Another important method for pipeline rehabilitation is pipe in pipe relining. This method applies to the drinking water, gas, sewerage and industrial pipeline networks, rehabilitation without excavation. The cornerstone of the system is introducing a new tube in the old pipe. For this rehabilitation method GRP pipes are used.

This product, from an economical and technical point of view, meets all of the requirements. The properties of G.R.P. pipes are: high chemical resistance, fast and easy installation, easy coupling and excellent hydraulic properties of the mirror-like smooth interior surface.

The method consists of pulling a polyethylene pipe of smaller diameter through the host pipe (steel or PREMO).
It involves placing a polyethylene tube of a certain length in the launch pit and pulling it into the pipeline which is being rehabilitated, followed by welding it together with the next tube, repeating the operation until finishing a section of pipelines in average up to 800 m.

To achieve pipe rehabilitation with G.R.P. pipes, the following steps should be followed:

  • Establishing the sections and the position of launching holes
  • Execution and insurance of launching pit
  • Launching and positioning the pipes
  • Connecting the pipes
  • Immobilizing the pipes

The position of the launching pits which delimits the sections must be established in order to make it possible to: launch, position and connect the pipes by respecting the technical specifications given by the manufacturer of the respective rehabilitation pipes.

The launching pit will be executed by mechanized and manual excavation. The pits edges will be insured with sheet piling (in accordance with security and safety regulations in force), and, also, cutting the upper cap of the old pipe.

Connecting the pipes can be made in the launching pit or in the final position. This operation is performed using manual or mechanical devices.

The pipe immobilization is a process for placing the new pipe into the old one; maintain its steady position throughout the period of use, of the new pipeline. This fact is accomplished by concrete injection with mixers and concrete pumps, in the space between the two pipes.

Main technological stages:

  • Opening the pipeline at both ends at the start and end points
  • Video Inspection (CCTV)– 2.1. Preliminary 2.2. Before installation 2.3. After installation
  • Cleaning the pipelines using the ‘HI-JET’ water method
  • Executing the access pits (having the length of 12-13 m, depending on the length and width of the polyethylene coupon and support according to the nature of the soil and the laying depth of the respective pipeline)
  • Electro-thermal “head to head” welding of the polyethylene pipe
  • Pulling the welded polyethylene pipe into the host pipe
  • Restoring connections (closing the pipeline)
  • Performing the pressure test and disinfection
  • Restoring the site to its original state

The advantages of rehabilitation with G.R.P. pipes:

  • It is a trenchless rehabilitation method that doesn’t involve the discomfort encountered in case of rehabilitation through excavation
  • Polyethylene is an accepted material for drinking water supply pipelines
  • Polyethylene has very low roughness (flow rate improves substantially)
  • Polyethylene has increased structural resistance
  • Complies to pressure resistance tests
  • Lengths of up to 600m can be executed in an installation adduction
  • It is not influenced by the degradation of the host pipeline – there will be no micro cracks resulted from cracks in the Premo host pipeline

Due to the characteristics of polyethylene pipes and easy installation, the innovative pipe rehabilitation technology with G.R.P. pipes ensures sustainable and durable rehabilitation.