentation
- Mill Test Reports (MTR) with full chemical and mechanical property data
- Positive Material Identification (PMI) via X-ray Fluorescence (XRF) spectroscopy
- Ultrasonic Testing (UT) reports for internal defect detection
- Hydrostatic test certificates at 1.5× design pressure
- Dye Penetrant Testing (PT) reports for surface defect detection
- Third-party inspection (TPI) available upon request
- Material traceability documentation from mill to final product
Unique Selling Points
- Seamless Construction: Eliminates weld seams entirely, removing the primary vulnerability point for localized corrosion in aggressive amine environments — a critical advantage over welded alternatives
- 316L Super-Low Carbon Grade: Superior resistance to intergranular corrosion compared to standard 316, ensuring long-term integrity at reboiler operating temperatures (120–150°C)
- Molybdenum-Enhanced Pitting Resistance: The 2.0–3.0% Mo content provides significantly enhanced resistance to chloride-induced pitting from heat-stable salt accumulation
- Application-Specific Engineering: Coil geometry optimized for maximum heat transfer efficiency in amine regeneration reboiler duty, reducing thermal cycling fatigue
- Full Traceability: Complete material documentation from raw steel mill through final fabrication, enabling lifecycle corrosion monitoring and maintenance planning
- Anti-Degradation Product Corrosion: Specifically designed to resist the unique corrosive cocktail of amine degradation byproducts (HSS, organic acids, polymers) that accelerate failure in conventional carbon steel or 304-grade alternatives
Engineering Note: While Type 316L provides excellent corrosion resistance in amine service, operators should implement a comprehensive corrosion monitoring program including periodic eddy current wall thickness measurements, iron count monitoring in amine solution, and HSS analysis. For extreme service conditions with high HSS concentrations (>1000 ppm), consideration of higher-alloy alternatives (e.g., duplex 2205 or super-austenitic 6Mo) may be warranted for extended asset life.