Dissimilar welds

When ferritic-martensitic steels are used for structural components, usually dissimilar welded joints with austenitic stainless steels are used, too. When these are subject to elevated temperatures, creep property evaluation and creep-fatigue evaluation are needed. In the case of dissimilar welds, close attention should be paid to the location of failure. Under certain conditions, failure could occur at the interface between the two materials [27]. 

S. Takaya, Evaluation of fatigue strength of similar and dissimilar welded joints of modified 9Cr—IMo steel, J. Pressure Vessel Technol. 138 (1) (2015), 011402-011402-9. 

Lastly, dissimilar weld filler metals can be successfully used. To avoid premature failure the dissimilar combination shonld be corrosion tested to ensure suitability for the intended service. 

C.C. Silva, H.C. Miranda, H.B. de Sant Ana, J.R Farias 2013. Austenitic and ferritic stainless steel dissimilar weld metal evaluation for the applications as-coating in the petroleum processing equipment. Materials and Design 47, 1-8. 

Dissimilar Material Welds Dissimilar material welds assumed for a transition from superalloy to titanium pressure boundary at cooler. Dissimilar welds assumed to be less reliable than normal welds due to potential brittle phases. Crack/Leak to space. 9990 per weld... 

BE-7301 Life optimization of dissimilar metal welds for high temperature components Mr. V. Bicego CISE SpA... 

FlOiei Evaluation of techniques for assessing corrosion cracking In dissimilar metal welds Dr D.R. Tice AEA Technology... 

Ultrasonic Testing of Austenitic and Dissimilar Metal Welds,... 

Stainless steel develops a passive protective layer (<5-nm thick) of chromium oxide [1118-57-3] which must be maintained or permitted to rebuild after it is removed by product flow or cleaning. The passive layer may be removed by electric current flow across the surface as a result of dissinulat metals being in contact. The creation of an electrolytic cell with subsequent current flow and corrosion has to be avoided in constmction. Corrosion may occur in welds, between dissimilar materials, at points under stress, and in places where the passive layer is removed it may be caused by food material, residues, cleaning solutions, and bmshes on material surfaces (see CORROSION AND CORROSION CONTROL). 

Galvanic corrosion may occur at stainless steel welds if sensitization has taken place or if welding has produced unfavorable dissimilar phases (see Chap. 15, Weld Defects, particularly Case History 15.1). These forms of microstructural galvanic corrosion do not involve the joining of two different metals in the usual sense. 

The micro-mechanical processes will be presented next, followed by the models used to describe them. The predictions of the models will then be compared with results obtained using well-defined coupling chains. Application of the models to the joining of dissimilar polymers will then be described. Finally welding of glassy polymers will be considered. 

In buried pipeline installations, avoid contact of piping with structures of dissimilar metals. Also, where possible, specify uniform quality, grade and surface conditions. Various quality sections should not be welded together in buried installations. 

The electrochemical examination of fusion joints between nine pairs of dissimilar metal couples in seawater showed that in most cases the HAZ was anodic to the weld metals" . Prasad Rao and Prasanna Kumarundertook electrochemical studies of austenitic stainless steel claddings to find that heat input and 5Fe content significantly affected the anodic polarisation behaviour under active corrosion conditions whilst Herbsleb and Stoffelo found that two-phased weld claddings of the 24Cr-13Ni type were susceptible to inter-granular attack (IGA) as a result of sensitisation after heat treatment at 600°C /pa was unaffected by heat input. 

Rowe, M.D., Nelson, T.W., and Lippold, J.C., Hydrogen-induced cracking along the fusion boundary of dissimilar metal welds, Welding Res., February, 1999, p. 31. 

Dissimilar Materials. When materials having different preheat requirements are welded together, it is recommended that the higher temperature shown in Table GR-3.5 be used. 

Transition joints are used to join dissimilar metals where flanged, screwed, or threaded connections are not practical. They are used when fusion welding of two dissimilar metals forms interfaces that are deficient in mechanical strength and the ability to keep the system leak-tight. Transition joints consist of a bimetallic composite, a stainless steel, and a particular kind of aluminum bonded together by some proprietary process. Some of the types in use throughout the cryogenic industry are friction- or inertia-welded bond, roll-bonded joint, explosion-bonded joint, and braze-bonded joint. 

Attachment of suction and discharge nozzles shall be by means of full-fusion, full-penetration welds. Weld neck flanges are required for pumps handling flammable or hazardous liquids. Dissimilar metal weldments are not allowed. 

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