Ultra-Pure Water (UPW) Final Rinse Process for Stainless Steel Coil Tubes

This document describes the proprietary Ultra-Pure Water (UPW) final rinse process applied to the internal surface of stainless steel coil tubes (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This critical final cleaning stage ensures that the inner bore of the tubing meets the stringent contamination control requirements demanded by the semiconductor, biopharmaceutical, and ultra-high purity fluid delivery industries.

Product Overview

The Ultra-Pure Water Final Rinse is the terminal internal surface treatment process in the manufacturing sequence of high-purity stainless steel coil tubes. Following initial mechanical forming, welding, and pre-cleaning operations, the tubing undergoes a multi-stage chemical cleaning protocol culminating in a final rinse with 18.2 MΩ·cm Ultra-Pure Water (UPW), followed by inert nitrogen (N₂) blow-drying. This process eliminates residual ions, particulates, and organic contaminants from the tube bore, achieving a surface cleanliness level suitable for the most demanding applications in semiconductor manufacturing and biopharmaceutical processing.

The coil tube configuration (Coiltube) provides inherent advantages over straight tubing, including superior flexibility for complex routing, reduced installation footprint, and enhanced thermal management in process systems. The UPW final rinse process is specifically optimized for the coiled geometry to ensure complete internal wetting and uniform drying throughout the entire coil length.

Material & Properties

Base Material

Post-Process Surface Characteristics

Specifications

Parameter Specification Test Method
UPW Resistivity 18.2 MΩ·cm (at 25 °C) ASTM D1126 / ISO 9459
UPW Conductivity ≤ 0.055 μS/cm Online conductivity probe
Nitrogen Purity (Blow-Dry) ≥ 99.999% (5N) or higher Gas chromatography / O₂ analyzer
Rinse Volume per Unit Length ≥ 5 tube volumes (minimum) Process verification
Final Residual Metal Ions < 1 ppb (Fe, Cr, Ni, Mo) ICP-MS (Inductively Coupled Plasma Mass Spectrometry)
Final TOC < 10 ppb UV-Fluorescence TOC Analyzer
Particulate (≥ 0.5 μm) < 1 particle / 100 mL Laser Particle Counter
Endotoxin Level < 0.25 EU/mL (biopharma grade) LAL (Limulus Amebocyte Lysate) Assay
Tube Diameter Range Φ1.5 mm – Φ50.8 mm (1/16" – 2") Caliper / Optical measurement
Wall Thickness Range 0.25 mm – 3.0 mm Ultrasonic thickness gauge
Coil Outer Diameter 200 mm – 600 mm (customizable) Physical measurement
Process Temperature (Rinse) 20 °C – 25 °C (controlled) Process monitoring
Shelf Life (Post-Clean, Sealed) ≥ 12 months with nitrogen inerting Accelerated aging study

Manufacturing Process

Process Flow

  1. Material Receiving & Inspection: Incoming stainless steel strip/tube material is verified against mill certificates (MTC) for chemical composition, mechanical properties, and physical dimensions.
  2. Cold Drawing & Forming: The seamless tube is cold-drawn to precise internal and external dimensions, then coiled to the specified coil diameter using CNC-controlled coiling equipment.
  3. Welding (if applicable):strong> Butt-welded or orbital-welded joints are performed under inert gas shielding, followed by internal grinding and polishing to achieve seamless-equivalent surface integrity.
  4. Pre-Cleaning: Initial degreasing with alkaline solution removes oils, lubricants, and processing residues. The tube is then rinsed with deionized (DI) water.
  5. Chemical Cleaning: The tube undergoes immersion in acid cleaning solutions (typically a mixture of nitric acid HNO₃ and hydrofluoric acid HF, or proprietary citric acid-based formulations) to remove oxide scales, metal contamination, and surface deposits.
  6. Passivation: Following acid cleaning, the tube is passivated using nitric acid (HNO₃) or citric acid (C₆H₈O₇) solutions per ASTM A967 or ASTM A380 standards. This step restores and enhances the native chromium oxide (Cr₂O₃) passive film, providing superior corrosion resistance.
  7. Intermediate Rinse: Multiple rinses with progressively purer water (DI water → 1 MΩ·cm water → 10 MΩ·cm water) remove all chemical residues and dissolved ions from the passivation step.
  8. Ultra-Pure Water (UPW) Final Rinse: The tube is flushed with 18.2 MΩ·cm Ultra-Pure Water through the internal bore at controlled flow rates. The UPW system incorporates mixed-bed ion exchange resins, ultrafiltration (UF), and ultraviolet (UV) oxidation to achieve the required resistivity. A minimum of 5 tube volumes of UPW is circulated to ensure complete displacement of all preceding rinse water.
  9. Nitrogen (N₂) Blow-Dry: Immediately following the UPW rinse, high-purity nitrogen gas (≥ 99.999%) is introduced into the tube bore at controlled pressure (typically 0.5 – 2.0 bar) to displace residual water. The nitrogen flow rate is optimized to prevent turbulence-induced re-contamination while ensuring complete drying within a specified time window (typically < 5 minutes per meter of tube length).
  10. Inert Sealing & Packaging: The tube ends are immediately capped or crimp-sealed under nitrogen atmosphere to prevent atmospheric re-contamination. The coiled tube is then packaged in protective materials (polyethylene wrapping, desiccant-included containers) suitable for long-term storage.
  11. Final Inspection & Certification: Each batch undergoes rigorous analytical testing including ICP-MS metal analysis, TOC measurement, particulate counting, and optional endotoxin testing. A Certificate of Conformance (CoC) and Certificate of Analysis (CoA) are issued with each shipment.

Process Control & Monitoring

  • In-Process Resistivity Monitoring: Continuous online monitoring of UPW resistivity with automatic process hold if values fall below 18.0 MΩ·cm
  • Nitrogen Dew Point Control: Dew point maintained at ≤ −60 °C to prevent moisture re-introduction during blow-dry
  • Clean Room Environment: Final rinse and drying operations conducted in ISO Class 7 (10,000) or ISO Class 8 (100,000) clean room environments
  • Batch Traceability: Each coil tube is assigned a unique batch identifier linked to full process parameter records, enabling complete traceability from raw material to finished product

Applications

Semiconductor Industry

  • Ultra-pure water (UPW) distribution systems in wafer fabrication facilities (fabs)
  • Chemical mechanical planarization (CMP) fluid delivery lines
  • EUV (Extreme Ultraviolet) lithography tool fluid circuits
  • Chemical supply systems (CDS) for high-purity acids, bases, and solvents
  • Gas delivery systems (GDS) requiring contamination-free internal surfaces

Biopharmaceutical Industry

  • Single-use and re-usable tubing in bioreactor systems
  • Water for Injection (WFI) and Purified Water (PW) distribution loops
  • Drug product transfer and filling systems
  • Bioprocessing equipment including chromatography and ultrafiltration skids
  • Endotoxin-critical fluid handling in sterile manufacturing environments

Additional Applications

  • Photovoltaic (PV) cell manufacturing fluid systems
  • Lithium-ion battery electrolyte handling
  • Food and beverage ultra-pure water systems
  • Research and analytical instrumentation (HPLC, ICP, mass spectrometry)
  • Medical device manufacturing fluid circuits

Quality Certifications

System Certifications

  • ISO 9001:2015 — Quality Management System
  • ISO 14001:2015 — Environmental Management System
  • ISO 45001:2018 — Occupational Health and Safety Management System
  • ISO 13485:2016 — Medical Device Quality Management System (for medical-grade tubing)
  • ASME BPV Code — Pressure Vessel Code compliance (for pressure-rated applications)

Product-Specific Certifications & Compliance

  • ASTM A269 / ASME SA-269 — Specifications for seamless austenitic stainless steel tubing
  • ASTM A967 — Standard Practice for Chemical Passivation of Stainless Steel Parts
  • ASTM A380 — Standard Practice for Chemical Passivation of Stainless Steel Parts (alternative method)
  • USP <665> — Elemental Impurities compliance for pharmaceutical applications
  • USP <643> — Extractables and Leachables testing compliance
  • EU GMP Annex 1 — Compliance with aseptic manufacturing requirements
  • SEMI F57 / F60 — Semiconductor equipment material specifications
  • RoHS 2.0 (EU 2011/65/EU) — Restriction of Hazardous Substances compliance
  • REACH (EC 1907/2006) — Registration, Evaluation, Authorization, and Restriction of Chemicals compliance

Third-Party Verification

  • Independent ICP-MS metal contamination analysis by accredited laboratories (e.g., SGS, Bureau Veritas)
  • Endotoxin testing by certified reference laboratories (LAL assay per USP <85>)
  • Particle count verification per ISO 14644 standards
  • TOC analysis per ASTM D6621 or equivalent

Unique Selling Points

1. Integrated UPW + N₂ Process: The seamless integration of 18.2 MΩ·cm UPW final rinse with immediate high-purity nitrogen blow-drying eliminates the critical window of re-contamination that occurs when water-exposed surfaces are exposed to ambient air. This closed-loop process ensures that the ultra-clean internal surface is preserved from rinse completion through final packaging.

2. Coil Tube Optimization: The UPW rinse process is specifically engineered for the coiled tube geometry, incorporating flow path optimization to ensure uniform cleaning throughout the entire coil length without dead zones or flow stagnation areas.

3. Dual-Industry Compliance: The process simultaneously meets semiconductor-grade (SEMI) and biopharmaceutical-grade (USP/GMP) contamination specifications, providing a single product solution for cross-industry applications and reducing supply chain complexity.

4. Full Traceability: Every coil tube is traceable to raw material mill certificates through complete in-process parameter documentation, enabling qualification and requalification support for regulated environments.

5. Scalable Production: The process is scalable from prototype quantities to high-volume production runs while maintaining consistent contamination control levels, supported by automated process monitoring and statistical process control (SPC).

Summary

The Ultra-Pure Water (18.2 MΩ·cm) Final Rinse with Nitrogen Blow-Dry process represents the gold standard for internal surface cleanliness in high-purity stainless steel coil tubes. By combining state-of-the-art water purification technology with inert gas drying and rigorous analytical verification, Wenzhou Jixing Metal Materials Co., Ltd. delivers coil tube products that meet the most stringent contamination control requirements in the semiconductor and biopharmaceutical industries. This process ensures that the internal bore of every coil tube is free of metal ions, organic residues, particulates, and endotoxins, providing customers with a qualified, traceable, and performance-verified product for their most critical fluid handling applications.