There are many detection methods for non-destructive testing of black steel seamless pipes. For surface defects, such as eddy current, magnetic flux leakage, penetration and visual inspection, ultrasonic and radiographic methods can be used for internal flaw detection.

Advantages of NDT

1) It will not damage the black steel seamless pipe; 100% inspection can be achieved;
2) Defects can be found and uated accordingly to ensure the quality of materials, workpieces or components;
3) Regular inspection and even long-term monitoring of the key components of the black steel pipe can be carried out in use to ensure safe operation and avoid accidents;
4) Find defects, point out the reasons and laws of their formation, and prompt relevant departments to take measures to improve the design or process to further improve the quality, prevent and reduce waste, and reduce production costs.

Non-destructive testing methods

1) Ultrasonic flaw detection (GB/T5777-1996, GB/T5777-2008)

The most widely used method is the pulse reflection method. A method of judging defects by transmitting ultrasonic waves into the metal under test and then receiving echoes reflected from defects. It is divided into vertical flaw detection method and oblique flaw detection method. The vertical flaw detection method is mainly used for the detection of castings, forgings, plates and composite materials. The bevel inspection method is mainly used to detect internal defects such as welds and pipe fittings.

Piezoelectric ultrasound mainly checks the longitudinal defects of black steel seamless pipes and is used for measuring diameter and thickness; electromagnetic ultrasound can check longitudinal and transverse defects. The main levels are C3 (L1), C5 (L2), C8 (L25), C10 (L3), C12 (L4). Among them, C5 is used for cold working high pressure boiler tubes; C8 is used for hot working high pressure boiler tubes; C10 and C12 are used for other purpose steel pipes.

2) Eddy current flaw detection ( GB/T7735-2004 )

The basic principle of eddy current testing is to use electromagnetic induction to detect defects in conductive materials. The eddy current detection probe or coil uses alternating current, and its alternating magnetic field induces the component under test to generate eddy current, and the defect of the component causes the change of the intensity and distribution of the eddy current, and displays it on the cathode ray tube or instrument, according to the change of the test eddy current to identify defects.

Mainly used for black steel seamless pipe surface, near surface flaw detection. Penetrating eddy current testing mainly detects lateral defects and delaminations. Eddy current can also be used to measure thickness, hardness, strength, diameter and distance. Acceptance levels are A and B. Acceptance level A can be used as an alternative to hydraulic tightness inspection. Acceptance level B is negotiated by both the supplier and the buyer and specified in the contract. The sample tube has drilled holes (through holes) and longitudinal grooves.

3) Magnetic flux leakage inspection ( GB/T12606-1999 )

It is mainly used for flaw detection on the surface of black steel seamless pipes and near-surface defects (such as cracks, folds, interlayers, channels, cold insulation, etc.). The acceptance level is divided into L2, L3 and L4 (the groove depth on the outer surface is 5%, 10% and 12.5% of the nominal wall thickness of the black steel pipe), and L2.5 is 8%.

4) Magnetic particle inspection ( GB/T15822-1995 )

The basic principle of magnetic particle inspection technology is to place ferromagnetic materials (iron, cobalt, nickel) in a strong magnetic field to magnetize them. If there are defects on the surface or near surface of the black steel seamless pipe, some of the magnetic lines of force will overflow to form a leakage magnetic field. The magnetic powder on its surface has an adsorption effect, and the defect site of the magnetic powder shows traces of the defect, reflecting the orientation, position and size of the defect.

Mainly used for flaw detection of black steel seamless pipe surface, near-surface cracks and other defects. There are three types of A-type standard test pieces, B-type standard test pieces and C-type standard test pieces. Magnetic particle inspection only detects vertical and horizontal flaws within 400mm of the pipe end.