What are the specific contents of wave inspection for straight seam steel pipe welds

Wave inspection technology for straight seam steel pipe welds is a relatively new testing process that plays a significant role in improving the stability of straight seam steel pipes. This article will provide a detailed introduction to the specific applications and common problems of wave inspection for straight seam steel pipes:

First, what are the common welding defects in straight seam steel pipe welds? How are they formed?

Common defects in straight seam steel pipe welds include porosity, slag inclusions, incomplete penetration, lack of fusion, and cracks.

1. Porosity occurs when the weld pool absorbs excessive gas during the high temperature of the weld pool or when gases generated by metallurgical reactions remain in the weld metal of the straight seam steel pipe before cooling and solidification. The main causes are insufficient drying of the welding rod or flux before welding, and inadequate cleaning of the weldment surface.

2. Incomplete penetration in straight seam steel pipe welds refers to the phenomenon where the base metal at the root of the weld joint is not fully fused. The main causes are insufficient welding current, excessively fast electrode movement, or improper welding specifications.

3. Lack of fusion in straight seam steel pipe welds refers to the failure of the filler metal to fuse with the base metal or between filler metals. The main causes of lack of fusion are unclean bevels, excessively fast electrode feeding speed, insufficient welding current, and improper electrode angle.

4. Slag inclusions: These are molten slag or non-metallic inclusions remaining in the weld metal of straight seam steel pipes after welding. The main causes of slag inclusions are insufficient welding current, excessively fast welding speed, and inadequate cleaning, preventing the molten slag or non-metallic inclusions from floating to the surface.

5. Cracks: These are localized fissures in the weld or heat-affected zone of the base metal of straight seam steel pipes that occur during or after welding. Cracks can be classified according to their cause as hot cracks, cold cracks, and reheat cracks. Hot cracks are caused by improper welding processes during welding; cold cracks are caused by excessive welding stress, high hydrogen content in the welding rod or flux, or significant differences in the rigidity of the weldment. They often occur after the weldment has cooled to its designated temperature, hence the name delayed cracks; reheat cracks generally occur when the weldment is reheated after welding (stress relief heat treatment or other heating processes).

Second, why is transverse wave testing commonly used in the weld flaw detection of straight seam steel pipes?

Porosity and slag inclusions in the weld of straight seam steel pipes are three-dimensional defects with relatively low hazard. Cracks, incomplete penetration, and lack of fusion are planar defects with high hazard. In the weld flaw detection of straight seam steel pipes, due to the influence of the reinforcing height and the fact that high-risk defects such as cracks, incomplete penetration, and lack of fusion are often perpendicular to or at an angle to the detection surface, transverse wave testing is generally used.

Third, what principles should be followed when selecting the probe K-value for transverse wave testing of straight seam steel pipe welds?

The selection of the probe's K-value should consider the following three aspects:

1. Ensuring the sound beam can scan the entire weld cross-section of the straight seam steel pipe.

2. Ensuring the sound beam centerline is as perpendicular as possible to the main hazardous defects.

3. Ensuring sufficient flaw detection sensitivity.

Fourth, what are the basic scanning methods of the angle probe when inspecting the weld of a straight seam steel pipe, and what are their main functions?

1. Zigzag inspection: This method uses simultaneous forward/backward, left/right, and corner scans, with the probe moving in a zigzag pattern. It can check for defects in the weld of the straight seam steel pipe.

2. Left/right scan: This method involves moving the probe parallel to the weld direction of the straight seam steel pipe. It can infer the length of longitudinal defects in the weld of the straight seam steel pipe.

3. Forward/backward scan: Inferring the depth and height of defects.

4. Corner scan: Determining the directionality of defects.

5. Simultaneous forward/backward, left/right, and corner scans can find defects with relatively large echoes, thus determining the defect location.

6. Circumferential Scan: Infers defect shape.

7. Parallel, Oblique Parallel, and Cross Scan: Detects transverse defects in the weld and heat-affected zone of straight seam steel pipes.

8. Tandem Scan: Detects planar defects perpendicular to the inspection surface.

Fifth, how to determine the location of defects in the weld of straight seam steel pipes during weld inspection?

After a defect wave is detected during weld inspection of a straight seam steel pipe, its location in the actual weld should be determined based on the position of the defect wave on the oscilloscope screen. Defect location methods include:

1. Sound Path Location Method: Used when the instrument's scanning speed is adjusted to a sound path ratio of 1:n to determine the defect location.

2. Horizontal Location Method: Used when the instrument's scanning speed is adjusted to a horizontal ratio of 1:n to determine the defect location.

3. Depth Location Method: Used when the instrument's scanning speed is adjusted to a depth ratio of 1:n to determine the defect location.

Sixth, what are the different methods for determining the defect indication length in the weld inspection of straight seam steel pipes? What are the applicable situations for each method?

When defects are found at or above the quantitative line during inspection, the indication length of the defect wave must be measured.

The JB/T4130.3-2005 standard stipulates: When the defect wave has only one peak, the 6dB method is used to measure its indication length. When the defect wave has multiple peaks, and the endpoint peak is located in Zone II, the endpoint 6dB method is used to measure its indication length. When the defect wave is located in Zone I, if present, the evaluation line can be used as the sensitivity to measure its indication length.