McElroy Discussion Forums

I have been working in the Oman Oil fields for the past 2 years as PE lining Inspector. Our company is specialised in installing Butt fusioned PE liners inside CS crude and water pipelines. Diameter varies from 4" to 16" with thickness starting from 5mm to 25mm.We install the fusioned liner inside CS pipes and stretched to .5 to 1% of its total length and other side flange adaptor is fusioned. After removal of the clamp the liner goes back inside the cs pipe and the flange adaptor becomes flush with the CS flange. Almost 10 to 15 sections are installed like this. (Length varies from 100 mtrs. to 500 Mtrs). After about 12 months of service when we unbolt the sections the PE liner comes out about 1 to 2 metrs and boltup becomes diffcult and sometimes pushing back the liner does not work and we have to cut the liner and replace the sections. Rarely we cut the elongated length and again stretch the liner and stub ends fusioned to restore the section. Can you give why this problem occurs.

Polyethylene pipe will elongate due to a temperature differential, at a rate of approx 12"/100 deg f/100 feet.
Also PE pipe in a hydrocarbon enviroment will increase in length as well as in the thickness of the pipe wall.
The combination of a rise in temperature as well as a hydrocarbon environment will cause the pipe to grow in length.
You mentioned you put the pipe in tension and fuse a flange adapter on, and when released it contracts and becomes flush. This contraction is momentary, over a period of time PE pipe will stress relieve itself and will no longer be in tension. As the pipe then rises in temperature it would grow in length, as you say, and unrestrained would become longer that the host pipe.
A 25 degree f. temperature increase would account for the 1 to 2 meters of growth you spoke of in 100 to 500 mtrs.

Dear Reghunath.
I trust Terry was able to help with his answer. If you are still concerned please call me and we can find alternative views or opinions. I will be in Dubai for the Trenchless Show in October. I will be delighted to meet you to discuss your usage and successes with the McElroy. You can find my numbers at McElroy Europe on our contacts page. Good luck.
Keith.