Hot tapping or pipe-freezing is the process of repairing waterpipes using liquid nitrogen without shutting own the entire water supply system. Fixing failed pipes and replacing faulty valves by isolating an area and installing a bypass ensure the uninterrupted flow of the complex piped water distribution networks. Traditional pipe-fixing methods required shutting down the entire system, resulting in losses of time and money. Hot tapping, on the other hand, is a cost-effective and time-saving method. (Note: use a photo with water distribution network and branch pipe).
Implementing the pipe-freezing method comes with several challenges. Since we use liquid nitrogen to turn water into an ice plug inside an isolated section of the waterpipe, it is often difficult to know when the process is effectively completed. We need to control the steady flow, because any flow in the isolated pipe would render the freezing method obsolete. We also need to pay attention to the thermal conductivity of the pipe wall, because with a low conductivity, the freezing method may not be successful. Finally, we should consider the liquid nitrogen mass flow rate, because when it is too slow, it cannot take away enough heat to form an ice plug. (Note: use a photo with water distribution network and pipe freezing).
Before carrying out repair works onsite, we need to undertake several experiments on different types of waterpipe to estimate the liquid nitrogen supply rate to ensure a safe and smooth completion of the ice plug formation process. There are generally two approaches to make sure that the pipe-freezing method is safe, time-sensitive and appropriate: (1) we measure the water pressure at both sides of the jacket; (2) we monitor the external characteristics and the frost growth to accurately predict the completion of ice plug formation inside the pipe. Approach #2 has already been patented ( Patent No. TW201938923A).
The success of the experiments, testing and onsite application confirmed that this innovative freezing method was safe, cost-effective and suitable to be used efficiently in semiconductor factories and modern buildings.