The creep behavior of A516 Grade 70 is critical for ensuring the long-term structural integrity and safe operation of pressure-containing components exposed to moderately elevated temperatures over extended periods. This study investigated the creep behavior of A516-Gr70 steel using the classical and nano-instrumented indentation test methods. In this regard, after performing the classical creep test method at high temperatures and extrapolating the stress exponents, the nano-instrumented indentation test method is performed at room temperature on A516-Gr70 steel, with the results used to calculate the stress exponents at high temperatures (400–600 °C). Based on the results, it is indicated that for the A516 Gr 70 steel, the nano-instrumented indentation test method performed at room temperature can predict the classical creep behavior at high temperature determined by the conventional creep test method. Based on experimental observations, it could be stated that the dominant creep mechanism in the indenter zone is the formation and slip of geometrically necessary dislocations.

High-temperature processes induce creep and corrosion, primarily resulting in failure of thin-walled pressure vessels. Investigating alloy creep behavior in these vessels is crucial due to its often undetected nature, leading to sudden and costly failures, posing irreversible risks to health and the environment. This study investigates the creep behavior of carbon steel A516-Gr70 at different loads at a constant temperature of 600 °C. The specimens were subjected to high-temperature creep tests until failure at the specified temperature and at different loads of 100, 150, and 250 kg. The results indicated a nearly linear correlation between the creep rate in the stable region and the applied load. Additionally, it was observed that utilizing the hardness versus time-to-failure diagram enables the prediction of the remaining creep life of the components.

One of the principles of corrosion management is proper inspection methodology, and in particular the risk-based inspection (RBI). Occasionally a large percentage of the total risk of a unit is concentrated in a small part of the equipment, which can be reduced by using risk management techniques. In this study, a semi-quantitative risk-based inspection method has been performed in a gas station with for its components (pipelines, filters, etc.), to identify the existing damage mechanisms and also to rank its equipment in terms of inspection intervals. In this regard, RBI was performed for the gas station which consisted of phases (Phase A & Phase B) with Class 300 and Class 600 equipment. According to documented conditions and reviewed records the main damage mechanism for the investigated components in the gas station was identified as wall thinning due to erosion corrosion and external corrosion. In terms of inspection, results showed that most of the equipment studied had medium risk level and a few had medium to high level of risk. In this regard, the corrosion rates of Class 300 and Class 600 equipment were also studied and compared, and it was indicated that the corrosion rates were higher at locations for Class 300 equipment where more pressure drop had occurred. Overall, based on the obtained corrosion rates and obtained risk matrixes, it was concluded that wall thinning (erosion-corrosion) was the determining risk factor for equipment inspected in the gas pressure reduction station.

Several leakages were detected in a desalinated water (DSW) line in a petrochemical plant made from ASTM A106. The piping had been in service for only a few months. Samples of water were taken for laboratory investigations. Electrical resistance, pH, alkalinity, total hardness, sulfide, and chloride concentration of samples were measured to calculate the corrosivity of water and saturation indices (Langelier index, Ryznar index, aggressiveness index, and Puckorius index). Microbial field evaluations were conducted according to the NACE TM 0106 to recognize the presence of microorganisms. Results showed many acid-producing bacteria (APB) were present in the water. Fouling and corrosion products were analyzed by SEM, EDS, and XRD techniques. Results confirmed the presence of biofilms on the internal surface of the pipe, just nearby the corroded area. The morphology of the corroded surface was also analyzed by SEM. All evidence showed APB’s activities could be the most probable cause of piping failure.

In this study, a pulse Cathodic Protection (CP) rectifier was designed and made. The performance of the pulse rectifier was monitored and compared with a conventional system. In this regard, different values of duty cycle (73% and 50%) and frequency (50 kHz and 60 kHz) were analyzed. Results showed that the AC voltage and current consumption dramatically dropped compared to the conventional rectifier. Also, the pulse CP protection potential was distributed more uniformly as a function of pulse parameters in the optimum combination of 50 kHz and 73% for frequency and duty cycle, respectively. This was explained by the changes in the electrochemical polarization resistance of the environment when utilizing the pulse CP.

In this study, the effect of hexamine, sodium nitrite, sodium benzoate, and trisodium phosphate corrosion inhibitors concentration on corrosion resistance of St37 carbon steel was studied (at 45 °C in closed-circuit cooling water) using weight loss, electrochemical impedance spectroscopy (EIS) and cyclic polarization tests. For hexamine and trisodium phosphate, with an increase in the concentration of the inhibitors, the corrosion rate decreased significantly. Therefore, the highest corrosion inhibition efficiency (IE

Coating disbondments on pipeline steels are regions with high resistivity where conventional cathodic protection (CP) could not fully protect. Therefore, in an attempt to mitigate this challenge, this study investigates the effect of pulse CP on corrosion mitigation and electrochemical conditions under a simulated coating disbondment on X-52 pipeline steel. In this regard, conventional and pulse CP of -870 mV(SCE) were applied to the open mouth of a simulated coating disbondment. For pulse CP, frequencies of 1, 5, and 10 kHz were used. Results showed while the conventional CP was not able to fully protect the 20 cm simulated coating disbondment, for the pulse CP with increase in frequency from 1 to 5 kHz, and from 5 to 10 kHz, improve in CP potential protection under the simulated coating disbondment was achieved. This was accompanied by considerably lower corrosion and a more uniform pH distribution under the simulated coating disbondment.

In this study, the microstructure and mechanical properties of transient liquid phase, dissimilar joints between UNS N08825 alloy and UNS S32750super duplex stainless steel was investigated. The joining process was carried out at 1050 ?C for 0, 60, 120, and 300 s using an BNi-2 interlayer. The transient liquid phase bonding area was divided into three zones: (i) the isothermal solidification zone which contained ?-Ni solid solution, (ii) the athermal solidification zone which consisted of Ni- and Cr-rich borides and Ni3Si precipitates, (iii) and the diffusion affected zone in which Cr-Ni-Fe-Mo-Cu-rich borides constituents existed. The hard and brittle eutectic compounds in the bonding zone posed deleterious effects on the mechanical properties of the joints. By increasing the holding time, the amount of these detrimental phases in the bonding zone decreased before finally a eutectic-free joint was achieved at the bonding time of 300 s, which was notably low as compared to the previous studies. The joint held for 0 s had the widest a-thermal solidification zone and the highest hardness was measured at the center of it (546 Hv). The average hardness of the diffusion affected zone on the UNS S3750 super duplex stainless steel side was approximately 450 Hv, which was markedly higher than that of the diffusion affected zone on the UNS N08825 side (302 Hv). The joint held for 0 s showed the lowest shear strength (239 MPa), while the maximum shear strength was obtained for the joint with a holding time of 300 s, approximately 487 MPa. Moreover, it was demonstrated that eutectic compounds were the principal cause of the brittle fracture in the joints containing the a-thermal solidification zone, whereas the joint with a complete isothermal solidification experienced a brittle fracture that occurred at the diffusion-affected zone of UNS N08825 alloy.

This study investigates failure of a shell-and-tube heat exchanger used in a natural gas treating plant. The shell was made of carbon steel grade A516, while its interior wall was cladded by grade 304 stainless steel. Tubes and tube-sheet of the heat exchanger were made of grade 304L austenitic stainless steel. After almost 6 years of service, tube failure was observed adjacent to the tube-sheet, which caused gas leakage, and consequently an increase in internal pressure of the shell. Detailed examinations were performed on the failed tubes. Results showed that crevice corrosion formed within the gap between tube external surface and tube sheet, followed by subsequent cracking was the main cause of failure. Mitigation strategies were suggested for future failure prevention.

The aim of this research was to investigate the effect of the grinding depth of cut on surface quality and corrosion behaviour of WC-10Co-4Cr cermet coatings. Accordingly, a WC-10Co-4Cr coating with 400 mu m thickness was deposited on the carbon steel substrate using a High-Velocity Oxygen Fuel (HVOF) process. Consequently, the effect of different depths of cut on the coating properties was evaluated. Porosity, surface roughness and microhardness of as-sprayed and ground coatings were measured in order to investigate the effect of grinding on the coating characteristics. The corrosion behaviour of the coatings was evaluated using open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarisation tests. The results indicated that after grinding, the porosity and microhardness of the coatings were increased and the surface roughness was decreased. Furthermore, the increase in the depth of cut increased the coating porosity and microcracks. Therefore, the corrosion resistance of the coating was decreased.

This work is focused on the effect of amorphous SiO2 addition on the phase transformation and microstructural evolution of ZrO2 particles. Considering the structural similarities between the amorphous ZrO2 and its tetragonal structure, XRD results showed initial nucleation of metastable tetragonal ZrO2 from its amorphous matrix upon heat treatment. This metastable phase is unstable in pure ZrO2 sample and transforms to a stable monoclinic phase at around 600 oC. However, addition of amorphous SiO2 to ZrO2 structure causes metastable tetragonal phase to remain stable up to around 1100 oC. The temperature range for stability of metastable tetragonal ZrO2 structure increased from about 150 oC in pure ZrO2 particles to around 500 oC in ZrO2-10 mol.% SiO2 composite powders. A further increase in SiO2 content up to 30 mol.% did not change the stabilization temperature range but the average particle size reduced around 1.6 times compared to pure ZrO2 particles. Stabilization of metastable tetragonal ZrO2 explained by constrained effect of SiO2 layer surrounding zirconia nuclei. The thickness of this SiO2 layer enhanced by increasing SiO2 content which limited the growth of ZrO2 nuclei resulting in finer particle sizes.

Herein, microstructural and mechanical characteristics and corrosion resistance of the UNS S32906 super duplex stainless steel (SDSS) welds are investigated. The gas tungsten arc welding technique is used with direct current electrode negative polarity. Welding is conducted in 1.19, 1.46, and 1.87 kJ mm −1 to evaluate the effect of heat input. The results show that the amount of ferrite phase decreases from 59.4% to 49.4% as the heat input increases. Moreover, only ferrite and austenite phases are observed in the microstructure without any other detrimental phases. Hardness test results show that the hardness of the weld metal rises up in comparison with that of the base metal. Furthermore, the more the heat input, the less the weldment hardness. The impact test shows that the toughness of the samples increases with heat input. Polarization tests show that base metal has a better corrosion behavior irrespective of the heat input of the weldments. With an increase in the heat input, the corrosion behavior is improved. It can be said that whether in terms of microstructure or mechanical properties or corrosion resistance, the specimens that are welded with the highest heat input show the best properties.

In order to overcome the poor adhesion of zirconia-silica coating electrophoretically deposited on 316 L stainless steel, graphene oxide (GO) was used as an interlayer. The effect of this interlayer on morphological, microstructural, corrosion performance and bioactivity behavior of ZrO2-10 at. % SiO2 coating was studied. The zirconia-silica coating with the GO interlayer revealed a higher barrier performance as a more compact and a greater adhesive layer to the substrate was created. Indeed, the GO interlayer led to an improvement in apatite formation on zirconia-silica coating surface probably due to create higher roughness. Briefly, the GO interlayer was effective on enhancement of electrochemical performance and biological property of zirconia-silica composite coating, making it a suitable candidate for biomaterials applications.

The current study is focused on refining effect of amorphous SiO2 on porosity and interlayer formation of sintered ZrO2-SiO2 composite coatings produced on anodic oxidized 316L substrate. The SiO2 improved particle interaction with the substrate surface and increased thickness of the interlayer formed at the coating/substrate interface. For porosity evaluation, the coatings were sliced and imaged layer by layer using focused ion beam-scanning electron microscopy and 3D visualizations reconstructed by stacking the acquired 2D images. Volume fraction, dimension, distribution and connectivity of pores as a function of coating composition were analyzed. The results showed that SiO2 also densifies the coating and decreases volume fraction of connected pores. Corrosion performance of ZrO2-SiO2 coatings was improved with increasing SiO2 content due to the higher barrier effect resulted by increasing the interlayer thickness as well as the lower permeability supported by lower percent of connected pores.

Tungsten carbide (WC) has been known as a hard and wear resistant material. Thermal spray coatings were used widely to deposit Ni and/or Co based WC. The high-velocity oxy-fuel (HVOF) spraying is one of the best methods among thermal spray processes that creates denser coatings with less pores for high corrosive environments applications. In this study, the effect of alumina sealing process on the HVOF WC-12Co coatings by the Sol-Gel method for corrosion and wear properties at high temperature applications was investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to characterize the morphology and properties of the coatings before and after the sealing process. High temperature wear properties of coatings before and after sealing were tested by ball-on-disk wear tester at 400 degrees C. The cross- section of the sealed coatings showed that open pores were filled after sol gel. The thickness of the sealed layer was about 14 mu m. Results indicated that the sealing process increased the microhardness of coating slightly from 1160 +/- 160 to 1250 +/- 150 HV. Comparing the results of polarization in 3.5 wt% NaCl solution and wear test showed that the corrosion current density decreased and the wear resistance increased after sealing. A sealed sample with filled open porosity led to recording a higher corrosion resistance (2.9 +/- 0.7 mu A cm(-2)) compared to the as sprayed coating (8.90 +/- 0.5 mu A cm(-2)). The friction profile of the sealed coating showed reduction of the friction coefficient between 0.25 and 0.5 in comparison to the as- sprayed coating at room temperature (04-0.6). Also, the high temperature wear behavior of the sealed coatings was improved. The weight loss was much lower for the sealed coating (5 mg) than that for the as-sprayed coating (13 mg).

The purpose of this study is to investigate the effect of thickness of adhesive graphene oxide (GO) layers electrophoretically deposited on 316 stainless steel substrate on corrosion resistance. Initially, GO was synthesized from graphite using the modified Hummer method. In order to improve the adhesion of GO coatings, substrates were subjected to electropolishing and anodizing procedures. The GO was deposited from acidic (GO/water) and alkaline (GO/water/PBS buffer) solutions. To obtain a range of coating thicknesses, the GO layers were deposited using various voltages and deposition times. The produced coatings were characterized using scanning electron microscopy, X-ray diffraction, Fourier Transform Infrared, Raman spectroscopy, thermal analysis and electrochemical tests. Based on the obtained results, a partial reduction of GO during electrophoretic process and drying steps was confirmed. Compared with electropolished surface, anodizing treatment of substrate induced a better barrier property. A higher reduction of oxygen group in GO was detected by the presence of K+ ions released from PBS buffer into the suspension. It was also found that the thin GO layers obtained from alkaline solution containing PBS buffer could improve the barrier property, while, an increase in GO layers degraded it.

The microstructure and wear behavior of Friction Stir Processed (FSPed) AISI 430 ferritic stainless steel were analyzed in the present study. FSP was performed with a tool rotation and advancing speeds of 1400 rpm 16 mm/min respectively by employing a tungsten carbide tool. The FSPed microstructure consisted of a mixture of ferrite and martensite. After FSP, microhardness increased with respect to that of the as-received material. The wear resistance of the FS processed material was significantly enhanced if compared to that of the as-received substrate. According to the SEM analyses of the worn surfaces and wear debris, a combination of adhesive wear and delamination was observed in the case of the base metal. The wear mechanism shifted to mild adhesive wear after FSP. The superior wear resistance of the FS processed AISI 430 steel was attributed to the pronounced grain refinement and to martensite formation in the stir zone.

Ten-millimeter-thick strain-hardened AZ31B-H24 magnesium sheets were subjected to friction stir processing (FSP) in air and submerged friction stir processing (SFSP) under water to investigate their microstructures and microhardness properties. Different rotational speeds of 500, 630, 800, and 1000 rpm and traverse speeds of 50, 100, 200, and 350 mm/min were employed for processing the materials. For SFSPed samples, the rotational speed of 500 rpm and 200 mm/min of traverse speed resulted in an ultra-fine-grained structure with a minimum grain size of about 400-500 nm, which is half compared to that of FSPed. It was found that both processes led to variation of crystallographic orientation, and enhancing the rotational speed and lowering the traverse speed promoted the development of a {0002} basal texture. The microhardness of SFSPed material increased significantly up to 110% (~ 95 Hv), while the microhardness was 45% (~ 65 Hv) higher than the base metal (~ 45 Hv) for FSPed material.

In this study, the effect of porosity on hardness and strength of as-cast and aged nickel-aluminum bronze (alloy C95800) has been investigated. Optical and scanning electron microscopes were used to examine the microstructures and to characterize the fracture surfaces of the alloy, respectively. After aging, α grains in the microstructure were refined, distribution of eutectoid particle phases became more uniform and volume fraction of β’ phase was increased. Hardness testing revealed that optimum aging was achieved at 350 °C with more than 90% increase compared to the as-cast alloy. In order to eliminate the effect of pores on tensile data, and to evaluate aging process in terms of tensile strength, the concept of “effective area” was introduced as the total cross-sectional area minus the projected area of pores as obtained by fractography. Based on this concept, the effective strength of the cast alloy was calculated. The effective strength was also obtained by Ghosh’s model; comparison of the results indicated good agreement of both methods. It was concluded that effective strength presented in this research could be an appropriate reference value when considering mechanical properties of porous casting alloys.