A coupled electrothermal damage theory model for pipelines is proposed to assess the failure behavior of buried pipelines under lightning strikes. This article considers local thermal nonequilibrium (LTNE) conditions in the soil-water porous medium and the nonlinear characteristics of lightning functions. The calculation results show that the proposed theoretical model has better applicability and accuracy compared with previous models. Parametric analysis shows that under lightning conditions of Im = 20 kA and T1/T2 = 1.2/50 mu s, the maximum local temperature of the soil around the pipeline can reach 2160 K, leading to pipeline breakdown. Metal pipelines are shown to be more effective in conducting charges, which alters the electric field distribution in the soil and impacts the formation of plasma channels. The half-peak value of the lightning waveform has a significant impact on pipeline breakdown, and its increase will increase the risk of pipeline breakdown gradually. When considering LTNE conditions, the change in the pipeline surface temperature becomes more pronounced. Under 8/30 and 8/40 mu s lightning waveforms, the pipeline surface temperature is approximately 150 and 550 K higher, respectively, compared with the thermal equilibrium conditions. The thermal conductivity and porosity of backfill soil can also affect the thermal damage of lightning-struck pipelines. With clay filling, the highest pipeline surface temperature can reach 2590 K, while with fine sand and coarse sand, it is 1980 and 1510 K, respectively. The pipeline lightning disaster model proposed in this article has engineering significance for the investigation of pipeline lightning failure and disaster prevention mechanisms.

Water-filled capillary tubes are a kind of standard component in both life science (e.g., blood vessels, interstitial pores, and plant vessels) and engineering (e.g., MEMS microchannel resonators, heat pipe wicks, and watersaturated soils). Under sufficiently low temperatures, water in capillary tubes undergoes phase transition and exhibits frost heave, which can cause deformation, damage, and even fracture of tube wall. However, the thermomechanical analysis of freezing water-filled capillary tubes remains obscure, particularly regarding the rapid change in water temperature due to thermal transient effects. We develop a thermal model of freezing in a waterfilled capillary tube that is suddenly exposed to cold air flow, with the time domain divided into two regimes, separated by the thermal penetration time tp. The effect of thermal penetration on temperature distribution is solved. Then, a distinction is made between freezing occurring before thermal penetration and those occurring after thermal penetration. We next analyze transient mechanical stresses acting at tube wall, with interfacial tension and frost heave effect accounted for. Results obtained are not only useful for preventing frost heave failure but also provide theoretical guidance for tailoring the freezing resistance of microfluidic devices used in MEMS.