Eddy Current Testing of Seamless Pipes

In the production and use of seamless pipes, flaw detection is a crucial step in ensuring product quality and safety. As a fundamental material in the industrial field, the quality of seamless steel pipes directly affects equipment safety and service life.

 

Eddy current testing is mainly used for surface and near-surface flaw detection. Through-type eddy current testing primarily detects transverse defects and delamination. Eddy currents can also be used for thickness measurement, hardness, strength measurement, diameter measurement, and distance measurement. Acceptance levels are A and B. Acceptance level A can be used as an alternative to water pressure tightness testing, while acceptance level B is negotiated between the supplier and the buyer and specified in the contract. Sample pipes include drilled holes (through holes) and longitudinal grooves.

Eddy Current Testing of Seamless Pipes

Eddy current testing is suitable for detecting surface and near-surface defects in seamless steel pipes made of conductive materials.

 

1. Detection Principle

When an alternating magnetic field approaches a conductive seamless steel pipe, eddy currents are generated inside the pipe. If defects exist on or near the surface of the seamless steel pipe, they will affect the distribution and magnitude of the eddy currents. The presence of defects is determined by detecting changes in the eddy currents.

 

2. Advantages

Fast detection speed, enabling automated inspection; high sensitivity for surface and near-surface defects; capable of inspecting seamless tubes made of various conductive materials.

 

3. Limitations

Qualitative and quantitative analysis of defects is relatively difficult; poor inspection results for seamless tubes with complex shapes; limited detection depth.

Eddy Current Testing Items for Seamless Pipe

1. Surface Crack Detection

Internal and external wall cracks, longitudinal cracks, transverse cracks, network cracks, stress corrosion cracks, fatigue cracks, manufacturing defect cracks, weld heat-affected zone cracks, service damage cracks, buried cracks, etc.

 

2. Pit and Corrosion Detection

Pitting depth, uniform corrosion area, local thinning, erosion pits, selective corrosion, crevice corrosion, microbial corrosion, weld corrosion, heat-affected zone corrosion, wall thickness reduction rate, etc.

 

3. Material Defect Detection

Inclusions, delamination, folds, porosity, looseness, white spots, coarse grains, segregation, forging cracks, rolling defects, etc.

 

4. Weld Quality Inspection

Incomplete fusion, incomplete penetration, undercut, weld beads, concave or convex welds, misalignment, excessive weld reinforcement, weld cracks, porosity, and slag inclusions.

 

5. Wall Thickness Measurement

Nominal wall thickness, minimum remaining wall thickness, average wall thickness, wall thickness reduction, ellipticity, out-of-roundness, local thickening, corrosion allowance, wall thickness distribution map, wall thickness variation rate, etc.

 

6. Near-Surface Defect Inspection

Subcutaneous cracks, near-surface porosity, delamination, folds, near-weld defects, heat treatment cracks, grinding cracks, quenching cracks, extrusion cracks, near-surface corrosion, etc.

 

7. Coating and Lining Inspection

Coating thickness, coating peeling, coating porosity, lining fit, lining cracks, anti-corrosion layer damage, lining thinning, coating adhesion, lining corrosion, interface defects, etc.

 

8. Geometric Dimension Inspection

Pipe outer diameter, pipe inner diameter, curvature, straightness, ellipticity, circumference, cross-sectional shape, beveling angle, pipe end preparation, length deviation, etc.

 

9. Material Property Inspection

Electrical conductivity, magnetic permeability, hardness, grain size, heat treatment state, material grade identification, microstructure, non-metallic inclusions, decarburized layer, hardened layer depth, etc.

 

10. Service Performance Assessment

Remaining service life, safety status, damage level, failure risk, applicability, inspection cycle, maintenance recommendations, service life prediction, risk level, conditions for continued use, etc.

 

Eddy Current Testing Methods for Seamless Pipes

1. Through-type Eddy Current Testing

Through-type eddy current testing is the most widely used method for eddy current testing of steel pipes. It is generally used for steel pipes with a diameter less than 180mm. Its advantages include fast testing speed, the ability to inspect the entire surface of the steel pipe, and relatively simple equipment adjustment and operation.

 

2. Rotating Point Probe Eddy Current Testing

Rotating point probe eddy current testing is an automated flaw detection method where a network of point probes rotates around a steel pipe, while the pipe moves linearly. The point probes are placed inside a rotating head, and the probes rotate to scan the surface of the steel pipe.

 

The rotating point probe method is more suitable for inspecting small to medium diameter steel pipes. The point probes have high sensitivity and are suitable for inspecting steel pipes with relatively smooth surfaces. It is not suitable for hot-rolled steel pipes, steel pipes with oxide scale, or other rough surfaces.

 

Eddy Current Testing Standards

ISO 15549, ISO 15548-1, ISO 15548-2, ISO 12718, ISO 20669, ASME BPVC SJianCeion V, ASME B31.3, ASTM E309, ASTM E571, ASTM E1316, EN 1711, EN 13860-1, EN 13860-2, JIS G 0588, GB/T 12604.6, GB/T 14480, GB/T 26953, GB/T 26954, GB/T 28705, GB/T 28706, GB/T 32538, GB/T 32565, GB/T 34361, GB/T 34634, GB/T 38894, JB/T 4730.6, JB/T 6912, NB/T 47013.6

 

Eddy Current Testing Equipment for Seamless Pipes

1. Multi-Frequency Eddy Current Detector

Capable of simultaneous multi-frequency excitation and signal processing, it can simultaneously detect defects of different depths, suppress interference signals, and improve the signal-to-noise ratio. Suitable for defect detection and classification under complex working conditions.

 

2. Far-Field Eddy Current Detection System

Utilizes far-field eddy current technology to detect defects across the entire wall thickness of ferromagnetic pipes. Unaffected by the skin effect, it can detect defects on both the inner and outer walls of pipes, suitable for oil and gas pipeline inspection.

 

3. Array Eddy Current Probe

Composed of multiple detection coils arranged according to specific rules, it can cover a large detection area at once, improving detection efficiency and generating two-dimensional or three-dimensional images of pipe defects for easy defect location and assessment.

 

4. Magnetic Saturation Device

Performs magnetic saturation treatment on ferromagnetic materials to eliminate the influence of changes in material permeability on eddy current detection, improving detection accuracy and reliability. Suitable for pipes made of magnetic materials such as carbon steel and alloy steel.

 

5. Pipeline Inspection Robot

Integrating an eddy current testing system and an automated movement device, this robot can autonomously move and inspect pipes inside, suitable for long-distance, large-diameter, and inaccessible pipelines.

 

6. Digital Eddy Current Signal Analysis System

Utilizing digital signal processing technology, this system filters, amplifies, performs phase analysis, and displays impedance planes on the detection signal, improving defect identification and quantitative accuracy.

 

7. High-Temperature Eddy Current Testing Equipment

Specially designed for pipeline inspection in high-temperature environments, this equipment features high-temperature resistant probes and cables, allowing for online inspection while the system is running, minimizing downtime.

 

8. Dedicated Eddy Current Probe Series

Includes various types such as absolute probes, differential probes, reflective probes, and through-type probes, optimized for different pipeline specifications, materials, and inspection requirements.

 

9. Automated Scanning Device

Enables precise positioning and uniform speed movement of the probe on the pipeline surface, ensuring comprehensive and consistent inspection coverage. Suitable for rapid inspection of large batches of regularly shaped pipelines.

 

10. Data Acquisition and Management System

This system collects, stores, and processes inspection data in real time, generates inspection reports, establishes a pipeline inspection database, enables historical data comparison and trend analysis, and supports pipeline integrity management.

 

Summary

In conclusion, eddy current testing plays a crucial role in the production and quality control of seamless pipes. It can improve product quality, ensure production safety, and optimize production processes, thus possessing significant practical application value.