316L Seamless Stainless Steel Coil Tube for Amine Regeneration Tower Reboiler
Product Overview
The 316L seamless stainless steel coil tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is purpose-engineered for use in amine regeneration tower reboilers within natural gas processing facilities. These coil tubes serve as critical heat exchange elements in acid gas removal systems where they are continuously exposed to harsh aqueous environments containing monoethanolamine (MEA) and diethanolamine (DEA) solutions operating at temperatures ranging from 120°C to 150°C. The tubes are designed to withstand the aggressive chemical environment generated by CO₂ and H₂S loading while maintaining long-term structural integrity and corrosion resistance.
This product addresses one of the most challenging corrosion scenarios encountered in petrochemical processing — the combined attack from amine solutions, their degradation products, and dissolved acid gases under elevated thermal conditions.
Material & Properties
Base Alloy — AISI 316L (UNS S31603)
The selection of 316L low-carbon austenitic stainless steel is driven by its superior resistance to pitting and crevice corrosion in chloride-containing amine environments. Key metallurgical features include:
- Molybdenum (Mo) content of 2.0–3.0%: Provides enhanced resistance to localized corrosion, particularly against chloride-induced pitting and amine degradation products such as carboxylic acids and thiodiglycolates.
- Low carbon grade (≤0.03% C): Eliminates the risk of intergranular corrosion during welding and heat treatment operations, ensuring weld zone integrity.
- Chromium (Cr) content of 16.5–18.5%: Forms a robust passive oxide film that self-heals in oxidizing environments.
- Nickel (Ni) content of 10.0–14.0%: Stabilizes the austenitic microstructure and improves resistance to stress corrosion cracking.
- Maximum service temperature: Up to 870°C in continuous air service; recommended operating range for amine service is well below 200°C.
Corrosion Resistance Considerations
In amine regeneration systems, the primary corrosion mechanisms include:
- General (uniform) corrosion due to hot amine solution attack
- Pitting and crevice corrosion from chloride ions and degradation products (e.g., methanesulfonic acid, N-methyldiethanolamine)
- Under-deposit corrosion caused by deposition of degradation products and heat transfer inhibitors on tube surfaces
- Stress corrosion cracking (SCC) in sensitized zones, mitigated by the low-carbon grade
Specifications
| Parameter | Specification |
|---|---|
| Product Type | Coil Tube (盘管) |
| Material Grade | AISI 316L / UNS S31603 |
| Tube Type | Seamless (no longitudinal weld) |
| Outer Diameter (OD) | Custom (typically 19 mm, 25 mm, 32 mm) |
| Wall Thickness | Custom (typically 2.0–4.0 mm) |
| Coil Diameter | Custom per design requirement |
| Operating Temperature | 120°C – 150°C |
| Service Medium | MEA / DEA aqueous solution with CO₂ and H₂S loading |
| Surface Finish | Pickled and passivated (Ra ≤ 0.8 μm) |
| Applicable Standards | ASTM A269 / A213, ASME SB-269 / SB-213 |
| Manufacturing Standard | EN 10216-5, GB/T 12771 |
| Length / Coil Length | Custom as per reboiler design |
Manufacturing Process
The production of 316L seamless coil tubes follows a rigorous multi-stage process to ensure dimensional accuracy, metallurgical homogeneity, and surface integrity:
- Hot Rolling & Piercing: Continuous casting slabs are reheated and hot-rolled into seamless hollow bars through a piercing mill, establishing the initial tube geometry.
- Hot Elongation: Tubes are drawn through a plug mill to achieve the target outer diameter and wall thickness with controlled reduction ratios.
- Annealing & Pickling: Solution annealing at 1050–1150°C followed by water quenching restores full austenitic structure. Subsequent acid pickling removes scale and oxide layers.
- Passivation: Nitric acid or citric acid passivation treatment establishes a clean, chromium-enriched passive film on the surface.
- Cold Drawing (if applicable): For tighter tolerances, cold drawing reduces dimensions to final specifications while maintaining the seamless integrity.
- Coiling / Forming: The straight tube is formed into the required coil geometry using precision bending equipment to avoid deformation, kinking, or work-hardening.
- Post-Forming Inspection: Visual and dimensional inspection of coil geometry, surface condition, and mechanical integrity.
Applications
Primary Application: Natural Gas Processing — Amine Regeneration Tower Reboilers
In natural gas sweetening units, amine regeneration towers (also known as "strippers") utilize reboilers to thermally regenerate rich amine solutions by stripping dissolved CO₂ and H₂S. The coil tubes function as the heat transfer medium within these reboilers, absorbing heat from the process stream to regenerate the lean amine for continuous acid gas removal.
Specific Operating Conditions:
- Aqueous MEA (typically 15–30 wt%) or DEA (typically 20–50 wt%) solutions
- Reboiler bottom temperature: 120–150°C
- Potential presence of degradation products: methanesulfonic acid (MSA), thiodiglycol (TDA), nitrates, and carboxylic acids
- Chloride contamination from upstream water injection or makeup water
- Operating pressure: typically 0.3–1.0 MPa
Secondary Applications:
- Refinery acid gas removal unit (AARU) reboilers
- Chemical plant amine circulation systems
- Hydrocarbon processing units with sour water service
Quality Certifications & Testing
Wenzhou Jixing Metal Materials Co., Ltd. adheres to international quality management and product certification standards:
- ISO 9001:2015 — Quality Management System certification
- ISO 3834 — Welding quality requirements (where applicable)
- Material Test Reports (MTR) — Full chemical composition and mechanical property verification per heat lot
- Positive Material Identification (PMI) — Spectrographic confirmation of alloy grade
- Non-Destructive Testing (NDT) — Eddy current testing and/or ultrasonic testing for seamless tube wall integrity
- Hydrostatic Testing — Pressure testing to verify weld-free integrity of each tube length
- Corrosion Testing — Available upon request: pitting resistance index (PREN ≥ 24), CPT (Critical Pitting Temperature) testing
- Compliance: ASTM A269 / A213, ASME SB-269 / SB-213, EN 10216-5
Unique Selling Points
- Seamless construction eliminates longitudinal weld seams — the primary initiation site for stress corrosion cracking and intergranular attack in amine service.
- 316L low-carbon grade provides superior resistance to intergranular corrosion compared to standard 316, critical for welded assemblies and heat-affected zones.
- 2%+ molybdenum alloying specifically targets the pitting and crevice corrosion mechanisms prevalent in degraded amine environments.
- Precision coiling with controlled forming parameters ensures uniform wall thickness and avoids cold-work hardening that could accelerate localized corrosion.
- Pickled and passivated surface finish provides an immediately corrosion-resistant oxide layer, reducing induction period for pitting initiation.
- Full traceability from mill heat number through final coil identification, supporting lifecycle corrosion monitoring and inspection planning.
Engineering Note: While 316L provides excellent general performance in amine reboiler service, operators should implement a monitoring program for amine degradation products. Periodic inspection of tube wall thickness (particularly at low-flow zones and under-deposit areas) is recommended. For severely degraded amine systems with high chloride content, consideration of higher-alloy alternatives (e.g., duplex stainless steel or Alloy 625) may be warranted for critical applications.