Stainless Steel Coil Tube — Conical Mandrel Bell Mouth Test Specification
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered seamless or welded tubing product supplied in coil form, designed for applications demanding superior process performance, mechanical integrity, and dimensional accuracy. A critical quality assurance parameter for this product is the Conical Mandrel Bell Mouth Test (锥形芯棒扩口试验), which serves as the core verification indicator for Compression Fitting (卡套接头) compatibility. This test evaluates the tube's ability to undergo controlled plastic deformation without cracking or failure, ensuring reliable field installation and long-term leak-free performance in fluid conveyance systems.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel grades, typically including AISI 304 (UNS S30400), AISI 316 (UNS S31600), and AISI 321 (UNS S32100), among other industry-standard designations. These materials exhibit the following key properties:
- Corrosion Resistance: Excellent resistance to atmospheric, chemical, and aqueous corrosion environments due to the formation of a stable chromium oxide passive film.
- Mechanical Properties: High ductility and formability, enabling the tube to withstand significant plastic deformation during bell mouth operations without fracture.
- Thermal Stability: Retention of mechanical properties across a wide temperature range, from cryogenic to elevated service temperatures.
- Weldability: Superior weldability with minimal sensitization, facilitating downstream fabrication and assembly.
Conical Mandrel Bell Mouth Test — Specifications
The Conical Mandrel Bell Mouth Test is performed in accordance with applicable international standards, including ASTM E271 (Standard Test Methods for Bellmouth Expansion of Thin-Wall Tubular Products) and ISO 6652 (Steel Tubes — Bellmouth Expansion Test). The test involves inserting a conical mandrel (tapered plug) into the tube end and forcing it outward to create a controlled flare or bell mouth. The degree of expansion is quantified as the Bell Mouth Ratio (扩口率), calculated as:
Bell Mouth Ratio (%) = [(Df − Di) / Di] × 100
where Df is the final outside diameter of the bell mouth and Di is the original inside diameter of the tube.
| Test Parameter | Specification | Acceptance Criteria |
|---|---|---|
| Bell Mouth Ratio Level 1 | 30% | No cracks, splits, or laps on the expanded surface or inner wall |
| Bell Mouth Ratio Level 2 | 45% | No cracks, splits, or laps on the expanded surface or inner wall |
| Bell Mouth Ratio Level 3 | 60% | No cracks, splits, or laps on the expanded surface or inner wall |
The tube is deemed passing (合格) when it sustains a bell mouth ratio of 30%, 45%, and 60% respectively, with zero occurrence of cracking (开裂) at any of the specified expansion levels. This multi-level verification ensures progressive confidence in the material's cold-workability and formability characteristics.
Manufacturing Process
The production of high-quality stainless steel coil tube involves a tightly controlled multi-stage manufacturing sequence:
- Slab Preparation and Hot Rolling: High-purity stainless steel slabs are hot rolled into hot-rolled coil (HRC) with precise chemical composition control.
- Pickling and Annealing: The hot-rolled coil undergoes acid pickling to remove scale, followed by controlled annealing in a protective atmosphere to achieve desired grain structure and ductility.
- Cold Reduction (Cold Rolling): The coil is cold rolled to achieve precise dimensional tolerances on wall thickness and outer diameter, enhancing surface finish and mechanical properties.
- Intermediate Annealing: Periodic annealing treatments are applied during cold reduction to prevent excessive strain hardening and maintain formability for downstream bell mouth operations.
- Tube Forming: The flat coil is formed into tubular geometry via precision forming techniques, followed by welding (for welded tube) or seamless piercing and sizing (for seamless tube).
- Final Annealing and Pickling: The finished tube is annealed to relieve residual stresses and restore maximum ductility, then pickled to produce a clean, corrosion-resistant surface.
- Coiling and Packaging: The tube is wound into coils at controlled tension, protected against mechanical damage, and packaged for shipment.
Applications
The Conical Mandrel Bell Mouth performance of this coil tube directly enables its use in the following critical applications:
- Compression Fitting (卡套接头) Systems: The primary application — the bell mouth test validates that the tube can be reliably expanded to interface with compression fittings, ensuring secure, leak-free mechanical connections in gas, liquid, and vacuum systems.
- Instrumentation and Control Lines: High-purity process control tubing in oil, gas, and chemical processing facilities where field-assembly fittings are essential.
- Automotive Fuel and Brake Lines: Precision tubing requiring reliable crimped or flared connections under high-pressure conditions.
- Medical and Pharmaceutical Piping: Sanitary-grade tubing where hygienic, leak-tight connections are mandated by regulatory standards.
- Cryogenic and Liquefied Gas Systems: Tubing in LNG, LPG, and industrial gas distribution systems requiring high formability at low temperatures.
- Semi-Conductor and Electronics Manufacturing: Ultra-clean gas delivery systems where contamination-free, leak-tight connections are critical.
- Food and Beverage Processing: Hygienic piping systems requiring frequent disassembly and reassembly via compression fittings.
Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications and complies with the following standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control.
- ISO 14001:2015 — Environmental Management System certification demonstrating environmental responsibility in production.
- ASTM A778 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service.
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service.
- ASTM E271 — Standard Test Methods for Bellmouth Expansion of Thin-Wall Tubular Products.
- ISO 6652 — Steel Tubes — Bellmouth Expansion Test.
- EN 10217 — Technical Delivery Conditions for Stainless Steel Tubes for Pressure Purposes.
- GB/T 12771 — Chinese National Standard for Stainless Steel Seamless Tubes for General Purposes.
Unique Selling Points
- Multi-Level Bell Mouth Verification: Unlike many suppliers who test at a single expansion ratio, this product is validated at three progressive levels (30%, 45%, 60%), providing comprehensive confidence in material formability and eliminating the risk of marginal performance at intermediate expansion ratios.
- Core Compression Fitting Compatibility: The bell mouth test results serve as a direct predictor of field-installation reliability with compression fittings, reducing the risk of connection failures and ensuring leak-tight integrity throughout the service life.
- Coil Supply Advantage: Delivered in coil form to maximize cutting efficiency, minimize material waste, and accommodate automated tube processing lines, reducing downstream fabrication costs.
- Zero-Defect Acceptance Criteria: The strict "no cracking" requirement at all three expansion levels ensures only the highest-quality material with optimal grain structure and mechanical properties reaches the end user.
- Full Traceability: Each coil is accompanied by a material test certificate (MTC) documenting chemical composition, mechanical properties, and bell mouth test results, enabling full product traceability for quality assurance and regulatory compliance.
Conclusion
The Conical Mandrel Bell Mouth Test at 30%, 45%, and 60% expansion ratios without cracking represents a rigorous and industry-recognized benchmark for evaluating the process performance of stainless steel coil tube. As the core verification indicator for compression fitting compatibility, this test ensures that the product meets the demanding requirements of modern fluid conveyance, instrumentation, and process control systems. Wenzhou Jixing Metal Materials Co., Ltd. delivers a coil tube product that combines superior material quality, precise manufacturing, and comprehensive quality assurance to meet the highest standards of the international stainless steel tube industry.