Item:

• Wall mounting brackets for heavy (40 Kg and 60Kg) transformers located within the train tunnels of a metropolitan underground railway system

Problem:

• Failures of the bracket at installation causes concern over the long term reliability and raises safety issues

Objective:

• To establish the root cause of the initial failures
• To propose redesign in the event that the root cause is found to be the design / installation of the bracket

Approach:

• Establish manufacturing processes and all loading conditions
• Establish all orientations in which the transformers can be located
• Determine the operating stresses from installation and normal operation
• Metallographic examination of the weld

Conclusions:

• Stress analysis concludes that all stresses are well below the limits imposed by good design practice
• Examination of weld show that it is of poor quality and the root cause of the failure

Benefits:

• Identification of the source of the cause of the failures
• Existing design acceptable, new design not required
• Inadequate quality procedures for welding identified as reason for poor welds