Prediction of Critical Exposure Temperature (CET) of Natural Gas Pipeline– a Practical Approach

Abstract The minimum working temperature of metal pipeline is a critical parameter for design and integrity management of pipelines and facilities piping. This design temperature is called Critical Exposure Temperature (CET). In this research, a novel practical approach to model CET of buried pipelines was proposed and explained. This approach can replace the transient models which are computationally costly, and in some situations, measurement thermal sensors, which can be expensive and practically challenging. The present technique considers a wide range of effective parameters governing pipeline temperature. The estimated CET is influenced by thermal interactions among gas flow, pipeline wall, surrounding soil and ambient air. It also takes into account the convection heat transfer inside the pipeline, conduction through the pipe wall, coating layer, soil, and convection heat transfer with ambient air. The developed transient heat transfer model was solved to obtain the minimum soil temperature over time. Then, a reduced order model (ROM) was derived to correlate the predicted minimum soil temperatures with soil type, soil depth and climate condition. The developed ROM was combined with an analytical thermal-hydraulic model for natural gas pipelines to predict CET. This novel method was programmed in Visual Basic for Applications (VBA) and finalized as a simplified calculation tool for CET prediction.