Stainless Steel Coil Tube (Coiltube) — Incoming Inspection Agreement & Acceptance Protocol
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered metallic product delivered in continuous coil configuration, designed for downstream processing including straightening, cutting, and forming operations. As a critical industrial intermediate material, coil tubes are widely employed in heat exchanger manufacturing, chemical processing, food-grade piping systems, and architectural applications.
The Incoming Inspection Agreement (到货检验协议) constitutes the contractual framework governing the acceptance criteria, verification methods, and dispute resolution mechanisms between the supplier and the purchaser. This agreement is established a priori to prevent post-delivery disputes and ensure mutual accountability for product quality conformance.
Material & Properties
Coil tubes are typically fabricated from austenitic, ferritic, or duplex stainless steel grades conforming to international standards including ASTM A213, ASTM A312, EN 10216-5, and GB/T 14976. Key material properties include:
- Chemical Composition: Verified through Positive Material Identification (PMI) testing to confirm compliance with specified grade requirements (e.g., 304, 316L, 321, 310S)
- Mechanical Properties: Tensile strength, yield strength, and elongation verified per applicable standards
- Corrosion Resistance: Confirmed through intergranular corrosion testing (ASTM A262) where applicable
- Microstructural Integrity: Assessed via metallographic examination for grain size, phase distribution, and absence of deleterious inclusions
Specifications
| Parameter | Specification / Requirement | Standard Reference |
|---|---|---|
| Product Form | Continuous coil (Coiltube) | — |
| Typical Outer Diameter (OD) | 6.00 mm – 323.85 mm | ASTM A312 / EN 10216-5 |
| Typical Wall Thickness | 0.50 mm – 12.70 mm | ASTM A312 / EN 10216-5 |
| Coil Weight Range | 500 kg – 5,000 kg (typical) | Supplier specification |
| Surface Finish | 2B, BA (Bright Annealed), Pickled & Passivated | ASTM A480 |
| PMI Re-inspection Ratio | 100% (lot-based) or minimum 3 samples per coil | Contractual agreement |
| NDT Sampling Scheme | 10% minimum per lot; full inspection for critical applications | ASTM E709 / EN 12195 |
| Acceptance Tolerance (OD) | ±0.10 mm or ±0.5% (whichever is greater) | ASTM A312 |
| Acceptance Tolerance (Wall) | ±10% of nominal | ASTM A312 |
Manufacturing Process
The production of stainless steel coil tubes involves the following key stages:
- Hot Rolling / Cold Rolling: Steel strip is rolled to the required thickness and width specifications
- Forming: The strip is formed into tube shape using continuous forming mills (slit-and-roll or seamless processes)
- Welding (if applicable): Longitudinal weld seam formed via TIG (Tungsten Inert Gas) or orbital welding for welded tubes
- Heat Treatment: Solution annealing at 1010°C – 1150°C followed by rapid quenching to achieve austenitic microstructure
- Pickling & Passivation: Removal of oxide scale and establishment of protective chromium oxide layer
- Coiling: Continuous tube wound onto coil cores for shipment
- Final Inspection: Dimensional verification, PMI testing, and NDT prior to dispatch
Quality Certifications & Inspection Protocol
PMI Re-inspection (Positive Material Identification)
PMI testing is conducted using XRF (X-ray Fluorescence) or OES (Optical Emission Spectroscopy) analyzers to verify chemical composition against the specified grade. The re-inspection ratio is pre-agreed in the Incoming Inspection Agreement and typically follows these guidelines:
- Standard lots: Minimum 3 samples per coil (head, middle, tail positions)
- Critical applications (nuclear, medical, aerospace): 100% lot verification with full chemical analysis
- Second-source materials: Enhanced sampling at 5 samples per coil minimum
NDT Sampling Scheme (Non-Destructive Testing)
Non-destructive testing ensures the absence of internal and surface defects. The agreed sampling scheme includes:
- Eddy Current Testing (ECT): 10% minimum per lot for surface and near-surface defect detection (ASTM E309)
- Ultrasonic Testing (UT): Applied for wall thickness verification and internal defect detection (ASTM E709)
- Visual Inspection (VT): 100% for surface defects, weld bead integrity, and coil condition
- Hydrostatic Testing: For pressure-containing applications, 100% per coil at 1.5× working pressure
Non-Conformance Handling Procedure
The Incoming Inspection Agreement defines a structured escalation pathway for non-conforming product:
- Identification: Defective coil is quarantined and documented with photographic and measurement evidence
- Notification: Formal Non-Conformance Report (NCR) issued to supplier within 48 hours of detection
- Root Cause Analysis: Supplier conducts 8D (Eight Disciplines) analysis within 7 working days
- Disposition: Options include rework, re-sorting, scrap replacement, or negotiated acceptance at reduced pricing
- Corrective Action: Supplier implements CAPA (Corrective and Preventive Action) with verification of effectiveness
- Closure: Agreement signed by both parties confirming resolution and prevention of recurrence
Applications
- Heat Exchangers & Boilers: Condenser tubes, evaporator coils, and boiler tubes in power generation
- Chemical Processing: Corrosive fluid transport in petrochemical and pharmaceutical plants
- Food & Beverage Industry: Hygienic piping systems requiring 304L/316L grade with sanitary finish
- Automotive: Exhaust systems, fuel lines, and structural components
- Architecture & Construction: Decorative railings, structural elements, and façade systems
- Medical Devices: Tubular components in surgical instruments and diagnostic equipment
Unique Selling Points
- Pre-agreed Inspection Framework: Eliminates post-delivery disputes through clearly defined PMI ratios, NDT protocols, and acceptance thresholds established before shipment
- Comprehensive Quality Traceability: Full material certification (Mill Test Certificate, MTC) with EN 10204 Type 3.1 compliance
- Flexible Coil Configuration: Available in multiple coil weights and diameters to optimize downstream processing efficiency
- Strict Non-Conformance Protocol: Structured 8D-based resolution ensures rapid corrective action and continuous improvement
- Multi-Grade Availability: Covers austenitic, ferritic, duplex, and precipitation-hardening grades from a single reliable source
Quality Certifications
Products are manufactured under a certified ISO 9001:2015 Quality Management System. Additional certifications include:
- EN 10204 Type 3.1: Third-party inspection certificate for material conformance
- NACE MR0175 / ISO 15156: For sour service applications (H₂S-containing environments)
- ASME Stamp: For pressure vessel and piping applications
- PED (Pressure Equipment Directive) 2014/68/EU: For European market compliance
- NSF/ANSI 61: For potable water contact applications
Note: All inspection ratios, sampling frequencies, and acceptance criteria are subject to the specific Incoming Inspection Agreement (到货检验协议) executed between the supplier and purchaser. The principle of "事前约定避免事后扯皮" (pre-agreement to avoid post-dispute) underpins the contractual integrity of the supply relationship, ensuring transparency, accountability, and mutual quality assurance.