Interpretation of Radiographs

Interpretation of Radiographs
Introduction
Interpretation of radiographs is a skill only gained through long experience.
The interpretation of a radiograph should not be confused with the acceptance
or rejection of a component. The radiograph must first be interpreted and any
defects observed assessed against the applicable standard. A weld or casting
must be accepted on its merits or rejected for its faults and should neither be
accepted nor rejected due to difficulties encountered in the interpretation of
radiographs. Any radiograph not meeting code requirements with regard to
radiographic quality must be rejected.
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The definition of the technological properties concept and the requirements for it. The technical and economic indicators of power sources. The criterion for selecting power sources for welding.

When selecting power sources for welding, take into account technological and economic indicators. The choice of sources will ultimately be based on economic calculations, but this economic calculation will be performed from the set of sources that satisfy the first two criteria. Therefore, it is necessary to know about these two criteria.

The power source is considered to be technological if it provides:

  1. the arc stability (estimated by the coefficient of stability– КУ);
  2. the arc elasticity;
  3. the minimum level of spattering of the electrode metal.

The arc elasticity is the ability of a stable arc to burn without breaks in its elongation.

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The heterogeneous nucleation.

If there are impurities in the liquid phase in the form of solid particles, then the crystallization often begins on them, as on finished substrates.

The role of such particles can play the walls of molds, non-metallic inclusions, oxides, etc. The foreign particles are active if the work of germs formation is less on them than the work of spontaneous generation of the germs. This is the case when the surface tension at the interface of the germ is an alien particle smaller than at the interface between the nucleus and the liquid phase. The interfacial energy is characterized by the wetting angle of the droplet of the mother phase on the Continue reading →

Dispersion hardening (aging) (Part 1).

The release of the excess phase from the supersaturated solution at the low temperatures leads to the increase in the strength and hardness of the alloy. This is called dispersion hardening or aging. During aging, there is usually a lot of precipitation, evenly distributed throughout the alloy. Especially, a lot of them during exposure at room temperature. In this case, the decomposition of the supersaturated solution occurs slowly and is termed natural aging.

With the heating of the alloy, the precipitation intensifies and is called artificial aging. At the initial stages of natural aging in the supersaturated solution (Fig. 1, a), Continue reading →

The amount of metal evaporating from the cathode spot (Part 2).

Since the total length of the cathode zone (the ionization zone and the free-motion zone of the ions adjacent to the cathode surface) is several mean free paths of atoms, we can assume that the concentration of iron atoms in the entire cathode zone is approximately equal to the concentration of atoms in the column of the arc and, taking that the flow of iron atoms emerging from the cathode zone displaces the atoms of the protective gas from the cathode spot, we can assume that the cathode zone is almost completely filled with only atoms of the cathode material, and the ion current in it is almost completely transferred by ions formed from the Continue reading →

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