TOFD/Phased Array Ultrasonic Testing for Stainless Steel Coil Tubes

Product Overview

The TOFD (Time of Flight Diffraction) and Phased Array Ultrasonic Testing (PAUT) systems employed at Wenzhou Jixing Metal Materials Co., Ltd. represent the state-of-the-art in non-destructive testing (NDT) for stainless steel coil tubes (Coiltube, Product No. 93). These advanced digital imaging techniques have emerged as the preferred alternative to conventional radiographic testing (RT) in high-end industrial applications, offering superior defect characterization capabilities through precise quantitative analysis.

Unlike traditional single-element ultrasonic testing, both TOFD and phased array methodologies utilize multi-element transducer arrays and sophisticated signal processing algorithms to generate high-resolution digital images of internal defects. This approach provides operators with comprehensive spatial information about defect geometry, orientation, and dimensions — capabilities that are fundamentally unattainable through conventional radiographic inspection alone.

Material & Properties

Applicable Stainless Steel Grades

Acoustic Properties Relevant to UT Inspection

Specifications

Parameter TOFD Specification Phased Array (PAUT) Specification
Transducer Configuration Paired wedge-mounted transducers (transmitter/receiver) Multi-element linear or matrix array (16–64 elements)
Frequency Range 2.5–10 MHz (typical 5 MHz for coil tubes) 0.5–15 MHz (adjustable per inspection requirement)
Element Pitch N/A (fixed transducer pair) 0.5–1.5 mm
Inspection Range (Wall Thickness) 2–100 mm 1–200 mm
Defect Detection Sensitivity ≥ 0.5 mm (diffraction-based) ≥ 0.3 mm (A-scan resolution)
Defect Sizing Accuracy ± 0.5 mm (length and height) ± 0.3 mm (length, height, and depth)
Image Acquisition Rate Up to 100 A-scans per second Up to 1,000 A-scans per second
Scanning Speed 0.5–5 mm/s (manual) or up to 200 mm/min (automated) 0.5–5 mm/s (manual) or up to 500 mm/min (automated)
Image Display B-scan, C-scan, TOFD image (diffraction-based) S-scan, B-scan, C-scan, D-scan, 3D volumetric rendering
Software Platforms Olympus OmniScan, Evident (formerly Sonatest), Sonatest Sonix Olympus OmniScan, Evident, Zetec, TRL
Applicable Standards ISO 17638, EN 17142, ASME V Article 8 ISO 13588, EN 17143, ASME V Article 9

Manufacturing & Inspection Process

Stage 1: Coil Tube Production

  1. Raw Material Verification: Ingot/slab acceptance with mill test certificates (MTC) per EN 10204 3.1/3.2, verifying chemical composition (C, Cr, Ni, Mo, N, etc.) and mechanical properties.
  2. Hot Rolling / Cold Drawing: Production of coil tube blank with controlled wall thickness tolerances (± 0.1 mm for precision grades).
  3. Forming & Welding: Cold forming to target outer diameter; optional longitudinal welding (TIG/GTAW) for welded coil tube variants.
  4. Heat Treatment: Solution annealing at 1050–1150 °C followed by controlled cooling to ensure uniform microstructure and stress relief.
  5. Surface Finishing: Pickling, passivation, and optional polishing to achieve specified surface roughness (Ra ≤ 0.8 μm for critical applications).

Stage 2: TOFD/Phased Array Inspection Protocol

  1. Pre-Inspection Preparation:
    • Couplant application (water-based or glycerine-based gel for stainless steel compatibility)
    • Surface preparation to Ra ≤ 6.3 μm for acoustic coupling
    • Probe calibration on reference blocks (e.g., IIW Type 1, ASTM E2330 reference standards)
  2. TOFD Inspection Execution:
    • Transmitting and receiving transducers positioned at fixed separation distance (typically 25 mm) on either side of the weld/seam
    • Diffraction signals from defect tips captured and time-resolved to calculate defect height
    • Automated scanning along the full circumference and longitudinal axis of the coil tube
  3. Phased Array Inspection Execution:
    • Electronic beam steering and focusing across the full thickness and circumference
    • Multiple scan modes deployed: sector scan, linear scan, and compound scan for comprehensive volumetric coverage
    • Real-time S-scan display enabling immediate defect identification and classification
  4. Data Acquisition & Analysis:
    • Full digital data recording for traceability and post-inspection review
    • Signal processing algorithms (gate definition, threshold setting, defect flagging) per applicable code requirements
    • Defect characterization: sizing (length, height, depth), location mapping, and classification (porosity, slag inclusion, lack of fusion, crack, etc.)
  5. Reporting & Acceptance Criteria:
    • Inspection reports issued per ASME BPV Section V, EN ISO 17635, or project-specific quality plans
    • Acceptance/rejection based on defect size limits defined by applicable pressure vessel or piping codes
    • Digital image archiving for long-term traceability

Applications

Primary Industrial Sectors

High-End Project Advantages Over Radiographic Testing

TOFD and phased array ultrasonic testing have become the preferred NDT method in high-end engineering projects for several compelling reasons:

  • Quantitative Defect Sizing: Unlike radiographic testing, which provides only a 2D projection, TOFD/PAUT delivers precise 3D defect dimensions, enabling accurate fitness-for-service evaluations.
  • No Ionizing Radiation: Eliminates the health, safety, and regulatory burden associated with X-ray/gamma-ray sources — a significant advantage for in-service inspections and environmentally sensitive sites.
  • Real-Time Imaging: Operators receive immediate visual feedback on defect location and characteristics, reducing inspection cycle time by 30–50% compared to film-based radiography.
  • Digital Data Retention: Full inspection data is digitally recorded, enabling remote expert review, trend analysis, and integration with digital twin and predictive maintenance systems.
  • Superior Sensitivity to Planar Defects: TOFD excels at detecting cracks, laminations, and lack-of-fusion defects that may be orientationally invisible to radiographic testing.

Quality Certifications & Compliance

Applicable International Standards

Personnel Qualification

Traceability & Documentation

Unique Selling Points

  1. Industry-Leading Technology Adoption: Wenzhou Jixing Metal Materials Co., Ltd. has invested in the latest generation of TOFD and phased array systems, ensuring that coil tube products meet the most demanding quality requirements of international energy, nuclear, and aerospace sectors.
  2. Digital Imaging Advantage: The transition from analog to fully digital NDT workflows enables superior defect quantification accuracy (± 0.3 mm), reducing false acceptance risk and supporting data-driven quality decisions.
  3. Strategic Alignment with Industry Trends: As radiographic testing is progressively displaced by advanced ultrasonic methods in high-end projects — driven by safety regulations, digital transformation mandates, and the need for quantitative defect data — this facility is positioned at the forefront of this industry shift.
  4. Comprehensive Inspection Coverage: The combination of TOFD and phased array techniques provides complementary defect detection capabilities, ensuring that both volumetric (porosity, inclusions) and planar (cracks, laminations) defects are reliably detected and characterized.