Steel pipe longitudinal cracks

Longitudinal cracks are formed as a result of excessive soil and traffic loads or inadequate pipe bedding. Visible longitudinal cracks observed at top and invert inside the pipe should be more severe than those on the outside because tensile stress occur at top and invert portion of the inside of the pipes.

Steel pipe weld defects affect the quality of the most immediate cause, and the welding crack is one of weld defects.

Longitudinal cracks manifestations are: crack fracture, with a smooth arc free surface, sometimes oxides, electron probe found no other inclusions.

Pipe joints waves using low hydrogen electrode porosity in the weld joints is often easy to show surface and internal pores, and their solution solder wave joints should be away from the forward direction of the weld crater 9 ~ 10mm at the beginning of arc, arc combustion , first make the reverse op rod back to the crater position, as fully melted and then move forward, or in the weld arc to avoid this type of porosity generated. Rigid pipe cracks were found in the weld seam often longitudinal cracks in the welding is mainly caused by the stress generated. In the following cases large welded structures welding stress rigidity; welding current, welding speed; weld metal cooling too fast. Which in the case above is susceptible to longitudinal length of cracks. Welding solutions using reasonable order or possible preheating the workpiece, to reduce the rigidity of the structure. The resulting pores reasons, such as to make proper adjustments and attention welding process and method of operation, it can be solved. Surface porosity generated surface pores causes and solutions to its solution or replace the base material, or slag system using low hydrogen electrode. Pipe welding parts unclean also prone pores. Therefore requires welding parts before welding clear oil, rust and other dirt. Use low hydrogen electrode welding requirements are more stringent. Welding current is too large. The latter part of the electrode coating red, but also prone pores. Therefore requested to take appropriate welding specifications. Electrode welding current to maximize the tail is not red is appropriate. Low hydrogen electrode is easy to absorb moisture, therefore required before use at a temperature of 350 ℃ bake for about 1 hour. Otherwise also prone pores.

Pipe material or equipment components during heat treatment should pay attention to the following questions: To prevent heat deformation of parts of the equipment shall be made of stainless steel reinforcement ring; pair installed furnace temperature, heating and cooling time should be strictly controlled; installed furnace, heat treatment pieces of pre- treatment, to prevent thermal cracking; steel after heat treatment process, such as thermal cracking, after the elimination to be polished by welding, the welding process to be used specifically. Steel structural rigidity to prevent this is to make it slow cooling weldments more, under the conditions of the weldment may be preheated, or using low hydrogen electrodes obtained a satisfactory solution. Arc blow using low hydrogen electrodes in DC welding on welding phenomenon often occurs blow.

Weled steel pipe specification, Standard and identification

Welded steel pipe (steel pipe manufactured with a weld) is a tubular product made out of flat plates, known as skelp, that are formed, bent and prepared for welding.



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