There are countless ways to construct a pressure vessel. One of which is to weld ANSI flanges to pipe. This method is safe and allowed by ASME’s Boiler and Pressure Vessel code. However, it is important that the pipe be fully welded to the top and bottom of the flange (or ID and OD in the case of a weld-neck). If you can’t figure out how both sides of the flanges were welded, force your equipment manufacturer to show you how it was done. It’s your safety, don’t be afraid to ask questions.
Following is a good link that shows the different types of flanges and when/where they should be welded (http://www.multalloy.com/pdfs/MA_Methods_of_Welding_Flanges_to_Pipe.pdf).
Apeks has over a decade of experience designing, building and testing CO2 extraction equipment. Our systems are built in accordance with ASME Code and we employ redundant safety controls on every vessel. We don’t take chances with your safety and neither should you.