Which of the following is NOT one of the four inspections performed on a boiler as it is manufactured?

The correct answer is C, which identifies that the inspection for insulation thickness is not one of the four standard inspections performed on a boiler as it is manufactured.

In the manufacturing process, key inspections are focused on critical aspects of the boiler's structure and functionality to ensure safety and compliance with operational standards. These typically include the inspection of the steel before shipping, which involves assessing the material's integrity and suitability for manufacturing. Additionally, a welding inspection is done after the boiler has been welded to verify that the welds are sound and meet safety standards, as improper welding can lead to catastrophic failures. A hydrostatic pressure test is then performed to check for leaks and ensure that the boiler can withstand its operating pressure safely.

Insulation thickness, while important for the overall efficiency and thermal performance of the boiler, is not classified as a critical inspection during the manufacturing phase. Instead, it is usually addressed during installation or maintenance, where the focus is more on energy efficiency and operating costs rather than the structural integrity of the boiler itself.