What does the term "allowed stress" refer to in API 650?

• A. The minimal stress for safety
• B. The average stress materials sustain
• C. The maximum stress level during service
• D. The stress limits after construction

Answer: (C)

The term "allowed stress" in API 650 refers to the maximum stress level that materials can sustain during service without causing deformation or failure. This concept is essential in ensuring the integrity and safety of welded tanks used for oil storage. Understanding allowed stress helps engineers and designers establish safe operating conditions, ensuring that the tank can withstand the various loads and environmental factors it may encounter throughout its operational life.

In the context of API 650, allowed stress is determined based on material properties, design factors, and safety considerations. It provides a clear guideline for ensuring that the tank operates within safe limits, thereby minimizing the risk of structural failure or leaks that could lead to environmental hazards or other serious consequences.