What is the maximum variation in pressure and temperature allowed for no more than 1 hour at once?

The maximum variation in pressure and temperature allowed for no more than 1 hour at once is 20%. This standard is crucial in high-pressure piping systems as it helps to ensure the safety and integrity of the system. Sudden changes in pressure and temperature can lead to mechanical stress and potential failure of pipes, joints, and equipment.

Allowing a variation of 20% provides a reasonable limit that accommodates the normal fluctuations in operating conditions while still prioritizing safety. This percentage is established based on industry standards and practical experience, reflecting a balance between operational flexibility and risk management. Operating within this range minimizes the risk of issues such as leaks, ruptures, or operational inefficiencies, which can arise from excessive variations.

In contrast, options such as 10%, 15%, and 25% represent limits that may either be too restrictive or too lenient for practical applications in the context of high-pressure systems, potentially leading to either unnecessary operational constraints or safety hazards. Therefore, the correct answer reflects an appropriate standard for safe and effective operation.