A Safe Frost Growth Screening Method to Accurately Predict Ice Plug Formation Completion during Waterpipe Freezing Repairs

Abstract

Fixing waterpipes using cryogenic technology is a complicated activity because it is difficult to see the transformation of water into ice inside a pipe. To solve this problem, a series of experiments and testing was carried out on three types of waterpipes—75, 100, and 150 mm cast-iron pipes (CIP), respectively—to monitor the external characteristics and the frost growth to accurately predict the completion of ice plug formation inside the pipe before applying the freeze-fixing method. A CCD camera was set up to capture four frosting images per minute and to send one image every 15 s to the computer for processing and for identifying the interface between frost and no frost. The results showed that when the brightness distribution along the pipe axis goes down from the 100% brightest and coldest region near the freezing jacket to 90% and hits the 1/10th mark away from the brightest area, which is the interface, the freezing process is finished, and the ice plug has completely formed and can effectively block water flow to allow safe repairs. In other words, the findings determined that the frost length was more or less equal to the ice plug length. Additional testing was done to increase water pressure up to 35 kg/cm2 for about 10 min on one end of the freezing jacket, which is higher than the regular pressure testing of 10 kg/cm2. When 0 kg/cm2 was recorded on the other end of the freezing jacket, it was concluded that the ice plug was strong enough to resist high pressure. The success of these experiments and testing confirmed that this innovative freezing method was safe, cost-effective, and suitable to be used efficiently in semiconductor factories and modern buildings.

Keywords

• hot tapping
• frosting
• ice plug
• image recognition
• pipe freezing
• cryogenic technology