Introduction of the Special Requirements for the TC2 Nondestructive Testing Certificate
Date:2025-08-19
I. Core Challenge: Steel Pipe Geometry and Process Characteristics
Curvature and Beam/Radio Path:
Ultrasonic Testing (UT): Pipe wall curvature causes variations in beam incidence angle, acoustic field distortion, and echo interference between internal and external surfaces, placing extremely high demands on probe matching, wedge design, and scan planning.
Radiographic Testing (RT): Circular cross-sections result in continuously varying wall thicknesses, affecting film/image density and contrast. This requires precise calculation of exposure parameters (such as when using double-wall single-shadow/double-shadow techniques), and imposes special requirements for Image Quality Indicator (IQI) placement and blackness assessment.
Weld Types and Accessibility:
Common welds include straight seam submerged arc welding (LSAW), spiral submerged arc welding (SSAW), electric resistance welding (ERW), and seamless butt welds. Defect characteristics vary depending on the process.
Limited Inspection Location: Probe/Radio Source placement and scan path planning are particularly challenging for small-diameter pipes (DN < 100mm) or densely packed pipe bundles.
Typical Defect Characteristics:
ERW Pipes: Cold welds, gray spots, linear defects, and centerline cracks/lack of fusion are critical defects.
LSAW/SSAW Pipes: Focus on incomplete penetration, lack of fusion, slag inclusions, porosity, and cracks, especially at the arc starting/ending points and T-joints.
Seamless Pipe Butt Welds: Incomplete root penetration, concavity, and misalignment are common.
Batch Inspection and Automation Requirements: Steel pipe production is typically large-scale and continuous, placing extremely high demands on inspection efficiency, automation (such as automated ultrasonic testing (AUT) and real-time radiographic imaging (DR/CR), and process stability.
II. Core and Special Requirements for the TC2 Certificate for Steel Pipe Inspection
In-depth Training Content Extension (Critical!):
In-depth Explanation of Steel Pipe Manufacturing Processes: A thorough understanding of the LSAW, SSAW, ERW, and seamless pipe production processes, the potential defect mechanisms at each stage, and typical morphological characteristics is essential. General welding knowledge alone is insufficient.
Mastery of Steel Pipe Standards: Focus on strengthening your understanding and application of the following core standards:
API SPEC 5L/5CT: Specification for Line Pipe/Casing Pipe for the Petroleum and Natural Gas Industry (American Standard, globally recognized).
ISO 10893 Series: Nondestructive Testing of Steel Pipe (International Standard, including specific requirements for methods such as UT, RT, MT, ET, and AUT).
ASTM A530/A53, ASTM A106, ASTM A333: General steel pipe material and testing standards.
ASME B31.3/B31.4/B31.8: Specification for Process Piping/Gas and Oil Pipeline Systems (involving testing requirements).
DNVGL-ST-F101: Specification for Subsea Pipeline Systems (strict offshore requirements).
Curvature Compensation Technology: UT personnel require in-depth instruction on curved probe selection (such as small wafers, short leading edges, and specialized wedges), the impact of curvature on beam angle and focus, the use of reference test blocks (with curvature!), and time-based linearity correction (TCG/DAC). RT personnel require mastery of thickness compensation techniques and double-wall transillumination parameter calculation.
Automated Testing System (AUT/DR): For Level 2/3 personnel, specialized training is required on automated system principles, equipment composition, channel setup, focal law development, encoder calibration, data acquisition software operation, and data analysis and interpretation (A-scan, B-scan, C-scan, fan charts, etc.).
Small Diameter Pipe and Confined Space Inspection Technology: Specialized probes (micro, water wedge), scanner design, and process development.
Typical Defect Image Library: Extensive study of the true characteristics of typical defects unique to steel pipes as measured by UT (A-scan waveforms), RT (film/images), and MT/PT (magnetic trace/penetration).
Special Requirements for Practical Test Samples:
Specimens Must Have Representative Curvature: The diameter range of steel pipe specimens (or curvature comparison test blocks) used for the test must cover common specifications (e.g., DN50-DN1200), and their curvature must accurately reflect the actual testing challenges. Flat specimens cannot meet the practical test requirements for TC2 steel pipe certification.
Highly Targeted Defect Settings: Man-made or natural defects must include the following:
ERW pipes: cold welds, gray spots, and linear defects.
LSAW/SSAW pipes: lack of groove fusion, lack of interlaminar fusion, incomplete root penetration, longitudinal cracks (especially in the heat-affected zone), and slag chains.
General: transverse cracks, porosity clusters, root concavity, and excessive misalignment.
Location: Defects must be placed in critical areas such as the weld center, fusion line, and heat-affected zone, and at varying depths and orientations.
Automated System Operation (if applicable): For Level 2/3 certification in AUT or DR RT, the practical examination may require the completion of the entire process of setup, calibration, scanning, data acquisition/imaging, analysis and result evaluation on a simulated or actual automated inspection system.
