Failure Analysis of the Squeeze-Off of PE Pressure Pipes [PE]

Squeeze-off is used in routine and emergency situations, to stop or nearly stop flow in polyethylene pipe by flattening the pipe between parallel bars. Gas and water industry utilizing polyethylene pipe in their systems have designed squeeze-off procedures to fit their pipe material environmental conditions and constructional needs, where it may be inconvenient and/or expensive to isolate and empty pipelines. The method provides a quick shut-off the lines, saving many hours, and eliminates the need for dangerous, costly and lengthy excavations. Despite its widespread use, it is not known if squeezing of the pipe damages the pipe, and if yes what is the degree of the damage and how it should be minimized? This paper is about the investigations of the squeeze-off of pipes made of PE 80, PE 100 grades high density polyethylene and crosslinked polyethylene (PE-Xb) pressure pipes of different dimensions. Experimental investigation on the damages related with the squeeze-off of the pipes are carried out to study the influence of squeeze-off phenomenon on the short and long term performance of the pipes. Hydrostatic pressure tests were performed on the squeezed pipe to examine the degree of damage on the pipes. The influence of squeezing ratio, pipe diameter and squeeze-off tool geometry on the overall pipe performance was also investigated. Stress analysis of polyethylene pipe squeeze-off was carried out with finite element method to investigate stress distribution on the pipe squeeze-off. The effect of squeeze-off tool geometry on the polyethylene pipe stress distribution was also investigated. Key Words : Polyethylene pipes, squeeze-off, failure analysis, finite element finite element analysis, failure analysis, hydrostatic pressure tests