Stainless Steel Coil Tube with Mechanical & Hydraulic Expansion Connection for Heat Exchanger Applications

Product Overview

The Stainless Steel Coil Tube (Product No. 222) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coil tube product specifically designed for heat exchanger tube-to-tubesheet connections. This product represents a critical component in the installation and maintenance of industrial heat exchange systems, where reliable sealing and structural integrity are paramount. The coil tube is supplied in a coiled configuration to facilitate efficient bending, forming, and installation in complex heat exchanger geometries, reducing the need for additional welding and minimizing potential failure points.

Wenzhou Jixing Metal Materials Co., Ltd. specializes in the production of high-performance stainless steel coil tubes that are compatible with both mechanical expansion and hydraulic expansion connection methods. These connection techniques provide a permanent, leak-tight, and mechanically robust joint between the heat exchanger tube and the tube sheet, ensuring long-term operational reliability in demanding industrial environments.

Unique Selling Points

Material & Properties

The stainless steel coil tube is manufactured from high-quality austenitic stainless steel grades, selected for their outstanding corrosion resistance, mechanical strength, and thermal compatibility in heat exchanger service. The material properties are carefully controlled to ensure predictable expansion behavior during the tube-to-tubesheet joining process.

Specifications

Parameter Specification Standard Reference
Product Code 222 —
Product Name Stainless Steel Coil Tube (盘管) —
Outer Diameter (OD) 6.0 mm – 25.4 mm (0.236" – 1.0") ASTM A269 / A213
Wall Thickness 0.5 mm – 3.0 mm (0.020" – 0.118") ASTM A269 / A213
Coil Length 10 m – 100 m (33 – 328 ft) per coil Manufacturer Standard
Minimum Bend Radius 3D (3× OD) without collapse ISO 11862
Surface Finish BA (Bright Annealed) / No. 4 Brushed / Polished ASTM A478
Surface Roughness (Ra) ≤ 0.8 μm (0.031 mil) ISO 4287
Dimensional Tolerance ±0.05 mm on OD; ±0.03 mm on wall thickness ASTM A213
Expansion Rate (Critical) 4% – 6% (controlled) TEMA Standards
Connection Method Mechanical Expansion / Hydraulic Expansion TEMA R / ASME VIII
Pressure Rating Up to 2.5 MPa (363 psi) at 200°C after expansion ASME Section VIII
Material Grades SUS304 / 304L / 316 / 316L / 321 / 310S ASTM A213 / A269
Delivery Condition Coiled, annealed, pickled and passivated —

Manufacturing Process

1. Coil Tube Production

  1. Steel Selection & Verification: High-purity stainless steel billets or ingots are selected based on the target grade. Incoming material undergoes spectroscopic analysis to verify chemical composition compliance with ASTM/ISO standards.
  2. Hot Rolling & Annealing: Billets are hot-rolled into tube blanks. The material is then annealed to achieve a fully recrystallized austenitic microstructure, ensuring maximum ductility for subsequent cold working and expansion processes.
  3. Piercing & Seamless Forming: The annealed stock is pierced and drawn through successive dies to produce seamless tubing with precise dimensional tolerances. This eliminates weld seams that could compromise expansion integrity.
  4. Cold Drawing: The seamless tube is cold-drawn to achieve final outer diameter and wall thickness specifications. Cold drawing improves dimensional accuracy and surface finish while enhancing mechanical properties.
  5. Intermediate Annealing: Periodic annealing treatments during cold drawing prevent work hardening and maintain the material's ductility for subsequent coil forming and expansion operations.
  6. Coil Winding: The finished tube is wound into coils of specified diameter and length. The coiling process is carefully controlled to prevent kinking, ovality, or surface damage.
  7. Pickling & Passivation: The coil tube undergoes acid pickling to remove oxide scale and surface contaminants, followed by passivation treatment to form a protective chromium oxide layer, ensuring optimal corrosion resistance.

2. Mechanical Expansion Process

  1. Tube Insertion: The stainless steel coil tube is inserted into pre-drilled holes in the tube sheet. The tube sheet hole diameter is slightly larger than the tube OD to allow insertion, typically 0.5–1.0 mm clearance.
  2. Roll Expansion: A set of hardened expansion rolls is fed through the tube, progressively expanding the tube wall outward against the tube sheet hole. The expansion is achieved through controlled mechanical deformation.
  3. Expansion Rate Monitoring: The expansion rate is critically controlled to remain within the 4%–6% range. This is calculated as:
    Expansion Rate (%) = [(Final Tube OD − Original Tube OD) / Original Tube OD] × 100
  4. Joint Integrity Verification: Post-expansion joints are inspected for uniformity, leak tightness, and absence of cracking. Hydrostatic or pneumatic pressure testing confirms seal integrity.

3. Hydraulic Expansion Process

  1. Tube Preparation: The coil tube is inserted into the tube sheet hole. The tube ends are sealed with hydraulic plugs or end caps capable of withstanding high internal pressures.
  2. Pressurization: High-pressure hydraulic fluid is introduced into the tube interior, generating uniform radial expansion force. The pressure is precisely controlled to achieve the target 4%–6% expansion rate.
  3. Uniform Expansion: Unlike mechanical expansion, hydraulic expansion produces a uniform expansion profile along the entire joint length, reducing stress concentrations and improving joint fatigue life.
  4. Pressure Hold & Release: The pressure is maintained for a specified duration to allow elastic springback stabilization, then gradually released. The residual interference fit ensures a permanent, leak-tight seal.

4. Critical Process Control — Expansion Rate Management

WARNING: The expansion rate must be strictly maintained between 4% and 6%. Expansion rates exceeding 6% cause excessive plastic deformation leading to micro-cracking and eventual fracture of the tube wall. Expansion rates below 4% result in insufficient interference fit, compromising both sealing integrity and mechanical strength of the joint.

The expansion rate is determined by the following factors:

Applications

The stainless steel coil tube with mechanical/hydraulic expansion connection is widely employed across multiple industries where reliable heat exchange and corrosion resistance are essential:

Quality Certifications

Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications to ensure product reliability and compliance with international standards:

Quality Assurance Procedures

  1. Incoming Material Inspection: 100% verification of chemical composition, mechanical properties, and dimensional accuracy of raw steel stock
  2. In-Process Monitoring: Continuous dimensional inspection, surface quality checks, and hardness testing at each manufacturing stage
  3. Expansion Rate Verification: Post-expansion joint inspection using calibrated gauges and/or ultrasonic testing to confirm expansion rate within 4%–6% specification
  4. Pressure Testing: Hydrostatic pressure testing at 1.5× operating pressure for minimum 30 minutes to verify joint integrity and leak tightness
  5. Non-Destructive Testing (NDT): Visual inspection, dye penetrant testing, and magnetic particle inspection of expansion joints to detect surface cracks or defects
  6. Final Documentation: Comprehensive mill test reports (MTRs), expansion records, pressure test certificates, and traceability documentation for each production batch

Technical Advisory

Important Note: Proper expansion rate control (4%–6%) is the single most critical factor determining the long-term reliability of the tube-to-tubesheet joint. Wenzhou Jixing Metal Materials Co., Ltd. provides comprehensive technical support including expansion parameter calculation, tubesheet hole sizing