What is the situation when horizontal indications on the edge of a plate appear on several levels?

The presence of horizontal indications on the edge of a plate at several levels is indicative of laminations. Laminations are internal defects that occur during the manufacturing process of plates, where the materials fail to bond properly. These defects can create layers or planes within the material that are not fully consolidated, which often manifests as horizontal lines or bands when examined.

In the context of visual testing, understanding the nature of these horizontal indications is crucial. If the laminations are extensive, they can significantly reduce the strength and integrity of the material, potentially leading to failure in applications where structural integrity is critical.

Other options relate to different kinds of defects. For example, poor burning practice might lead to irregularities in material, while porosity refers to voids within the material, and pipe typically describes internal defects related to structural issues in casting. Each of these defects presents different characteristics and implications for material quality, but the specific observation of horizontal lines at multiple levels is a clear sign of laminations.