Root cause failure analysis of defected J-groove welds in steam generator drainage nozzles

• During the Re-Fuelling Outage of Ringhals 2 in 2004, visual examinations of the outer parts of the bottom dome of the Steam Generators, SG, before the scheduled SG-pipe inspections, revealed a boron deposit outside drainage pipes from the manhole covers in two positions. The drainage pipes are made from stabilized stainless steel and are connected to the Low Alloy Steel lower dome by a nickel based dissimilar J-groove weld of alloy 82 equivalent weld metal. Dye penetrant and replica-moulding examinations of the surfaces of the J-groove welds inside the manhole both showed similar results. Two radially oriented defects were indicated in the 12 o'Clock position in one of the nozzle welds on the hot side on one of the steam generators, and one similarly oriented and positioned defect in one of the cold side manhole cover nozzles in another steam generator. These defects comply well with the observations made from the external examinations during the initial stages of the Refuelling outage. Two boat samples were removed by EDM, one from each of the defected areas of the J-groove welds. Metallographic examination of the boat samples showed not only an extensive, most likely service induced, degradation of the Alloy 82 weld material, but also the presence of a manufacturing induced circumferential defect in the root pass of the J-groove weld not exposed to primary water. Given the manufacturing situation, this defect is not a complete surprise, and it was also seen when investigating the weld mock-ups that were manufactured in order to train the personnel before the weld repair that was conducted as part of the program.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Teknisk mekanik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Applied Mechanics (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

Nyckelord

Alloy 82

failure analysis

steam generator

weld defects

Hållfasthetslära

Solid Mechanics

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