Cookware becoming convex (bowing outwards on the cooking surface) is a problem, commonly caused by physical or thermal stress.
Below is a list of various reasons why this happens. It’s recommended to avoid all of them.
Thermal Shock, such as sudden changes in temperature can cause metal to warp. Especially placing a hot pan under cold water is a common mistake. The rapid contraction of the metal can lead to permanent deformation, making the pan convex.
Overheating or prolonged exposure to very high heat can weaken the metal or cause it to warp. Overheating creates uneven thermal expansion across the pan, leading to a bowed or convex shape.
Uneven Heating is possible when cooking on a burner or hob that’s too small or too large for the pan. This leads to uneven heat distribution and puts stress on the metal so it can warp over time. (Induction) cooktops, which heat only certain areas of the pan, can make this effect even worse.
Impact Damage by dropping the cookware or banging it against hard surfaces can deform the metal, causing it to become convex or uneven.