Chemical degradation driven cracking in PE pipes

Stress corrosion cracking (SCC) in polyolefin pipes usually starts as a microcrack colony within a degraded layer adjacent to the pipe surface exposed to combine action of mechanical stress and chemically aggressive environment. One can distinguish four stages of SCC: 1) microcracks initiate within the degraded polymer; 2) slow growth of individual cracks; 3) strong interaction of cracks and formation of clusters; and 4) clusters growth and crack/or cluster instability leading to the ultimate failure. The stage of crack initiation is primarily controlled by chemical degradation, and the second stage is strongly related with the effect of mechano-chemical degradation at process zone. The interaction of multiple cracks and clusters are typically observed after the many cracks grow individually. In this paper, the mechanism of crack initiation and growth due to mechano-chemical degradation is addressed and modeled.