Stress corrosion behavior of X80 pipeline steel in natural seawater with different dissolved oxygen

Slow strain rate stress corrosion test of X80 steel in the natural seawater are carried out to study to effect of dissolved oxygen on the sensitivity of stress corrosion. Scanning electron microscope (SEM) combined electrochemical measurement are adopted to analyze mechanism and the influencing factor of stress corrosion cracking. The results show that the sensitivity of SCC in the natural seawater increases, and the stress corrosion cracking gradually transforms from ductile to quasi-brittle fracture, with the increase of dissolved oxygen. Tafle polarization and electrochemical impedance spectroscopy of X80 show that dissolved oxygen aggravates electrochemical corrosion and reduces corrosion resistance. Corrosion pits and micro cracks at the lateral and fracture surface trigger stress concentration and promote anodic dissolution under stress, thereby accelerate the process of stress corrosion cracking of X80 steel in the seawater

Hydraulic Fracturing Mechanism in Reservoirs with a Linear Inclusion Fissure

Hydraulic fracturing technology is widely used in most oil-water wells to improve production. However, the mechanism of fracturing in a reservoir with inclusion fissures is still unclear. In this study, a theoretical model was developed to determine the stress distribution during hydraulic fracturing. The line inclusion fissure was regarded as a thin bar and the stress around the artificial fracture, which is affected by a single line inclusion, was determined using the Eshelby equivalent inclusion theory. Stress intensity factors at the tip of both the artificial fracture and the inclusion were achieved, and initiation of the fracture was predicted. Furthermore, to validate the theoretical model, re-fracturing experiments were performed on a large-scale tri-axial system. The results showed that the defects reduce the intensity of the rock, which introduces the possibility that more complex fractures emerge in the reservoir. The results also showed that the fracture direction is governed by far-field stress. The obtained conclusions are helpful to better understand the mechanism of hydraulic fracturing in reservoirs

Experimental study on shale fracturing assisted by low-temperature freezing

Under the cold impact of liquid nitrogen, the shale suffers from the significant freezing damage, which provides the possibility of liquid nitrogen fracturing. Moreover, shale fracturing assisted by liquid nitrogen can effectively reduce reservoir pollution. In this paper, the hydraulic fracturing experiments of natural shale samples frozen by liquid nitrogen were carried out to investigate the factors affecting the crack propagation of shale after low temperature fracturing. The results show that a large number of cracks or macropores form inside the natural shale sample after freezing treatment by liquid nitrogen. The fracture pressure of the shale decreases with increasing impact time at the beginning of the immersion time, and remains substantially stable after an immersion of 2 hours. When the freezing time increases, the crack initiation time increases accordingly. After low temperature impact, the fracture pressure of shale decreases with the increase of stress difference, but the cracking times vary with the stress with obvious regularity. It is easier to form main fracture with larger displacement on the premise of well-developed shale bedding

Non-neuronal cholinergic activity is potentiated in myasthenia gravis

Background: Non-neuronal acetylcholine (ACh) restricts autoimmune responses and attenuates inflammation by cholinergic anti-inflammation pathway. To date, the implication of ACh in myasthenia gravis (MG) remained unexplored. This study aimed to investigate the possible relationship between ACh levels, anti-muscle-specific tyrosine kinase (MuSK) antibody titers, main clinical features and outcomes of MG patients. Methods: We successfully measured ACh levels in human peripheral blood mononuclear cells (PBMCs) from 125 MG patients and 50 matched healthy controls by using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). We assessed the quantitative MG (QMG) scores for each patient and titered anti-MuSK antibody. Results: We found that PBMC-derived ACh level was significantly higher in MG patients, especially in patients of class III, IV-V, compared with that in controls (0.142 ± 0.108 vs. 0.075 ± 0.014 ng/million cells, p = 0.0003) according to the Myasthenia Gravis Foundation of America clinical classification. Importantly, we also found that ACh levels were positively correlated with QMG scores (r = 0.83, p \u3c 0.0001) and anti-MuSK Ab levels (r = 0.85, p \u3c 0.0001). Conclusions: Our demonstration of elevated ACh levels in PBMCs of MG patients foreshadows potential new avenues for MG research and treatment

GA-BP in Thermal Fatigue Failure Prediction of Microelectronic Chips

A thermal fatigue life prediction model of microelectronic chips based on thermal fatigue tests and solder/substrate interfacial singularity analysis from finite element method (FEM) analysis is established in this paper. To save the calculation of interfacial singular parameters of new chips for life prediction, and improve the accuracy of prediction results in actual applications, a hybrid genetic algorithm–artificial neural network (GA–ANN) strategy is utilized. The proposed algorithm combines the local searching ability of the gradient-based back propagation (BP) strategy with the global searching ability of a genetic algorithm. A series of combinations of the dimensions and thermal mechanical properties of the solder and the corresponding singularity parameters at the failure interface are used to train the proposed GA-BP network. The results of the network, together with the established life prediction model, are used to predict the thermal fatigue lives of new chips. The comparison between the network results and thermal fatigue lives recorded in experiments shows that the GA-BP strategy is a successful prediction technique

Investigations on corrosion behaviors of super-strength sucker rod FG20 steel in high SO42− environment

In some sour reservoirs and tertiary oil recovery blocks, SO42− in the well fluid can cause the corrosion and corrosion fatigue of the sucker rods. In this paper, the corrosion behaviors of super-strength sucker rod FG20 (16Mn2SiCrMoVTiA) steel in the well fluid are investigated by electrochemical measurements, and electron probe micro-analyzer (EPMA) analysis. The results show that FG20 steel has a favorable corrosion resistance in neutral solution. When the hydrogen ions increase, the hydrolysis of SO42− greatly accelerates the corrosion of FG20 steel. The energy dispersive X-ray (EDX) results demonstrate that the corrosion process of FG20 steel in neutral well fluid is an oxygen concentration process, and the protective FeCO3 and Fe2O3 on the surface of the samples can prevent the further corrosion. With the increase of the acidity in the well fluid, the corrosion process converts into a sulphide concentration process, and the sloppy FeS and mackinawite film cannot provide effective protection for the specimens, resulting in the increase of corrosion rate. Keywords: Corrosion behavior, FG20, Electrochemical measurements, EPMA, Corrosion mechanis