A Re-Examination of Failure Analysis and Root Cause Determination

23tensile properties for the material. The use of protective coatings or shielding the shaftfrom the corrosive environment should prolong the service life of the drive shaft.IMPORTANT FAILURE ANALYSIS PRINCIPLES REPRESENTED INTHIS CASE HISTORY1. The analysis showed that the product involved failed because it could notwithstand the environment in which it was used. Thus the materials specification forthe product should have included either:• surface corrosive prevention by a protective coating or• selection of a material which would be resistant to the corrosive environment.2. Corrosion fatigue can cause failure below the yield strength.3. Corrosion fatigue should be distinguished from fatigue initiating from pits. Incorrosion fatigue the corrosion activity is in the crack.Case History #3. Metallurgical Failure Analysis of A Welded Hydraulic CylinderINTRODUCTIONA failed hydraulic cylinder was submitted for examination along with a working drawinggiving the dimensions of the cylinder. The failure had occurred at the circumferentialweld at the closed end of the cylinder (red arrow, Figure 1). The cylindrical barrel wasspecified to be grade 1026 and the end cap to be grade 1045, both plain carbon steel.The cylinder assembly had been fabricated by stick welding using a 7018 electrode.We were requested to determine the cause of failure.Figure