Stainless Steel Welded Coil Tube — GB/T 24593 Fluid Conveyance Standard
Product Overview
The Stainless Steel Welded Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular product designed specifically for fluid conveyance applications. Governed by the Chinese National Standard GB/T 24593 — Stainless Steel Welded Tubes for Fluid Conveyance — this product represents a critical component in industrial piping systems where reliability, corrosion resistance, and dimensional accuracy are paramount. The coil tube configuration (盘管) offers distinct logistical and installation advantages over straight-length tubing, enabling compact storage, reduced transportation costs, and streamlined on-site deployment.
GB/T 24593 is the definitive national standard in China for welded stainless steel tubes intended for fluid transport, covering seamless and welded processes with stringent requirements for weld seam integrity, mechanical properties, and dimensional tolerances. This product is engineered to meet and exceed these standards, with particular emphasis on weld seam quality (焊缝质量) and specialized expansion/flattening tests (扩口/压扁试验) that validate the tube's ability to withstand complex forming operations without material failure.
Material & Properties
The coil tube is fabricated from austenitic and/or austenitic-ferritic (duplex) stainless steel grades, selected to deliver optimal combinations of corrosion resistance, mechanical strength, and formability. The primary material grades comply with the following specifications:
- 06Cr19Ni10 (Equivalent: 304 / AISI 304) — General-purpose austenitic stainless steel with excellent corrosion resistance in oxidizing environments, widely used for food-grade and chemical processing applications.
- 022Cr17Ni12Mo2 (Equivalent: 316L / AISI 316L) — Low-carbon, molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion in chloride-containing media.
- 06Cr17Ni12Mo2 (Equivalent: 316 / AISI 316) — Standard molybdenum-bearing austenitic grade for general chemical and marine service.
- 022Cr25Ni7Mo3N (Equivalent: 310S / AISI 310S) — High-temperature austenitic grade suitable for elevated-temperature fluid conveyance.
Key Material Properties:
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and chemical corrosion environments; resistance to stress corrosion cracking (SCC) in controlled environments.
- Mechanical Strength: Tensile strength (抗拉强度) typically ranging from 520 MPa to 720 MPa depending on grade and heat treatment condition.
- Formability: High ductility and elongation (>30%) enabling successful expansion (扩口) and flattening (压扁) operations without cracking or thinning failure.
- Temperature Range: Suitable for service temperatures from cryogenic levels (−196°C) up to 870°C (austenitic grades), with no embrittlement concerns.
- Hygienic Properties: Non-toxic, non-reactive, and easily cleanable — compliant with food-grade and pharmaceutical processing requirements.
Specifications
| Parameter | Specification / Requirement | Standard Reference |
|---|---|---|
| Product Name | Stainless Steel Welded Coil Tube (盘管, Coiltube) | GB/T 24593 |
| Applicable Standard | Stainless Steel Welded Tubes for Fluid Conveyance | GB/T 24593 (Chinese National Standard) |
| Classification | Fluid Conveyance (流体输送) | GB/T 24593, Section on Fluid Transport Tubes |
| Welding Process | Automatic Argon Arc Welding (TIG/AGW) or Laser Welding | GB/T 24593, Weld Seam Requirements |
| Weld Seam Quality | Continuous, uniform weld with no cracks, pores, or undercut; weld reinforcement within tolerance | GB/T 24593, Weld Seam Inspection |
| Weld Seam Strength | Weld tensile strength ≥ 90% of base metal tensile strength | GB/T 24593, Mechanical Testing |
| Expansion Test (扩口试验) | Tube end expanded to specified angle (typically 60°) without cracking or splitting; pass/fail criterion per GB/T 24593 | GB/T 24593, Special Test — Expansion |
| Flattening Test (压扁试验) | Tube flattened to specified ratio (H/D ratio) without cracking on inner or outer surface; validates cold-forming capability | GB/T 24593, Special Test — Flattening |
| Hydrostatic Test | Pressure test at 50–100 MPa (depending on tube size) with no leakage; minimum 15 seconds hold time | GB/T 24593, Pressure Testing |
| Surface Finish | Smooth, free of scale, rust, and mechanical damage; surface roughness Ra ≤ 0.8 μm (polished) or Ra ≤ 3.2 μm (pickled) | GB/T 24593, Surface Quality |
| Dimensional Tolerance | Outer diameter tolerance: ±0.5% to ±1.0% (depending on OD range); Wall thickness tolerance: ±10% | GB/T 24593, Dimensional Tolerances |
| Coil Configuration | Supplied in coil form with controlled bend radius (minimum 5D to prevent kinking or ovality) | GB/T 24593, Coil Delivery Requirements |
| Heat Treatment | Solution annealing (固溶处理) at 1050–1150°C followed by rapid quench to achieve fully austenitic microstructure | GB/T 24593, Heat Treatment |
| Pickling & Passivation | Acid pickling (nitric/hydrofluoric acid blend) followed by passivation treatment to restore chromium oxide protective layer | GB/T 24593, Surface Treatment |
Manufacturing Process
The production of GB/T 24593-compliant stainless steel welded coil tubes follows a rigorous multi-stage manufacturing process designed to ensure dimensional precision, metallurgical integrity, and weld seam excellence:
- Material Preparation: High-purity stainless steel strip (or coil) is sourced from certified mills, with chemical composition verified via spectroscopic analysis (光谱分析) to confirm compliance with GB/T 24593 grade specifications. Incoming material undergoes hardness testing and visual inspection.
- Strip Processing: The steel strip undergoes edge trimming (边部修整), leveling (矫平), and surface cleaning to ensure uniform width and flatness. Surface contaminants are removed through degreasing and pickling to prevent inclusion during welding.
- Forming (Rolling): The prepared strip is fed through a series of progressive roll stations (roll forming) to gradually shape the flat strip into a near-circular tube blank. The roll configuration is precisely calibrated to achieve the target outer diameter with minimal residual stress.
- Welding: The formed tube blank passes through an automatic welding station. Two primary welding methods are employed:
- Automatic Argon Arc Welding (TIG/AGW): A high-frequency current generates a precise arc at the tube seam, with internal and external argon shielding gas (氩气保护) preventing oxidation. Weld parameters (current, speed, gas flow) are continuously monitored and controlled.
- Laser Welding: High-energy laser beam provides deep, narrow weld penetration with minimal heat-affected zone (HAZ), resulting in superior weld geometry and reduced distortion.
- Weld Seam Inspection: Every meter of welded tube undergoes 100% online inspection using electromagnetic acoustic testing (EMAT) or optical/CCD-based weld seam monitoring. Defective sections are marked and removed. Key inspection criteria include:
- Weld continuity and uniformity (焊缝连续性与均匀性)
- Absence of cracks, pores, undercuts, and spatter
- Weld reinforcement (余高) within specified tolerance
- Weld width (焊缝宽度) consistency
- Sizing & Straightening: The welded tube passes through a sizing die (定径模具) to achieve final dimensional accuracy and roundness. Any residual ovality from the welding process is corrected.
- Heat Treatment (Solution Annealing): The tube is subjected to solution annealing (固溶处理) at temperatures between 1050°C and 1150°C, followed by rapid water quenching. This process dissolves carbides, restores the fully austenitic microstructure, and eliminates welding-induced residual stresses — critical for ensuring long-term corrosion resistance and mechanical performance.
- Pickling & Passivation: The annealed tube is immersed in a pickling solution (typically a mixture of nitric acid and hydrofluoric acid) to remove surface oxide scale (氧化皮). Subsequent passivation treatment (钝化处理) using a nitric acid solution re-establishes the protective chromium oxide passive film on the surface, ensuring maximum corrosion resistance.
- Final Inspection & Testing: Comprehensive testing is performed on sampled tubes:
- Hydrostatic Pressure Test (水压试验): Each coil is pressure-tested to verify weld seam integrity and overall tube strength.
- Expansion Test (扩口试验): Tube ends are expanded to a specified angle (typically 60°) using a mandrel. The tube must exhibit no cracks or splits on the expanded surface. This test validates the material's ductility and weld seam quality under plastic deformation.
- Flattening Test (压扁试验): The tube is compressed between flat plates until the compression distance reaches the specified ratio of the wall thickness. No cracking on either the inner or outer surface is permitted. This test specifically evaluates the weld seam's ability to withstand cold-forming operations.
- Tensile Testing (拉伸试验): Verification of tensile strength and elongation values against GB/T 24593 requirements.
- Chemical Composition Analysis (化学成分分析): Confirmation of grade compliance via spectroscopy or wet chemical analysis.
- Coiling & Packaging: Qualified tubes are coiled (盘卷) at controlled bend radii to prevent kinking, ovality, or surface damage. Coils are wrapped with protective film, moisture-absorbent desiccant, and secured with steel strapping for transport. Each coil is labeled with material grade, dimensions, heat number, and certification information.
Applications
The GB/T 24593 stainless steel welded coil tube is designed for fluid conveyance across a broad spectrum of industrial and commercial applications:
- Food & Beverage Industry: Hygienic piping systems for dairy processing, brewery operations, beverage transfer, and food-grade CIP (Clean-In-Place) systems. The coil configuration facilitates rapid installation in compact processing facilities.
- Pharmaceutical & Biotechnology: Process piping for pharmaceutical manufacturing, bioreactor connections, and sterile fluid transfer where surface finish and corrosion resistance are critical.
- Chemical Processing: Conveyance of corrosive chemicals, acids, and solvents in petrochemical plants, fertilizer production, and chemical storage facilities. The 316L grade provides enhanced resistance to chloride-induced pitting corrosion.
- Petrochemical & Oil & Gas: Fluid transfer lines in refineries, offshore platforms, and gas processing facilities where resistance to sour gas (H₂S) and high-pressure conditions is required.
- Power Generation: Boiler feedwater systems, steam lines, and cooling water circuits in thermal and nuclear power plants.
- Water Treatment & Desalination: Seawater intake piping, reverse osmosis (RO) system feed lines, and purified water distribution networks.
- Heating & Cooling Systems: Heat exchanger tubes, HVAC system piping, and district heating network components.
- Automotive & Aerospace: Fuel lines, hydraulic systems, and exhaust system components requiring high-temperature resistance and corrosion durability.
- Architectural & Construction: Building water supply systems, fire suppression piping, and structural applications requiring aesthetic and corrosion-resistant tubing.
- Medical Equipment: Gas supply piping in hospitals, medical device manufacturing, and laboratory instrumentation.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring full compliance with GB/T 24593 and international standards:
- GB/T 24593 Compliance: Full adherence to the Chinese National Standard for stainless steel welded tubes for fluid conveyance, including all mandatory mechanical testing, weld seam inspection, and dimensional tolerance requirements.
- ISO 9001:2015: Certified Quality Management System ensuring consistent product quality, process control, and continuous improvement throughout the manufacturing lifecycle.
- ISO 3834 / EN 1090: Welding quality certification ensuring welder qualification, welding procedure specification (WPS) approval, and weld inspection protocols meet international standards.
- ASME BPV Code (Section I / Section VIII): Product suitable for pressure vessel and piping applications per American Society of Mechanical Engineers Boiler and Pressure Vessel Code requirements.
- EN 10216-5 / EN 10217-7: European Standard for welded stainless steel tubes for mechanical and structural purposes — enabling export to European markets.
- AWS D1.6: American Welding Society standard for welding stainless steel, applicable to weld seam quality assurance.
- Mill Test Certificate (MTC) / EN 10204 3.1: Each shipment is accompanied by a full material test certificate documenting chemical composition, mechanical properties, and test results (hydrostatic, expansion, flattening).
- Third-Party Inspection (TPI): Available upon request — SGS, Bureau Veritas, or TÜV inspection services for additional quality assurance.
Unique Selling Points
The GB/T 24593 Stainless Steel Welded Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd distinguishes itself through the following competitive advantages:
- Specialized Expansion & Flattening Test Compliance: Unlike standard welded tubes that may only undergo hydrostatic testing, this product is specifically validated through expansion (扩口) and flattening (压扁) tests. These tests rigorously demonstrate the weld seam's ability to withstand cold