Material and Weld Defects

The true influence of flaws and defects on component failure is commonly misunderstood. This misunderstanding often arises from one of two misconceptions. The first misconception can be clarified by simple definitions of a flaw and a defect. 

A flaw can be defined as an imperfection in a material that does not affect its usefulness or serviceability. A component may have imperfections and still retain its usefulness. This fact is recognized by most material codes that permit, but limit, the size and extent of imperfections. This is particularly true of welds, which commonly contain harmless imperfections. It is not uncommon for failures to occur in the vicinity of flaws that have contributed nothing to the failure mode. 

Defect. A defect is an imperfection in a component, resulting from the way it was manufactured, shipped, handled, or installed, that may contribute materially to failure or limited serviceability. Failures resulting directly or indirectly from defects account for less than 1% of all failures. 

The second misconception involves the perception of what constitutes a defect. A defect is not simply a visually observable discontinuity such as a hole, lap, or seam in a component. Defects, from a failure-analysis standpoint, may also be such things as a high residual stress that may lead to cracking or unfavorable microstructures that can lead to either 

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