Study of Crack Sensitivity of Peritectic Steels

By comprehensively considering both the high temperature mechanical properties and peritectic transformation during peritectic steel solidification, the strain εCth is proposed to evaluate the crack sensitivity of peritectic steels produced in the brittle temperature range in the present work. The zero ductility temperature (ZDT) and the zero strength temperature (ZST) of Fe–C–0.32Si–1.6Mn–0.01P–0.015S steel under nonequilibrium conditions by taking the effect of the peritectic transformation on the solute segregation into account were calculated by the CK microsegregation model (Clyne–Kurz model) and were compared with the measured data. The comparison results show that this model can well simulate the nonequilibrium solidification process of peritectic steel. Then, based on the calculation of the CK microsegregation model, the strain during the peritectic phase transformation in the brittle temperature range (ZDT < TB < LIT) was calculated under nonequilibrium conditions. The results show that the calculated strain is in good agreement with the actual statistical longitudinal crack data indicating that the strain can therefore be used to predict the crack sensitivity of peritectic steels effectively.

Application of regression methods for classification of sewers’ damages

The paper presents possibilities of application of selected regression methods (classification trees, support vector machines, K-nearest neighbours, artificial networks) for classification of sewers’ damages. Operational data from the time span 2006–2011 obtained from water utility were used for deterioration analysis. On the basis of the following independent variables, the modelling was carried out: diameter, depth, year of construction, material and season of damage’s occurring. The following kinds of damages were classified: corrosion, crack, longitudinal crack, displacement, unsealing, failure, collapse. The main aim of the paper was to check if prediction methodology could be useful for classification of different kinds of sewers’ damages. The obtained results pointed out that proposed classification methods are not appropriable in quality analysis of registered damages of sewers. Moreover, it is recommended for water and sewerage companies to register types of failures using unified notation which make easier preliminary classification before applying modelling approach. The calculations were performed in Statistica 13.1 software.

Theoretical Analysis of the Variation of Hydraulic Pressure in Cracks Under Uniaxial Compression of Water-saturated Rock Pillar

In order to analyse the variation of hydraulic pressure in cracks of water-saturated rock pillar under uniaxial compression,taking the water-saturated rock pillar as the research object,in which the cracks are divided into two types: longitudinal crack and inclined crack, and the elastic-brittle plastic model is used to describe the mechanical behavior of rock. Assuming that the long axial direction of the crack is consistent with the axial direction of the rock pillar, the expression of tensile stress in the direction perpendicular to the long axial direction of the crack under axial compression is derived by using Maxwell model and Inglis formula. Simplifying the crack to flat elliptic, clinical hydraulic pressure in the case of tensile shear failure and compressive shear damage of the cracks are deduced, and the distribution of clinical hydraulic pressure in uniaxial compression cracks with different growth pattern is analysed. The results show that with the propagation of cracks, the clinical hydraulic pressure near the tip is approach to zero, and in case of hydraulic fracturing, the extension should exhibit the characteristic of discontinuity.

Modeling the material of the cylindrical work with welded seam at compression distribution of vehicle parts

It is shown that the distribution of the ends of tubular billets, which are the main connecting elements of the vehicle brake system, is accompanied by a loss of stability in the circumferential and axial directions, as well as localization of deformations, followed by destruction in the form of a longitudinal crack that occurs at the end of the preform. The presence of the weld complicates the general conditions of deformation during crimping and distribution and leads to the destruction of the workpiece along the weld. To prevent cracking, it is necessary to tighten the crimping and distributing factors, which inevitably leads to an increase in the number of transitions, the complexity of the process and the cost of manufacturing the part as a whole. The issue of deformation of welded structures is of interest with the development of new materials for the automotive industry, such as joining two or more steel sheets with different mechanical properties, thickness or type of coating, which are important for reducing weight, minimizing costs and reducing scrap. It is shown that the deformation of the pipe billet will depend not only on the plasticity characteristics of the base metal and the weld metal, which is obvious, but also on the ratio of the squares of the pipe billet. The increase in the above modulus of plasticity is accompanied by hardening of the welded joint compared with the initial metal of the workpiece, respectively, a decrease in the value of the secant modulus in both directions – a decrease in the strength characteristics of the weld metal. Further analysis of the deformation of the welded workpiece should be carried out taking into account the local anisotropy caused by the welding seam, which will make it possible to determine the conditions of sustained plastic deformation and create an additional effect on the weakened area.

Pavement Crack Detection Method Based on Deep Learning Models

Severe weather and long-term driving of vehicles lead to various cracks on asphalt pavement. If these cracks cannot be found and repaired in time, it will have a negative impact on the safe driving of vehicles. Traditional artificial detection has some problems, such as low efficiency and missing detection. The detection model based on machine learning needs artificial design of pavement crack characteristics. According to the pavement distress identification manual proposed by the Federal Highway Administration (FHWA), these categories have three different types of cracks, such as fatigue, longitudinal crack, and transverse cracks. In the face of many types of pavement cracks, it is difficult to design a general feature extraction model to extract pavement crack features, which leads to the poor effect of the automatic detection model based on machine learning. Object detection based on the deep learning model has achieved good results in many fields. As a result, those models have become possible for pavement crack detection. This paper discusses the latest YOLOv5 series detection model for pavement crack detection and is to find out an effective training and detection method. Firstly, the 3001 asphalt crack pavement images with the original size of 2976 × 3978 pixels are collected using a digital camera and are randomly divided into three types according to the severity levels of low, medium, and high. Then, for the dataset of crack pavement, YOLOv5 series models are used for training and testing. The experimental results show that the detection accuracy of the YOLOv5l model is the highest, reaching 88.1%, and the detection time of the YOLOv5s model is the shortest, only 11.1 ms for each image.

Tubing Failure in HP/HT Wells Investigated and Mitigated

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 20136, “Research and Application of Fracture Failure Control Technology for 13Cr Tubing in HP/HT Gas Wells,” by Lei Ma, Hongtao Liu, and Hailong Geng, PetroChina, et al., prepared for the 2020 International Petroleum Technology Conference, Dhahran, Saudi Arabia, 13-15 January. The paper has not been peer reviewed. Copyright 2020 International Petroleum Technology Conference. Reproduced by permission. Super 13Cr-110 tubing used in high-pressure, high-temperature (HP/HT) gas wells in the Tarim oil field has experienced numerous failures. After a series of investigations for root-cause analysis, the conclusion was that fracture of the tubing mechanistically is categorized as stress corrosion cracking (SCC) and is closely related to the application of phosphate-based completion fluid. Further tests indicated that Super 13Cr (S13Cr) tubing specimens experienced SCC with phosphate-based completion fluids contaminated with mud and oxygen, whereas formate-based completion fluid is compatible with S13Cr tubing. At present, 55 HP/HT gas wells in the field have used formate-based completion fluid with no tubing string fracture. Introduction Compared with the Gulf of Mexico, the North Sea, the South China Sea, the Qiongqiong Basin, and various Chinese oil and gas fields, the oil pipelines in the Tarim field are among the most difficult with regard to service conditions, which are characterized by extreme operating conditions such as high pump pressure and large displacement reform. Construction and high-yield alternating loads on tubing string and joint and a harsh, corrosive environment [chloride content greater than 80 000 mg/L, carbon dioxide (CO2) partial pressure greater than 1 MPa, and the presence of fresh and residual acid] pose significant challenges to the safe service of the tubing string. In the early stages of production, S13Cr oil pipe was selected as the completion string of the HP/HT gas well in the Kuqa mountain front, but in recent years, the S13Cr-110 pipe of the HP/HT gas well in the Tarim field has been continuously fractured. Failure accidents have caused serious economic losses. In the complete paper, through lateral comparison analysis of the failed tubing and indoor simulation experiments, the cause of the tubing fracture is discovered, solution measures are initiated, and good application results are achieved. Comparative Analysis of Oil-Pipe Failures Comparative Analysis of Fracture Macroscopic Morphology. When comparing the macroscopic topographic maps of oil-pipe failures seen in six studied wells, fracture locations of three wells are located in the coupling, while fracture locations of the other three wells are located on the body. In five wells (Wells A through E), the tubing fracture is neat, indicating brittle fracture with no plastic deformation. Well F, however, has a visible longitudinal crack on the surface of the tubing, and many burrs are visible at the fracture. Comparison and Analysis of Working Conditions of Failed Tubing. Through comparative analysis, it was determined that five of the six wells have under-gone acidification. The service shaft temperature, pressure, CO2 content, and formation water salinity of the failed wells differ, but, in five of the six wells, the tubing was exposed to a phosphate-based completion fluid.

Investigating the Underlying Effect of Thermal Modification on Shrinkage Behavior of Bamboo Culm by Experimental and Numerical Methods

This study probes into the root cause of split in thermally modified bamboo culm by investigating the underlying effect of thermal contraction with respect to its orthotropic nature by experimental and numerical methods while concurrently monitoring the chemical variation of its structure by Fourier transformed infrared spectroscopy (FTIR). In first part of this study, a non-linear increase in dimensional and weight changes of small clear bamboo specimens were observed with increasing temperature. The dimensional changes in the radial and tangential directions significantly exceeded that in the longitudinal direction. From FTIR results, shrinkage effect between 150 °C to 200 °C was associated with weight loss engendered by reduction in weakly bound water and increase in desorption of water content while alteration of its mechanical properties was attributed to changes in cellulose, hemicellulose, and lignin. From results of finite element method (FEM), the graded variation in thermal expansion coefficient, which showed the formation of a narrowed region of strain concentration corresponding to longitudinal crack propagation, was associated with the inducement of internal forces, namely tensile and compressive forces, at specific regions along the culm length. The results of this study can be useful to achieve optimized durability in modified bamboo for construction.