How much pressure can the second safety valve be set above MAWP?

The correct answer indicates that the second safety valve can be set no more than 3% above the Maximum Allowable Working Pressure (MAWP). This is in alignment with safety regulations that ensure the protection of both the equipment and personnel.

The reason for having a second safety valve is to provide an additional layer of safety in case the primary safety valve fails. Setting this second valve at a pressure above the MAWP, but within the 3% limit, ensures that if the primary valve does not operate as intended, the secondary one will intervene without risking overpressure conditions that could lead to catastrophic failure. This percentage is determined by national codes and standards, such as ASME, which establish maximum allowable settings to prevent excessive pressure build-up that could endanger the system's integrity.

Setting the second safety valve beyond this permissible range could lead to significant risks, including the potential for valve malfunction and overpressure scenarios. Therefore, adhering to the 3% guideline helps maintain operational safety while ensuring that any pressure relief systems are effective and reliable.