Standard Practice for Qualification of a Combination of Squeeze Tool, Pipe, and Squeeze-Off Procedures to Avoid Long-Term Damage in Polyethylene (PE) Gas Pipe

Importancia y uso:

4.1 This practice relies on a screening process using visual inspection followed by 80 °C sustained pressure testing to qualify a squeeze-off process.

4.2 Squeeze-off is widely used to temporarily control the flow of gas in PE pipe. Squeeze tools vary in squeeze bar shape and size, operating method, and available stop gaps depending on the tool manufacturer and the size of the pipe the tool will be used on. Multiple squeeze tools are required for a range of pipe size and DR combinations. Squeeze-off procedures can vary depending on the tool design, pipe material, pipe size and DR, pipe operating conditions, and pipe environmental conditions.

4.3 Experience indicates that damage leading to gas pipe failure is possible with some combinations of polyethylene material, pipe temperature, tool design, wall compression percentage, and procedure. This practice is useful for determining the suitability of a tool for squeeze-off and for determining acceptable limits for squeeze-off such as acceptable minimum and maximum pipe temperature for squeeze and acceptable line pressure for squeeze. Tests conducted at different pipe temperatures with various sizes of tools and pipes can be used to verify a range of temperatures, tool sizes, and pipe sizes for which the squeeze-off procedure is applicable.

4.4 The area of wrinkling at the ears on the inside diameter (ID) of the pipe and the area on the outside of the pipe opposite the ears are examined. Evidence of any one or a combination of void formation, cracks or extensive localized stress whitening, or failure during sustained pressure testing disqualifies the squeeze-off process.

4.5 Typical unacceptable features implying long-term damage are shown in Appendix X1 photographs.

4.6 Studies of polyethylene pipe extruded in the late 1980s (PE2306 and PE3408) show that damage typically does not develop when the wall compression percentage is 30 % or less, when closure rates are 2 in./minute or less and release rates are 0.5 in./minute or less, and when squeeze bars have radii 4 times or greater than the pipe maximum wall thickness.

4.7 This practice provides a method to qualify a combination of squeeze tool, pipe size and material, and squeeze-off procedure to ensure that long-term damage does not occur. This practice is useful for all polyethylene gas pipe, for all pipe diameters, for new or revised squeeze tool designs, and for new or revised squeeze-off procedures.

Subcomité:

F17.60

Referida por:

F1041-20, D2513-24

Volúmen:

08.04

Número ICS:

23.040.20 (Plastics pipes)

Palabras clave:

damage; flow; gas ; pipe; procedure; polyethylene; qualification; squeeze; squeeze-off; tubing ;