Stainless Steel Coil Tube — Pressure Testing and Seal Integrity Verification Specification
Product Reference: Item No. 1700 — Coil Tube (盘管) | Supplier: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The stainless steel coil tube is a continuous-length tubular product wound into a helical coil configuration, distinguished from straight-length seamless or welded pipe by its coiled delivery form. This format offers significant advantages in handling efficiency, storage density, and downstream processing productivity. The coil tube is manufactured primarily from austenitic stainless steel grades and is engineered for applications demanding corrosion resistance, mechanical integrity under pressure, and long-term service reliability in hygienic, industrial, and infrastructure environments.
The technical specification presented herein draws upon systematic learning and practical verification of pressure testing (hydrostatic and pneumatic) and seal integrity inspection protocols — critical quality assurance milestones that validate the structural soundness and dimensional fidelity of every coil tube unit prior to shipment.
2. Material Composition and Properties
2.1 Commonly Available Grades
- SUS304 / AISI 304 / 06Cr19Ni10 — General-purpose austenitic grade with excellent corrosion resistance and formability.
- SUS316 / AISI 316 / 06Cr17Ni12Mo2 — Enhanced molybdenum content for superior resistance to pitting and crevice corrosion in chloride environments.
- SUS321 / AISI 321 / 06Cr18Ni11Ti — Titanium-stabilized grade offering improved resistance to intergranular corrosion at elevated temperatures.
- SUS304L / AISI 304L / 022Cr19Ni10 — Low-carbon variant optimized for welding applications requiring minimal sensitization risk.
- SUS316L / AISI 316L / 022Cr17Ni12Mo2 — Low-carbon, high-molybdenum grade for demanding sanitary and chemical processing applications.
- SUS310S / AISI 310S / 06Cr25Ni20 — High-temperature alloy grade suitable for furnace and combustion line applications up to 1150 °C.
2.2 Mechanical Properties (Typical — Annealed Condition)
| Property | SUS304 | SUS316 | SUS321 |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ≥ 515 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HB) | ≤ 217 | ≤ 217 | ≤ 217 |
| Modulus of Elasticity (GPa) | 193 | 193 | 193 |
2.3 Surface Finishes
- No. 1 Finish — Hot-rolled, pickled, and annealed; standard industrial surface.
- 2B Finish — Cold-rolled, annealed, and passivated; smooth, uniform appearance.
- No. 4 Finish (Satin/Hairline) — Ground to 100–200 grit; decorative industrial finish.
- BA (Bright Annealed) — Annealed in controlled atmosphere; highly reflective, hygienic-grade surface.
- Electropolished — Electrochemical polishing to Ra ≤ 0.4 μm for pharmaceutical and food-grade compliance.
3. Technical Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ114.3 mm (custom sizes available upon request) |
| Wall Thickness (WT) | 0.3 mm – 6.0 mm (tolerance: ±10% or per applicable standard) |
| Coil Length | Continuous coil; typical cut lengths 1 m – 12 m; full coil delivery available |
| Coil Weight | Typically 500 kg – 2,000 kg per coil (depending on OD, WT, and grade) |
| Manufacturing Process | Seamless (hot/cold drawn) or ERW (Electric Resistance Welded) with full weld annealing |
| Applicable Standards | ASTM A554, ASTM A269, ASTM A312, GB/T 12771, GB/T 14976, EN 10217-7 |
| Hydrostatic Test Pressure | P = 2 × S × t / D (minimum 150% of maximum allowable working pressure) |
| Seal Integrity Test | 100% visual and dye-penetrant inspection; helium leak testing available for critical applications |
| Operating Temperature | −196 °C to +870 °C (grade-dependent; 310S extends to +1150 °C) |
| Passivation Treatment | Citric acid or nitric acid passivation per ASTM A967; minimum 10% nitric acid, 45 °C, 10 min immersion |
4. Manufacturing Process
4.1 Seamless Coil Tube Production Route
- Raw Material Preparation: Stainless steel billets or slabs are inspected for chemical composition and mechanical properties per ASTM E415 and ASTM E10.
- Hot Rolling / Piercing: Billets are heated to 1150–1250 °C and pierced to produce hollow blanks with precise wall thickness control.
- Cold Drawing / Cold Pilgering: Blanks are drawn through precision dies at ambient or reduced temperature to achieve final OD and WT with tight dimensional tolerances (typically ±0.10 mm).
- Solution Annealing: Tubes are reheated to 1040–1120 °C in a controlled-atmosphere furnace and rapidly quenched to restore full austenitic microstructure and eliminate cold-work stresses.
- Pickling and Passivation: Surface oxides are removed via acid pickling; a protective chromium oxide film is re-established through passivation treatment.
- Coiling: Finished straight tubes are wound into continuous coils using automated coiling equipment with tension control to prevent kinking or ovality distortion.
4.2 ERW Coil Tube Production Route
- Strip Uncoiling and Straightening: Cold-rolled stainless steel strip is fed from a coil into a forming station.
- Roll Forming: A series of progressive rolls shapes the flat strip into a tubular geometry with controlled OD and WT.
- Electric Resistance Welding (ERW): The formed seam is welded using high-frequency induction current, producing a narrow, heat-affected zone with minimal distortion.
- Full Weld Annealing: The entire tube (not merely the weld zone) is annealed to homogenize microstructure and eliminate residual welding stresses — a critical differentiator from standard ERW carbon steel pipe.
- Sizing and Coiling: The annealed tube passes through final sizing rolls before being coiled for delivery.
5. Pressure Testing and Seal Integrity Verification
This section addresses the core technical focus of the referenced learning document — 耐压试验与密封性检查 (Pressure Testing and Seal Integrity Inspection) — which constitutes a non-negotiable quality gate in the coil tube manufacturing value chain.
5.1 Hydrostatic Pressure Testing
Hydrostatic testing is the primary method for verifying the structural integrity of stainless steel coil tubes. The procedure follows ASTM A554, EN 10217-7, or GB/T 24511 as applicable.
- Test Medium: Deionized water (conductivity ≤ 10 μS/cm) to prevent chloride-induced stress corrosion cracking during the test cycle.
- Test Pressure Calculation: Ptest = 2 × S × t / Do, where S is the specified minimum yield strength, t is the nominal wall thickness, and Do is the outer diameter.
- Hold Time: Minimum 15 seconds at full test pressure; extended hold times (60–120 seconds) for tubes with OD > 50 mm or WT < 1.0 mm.
- Acceptance Criteria: No visible leakage, no surface wetness, no pressure drop exceeding 0.5% of test pressure during the hold period, and no permanent deformation (elongation ≤ 0.2% of original length).
- Post-Test Requirement: Tubes must be drained, dried, and re-passivated if exposed to non-deionized water or chloride-containing test media.
5.2 Pneumatic Pressure Testing
Pneumatic testing is employed when hydrostatic testing is impractical (e.g., high-elevation installations, cryogenic service qualification, or when residual moisture is unacceptable).
- Test Pressure: 1.25× the maximum allowable working pressure (MAWP), not exceeding 1.5× MAWP.
- Medium: Dry, oil-free compressed air or nitrogen (oxygen content ≤ 50 ppm).
- Safety Protocol: All personnel must be evacuated from the test zone; remote actuation and pressure relief valves are mandatory per OSHA 29 CFR 1910.250.
- Leak Detection: Soap-solution application at joints and weld seams; ultrasonic acoustic leak detection for larger assemblies.
5.3 Seal Integrity Inspection
Seal integrity verification ensures that the tube maintains a hermetic barrier under service conditions. Multiple complementary methods are deployed:
- Visual Inspection (VT): 100% examination of tube ends, weld seams, and surface for defects including cracks, pits, inclusions, and surface contamination per ASTM E165.
- Dye Penetrant Testing (PT): Application of fluorescent or visible-dye penetrant to detect surface-breaking defects such as hairline cracks, laps, and seams per ASTM E709.
- Eddy Current Testing (ET): Non-contact electromagnetic inspection of the tube interior and exterior for subsurface and surface defects, dimensional variations, and weld integrity per ASTM E709 and ASTM E3098.
- Helium Leak Testing: For ultra-high-integrity applications (e.g., semiconductor processing, nuclear instrumentation), helium mass spectrometry leak testing achieves detection limits of 1 × 10⁻⁹ Pa·m³/s per ISO 14236.
- Dimensional Inspection: OD and WT verification using ultrasonic thickness gauges (UT) per ASTM E797; roundness and straightness checks using laser profilometry.
5.4 Quality Assurance Workflow
- Incoming raw material certification review (Mill Test Reports per ASTM A976)
- In-process dimensional and surface inspection at forming and welding stations
- Post-annealing chemical composition verification via OES (Optical Emission Spectroscopy)
- 100% hydrostatic or pneumatic pressure testing
- 100% seal integrity inspection (VT + PT + ET)
- Final passivation verification via contact-angle test (water contact angle ≥ 70°)
- Coil bundling, labeling, and traceability documentation
6. Applications
- Food and Beverage Processing: Sanitary-grade coil tubing for CIP (Clean-In-Place) and SIP (Sterilize-In-Place) systems; dairy, brewery, and pharmaceutical processing lines.
- Chemical Processing: Reactor feed lines, heat exchanger tubes, and corrosive fluid transfer in petrochemical and specialty chemical plants.
- Automotive and Aerospace: Exhaust systems, fuel lines, hydraulic circuits, and structural tubing requiring high strength-to-weight ratios.
- Medical Devices: Endoscopy instrument tubing, implantable device components, and sterilizable fluid delivery lines.
- Energy and Power Generation: Solar thermal collector tubes, geothermal well casings, and heat exchanger bundles in combined-cycle power plants.
- Construction and Architecture: Structural bracing, handrails, decorative elements, and fire suppression piping in commercial and residential buildings.
- Semiconductor and Electronics: Ultra-pure gas delivery lines, vacuum chamber components, and cleanroom fluid handling systems.
7. Quality Certifications and Compliance
- ISO 9001:2015 — Quality Management System certification for consistent product quality and process control.
- ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- EN 10204 3.1 / 3.2 — Inspection and Test Reports with third-party witness and certification options.
- ASTM A976 — Standard for Certification or Test Reports for Product for Use as Materials of Construction in Pressure Vessels.
- CE Marking (PED 2014/6