All major weld repairs to boiler headers require a hydrostatic test at what percent of boiler design pressure?

The correct choice indicates that all major weld repairs to boiler headers require a hydrostatic test at 150% of the boiler design pressure to ensure the integrity and safety of the repairs made. This testing helps to verify that the repair can withstand pressure conditions that are significantly higher than normal operating levels.

Conducting the hydrostatic test at this elevated percentage acts as a safeguard against potential failure, since it ensures that the material and the repair can handle unforeseen stresses that may occur during operation. It is a standard safety practice within the industry that recognizes the critical nature of boiler systems and the high risks associated with them.

In contrast, lower percentages such as 100%, 125%, or 175% do not meet the established safety protocols that dictate the necessity of applying a test that is at least 150% of the design pressure. A lower percent may not provide adequate assurance, while a higher percentage, such as 175%, could be unnecessarily excessive for standard procedures, leading to increased costs or operational disruptions without clear benefits.