CO2环境下油酸咪唑啉对X65钢异种金属焊缝电偶腐蚀的抑制作用研究

研究了X65管线钢与316L不锈钢、Inconel 625双金属复合管的异种金属焊缝在CO2环境下的电偶腐蚀行为,以及油酸咪唑啉的缓蚀作用。结果表明,随着电偶电位差的增大,异种金属焊缝的腐蚀速率明显升高,并且都显著高于母材。添加油酸基咪唑啉缓蚀剂能降低异种金属焊缝在CO2环境下的均匀腐蚀速率。但是,当缓蚀剂浓度添加较低时,异种金属焊接试样的碳钢一侧出现了严重的沟槽腐蚀或密集的点蚀坑;进一步增加缓蚀剂浓度才能消除沟槽腐蚀现象。讨论了缓蚀剂对异种金属焊缝电偶腐蚀的抑制机理,该项研究可为异金属焊接接头处的腐蚀防护提供借鉴。     

Local electrochemical properties of laser beam‐welded high‐strength Al–Zn–Mg–Cu alloys

Butt welds of two high‐strength Al–Zn–Mg–Cu alloys with different zinc contents were welded by a laser beam welding technique. Due to the high energy density of the laser beam, the microstructural changes are confined to very thin regions. Electrochemical properties of the weld heat‐affected zones are investigated by local electrochemical measurement techniques and correlated with microhardness measurements, macroscopic corrosion behaviour and metallographic sections. It turned out that microelectrochemical techniques, especially the EC‐pen is a versatile and easy to handle tool for the resolution of changes in the electrochemical properties across a weld bead. It unveils modifications, which cannot be resolved by hardness measurements. By microcell measurements, local corrosion kinetics can be estimated.     

Resistance A La Corrosion D'ensembles Soudes En Alliages De Titane—Influence De L'etat Structural

An investigation of the potentiodynamic polarization behaviour of some titanium alloys welds has shown that their corrosion resistance is not significantly influenced by variation of micro-structure, even in melted and heat-affected zones. For comparison, some microstructures similar to those observed in welds were also studied. Slight variations concern only the passive behaviour of these alloys which are unaffected in the active state by microstructural changes. Interpretations of peculiar behaviour of Ti–2, 5%Cu alloy are suggested.     

Dilution and microsegregation in dissimilar metal welds between super austenitic stainless steel and nickel base alloys

Abstract

Super austenitic stainless steels are often welded using high Mo, Ni base filler metals to maintain the corrosion resistance of the weld. An important aspect of this processing is the weld metal dilution level, which will control the composition and resultant corrosion resistance of the weld. In addition, the distribution of alloying elements within the weld will also significantly affect the corrosion resistance. Dissimilar metal welds between a super austenitic stainless steel (AL-6XN) and two Ni base alloys (IN625 and IN622) were characterised with respect to their dilution levels and microsegregation patterns. Single pass welds were produced over the entire dilution range using the gas tungsten arc welding process. Microstructural characterisation of the welds was conducted using light optical microscopy, scanning electron microscopy, and quantitative image analysis. Bulk and local chemical compositions were obtained through electron probe microanalysis. The quantitative chemical information was used to determine the partition coefficients k of the elements in each dissimilar weld. The dilution level was found to decrease as the ratio of volumetric filler metal feedrate to net arc power increased. Reasons for this behaviour are discussed in terms of the distribution of power required to melt the filler metal and base metal. In addition, the segregation potential of Mo and Nb was observed to increase (i.e. their k values decreased) as the Fe content of the weld increased. This effect is attributed to the decreased solubility of Mo and Nb in austenite with increasing Fe additions. Since the Fe content of the weld is controlled by dilution, which in turn is controlled by the welding parameters, the welding parameters have an indirect influence on the segregation potential of Mo and Nb. The results of the present work provide practical insight for corrosion control of welds in super austenitic stainless steels.     

Korrosionsuntersuchung an geschweißten Proben aus AlMg3 unter Einwirkung von 2%iger Ammoniaklösung

Corrosion tests on welded specimens of AlMg 3, exposed to a 2% ammonia solution The welds of specimens of AlMg 3, welded with AlSi 5, AlMg 3 and AlMg 3, were found to be highly corrosion-prone. In the weld deposit from AlSi 5, there is a strong corrosion effect in the form of notches in the transition zone. This is also accompanied by an abrupt change in the potential of about 1200mV. In the weld itself, the non-homogeneity of the structure gives rise to strong pitting corrosion. With AlMg 3 as weld material, corrosion is less marked but there are numerous small pits along the transition zone. Here again, the difference in potential between base metal and weld deposit (approx. 200mV) is sufficient to account for the corrosion proneness. The potentials of the specimens welded with AlMg 5 showed virtually the same behaviour in the structure as those welded with AlMg 3.     

Ar-Ar变动送气条件下5A03铝合金TIG焊焊缝组织和性能

5A03铝合金在传统TIG焊接过程中,焊缝易存在强度低、晶粒粗大的问题. 为了改善5A03铝合金焊缝性能,在传统TIG焊接方法的基础上,改变保护气的送给方式,针对板厚为2.5 mm的5A03铝合金板进行对接焊接试验. 焊后分别对焊缝进行拉伸试验、断口形貌分析、偏振光电子显微镜和扫描电镜的观察及电化学分析. 结果表明,与传统焊获得的焊缝相比,1 Hz变动送气TIG焊所获得的焊缝抗拉强度提高了18.5 MPa,提升强度约为传统焊缝强度的10%,两种焊缝的断裂形式均为塑性断裂. 对比焊缝晶粒尺寸发现,1 Hz变动送气条件下获得的焊缝晶粒更加细小,并且β相Al₈Mg₅在铝基体上呈现弥散形态分布;电化学结果分析表明,变动送气TIG焊焊缝自腐蚀电流密度增大,容抗弧半径减小,自腐蚀电位负移0.04 V,传统焊焊缝的耐蚀性较好.     

Potential- und Polarisationsmessungen an Korrosionselementen

Potential and polarization measurements on corrosion elements The polarization behaviour of heterogeneous mixed electrodes is of interest in connection with the assessment of the corrosion state of large objects involving macroelements and localized anodes, and in connection with the evaluation of the corrosion behaviour of weld seams. Measurements on a tube section have shown, that the influence of polarization and stray currents on local tube potentials and potential gradients in the electrolyte is increased by increased anodic polarization levels, provided, however, the current density: potential curves of the two partners diverge. Local anodes on welded connection can be found by measuring the surface potential; anodic polarization makes this method, too, more sensitive.     

相控阵探头扫查器检测管节点焊缝的位姿

海洋平台多为钢质材料焊接而成,其焊缝主要为管节点焊缝.这种焊缝与以往管道的环形、直线和螺旋线焊缝相比,具有形状复杂,不易实现焊缝自动检测的难点问题.根据管节点焊缝的特点,设计制造出了具有三自由度的超声相控阵探头扫查器,建立了该扫查器与管节点焊缝之间的位姿关系,给出了相控阵探头与管节点焊缝及扫查器基体之间的位姿矩阵计算方法,为扫查器的运动控制提供了理论基础.该扫查器可实现对管节点复杂焊缝的自动检测.用该扫查器对对比试块进行了检测试验,结果表明,能够准确检测出对比试块的缺陷,可满足对管节点焊缝质量进行自动检测的要求.     

Electrochemical corrosion behavior and microstructural characteristics of electron beam welded UNS S32205 duplex stainless steel

Different electrochemical techniques were used to study the corrosion behavior of UNS S32205 duplex stainless steel (DSS) welded autogenously using a single-pass by electron beam welding process, supplemented by microstructural characterization. Furthermore, a comparative study was also performed between multipass gas tungsten arc (GTA)-welded and EB-welded DSS for their microstructure and corrosion behavior. The differences in weld thermal cycle and chemical composition influenced the fusion zone microstructure of both the welds and eventually their corrosion properties. The general corrosion resistance of the EB weld was lower than the base metal and higher than the GTA weld despite its weld zone being characterized by a relatively unbalanced phase ratio (α/γ) in comparison to the GTA weld. However, the EB weld showed relatively higher susceptibility to pitting corrosion than the base metal and GTA weld due to its poor repassivation characteristics and poor resistance to pit growth.     

异质污染对316L不锈钢焊缝组织及耐蚀性影响的显色研究

目的 针对核电站管道焊缝中不明原因显色现象,设计了一种模拟工程现场引入异质污染的情形,研究异质污染对管道焊缝的影响.方法运用邻菲罗啉显色检测法,分别评价了以ER316L焊丝、掺杂了铁丝与铁粉的焊丝以及纯铁丝作为焊丝的316L不锈钢焊缝异质铁污染,结合能谱和动电位极化测试,分析了异质铁污染对焊缝组织和耐蚀性的影响.结果焊...     

Intergranular precipitation and corrosion in weld of low Cr ferritic stainless steel

In the present research, intergranular precipitation and corrosion in the weld of low Cr ferritic stainless steel was investigated. Free-exposure and double loop electrochemical potentiokinetic reactivation corrosion test results revealed that IGC occurred in both the weld metal and heat-affected zone of the welds aged for more than 1 h at 500 °C. Intergranular Cr segregation was observed around the TiC precipitation of the weld in which IGC developed during the corrosion tests. This observation is subsequently discussed in the experimental results.     

Untersuchung der lokalen Korrosionserscheinungen an den Schweißnähten in Apparaturen aus nichtrostendem Stahl

Investigation into local corrosion phenomena at the welds in chemical apparatus of stainless steel Corrosion phenomena at the welds of apparatus consisting of stainless steel can only be investigated in an active medium. The active medium used for this purpose was a 5 pC hydrochloric acid where virtually all the incidental electro–chemical phenomena disappear, and where the corrosion rate is exclusively determined by the transit potential at the boundary between plate and weld. The paper describes the preparation of the specimens, the design of the measuring cell, and the testing procedure adopted. In this way, a “hydrochloric acid test” was developed which permits a rapid distinction between “good” and “poor” welds of specimens. The reliability of the hydrochloric acid test is corroborated by recording the current density/potential characteristics in 5 pC hydrochloric acid. The technique of recording these characteristics with the aid of the potentio-kinetic method is described, and illustrated by photographs and diagrams.     

Elektrochemische Methode zur Prüfung des Korrosionsverhaltens austenitischer CrNiMo-Stähle im Schweißnahtbereich

Electrochemical method for testing of the corrosion behaviour of austenitic CrNiMo-stainless steel weldments Austenitic CrNiMo stainless steel welds can be more susceptible to pitting and crevice corrosion than the base material owing to segregation and precipitation in the heat affected zone, in the high temperature zone and in the welded zone. Suitable test methods are needed to optimize welding technology. Comparison of potential curves (DIN 50919), comparison of critical pitting corrosion temperatures in FeCl₃- or other model solutions, visual estimation after longterm corrosion tests with or without electrochemical load are discussed. A small measurement cell heated from the rear with circulating and temperature controlled electrolyte is shown. With its help separate areas of a weld can be electrochemically investigated. Welds of the materials X 2 CrNiMoN 17 12 2 (1.4406), X 2 CrNiMoN 17 13 5 (1.4439) and X 1 NiCrMoCu 31 27 4 (1.4563) are tested in acidic NaCl solutions in the range of 25 to 75°C. Critical pitting corrosion potentials are obtained for base materials, heat affected zone and weld material. An influence of the welding energy is probable, but cannot be proved in this case without statistical certainty.     

Allgemeine Beständigkeit von Schweißnähten unter Berücksichtigung der Spannungs- und Schwingungsrißkorrosion

General resistance of weld seams with a view to stress corrosion cracking and corrosion fatigue The corrosion of welds is due to thermal effects during welding which give rise to structural changes and, frequently, compositional changes in the transition zone. The welded material is rapidly cooled and may thus be heterogeneous and may present residual stresses resulting in increased susceptibility to selective and stress corrosion. The manganese content is of high importance in low alloy steels, as well as residual martensite or austenite embedded in a ferrite matrix. Low ferrite contents are generally beneficial because they counteract high temperature cracking; however, ferrite contents should be hept below 10% in order to prevent the formation of a continuous network giving rise to selective corrosion. Corrosion susceptibility may also be produced by carbide or carbonitride precipitation in austenitic and ferritic steels and nickel base alloys. Weld zones in aluminium alloys are attacked in rare cases (e.g. by HNO₃) and the susceptibility of Ta, Zr and Ti depends from the properties of the protective atmospheres.     

Untersuchungen über die Lochfraßkorrosion des passiven Eisens in chlorionenhaltiger Schwefelsäure

Investigation into pitting corrosion of passive iron in sulphuric acid containing chloride ions Pitting corrosion of metallic materials is generally connected with presence of a surface layer giving rise to a local differentiation of the electrochemical behaviour of the metal surface. The pitting corrosion by halogen ions on passive metals is investigated using passive iron in chloride ion-containing sulphuric acid as the model system. Quantitative data are presented concerning the mechanism and kinetics of the individual processes giving rise to pitting corrosion in a chloride ion concentration range covering three powers of ten, and in the whole potential range of iron passivity, from the Flade potential to the transpassive breakthrough potential. Pit formation normally follows a linear kinetic law, the rate depending in particular from the chloride ion concentration and from the thickness of the passive layer. The growth of pit diameters follows a linear kinetic law, too; the dissolution current density in the pits depends from the chloride ion concentration. Comparative investigations carried out on active iron, and potential distribution as measured in the pits show that the metal is active in the pits, too. The heterogeneous mixed electrode condition — active pit/passive metal surface — is stabilised by resistance polarisation. The investigations so far do not permit any statement concerning the specific effect of the chloride ions.     

Stromdichte-Spannung-Messungen an nichtrostenden Stählen in aktivierenden Medien

Current density-potential measurements on stainless steels in active media In order to elucidate the susceptibility to selective corrosion of weld seams in stainless steels potentio-kinetic current density-potential measurements have been made. When the polarisation curve for the weld seam is more anodic in the vicinity of the rest potential than the curve corresponding to the base material the weld seam is selectively attacked; when, however, the weld seam is moer cathodic than the base metal there is almost no corrosion in the adjacent areas because of the large area ratio (large anode, small cathode). It is only in extreme cases (very high potential difference between cathodic weld seam and anodic plate) that local corrosion is found in the base metal. Tests with Hastelloy B in 20% hydrochloric acid show that this material cannot be welded successfully with identical material; it might, however, be feasible to weld it with cathodically alloyed weld fillers (alloyed with Pt or Pd).     

Microstructure and mechanical properties of dissimilar welds between 16Mn and 304L in underwater wet welding

Dissimilar joint between 304L austenitic stainless steel and low-alloy steel 16Mn was underwater wet welded using self-shielded nickel-based tubular wire. Microstructure, mechanical properties and corrosion behaviour of dissimilar welded joints were discussed. Ni-based weld metal was fully austenitic with well-developed columnar sub-grains. Type II boundary existed between Ni-based weld metal and ferritic base metal in underwater welds similar to that in air welds. Major alloying elements distributed non-uniformly across the austenitic weld metal/16Mn interface. Maximum hardness values in wet welding appeared in a coarse-grained heat-affected zone at the 16Mn side, which possessed very low impact toughness. Underwater Ni-based welded joints fractured at Ni-based weld metal under tensile test. Ni-based weld metal had favourable corrosion resistance similar to 304L base metal.     

Effect of Austenitic and Austeno-Ferritic Electrodes on 2205 Duplex and 316L Austenitic Stainless Steel Dissimilar Welds

This study addresses the effect of different types of austenitic and austeno-ferritic electrodes (E309L, E309LMo and E2209) on the relationship between weldability, microstructure, mechanical properties and corrosion resistance of shielded metal arc welded duplex/austenitic (2205/316L) stainless steel dissimilar joints using the combined techniques of optical, scanning electron microscope, energy-dispersive spectrometer and electrochemical. The results indicated that the change in electrode composition led to microstructural variations in the welds with the development of different complex phases such as vermicular ferrite, lathy ferrite, widmanstatten and intragranular austenite. Mechanical properties of welded joints were diverged based on compositions and solidification modes; it was observed that ferritic mode solidified weld dominated property wise. However, the pitting corrosion resistance of all welds showed different behavior in chloride solution; moreover, weld with E2209 was superior, whereas E309L exhibited lower resistance. Higher degree of sensitization was observed in E2209 weld, while lesser in E309L weld. Optimum ferrite content was achieved in all welds.     

Evaluation of techniques for measuring corrosion activity of carbon steel welds

Abstract

Three test methods, namely immersion tests, galvanostatic anodic dissolution tests and the scanning vibrating probe technique, have been evaluated as candidate methods for ascertaining the susceptibility of welds in carbon steels to preferential corrosion. The use of hardness measurements by profiling and mapping was also evaluated. Three welds were tested for which the production had been controlled to produce different types of corrosion behaviour. In addition, a weld that had failed 'in service' was used to validate the findings of this assessment. In the immersion tests, lasting 9 months, the three controlled weld specimens ex posed to ASTM D1141 sea water behaved as expected, in terms of which region of the weld was most susceptible to corrosion. The results of the rapid galvanostatic anodic dissolution tests compared well with those of the immersion tests, with the same regions of the controlled welds showing susceptibility to corrosion. The galvanostatic anodic dissolution test on the failed weld produced corrosion in the regions that had been susceptible to corrosion in service. However, at very high current densities the differential corrosion loss between different regions of the weld was not maintained and careful control of this parameter is therefore necessary in testing. The scanning vibrating probe technique successfully identified the areas susceptible to preferential corrosion in both the controlled weld specimens and the in service failure. The electrolyte used was ASTM D1141 sea water diluted 10 : 1 with distilled water. However, these trends were not apparent when tests were conducted in distilled water owing to the lower solution conductivity. Hardness mapping produced a two-dimensional visual representation of the specimen hardness. This was very effective in locating small regions of high hardness, in contrast to conventional hardness profiling, and would be effective in locating hot spots for hydrogen embrittlement. However, no correlation between hardness and corrosion susceptibility was observed in the three weld specimens that were examined. The galvanic anodic dissolution test is recommended as a rapid and reliable test to determine the relative corrosion susceptibility of carbon steel welds. The scanning vibrating probe technique can also be effective but at considerably greater expense.     

Electrochemical Behaviour of Nickel-Containing Alloys in Phosphoric Acid Solutions

Abstract

The electrochemical behaviour of a number of nickel-containing alloys has been studied in solutions of pure phosphoric acid, and the effect of varying the acid concentration and the alloy composition determined.

The potential/current density curves show active, passive and transpassive regions, but the corrosion appears to take place mainly under conditions of active dissolution. The active regions of the curves are complex and show as many as four distinct current maxima. The appearance of these maxima is related to the corrosion behaviour of the alloys, and to the effect that compositional changes have upon this behaviour, which is in turn attributed to the formation of various orthophosphate and pyrophosphate complexes.