A study on properties of corrosion fracture surfaces of GFRP in synthetic sea water

In this paper we investigate the stress corrosion cracking (SCC) mechanism and the properties of the corrosion fracture surface of glass fiber reinforced plastics (GFRP) produced by hand lay-up (HLU) in synthetic sea water. The test material is a GFRP with vinylester type epoxy acrylate resin (an unsaturated polyester) as the matrix and chopped strand mat (CSM) type E-glass fiber as the reinforcement. The slow strain rate test (SSRT) was perormed on dry and wet specimens in air and sea water. Here the pH concentration of synthetic sea water was controlled to 6.0, 8.2 and 10.0, and the strain rates varied from 1×10⁻⁴ (sec⁻¹) to 1×10⁻⁷ (sec⁻¹). The results confirm the fact that in wet specimens tested at a particular strain rate, evidence of SCC such as co-planar, mirror and hackle zone appear. Moreover, stress corrosion of GFRP in sea water was characterised by flat fracture surfaces with only small amounts of fiber pull-out.     

Environmental strength evaluation of welded steel joint in sea water

Corrosion fatigue crack growth behaviours were experimentally evaluated for the parent metal, as-welded and PWHT specimens of SM53B steel. Multi-pass welding was done by a submerged arc welder. Metallographic observations along the weld fusion boundary were made to investigate the variation of microstructures through the thickness direction. PWHT was carried out at 650°C with holding time of 1/4hr and 40hr. The corrosion fatigue test was conducted in 3.5% NaCl solution with the frequency of 3Hz. In all cases, crack growth in corrosive environment was faster than that of in air. Besides, at the low †K region, crack growth was greatly influenced by corrosive environment and the heat treatment condition.     

Evaluation of fracture behavior of SA-516 steel welds using acoustic emission analysis

The purpose of this study is to evaluate the AE characteristics for the basemetal, PWHT (post-weld heat treatment) and weldment specimens of SA-516 steel during fracture testing. Four-point bending and AE tests were conducted simultaneously. AE signals were emitted in the process of plastic deformation. AE signal strength and amplitude of the weldment was the strongest, followed by PWHT specimen and basemetal. More AE signals were emitted from the weldment samples because of the oxides, and discontinuous mechanical properties. AE signal strength and amplitude for the basemetal or PWHT specimen decreased remarkably compared to the weldment because of lower strength. Pre-cracked specimens emitted even lower event counts than the corresponding blunt notched specimens. Dimple fracture from void coalescence mechanism is associated with low-level AE signal strength for the basemetal or PWHT. Tearing mode and dimple formation were shown on the fracture surfaces of the weldment, but only a small fraction produced detectable AE.     

Evaluation of sensitization and corrosive damages of the weldment for SUS 316 stainless steel

The anodic polarization method was verified to be suitable for evaluating the degree of sensitization for the weldment of stainless steel at the passive region. Heat treated weldment and parent are more sensitized than untreated weldments and parents. Specifically, weldments treated at 730°C with a 4 h holding time and then cooled in a furnace are the most sensitized. An unstable passive film formed on the surface of the heated-treated weldment because of the Cr-depletion zone at the passive region. The time to failure (TTF) for the parent in synthetic seawater requires a longer amount of time than that in air. However, the TTF for the weldment is shorter than that in air. The heat treated-weldment in a corrosive environment was the most severely damaged among the specimens. For the heat-treated weldment, most acoustic emission (AE) counts were emitted until 4 × 10⁵ s, whereas those for the untreated weldment were produced over the elastic-plastic deformation range. Moreover, the number of AE counts per hour for the heat-treated weldments and parents decreased considerably compared with the untreated weldments and parents.     

SPV50Q钢在湿H2S环境下抗应力腐蚀性能试验研究

用楔形张开加载(WOL)预裂纹试样研究了SPV50Q钢在湿H2S环境中的抗应力腐蚀性能。测定了SPV50Q钢母材及热影响区在湿H2S环境下的临界应力强度因子KISCC和应力腐蚀裂纹扩展速率;同时研究了H2S浓度、材质、热处理对SPV50Q钢应力腐蚀开裂的影响。     

Environmental strength evaluation of welded steel joint in seawater

A study on corrosion fatigue was experimentally conducted for the as-welded and PWHT specimens of the steels, HT80 and SM53B in 3.5% NaCl solution. Submerged arc welding was done. PWHT was carried out at comparatively high temperature of 650° C. Besides, in order to simulate the residual stress in weld HAZ, the stress of 98MPa was applied during PWHT. Corrosion fatigue crack growth was dependent upon the materials and PWHT conditions. In the case of HT80, crack growth in corrosion environment was faster than that in air. However, the crack growth of the main crack for SM53B in 3.5% NaCl solution was decreased in comparison with that in air, unlike HT80. The sensitivity to corrosion environment was reduced due to PWHT. The applied stress in HAZ during PWHT acted to enhance the crack growth compared with that of the PWHT specimen without stress.     

Effect of single overload on fatigue behavior in the welded haz of low alloy steel

Room temperature fatigue crack growth behavior was obtained for 4140 parent steel, parent heat treated (same as PWHT), as-welded HAZ and PWHT HAZ material under R≈O constant amplitude loading and single tensile overloads with an over load ratio (OLR: P_over/P_max) of 2.5. Double pass automatic submerged arc welding with AWS EM2 electrode was used. PWHT was performed at 650°C for one hour. Constant amplitude fatigue crack growth behavior was very similar for all four material conditions in the log-log linear Paris region. All material conditions responded favorably to the single tensile overloads with fatigue crack growth retardation ranging from 2.5×10⁵ to 4.5×10⁵ cycles which corresponded to life increases of 250 to 400 percent. SEM analysis indicated many similarities on the fatigue fracture surfaces with predominant ductile quasi-striation morphology.     

Evaluation of fracture strength and material degradation for weldment of high temperature service steel using advanced small punch test

This paper presents an effective and reliable evaluation method for fracture strength and material degradation of the micro-structure of high temperature service steel weldment using advanced small punch (ASP) test developed from conventional small punch (CSP) test. For the purpose of the ASP test, a lower die with a minimized Φ1.5 mm diameter loading ball and an optimized deformation guide hole of Φ3 mm diameter were designed. The behaviors of fracture energy (E_sp), ductile-brittle transition temperature (DBTT) and material degradation from the ASP test showed a definite dependency on the micro-structure of weldment. Results obtained from ASP test were compared and reviewed with results from CSP test, Charpy impact test, and hardness test. The utility and reliability of the proposed ASP test were verified by investigating fracture strength, behavior of DBTT, and fracture location of each micro-structure of steel weldment for test specimen in ASP test. It was observed that the fracture toughness in the micro-structure of FL + CGHAZ and ICHAZ decreased remarkably with increasing aging time. From studies of all micro-structures, it was observed that FGH AZ microstructure has the most excellent fracture toughness, and it showed absence of material degradation.     

Abrasion–Corrosion Behaviors of Steel–Steel Contact in Seawater Containing Abrasive Particles

Materials working in slurries containing seawater and abrasive particles degrade gradually because of the synergic effects of mechanical wear and electrochemical corrosion. In this study, the abrasion–corrosion behaviors of a steel–steel tribopair in an environment with artificial seawater and SiO₂/Al₂O₃ particles were investigated. Corrosion is responsible for surface degradation at low concentrations of SiO₂ particles, whereas abrasion is the primary cause for steel damage at high SiO₂ concentrations. When Al₂O₃ particles were used, abrasion was found to be the dominant factor for material loss at all concentrations. Results from this study indicate that at low concentrations of hard particles, abrasion–corrosion behavior is determined by the properties of particles.     

Erosion–corrosion and corrosion properties of DLC coated low temperature gas-nitrided austenitic stainless steel

Low temperature nitriding of stainless steel leads to the formation of a surface zone of so-called expanded austenite, i.e. by dissolution of large amounts of nitrogen in solid solution. In the present work the possibility of using nitrogen expanded austenite “layers” obtained by gaseous nitriding of AISI 316 as substrate for DLC coatings are investigated. Corrosion and erosion–corrosion measurements were carried out on low temperature nitrided stainless steel AISI 316 and on low temperature nitrided stainless steel AISI 316 with a top layer of DLC. The combination of DLC and low temperature nitriding dramatically reduces the amount of erosion–corrosion of stainless steel under impingement of particles in a corrosive medium.     

An assessment of hardness, impact strength, and hot corrosion behaviour of friction-welded dissimilar weldments between AISI 4140 and AISI 304

Understanding the behavior of weldment at elevated temperatures and especially their corrosion behavior has recently become an object of scientific investigation. Investigation has been carried out on friction-welded AISI 4140 and AISI 304 under Na₂SO₄?+?V₂O₅ (60%) environment at 500 to 600°C under cyclic condition. The resulting oxide scales in the weldment have been characterized systematically using surface analytical techniques. Scale thickness on the low alloy steel side was found to be higher and was also prone to spalling. Weld area was found to be more susceptible to degradation than in base metals. The influences of welding parameters on the hot corrosion are discussed.     

16MnR钢和15MnVR钢在碳酸盐环境中的应力腐蚀研究

采用楔形张开加载（WOL）恒位移预裂纹试样研究了16MnR钢和15MnVR钢在碳酸盐环境中的抗应力腐蚀性能。试验选择常温、90℃和150℃分别在两种碳酸盐浓度下加载不同应力强度因子K1,经一定时间的应力腐蚀试验,测得各试样的扩展速率处于10^-7～10^-8mm／s之间,结果表明两种材料在所选碳酸盐浓度下裂纹基本没有扩展,其应力强度因子临界值KISCC分别不小于126和116MPa√m。同时采用扫描电镜和能谱技术对断口和试样表面膜进行了相应的观察和理论分析。总体而言,这两种材料在单一的碳酸盐溶液中应力腐蚀敏感性较低。     

Monitoring corrosion of reinforcement in concrete structures via fiber Bragg grating sensors

Corrosion of steel and rebar in concrete structures is one of the most frequent reasons for civil infrastructure failures. Thus, improving the effective corrosion sensor technology can greatly reduce cost and provide safe structures with long service lives. However, assessing the corrosion condition of rebars is not simple because they are buried in concrete. In this paper, using fiber Bragg grating (FBG), a corrosion sensor for monitoring steel rebars embedded in a concrete structure is developed and validated by experiments. Based on the fact that the volume and diameter of a rebar embedded in concrete will enlarge due to corrosion, an FBG packaged with fiber-reinforced plastics (FRP) is wrapped on the steel bar. During corrosion, the increase in the bar diameter leads to the increase in fiber strain, which can be measured by the shift of the wavelength of FBG. Performances of the corrosion sensor are validated by accelerating corrosion in lab experiments. The corrosion sensor is embedded in a concrete specimen put in a 5% sodium chloride solution with a constant current. Experimental results show that the corrosion sensor can monitor the concurrence of corrosion of rebars in concrete. The corrosion extent can be quantitatively evaluated through the change in the wavelength of FBG. Therefore, the corrosion sensor developed in this paper is feasible for monitoring the early corrosion of rebars in concrete.     

Assessment of the sulfide corrosion fatigue strength for a multi-pass welded A106 Gr B steel pipe below the low SSCC limit

In the area of heavy construction, welding processes are vital in the production and maintenance of pipelines and power plants. Welding processes happen to produce residual stresses and change the metal structure as a result of the large nonlinear thermal loading that is created by a moving heat source. The fusion welding process generates formidable welding residual stresses and metallurgical change, which increase the crack driving force and reduce the resistance to the brittle fracture as well as the environmental fracture. This is a serious problem with many alloys as well as the A106 Gr B steel pipe. This pipe that is used in petrochemical and heavy chemical plants either degrades due to corrosive environments, e.g., chlorides and sulfides, and/or become damaged during service due to the various corrosion damage mechanisms. Thus, in this study, after numerically and experimentally analyzing the welding residual stress of a multi-pass welded A106 Gr B steel pipe, the sulfide stress corrosion cracking (SSCC) characteristics were assessed in a 3.5 wt.% NaCl solution that was saturated with H₂S gas at room temperature on the basis of NACE TM 0177-90. The specimens used are of two kinds: un-notched and notched. Then, the sulfide corrosion fatigue (SCF) strength for the un-notched specimen was assessed below the low SSCC limit that was previously obtained from the SSCC tests for the notched specimen. From the results, in terms of the SSCC and SCF, all the specimens failed at the heat-affected zone, where a high welding residual stress is distributed. It was found that the low SSCC limit of un-notched specimens (σ_{SSCCun-notched}) was 46% (230 MPa) of the ultimate tensile strength (σ_U=502 MPa) of a multi-pass welded A106 Gr B steel pipe, and the notched specimens (σ_SSCCnotched) had 40% (200 MPa) of the ultimate tensile strength. Thus, it was determined that σ_{SSCCun-notched} was 13% lower than σ_SSCCnotched. Further, the sulfide corrosion fatigue limit (σ_{SCFun-notched}) was 32% (160 MPa) of the ultimate tensile strength of welded specimens. This σ_{SCF un-notched} was 20% lower than σ_SSCCnotched.     

Effects of temperature and pressure on stress corrosion cracking behavior of 310S stainless steel in chloride solution

310S is an austenitic stainless steel for high temperature applications, having strong resistance of oxidation, hydrogen embrittlement and corrosion. Stress corrosion cracking(SCC) is the main corrosion failure mode for 310 S stainless steel. Past researched about SCC of 310 S primarily focus on the corrosion mechanism and influence of temperature and corrosive media, but few studies concern the combined influence of temperature, pressure and chloride. For a better understanding of temperature and pressure's effects on SCC of 310 S stainless steel, prepared samples are investigated via slow strain rate tensile test(SSRT) in different temperature and pressure in NACE A solution. The result shows that the SCC sensibility indexes of 310 S stainless steel increase with the rise of temperature and reach maximum at 10 MPa and 160℃, increasing by 22.3% compared with that at 10 MPa and 80 ℃. Instead, the sensibility decreases with the pressure up. Besides, the fractures begin to transform from the ductile fracture to the brittle fracture with the increase of temperature. 310 S stainless steel has an obvious tendency of stress corrosion at 10 MPa and 160℃ and the fracture surface exists cleavage steps, river patterns and some local secondary cracks, having obvious brittle fracture characteristics. The SCC cracks initiate from inclusions and tiny pits in the matrix and propagate into the matrix along the cross section gradually until rupture. In particular, the oxygen and chloride play an important role on the SCC of 310 S stainless steel in NACE A solution. The chloride damages passivating film, causing pitting corrosion, concentrating in the cracks and accelerated SSC ultimately. The research reveals the combined influence of temperature, pressure and chloride on the SCC of 310 S, which can be a guide to the application of 310 S stainless steel in super-heater tube.     

Fracture strength evaluation of welded steel joint by means of small punch test

It has been well known that the ductile-brittle transition temperature (DBTT) of each weld structure or its shift (ΔDBTT) from parent material is one of the very useful measures of the fracture characteristics in steel weldment. In order to present an applicability of small punch (SP) test technique to weldments, in this study, a fracture strength of microstructure at any localized region of interest on HAZ, weld metal and parent material in two steels was evaluated by using DBTT or ΔDBTT obtained from the SP test in relation to the data obtained from the COD test. The empirical correlation, (ΔDBTT) _SP ⋟0.55 (ΔDBTT) _COD , was obtained from the SP and COD test. In addition, the effects of test materials, that is the microstructures of welded region and the orientations of specimens etc, did not appear at the empirical correlation.     

Multichannel wire gas electron multipliers with 1- and 3-mm gaps

The operation of multichannel wire gas electron multipliers (MWGEMs) with gaps between electrodes δ = 1 and 3 mm, when the chamber is filled with commercial neon under a 0.4- and 1.0-atm (abs.) pressure and irradiated with α and β particles, is studied. The following maximal proportional electron multiplication coefficients are obtained: 6 × 10³ (α, irradiation, δ = 3 mm, 1 atm, and 20% streamers), 1.2 × 10⁴ (β⁻, 3 mm, 1 atm, and 50% streamers), 6 × 10³ (α, 3 mm, 0.4 atm, and 20% streamers), and 10⁵ (β⁻, 3 mm, 0.4 atm, and 50% streamers). The maximal proportional electron multiplication coefficients are obtained in the MWGEM and its anode (induction) gap in the sequential electron multiplication mode: 1.08 × 10⁵ (β⁻, 1 mm, 0.4 atm, 50% streamers), 2 × 10⁶ (β⁻, 3 mm, 0.4 atm, 20% streamers), and 1.12 × 10⁵ (α, 3 mm, 0.4 atm, 50% streamers).     

Corrosion inhibition of mild steel using Novel Bis Schiff’s Bases as corrosion inhibitors: Electrochemical and Surface measurement

Purpose: The aim of the present investigation is to evaluate the corrosion inhibiting properties of four novel synthesize compounds namely N¹,N^1′-(1,4-phenylene)bis(N⁴-(4-nitrobenzylidene)benzene-1,4-diamine) SB-I, N¹,N^1′-(1,4-phenylene)bis(N⁴-benzylidenebenzene-1,4-diamine) SB-II, N¹,N^1′-(1,4-phenylene)bis(N⁴-(4-methylbenzylidene)benzene-1,4-diamine) SB-III, N¹,N^1′-(1,4-phenylene)bis(N⁴-(4-methoxybenzylidene)benzene-1,4-diamine) SB-IV for mild steel in 1 M HCl. Corrosion inhibitors find wide application in industries during pickling of steel, descaling and oil well acidization. Inhibitors have attracted great attention due to cost effectiveness and simplicity of the methods. Method: Different experimental techniques such as weight loss, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to evaluate the corrosion inhibition performance of SBs for mild steel in acid solution. After the corrosion experiments, the surface morphology of metal surface in the absence and presence of SBs were studied by scanning electron microscopy (SEM) and Atomic force microscopy (AFM). Findings: The corrosion inhibition efficiency of SBs for mild steel are 71.42% (SB-I), 89.52 (SB-II), 92.85 (SB-III), 96.19 (SB-IV). Tafel polarization revealed that all the SBs behaved as mixed-type inhibitor but predominantly of cathodic type. The inhibition actions of these Schiff base molecules blocked the electrode surface by means of adsorption of the inhibitor molecule on metal surface, obeying the Langmuir adsorption isotherm. SEM/AFM studies of the metal surfaces confirm the protection of metal surface in presence of inhibitor as compared to the damaged surface in blank acid solution.     

Two-phase flow heat transfer of propane vaporization in horizontal minichannels

Experiments were performed on the convective boiling heat transfer in horizontal minichannels using propane. The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm and lengths of 1000 mm and 2000 mm, respectively, and it was uniformly heated by applying an electric current directly to the tubes. Local heat transfer coefficients were obtained for a heat flux range of 5–20 kW m⁻², a mass flux range of 50–400 kg m⁻² s⁻¹, saturation temperatures of 10, 5, and 0°C and quality ranges of up to 1.0. The nucleate boiling heat transfer contribution was predominant, particularly at the low quality region. Decreases in the heat transfer coefficient occurred at a lower vapor quality with a rise of heat flux and mass flux, and with a lower saturation temperature and inner tube diameter. Laminar flow appeared in the minichannel flows. A new boiling heat transfer coefficient correlation that is based on the superposition model for propane was developed with 8.27% mean deviation. This paper was recommended for publication in revised form by Associate Editor Jae Young Lee Jong-Taek Oh received his B.S., M.S. and Ph.D. degrees in Refrigeration Engineering from Pukyong National University, Korea. Dr. Oh is currently a Professor at Department of Refrigeration and Air Conditioning Engineering, Chonnam National University at Yeosu, Korea. Dr. Oh’s research interests are in the area of boiling and condensation heat transfer and pressure drop of refrigerants with small tubes, heat pump and transportation refrigeration.     

15MnVR与16MnR钢在氢氧化钠溶液中的抗应力腐蚀试验研究

采用楔形张开加载（WOL）恒位移预裂纹试样研究了16MnR钢和15MnVR钢在氢氧化钠溶液中的抗应力腐蚀性能。测得了180℃下30％NaOH溶液中两种材料的应力腐蚀临界应力强度因子和裂纹扩展速率,即16MnR材料的应力府蚀裂纹扩展速率da／dt为0．039～0．040mm／h,KISCC不大于82．75～90．85MPa·m^0.5,15MnVR材料的应力腐蚀裂纹扩展速率da／dt为0．018mm／h,KM。不大于87．58～102．44MPa·m^0.5。同时采用扫描电镜和能谱技术对断口进行了相应的观察和理论分析,得出NaOH溶液中两种材料均为沿晶开裂。