Weld Corrosion Research Articles

Effect of shielding gas composition on intergranular corrosion of stabilized ferritic stainless steel GMA welds

The effect of shielding gas composition on intergranular corrosion of the fusion zone formed by bi-stabilized ferritic stainless steel plates (AISI 441) and ER430Ti and ER430LNb filler metals during gas metal arc welding was investigated. Double loop electrochemical potentiokinetic reactivation tests were conducted to examine the influence of the shielding gas content (Ar + 2%O2, Ar + 8%CO2 and Ar + 25%CO2) on intergranular corrosion of the ferritic stainless steel welds. It was possible to observe an increase in the tendency toward sensitization with the increase in the CO2 content in the shielding gas, especially with the ER430Ti filler metal. Analysis of the formed precipitates by means of optical microscope, scanning electron microscope an energy-dispersive X-ray spectroscopy allowed to notice that high levels of CO2 blended in the shielding gas increase the intergranular precipitates and lead to significant intergranular corrosion, which was induced by the Cr-depletion zone formation, especially for the welds produced with the ER430Ti filler metal.

Study on Welding Techniques of 316L Lined Bimetallic Pipe

It is well known that welding technique was often a knotty problem for bimetallic lined steel pipes to use widely. A number of failures in secession of weld cracking and weld corrosion had been observed in oil fields in recent years, which seriously disrupted the order of oil and gas production. To solve welding problems of 316L bimetallic lined pipes, works outcome about failure analysis and welding process research were presented in this paper. Failure analysis results confirmed that Welding defects, high hardness regions was the main reasons about failure problems of weld crack while structure design defects of seal weld and bad back-protection effects of flux-cored wire resulted in weld corrosion. Welding defects in the regions of seal weld became the failure source while the high hardness both in the region of seal weld and weld joint formed the crack propagation channel, and therefore both initially contributed to weld cracking. Additionally owing to the structure design of seal weld, liner layer would be heated over and over again during the period of seal weld and then it was not enough to protect CRA layers from being damaged during the period of girth weld. As a result the corrosion resistance in the welding area was reduced to become a weak area. On the basis of failure analysis, further research work was carried out to improve welding performance. Seal weld structure and girth weld process was improved. The difference of welding wires and welding process was analyzed, and their defects were described separately. Results showed that the welding performance welding by ERNiCrMo-3 and supporting technology was more reliable than ATS-F309L and supporting technology, whether seal weld or butt welding. The distribution and value of the hardness could be effectively controlled; Moreover, corrosion resistance performance was also better. Therefore, the seal weld and girth weld conducted by ERNiCrMo-3 and supporting technology was feasible.

Influence of Tool Traverse Speed on Structure, Mechanical Properties, Fracture Behavior, and Weld Corrosion of Friction Stir Welded Joints of Aluminum and Stainless Steel

Herein, the effect of traverse speed on friction stir welding (FSW) of aluminum (Al) and stainless steel (SS 304) plates is studied. The microstructure of the joint sample is examined using optical microscope and scanning electron microscope equipped with energy dispersive spectroscopy. The intermetallic compound detected at the interface of friction stir welded (FSWed) joint is Al3Fe. X‐ray diffraction results reveal the formation of intermetallic compound like Al3Fe, Al5Fe2, AlFe, and Al13Fe4. Tensile results show that with the increase in tool traverse speed, the tensile strength increases to reach a maximum value and then decreases. The maximum tensile strength achieved is ≈75% of Al base metal at tool traverse speed of 75 mm min−1. Maximum hardness is observed at the Al|SS‐304 interfaces due to the presence of intermetallics. Interfacial hardness for slower tool traverse speed is higher when compared to higher traverse speed. The electrochemical behavior of the FSWed joint is measured using potentiodynamic polarization test so as to understand the corrosion failures of the FSWed joints. FSWed samples at higher traverse speed shows inferior corrosion resistance when compared to the slower traverse speed.

Microstructures and properties of single-pass laser-arc hybrid welded stainless clad steel plate

The effects of wire Cr content on the microstructures and properties of single-pass laser-arc hybrid welded stainless clad steel plate (SCSP) were studied. Increasing Cr content strengthened the weld corrosion resistance, but it increased the average grain size of fusion zone (FZ), deteriorated the weld microstructure uniformity, and weakened the weld mechanical property. The variations of the weld properties were closely related to the microstructure changes. The solidification mode and microstructure transformation mechanism of the SCSP hybrid weld were clarified based on the quantitative calculation of the Cr and Ni equivalent contents (Creq and Nieq) after the mixing of the wire and base metal. The calculated ratio of the Creq and Nieq (θ) could effectively predict the solidification mode and microstructure of the SCSP weld, and then indicate its properties. The skeletal and acicular ferrites formed in the FZ when the θ was larger than 1.35, which benefited to strengthen the SCSP weld.

Corrosion of welds in biomass power plants

In addition to understanding the corrosion of base materials in superheater tubes in biomass power plants, it is also important to understand how welded joints are subjected to corrosion or degradation. In the course of corrosion testing in the boiler, two different filler materials were used to weld together 18%Cr 12%Ni austenitic tubes. The two filler materials compared were a high alloyed Ni‐based filler material (wt% approx. 20% Cr, 12% Fe, 3.6% Nb, Ti, balance Ni) and the CN 18/11 IG filler material (18%Cr, 10%Ni, balance Fe). Austenitic steel test tubes were exposed in two different plants where the different filler materials were utilized and the attack of the welds and tubes adjacent the welds are described. Preferential attack of the tube material immediately adjacent the weld only occurred for the Ni rich weld and the indications are that this is galvanic corrosion. This type of attack decreased with decrease in steam temperature.

The effect of welding atmosphere on the pitting corrosion of AISI 304L resistance spot welds

Austenitic stainless steel has excellent properties with respect to general corrosion resistance, while it is sensitive to localized corrosive attacks, such as pitting and crevice corrosion in humid and chloride-containing atmospheres. This pitting corrosion susceptibility increases when it is exposed to conditions like resistance spot welding (RSW) process. The current research deals with the effect of RSW shielding gas atmosphere on the pitting corrosion behavior of AISI 304L austenitic stainless steel weld joints. Optical and SEM investigations show several types of pit sizes and morphologies depending on heat input and shielding gas. Cyclic potentiodynamic polarization (CPP) of welded nuggets shows that argon gas is more effective in the improvement of pitting corrosion resistance at low heat input, while nitrogen demonstrates better corrosion resistance at high heat input.

Analyzing the Failure of Welded Steel Components in Construction Systems

Failure of welded construction steel components can occur due to inappropriate design, wrong steel choice or quality, substandard welding processes and through defective maintenance. Welded constructional steel joints in particular are highly sensitive to issues of fatigue, weld corrosion and/or weld quality. A key concern is on placing welds in regions of nominal stress. Welded joints are produced to a specification, which is used to minimize the heat-affected zone and any residual stress within the weld. In this article, numerous examples of weld fracture are shown together with the causes and of weld failure.

Corrosion Mechanisms in Dissimilar AZ31/AZ80 Friction Stir Welds

Corrosion of dissimilar friction stir welds (FSW) made in AZ31/AZ80 magnesium alloys was investigated using the scanning reference electrode technique (SRET), and microcapillary polarization technique, complemented by optical and SEM/EDX microscopy. The corrosion rate of the base metals along with the welded specimen was estimated by mass loss testing. The stir zone material in both alloys showed a higher corrosion potential than the base metal due to the partial dissolution of β-Mg17Al12 and Al-Mn particles. The basic corrosion mechanism in dissimilar welds was determined to be different from that of a similar joint. The corrosion behavior of the dissimilar FSW joint was governed by the galvanic coupling of the two alloys, and not by the microstructural evolution occurring during the welding process. The corrosion behavior of the joint was governed by the galvanic coupling between the α-Mg matrix in AZ31 and the Al-rich intermetallics in AZ80. The welded specimens exhibited the highest corrosion rate, while AZ80 was the most corrosion resistant material.

Atmospheric Corrosion of Welded Mild Steel

Mild steel is commonly used for structural purposes in Mauritius. Arc welding is one of the main joining methods used, with Manual Metal Arc (MMA), Metal Inert Gas (MIG) and Tungsten Inert Gas (TIG) welding techniques being the preferred ones. This paper compares the corrosion resistance of mild steel, joined using these welding techniques. Mild steel samples, welded using MMA, MIG and TIG welding techniques, were exposed outdoors for a very short duration of 9 days, according to ASTM G50, and subjected to alternative immersion tests, according to ASTM G44, for 130 cycles. For the atmospheric exposure tests, digital image processing techniques were used to determine the amount of corrosion in the samples. For the alternate immersion tests, the weight loss method was used. The results of the three welding techniques were then compared. The microstructure of the weld area was also analysed to this end. For the atmospheric exposures, it was observed that the MIG welded specimens suffered from preferential weld corrosion, whereas for the TIG welded specimens, the welded area corroded the least. For the alternative immersion tests, it was again observed that the MIG welded samples were less corrosion-resistant compared to the other samples. Also, the TIG welded specimens were found to be the most corrosion resistant.

Dendritic Boundary Corrosion of AA2198 Weld Using Fiber Laser Welding with Al–Cu Filler Wire

The microstructures and corrosion behaviors of AA2198–T851 alloy and weld were analyzed under corrosive conditions. Weld was formed using an innovative fiber laser welding process with AA2319 Al–Cu filler wire. The metallurgic morphology and distribution of the chemical compositions were determined using imaging techniques such as optical micrograph, scanning electron micrograph, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. Corrosion was evaluated using an immersion test and electrochemical impedance spectroscopy in 3.5% NaCl solution at room temperature. Results indicate that the parent alloy suffered from pitting corrosion during the initial 4-h immersion which was caused by the inhomogeneous distribution of its chemical components and the different intermetallics formed during the rolling process. The weld experienced dendritic boundary corrosion under the same conditions due to the addition of the Al–Cu filler and rapid solidification during laser welding, which led to the precipitates Cu enrichment along the grain boundary. When a welding joint was immersed in the solution for 5 days, a big crack was observed across the center of the weld. In comparison, there was good corrosion resistance in the heat-affected zone with a compact protective film.

Low heat input welding of nickel superalloy GTD-111 with Inconel 625 filler metal

Abstract GTD-111 precipitation-strengthened nickel-based superalloy is widely used in blades of gas turbine engines which operate at high temperature and in a hot localized corrosion atmosphere. After long-term exposure to high temperature, γ' precipitate is known to exhibit catastrophic changes in size and distribution which cause deterioration of its properties and failure of the component. In this study, a damaged blade removed froma land-based gas turbine generator was subjected to nonpre-heat-treated GTAW and laser welding repair with various welding powers in the range of 135 to 295 J × mm−1, followed by post-weld heat treatment (PWHT) at 1473 K for 7200 s and strain aging at 1118 K for 86 400 s. Results show no significant relationship between welding powers, size and area fraction of the γ' precipitate in the fcc γ matrix in both GTAW and laser-welded specimens. The final γ' precipitate size and distribution depend mainly on PWHT parameters as γ' precipitates in all GTAW and laser welded specimens showed similar size and area fraction independently of the heat input from welding. Unmixed zones are observed in all laser welding specimens which may cause preferential weld corrosion during service. Microcrack occurrence due to welding and PWHT processes is also discussed.

Effects of alloying element on weld characterization of laser-arc hybrid welding of pure copper

Effects of alloying elements of Si and Sn on weld characterizations of laser-arc hybrid welded pure copper (Cu) with thickness of 2 mm was studied in detail by using different wires. The weld microstructure was analyzed, and the mechanical properties (micro-hardness and tensile property), conductivity and corrosion resistance were tested. The results showed that the alloying elements benefit the growth of column grains within weld fusion zone (FZ), increase the ultimate tensile strength (UTS) of the FZ and weld corrosion resistance, and decrease weld conductivity. The mechanisms were discussed according to the results.

An overview of the Canadian corrosion program for the long-term management of nuclear waste

ABSTRACTThe Nuclear Waste Management Organization (NWMO) has developed a comprehensive Proof Test Plan to evaluate the feasibility and safety of its deep geological repository solution for nuclear waste. This work plan includes many active research programs to build confidence in the Canadian used nuclear fuel container design, a copper-coated steel vessel that is optimised for the CANDU waste form. Ongoing research within the Proof Test Plan includes several programs to evaluate the possible extent of damage that may be caused by various corrosion mechanisms: the anoxic corrosion of copper in pure water, concentrated chloride solutions, and in the presence of sulphide; a comparison of the corrosion behaviour of copper coatings on steel with wrought copper; the localised corrosion and surface roughening of copper; the γ-radiolysis-induced corrosion of copper; the galvanic corrosion of through-coating defects; and the localised corrosion of the internal steel weld region.This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

Effects of laser-arc distance on corrosion behavior of single-pass hybrid welded stainless clad steel plate

Single pass laser-arc hybrid welding of stainless clad steel plate was first carried out to develop alternatives to multi-pass welding with low efficient or single pass welding with poor corrosion resistance. The results demonstrated that the weld corrosion resistance increased with the increase of laser-arc distance (DLA), and the corrosion morphologies changed from big and deep ‘nail’ pits to small and shallow hemispherical pits. The weld with nearly equal corrosion resistance to the base metal (BM) could be obtained at the DLA of 9mm, where the charge transfer resistance increased to 89% of the BM and the corrosion current density decreased by ten times to close to the BM, only 0.13μA·cm−2 lower. The corrosion resistance improvement had a good agreement with the microstructure homogenization and the increase of Cr content. The microstructure formation was discussed by the molten pool behavior and the laser-arc interaction. The corrosion resistance improvement was explained by the formation and damage mechanism of the passive film.

Effect of metallurgical factors on the pitting corrosion behavior of super austenitic stainless steel weld in an acidic chloride environment

Abstract

Galvanic corrosion of the seam weld in Zn–Al coated steel pipes manufactured by electric resistance welding

Severe corrosion attack at the seam weld was observed in Zn–Al coated steel pipes of a closed heating system. This system was operating with tap water at about 70 °C and in the presence of an unknown amount of oxygen due to water reintegration. The corroded pipes showed a preferential corrosion of the seam weld along the longitudinal direction of the pipe. In order to investigate the cause of this attack, the electrochemical behavior of the seam weld was studied by means of an electrochemical micro‐cell. This technique was used for the characterization of non‐corroded and corroded pipe samples. The study proves that the damage mechanism is due to Zn–Al coating depletion at the seam weld and the potential coupling reversal between the coating and the steel substrate under service conditions. This caused strong galvanic corrosion between the steel exposed along the seam weld and the Zn–Al coating leading to the failure of the pipes.

Metallurgical and Electrochemical Characterization of the Corrosion of AZ31B-H24 Tungsten Inert Gas Weld: Isolated Weld Zones

The corrosion behavior of a magnesium (Mg) alloy, AZ31B-H24, joined by tungsten inert gas welding was investigated. The corrosion rates and morphology were characterized for each weld zone in isola...

Recommend design of filler metal to minimize carbon steel weld metal preferential corrosion in CO2-saturated oilfield produced water

The paper proposes a recommend design for the alloying elements in the filler metal to minimize preferential weld corrosion of carbon steel. The tensile and corrosion resistance properties of the weld metal are considerably improved by using a filler metal containing alloying elements according to the recommended design. Analysis of the morphology and composition of corrosion products on weld metals showed that the common weld metal suffered severe localized corrosion, whereas the weld metal with the alloying elements exhibited uniform corrosion. Based on these results, a tentative mechanism of CO2 corrosion resistance for both weld metals has been proposed.

Structural integrity of corroded girth welds in vintage steel pipelines

Girth welds of old steel pipelines and their surrounding heat affected zones are susceptible to corrosion attack. The resulting reduction in wall thickness may reduce the axial load or internal pressure bearing capacity to an unsafe level. Since standards provide limited guidance on weld corrosion assessment, the authors have executed an extensive experimental program to evaluate the axial load bearing capacity of corroded girth welds. To this end, curved wide plate tests have been executed and were analyzed by means of 3D digital image correlation. This paper discusses key influence factors related to weld geometry and material (strength and toughness). Then, the results are used to develop an assessment approach, based on Annex G of BS 7910:2013 and modified to account for the elastic–plastic stress–strain concentration resulting from weld misalignment.

FCAW repair welding cycles, HAZ microstructure and corrosion resistance of 2304 duplex stainless steel

Flux-cored arc welding (FCAW) is an automatic welding process widely employed to join duplex stainless steel (DSS) structures in industrial plants because of its high productivity. However, when multiple passes are performed, this process can lead to the formation of non-metallic inclusions originating from the slag in the fusion zone. In this case, the welded joint can be repaired using the same welding process. Some regions next to the heat-affected zone are not removed during the repairing operation. Thus, these regions are subjected to repeated welding cycles and to a high heat input, which can cause microstructural alteration that impairs the corrosion resistance of the welded material. The aim of this work was to study the corrosion resistance of 2304 DSS plates joined using the FCAW process and repaired using the same process. The influence of the repair procedure on the corrosion resistance of the welded joints was evaluated using potentiodynamic polarisation and chronoamperometric curves, which allow the determination of the critical pitting temperature of the samples. The microstructure obtained after each repair cycle was evaluated using optical microscopy and scanning electron microscopy. The results showed that the corrosion resistance was depressed as the number of repair cycles increased.