A Re-Examination of Failure Analysis and Root Cause Determination

19characteristic of ASTM A572 grade 50 high-strength low-alloy steel. This is the normalmicrostructure for this productSince the column met hardness requirements and had a normal microstructure, itwas concluded that the cracks in the flanges of the steel column were likely to havebeen produced during hot rolling stage of production of the beams. Because themajor crack might propagate under adverse conditions, it was recommended that itbe removed by grinding and that the column then be repair welded. The necessaryrepair work was to be performed by competent welders in accordance with AWSSpecification A5.1. It was further recommended that all of the column flanges in thestructure be subjected to one hundred percent ultrasonic inspection to determine ifany other cracks exist.IMPORTANT FAILURE ANALYSIS PRINCIPLES REPRESENTED IN THIS CASEHISTORY:1. Applicable specifications were available for the failed part, making conformancedetermination routine.2. Field metallurgical procedures, including acetate peel replicas, were animportant part of the process.3. Non-destructive on-site testing also important4. The source of the problem was determined not to be non-conformance with thespecifications but rather production procedures.5. The defect can readily be fixed in place. There was no need for replacement ofcolumns which would have been extremely costly.Case History #2. Failure Analysis of a Conveyor Drive ShaftIntroductionA German-made steel coal-conveyor drive shaft was submitted for root-cause failureanalysis. The shaft had cracked in service.Visual ExaminationThe as-received drive shaft is shown in figure 1. A transverse crack had passedthrough the right keyway near the center of the keyway length, at the red arrow,on line A-A’. The shaft was cut so that the crack could be opened to expose themating fracture surfaces. The fracture surfaces were found to be corroded; They