Double Submerged Arc Welded Steel Pipe Weld Heat Affected Zone

Apr 30 15:27 2014 Allice S Lee Print This Article

Welded joints from the weld and heat affected zone. Cooling the molten weld pool from a high temperature to room temperature during the process of change experienced two organizations: the first is a liquid metal into solid metal crystallization process, called primary crystals; the temperature is lowered to a second phase transition temperature, the occurrence of tissue change, called secondary crystallization. 

Crystals not only in the secondary weld,Guest Posting the weld also occurs near the base metal region, which are subject to different degrees of heat in the welding process, the residence time at different temperatures and then cooled down at different speeds, the finally obtained not identical microstructure and mechanical properties, known as the heat-affected zone. According to the organization can be characterized by the fusion heat affected area is divided into zones, overheating zone recrystallization phase transition zone and incomplete recrystallization area. Which the fusion zone and overheated zone of coarse grains, low plasticity, is the birthplace of cracks and local brittle failure, is the weak link of welded joints. Therefore, defects in the heat affected zone (less) issue is different from the weld defects, to deal with more complex, a greater impact on the physical quality of the steel pipe. Ultrasound (transverse) alarm beyond the site of sample acceptance criteria, such as thermal etching chemical analysis, carbon arc gouging (carbon arc gouging repair defects observed in ideal) and ray film examination, results caused ultrasound (transverse ) cause of the alarm. Non-discrimination defect reflected wave reflected signal is due to the non-defective fillet weld and base metal junction reflection in rippled waves generated by the deformation, and therefore it need to accurately adjust the ultrasonic testing equipment to determine the position of the reflected wave generated. The double-sided submerged arc welded steel pipe weld shear testing probe position and the reflected wave, when transverse beam incident on the surface of some parts of the opposite side of the weld under probe, the reflected transverse and longitudinal wave reflection oriented perpendicular to the surface of some incident special parts, then backtrack along the vertical reflection, forming transverse deformation and deformation longitudinal waves, with the first end of wave (reflected wave fillet) together, displayed on the screen in the oscilloscope screen, some just in the groove deformation wave within the scope of the second wave detection, may often be mistaken for the second wave of the defects found. Identification method: wave distortion in a wide range, even around the entire weld has. Therefore, the probe can be moved parallel to the weld to examine identification. Because some metallurgical discontinuities will produce uncorrelated signals, so not all defects have said reflected ultrasonic signals, these reflected signals include heat-affected zone of the plane segregation, segregation in the manufacture of this will be reflected. Steel pipe weld inspection found a seam in the center of the plate thickness, there is a reflected signal appears. When the reflected wave appears, like tiny cracks waveform waveform characteristics, reflected waves tend to weld bevel edge position of the base metal side, begin to appear along the weld length. Reasons for confirmation signal, select a gouging, carbon arc gouging repair process, the naked eye did not find any defects, welding ultrasonic testing after retesting, the reflected waves are still. In the position indicated on the reflected waves, cut the sample for analysis, observed after boiling hydrochloric polished surface after grinding metallographic observation, found no cracks and other defects in ultrasonic testing side of the base metal area found a bright arc White areas, the determination of the curved white zone is greater than the other parts of the ultrasonic attenuation coefficient, indicating that the grain structure of the arc of thick white area, have a significant impact on the spread of ultrasound. Microstructure was observed curved white zone and base metal color different parts of the organization was serious zonal distribution, which is one kind of coarse grains because segregation caused. Significant effect on the propagation of coarse grains, so the shear testing, the position of the arcuate white area, the reflected wave signal is generated. According to the situation encountered in testing, ultrasonic reflected wave signal to determine the initial metal element segregation. Static wave characteristics analyzed, reflected wave signal segregation volatility low and stable, crest sharp, steep wave root stenosis; from the dynamic wave characteristics analyzed, the probe is moved to the reflected wave signal position, reflecting volatility is not high, defect depth appears In the middle of the plate thickness, bias seam edge, when the probe is perpendicular to the weld, move back and forth, the reflected wave will soon disappear, similar to the effects of the sandwich plate weld edge, the probe is moved parallel to the weld, the reflected wave stability can move a certain distance, then gradually disappear. Such wave easily mistaken for cracks in waves.

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