Elongation of a pipe is the increase in its diameter when stressed under tension. Flexible pipe materials such as high density polyethylene (HDPE) and polyvinyl chloride (PVC) can elongate when the embedment soil along the pipeline is compacted. Buried pipes are subject to soil pressure from the sides as well as the top and also to effects of gravity, temperature changes and external loading either dead or live.
All of these factors can cause a change in pipe diameter resulting in elongation along the vertical or horizontal axis.
Trenchlesspedia Explains Elongation
Flexible pipes are those which can bend or flex under pressure. The ability to support dead and live loads depends greatly on the quality of the backfill and support provided to the pipe. Inadequate support either at the sides or the top can result in failure of the pipe to carry its load effectively or fail to support the ground above it.
Large deflections in flexible pipes can lead to buckling when critical loads are reached. A five percent decrease in mean vertical diameter of a flexible pipe is acceptable but it can deflect up to 20 percent before failure occurs. Percent elongation can be measured as change in diameter divided by original diameter multiplied by 100.