GB/T 31925-2015Ultrasonic test methods of heavy wall thickness seamless steel pipes and tubes (English PDF)

6.1 Use

Reference pipes are used for the commissioning of flaw-detection device, comprehensive performance test, and fixed-time calibration. The artificial defects on the reference pipes serve as the assessment basis for the natural defect equivalence, however, which shall not be understood, when the signal amplitude of the tested natural defects equals to that of the artificial defects, the size of the two kinds of defects equals absolutely; neither can it be understood the minimum defect size that can be detected by this device.

6.2 Materials

Reference pipes and the tested steel pipes shall have the same nominal size, and have the same or similar surface state, delivery state and acoustic performance.

Reference pipes shall not have the natural defects that may influence the calibration f the test equipment.

6.3 Length

The length of reference pipes shall meet the requirements of test methods and test equipment.

6.4 Artificial defect

6.4.1 Shape

The artificial defect for testing the longitudinal and transverse defects shall be the longitudinal notch paralleling to the pipe axis and the transverse notch perpendicular to the pipe axis; while their shapes of the cross-section shall be rectangular or V-shaped (see Figure 3, and 4). The two side surfaces of rectangular notch shall be parallel to each other and perpendicular to the bottom surface of the notch. When processing through the electric erosion method, the notch's bottom surface and corners on the bottom surface are allowed to be slightly rounded. The angle of V-shaped notch shall be 60°.

Artificial defects can be processed through the electronic erosion, mechanical and other methods.

Longitudinal artificial defect shall be parallel to the steel pipe axis, the notch shall be perpendicular to the steel pipe surface; transverse artificial defect shall be perpendicular to the steel pipe axis, the notch shall be perpendicular to the steel pipe surface.

Geometric dimension and shape of artificial defects shall be verified as per the national measurement regulation. The depth of artificial defect can be measured through optical, overriding and other methods. The reference pipes shall have obvious label or number.

7.1 Flaw detector

7.1.1 Flaw detector shall be pulse reflective multi- or single-channel ultrasonic flaw detector; its performance shall conform to the provisions of JB/T 10061; its attenuator (gain) accuracy, vertical linearity and dynamic rang shall be calibrated qualified.

7.1.2 Flaw detector repletion frequency's adjustable range shall meet the requirement of flaw detection.

7.1.3 Flaw detector has the automatic alarm or defect signal output functions.

7.2 Probe

7.2.1 Piezoelectric ultrasonic probe's working frequency can be selected within 1MHz~15 MHz; single probe's wafer length or diameter shall be no more than 25mm; but when the artificial defect length is less than 20mm, it shall be no more than 12mm.

7.2.2 Piezoelectric ultrasonic flaw detection can use line-focus or point-focus probe.

7.3 Detection device

The detection device for automatic inspection shall be equipped with high precision adjustable mechanism for probe against the steel pipe's relative location; and can reliably lock or achieve good mechanical tracking; so as to ensure, under the dynamic state, unchanged incident condition for acoustic beam against the steel pipe.

7.4 Transmission device

Transmission device for automatic inspection shall make the steel pipe pass through the detection device at a uniform speed; and ensure, in the test, the steel pipe has detection device's circumferential sensitivity difference, the test result shall conform to the provision of this Standard. When the longitudinal internal and external defects are tested for twice, the length of blind area shall only be determined by testing the longitudinal external defect.

9.3 Flaw detection

9.3.1 After the test results conform to the requirement of 9.2.1, can the flaw detection be carried out. Flaw detection shall be implemented batch by batch, and piece by piece.

9.3.2 Flaw detecting staff shall, during the inspection period, take reliable monitoring measures for the defect indication signals, so as to prevent the undetected defects.

9.4 Device calibration

9.4.1 For the same-specification steel pipe, during its continuous flaw detection period, use the reference pipes to conduct fixed-time calibration against the flaw detection device, and the calibration time interval shall not exceed 4h. For the same-specification steel pipe, during the commencement, completion, and intermediate of continuous flaw detection period, if the device operators are changed, then the device needs calibration, too. The calibration content can refer to 9.1.4 and 9.2.

9.4.2 If calibration result doesn't conform to the requirement, then conduct re-commissioning and re-test against the device; after it meets the requirement, then the tested steel pipe after the previous calibration need repeat the flaw-detection. […]