Papers by Author: Jian Ming Gong

Abstract: Silicon rubber is a potential material for gaskets in proton exchange membrane (PEM) fuel cell. So its long term stability and durability is crucial to the electrochemical performance of fuel cell especially in an acidic, high temperature, humid environment. In present paper, the aging process of silicon rubbers has been studied in one simulated PEM fuel cell medium and two accelerated durability test (ADT) mediums for short time test at 70oC and 90oC, respectively. Effect of exposure time, temperature and exposure medium on aging of silicone rubber is also compared. Weight loss is measured by electronic balance; topographical changes on samples’ surfaces are monitored by optical microscopy; Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was employed to study the surface chemistry of samples before and after exposure over time. The results show that the weight loss increased over time. Surface conditions of samples change over time from initially smooth to rough, crack appearance and finally crack propagation through Optical microscopy. ATR-FTIR results show that the surface chemistry changed significantly via de-crosslinking and chain scission in the backbone for materials over time. The aging degree is severe at high temperature or in high concentration acidic solution over time.

Abstract: Stress corrosion cracking (SCC) of austenitic stainless steel serviced in aggressive environment often occurs in power, petrochemical industry, and leads to premature equipment failure and great economic loss. This paper focuses on the problem of the SCC on the 304L stainless steel nozzle of a hydrogenation reactor, which is caused due to on-line alkali cleaning. Susceptibility for SCC was evaluated by Slow Strain Rate Test (SSRT) for as-rolled and sensitized 304L stainless steel in low concentration sodium hydroxide solution with high temperature. The effects of different strain rates, different concentration of sodium hydroxide and different solution temperatures on SCC were investigated. On the basis of this, the contrast tests were also performed in high temperature pure water. After SSRT, fractograph of the fractured specimens was analyzed by using scanning electron microscopy (SEM).

Abstract: The difference in microstructures of the base metal (BM), weld metal (WM) and heat-affected zone (HAZ) in the weldment is one of the major reasons for the failure of the welded equipments, which can be essentially attributed to the non-homogeneous corrosion occurred electrochemically on the weldment. Therefore, it is necessary to explore the corrosion properties of weldment. In this paper, the electrochemical behavior of SPV50Q steel weldment was investigated. The polarization curves of BM, WM and HAZ in 5wt.%NaCl-0.5wt.%HAc solution containing H2S were measured by potentiodynamic polarization. Interface characterization was also conducted by electrochemical impedance spectroscopy (EIS). The results show the anodic curves are almost same regardless of various pH or H2S content, but the cathodic curves show some difference. Relatively large variation in corrosion current density (icorr) obtained by fitting technique exists among BM, WM and HAZ. icorr of WM and HAZ is larger than that of BM, and icorr of WM is maximum. According to EIS results, polarization resistance (Rp) increases in the orders of WM, HAZ and BM. It is concluded that WM and HAZ are less resistant to corrosion than BM, which can be correlated to the premature failure of the weldment serviced in H2S-containing environment such as sulfide stress corrosion cracking (SSCC) and /or stress oriented hydrogen-induced cracking (SOHIC) etc.

Abstract: A new methodology of computer simulation is proposed to perform finite element (FE) calculations of uniaxial tensile deformation on the three-dimensional (3D) complex microstructures, through its application to the microstructure of aluminum matrix containing randomly distributed and oriented SiC particles of highly variable and angular geometry. Compared with the simplified microstructure model, the complex microstructure model shows significant differences in terms of micromechanical fields and macroscopic uniaxial deformation. The results reveal that a quantitative and convenient reconstruction of microstructure of particulate composites is crucial for both the prediction and design of material properties.

Abstract: The brazed plate-fin structure is the key component of a compact plate-fin heat exchanger (PFHE). The thermal deformation and residual stresses induced by vacuum brazing may bring negative effects on the quality and the life of the plate-fin structure. Thus it is important to optimize the brazing parameters in order to minimize such effects. This paper presents a three-dimensional finite element analysis for determining the thermal deformation and residual stresses of a three layers of stainless steel plate-fin structure fabricated by nickel-based brazing. The feature of thermal deformation and residual stresses distribution are discussed. The effects of three major factors including brazing temperature, clamping pressure and filler metal on the thermal deformation and residual stresses are investigated respectively.

Abstract: Metal dusting is a catastrophic corrosion phenomenon that leads to the disintegration of structural metals and alloys into dust composed of fine particles of the metal/alloy and carbon at high temperature. Considerable research efforts has been taken on the initiation of metal dusting in the alloy since it was observed. However, the previous researches were focused mostly on the initiation mechanisms of metal dusting without external applied loads. In fact, structural materials are mostly used with external applied loads. It is thus necessary to study the initiation and propagation mechanism of metal dusting in the stressed condition. In the present work pure bending testing of Cr-Mo alloy in metal dusting condition was performed. The laboratory experiments were performed at 560°C, using a synthesis gas mixture with composition 75%H2 + 25%CO. The maximum bending stresses were 100MPa, 50MPa, 10MPa and 0MPa, respectively. Post exposure metallographical examinations, SEM, EDX analysis were made in order to identify the difference between loaded and unloaded specimens. The effect of mechanical and chemical interaction on high temperature corrosion was preliminary discussed.

Abstract: This paper is aimed at investigating the damage and remaining life of a whole HP-Nb hydrogen reformer tube serviced for 12 years. The damage and remaining life evaluation of different parts of the tube were made using metallographic examination, ambient and high temperature uniaxial tensile tests, creep rupture tests and damage mechanics analysis. The results showed that different parts of the tube have the different damage and remaining life due to different service temperature, higher the service temperature, severer the damage and shorter the remaining life. Based on these research results, a case of local maintenance of the reformer tube was introduced.

Abstract: To assess the failure risk of high temperature structures, it is essential to obtain the creep fracture toughness of materials. In the present paper, Creep crack growth (CCG) tests for 2¼Cr1Mo steel have been carried out by utilizing the side grooved compact tension (CT) specimen and direct current (DC) electrical potential technique. The material parameter of creep fracture toughness, c mat K , were obtained from analysis of 11 CCG tests at temperatures of 500 and 565oC. It has been found that for 2¼Cr1Mo steel c mat K decreases with increasing time and increases with elevating temperature. For this reason, the value of c mat K at lower temperature or longer service time can be used to extract a conservative result in the high temperature defect assessment where the accurate value of c mat K is unavailable. It is also validated from this test that the proposed formula by Ainsworth et al can be adopted in practice.

Abstract: JIS-SPV50Q high strength steel is often employed in construction of liquid petroleum gas (LPG) spherical tanks due to its high strength and good ductility. In general, post weld heat treatment is not performed after welding of SPV50Q high strength steel and welding residual stress will be retained in weldment. Service experience and inspection indicate that higher H2S concentration and welding residual stress result in the environmental failure, such as blistering or hydrogen induced cracking (HIC), sulfide stress corrosion cracking (SSCC) and stress oriented hydrogen induced cracking (SOHIC). In the present paper, the cracking behavior of SPV50Q high strength steel weldment by manual electric arc welding has been investigated in various saturate solutions with different concentrations of H2S. The results of slow strain rate testing, performed at a strain of 1×10-6s-1, reveal the presence of SSCC and HIC in the base metal adjacent to HAZ. The ffects of the different temperatures of post weld heat treatment on cracking are discussed. The suitable post weld heat treatment could increase the resistance of SPV50Q weldment on SSCC or HIC and does not decrease the mechanical properties of SPV50Q weldment.