what are the defects in pipe manufacturing

From the pipe billet to the steel pipe generally requires two heating products, namely the pre-heating and rolling tube perforated base tube is heated in a given path before; production of cold-rolled (pull) pipe requires the use of intermediate annealing to remove residual stress; For some steel special requirements, in order to improve the mechanical properties of steel pipe and improving organizational and process performance, but also its heat treatment. Steel heating tube defects uneven heating, oxidation, decarbonization, heating cracks, overheating, over-burning.

Effects of temperature on the pipe billet heating heating quality mainly reflected that the heating temperature is too low, too high or uneven heating. When the heating temperature is too low, it will increase the deformation resistance of the metal and reduce the plasticity of metals. In particular, when the heating temperature tube can not guarantee the complete conversion of the steel microstructure of austenite grains during hot tube, the trend will greatly increase the generation of cracks. When the tube is heated at a high temperature, the tube surface will be severe oxidation, decarburization overheating or even burnt. Overheating of the heating tube main tube temperature, or at a higher heating temperature and the heating time is too long causes excessive austenite grain coarsening caused by defects. When the tube is heated near the solidus temperature, the austenite grain boundaries or grain boundary oxidation of partially melted, the tube will produce a burnt. Burnt tube, the heating process is a very serious fault. Overheating perforated capillary tube will produce a lot of the fold; while burnt steel billets will be scrapped. The heating rate of the thermal cracking tube to produce the large tube has a close relationship, when the tube into the furnace, the furnace temperature is too high or if the tube is heated in the furnace too fast, then the tube is easy thermal cracking. That the surface of the heating tube cracks of both, may also be present in the interior of the tube, when the tube is perforated with a heat crack, the crack easily formed or folded inner and outer surfaces of capillary tubes.

According to their carbon content and the type of different cooling rate, the pearlite structure can be obtained, bainite, martensite. If not properly controlled heat treatment may produce widmanstatten. Widmanstatten an overheating tissue. It will have an adverse impact on the overall performance of steel (the organization is relatively excellent performance in high temperature durable), will reduce the strength of steel at room temperature, increased brittleness. Widmanstatten lighter can be used to eliminate normalizing the proper temperature, and the extent of the heavier widmanstatten can be eliminated by normalizing the secondary.