Welding cracks and their classification.

According to dimensions and influence on metal density are there two categories of cracks (local ruptures): microcracks (their dimensions are comparable to dimensions of crystal lattice parameters; are available almost always in real crystals) and macrocracks which appear in weld joint in the course of welding or use of product (are dangerous defect – reason for structural failure).

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Crystals nucleation in liquids (Part 2).

For formation of nucleuses of critical size there is not enough energy, exuded during atoms transfer from liquid to crystals. It compensates these energetic consumptions for two thirds, connected with surface energy or for half of energy, released owing to atoms transfer from liquid to crystal phase.

Nucleus critical size is decreasing with increasing of overcooling. The value of Continue reading →

Welding procedure qualification (Part 5).

Each set of norms and rules specifies defined criteria for performance of tests in the course of welding procedure qualification. Acting as a welding inspector you may need to participate in this estimation as well as in the performance of tests themselves. Probably the most important task of the welding inspector during performance of qualification consists in close observation over performance of Continue reading →

Tensile test (Part 4).

After the specimen for tensile test was measured and marked, it needs to be fastened safely in gripper of mobile and motionless heads of machine for tensile testing.

After setting the specimen in gripper, the increasing with constant speed tensile stress is applied to the specimen. If increasing speed of tensile stress is not constant, the test results can be unstable. Before the stress is applied to the Continue reading →

Inclusions in the weld seams (Part 2).

The slag density is significantly less than the metal density, in the radiographic picture slag inclusions look like relatively dark irregular-shaped sections. However, several coated welding electrodes form slags approximately of the same density as the metal density. Expectedly, in case of slag inclusions which are formed as a result of use of such electrodes it is highly difficult to detect them by means of Continue reading →

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