Pipe Weld Repair

Aug 19 20:38 2014 Allice S Lee Print This Article

No internal defects steel weld penetration refers to a defect between the workpiece and the weld metal or weld layer partially unfused. Incomplete penetration welds weakened section of the work, resulting in severe stress concentration, greatly reduce joint strength, it often becomes the root of the weld cracking. Weld slag sandwiched nonmetallic slag, that is called slag. Weld slag reduces work-section, causing stress concentration will reduce weld strength and toughness.

Porosity of the weld metal at high temperatures,Guest Posting excessive absorption of dissolved gases or gas within the cell due to the metallurgical reaction, the time to discharge when the bath is cooled and solidified, while cavities formed on the surface or inside the weld, namely pores. Blowhole work effectively reduces the cross section of the weld and reduce the mechanical strength of the joint. If penetrating pores or continuity exists, it will seriously affect the tightness of the weldment. After the welding process, cracks or welding, metal in the welded joint region appears is called a partial rupture of the crack. Cracks may occur in the weld may also be generated on both sides of the weld heat affected zone. Sometimes it produced in the metal surface, the metal may be generated internally. Generally, in accordance with the mechanism of crack formation, it can be divided into two types of thermal cracking and cold cracking. It is produced by thermal cracking of liquid to the solid state crystallization process in the weld metal, mostly produced in the weld metal. The main causes of the low-melting substance is present in the weld, which weakens the contact between the grains when subjected to high welding stress, it is easy to cause breakdown between the grains. Thermal cracks along the grain boundary characteristic distribution. When the crack through the surface and the outside world, the tendency has obvious hydrogenation. Cold cracks are generated in the cooling process after welding, mostly produced in the base metal or base metal and the weld at the junction of the fusion line. The main reason is due to the generation of weld heat affected zone or formed within the quenched structure, under high stress, caused by the rupture of the grains, when welding high carbon content of the alloying elements more easily or hardened steel, the prone to cold cracking. Excessive weld melt into hydrogen, can cause cold cracking. Crack is the most dangerous kind of defect, which in addition to reducing carry-section outside, but also have serious stress concentration in the use of crack will gradually expand, may eventually lead to the destruction member. So welded structures generally do not allow the existence of such defect, a shovel was found to be necessary to re-welding. Performance is determined by the performance of welded pipe and weld a comprehensive assessment of two parts Yin Ge metal, either party will decide to use the most weak performance pipes. Pipe welding too, the role of high-temperature corrosion spiral pipe welding, the weld metal and heat affected zone organizational changes hands grain coarsening, but there are still a lot of stress. Combined result of these changes, so that the performance of inflammation zone metal and base metal (tube) makes a big difference. Moreover, the weld metal strength overall performance was significantly lower than the tube. Therefore, we must come up through the elimination of weld heat treatment, making it consistent with the overall performance "seamless steel pipe." Eliminate the internal stress due to heat generated by the welding shadow baa welded seam formed on both sides, anti-corrosion steel pipe and tube formation with three organizations, grain size. Due to the different heating temperature and cooling rate of the weld heat-affected zone, the tube, the inner portion of the existence of different stress Qi, the maximum stress in the weld heat-affected zone, followed by a minimum pipe paradox. When the spiral steel corrosion stress exceeds the yield limit of the metal causes plastic deformation, causing the tube bend; stress exceeds the ultimate strength, the cracks will cause the weld metal grain boundary cracks, crack development.

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