What is the definition of a pressure vessel?

A pressure vessel is defined as a container designed to hold gases or liquids at a pressure significantly different from the ambient pressure. This includes various design specifications such as material strength, thickness, safety mechanisms, and compliance with safety codes to ensure that it can safely withstand the internal pressure.

Choosing the definition related to being "designed according to safety codes" highlights the critical safety considerations involved in pressure vessel design and operation. Code requirements, like those from the American Society of Mechanical Engineers or other regulatory bodies, ensure that pressure vessels are constructed to prevent failure or leaks, which can lead to hazardous situations.

The other options describe different types of containers but do not capture the essential features that classify a pressure vessel. A portable tank for gases may hold gases but lacks the comprehensive safety design aspect. An open container for liquid storage does not meet the criteria for pressure vessels as it does not operate under pressure. A flexible pouch for holding gases implies a certain level of flexibility and does not suggest the rigid design and safety features characteristic of pressure vessels. Thus, the definition focusing on safety codes accurately encapsulates the core attributes that define a pressure vessel.