The Five Detection Methods For Steel Pipes

Five major non-destructive testing methods for steel pipes

(Including principles, features and applicable scenarios)

1. UT - Ultrasonic Inspection
2. ET - Eddy Current Testing
3. MT - Magnetic Particle Inspection
4. PT - Penetrant Inspection
5. RT - Radiographic Inspection

Theory:

High-frequency mechanical sound waves are emitted to penetrate the steel pipe. When encountering defects or the bottom surface of the pipe wall, the reflected echoes are detected. Based on these echoes, the internal defects can be determined.

Characteristics:

• √ Advantages: The penetration power is the strongest. It can accurately measure wall thickness, internal cracks, interlayers, delamination, shrinkage cavities, etc. It has no radiation and the cost is low.

• × Disadvantages: Coupling agent is required. The surface is rough and difficult to measure. Fine surface cracks are not sensitive. It is inconvenient to detect thin-walled small pipes.

Applicable to steel pipes:
Thick-walled steel pipes, seamless pipes, pipe billets, welds, high-pressure pipelines. The main focus is on detecting internal deep-seated defects.

Theory:

Electromagnetic induction generates eddy currents. Defects on the surface of the steel pipe alter the distribution of these eddy currents, which can be identified through electrical signals.

Characteristics

• √ Advantages: Non-contact, extremely fast, no need for coupling agent, suitable for online high-speed flaw detection in production lines, with extremely high sensitivity for surface micro-cracks

• ×  Disadvantages: Only detects surface and near-surface areas, cannot detect deep layers, only measures conductive metals

Applicable to steel pipes
Thin-walled steel pipes, precision tubes, galvanized pipes, welded pipes for online full-line flaw detection, to detect surface longitudinal cracks.

Theory:

When ferromagnetic steel pipes are magnetized, surface cracks will cause magnetic leakage, and the magnetic powder will adhere to these cracks to reveal the defects.

Characteristics

• √ Advantages: Simple operation, low cost, clear and visible surface cracks

• × Disadvantages: Only applicable to carbon steel and alloy steel, not stainless steel; can only measure the surface and near-surface areas, requires magnetization and demagnetization

Applicable to steel pipes:
Carbon steel seamless pipes, pipe fittings, pipe end bevels, end cracks

Theory:
The penetrant seeps into the opening cracks, and after cleaning, it is subjected to imaging, revealing the surface opening defects.

Characteristics：

• √ Advantages: Can be used for any material, including carbon steel, stainless steel, and alloys. It is visible to the naked eye.

• × Disadvantages: Can only detect exposed cracks on the opening, but cannot detect internal or closed defects. The process is slow.

Applicable to steel pipes：
Stainless steel pipes, alloy steel pipes, weld seam surfaces, re-inspection after grinding

Theory:
The rays penetrate the steel pipe. At the defect area, the penetration amount is large, and the film image becomes black. The defect can be identified.

Characteristics

• √ Advantages: Provides clear imaging, most accurate for detecting pores, slag inclusions, and volumetric defects such as porosity and looseness.

• × Disadvantages: Unsafe due to radiation exposure, high cost, slow speed, and average crack detection rate.

Applicable to steel pipes
Used for radiographic inspection of steel pipe welds, quality inspection of pressure-bearing steel pipe welds, rarely used for full-length steel pipe flaw detection.

1. UT Ultrasonic: Inspect the interior, measure the wall thickness, preferred for thick tubes
2. ET Eddy Current: Scan the surface, fast speed, suitable for online production
3. MT Magnetic Particle: Detect surface cracks in carbon steel, inexpensive and easy to use
4. PT Penetrant: Suitable for all materials, only checks open cracks
5. 5RT Radiographic: Detect weld seam pores, less radiation, less commonly used

1. Ordinary carbon steel thick-walled seamless pipe
Internal defects → UT; surface cracks → MT

2. Thin-walled precision welded pipe/flow pipe
Whole production line flaw detection → ET eddy current

3. Stainless steel pipe
Surface cracks → PT penetrant (cannot use magnetic powder)

4. Quality inspection of steel pipe welds
Internal defects → UT, pores and slag → RT

5. High-speed mass production of steel pipes
Always give priority to eddy current ET, with the highest efficiency

6. High-pressure, boilers, and special equipment steel pipes
UT +ET  double inspection, covering all internal and external defects

• For internal inspection: UT (Ultrasonic Testing)
• For surface mass production inspection: ET (Electromagnetic Testing) or ET (Eddy Current Testing)
• For carbon steel surfaces: MT (Magnetic Particle Testing)
• For stainless steel surfaces: PT (Penetrant Testing)
• For weld inspection: RT (Radiographic Testing)