What hydrostatic test methods utilize the boiler's steady state operating pressure?

The correct answer is based on the understanding of hydrostatic testing, which is an important procedure for ensuring the integrity and safety of pressure vessels, such as boilers. Utilizing the boiler's steady state operating pressure means conducting tests that gauge the vessel's capacity to withstand its maximum operating conditions without failure.

Option B, which includes testing at 100% and 125% of the operating pressure, reflects a standard practice in hydrostatic testing. Testing at 100% assesses the boiler at its design limits, while testing at 125% is necessary for evaluating the safety margins and stress tolerances of the materials used in the boiler under pressure. It helps in identifying any potential weaknesses in the system that could lead to failure during regular operations.

In contrast, other options involve either lower or excessively high pressure levels that do not accurately represent safe operational limits or testing protocols recognized in engineering practices. Therefore, 100% and 125% align with the purpose and philosophy of pressure testing in industrial settings, particularly for ensuring that boilers maintain their structural integrity under conditions similar to those that they will face during normal operations.