Electrolytically Polished (EP) Stainless Steel Coil Tube — Internal Surface Treatment
Product Overview
Wenzhou Jixing Metal Materials Co., Ltd. offers premium-grade stainless steel coil tubes with advanced internal electrolytic polishing (EP) treatment, engineered to deliver exceptional surface integrity, chemical resistance, and purity performance. This electrochemical finishing process transforms the inner bore of the coil tube into an ultra-smooth, corrosion-resistant surface that meets the most demanding requirements in pharmaceutical, food-grade, semiconductor, and high-purity fluid handling applications.
Unlike conventional mechanical polishing or passivation methods, electrolytic polishing removes the work-hardened and contaminated surface layer through controlled anodic dissolution, resulting in a mirror-like finish that significantly reduces product contact time, eliminates dead zones, and minimizes the risk of microbial contamination or particulate generation.
Unique Selling Points
- Ultra-Low Surface Roughness: Achieves a consistent Ra ≤ 0.38 μm internal finish, far exceeding standard electropolished specifications and ensuring minimal fluid resistance and flow turbulence.
- Complete Removal of Decarburized/Altered Layer: The EP process chemically dissolves the heat-affected and decarburized layer formed during prior manufacturing steps, restoring the full alloy composition and mechanical integrity of the base material.
- Reduced Ion Leaching: The polished surface significantly lowers chromium, nickel, and iron ion migration into process fluids, ensuring product purity compliance in sensitive applications.
- Enhanced Corrosion Resistance: EP thickens and stabilizes the passive chromium oxide film, providing superior long-term resistance to pitting, crevice corrosion, and general degradation.
- Improved Cleanability: The smooth internal surface eliminates micro-pores, micro-cracks, and pits that can harbor bacteria or trap residues, simplifying CIP (Clean-in-Place) and SIP (Sterilize-in-Place) procedures.
Material & Properties
The coil tube is manufactured from high-purity austenitic stainless steel grades, typically including 304L (UNS S30403), 316L (UNS S31603), and 316L Ti (UNS S31635), selected for their excellent weldability, formability, and resistance to oxidation and chemical attack. After electrolytic polishing, the internal surface exhibits the following enhanced properties:
- Chromium oxide passive layer thickness increased by 30–50% compared to mechanical polishing
- Homogeneous surface free of micro-voids, cracks, and inclusion pits
- Improved fatigue resistance due to elimination of surface stress concentrators
- Enhanced thermal conductivity at the fluid-wall interface due to reduced boundary layer resistance
Specifications
| Parameter | Specification |
|---|---|
| Surface Roughness (Internal) | Ra ≤ 0.38 μm (typical), Ra ≤ 0.25 μm (upon request) |
| Surface Treatment Method | Electrolytic Polishing (EP) — Internal Wall |
| Passive Film Enhancement | Chromium-rich passive layer, thickness increased by 30–50% |
| Decarburized Layer Removal | Complete removal via controlled anodic dissolution | Ion Leaching Reduction | Significantly reduced Cr/Ni/Fe ion migration into process fluids |
| Available Grades | 304L, 316L, 316L Ti, 904L, 2205 (Duplex) |
| Coil Tube Outer Diameter Range | Φ6.0 mm – Φ50.8 mm (custom sizes available) |
| Wall Thickness Range | 0.5 mm – 3.0 mm |
| Coil Diameter | Standard and custom coil diameters available |
| EP Solution Temperature | 50–80 °C (controlled process parameters) |
| Current Density | 100–400 A/dm² (optimized per tube geometry) |
| Applicable Standards | ASTM A269/A270, ASME BPE, EN 10217, ISO 14283, ASTM A967 |
Manufacturing Process
The internal electrolytic polishing of coil tubes at Wenzhou Jixing Metal Materials follows a rigorous, multi-stage process to ensure consistent quality across every coil:
- Material Selection & Incoming Inspection: Only certified, high-purity stainless steel coils are accepted. Incoming materials undergo spectroscopic verification (PMI) to confirm grade compliance and traceability.
- Precision Forming & Coiling: The tube is cold-drawn or seamless-formed to exact dimensional tolerances and wound into the required coil configuration with controlled bend radii to prevent wall thinning or ovality.
- Preliminary Cleaning & Degreasing: The coil tube undergoes alkaline cleaning and acid pickling to remove surface contaminants, mill scale, and residual oils that could interfere with the EP process.
- Electrolytic Polishing (EP): The coil is immersed in a heated phosphoric-sulfuric acid electrolyte bath. A controlled DC current is applied, with the tube serving as the anode. The process selectively dissolves surface micro-irregularities, work-hardened layers, and the decarburized zone, producing a uniform, ultra-smooth finish at Ra ≤ 0.38 μm. Process parameters (current density, temperature, immersion time) are precisely optimized for each tube diameter and wall thickness.
- Neutralization & Deionized Water Rinse: After EP, the coil is immediately neutralized and rinsed with high-purity deionized water (resistivity ≥ 15 MΩ·cm) to prevent residual acid corrosion and ensure surface cleanliness.
- Passivation Verification: A ferrite contamination test (ASTM A967) and visual inspection confirm the integrity of the enhanced passive film.
- Final Inspection & Packaging: Each coil undergoes dimensional verification, surface roughness measurement (internal profilometry), and visual inspection before being protected with moisture-absorbing packaging and shipped.
Applications
The electrolytically polished internal surface makes these coil tubes ideal for the following high-purity and critical-process applications:
- Pharmaceutical Manufacturing: Bioreactors, CIP/SIP distribution lines, sterile fluid transfer, and process coils requiring ASME BPE compliance.
- Food & Beverage Industry: Dairy processing, beverage heat exchangers, brewing equipment, and sanitary fluid transport systems.
- Semiconductor & Electronics: Ultra-pure water (UPW) distribution, chemical supply lines, and high-purity gas delivery systems where particle and ion contamination must be minimized.
- Biotechnology & Cell Culture: Perfusion bioreactors, single-use process connections, and GMP-compliant fluid handling.
- Medical Devices: Dialysis equipment, medical gas delivery, and implant manufacturing fluid systems.
- Chemical Processing: Corrosive fluid transfer, reactor internals, and heat exchange coils handling aggressive media.
- Energy & Power Generation: Condenser tubes, desalination systems, and nuclear-grade fluid handling components.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and complies with industry standards to ensure every electrolytically polished coil tube meets international quality benchmarks:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ISO 45001:2018 — Occupational Health & Safety Management
- ASME BPE — Bioprocessing Equipment compliance for pharmaceutical-grade tubing
- CE Marking — European conformity for pressure equipment directives
- ASTM A967 — Passivation of stainless steel parts verification
- ASTM A269 / A270 — Standard specifications for austenitic stainless steel tube
- EN 10217 — European standard for seamless stainless steel tubes
- ISO 14283 — Surface roughness measurement and reporting
- Mill Test Certifications (MTC) — EN 10204 3.1/3.2 certificates available for every batch
- Third-Party Inspection — Available upon request (SGS, Bureau Veritas, TÜV)
Why Choose Wenzhou Jixing? With decades of expertise in stainless steel coil tube manufacturing and advanced surface engineering, Wenzhou Jixing Metal Materials Co., Ltd. delivers electrolytically polished coil tubes that combine exceptional surface quality, dimensional precision, and full traceability. Our internal EP capability ensures that every coil tube leaves our facility ready for the most demanding purity and performance requirements — reducing your commissioning time, minimizing contamination risk, and extending service life.