The inhibition of stress corrosion cracking of stainless steels in chloride solutions

The inhibition of s.c.c. n AISI 316S stainless steel in 2N HCl by aromatic and heterocyclic substances has been studied. The evaluation of the inhibitors in reducing the s.c.c. of U-bend specimens has been carried out by micrographic measurements.The determination of anodic and cathooic polarization curves shows that the inhibiting action on s.c.c. is related to the effect of the organic compounds on the anodic dissolution process of the metal. An interpretation of s.c.c. in the chloride solutions is hypothesized involving an adsorbed layer of chloride ions. Tests performed with scratched electrodes seem to confirm the proposed interpretation.     

The stress corrosion cracking of admiralty brass in sulphate solutions

The field of occurrence, the severity and the morphology of the stress corrosion cracking (s.c.c.) of Admiralty brass exposed, under open circuit conditions, to sulphate solutions have been determined, as a function of acidity and of Cu²⁺ content, by means of ‘U’-bend and of constant load tests. Depending upon the solution pH, cracking exhibits two different modes: intergranular in strongly acidic solutions and transgranular in a wide range of moderately acidic and in alkaline solutions. The transition in the cracking mode occurs near the borderline conditions of Cu₂O stability; in the same conditions the maximum susceptibility to s.c.c. has been observed. Different roles played by Cu₂O in the nucleation and in the propagation stages of transgranular cracking are discussed.     

二氧化碳缓蚀剂的研究进展

为了有效应对全球气候变暖达到碳中和的目标,碳捕集、利用与封存(CCUS)技术被大力推广和应用。CCUS过程,油气开发和集输过程始终面临着严重的二氧化碳(CO2)腐蚀问题。CO2腐蚀会带来严重的经济损失、环境污染和人身安全等问题。相比于采用昂贵的合金材料防腐措施,在普通碳钢基础上添加缓蚀剂是应对CO2腐蚀较为简单、经济的防腐方法之一。总结了近几年不同类型CO2缓蚀剂的研究进展,包括传统的含有N、O、S、P等杂原子的有机缓蚀剂,含有杂环的有机缓蚀剂,具有两亲性的表面活性剂类缓蚀剂,新型无机纳米材料类缓蚀剂(如石墨烯、碳量子点、离子液体和金属配合物等),以及植物提取物、氨基酸、天然油和生物聚合物等天然型绿色环保缓蚀剂。分析了这些不同缓蚀剂的优缺点和适用性,并讨论了这些缓蚀剂的研究现状。同时,总结了缓蚀剂构效关系和协同效应的研究热点及其存在的问题。最后针对这些不同缓蚀剂的特点和研究现状,对未来CO2缓蚀剂的研究方向进行了分析与展望。     

Stress corrosion cracking of type aisi 304 stainless steel at room temperature; influence of chloride content and acidity

The influence of chloride concentration and acidity on the occurrence of stress corrosion cracking (s.c.c.) of type AISI 304 austenitic stainless steel at room temperature has been studied. The results obtained show that s.c.c. in acidic chloride solutions can occur in a wide range of acidity as a function of the total chloride content. Cracking occurs in the active potential range.     

Intergranular and transgranular stress corrosion cracking of Cu---30Au

The mechanism of stress corrosion cracking (SCC) of Cu-30Au in 0.6 M NaCl was investigated by a series of experiments in which samples were de-alloyed by potentiostatic anodic polarization at 475 mV (Ag/AgCl) and at zero applied stress (i) for varying lengths of time (10 to 30 min) and then impact bent, and (ii) for 30 min followed by a period of time (5–30 s) at the open circuit potential and then impact bent, and (iii) for 30 min followed by anodic polarization at +150 mV (Ag/AgCl) for a period of time (5–30) and then impact bent. The results indicate that de-alloying at zero applied stress produces a surface layer that is capable for a brief period of time of inducing intergranular cleavage failure of the normally ductile substrate. In addition, samples were de-alloyed and simultaneously stressed at various nominal values (0.5–1.7 σ_y). At low values of stress, failure occurred by brittle intergranular cracking, and at high values of stress, failure occurred by brittle transgranular cracking. The results indicate that the electrochemical contribution to the SCC of Cu-30Au in 0.6 M NaCl is the same for both intergranular stress corrosion cracking (IGSCC) and transgranular stress corrosion cracking (TGSCC) and that the mode of fracture is dictated by the magnitude of the applied stress.     

Contribution to the Interpretation of the Formation of the Active Path in Stress Corrosion Cracking of Aluminium Alloys: I. Indirect evidence from electrolytically notched specimens

Abstract

With the object of interpreting the formation of the active path in stress corrosion cracking (s.c.c.) of metals and alloys, a new, electrolytic, method of preparing notched specimens was employed. Double notched specimens of Al–2 · 5 wt- % Mg alloy were so prepared, using several different current densities to prepare the notches. Their behaviour was then compared with that of mechanically notched specimens under accelerated laboratory stress corrosion conditions in M NaCl with differing impressed current densities. In some instances the notches were removed mechanically before testing (‘denotched’ specimens).

For each category of specimen, applied stress vs specimen life (time to cracking) was established. Results obtained from this procedure indicated that, for this alloy, a sensitisation takes place during the first step of stress corrosion cracking, i.e., localised anodic dissolution (pitting) of the stressed zone. In the second part of this work, based on further measurements (to be published) it will be shown that this sensitisation corresponds to active path formation, attributable to de-cohesion as a result of fast solid diffusion of mobile (reversibly disordered) Al³⁺.     

The influence of arsenic and phosphorus on the stress corrosion cracking of aluminium brass in chloride-citrate solution

The presence of As and P, in the range usually found in commercial Al brass, strongly influences the stress corrosion cracking (s.c.c.) behaviour of the alloy tested in acidified (pH 4.0) 1 M sodium chloride + 0.25 M tri-sodium citrate + 0.015 M cuprous chloride solutions. Time to failure, recorded during constant load tests, and maximum crack depth measurements on sections of U-bend specimens both confirmed the deleterious effect of the presence of As and P, in relatively high amounts, to the s.c.c. resistance of the alloy. General corrosion, dezincification, intergranular and/or transgranular cracking were found during metallographic examination of the fracture zones.     

Stress corrosion cracking of bone implants

A diagnostic investigation has been carried out on some AISI type 316 stainless steel fixation nails that failed during service in the recovery treatment of femoral fractures. The association of pitting and cracking at the nail edges where the cracking process appears to start together with fractographic features of the ruptured surfaces has led to the belief that pitting in crevice-induced stress corrosion cracking from acid chlorides is the cause of failure. In this respect, consideration should be given to the new high-Cr ferritic stainless steels, extra-low in interstitial elements, which are much more resistant than ordinary austenitic grades to pitting and s.c.c. in chloride media.     

高温高压水环境下传热管失效形式及防腐措施研究进展

分析了在高温高压水环境下，压水堆(PWR)蒸汽发生 器传热管的失效形式及原因，总结了应力腐蚀开裂(SCC)的相关机理，并针对奥氏体不锈钢的应力腐蚀开裂—一种严重的环境促进腐蚀开裂(EAC)形式，分析了相应的解决措施，特别是缓蚀剂解决措施.     

离合器壳体铸造工艺改进

介绍了离合器壳体铸件的铸造生产工艺,分析了原工艺出现砂眼、裂纹等缺陷的原因.采取了如下的改进措施:①减少#2砂芯的芯头尺寸,保证了砂型的表面强度；②优化浇注系统,避免了铁液对砂型局部过度冲刷；③选取合理的砂芯、砂型分型面,增加铸造圆角；④降低浇注温度,减短浇注时间,降低了铁液对砂芯、砂型的烘烤程度及砂芯、砂型的发气量；⑤改变清理方法,减少了裂纹发生的几率.由于上述改进的结果,所有铸造缺陷均已消除.     

A mathematical model for prediction of time from corrosion initiation to corrosion cracking in RC structures

Prediction of time from corrosion initiation to corrosion cracking is a crucial factor in evaluating concrete structures' durability and integrity deteriorated by reinforcement corrosion. This paper presents a mathematical model to predict the time from corrosion initiation to corrosion cracking. A dynamic corrosion rate model based on Bulter–Volmer kinetics and a rust expansion model based on Faraday's law are developed. An analytical model is developed to demonstrate the mechanical consequences of rust buildup around the rebar. The time to corrosion cracking is found to be a function of surrounding concrete material properties, chemical composition of rust, ratio of concrete cover thickness to rebar diameter, and corrosion current density. Comparisons with available experimental results are conducted to show the accuracy and reliability of the present model. Further parametric analysis is carried out to show the influences of various parameters included in the model on the time to corrosion cracking.     

二氧化碳腐蚀缓蚀剂及其缓蚀机理的研究进展

首先分别论述了单组分缓蚀剂和复配型缓蚀剂的缓蚀机理,即不同类型的缓蚀剂在金属表面所具有的不同吸附过程。单组分缓蚀剂中特殊的分子基团在金属表面通过物理吸附、化学吸附或混合吸附过程起到缓蚀作用,复配型缓蚀剂在金属表面通过各组分间协同吸附或竞争吸附过程起到缓蚀作用,并指出了缓蚀机理的研究所存在的问题。然后,主要综述了近几年来国内外对用于二氧化碳腐蚀缓蚀剂的研究进展,包括咪唑啉衍生物、表面活性剂、季铵盐、有机胺和复配型缓蚀剂,结合缓蚀剂的分子结构和缓蚀效率等对其进行了阐述。介绍了几种用于二氧化碳腐蚀的新型缓蚀剂,如多活性位点有机化合物、硫醇、席夫碱和聚合物等。最后针对二氧化碳腐蚀环境的复杂性,对未来缓蚀剂及其缓蚀机理的研究方向进行了展望。     

脱硫装置碳钢腐蚀缓蚀剂研发

为了减缓或抑制脱硫装置中碳钢的H2S应力腐蚀开裂,通过挂片试验和极化曲线测试筛选出了N-甲基二乙醇胺(MDEA)、单油咪唑啉两种缓蚀剂,对减缓腐蚀和抑制氢鼓泡的效果都很好。还通过恒应变速率拉伸试验分别对它们在饱和H2S水溶液中的缓蚀效果进行定量评价,结果表明,这两种缓蚀剂的加入,都能够很大程度地降低碳钢应力腐蚀的敏感性。     

Reinforcement corrosion-induced cover cracking and its time prediction for reinforced concrete structures

A relation between the radial pressure induced by expansion corrosion products and weight loss percentage of corroded steel was developed and simplified by investigating the influence of the mechanical properties of corrosion layer on cover cracking. By taking account of the penetration of the rusts into open cracks, a mathematical model that predicts the cover cracking time was proposed based on Faraday’s law. Some experimental observations were compared with the predictions made by the proposed model and two existing models, which indicates that the presented model is more suitable for predicting cracking time for both accelerated and long-term corrosion conditions.     

Über den Einfluß von Kohlenstoff und Stickstoff auf die Empfindlichkeit niedriglegierter Stähle gegen Spannungsrißkorrosion

The influecne of carbon and nitrogen on the sensitivity of low-alloyed steels to stress corrosion Application of stress to steels under the influence of certain media produces stress-corrosion cracking. This can be examined through experimental methods only, by which the specimens are kept under constant stress. The cracking time required for the specimen is then a measure of resistance of stress-corrosion failure. In this way it is possible to investigate the influence of alloying metals and the heat treatment on susceptibility of steels, by considering the respective strenght. Experiments were carried out to determine the effect of carbon content and the combined effect of carbon and nitrogen in a series of medium frequency and vacuum steels. It is found that increasing carbon content improves the resistance of specimens, taking also the higher strength into account. A higher nitrogen content shortens the cracking time. This shortening of resistance due to nitrogen content was much more note worthy in the case of high-carbon steels than in the case of low-carbon steels which were already sensitive in this respect. Comparing an open-hearth steel with the above steels, it seems as if there are other alloying metals which make the steels susceptible to stress-corrosion cracking. The effect of these alloying metals shall be investigated further.     

The role of oxide films in stress corrosion cracking initiation

In the low-potential transition range, passivatable alloys undergo electrolytic crevice corrosion i.e. localized anodic attack at any area prevented from passivating by shielding effects. A possible role of stress in this range may be seen, accordingly, in producing at every film rupture uncontrollable localized attack in critical underfilm crevices at the feet of emerging slip steps. The fundamental condition for s.c.c. would be that the incubation time, i.e. the time of attack required to form a critical notch, must be shorter than the film lifetime. The resulting model for s.c.c. initiation at the active-passive transition fits in with the mostly accepted slip-dissolution mechanism. A simple mathematical treatment is given for such model and applied to three typical systems, that are the combination of steel with K₂CO₃-KHCO₃, NaOH and NH₄NO₃ solutions, respectively. Calculated incubation times are consistent with experimental times to rupture and cracking rates from s.c.c. tests.     

The role of oxide films in stress corrosion cracking initiation

In the low-potential transition range, passivatable alloys undergo electrolytic crevice corrosion i.e. localized anodic attack at any area prevented from passivating by shielding effects. A possible role of stress in this range may be seen, accordingly, in producing at every film rupture uncontrollable localized attack in critical underfilm crevices at the feet of emerging slip steps. The fundamental condition for s.c.c. would be that the incubation time, i.e. the time of attack required to form a critical notch, must be shorter than the film lifetime. The resulting model for s.c.c. initiation at the active-passive transition fits in with the mostly accepted slip-dissolution mechanism. A simple mathematical treatment is given for such model and applied to three typical systems, that are the combination of steel with K₂CO₃KHCO₃, NaOH and NH₄NO₃ solutions, respectively. Calculated incubation times are consistent with experimental times to rupture and cracking rates from s.c.c. tests.     

热强碱介质中耐磨高锰钢冲击韧度的研究

采用浸泡腐蚀试验和腐蚀前后的冲击试验并借助于扫描电镜观察,研究了热强碱介质中高锰钢的腐蚀速率和冲击韧度.结果表明,高锰钢的平均腐蚀速率显著高于中碳铬合金钢,腐蚀过程中高锰钢有较严重的碱脆开裂现象.随着热强碱腐蚀时间的延长,高锰钢的冲击韧度明显降低,碱脆开裂是造成高锰钢冲击韧度下降的主要原因.在伴有冲击的热强碱腐蚀磨损工况,高锰钢有过早失效的危险.     

Use of the scratching electrode technique to interpret the stress corrosion cracking behaviour of α-brass in ammoniacal copper sulphate solutions

Stress corrosion cracking (s.c.c.) of α-brass in Mattsson solutions [1 M (NH₃ + NH₄⁺); 0.05 M CuSO₄] at a given strain-rate intensifies in pH order: 4.75 < 7.35 < 11.35. There is no cracking at pH 8.9 or when tarnishing at pH 7.35 is prevented by reducing [NH₃ + NH₄⁺] to 0.25 M. A technique of continously scratching a shallow circular track on a rotating electrode has been used to investigate the electrochemical behaviour of bared metal surfaces in these environments with the object of examining the relative contributions of slip-dissolution and tarnish-rupture in the crack propagation mechanism. It is shown that the observed s.c.c. propensity correlates well with: (i) the physico-chemical nature of the reaction products, (ii) the bare surface current density at the applied potential and (ii) oxide growth kinetics on the bare surface. Thus, in non-tarnishing solutions s.c.c. does not occur if either the rate of protective oxide formation is sufficiently rapid [pH 7.35 (0.25 M NH₃)] or the whole surface is dissolving uniformly (pH 8.9); in the intermediate case (pH 4.75) cracking is observed. In tarnishing solutions [pH 7.35 (1 M NH₃) and pH 11.35] the crack propagation rate increases with the tarnishing rate. Qualitative agreement between s.c.c. behaviour and bare surface oxide growth rate, as determined by the scratching electrode method, supports a slip-dissolution model of propagation.     

Prediction of stress corrosion cracking in 10% caustic soda solutions at 315°C (600°F)

Electrochemically controlled test methods have been used to evaluate the stress corrosion cracking (s.c.c.) resistance of nickel-based alloys in 10%NaOH solutions at 315°C (600°F). In this environment the s.c.c. behaviour is markedly dependent on the electrode potential, with the maximum susceptibility to s.c.c. being observed when the electrode potential is controlled within the potential range corresponding to the active-passive transition region of the anodic polarization diagram. The advantages and predictive capabilities of such techniques are discussed in terms of the relation between electrochemically controlled tests of short duration (days) and conventional immersion tests which frequently necessitate much longer test periods (months) to produce s.c.c. in similar environments.