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The development of fast response, highly accurate methane sensor becoming an important target for their indispensable role in the detection of methane during the coal mine and natural gas transportation, supply and use. In this cut-edge review, we summarized the development of gas sensors in these years in both technology and materials aspects. We believe this review could inspire scientists, inventors, researchers and engineers in this field. The methane sensors can be divided into semiconductor resistive-type gas sensors, optical fiber gas sensors and mass-sensitive gas sensors according to their functions. For example, the typical methane gas-sensing materials can be divided into semiconductor metal oxides, nanocomposites, organic polymer composites, cryptophane-A, carbon nanotubes and their doping materials etc. Semiconductor metal oxide nanomaterials such as SnO2, ZnO, In2O3, Fe2O3, Co3O4 are the most used methane gas-sensing materials. In a certain temperature range, the resistance of the gas sensor can be changed by the adsorption and desorption of methane molecules with the surface of semiconductor metal oxide film. In order to promote the sensitivity and lower the working temperature of methane sensors with semiconductor metal oxides, noble metal nanoparticles, carbon nanotubes or graphene were doped into metal oxides to form nanocomposites. The methane sensor prepared by doped polymer composites could work at room temperature which made it more applicable in closed, flammable and explosive places. Cryptophane-A has an amazing affinity for methane. When cryptophane-A was exposed to the methane gas, the methane molecules would enter the cavity of the cryptophane-A. Furthermore, some studies have shown that CNTs doped with noble metals were sensitive to methane but remain controversial. The future challenges and opportunities in this field are also discussed in the perspective section. The exploitation of high-response, high sensitivity and selectivity methane-sensing materials which can work at room temperature remains a major challenge. The properties of methane sensors can be improved from grain size, porosity and thickness of gas-sensing materials. With the development of preparation process of gas-sensing materials and intelligent control technology, the intelligent gas sensors which could monitor many kinds of gas would be one trend in development of methane gas sensor.

Many buried oil and gas pipelines are parallel to the high-voltage transmission lines and electrified railways in a long distance. Alternating current (AC) corrosion of these pipelines are very significant in such cases, and might lead to leakage even serious accidents. Laboratory experiment was carried out through weight-loss method in a simulated soil solution at various AC densities from 0 to 200 A/m2 and frequencies from 10 to 200 Hz. The results indicated that the corrosion rate increased with the increasing of AC current density. Furthermore, with the increase of AC interference frequency, the AC current involved in the electrode reaction process is decrescent, which caused a lower corrosion rate of pipeline steel. Morphology and corrosion product investigations explained that a better anti-corrosion behavior of X80 than that for X60 and X70 under AC interference. The investigation results are benefit to provide a new strategy to forecast and evaluate of the AC-induced corrosion, and design of the buried X series oil/gas pipelines.

Oil spill caused by the erosion in elbows is widely encountered in long-distance crude oil transmission pipelines and will lead to a considerable economic loss and potential safety hazards. In order to prevent the equipment failure and evaluate the campaign life of piping systems, there exists an urgent need to identify the positions suffering severe erosion damage and predict the erosion rate in pipelines for multiphase flow. In this study, a mathematical model is established to predict the solid particle erosion in the elbows of petroleum pipelines, in which the particle-fluid interaction is taken into account. The effects of bend orientation and particle properties on the erosion process are investigated in details. In order to understand the erosion mechanism related with the dynamic behavior of flow fluid and entrained particles, the relationship between the secondary flows and the particle trajectories is analyzed emphatically. The results indicate that erosion mainly occurs in the regions near the elbow exit, especially the side walls of the downstream straight pipe and extrados of the bend section. However, erosion on the side walls could not always happen when the effect of the secondary flows is not remarkable. It is also found that the erosion behavior depends upon both the centrifugal effect of pipe flow and the forces acting on particles. Finally, an erosion pattern based on Stokes number is developed to quantify the complex coupled effects of the flow field and particle properties.

Pipeline transportation is a safe and reliable way for transporting dangerous and flammable substances, such as oil and gas. In the process of transportation, third-party damage, corrosion destruction, design flaws, misuse of factors and other risk factors can also cause leakage or rupture of pipelines, which has a serious influence on social security and environment. In this paper, a comprehensive risk evaluation method based on a fuzzy Petri net (FPN) model for long-distance oil and gas transportation pipelines is proposed. In the process of the fuzzy reasoning, to tackle the impact of subjective factors and objective factors, the related parameters are optimized. In terms of risk factors weights, the combination weighting method is proposed, which combines AHP model and EM model. To reflect the fuzziness and randomness of risk factors, apply the cloud model to calculate the initial degrees of membership of the risk factors under the different risk grades. Furthermore, the risk evaluation values can be modified via the credibility. It is verified that the risk evaluation method based on the FPN model applies for the long-distance oil and gas transportation pipelines and provides some decision support for the risk management of the oil and gas pipelines.

A CFD–DEM-based liquid-particle two-phase flow erosion prediction model occurring over such pipeline connection as elbows, which takes the interaction of liquid–particle, particle–particle and particle–wall into account, is proposed in this study. The standard k − e model is adopted for fluid turbulent flow, the standard wall functions for near-wall zone treatment, and the Hertz–Mindlin (no slip) model for particle–particle and particle–wall contact. Numerical simulations have been performed by combining CFD code ANSYS FLUENT with DEM code EDEM to predict the maximum erosion rate and location in 90°, 60° and 45° elbows with diameter 40 mm. The fluid is water with inlet velocity 3 m/s, and the particles are 150 μm in diameter and 2650 kg/m3 in density. While the maximum erosion rates of the three are found to be quite different, the maximum erosive locations have been indicated to be at or near the exit of the elbows. In addition, the effect of bend-angle on erosion, particle motion and flow field has been discussed.

Field signature method (FSM) is used today by many of the world's major oil companies in a wide range of monitoring applications, with advantages of high degree of reliability and accuracy, non-intrusive, reflecting wall thickness visually. In this paper, the theory of FSM used in inner corrosion monitoring was analyzed and the expression of defects evaluation parameter (F c ) was deduced based on the corresponding relation between wall thickness (T t ) and potential drop (E t ) of plate model. Numerical simulations with a finite element (FE) model were used for current conduction analysis, the models with defect of various depths were simulated, the relation between F c and defects was summarized, and the validity of model formula was verified. The correction formulas was given by data fitting and proved to be effective by examples.

A numerical model for predicting the burst failure of corroded pipeline is constructed using the non-linear finite element method, in which the technical points including element mesh, materials model, non-linear solution and failure criterion are recommended. Using this model, the full-size pipe burst experiments in different material, size and defect was analyzed and computed. The proposed FEM model was validated. Based on the calculation result using the model, a new formula predicting failure pressure is proposed, in which depth, length and width of a defect was involved. Comparison of the formula with the other assessment method and experiments show the formula had a satisfactory precision.Copyright © 2008 by ASME

In general, the pipeline external corrosion direct assessment should be synchronously done by two or more inspection tools. Hence, it is very important to know how to develop the high-efficient and accurate combinatorial inspection techniques for engineering application. In this paper, the advantages, disadvantages and adaptabilities of the existing techniques and instruments are reviewed. Considering the technical difficulties in Chinese engineering practices, five different combinatorial inspection techniques were then brought forward. The proper selection of the combinational inspection technique can be determined by the inspection aim, servicing environment and type of the pipeline, soil, and so on. However, it should be noted that each combinatorial inspection technique can be used most of the time with some demerits. Engineering application showed that the proposed techniques can be directly and efficiently used to assess the pipeline external corrosion.Copyright © 2006 by ASME

In general, Rg Value, Y value and holiday density can be used to evaluate the performance of the coating deposited on the buried steel pipelines. However, the evaluation may be misleading when a single parameter is used. A new combination method for assessing the performance of the coating on the steel pipelines is developed in this paper. Using this approach, Rg Value, Y value and holiday density play appropriate role on the assessment. Some new modules are presented in this approach, including current distributary module, holiday module, intelligent critical curve of AC attenuation. Additionally, a computer program is compiled that can finish data processing of AC attenuation automatic, and the result report can be synchronously printed.Copyright © 2006 by ASME