Erosion corrosion failure analysis of the elbow in sour water stripper overhead condensing reflux system

The erosion corrosion failure of elbow of one oil refinery was investigated by using Aspen software, CFD technology and experiments. And the gas–liquid equilibrium distribution of H₂S and NH₃ and multiphase flow simulation in the overhead system of a sour water stripper were obtained. The result shows that the component mole fraction of H₂S and NH₃ rises markedly with decreasing temperature. At the outlet of air cooler, the temperature drops to 85 °C to form high concentration of ammonium bisulfide (NH₄HS), which would cause serious erosion corrosion at a certain flow rate and reveals an inhomogeneous thinning. The liquid phase fraction mainly distributes on the outside part of elbow, the more sour water accumulates there resulting in localized corrosion thinning. Meanwhile, the experiments show that when the concentration of NH₄HS reaches 10 wt.%, the corrosion rates increase rapidly with increased velocity. Thus controlling the concentration of NH₄HS below 10 wt.% in reflux drum would reduce the risk of erosion corrosion failure.     

Top of the REAC tube corrosion induced by under deposit corrosion of ammonium chloride and erosion corrosion

The crystal and deposition behavior of ammonium chloride salt (NH₄Cl) and multiphase flow simulation were investigated by using Aspen software and CFD technology. And the corrosion failure causes of inlet tube explosion of a refinery hydrocracking reactor effluent air cooler (REAC) were studied. The top of 10# carbon steel base tube corrosion is severe, and reveals an inhomogeneous thinning. The field with localized corrosion is mainly distributed in a range of approximately 1.5 m away from the liner tube. The NH₄Cl crystal temperature increases with the increase of feedstock chloride content, and the decrease of injected water volume. The NH₄Cl salt granules mainly distribute in the forepart of an inlet tube of the REAC system. The liquid phase mainly exists in the bottom of an inlet tube, and the gas phase in the top of the tube. Without the enough liquid water, the NH₄Cl in the gas phase crystallizes and deposits on the top of a pipeline, resulting in under deposit corrosion, which interacts with the flow erosive action accelerates the localized corrosion thinning at the top of forepart of an inlet tube. Outside of the range of corrosion failure, the possibility of ammonium salt crystal decreases with decreasing temperature, and the condensed water increases gradually, then the deposited ammonium salts completely dissolve, and reduces the corrosion of downstream system.     

Investigation on the deposition failure of a reactor effluent air cooler in hydrocracking unit

The deposition failure of a reactor effluent air cooler (REAC) is investigated by the technical analysis and multiphase flow simulation. The blockages of REAC tubes are mainly induced by the corrosion products come from the upstream heat exchangers, a result of the high temperature H₂S-H₂ corrosion. Meanwhile, NH₄Cl salts crystallize upstream the air coolers and enter into the REAC tubes, flowing along with the corrosion products. Through analyzing the residence times and deposition rates of salts, it is found that the corrosion products tend to deposit on two sides of the header box, the third row of tubes and the regions of low velocities. The temperatures inside the REAC tubes significantly decrease once the tubes are blocked. Fouling of NH₄HS salts occurs when the temperature falls below 30 °C. The expansion and contraction of carbon steel with large difference in temperature lead to the bucking of tubes. The regions with high risk deposition are obtained from simulation, which agree well with the actual failure phenomenon.     

Initial phase hot corrosion mechanism of gas tunnel type plasma sprayed thermal barrier coatings

The hot corrosion resistance of the top layer in TBC is one of the main constructive factors which determines the lifetime of the coatings under critical operating environments. In the present study, 8 wt% yttria stabilized zirconia (8YSZ), lanthanum zirconate (La₂Zr₂O₇) and equal weight percentage of its composite (50%8YSZ + 50% La₂Zr₂O₇) coatings were prepared by using gas tunnel type plasma spray torch at optimum spraying conditions. The hot corrosion performances of the above thermal barrier coatings were examined against 40 wt%V₂O₅–60 wt%Na₂SO₄ corrosive ash at 1173 K for 5 h in open air atmosphere. After hot-corrosion testing, the coating surface was studied using a scanning electron microscope to observe the microstructure and X-ray diffraction techniques were used to identify the phase compositions. The results showed that LaVO₄ and YVO₄ are the main hot corrosion products along with the ZrO₂ phase transformation from tetragonal to monoclinic phases in La₂Zr₂O₇ and 8YSZ coatings respectively. The microstructure and phase formation mechanism of the hot corrosion products varied with each coating and among these, composition of 50%8YSZ + 50%La₂Zr₂O₇ coating exhibited least degradation against V₂O₅–Na₂SO₄ corrosive environment compared to the other coatings.     

Failure analysis of 316L stainless steel tubing of the high-pressure still condenser

Sherritt International Corporation experienced corrosion failures with the 316L stainless steel tubing in a high-pressure still condenser employed for ammonia recovery. A detailed failure analysis was conducted on the condenser tubing to determine the mode and the root cause of the failure. The analysis included both optical and scanning electron microscopy (SEM) of the inner and outer surfaces of the tube as well as characterization of the corrosion products using energy-dispersive X-ray spectroscopy (EDX). Results revealed that the corrosion attack was confined to the first ～100 mm of the tubing at the inlet where the tube was connected to the top tubesheet. The tube suffered both external stress-corrosion cracking (SCC) and crevice corrosion from the shell side (water side), and wall thinning of the inner surface (the tube side) due to erosion corrosion. It was evident that failure of one of the tubes occurred due to SCC that penetrated the whole wall thickness and resulted in a leak failure. Some prevention measures are proposed to avoid this type of corrosion attack in the future.     

Experimental and numerical studies on corrosion failure of a three-limb pipe in natural gas field

A bursting incident occurred in a three-limb pipe, having 16Mn steel for the main pipe and 316L + L416 composite metal for the branch pipe, in a natural gas field. The failure analysis was performed by means of inspection, experiments and computational fluid dynamics (CFD) simulation. The CFD results indicated the radical change in the flow characteristics inside the three-limb pipe due to its upright structure and the formation of a low vortex in the downstream near the junction, which indicated the condensation of water vapor containing high salinity. The condensed brine saturated with CO₂ adhered to the inner wall surface of the main pipe. In such a corrosive medium, 16Mn steel acts as an anode and is preferentially corroded due to galvanic corrosion. In addition, the downstream area, covered by low vortex, exhibited high shear stress and droplet impingement stress, resulting in an increase in flow erosion. Thus, the failure of the three-limb pipe can be attributed to the synergistic effect of galvanic corrosion and flow erosion.     

Microstructure and photoluminescent properties of Sr2SiO4:Eu3+ phosphors with various NH4Cl flux concentrations

In this paper, effect of NH₄Cl flux concentrations (0, 1, 2, 3 and 4 wt%) on the crystal structure, morphology and photoluminescent properties of Sr₂SiO₄:Eu³⁺ phosphors synthesized by a microwave sintering at 1200 °C for 1 h was investigated and discussed. X-ray powder diffraction analysis showed the crystal structure was not affected and the pure Sr₂SiO₄ phase was formed without second phase or phases of starting materials when adding with the NH₄Cl flux. The SEM images indicated that increase of the NH₄Cl flux enlarged the particle size of the phosphor particles. The photo-luminescence results showed the addition of 1 wt% NH₄Cl flux much improved the emission intensity at λ_em of 617 nm as the excitation spectrum at λ_ex of 395 nm. The decay times of Sr₂SiO₄:Eu³⁺ phosphors with different NH₄Cl flux concentrations were obtained around 2.47–2.52 ms.     

Effects of Al content on structure and mechanical properties of hot-rolled ZrTiAlV alloys

Zirconium alloys show attractive properties for astronautic applications where the most important factors are anti-irradiation, corrosion resistance, anti-oxidant, very good strength-to-weight ratio. The effects of Al content (2.2–6.9 wt%) on structure and mechanical properties of the hot-rolled ZrTiAlV alloy samples were investigated in this study. Each sample of the hot-rolled ZrTiAlV alloys with Al contents from 2.2 wt% to 5.6 wt% is composed of the α phase and β phase, meanwhile, the relative content of the α phase increased with the Al content. However, the (ZrTi)₃Al intermetallic compound was observed as the Al content increased to 6.9 wt%. Changes of phase compositions and structure with Al content distinctly affected mechanical properties of ZrTiAlV alloys. Yield strength of the alloy with 2.2 wt% Al is below 200 MPa. As Al content increased to 5.6 wt%, the yield strength, tensile strength and elongation of the examined alloy are 1088 MPa, 1256 MPa and 8%, respectively. As Al content further increased to 6.9 wt%, a rapid decrease in ductility was observed as soon as the (ZrTi)₃Al intermetallic compound precipitated. Results show that the ZrTiAlV alloys with Al contents between 3.3 wt% and 5.6 wt% have excellent mechanical properties.     

Improving the hot corrosion resistance of plasma sprayed ceria–yttria stabilized zirconia thermal barrier coatings by laser surface treatment

Ceria–yttria stabilized zirconia (CYSZ) thermal barrier coatings (TBCs) were deposited by air plasma spraying on NiCoCrAlY-coated Inconel 738LC substrates. After that, the surface of plasma sprayed CYSZ TBCs were glazed using a pulsed Nd:YAG laser. The effects of laser glazing on hot corrosion resistance of the coatings were evaluated in presence of 45 wt%Na₂SO₄ + 55 wt%V₂O₅ corrosive molten salt at 1000 °C. The results revealed that the hot corrosion resistance of plasma sprayed CYSZ TBCs were enhanced more than twofold by laser surface glazing due to reducing specific reactive area of the dense glazed surface layer and consequently, decreasing the reaction between molten salt and zirconia stabilizers.     

Microstructure,mechanical property and corrosion behavior of interpenetrating (HA + β-TCP)/MgCa composite fabricated by suction casting

The novel interpenetrating (HA + β-TCP)/MgCa composites were fabricated by infiltrating MgCa alloy into porous HA + β-TCP using suction casting technique. The microstructure, mechanical properties and corrosion behaviors of the composites have been evaluated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), mechanical testing, electrochemical and immersion tests. It was shown that the composites had compact structure and the interfacial bonding between MgCa alloy and HA + β-TCP scaffolds was very well. The ultimate compressive strength of the composites was about 500–1000 fold higher than that of the original porous scaffolds, and it still retained quarter-half of the strength of the bulk MgCa alloy. The electrochemical and immersion tests indicated that the corrosion resistance of the composites was better than that of the MgCa matrix alloy, and the corrosion products of the composite surface were mainly Mg(OH)₂, HA and Ca₃(PO₄)₂. Meanwhile, the mechanical and corrosive properties of the (HA + β-TCP)/MgCa composites were adjustable by the choice of HA content.     

Thermal and rheological properties of highly concentrated PET composites with ferrite nanoparticles

Ferrite nanoparticles were introduced into poly(ethylene terephthalate) (PET) in a melt state at 270 °C upto 20 wt%, and the thermal and rheological properties of the nanocomposites were investigated. The introduction of ferrite nanoparticles increased a little the crystallization temperature (T_c) of PET by ca. 3 °C, while it had little effect on the melting temperature (T_m). In addition, it increased both heat of crystallization (ΔH_c) and heat of fusion (ΔH_m) with ferrite content. PET nanocomposites with ferrite 5 wt% and above exhibited an increased thermal stability and a two-stage degradation. The dynamic viscosity of PET nanocomposites was increased with ferrite content. However, ferrite loading of 5 wt% and above produced a high degree of shear thinning leading to even lower viscosity in a high frequency range than that of pure PET. The nanocomposites gave a non-zero positive value of yield stress, which was notably increased particularly from 5 wt% loading. In the Cole–Cole plot, at contents 1 wt% and above, ferrite nanoparticles caused the deviation from the master curve and a reduced slope. In addition, the relaxation time was increased with ferrite content and an increasing degree was more notable at a lower frequency.     

The hot corrosion of 310 stainless steel with pre-coated NaCl/Na2SO4 mixtures at 750 °C

The high-temperature corrosion behavior of 310 stainless steel has been studied at 750 °C in air with 2 mg cm⁻² mixtures of various NaCl/Na₂SO₄ ratios. The corrosion behavior and morphological development were investigated by weight gain kinetics, metallographs, depths of attack, metal losses, and X-ray analyses. The results show that weight gain kinetics in simple oxidation reveals a steady-state parabolic rate law after 3 h, while the kinetics with salt deposits display multi-stage growth rates. NaCl is the main corrosive specie in high-temperature corrosion involving mixtures of NaCl/Na₂SO₄ and is responsible for the formation of internal attack. The most severe corrosion takes place with the 75% NaCl mixtures. Uniform internal attack is the typical morphology of NaCl-induced hot corrosion, while the extent of intergranular attack is more pronounced as the content of Na₂SO₄ in the mixture is increased.     

The microscopic features of cavitation erosion and the solution in the plastic injection moulding machines

The premature failure mode of the nozzle unit in the plastic injection moulding machines was discovered to be cavitation erosion, rather than corrosion. The microscopic features of the cavitation erosion on the soft aluminium alloy have its own distinct characteristics. Three types of erosion pits in different size order have been discovered: a large round pit with very smooth surface are in the size range of 1–2 mm, small round overlapping pits in the pattern of parallel line are approximately 100 μm, and micro erosion pits are about 5 μm. These different size order erosion pits might be associated with the different size order of bubbles imploding. The root cause of the bubble formation was the alteration in surface tension and the vapour pressures due to the dosing chemicals in the coolant. The solution to the cavitation erosion with substituting stainless steel to aluminium alloy has been successful.     

Preparation and characterization of a titanium bonding porcelain

The titanium bonding porcelain was synthesized through normal melting-derived route using borate–silicate system. The porcelain was characterized by thermal expansion, X-ray diffraction, scanning electron microscope and cytotoxicity tests. The results of X-ray diffraction showed that the main phase of the bonding porcelain was SnO₂. The SnO₂ microcrystals precipitated from the glass matrix when the SnO₂ content was increased. The thermal expansion coefficient of bonding porcelains decreased with the increasing concentration of SiO₂. The thermal expansion coefficient of bonding porcelains first decreased slightly with the increasing of B₂O₃ concentration (from 0 wt% to 10 wt%) and then increased to about 9.4 × 10^? 6/°C(from 10 wt% to 12 wt%). As an intermediate, B₂O₃ can act as both network formers and modifiers, depending on the relationship between the concentration of basic oxides and intermediates. The Vickers hardness of bonding porcelains increased with the increase of SnO₂ concentration. When SnO₂ concentration was 6 wt%, only Si and Sn elements attended the reaction between titanium and porcelain and mainly adhesive fracture was found at Ti-porcelain interface. When SnO₂ concentration was 12 wt%, failure of the titanium–porcelain predominantly occurred in the bonding porcelain and mainly cohesive fracture was found at Ti-porcelain interface. The methyl thiazolyl tetrazolium assay results demonstrated that the cytotoxicity of the titanium porcelain was ranked as 0.     

Effect of polymer modifier chain length on thermal conductive property of polyamide 6/graphene nanocomposites

The influence of polymer modifier chain length on the thermal conductivity of polyamide 6/graphene (GA) nanocomposites, including through-plane (λ_z) and in-plane (λ_x) directions were investigated. Here, three chain lengths of double amino-terminated polyethylene glycol (NH₂–PEG–NH₂) were used to covalently functionalize graphene with graphene content of 5.0 wt%. Results showed that λ_z was enhanced with the chain length of NH₂–PEG–NH₂ increased, but λ_x reached a maximum value at a certain chain length of NH₂–PEG–NH₂. The maximum λ_z and λ_x of GA are 0.406 W m⁻¹ K⁻¹ and 9.710 W m⁻¹ K⁻¹, respectively. This study serves as a foundation for further research on the thermal conductive property of graphene nanocomposites using different chain lengths of polymer modifier to improve the λ_z and λ_x of the thermal conductive materials.     

The effect of phosphate ions on the electrochemical behaviour of brass in sulphate solutions

In this study, we have investigated the effect of phosphate ions on the corrosion behaviour of brass in 0.1 M Na₂SO₄ solution in acidic (pH 2.1), neutral (pH 7.2) and alkaline (pH 12.3) solutions. For this purpose, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) techniques were used. The surface morphology of the metal surface after exposed to corrosive medium was investigated by scanning electron microscopy (SEM). The effect of temperature has also studied in the temperature range from 293 K to 353 K. Some thermodynamic parameters were calculated and discussed. It was found that, PO₄^3? ions could inhibit the corrosion of brass in Na₂SO₄ solution. However, the inhibition efficiency decreased with increasing temperature. The inhibition effect of PO₄^3? ions was explained by complex formation between phosphate ions and corrosion products which physically adsorbed on the metal surface.     

Preparation of MgH2 composite with a composition of 40%MgH2 + 30%LiBH4 + 30%(2LiBH4 + MgF2)

A mixture of containing two chemical equivalents of lithium borohyride and one equivalent of magnesium fluoride is known to yield hydrogen in an amount of about 7.6 wt% of the mixture when heated to about 150 °C at atmospheric pressure by the following reaction; 2LiBH₄ + MgF₂ = 2LiF + MgB₂ + 4H₂. In order to increase hydrogen storage capacity of Mg-based materials, a mixture with a composition of 2LiBH₄ + MgF₂ and LiBH₄with a higher hydrogen storage capacity of 18.4 wt% were added to MgH₂. MgH₂ composite with a composition of 40 wt%MgH₂ + 30 wt%LiBH₄ + 30 wt%(2LiBH₄ + MgF₂) was prepared by reactive mechanical grinding. The hydrogen storage properties of the sample were then examined. Hydrogen content vs. desorption time curves for consecutive 1st desorptions of 40 wt%MgH₂ + 30 wt%LiBH₄ + 30 wt%(2LiBH₄ + MgF₂) at 533–873 K showed that the total desorbed hydrogen quantity for consecutive 1st desorptions is 7.07 wt%.     

Understanding the effect of soil particle size on corrosion behavior of natural gas pipeline via modelling and corrosion micromorphology

The effect of particle size on the electrochemical corrosion behavior of natural gas pipeline steel in a 1.5 wt% NaCl sandy soil corrosive environment was investigated by standard quartz sand. A mathematical model of gas/liquid/solid three-phase boundary (TPB) zone and the soil particle size was developed, and then the theoretical calculation indicated that a critical particle size corresponded to 1.2 mm radius. The laboratory experiments indicated that the corrosion rate of natural gas pipeline steel increased with decreasing soil particle size to < 1.0 mm and was mainly determined by a cathodic reaction. Whereas the corrosion rate of pipeline steel increased with increasing soil particle size exceeding 1.0 mm and the dominant reaction was metal dissolution in the bulk zone and the corrosion rate was determined by anodic reaction. The modelling result is in good agreement with experimental data.     

Corrosion failure analyses of an elbow and an elbow-to-pipe weld in a natural gas gathering pipeline

The internal corrosion of a 90° elbow was found in a natural gas gathering pipeline in Northeast China. The welded joint between the elbow and the downstream pipe was also severely corroded. The 90° elbow was forged of 16Mn steel. The downstream pipe (Φ 76 mm × 9 mm) was made of 20G steel. To determine failure causes, the elbow and the welded joint were taken as a whole and investigated systematically. The influence of the flow disturbance induced by the elbow on the damage at the welded joint was considered. The internal damage at the elbow and that at the welded joint were studied using field investigation, visual examination, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), hardness tests, and computational fluid dynamics (CFD) techniques. The results showed that erosion corrosion from solid particles and corrosive liquid droplets entrained in the natural gas flow was the main cause of the internal damage at the elbow and the welded joint. The welded joint was attacked by the particles with the highest velocity magnitudes and the most dangerous impact angles. The flow disturbance induced by the elbow, the special location of the welded joint, and the angular misalignment due to poor welding quality jointly caused the substantially more severe damage at the welded joint.     

Comparison of friction and wear performances of brake materials containing different amounts of ZrSiO4 dry sliding against SiCp reinforced Al matrix composites

Low friction levels for brake materials dry sliding against Al matrix composites (Al-MMCs) were observed. Al matrix composites reinforced with 30 vol.% SiC_p (34 μm) were used first to fabricate a new brake drum in place of the conventional cast iron brake drum for a Chase Machine. Experimental studies on the brake materials differing in amounts of zirconium silicate (0 wt%, 4 wt%, 8 wt%, and 12 wt% ZrSiO₄) dry sliding against the Al-MMCs drum were performed on the Chase Machine in order to examine their effects on friction and wear performances. The test procedures include friction fade and recovery, load and speed sensitivities at 177 °C and 316 °C, and wear. Experimental results show that the brake material containing 8 wt% ZrSiO₄ had the best wear resistance and higher friction level. The brake material containing 12 wt% ZrSiO₄ had the highest friction level, but wear increased rapidly. The deterioration of the latter wear suggests that this brake material is unreliable in commercial applications.