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Heat exchangers play essential roles in the oil and gas production process for convective heat transfer and heat conduction. The health management of heat exchangers stays in the direct monitoring of performance parameters. Aiming at the difficulty of precise fault identification and quantification for heat exchangers in multiple unknown failure modes, a data-model fusion-driven fault quantitative diagnosis method is proposed. Firstly, based on the monitoring data such as temperature, pressure and flow rate, the secondary parameters characterizing the heat exchanger running state are constructed combined with structural physical parameters. Then, by analyzing the correlation among parameter variation, failure modes and deterioration degree, a qualitative inference model of heat exchanger is formed for fault identification, where weights of parameters are introduced based on their sensitivity for different failure modes. After the fault mode is identified, to achieve quantitative analysis of the failure degree, an index-integrated mechanism equation is constructed using monitoring data and secondary parameters, where the index is dynamically modified by online data. Finally, a heat exchanger experiment is carried out to demonstrate the robustness and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

Jointed rigid pipes are vulnerable to permanent ground deformation (PGD). Compressible and lightweight materials, such as tire-derived aggregate (TDA), geofoams and straws, can be placed around buried pipes to reduce the loads from PGD and minimize the risk of pipe failures. In this study, a calibrated three-dimensional finite element model incorporating a modified Mohr-Coulomb model for simulating the strain softening behavior of surrounding soils is employed to analyze the failure modes of jointed rigid pipes under ground subsidence with various crossing scenarios, where the fault plane intersects different positions of the pipeline. Then, the efficiency of TDA mitigation in reducing the risk of pipe failure is evaluated, considering variations in geometry, size and density of TDA zone. It is found that the most detrimental fault-pipe crossing position locates at 3/4 L of the pipe barrel, where excessive bending moment can lead to longitudinal cracking. TDA mitigation mainly prevents structural failure of pipelines, while its influence on the kinematics of joints is negligible. The most pronounced loading reduction for pipelines is achieved by employing TDA with a lower degree of compaction, combined with the burial configuration of full-surrounded layout pattern of TDA. • A 3D numerical model is established for calculating the responses of jointed pipes under ground subsidence. • Failure modes and criterion of jointed pipes with various crossing scenarios are numerically analyzed. • The tire-derived aggregate (TDA) mitigation effects for jointed pipes are evaluated and design suggestions are proposed. [ABSTRACT FROM AUTHOR]

• Analytical solution is proposed to evaluate pipeline response under normal faulting. • Larger pipe wall thickness or lower D / t ratio should be a high priority in pipe design. • Shallower burial depth and less stiff soil with lower modulus can reduce pipe strains. • Controlled failure mode is dominated by pipe size, faulting condition, and burial condition. • Empirical functions are proposed to evaluate the critical states of pipelines. Buried pipelines are one of the critical lifeline structures, and the evaluation of pipeline performance under seismic faulting is essential for protection of pipeline networks. This paper explores an analytical solution incorporating implementation of Winkler models around a beam-type structure using the finite difference method to evaluate the pipeline response under normal faulting. The effectiveness of the analytical solution is assessed by comparing the calculated pipe strains with centrifuge and full-scale laboratory testing measurements. Subsequently, the effect of pipe size, faulting condition, and burial condition on pipe response are investigated. It can be found that a pipeline with a smaller pipe wall thickness or larger pipe diameter is generally more prone to failure. Larger pipe wall thickness or lower D / t ratio should be used for pipe design crossing an active fault. In geotechnically problematic areas, shallow burial depth and less stiff soil with lower modulus are recommended to reduce the probability of exceedance of allowable limit states due to normal faulting. In the end, empirical functions relating to critical D / t ratio are proposed to evaluate the critical states of fault displacement, burial depth, and spread of fault rupture with different diameter-to-thickness ratio considering the controlled limit of failure modes. [ABSTRACT FROM AUTHOR]

Abrupt ground movements induced by earthquake, landslide, tunnelling and excavation, etc., pose significant threats to the safety of underground jointed pipelines. Most previous studies have investigated the response of buried pipelines through experimental tests and numerical simulations, but analytical solutions for the safety evaluation of jointed pipelines are limited. In this study, enhanced analytical solutions of pipe bending moment and joint shear force are derived, in which the effects of different pipe-fault crossing configurations and pipe-soil interactions are considered. Then, the allowable offset distances are investigated using the proposed solutions, respectively, for three different failure modes, i.e., joint shear failure, pipe bending failure, and joint pull-out failure. The results show that the joint pull-out failure governs the pipe safety when the burial depth is relatively shallow, while the pipe bending failure dominates when they are buried deeply. The worst pipe-fault crossing position is not at the pipe joint or the midspan of the pipe segment, but at one tenth of the pipe segment adjacent to the joint. The results offer new insights into buried DI pipe failure mechanism and provide a basis for the protection of buried DI pipes under abrupt transverse ground movement conditions. • Enhanced solutions are proposed for internal forces of ductile iron pipes under various fault-pipe crossing conditions. • Different failure modes for ductile iron pipes under under various strike-slip fault-pipe crossing scenarios are assessed. • Maximum allowable offset distances for ductile rion pipes under various strike-slip faulting conditions are evaluated. [ABSTRACT FROM AUTHOR]

• Interaction between DI pipelines and dip-slip faults is studied numerically. • Self-locking can cause a joint to lose its free rotational capacity completely. • Joint self-locking alters the pipe failure mode from kinematic- to mechanical-controlled. • Joint pull-out failure controlled by tension should be given a highest priority. • Pipe body shows a rapid growth of inward buckling at 0.65–1.27 times the pipe diameter. Effective identification of failure modes for buried pipes subjected to earthquake-induced fault movements is crucial in the design and assessment of underground water supply networks. For bell-spigot jointed ductile iron (DI) pipes, the relationship between pipe failure mode and dip angle is still unclear. In this study, a three-dimensional finite element model of buried DI pipelines crossing dip-slip faults perpendicularly is established, based on which the joint kinematics and mechanical responses of DI pipes subjected to dip-slip faults with a dip angle between 50° and 130° are systematically evaluated. Four failure modes controlling the joint sealing performance and structural integrity of DI pipes are identified, i.e., joint pull-out failure, joint rotation failure, joint compressive failure, and excessive local buckling in the pipe segment. The results reveal that joint self-locking induced by the action of horizontal compression can reduce the joint rotational capacity greatly, rendering a segmented pipeline to behave like a continuous pipeline. Upon the occurrence of joint self-locking, the pipe mode changes from kinematic-controlled failure (joint pull-out or rotation failure) to mechanical-controlled failure (joint compressive failure or excessive local buckling). Finally, the relationship between failure mode and allowable dip angle is derived for use in design. [ABSTRACT FROM AUTHOR]

• A novel large-scale testing chamber on laterally loaded flexible pipes is assembled. • Surrounding soil changes from the general to the local shear failure mode with a higher burial depth. • Soil arching effect occurs in both the active and passive loading areas. • Current design cannot estimate both the ultimate soil resistance and the yield displacement adequately. • Simplified method is proposed to predict the maximum strain from the pipe yield displacement. As a key part of global lifeline infrastructure, buried pipelines play a vital role in transporting products for the daily life of human beings. However, the ultimate soil resistance and yield displacement are only derived for rigid pipes in current design guidelines, which are difficult to guide the analysis of flexible pipes. This investigation presents large-scale laboratory tests on flexible UPVC pipes subjected to lateral ground movements. The soil failure mechanism and pipe deformation were tracked. The reaction developing on UPVC pipe was measured as a function of pipe lateral displacement, embedment depth, sand bed density and pipe wall thickness. Analysis results reveal that the failure mode of soil changed from the general shear failure to the local shear failure, in which the soil arching effect occurred in both the active and passive loading areas, as the embedment ratio increased. Current design approaches could overestimate or underestimate the ultimate soil resistance of UPVC pipe heavily under various conditions, while the measured yield displacement was 2 to 3 times the prediction from the design guidelines. Finally, a simplified design method was proposed based on the pipe yield displacement for predicting the maximum longitudinal strain of UPVC pipes under lateral loading. [ABSTRACT FROM AUTHOR]