First, ice has an amazingly high adhesion to steel (you’ve witnessed that if you’ve ever tried to chip ice from steel surfaces in the winter). This, combined with friction of the long ice plug inside the irregular surface of the pipe would be enough to assure the plug isn’t going anywhere. Additionally, Cryostop freeze plugs lock themselves in place due to a phenomenon known as “hour-glassing”. As the Cryostop freeze plug begins forming, the pipe cylinder being chilled temporarily elastically reduces in diameter at a localized area inside our equipment. The Cryostop freeze plug then conforms to this shape, having large ends on either side of a narrower middle. This dimensional change of the pipe is small and only lasts as long as Cryostop International maintains the Cryostop freeze plug. It is one of the reasons why Cryostop freeze plugs can be used to hold back thousands of pounds of line pressure.