CO2 corrosion control in steel pipelines. Influence of turbulent flow on the performance of corrosion inhibitors

Corrosion associated with aqueous environments containing carbon dioxide (CO₂) and/or hydrogen sulphide (H₂S), is a well-known phenomenon in oil and gas industries. This type of corrosion is of particular importance in transportation through steel pipelines. This transportation process could involve the movement of a complex mixture of gas and liquids. This moving mixture is in close contact with the inner surface of the steel pipelines and corrosion can occur. It has been demonstrated that this corrosion is influenced by flow.In oil and gas industries, film-forming corrosion inhibitors are the main tool used to control inner corrosion in pipelines. The movement of the environment generates mechanical shear stresses on the surface of the steel that can interfere with the formation of the film. This phenomenon is frequently not taken into account in corrosion control strategies and could cause problems. Despite the importance of this, there are few scientific studies available, which can provide control criteria.This work presents some ideas developed in order to understand the influence of flow on the corrosion process, making emphasis in the corrosion process associated with carbon dioxide (CO₂).     

Hybrid H2/Al dust explosions in Siwek sphere

Explosion indices and explosion behaviour of Al dust/H₂/air mixtures were studied using standard 20 l sphere. The study was motivated by an explosion hazard occurring at some accidental scenarios considered now in ITER design (International Thermonuclear Experimental Reactor). During Loss-of-Vacuum or Loss-of-Coolant Accidents (LOCA/LOVA) it is possible to form inside the ITER vacuum vessel an explosible atmosphere containing fine Be or W dusts and hydrogen. To approach the Be/H₂ explosion problem, Be dust is substituted in this study by aluminium, because of high toxicity of Be dusts. The tested dust concentrations were 100, 200, 400, 800, and 1200 g/m3; hydrogen concentrations varied from 8 to 20 vol. % with 2% step. The mixtures were ignited by a weak electric spark. Pressure evolutions were recorded during the mixture explosions. In addition, the gaseous compositions of the combustion products were measured by a quadruple mass-spectrometer. The dust was involved in the explosion process at all hydrogen and dust concentrations even at the combination ‘8%/100 g/m3’. In all the other tests the explosion overpressures and the pressure rise rates were noticeably higher than those relevant to pure H₂/air mixtures and pure Al dust/air mixtures. At lower hybrid fuel concentrations the mixture exploded in two steps: first hydrogen explosion followed by a clearly separated Al dust explosion. With rising concentrations, the two-phase explosion regime transits to a single-phase regime where the two fuel components exploded together as a single fuel. In this regime both the hybrid explosion pressures and pressure rise rates are higher than either H₂ or Al ones. The two fuels compete for the oxygen; the higher the dust concentration, the more part of O2 it consumes (and the more H₂ remains in the combustion products). The test results are used to support DUST3D CFD code developed at KIT to model LOCA or LOVA scenarios in ITER.     

A spatial-temporal approach for corrosion prediction in time-varying marine environment

Corrosion in seawater is simultaneously influenced by multiple environmental factors including dissolved oxygen (DO), temperature, salinity, pH, and so on. These factors vary along with time and are different in different locations. The spatial-temporal variation of the actual marine environment cannot be ignored in corrosion prediction models. This paper proposes a new method for corrosion prediction in the actual time-varying marine environment which includes the design of experiments, calibration of acceleration models, and the modeling of marine environment. Acceleration models capture the effects of environmental factors and acts as the link between the environment and the corrosion process. The marine environment is described with the Kriging spatial-temporal model. Then the proposed method is used to give corrosion predictions for metals in different locations and vessels travel in different waters. This method could be helpful for corrosion resistance evaluation and environment corrosivity assessment.     

Medium-scale experiments on vented hydrogen deflagration

A series of medium-scale experiments on vented hydrogen deflagration was carried out at the KIT test side in a chamber of 1 × 1 × 1 m³ size with different vent areas. The experimental program was divided in three series: (1) uniform hydrogen–air mixtures; (2) stratified hydrogen–air mixtures within the enclosure; (3) a layer deflagration of uniform mixture. Different uniform hydrogen–air mixtures from 7 to 18% hydrogen were tested with variable vent areas 0.01–1.0 m². One test was done for rich mixture with 50% H₂. To vary a gradient of concentration, all the experiments with a stratified hydrogen–air mixtures had about 4%H₂ at the bottom and 10 to 25% H₂ at the top of the enclosure. Measurement system consisted of a set of pressure sensors and thermocouples inside and outside the enclosure. Four cameras combined with a schlieren system (BOS) for visual observation of combustion process through transparent sidewalls were used. Four experiments were selected as benchmark experiments to compare them with four times larger scale FM Global tests (Bauwens et al., 2011) and to provide experimental data for further CFD modelling. The nature of external explosion leading to the multiple pressure peak structure was investigated in details. Current work addresses knowledge gaps regarding indoor hydrogen accumulations and vented deflagrations. The experiments carried out within this work attend to contribute the data for improved criteria for hydrogen–air mixture and enclosure parameters to avoid unacceptable explosion overpressure. Based on theoretical analysis and current experimental data a further vent sizing technology for hydrogen deflagrations in confined spaces should be developed, taking into account the peculiarities of hydrogen–air mixture deflagrations in presence of obstacles, concentration gradients of hydrogen–air mixtures, dimensions of a layer of flammable cloud, vent inertia, etc.     

基于RBI的苯乙烯/环氧丙烷装置压力管道在线检验研究

对苯乙烯／环氧丙烷装置进行腐蚀回路划分,并将腐蚀回路中的压力管道按照管径、材质及用途等因素划分为不同的组别后进行RBI分析。根据风险评估结果,结合压力管道的使用情况、失效机理及剩余使用寿命等确定下一个检验周期和检验策略。以腐蚀回路中的组别作为检验单元,根据其失效可能性及风险等级确定各检验单元的检验比例和检验方法进行在线检验。结果表明：基于RBI分析结果的压力管道在线抽检方法可以验证风险评估的结果,同时还可以满足使用单位对管道的风险控制要求。     

Flammability of methane,propane, and hydrogen gases

This paper reports the results of flammability studies for methane, propane, hydrogen, and deuterium gases in air conducted by the Pittsburgh Research Laboratory. Knowledge of the explosion hazards of these gases is important to the coal mining industry and to other industries that produce or use flammable gases. The experimental research was conducted in 20 L and 120 L closed explosion chambers under both quiescent and turbulent conditions, using both electric spark and pyrotechnic ignition sources. The data reported here generally confirm the data of previous investigators, but they are more comprehensive than those reported previously. The results illustrate the complications associated with buoyancy, turbulence, selective diffusion, and ignitor strength versus chamber size. Although the lower flammable limits (LFLs) are well defined for methane (CH₄) and propane (C₃H₈), the LFLs for hydrogen (H₂) and its heavier isotope deuterium (D₂) are much more dependent on the limit criterion chosen. A similar behavior is observed for the upper flammable limit of propane. The data presented include lower and upper flammable limits, maximum pressures, and maximum rates of pressure rise. The rates of pressure rise, even when normalized by the cube root of the chamber volume (V^1/3), are shown to be sensitive to chamber size.     

Zn composite corrosion resistance coatings: What works and what does not work?

Corrosion is one of the most significant contributors to structural degradation in process industries. It causes process equipment failure, which can led to severe safety issues. One approach to address this concern is to provide a preventive barrier-coating to equipment. Due to its superior reductive property, zinc is usually employed as a sacrificial anode in conventional corrosion-resistance methods. Nickel is also used to both mechanically strengthen the barrier and improve overall corrosion resistance; therefore, zinc, zinc-nickel alloys, and zinc-nickel-oxide composite coatings are commonly employed for anti-corrosion purposes. The complexation of zinc and nickel ions by agents (citrate, acetate and EDTA) can stabilize the electrodeposition bath and extend the pH of Ni(OH)₂ and ZnO precipitation to improve corrosion resistance in the resultant coating. This paper reviews the challenge with these type of coatings and presents progress in Zn and Zn-Ni composite corrosion resistance coatings co-deposited with Al₂O₃, TiO₂, ZrO₂, SiO₂, and Fe₂O₃ as means of corrosion control to reduce the probability of process equipment failure due to corrosion, which will improve the overall safety and reliability of processing equipment.     

Process safety aspects in water-gas-shift (WGS) membrane reactors used for pure hydrogen production

The syngas produced by coal gasification processes can be utilized in Pd-based water-gas-shift membrane reactors for the production of pure H₂. Pd/alloy composite membrane reactors exhibit comparative advantages over traditional packed bed reactors such as simultaneous reaction/separation in one compact unit and increased reaction yields. Furthermore, the development of comprehensive process intensification strategies could further enhance membrane reactor performance resulting in a substantially smaller and functional, inherently safer, environmentally friendlier and more energy efficient process.A systematic non-isothermal modeling framework under both steady state and dynamic/transient conditions for a catalytic high temperature water-gas shift reaction in a Pd-based membrane reactor has been developed to characterize the dynamic behavior of the process system at various operating conditions from a process safety standpoint. In particular, various reaction conditions as well as key process variables such as feed temperature and flow rate, catalyst loading, driving force for H₂ permeation are considered as they are critically related to various safety aspects in the operation of a Pd-based membrane reactor. Within the proposed framework, process parameters and operating conditions which may induce hazards and compromise process safety are identified, analyzed and characterized. Finally, the proposed approach is evaluated through detailed simulation studies in an illustrative case study involving a real Pd-based membrane reactor used for pure hydrogen production and separation that exhibits complex behavior over a wide operating regime.     

Inerting effect of N2 on explosion of LDPE dust/ethylene hybrid mixtures

Explosion flame propagation characteristics and overpressure distribution of low density polyethylene (LDPE) dust and ethylene hybrid mixture were investigated under N₂ inerting conditions using a custom-designed 12 L cylindrical explosion tank. The results showed that a small amount of ethylene could promote the explosion characteristics of LDPE dust. N₂ inerting had different inhibitory effects on the explosion flame of LDPE dust and its mixture with ethylene. The explosion overpressure strength of the LDPE dust/ethylene hybrid mixture decreased with increasing N₂ concentration. The overall suppression effect of N₂ on the explosion overpressure of the LDPE dust was better than that of the LDPE dust/ethylene hybrid mixture explosion. As the ethylene concentration increased from 0% to 2.5%, the limiting oxygen concentration decreased by 13% oxygen. This small amount of ethylene restricted the traditional inerting process. The study conclusions can provide further scientific basis for the inerting and explosion proofing design of production process equipment involving LDPE dust.     

Study on the effect of explosion suppression equipment on hydrogen explosions

Hydrogen safety is a critical component of modern industrial safety production. In this study, a set of hydrogen explosion suppression equipment is designed independently. The suppression effects of the equipment on hydrogen explosions are studied at normal room temperature and pressure. The experimental results show that the actuation time of the equipment and the spraying mode of the suppressant are the main factors leading to the failure of the hydrogen explosion suppression equipment. The flame, with a hydrogen equivalence ratio of 0.7 and 1.0, spreads out of control when the suppressant touches the flame front. At this time, the addition of the suppressant enhances flame propagation and increases pressure. In addition, because the suppressant does not fully cover the developing flame, the hydrogen flame with the equivalence ratio of 0.5 eventually breaks through the suppressant cloud, and the explosion happens. However, when the initial flame is completely covered by the suppressant, the hydrogen explosion is suppressed by hydrogen explosion suppression equipment. This research provides a solid and reliable foundation for hydrogen explosion suppression equipment in industrial safety and production protection.     

Failure of a heat exchanger generated by an excess of SO2 and H2S in the Sulfur Recovery Unit of a petroleum refinery

The aim of this work is to investigate the level of damage to the heat exchanger in a Sulfur Recovery Unit (SRU) of a petroleum refinery. The by-products of oil refining are submitted to special treatment in order to meet technical specifications of corrosivity, sulfur content, acidity, formation of pollutant compounds, and color alteration. Sulfur is removed from the by-products in the form of H₂S, which is an acid gas that is sent to the SRU for sulfur production. The gases in the SRU are H₂S, CO₂, SO₂, and SO₃, which are corrosive to the mild steel equipment. The Unit is frequently forced to paralyze its activities due to the corrosion of its heat exchangers and pressure vessels, and the acid gas load is burnt causing the release of SO_x into the atmosphere. The above occurs when generalized corrosion damages SRU equipment. The importance of this work is to emphasize that the leakage of acid gas and sulfur into the atmosphere is a direct result of corrosion, which causes economical and environmental damage. This study may be used to improve the control of The Claus Process and to minimize corrosion damage. The SRU does not, at present, carry out any corrosion prevention methods. The corrosion of mild steel is controlled by correct air admission to oxide H₂S, and to produce SO₂, which is the reagent in the reaction of sulfur production.     

Un-ignited and ignited high pressure hydrogen releases: Concentration – turbulence mapping and overpressure effects

Safety studies for production and use of hydrogen reveal the importance of accurate prediction of the overpressure effects generated by delayed explosions of accidental high pressure hydrogen releases. Analysis of previous experimental work demonstrates the lack of measurements of turbulent intensities and lengthscales in the flammable envelope as well as the scarceness of accurate experimental data for explosion overpressures and flame speeds. AIR LIQUIDE, AREVA STOCKAGE ENERGIE and INERIS join in a collaborative project to study un-ignited and ignited high pressure releases of hydrogen.The purpose of this work is to map hydrogen flammable envelopes in terms of concentration, velocity and turbulence, and to characterize the flame behaviour and the associated overpressure. These experimental results (dispersion and explosion) are also compared with blind FLACS modelling.     

Mesoporous simonkolleite–TiO2 nanostructured composite for simultaneous photocatalytic hydrogen production and dye decontamination

In the present work, mesoporous simonkolleite–TiO₂ composite was prepared with sol–gel method. The composite photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and Raman spectroscopy. Also, surface area and particle size were analyzed using BET equation. The photocatalytic hydrogen production with simultaneous decolorization of Remazole Red (F3B) dye was investigated over TiO₂ and simonkolleite–TiO₂ composite under UV–vis light irradiation. It was worthy to be noted that the rate of hydrogen production over simonkolleite–TiO₂ is higher that produced over TiO₂. The maximum amount of photocatalytic-produced hydrogen was 2.1 mmol and 3.3 mmol within 240 min using TiO₂ and simonkolleite–TiO₂ composite, respectively. The specific production rate of hydrogen from photocatalytic conversion of dye was calculated. Improvement of apparent quantum yield (22.07%) after 5 h was achieved upon addition of simonkolleite to TiO₂. This high apparent quantum yield proves that the system proposed in this study could be a hopeful approach toward using sunlight energy as outlook energy source. The obtained results suggested that a new process for H₂ production from wastewater could be achieved. The process also provides a method for degradation of organic pollutants with simultaneous H₂ production.     

Application of the TNO multi-energy and Baker-Strehlow-Tang methods to predict hydrogen explosion effects from small-scale experiments

Analytical models or abacus are of importance to predict explosion effects in open and congested areas for industrial safety reasons. The goal of this work is to compare overpressure and flame speed values of small-scale deflagration experiments to predicted values from the TNO multi-energy (TNO ME) method and the Baker-Strehlow-Tang (BST) method. Experiments were performed in cylindrical congested volumes of hydrogen – air mixtures varying from 1.77 L to 7.07 L. The reactivity was controlled by the equivalence ratio of hydrogen-air mixtures, ranging from 0.5 to 2.5. The congestion was realized with varying numbers of grid layers and configurations. The influence of the obstacle density and the importance of the mixture reactivity to choose the strength index in order to predict the effects of an explosion has been highlighted for the TNO ME method. Predictive flame speed values from the BST method are in accordance with almost half of the experimental results and the method is conservative in most tested configurations. The use of the TNO ME method has been validated on a small-scale experiment to predict maximal overpressures generated by the deflagration of medium and large-scale H₂/air clouds.     

The explosion parameters of methanol under variable pressures and 423 K

The high-temperature and high-pressure methanol one-step oxidation has been the primary process for the mass production of dimethoxymethane. However, the risk of explosion for this process is still not properly defined. This paper presents new results from the experimental study on the explosion characteristics, including the explosion pressure and the explosion limits for methanol/air mixtures with a variable oxygen level, under an initial pressure between 0.3 MPa and 0.75 MPa and at the initial temperature of 423 K. The upper explosive limits were found to increase along with the initial pressure. If the limits for normal air are known, the oxygen effect on flammability is predictable from the thermal balance method. With a correlation for the pressure effect and a method for the oxygen effect, we can have the flammable range predictable.     

受限空间瓦斯爆炸与氢气促进机理研究

为探索受限空间中瓦斯爆炸及氢气对爆炸过程的影响,采用GRI-Mech 3.0甲烷燃烧机理,建立受限空间中瓦斯爆炸的数学模型,应用CHEMKIN软件,对受限空间内瓦斯爆炸过程及氢气对反应物浓度、活化中心浓度、主要致灾性气体浓度的影响进行模拟分析。通过对反应机理的敏感性分析,找出影响瓦斯爆炸及爆炸后主要致灾性气体生成的关键反应步。结果表明:混合气中分别充入0.5%,2%,3.5%氢气时,爆炸时间分别提前0.005 7,0.010 5,0.011 1 s;爆炸后压力分别提高2.53,4.05,7.60 kPa;爆炸后温度分别提高20,60,100 K。由此可见,随着混合气中氢气含量的增加,瓦斯引爆时间越来越短,其爆炸强度也随之增大,且氢气在一定程度上对有害气体CO,CO2,NO,NO2的生成有很大影响。     

Mitigation performance of the process protection system on the accident consequences of H2S-containing natural gas release and explosion

Toxic loads and explosion overpressure loads pose grave threats to the offshore oil and gas industry. Many safety measures are adopted to prevent and mitigate the adverse impacts caused by toxic loads and explosion overpressure loads. As a general safety barrier, the process protection system has been widely used but rarely evaluated. In order to assess the barrier ability, the mitigation performance of the process protection system is concerned in this study. Firstly, several chain accidents of H₂S-containing natural gas leakage and explosion are simulated by varying the response time of the process protection system with CFD code FLACS. Qualitative assessment is conducted based on the variation of the dangerous load profiles. Furthermore, the quantitative assessment of the mitigation performance is accomplished by considering its ability in reducing the probability of fatality. Emergency evacuation and no emergency evacuation are considered respectively in the quantitative assessment. The results prove that the process protection system takes effect on mitigating the toxic impact and explosion overpressure impact. The results also demonstrate that although the emergency evacuation may result in a severer explosion load to the operator, the process protection system can mitigate the adverse impacts regardless of whether the emergency evacuation is conducted or not.     

Accident modeling of toxic gas-containing flammable gas release and explosion on an offshore platform

Toxic gas-containing flammable gas leak can lead to poisoning accidents as well as explosion accidents once the ignition source appears. Many attempts have been made to evaluate and mitigate the adverse effects of these accidents. All these efforts are instructive and valuable for risk assessment and risk management towards the poisoning effect and explosion effect. However, these analyses assessed the poisoning effect and explosion effect separately, ignoring that these two kinds of hazard effects may happen simultaneously. Accordingly, an integrated methodology is proposed to evaluate the consequences of toxic gas-containing flammable gas leakage and explosion accident, in which a risk-based concept and the grid-based concept are adopted to combine the effects. The approach is applied to a hypothetical accident scenario concerning an H₂S-containing natural gas leakage and explosion accident on an offshore platform. The dispersion behavior and accumulation characteristics of released gas as well as the subsequent vapor cloud explosion (VCE) are modeled by Computational Fluid Dynamics (CFD) code Flame Acceleration Simulator (FLACS). This approach is concise and efficient for practical engineering applications. And it helps to develop safety measures and improve the emergency response plan.     

含氧氢气钢瓶释放过程危险性分析及处置

针对一起空气误充入氢气钢瓶而导致使用时发生多起爆炸的事故,详细分析了氢氧混合气钢瓶在释放过程中的主要危险性,对释放过程中最可能存在的点火源即静电的产生机理及静电的放电条件进行了详细的论述,应用TNT当量法对可能发生的氢气钢瓶爆炸事故的破坏强度进行了估算。针对爆炸事故的高危险性,制定了以电机作为开阀动力的远距离放空方案,并提出了接地、洒水增湿等预防静电产生的有效措施,综合考虑冲击波超压伤害和人员操作的方便,确定了合理的安全操作距离,为防止爆炸产生的碎片对周围人员、建筑的伤害,在释放场所周围及人员操作场所设置了沙包墙作为防爆掩体。