Why is reinforcement needed after the pressure vessel is opened?

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Pressure vessels commonly used require openings to be made in them and nozzles to be installed, due to various process and structural requirements. Since the opening removes some of the load-bearing metal, it not only weakens the strength of the container walls but also causes high local stress concentrations near the opening due to the disruption of structural continuity. This local stress peak is very high, reaching 3 times or even 5 to 6 times the basic film stress. Furthermore, the flanged connections are sometimes subject to various external loads and temperature effects. Due to factors such as differences in material quality, manufacturing defects, and difficulties in inspection, many failures occur at the edges of the openings. It is mainly characterized by fatigue failure and brittle cracking; therefore, necessary reinforcement design calculations must be carried out to provide appropriate reinforcement.