Stainless Steel Coil Tube — Arrival Inspection & Acceptance Protocol Specification
1. Product Overview
The Stainless Steel Coil Tube (Product Code: No. 207) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered cold-drawn or hot-finished tubular product supplied in coiled configuration for downstream forming, bending, and fabrication operations. This specification document defines the comprehensive Arrival Inspection Agreement (到货检验协议) governing the verification, acceptance, and disposition of coil tube lots upon delivery to the buyer's premises.
The inspection framework is structured around three core pillars:
- PMI (Positive Material Identification) Re-Inspection Ratio — verifying chemical composition conformance
- NDT (Non-Destructive Testing) Sampling Inspection Scheme — ensuring structural integrity and dimensional accuracy
- Non-Conformance Handling Process — establishing a transparent dispute resolution mechanism
The overarching principle of this protocol is pre-agreed standards to eliminate post-delivery disputes (事前约定避免事后扯皮), ensuring both supplier and buyer share a unified acceptance framework prior to shipment.
2. Material & Properties
Stainless steel coil tubes supplied under this agreement are typically fabricated from austenitic, ferritic, or duplex stainless steel grades conforming to international standards including ASTM A269, ASTM A312, EN 10217, and GB/T 12771. The following material characteristics are verified during arrival inspection:
- Chemical Composition — Cr, Ni, Mo, C, Si, Mn, P, S content verified via PMI (spark OES or XRF spectroscopy)
- Mechanical Properties — Tensile strength, yield strength, elongation, and hardness per applicable grade
- Microstructure — Phase integrity (austenite/ferrite ratio for duplex grades), grain size, and absence of delta ferrite (for 300-series grades)
- Surface Finish — Cold-rolled (2B), pickled (No. 1), or polished (BA/HL) as specified in the purchase order
3. Specifications & Inspection Parameters
3.1 Dimensional Tolerances
| Parameter | Tolerance (mm) | Acceptance Basis | Inspection Method |
|---|---|---|---|
| Outer Diameter (OD) | ±0.05% to ±0.10% of nominal | ASTM A269 / ASTM A312 | Micrometer / OD gauge |
| Wall Thickness (WT) | ±10% of nominal | ASTM A269 | Ultrasonic thickness gauge |
| Coil Flatness | ≤ 0.2% of width (for flattened coil) | Supplier agreement | Flatness gauge / straightedge |
| Roundness (Ovality) | ≤ 1.5% of OD | ASTM A312 | Roundness gauge |
| Length (cut lengths, if applicable) | ±3.0 mm | Purchase order specification | Measuring tape / laser |
3.2 PMI Re-Inspection Ratio
| Lot Size (Tons) | Minimum PMI Samples | Sampling Frequency | Acceptance Criteria |
|---|---|---|---|
| 0 – 5 tons | 2 samples | 1 per coil + 1 spare | 100% conformance to grade specification |
| 5 – 20 tons | 3 samples | 1 per coil + 2 random | Zero deviations permitted |
| 20 – 50 tons | 5 samples | 1 per 10 tons minimum | Zero deviations permitted |
| > 50 tons | 5 + 1 per additional 50 tons | Proportional increase | Zero deviations permitted |
PMI Method: Spark Optical Emission Spectroscopy (OES) or X-ray Fluorescence (XRF) analysis performed on the coil surface and, where accessible, on the inner wall. Results must demonstrate that all major alloying elements (Cr, Ni, Mo, Ti, etc.) fall within the specified grade ranges per ASTM or equivalent standards.
3.3 NDT Sampling Inspection Scheme
| NDT Method | Application | Sampling Ratio | Acceptance Criteria | Standard Reference |
|---|---|---|---|---|
| Eddy Current Testing (ECT) | Surface & subsurface defect detection | 100% inline (if available) or ≥10% of lot | No cracks, laminations, or inclusions exceeding 0.5 mm equivalent | ASTM E309 / ASTM E2785 |
| Ultrasonic Testing (UT) | Wall thickness & internal flaw detection | ≥5% of coils per lot (minimum 2 coils) | No internal discontinuities > 25% of wall thickness | ASTM E2785 / ASTM E127 |
| Visual Inspection (VT) | Surface quality, weld seams, markings | 100% of coils | No visible defects, proper heat number marking | ASTM A312 §9 |
| Magnetic Particle Testing (MT) | Surface-breaking defects (ferritic/duplex grades) | ≥10% of coils per lot | No indications exceeding 3 mm in length | ASTM E709 |
3.4 Non-Conformance Handling Process
- Identification & Notification: Upon discovery of non-conforming material during arrival inspection, the buyer must notify the supplier within 72 hours of receiving the shipment, accompanied by photographic evidence and inspection data.
- Supplier Response: The supplier shall acknowledge receipt of the non-conformance report within 24 hours and provide a Root Cause Analysis (RCA) within 5 working days.
- Disposition Options:
- Return & Replacement: Non-conforming coils returned at supplier's expense; replacement material shipped within the agreed lead time.
- Sorting & Acceptance: If only partial non-conformance exists (e.g., dimensional deviation in a limited length), the buyer may sort usable material and accept the remainder with a price adjustment.
- Use-As-Is with Concession: For minor deviations not affecting functional performance, the buyer may issue a Material Concession Request (MCR) with written approval from the supplier's quality authority.
- Re-work: For correctable surface defects, re-work may be authorized with re-inspection at supplier's cost.
- Escalation & Arbitration: In the event of disagreement on inspection results, a mutually agreed third-party inspection agency (e.g., SGS, Bureau Veritas, TÜV) shall perform independent verification. The cost of arbitration is borne by the party whose position is not upheld.
- Closure: The non-conformance record is formally closed upon acceptance of the disposition action, with documentation filed in both parties' quality management systems.
4. Manufacturing Process
Stainless steel coil tubes are produced through the following key process steps:
- Hot Rolling / Billet Preparation: Continuous casting of stainless steel slabs or billets, followed by hot rolling to reduce thickness to the required range.
- Acid Pickling & Descaling: Removal of mill scale via mixed acid (HNO₃ + H₂SO₄) pickling to achieve a clean, corrosion-resistant surface.
- Cold Drawing / Cold Rolling: The tube blank is drawn through precision dies or cold-rolled to achieve final dimensions with tight tolerances. This step ensures mechanical property improvement and surface quality enhancement.
- Heat Treatment (Solution Annealing): Heating to 1050–1150°C followed by rapid water quenching to dissolve carbides, restore full austenitic structure, and maximize corrosion resistance.
- Piercing / Forming: For seamless tubes, the heated billet is pierced to form a hollow tube; for welded tubes, the coil strip is formed and TIG/ERW welded.
- Coiling: The finished tube is wound onto a coil mandrel of specified inner diameter (typically 300–600 mm) for transport and downstream processing convenience.
- Final Inspection & Packaging: Dimensional verification, PMI confirmation, surface inspection, and protective packaging (wooden pallets, moisture-proof wrapping, coil banding).
5. Applications
Stainless steel coil tubes find extensive application across multiple industries due to their combination of corrosion resistance, mechanical strength, formability, and hygienic surface properties:
- Food & Beverage Processing: Heat exchangers, piping systems, and sanitary equipment (304/316L grades)
- Petrochemical & Oil & Gas: Downstream process piping, heat exchanger tubes, and chemical transfer lines (316, 321, duplex 2205)
- Medical & Pharmaceutical: Equipment housings, sterilization systems, and fluid transport lines (304L, 316L)
- Automotive: Exhaust system components, fuel lines, and structural brackets
- Construction & Architecture: Decorative railings, structural tubing, and façade elements
- Energy & Power Generation: Boiler tubes, condenser tubes, and solar thermal systems
- Downstream Forming: The coil format enables continuous bending, cutting, welding, and machining operations, making it ideal for high-volume fabrication environments
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality assurance credentials and certifications to ensure product conformity and traceability:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System
- EN 10204 3.1 Certificate — Mill test certificates with independent inspection authority verification
- ASTM A269 / A312 Conformance — Product testing and certification per American standards
- EN 10217 Conformance — European standard compliance for welded and seamless tubes
- GB/T 12771 Conformance — Chinese national standard compliance for stainless steel tubes
- Third-Party Inspection (TPI): Available upon request via SGS, Bureau Veritas, or TÜV Rheinland
- Material Traceability: Full heat number traceability from raw material mill to finished coil, with PMI verification at each critical control point
7. Unique Selling Points
- Pre-Agreed Inspection Protocol: The Arrival Inspection Agreement establishes unambiguous acceptance criteria prior to shipment, eliminating ambiguity and preventing costly post-delivery disputes (事前约定避免事后扯皮).
- Structured PMI Re-Inspection: Defined sampling ratios ensure material authenticity verification is neither excessive nor insufficient, balancing cost efficiency with quality assurance.
- Multi-Method NDT Coverage: Combined use of eddy current, ultrasonic, visual, and magnetic particle testing provides comprehensive defect detection across surface, subsurface, and volumetric domains.
- Transparent Non-Conformance Workflow: Clearly defined timelines, disposition options, and escalation mechanisms ensure rapid resolution of quality issues with minimal production disruption.
- Full Traceability: Heat-number-based traceability from raw steel mill through all manufacturing stages to final delivery ensures complete supply chain accountability.
Note: This specification serves as the contractual basis for arrival inspection and acceptance. All parties must agree upon the inspection parameters, sampling ratios, and non-conformance procedures prior to order confirmation. Any deviations from this agreement require written amendment signed by both the buyer and the supplier's authorized quality representative.