NB/T 47013.4-2015Nondestructive testing of pressure equipments - Part 4: Magnetic particle testing (English PDF)

3.1 Relevant indication

It refers to the magnetic mark indication as formed due to the magnetic particle absorption by the leakage magnetic field which is due to the presence of flaw in the process of magnetic particle testing.

3.2 Non-relevant indication

Non-related indication is non-relevant.

It refers to the magnetic mark indication as formed by the magnetic particle absorption by the leakage magnetic field due to the change of the cross section or material permeability in the process of magnetic particle testing.

3.3 False indication

It refers to the magnetic mark indication which is not formed due to the magnetic particle absorption by the leakage magnetic field.

3.4 Combinatorial magnetization

It refers to the magnetization method to produce a magnetic field the size and direction of which is in circular, oval or spiral changes with time in the workpiece.

3.5 Longitudinal/transverse flaw

When the included angle between the long axis direction of the flaw magnetic mark and the workpiece (shaft or tube) axis or the busbar is greater than or equal to 30", it is treated as transverse flaw; AND the rest is treated as longitudinal flaw.

4.1 Inspectors

4.1.1 Personnel engaged in magnetic particle testing shall comply with the relevant requirements of NB/T 47013.1.

4.1.2 The uncorrected or corrected near (fractional) visual acuity and distant (distance) visual acuity of the magnetic particle inspector shall be not less than […]

4.2 Magnetic particle testing procedures

Magnetic particle testing procedures are as follows. […]

4.3 Testing process documents

4.3.1 The testing process documents include process specifications and operating instructions.

4.3.2 The process specifications shall, in addition to complying with the requirements of NB/T 47013.1, specify the specific scope or requirements of the following relevant factors; when one or more of the relevant factors change and exceed the requirements, it shall re-draft or revise the process.

4.3.3 It shall compile the operating instructions in accordance with the contents of the technical specifications and the testing requirements of the workpiece to be tested. The contents shall, in addition to complying with the requirements of NB/T 47013.1, include at least.

4.3.4 The operating instruction shall, before the first use, be subjected to the process verification using the standard test piece, in order to confirm whether it can reach to the requirements as specified by the standard.

4.4 Safety requirements

4.4.1 Electric shock caused by a short circuit or the burn caused by a large current at a relatively low voltage.

4.4.2 When using fluorescent magnetic particle for testing, the adverse impact of the black light from the black light lamp onto the eyes and skin.

4.5 Equipment and materials

4.5.1 Equipment

Magnetic particle testing equipment shall comply with the provisions of JB/T 8290.

4.5.3 Power off phase controller

When using the remanence method, the AC flaw detector shall be equipped with a power-off phase controller.

4.6 Magnetic particle, carrier and magnetic suspension

4.6.1 Magnetic particle

Magnetic particle shall have high permeability, low coercivity and low remanence, AND the non-fluorescent magnetic particle and the tested workpiece surface color shall have a higher contrast. The magnetic particle size, the performance requirements, and so on shall comply with the requirements of JB/T 6063.

4.6.2 Carrier

In case of using wet method, it shall use water or low viscosity oil based carrier as a dispersion medium. If water is used as carrier, it shall add appropriate rust inhibitor and surfactant, AND if necessary, add defoamer. The kinematic viscosity of the oil-based carrier is less than or equal to 3.0mm²/s at 38°C, it is less than or equal to 5.0mm²/s at the minimum operating temperature, the flash point is not less than 94°C, AND it shall be free from fluorescence, activity, or odor.

4.7 Standard sample

4.7.1 Standard test piece

4.7.1.1 The standard test piece is mainly used to check the comprehensive performance of the magnetic particle testing equipment, magnetic particle and magnetic suspension. It shows whether the surface of the workpiece has sufficient effective magnetic field strength and direction, AND whether the effective testing region and the magnetization method are correct. The standard test pieces include A1-type, C-type, D-type and M1-type, the specifications and sizes of which are as shown in Table 2. The and D-type standard test pieces shall comply with the provisions of GB/T 23907.

4.10 Magnetization specification

4.10.1 Magnetic field strength

The magnetic field strength can be determined by the following methods.

4.10.2 Axial energization method and center conductor method

4.10.2.1 The magnetization specification of the axial energization method and the center conductor method is calculated in accordance with the formula in Table 3.

5.1 Testing method classification

In accordance with different classification conditions, the classification of magnetic particle testing methods is shown in Table 5.

5.2 Dry method

5.2.1 The dry method is usually used for continuous testing with AC or half-wave rectified magnetization current or magnetic yoke; when using the dry method, it shall determine whether the testing surface and the magnetic powder are totally dry, before applying the magnetic particle.

5.3 Wet method

5.3.1 The wet method is mainly used for continuous and remanence testing.

When using the wet method, it shall make sure that the entire tested surface is wetted by the magnetic suspension.

5.4 Continuous method

When using the continuous method, the application of the magnetic particle or magnetic suspension and the observation of the magnetic mark indication shall be completed within the magnetization energization time, AND the magnetization can be stopped at least 1s after stopping application of the magnetic particle or magnetic suspension;

5.5 Remanence method

5.5.1 The remanence method is mainly used for the testing of the workpiece with material coercivity greater than or equal to 1kA/m AND the maintained residual magnetic field after magnetization greater than or equal to 0.8T.

5.5.2 When using the remanence method, the magnetic particle or magnetic suspension shall be applied after finishing the energization, with the energization time usually in 0.25s ~ 1s. Before applying a magnetic particle or magnetic suspension, it is not allowed for any ferromagnetic object to touch the surface of the workpiece.

5.6 Cross-yoke method

5.6.1 When using the cross-yoke device, the four magnetic pole end faces and the tested surface shall be maintained good fit, with the maximum gap not exceeding 0.5mm. When making the continuous drag testing, the testing rate shall be as uniform as possible, generally not greater than 4m/min.

6.1 Classification and processing of magnetic marks

6.1.1 Magnetic mark indications are divided into relevant indication, non-relevant indication, and false indication.

6.1.2 The flaw magnetic mark having a length to width ratio of more than 3 is treated as linear magnetic mark; AND the flaw magnetic mark having a length to width ratio of more than 3 are treated as the of the ratio of not more than 3 is treated as circular magnetic marks.

6.2 Observation

6.2.1 The observation of the flaw magnetic marks shall be carried out immediately after the formation of the magnetic marks.

6.2.2 During non-fluorescent magnetic particle testing, the assessment of the flaw magnetic marks shall be carried out in visible light, AND the visible light irradiance on the tested surface of the workpiece shall be greater than or equal to 1000lx; in case of site testing, the visible light irradiance shall be not less than 500lx due to restrictions.

6.2.3 Unless otherwise it may confirmed that the magnetic mark is due to local magnetic unevenness of the workpiece material OR improper operation, the other magnetic mark indications shall be treated as the flaw magnetic marks.

To identify the small magnetic marks indication, observation shall be supported by using a 2 ~ 10 fold magnifying glass.

6.3 Records

It may use one or more of the following methods to record the indications.

8.1 General demagnetization requirements

The workpiece shall be demagnetized in the following cases.

8.2 Demagnetization method Demagnetization can be divided into AC

demagnetization method and DC demagnetization method.

8.2.1 AC demagnetization method

Slowly DRAW out the workpiece to be demagnetized from the energized magnetizing coil, until the workpiece leaves the coil for at least 1m; CUT off the current. Or otherwise PLACE the workpiece into the energized magnetizing coil; gradually REDUCE the current in the coil to zero or directly MAKE the AC pass through the workpiece and meanwhile gradually REDUCE the current to zero.

8.2.2 DC demagnetization method

PLACE the workpiece to be demagnetized into the DC electromagnetic field; constantly CHANGE the current direction; and gradually REDUCE the current to zero.

8.3 Remanence measurement

The demagnetization effect of the workpiece can be generally measured by magnetic field strength meter or other remanence magnetometer; AND the remanence strength after demagnetization shall not be greater than 0.3mT (240A/m) OR otherwise in accordance with product technical conditions.