Butt Fusion Cooling Times: Speeding Up the Process

Session 9B
10:40 am

Ted Striplin, McElroy Manufacturing Inc.

The polyethylene (PE) pipe system has many attributes that make it the most reliable and highest quality system within the prescribed pressure and temperature limitations. However the process itself is the weakest link in the PE pipe sales chain. While easier to join in large diameters it can require the most time to install. Long cooling times can make it more difficult to sell a PE system. With the introduction of ISO 21307 there was a new answer to this problem for the rest of the world. The rest of the world because the USA and some other countries have been using this procedure for may years. Using the higher interfacial pressures proved to speed up the cooling time so that a strong safe joint can be removed the machine without taking ay undue risk in weld failure in the near or long term.

Since ISO 21307 was published there have been many questions as to how soon can fusion joints be removed from the machine without risking possible weakening or failure. A combined industry and PPI testing regimen was carried out to establish based on various fusion standards, the actual temperature of the internal pipe wall when the standard allows removal of clamps or pipe from the machine and what approximate strength the fused weld has. The testing was carried out on pipes from 200mm (8” IPS) to 900mm (36”) and DRs ranging from 11 to 4) and revealed the actual interfacial temperatures and the actual times required to cool the joint interface to a safe temperature. Why are the required cooling times so different for some of these standards and how strong is the joint when it is lifted from the machine? Can we use this information to establish a desired joint temperature and thus appropriate cooling time per standard?