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sharp focus. No weld defects wefe revealed by fluorescent-penetrant inspection. However, metallographic examination revealed that weld penetration was about 45 mils rather than the desired 100 mils. We will try to overcome this shortcoming on the next practice weld by using a more sharply focused beam and a higher beam current. The other two sets of headers were joined using the manual gas tungsten-arc process in an argon-filled chamber. Two weld passes were required to fill the 90"

vee-groove weld joint (Fig. 14.5), using low-carbon, low-oxygen molybdenum filler wire. No weld preheat was required. One of these welded pots is shown in Fig. 14.6 together with the two backextruded headers. No defects were detected on either arc-welded feed pot when they were fluorescent-penetrant inspected. To more closely simulate conditions required in fabrication of the test stand, additional tube-to-tube welds have been made with the orbiting arc weld head. Longer lengths of tubing were joined with the axis of Y-106804


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Fig. 14.6. Molybdenum backextrudedhalf sections joined by GTA welding.