D0 Silicon Upgrade: Calorimeter Installation Bridge Non-Destructive Test Result

After the central calorimeter was installed on the center beam a cracked weld was found on the bridge. The weld was a partial penetration between the top rail plate and the T-1 steel nose section. The crack is fully across the width of the rail plate and the rail is depressed in a concave shape. That is, the depression is deeper in the center and feathers out to zero at the end of the rail. Upon close inspection it was obvious that there was no penetration of weld metal into the T-1 material. The assumption is that the T-1 was not properly pre-heated before welding. The reason for the concave depression comes from the fact that the rail plate rests on the flanges of the 'S' beams and that during welding the plate pulled off the beams. This weld failure can not propagate to any other welds and therefore, will not start a chain of failures. Clearly the failure of this weld did not hinder the installation of the central calorimeters. This weld failure occurred on both sides of the bridge. This failure did, however, alert us to check the critical weld on the bridge, S-beam webs to T-1 nose section, to assure us we had a sound weldment. (Note: it must be used again for both EC's). We contacted M.Q.S. Inspection Inc. (Lab contractor for N.D.T.). A technician from M.Q.S. came to DAB and performed an ultrasonic examination of the welds in question. The exam showed that we don't have a full penetration weld of the S Beam web, but that it is between 67-83%. A calculation was performed based on 67% penetration and the CC and EC loads. In both cases the weld stresses were well within acceptable limits (see calculations attached). Based on this result, it is not deemed necessary to modify the current weldment.