UG-28 refers to which type of pressure in code?

• A. Internal pressure
• B. External pressure
• C. Temperature
• D. Vacuum

Answer: (A)

Internal pressure is what UG-28 addresses. In the ASME Boiler and Pressure Vessel Code, the stresses and design rules you apply to a vessel are different depending on whether the vessel is pressurized from inside or subjected to external loads. Internal pressure acts outward from within the shell, driving tensile stresses in the walls that the code specifically governs through allowable stresses and thickness requirements. This focus on the pressure contained inside the vessel distinguishes it from external pressure, which raises different concerns such as buckling, and from vacuum, which is a negative external pressure scenario. Temperature, while it affects material properties and stress levels, is not itself a type of pressure. So UG-28 is about the design considerations for vessels under internal pressure.