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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.

Welding stress, the stress is produced due to the welding and welded components. Changes in the shape and size of the weldment and soldering thermal stress generated during the welding process caused by weldment. Uneven temperature field of welding process and caused by its local plastic deformation and volume of different organizations is the root cause of the welding stress and deformation.

Weldability refers to material welded construction under limited conditions into components according to the design requirements and meet the requirements of pre-service capabilities. By welding materials, welding methods, component type and requirements affecting the four factors.

Welded joints cooled to a lower temperature ( for steel, in the martensitic transformation start temperature Ms less ) generated by the weld cracking. Commonly known as cold cracking, which is divided into delayed cracking, thermal stress cracking and lamellar tearing three kinds. Cold cracks sometimes appear immediately after welding, but sometimes after a few hours, days, or even longer to appear. These weld after a period of time before the emergence of crack called delayed cracking. Delayed cracking in the manufacturing process may not be found, and in the process of using it may cause extremely serious consequences. So it is more harmful than crack.

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1. The transverse cracks of the thick-walled LSAW steel pipe

Welding current and arc voltage: Welding current and arc voltage has an important influence on the weld shape and weld quality M, it is an important bee submerged arc welding parameters.

For the practical application of fertilizer tube to overcome the lack of fire prevention, fire protection must be handled, its purpose is to improve the fire resistance of steel structures to the design specification limits. Here are several different steel structure fire protection measures.

Steel weld shrinkage prone to cracks reasons:

Roundness: mainly for the circular cross-section rolled products, such as the cross section round and round steel pipe, unequal diameters in all directions.

Because of the pre-weld own characteristics, in the back of the welding operations, there often produce tumors, burn, wrong side, solder partial, broken weld (broken arc), weld reinforcement is too low or too high, porosity and slag and other defects. Among them burn, broken weld (broken arc) more likely to be found to take timely repair welding, generally does not have a significant impact on the internal and external welding quality.

NONDESTRUCTIVE TESTING METHODS An NDT method is classified according to its underlying physical principle.