Because ssaw steel pipe can be made by a coil width continuous forming welding production, easy automation, and using double-sided automatic submerged arc welding type, there are a variety of testing method to check weld quality assurance checks. Therefore, when laying oil pipelines, spiral welded pipe has been widely used. However, in forming the welding process, the process by mistake or due to other reasons mature operation, resulting in a variety of pipe defects generated.
No penetration weld means between the base metal and the base metal, not the spaces left by the arc melting, the double-sided spiral welded pipes produced generally in the middle of the weld. Due to the use of double-sided spiral submerged arc welded pipe, it is not automatic weld penetration welded joints of the causes, which is too small for the gap, too small welding current and welding speed is too fast, or if improper wire angle welding arc is caused by partial blow When it is not prone to partial penetration.
Porosity in the weld pool is absorbed much of the high temperature gas and the cooling gas in the melting of the metal in a sharp decline in the residual gas is too late to escape, which is formed in the weld metal. Porosity can be divided into isolated pores, pore density, porosity and worm holes chain, are generally a number of factors can lead to gas welding process are the cause of porosity. Gas pores in the weld formed primarily of hydrogen and carbon monoxide, which ray intensity attenuation tends to zero, therefore, appears as black holes is greater than the background image porphyritic blackness, blackness generally larger, image clarity is easy to identify.
Crack is harm serious welding defects, as well as the common defects in welding seam. Cracks in the welding stress-induced embrittlement and other factors together, the binding force of welded joints of metal atoms localized destruction and the formation of the new interface (the gap). Cracks can be classified according to their causes hot cracking, cold cracking, reheat cracking, lamellar tearing, stress corrosion cracking. As the spiral welded pipe is generally of high quality carbon steel and low alloy steel materials, welding and heat treatment after the process is no longer carried out, so most of the thermal cracking and cold crack.
