Department of Metallurgical and Materials Engineering

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Browsing Department of Metallurgical and Materials Engineering by Author "Adetayo, A.O."

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    TRACKING LOCAL BRITTLE ZONE IN THE HEAT AFFECTED ZONE OF GIRTH-WELDED API 5L X46 PIPE
    (Nigerian Journal of Technology (NIJOTECH), 2020-04) Amuda, M.O.H.; Osoba, L.O.; Etuk, N.N.; Lawal, T.F.; Adetayo, A.O.
    In this study, microhardness variation as well as macro and micro structural examination of the heat affected zone (HAZ) of a girth welded API 5L X46 pipeline material were conducted as a means of tracking local brittle zone (LBZ) in the HAZ region. The weldment analysed were built from heat input range of 695 J/mm – 2567 J/mm. Analysis of the results revealed that the HAZ profile changes with variation in the heat input and becomes shallow but wide r as the heat input increases. Defects f r e e w e l d s w e r e a c h i e v e d u n d e r t h e h e a t i n p u t r a n g e o f 1 6 5 0 J / m m – 2 0 1 7 J / m m w e l d i n g condition. Localized high hardness values were obtained at certain locations within the HAZ of intermediate heat input welds produce d at 1467 J/mm due to thermal stresses induced strains at this heat input in the resolidified weld. Other than this, non - equilibrium rapid heating/cooling that is common during welding as well as the magnitude of mechanical strain generated on cooling vary with heat input and was attributed to the development of high hardness value at localized region within the HAZ of the welds in low heat input welding condition. The macrographic profile at these locations, contrasted against that of a failed pipeline mat erial of similar specification obtained from typical oil and gas infrastructure, established that crack initiation and propagation followed the trend of microhardness variations in the girth welded pipe. The crack initiates at specific location in the HAZ with very high hardness in the range 186 - 216 Hv within a radius of about 3 - 5 mm from the edge of the fusion zone