When two steel plates with different thicknesses are butted together, in order to avoid serious stress concentration caused by rapid change of the cross section, the thicker edges of the plates are often thinned gradually to reach the same thickness at both edges. Butt joints have higher static strength and fatigue strength than other joints. For joints that work under alternating loads, impact loads or in low-temperature high-pressure vessels, the welding of butt joints is often preferred.