Titanium Coil Tube (Ti Coil Tube) — Technical Product Specification
1. Product Overview
The Titanium Coil Tube (hereinafter referred to as "Ti Coil Tube") is a precision-engineered coiled tubular product manufactured from high-purity titanium or titanium alloy stock. Produced by Wenzhou Jixing Metal Materials Co., Ltd., this product is specifically designed for use in shell-and-tube heat exchangers, condensers, evaporators, and other thermal exchange systems operating in highly corrosive environments. The coil geometry maximizes heat transfer surface area within a compact volumetric footprint, making it an indispensable component in chemical processing, marine engineering, and pharmaceutical manufacturing sectors.
This specification document synthesizes critical technical knowledge derived from the study and practice of titanium coil tube welding (钛盘管的焊接), emphasizing the metallurgical, mechanical, and process considerations that govern the fabrication, assembly, and performance assurance of titanium coil tube assemblies.
2. Material & Properties
Titanium coil tubes are predominantly fabricated from commercially pure titanium (CP Ti) grades or titanium alloys, each selected based on the specific service conditions. The following table summarizes the principal material grades and their characteristic properties:
| Grade (ASTM B381 / B348) | Composition Highlights | Tensile Strength (MPa, min.) | Elongation (%) | Maximum Service Temperature (°C) | Corrosion Resistance Rating |
|---|---|---|---|---|---|
| Grade 1 (CP Ti-1) | ≥99.5% Ti, ≤0.25% Fe, ≤0.20% O | 240 | 25 | 300 | Excellent in chloride, seawater, and oxidizing acids |
| Grade 2 (CP Ti-2) | ≥99.0% Ti, ≤0.30% Fe, ≤0.30% O | 275 | 20 | 350 | Superior in seawater, brine, and dilute mineral acids |
| Grade 5 (Ti-6Al-4V) | 6% Al, 4% V, balance Ti | 895 | 9 | 400 | Good; enhanced mechanical strength for high-pressure service |
| Grade 7 (CP Ti-7) | ≥99.0% Ti, 0.12–0.25% Pd | 345 | 20 | 300 | Exceptional resistance to reducing acids (HCl, H₂SO₄) |
| Grade 12 (CP Ti-12) | ≥99.0% Ti, 0.10–0.25% Pd | 380 | 15 | 300 | Outstanding resistance to hot reducing acids |
Key Metallurgical Characteristics
- Specific Strength: Titanium alloys exhibit an exceptional strength-to-weight ratio, approximately 60% higher than steel at half the density (4.5 g/cm³ vs. 7.8 g/cm³).
- Passive Oxide Film: The naturally formed titanium dioxide (TiO₂) passive layer provides outstanding corrosion resistance in a wide range of aggressive chemical environments, including seawater, chlorinated media, and dilute mineral acids.
- Low Thermal Conductivity: At approximately 6.7 W/(m·K) for Grade 2 Ti, thermal conductivity is significantly lower than copper or steel, which must be accounted for in heat exchanger design.
- Galvanic Compatibility: Titanium is cathodic relative to most structural metals (carbon steel, stainless steel, aluminum), necessitating careful consideration of galvanic corrosion in mixed-material assemblies.
3. Specifications
| Parameter | Specification / Range | Applicable Standard |
|---|---|---|
| Outer Diameter (OD) | 1.5 mm – 25.0 mm (custom available up to 50 mm) | ASTM B381 / B348 |
| Wall Thickness | 0.3 mm – 3.0 mm | ASTM B381 / B348 |
| Coil Pitch | 15 mm – 80 mm (adjustable per design) | Customer specification |
| Coil Diameter | 30 mm – 300 mm | Customer specification |
| Tube Length (per coil) | 5 m – 50 m (continuous coil) | Customer specification |
| Pressure Rating | Up to 2.5 MPa (depending on grade and wall thickness) | ASME Section VIII Div. 1 |
| Surface Finish | Inside Ra ≤ 1.6 μm; Outside Ra ≤ 3.2 μm (standard); Ra ≤ 0.4 μm (electropolished) | ASTM B381 |
| Welding Method | Tungsten Inert Gas (TIG) / Gas Tungsten Arc Welding (GTAW), ASTM B370 | ASTM B370 / AWS D10.9 |
| Weld Filler Wire | ASTM B335 Grade 2 or Grade 5 Ti wire (matching base metal) | ASTM B335 |
| Shielding Gas | High-purity Argon (Ar ≥ 99.99%) or Helium (He ≥ 99.99%) | AWS D10.9 |
| Residual Oxygen in Weld Zone | ≤ 20 ppm (background); ≤ 50 ppm (weld atmosphere) | AWS D10.9 |
4. Manufacturing Process
The production of titanium coil tubes involves a multi-stage process chain that demands rigorous contamination control, particularly during forming and welding operations. The following describes the principal process steps:
4.1 Raw Material Preparation
- Ingot Smelting: Titanium sponge is melted via vacuum arc remelting (VAR) or electron beam melting (EBM) in a controlled atmosphere to produce high-purity master ingots conforming to ASTM B348 specifications.
- Hot Rolling & Extrusion: Ingots are hot-rolled or extruded into seamless tube blanks with the desired outer diameter and wall thickness tolerances.
- Cold Drawing & Sizing: Tubes undergo cold drawing to achieve precise dimensional tolerances (typically ±0.05 mm on OD and ±0.02 mm on wall thickness) and to induce work hardening for enhanced mechanical properties.
- Annealing: Stress-relief annealing at 550–650 °C in a vacuum or argon atmosphere eliminates residual cold-work stresses and restores ductility.
4.2 Coil Forming
- Coiling Machine Setup: The straight titanium tube is fed into a precision coiling machine equipped with hardened guide rolls to ensure uniform pitch and coil diameter.
- Forming Parameters: The minimum bending radius must not be less than 3× the tube outer diameter (3D) for CP Ti grades to prevent wall thinning or ovality exceeding 5%.
- Springback Compensation: The coiling die geometry is pre-adjusted to account for titanium's elastic springback, ensuring the final coil pitch meets specification after release.
4.3 Welding — Critical Process Knowledge
Welding is the most technically demanding operation in titanium coil tube assembly. The following principles, derived from the study of titanium coil tube welding (钛盘管的焊接), are fundamental:
- Atmospheric Protection: Titanium is extremely susceptible to oxidation and nitrogen pickup above 400 °C. A dual shielding system is mandatory:
- Primary Shield: A concentrated argon (Ar ≥ 99.99%) gas lance at the weld arc, with a flow rate of 10–20 L/min.
- Back Purge: Argon gas purged through the tube interior at a flow rate of 5–10 L/min to protect the inner surface from oxidation. For coil tubes, the purge must be continuous along the entire length during welding.
- Welding Technique (GTAW / TIG):
- DC polarity (non-consumable tungsten electrode negative) is used for stable arc and deep penetration.
- Electrode diameter: 1.6–3.2 mm depending on wall thickness.
- Travel speed: 50–150 mm/min to minimize heat input and reduce grain coarsening.
- Heat input should be kept below 1.5 kJ/mm to preserve the microstructure and avoid excessive HAZ (Heat-Affected Zone) softening.
- Filler Wire Selection: Filler metal must be the same grade or a compatible grade per ASTM B335. The filler wire must be cleaned with a titanium-compatible abrasive and inspected for surface contamination prior to use.
- Weld Defect Prevention:
- Oxidation (blue/purple discoloration): Indicates oxygen ingress; weld is unacceptable per ASTM B370.
- Porosity: Caused by inadequate purge or contaminated surfaces; requires re-welding.
- Cracking: Can occur in high-strength alloys (e.g., Grade 5) due to excessive cooling rates; preheating to 150–250 °C may be necessary.
- Post-Weld Inspection: Visual inspection (VT) per AWS D10.9, supplemented by dye penetrant testing (PT) for surface defects and radiographic testing (RT) for critical joints. The weld surface must exhibit a uniform straw-gold or silver color; any blue, purple, or gray discoloration indicates unacceptable oxidation.
4.4 Post-Weld Heat Treatment (if required)
For high-strength alloy grades (e.g., Grade 5 Ti-6Al-4V), a solution treatment at 950–1050 °C followed by aging at 540–590 °C may be applied to achieve optimal mechanical properties. CP Ti grades typically do not require post-weld heat treatment but may undergo stress-relief annealing at 550 °C for 1 hour in argon or vacuum.
4.5 Surface Treatment & Finishing
- Pickling & Passivation: Removal of any residual oxide or weld discoloration using a dilute hydrofluoric-nitric acid (HF-HNO₃) solution, followed by passivation in nitric acid (HNO₃) to restore the protective TiO₂ film.
- Electropolishing (optional): For pharmaceutical and food-grade applications, electropolishing achieves an internal surface roughness of Ra ≤ 0.4 μm.
5. Applications
Titanium coil tubes find critical application in industries where corrosion resistance, lightweight construction, and biocompatibility are paramount:
- Chemical Processing: Heat exchangers for handling hydrochloric acid (HCl), sulfuric acid (H₂SO₄), hydrofluoric acid (HF), and other aggressive chemicals. Titanium coil tubes in reactors and condensers for the chlor-alkali, titanium dioxide (TiO₂) production, and petrochemical industries.
- Marine & Offshore Engineering: Seawater coolers, condensers for ship engines, and heat exchangers for offshore oil platforms where resistance to chloride-induced pitting and crevice corrosion is essential.
- Power Generation: Condensers in nuclear power plants and coastal thermal power stations utilizing seawater as a cooling medium.
- Pharmaceutical & Biomedical: Heat exchangers in pharmaceutical manufacturing processes requiring clean, non-reactive, and biocompatible materials. Titanium's non-toxicity and excellent corrosion resistance make it ideal for CIP (Clean-In-Place) compatible systems.
- Food & Beverage Industry: Pasteurizers, evaporators, and heat exchangers in dairy, brewery, and seafood processing where contact with acidic or saline food products is routine.
- Desalination: Multi-stage flash (MSF) and multi-effect distillation (MED) systems where titanium coil tubes serve as the primary heat transfer elements in contact with brine and seawater.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. adheres to internationally recognized quality standards and certifications to ensure product conformity and traceability:
- ISO 9001:2015 — Quality Management System (QMS) certification for consistent manufacturing quality.
- ISO 14001:2015 — Environmental Management System (EMS) certification for environmentally responsible operations.
- ASTM B381 / B348 Compliance — Full material conformity with ASTM specifications for titanium and titanium alloy tube.
- ASTM B370 Compliance — Welding procedures and welder qualification per ASTM B370 for titanium and titanium alloy welding.
- AWS D10.9 Compliance — Welding procedures conforming to AWS D10.9 for titanium and titanium alloy welding.
- ASME Section VIII Div. 1 — Pressure vessel and heat