What is a lamination and where do they come from?
A lamination is a phenomenon that occurs in steel plates during rolling. A non-metallic inclusion in the ingot is squished out like a pancake when the ingot is rolled into a plate. The non-metallic inclusion may start out round or irregularly shaped, but as the plate is rolled, it becomes flat and elongated like rolling out a ball of dough with a rolling pin (see Figure 1). Laminations are usually sub-surface and parallel to the surface of the plate.
The Good News
In and of themselves, laminations usually don’t create much of a problem. Pressure-induced membrane stresses in pressure vessels and pipes act in the plane of the lamination. Since laminations have little through-wall thickness, the cross-sectional area available to react the hoop and longitudinal stress is hardly changed. In this case, the lamination doesn’t decrease the strength of the component and is essentially benign.
Biggest Lamination Ever!
In fact, there is one type of pressure vessel that is deliberately fabricated with extensive laminations: multilayered pressure vessels.
Multilayered vessels have been used for decades, particularly in high pressure applications. Typically, multiple concentric cylindrical sections are fabricated independently and shrink-fit over one another.
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