Abstract
A mathematical model for one-dimensional heat transfer in pipelines undergoing freezing induced by liquid nitrogen is elaborated. The basic premise of this technology is that the content within a pipeline is frozen to form a plug or two plugs at a position upstream and downstream from a location where work a modification or a repair must be executed. Based on the variable separation method, the present model aims to solve the related coupled heat conduction and moving-boundary phase change problem. An experiment with a 219 mm long pipe, where water was taken as the plugging agent, is presented to demonstrate the relevance and reliability of the proposed model (results show that the error is within 18%). Thereafter, the model is applied to predict the cooling and freezing process of pipelines with different inner diameters at different liquid nitrogen refrigeration temperatures when water is used as the plugging agent.
Highlights
In the gas pipelines industry, due to the factors such as corrosion, topography and process transformation, it is often necessary to replace the pipes or valves, or change the line [1]
It was considered that the pipeline freezing and plugging technique is only applicable to pipelines where the medium in the pipe was liquid
(2) The heat transfer model was verified by a self-designed freezing and plugging experiment with water as a plugging agent
Summary
In the gas pipelines industry, due to the factors such as corrosion, topography and process transformation, it is often necessary to replace the pipes or valves, or change the line [1]. Non-spark cutting equipment is required to cut it off, and operators could conduct their assignment with the help of welding [2] This method is very safe, but high-cost and time-consuming, which is not environmentally friendly yet [3]. The commonly technique for gas pipeline plugging includes mechanical plugging and bladder plugging [4] The former one is good at plugging [5], but non-economic and complex in operation [6]. It was considered that the pipeline freezing and plugging technique is only applicable to pipelines where the medium in the pipe was liquid The reason for this idea is that the gas cannot be frozen, besides, injecting freezable fluid into the pipeline could not fill the pipe section to form a closed freezing plug. Wang et al [13] and Liang et al [14] conducted experiments to test the plugging performance of different diameter natural gas pipelines
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