Stainless Steel Coil Tube for Heat Exchanger Applications — Technical Specification

Product Overview

The Stainless Steel Coil Tube (Product No. 1319) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled stainless steel tubing designed specifically for use in coolers, condensers, and various heat exchanger assemblies. This product category falls under the technical literature and reference category, with a particular emphasis on failure analysis and preventive measures for cooler coil tubes in industrial service conditions.

Coil tubes differ fundamentally from straight seamless or welded tubes in their geometry and residual stress state. The coiling process introduces complex multi-axial residual stresses, microstructural anisotropy, and potential work-hardening gradients that directly influence the long-term mechanical performance, corrosion resistance, and fatigue life of the tube in thermal cycling service. Understanding these characteristics is essential for selecting the appropriate material grade, manufacturing process, and operational parameters to maximize service life and prevent premature failure.

Material & Properties

Commonly Available Grades

Mechanical Properties (Typical for SUS304 Coil Tube, Solution-Annealed Condition)

Corrosion Resistance Characteristics

Coiling-Induced Property Variations

The coil manufacturing process introduces distinct metallurgical effects that must be accounted for in service design:

Specifications

Parameter Specification Standard Reference
Product Designation Stainless Steel Coil Tube (盘管 / Coiltube) —
Product Number 1319 —
Material Grades SUS304, SUS304L, SUS316, SUS316L, SUS321, SUS317L, 2205 Duplex, 2507 Super Duplex ASTM A213 / A269 / A778
Outer Diameter (OD) 3.0 mm – 159.0 mm (1/8" – 6") ASTM A213 / EN 10216
Wall Thickness 0.3 mm – 6.0 mm (0.012" – 0.236") ASTM A213
Coil Inner Diameter (CID) 50 mm – 500 mm (2" – 20") Customer-Specified
Coil Length Up to 500 m per coil (custom lengths available) —
Surface Finish Pickled & Passivated (2B), Electropolished, Brushed ASTM A967
Surface Roughness (Ra) ≤ 0.5 µm (electropolished); ≤ 1.6 µm (2B finish) ISO 4287
Welding Process ERW (Electric Resistance Welded) / Seamless ASTM A269 / A213
Heat Treatment Solution Annealing at 1050–1150°C with water quench; Stress Relief at 300–450°C for coil configuration ASTM A967
Maximum Operating Temperature Up to 870°C (304/316); Up to 1100°C (310/309) ASTM A213
Minimum Operating Temperature Down to −196°C (LN₂ service) for austenitic grades —
Dimensional Tolerance OD: ±0.05 mm; Wall: ±0.03 mm; Straightness: ≤ 1 mm/m ASTM A213 / EN 10216
Residual Stress ≤ 100 MPa (after stress relief treatment) X-ray diffraction measurement
Hydrostatic Test Pressure 5–10 MPa (depending on OD and wall thickness) ASTM A213

Manufacturing Process

1. Raw Material Selection and Incoming Inspection

High-purity stainless steel ingots or continuous-cast slabs are sourced from certified mills. Incoming materials undergo spectrographic analysis (OES / PMS) to verify chemical composition within ASTM/EN specification limits. Heat number traceability is maintained throughout the entire manufacturing chain.

2. Hot Rolling and Coiling

The slab is reheated to 1150–1250°C and hot-rolled into a hot-rolled coil (HRC) or hot-rolled pipe blank. The coiling temperature is carefully controlled (typically 550–750°C) to minimize grain growth and ensure uniform microstructure. The coil diameter is selected based on the final product OD, wall thickness, and the target bending radius to avoid excessive plastic deformation.

3. Pickling and Descaling

The hot-rolled coil is subjected to acid pickling (typically a mixture of nitric acid and hydrofluoric acid, or citric acid for environmentally compliant processes) to remove the mill scale formed during hot rolling. This step is critical for restoring the passive chromium oxide layer and achieving the required surface finish.

4. Cold Drawing / Cold Reduction (for Seamless Tubes)

For seamless coil tubes, the hot-rolled pipe blank is cold-drawn through calibrated dies to achieve the final OD and wall thickness with tight dimensional tolerances. Multiple passes may be required for large reductions. Intermediate annealing (at 1050–1100°C with water quench) may be performed between passes to relieve accumulated work hardening and restore ductility.

5. Electric Resistance Welding (ERW) — for Welded Tubes

For welded coil tubes, the pickled strip is formed into a tube shape and welded using high-frequency electric resistance welding. The welding parameters (current, voltage, speed, roll gap) are precisely controlled to ensure full penetration and a sound weld seam. Post-weld heat treatment (solution annealing) is performed to homogenize the weld zone microstructure.

6. Solution Annealing (Stress Relief)

This is a critical process step for coil tubes. After coiling, the tube is subjected to stress relief heat treatment at 300–450°C for 1–4 hours (depending on coil diameter and wall thickness) to reduce coiling-induced residual stresses to acceptable levels (≤ 100 MPa). For full solution annealing, the temperature is raised to 1050–1150°C with rapid water quench to dissolve carbides and restore maximum corrosion resistance.

7. Final Coiling and Surface Treatment

The tube is coiled to the specified coil inner diameter (CID) using precision coiling equipment with controlled tension to avoid ovality or distortion. The final surface treatment includes passivation (per ASTM A967) to enhance the protective chromium oxide layer, and optionally electropolishing for applications requiring ultra-low surface roughness (e.g., pharmaceutical, food processing).

8. Quality Inspection and Testing

Applications

Primary Application Areas

Failure Analysis Context

The technical literature associated with this product (Product No. 1319) addresses the critical topic of cooler coil tube failure analysis and prevention. Common failure modes in coil tube service include:

Preventive Measures and Design Recommendations