Hi Guillermo, to build on ...

Hi Guillermo, to build on what others have advised and answer your question it depends on the size and strategic nature of the pipeline. Sahara as Anthony advises sends a line through and a microphone picks up the sound of the leak. Very well used and effective. Smartball is an emerging technology and you need points to launch and catch the ball. 

You can set up a test to look at head loss through the pipe which might help quantify the leak. 

PE is a very difficult material to adhere anything to - fusion by melting the material is the only way to achieve a bond. Electrofusion or mechanical jointing is the normal way to joint pipes. 

To achieve a long term solution you may consider sliplining another pipe inside the parent pipe. Alternatively you may consider pipe bursting, if you nee the capacity which entails breaking out the old pipe and pulling another on in - essentially you make use of the hole in the ground. 

Lots of detail on these technologies and fixings can be found at the ISTT (International Society for Trechnless Technology) web-site. 

Hope this helps? 

Steve