One of the most important conditions to become an excellent stainless steel industrial welded pipe is to have superior weld quality. Because how the quality of the weld determines whether the welded pipe can withstand the test of the post-process. Common post-processes include: flattening, reducing diameter, punching and bending, etc. If the weld quality is not strong enough, it will cause a lot of scrap, and the cost will be greatly increased.
Automatic stainless steel pipe production lines have become very popular in modern production workshops. Manual monitoring cannot guarantee that there will be no leakage or perforation in the 24-hour monitoring. Therefore, some clients mentioned this phenomenon before. As preventive surveillance, Hangao Tech (SEKO Machinery) will suggest to install an instrument dedicated to monitoring the quality of the weld. When the instrument monitor detects damage to the weld, the buzzer will sound an alarm to remind workers to handle or mark it.
Common non-destructive testing methods for welds include:
(1) Radiographic inspection method (RT)
At present, the widely used radiographic flaw detection method is to use the penetrating rays from (X, γ) ray sources to penetrate the weld to make the film photosensitive, and the defect image in the weld is displayed on the processed radiographic negative. It is mainly used to find defects such as pores, slag inclusions, cracks and incomplete penetration in the weld.
(2) Ultrasonic flaw detection (UT)
Using piezoelectric transducers, pulse vibration is generated by instantaneous electrical excitation, and ultrasonic waves are formed in the metal by means of acoustic coupling medium. When ultrasonic waves encounter defects during propagation, they will be reflected and returned to the transducer, and then the acoustic pulses will be converted into electrical The location and severity of defects in the workpiece can be assessed by measuring the amplitude and propagation time of the signal. Ultrasonic has higher sensitivity than radiographic flaw detection, is flexible and convenient, has a short cycle, low cost, high efficiency, and is harmless to the human body. However, there are also disadvantages. For example, the display of defects is not intuitive, and the judgment of weld defects is not accurate, which is greatly affected by the experience and technical proficiency of the inspection personnel.
(3) Penetrating flaw detection (PT)
When the penetrant containing pigment or fluorescent powder is sprayed or coated on the surface of the weld to be inspected, the capillary action of the liquid is used to make the penetrant that penetrates into the defect of the surface opening adsorbed on the surface of the weld, so as to observe the defect display traces. Liquid penetrant inspection is mainly used for: checking the groove surface, the gouging surface after carbon arc gouging or after the weld defect is removed, the surface removed by the tool and the surface opening defect of the inconvenient magnetic particle inspection part.
(4) Magnetic flaw detection (MT)
A method of recording and displaying defects by using magnetic powder, magnetic tape or other magnetic field measurement methods to cause a change in the radiance rate by using surface and near-surface defects of magnetic materials, and a leakage magnetic field occurs on the surface during magnetization. Magnetic flaw detection is mainly used for: inspection of surface and near-surface defects. Compared with the penetration detection method, this method not only has high detection sensitivity and high speed, but also can detect defects at a certain depth on the surface.
(5) Other detection methods
Other detection methods include: metallographic analysis of large workpieces, ferrite content inspection; spectral analysis; portable hardness test; acoustic emission test, etc.
