Hydrogen interaction and stress-corrosion in hydrocarbon storage vessel and pipeline weldings

Abstract:

This paper addresses important technical problems of H-embrittlement/safety and stress corrosion cracking (SCC) phenomena which can be of concern in various industrial sectors of vessels and pipeline production, including H storage.

Intercrystalline and intergranular cracks have been detected in narrow welded zones having particular hardness, gradually rising from little dimensions till crossing all the plate thickness. Such cracks are due to the residual stresses (RS) produced by the construction technique and to the presence of aggressive elements. H+ diffusion from sulphured hydrogen molecule toward the ferritic material of the internal surface can produce fissures similar to hydrogen-induced cracking (HIC), especially in the presence of RS. Microanalyses have revealed a sulphur deposit formation in the cracks fracture surfaces, as a presence of H2S dragged by LPG fluids. The LPG release due to such cracks in interred vessels near domestic buildings can be dangerous, and an analysis project of its process is under development.

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Influence of Diffusion Welding Time on Homogenous Steel Joints

Abstract:

The paper deals with assessment of influence of welding time on welding joint creation. Diffusion welding method in inert gas (Ar 4.8) at low pressure was used. Homogenous welding joints were created from steel E296 (according to EN ISO 10025-2). Homogeneous welds were done for easy assessment of influence of diffusion welding time and temperature on resulting welding interface, which was closely observed. Due to diffusion of carbon and manganese, on the joint interface were created complex iron and manganese carbides (FeMn)3C. It was found that the amount of created carbides depended on temperature and time. At temperature 1000 °C the biggest quantities of carbides were created, already at time 900 s the continuous carbidic strip was created with thickness 1-2 ..m. This strip is very brittle and is detrimental to joint properties.

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Microstructural characterization of dissimilar welds between alloy 800 and HP heat-resistant steel

Abstract:

In this study, dissimilar welds between HP heat-resistant steel and Incoloy 800 were made with four different filler materials including: 309 stainless steel and nickel-based Inconel 82, 182 and 617. The microstructure of the base metals, weld metals and their interfaces were characterized by utilizing optical and scanning electron microscopy. Grain boundaries migration in the weld metals was studied. It was found that the migration of grain boundaries in the Inconel 82 weld metal was very extensive. Precipitates of TiC and M23C6 (M=Cr and Mo) in the Inconel 617 weld metal are identified. The necessary conditions for the formation of cracks close to the fusion line of the 309-HP joints are described. Furthermore unmixed zone near the fusion line between HP steel base metal and Inconel 82 weld metal is discussed. An epitaxial growth is characterized at the fusion line of the 309-Alloy 800 and Inconel 617-Alloy 800 joints.

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Investigations on Dissimilar Weldments of Inconel 625 and AISI 304

Abstract:

This paper investigates the weldability, metallurgical and mechanical properties of the dissimilar joints of Inconel 625 and AISI 304. Dissimilar joints were obtained by gas tungsten arc welding process employing ERNiCrMo-3. Tensile fracture occurred at the parent metal of AISI 304 in all the trials. The structure-property relationships on these dissimilar weldments were evaluated using the combined techniques of optical microscopy and SEM /EDAX techniques.

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Welding: Solidification and Microstructure

Parameters that control the solidification of castings also control the solidification and microstructure of welds. However, various physical processes that occur due to the interaction of the heat source with the metal during welding add a new dimension to the understanding of the weld pool solidification. Conventional theories of solidification over a broad range of conditions can be extended to understand weld pool solidification. In certain cases, because of rapid cooling rate effects, it is not unusual to observe nonequilibrium microstructures. Recent developments in the application of computational thermodynamics and kinetic models, studies on singlecrystal welds, and advanced in-situ characterization techniques have led to a better understanding of weld solidification and microstructures.

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The Processes Of Fragmentation, Intermixing And Fusion Upon Explosion Welding

Abstract:

On the basic of the results obtained for joints of dissimilar metals such as copper-tantalum, iron-silver, it has been cleared out the reason of immiscible suspensions mixing upon explosion welding. It has been found that the interface (waveless or wavy) is not smooth and contains inhomogeneities, namely, cups and local melting zones. The role of granulating fragmentation providing partitioning of initial materials as a main channel of input energy dissipation has been revealed. It has been shown that in joints of metals possessing normal solubility  the local melting zones are true solutions, but if metals possess no mutual solubility the local melting zones are colloidal solutions. During solidification emulsions is a danger to the joint continuity because of possible delamination, and suspension, by contrast, can contribute to the dispersions hardening of joint.

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Design of Creep-Resistant Steel Welds

Abstract:

Creep resistant welding alloys must be reliable over long periods of time in severe environments. Their microstructures have to be very stable, both in the wrought and in the welded states. This paper deals with quantitative methods for the design of steel weld metals for elevated temperature applications. A methodology is described for the calculation of complex precipitation reactions over periods extending many tens of years. However, microstructure alone is clearly not enough in the design of alloys. The complex mechanical properties, such as the creep rupture strength, can be estimated quantitatively using the neural network technique which interprets the vast quantities of experimental data that are now available.

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دانلود 10 مقاله با موضوع جوشکاری قوس پلاسما (Plasma Arc Welding)

جوشکاری پلاسما یکی از فرآیندهای جوشکاری قوس الکتریکی است که درجه حرارت آن به بیش از 20000 درجه سانتیگراد می رسد. در این روش قوس الکتریکی میان الکترود تنگستنی داخل نازل جوشکاری و قطعه کار ایجاد می شود و حفاظت از حوضچه جوش عمدتا به عهده یک گاز داغ یونیزه شده که از نازل متمرکز کننده بیرون می آید، انجام می شود. اما منبع گاز محافظ دیگری نیز برای حافظت جوش در برابر هوا به کار می رود که می تواند گاز محافظ خنثی یا گاز Mix باشد. در این بخش 10 مقاله به زبان انگلیسی با موضوع جوشکاری قوس پلاسما  (Plasma Arc Welding) در یک فایل فشرده قرار داده شده است که همگی از سایت بسیار معتبر Science Direct می باشند. لیست مقالات موجود در این فایل را در ذیل مشاهده می کنید:

I- Effect of the micro-plasma arc welding technique on the microstructure and pitting corrosion of AISI 316L stainless steels in heavy LiBr brines

II- Effect of the plasma arc welding procedure on mechanical properties of DP700 steel

III- Energy propagation in plasma arc welding with keyhole tracking

IV- Experimental observation of both keyhole and its surrounding thermal field in plasma arc welding

V- Numerical analysis of keyhole geometry and temperature profiles in plasma arc welding

VI- Plasma arc welding of ZrB2–20 vol% ZrC ceramics

VII- Plasma arc welding: Process, sensing, control and modeling

VIII- Single vision system for simultaneous observation of keyholeand weld pool in plasma arc welding

IX- Weldability of a 2205 duplex stainless steel using plasma arc welding

X- Welding of Ti-6Al-4V alloy using dynamically controlled plasma arc welding process

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Dissimilar Electron Beam Welding of Nickel base Alloy 625 and 9% Cr Steel

Abstract:

To improve the thermal efficiency of fossil running power plants increasing the live steam temperature is essential. In power plant construction, 9-12% chromium martensitic steels are widely used but if steam temperatures rise above 625°C there is no way around nickel base alloys.

The scope of this study was to ascertain the weldability of cast nickel base alloy 625 with cast martensitic 9% chromium steel COST CB2, using electron beam welding (EBW). Similar (A625/A625) and dissimilar joint welding experiments on 50mm thick plates were executed. Microstructure of welded joints was investigated and mechanical-technological tests were carried out. Results show that work pieces were completely welded and the microstructure of the seam shows no problems except some δ ferrite grains near the fusion line on the CB2 side. The joints exhibit good mechanical properties in spite of the presence of a thin layer with very high hardness in the heat affected zone (HAZ) on the CB2 steel side.

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Microstructural Analysis Of Heat-Resistant Welded Pipes

Abstract:

Microstructural analysis of welded joints in pipes of a heat-resistant alloy was carried out. The samples that were studied were cut from pipes that were kept at 800 jC for 10 months in a gas heater used to heat up the gas used for the direct reduction of iron ore. This work is concentrated on the analysis of a series of cracks detected in the base metal and the heat-affected zone (HAZ) of welded joints. It was found that such cracking was of intergranular nature and that the cracks propagated through the primary carbides. Two different types of carbides, which differed in silicon content, were detected. It was also observed that cracks propagated in a preferential way through the rich carbides. This analysis allows for the conclusion that the presence of silicon in the carbides increases the cracking susceptibility of the alloy.

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