What is the minimum internal or external pressure below which most pressure vessel codes do not apply?

The threshold for the applicability of most pressure vessel codes is set at a minimum internal or external pressure of 15 PSIG. This standard is primarily established to ensure that the design and safety regulations that apply to pressure vessels are relevant and necessary. Below this pressure, the risks and operational conditions become significantly different, and many of the potential hazards associated with pressure vessels under high pressure diminish.

Pressure vessel codes, such as those from the ASME (American Society of Mechanical Engineers), focus on maintaining structural integrity and safety due to high-pressure conditions, which are less of a concern at pressures lower than 15 PSIG. Therefore, vessels designed and operated under these lower pressures may not require the same rigorous standards, allowing for simpler design and operation.

This understanding is critical for engineers and operators to inform decisions on design, maintenance, and safety practices in pressure vessel systems, ensuring compliance with the appropriate codes where applicable.