Ultrasonic testing for full penetration weld inspection

The sound wave frequency exceeds the human hearing and the sound wave with a frequency higher than 20 kHz is called ultrasonic wave. The frequency of ultrasonic wave used for flaw detection is 0.4-25 MHz, of which 1-5 MHz is the most commonly used. Ultrasonic flaw detection has the characteristics of large detection distance, small size and light weight of the flaw detection device, easy to carry to the site for flaw detection, fast detection speed, and only consumes coupling agent and wear probe during flaw detection, and the total detection cost is low. At present, this method is mainly used for detection in the construction industry market.

At present, the acceptance standard of steel structure is implemented according to GB50205-95 "Code for Construction and Acceptance of Steel Structure Engineering". The standard stipulates: when the drawing requires the welding quality grade of the weld to be Grade 1 and the assessment grade is Grade Ⅱ, the standard stipulates that 100% ultrasonic flaw detection is required; when the drawing requires the welding quality grade of the weld to be Grade 2 and the assessment grade is Grade Ⅲ, the standard stipulates that 20% ultrasonic flaw detection is required; when the drawing requires the welding quality grade of the weld to be Grade 3, no ultrasonic internal defect inspection is performed. Before each flaw detection operation, the comprehensive performance of the instrument must be calibrated using the standard test block (CSK-IA, CSK-ⅢA) and the panel curve must be calibrated to ensure the accuracy of the flaw detection results.

1. Repair of detection surface: Spatter, scale, pits and rust on the welding work surface should be removed, and the finish is generally less than ▽4. The repair width of the flaw detection surface on both sides of the weld is generally greater than or equal to 2KT+50mm, (K: probe K value, T: workpiece thickness). Generally, a probe with a K value of 2.5 is selected according to the weld parent material. For example: if the thickness of the workpiece parent material to be tested is 10mm, then 100mm should be repaired on both sides of the weld.

2. The selection of coupling agent should take into account viscosity, fluidity, adhesion, non-corrosiveness to the workpiece surface, easy cleaning, and economy. Considering the above factors, paste is selected as the coupling agent.

3. Since the thickness of the base material is relatively thin, the detection direction is carried out on one side and both sides.

4. Since the plate thickness is less than 20 mm, the horizontal positioning method is used to adjust the scanning speed of the instrument.

5. Rough and fine flaw detection are used during the flaw detection operation. Fine flaw detection is used to roughly understand the presence and distribution of defects, quantify and locate them. Several scanning methods such as zigzag scanning, left and right scanning, front and back scanning, corner scanning, and surrounding scanning are used to find various defects and determine the nature of the defects.

6. Record the detection results, and if any internal defects are found, evaluate and analyze them. The classification of internal defects of weld joints should comply with the provisions of the current national standard GB11345-89 "Manual ultrasonic flaw detection method and flaw detection result classification of steel welds" to judge whether the weld is qualified. If defects exceeding the standard are found, a rectification notice will be issued to the workshop, requiring them to make rectifications and re-test until they are qualified.