What is third party inspection and why is it mandatory for Section I construction? In the simplest terms, third party inspection refers to the system evolved by the Code committee to assure that code rules are actually followed. That is a basic truth, but it does not fully answer the question regarding why it is mandatory. It is not mandatory for other code constructions such as that governed by ASME B31.1, so why is it so for Section I construction? The answer is twofold; (1) to assure consistent, uniform application of code rules thus assuring a certain degree of safe...