Which of the following is NOT one of the three general types of flange connections?

The choice indicating "seamless" as not being one of the three general types of flange connections is correct because flange connections typically involve mechanical fastening methods that allow for easy assembly and disassembly, accommodating different types of piping systems.

The three general types of flange connections are generally classified as screwed, welded, and sometimes include types like slip-on or blind, where the method of connection varies based on installation requirements and potential mechanical stresses.

Screwed flanges are attached to piping by threading, allowing for easy installation without the need for welding. Welded flanges are permanently attached to the pipe, providing a strong and durable connection suitable for high-pressure applications.

Although "Van Stone" is a term related to a specific type of flange design that helps to facilitate installation, it does not represent a general category of connection method in the same way that screwed and welded do.

"Seamless" refers to a manufacturing process for pipes and tubes that lack seams and is not a method of connecting flanges. Thus, it does not fit within the categorization of flange connection types. Understanding these classifications is crucial for selecting appropriate connecting methods based on application needs in power engineering.