## Pressure Vessel Primary Bending Stresses

Primary bending stresses vary from tension to compression through the crosssection of a pressure vessel shell component. They are generally at a maximum at the surface. Higher average stresses are required to produce failure by plastic deformation in bending than for uniform tensile or compressive loads. Bending stresses are most likely to be the predominant primary stress in the following cases:

1. The bending stress in the center of a flat head.

2. The bending stress between the ligaments of closely spaced openings.

The stress limits for components, when primary bending stresses predominate, are 1.5 times the maximum allowable design stress for the material of construction at the design temperature. This higher stress limit is usually incorporated into the design rules and equations for components that conform to the acceptable design details depicted in the ASME Code. The allowable design stress can be multiplied by 1.5 only if a stress analysis is made of the component.

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