Ultrasonic Flaw Detection Of Steel Structure Welding Quality Analysis

In recent years, the global manufacturing industry is becoming more and more competitive, and the welding requirements for steel structure are becoming higher and higher, and in order to gain a foothold and occupy a leading position in certain fields, it is necessary to ensure the quality of the enterprise's products. In the steel structure welding quality inspection, the main use of non-destructive testing technology, non-destructive testing is mainly ultrasonic testing, magnetic particle testing, penetration testing and other detection methods combined to carry out testing, greatly improving the speed and accuracy of detection. This paper focuses on the application of ultrasonic flaw detection in steel structure welding, and how to analyze and prevent its defects.

Due to the ultrasonic flaw detection distance is large, depth is deep, the detection device is small and light weight, so the detection speed is very fast. Ultrasonic flaw detection in general does not require to accurately give the type and nature of defects, but after a long period of practice, according to the sound wave to find a variety of wave formation patterns, and then combined with the type of welded structure and the type of material to determine the severity of defects.

(1) Preliminary Flaw Detection

When receiving the task of flaw detection, first of all, to understand the technical requirements of welding quality in the drawings, according to the current acceptance standards of steel structure to implement, not blind operation. In this regard, it is necessary to master a lot of professional basic knowledge. For the requirements of the steel structure welding quality level one to assess the level of the second level of planning to operate, to do 100% ultrasonic flaw detection, and so on, until the quality level of the third level of standards. In the preliminary flaw detection, to pay close attention to all the echo signals on the oscilloscope screen, once found to have more than the evaluation line of the echo, to make a mark, for the next step of defect quantitative preparation.

(2)Precise Flaw Detection

Precision flaw detection to be accurate, the method used is still the same, just slow down the speed, careful inspection, to prevent missed tests. For the first time the defects measured this time should also be tested again, to find out the real defects of the highest number of echoes, make a good record, easy to improve. Always be careful when probing, the probing ratio is calculated according to the percentage of the length of each weld. For those partial flaw detection of the weld, if there is allowed to appear when the defects should be in the defects at both ends of the site to increase the length of the flaw, and the length of the increase should not be less than 10%. In the detection of flaws, but also accurately understand the characteristics of the steel structure, each time the defects can make a relatively accurate judgment.

(3) Repeat Flaw Detection

The further probing is a check as well as a review of the previous two probes, the probing method is basically the same, because after the previous two probes, this time the probing should be faster and save time and energy.

(1) Slagging
In the steel welding, there must be more or less material slag, which affects the quality of steel and welding, these slag in the ultrasonic wave is usually presented in the following phenomena: first, the point-like slag will be presented like air holes similar to the echo signal, which the inspector will find, make a record. Secondly, if there is a strip of slag, it will show a jagged waveform. Finally, if there is a waveform that is shaped like a dendrite, then the amplitude of the reflection made by the detection in all directions is different. The first reason for this type of defect is that during the welding process, the welding current is too small and its speed is very fast, resulting in some slag entrapment before it has time to be cleaned up.

(2) Inadequate Welding

This type of problem also occurs from time to time in steel structures and is revealed by ultrasonic detection. When encountered, these defects have a high amplitude and are serious enough to cause cracks, which can be caused by welding at too low a current or too fast a speed and at incorrect angles.

(3)Porosity in Welding

The ultrasonic waveform varies with the size of the air holes, like some single air holes, the waveform is more stable and single slit. Since different directions of probing can lead to different results, it is necessary to go back and forth several times to minimize errors. The causes of porosity are as follows: when welding these steels by hand, the current is too high, as well as the impurities are not cleaned up, or due to the formation of too high voltage.

(4) Cracks in Welding

For staff who have had experience in this area, cracks are reflected in ultrasound with a wide waveform and a large height. Compared to other defects, cracks are the most harmful one, so it is especially important to do a good job of crack prevention. Cracks are caused by: in the welding process, uneven heating, under the action of external forces, cooling speed and too fast, resulting in not yet fully merged together, there is a small or large crack.