Drain Repair Using Drain Lining & Pipe Lining Techniques

As soon as we had the ability to inspect pipes, drains and sewers from the inside with cameras it was only a matter of time before somebody came up with the idea for a No Dig drain repair, now some 35 to 40 years on there are numerous trenchless drain lining methods on the market for repairing defective systems. These include Slip Lining, Spray Lining, Draw Lining, Roll Down, Pipe Bursting and CIPP Lining.

The latter of these CIPP (cured in place pipe) Lining is the most commonly used drain lining technique on domestic drainage systems within the UK  with most drainage contractors now offering at least one method of CIPP drain repair as a standard service. This has had a major affect on the industry and these trenchless drain repair techniques benefit all parties when a repair is required.

• The Homeowner - no longer has to endure a full blown excavation with the noise, mess and upheaval that this kind of work can involve.
  
  
• The Contractor - has a quicker turn around of jobs and therefore more profit, the reduction of excavation works also means less reinstatement and therefore a smaller snagging list at the end of the job, less tipping charges and reinstatement costs.
  
  
• The Insurance Company - In the good old days you could charge the same for relining a system as you would for a full excavation, however as with any competitive market place prices have come down and it is now much cheaper to reline a system than it is to excavate.
  
  
• The Environment - Many of these drain lining techniques are used in the repair and renovation of public sewers beneath our roads and highways, this greatly reduces time lost to commuters in traffic jams and therefore our carbon footprint.
  

We also have the ability to patch repair specific defects, to reline around sharp bends, to reline several bends at once, to re-open junctions and lateral connections using robotic cutters and to reline the junctions themselves. Cipp liners can be modified to deal with harsh industrial environments and undue loading scenarios.

Basic Cipp Drain Lining Methodology

The drain liner itself is a felt tube with a thin plastic coating on its outer wall, a mixture of resin, a catalyst and an accelerator are poured into the tube and the liner is then `wetted out`, this is the process of ensuring that the resin soaks into the felt evenly throughout the length of the liner. The liner is then inserted into the defective drain and inflated using either water or air, as the liner is held mechanically to the wall of the host pipe the resin cures over a short period of time forming a pipe within the host pipe.

Click the images below to enlarge.
Felt Liner	Wetted Out Liner	Cured Liner

• Drag In Drain Liners 
  These are pulled into place or pushed down a drain and would typically have a wall thickness of 3mm up to 6mm dependant on the pipe size and depth, the liner is then inflated using an inversion hose or tube.
  
  
• Inversion Drain Liners
  These liners can have a thinner wall or coating and can be inverted into the drain or sewer without the use of an inversion hose, more flexible than the drag in liners they can negotiate bends and changes of direction whilst still leaving a smooth internal finish.
  

If you click on the image to the right you should see a video showing how the inversion hose opens up the liner within the drain.

Re-Opening Lined & Capped Junctions 

When you reline a length of drainage system you in affect `cap off` any incoming branch lines or connections so through necessity methods were developed to either re-open these connections with techniques also developed so as not to cap them off in the first place.

The worst of these techniques was by far the method of cutting out a window in the liner before it was installed and then trying to align the window with the junction, this was a very hit and miss approach given that drag in liners stretch to some degree during installation and then shrink again during the curing process.

To compensate for this the cut out window tended to be twice the size of the connection in order to have more chance of hitting the mark and i have seen liners with two or three windows cut out in one length, the downside of this practice is that by cutting out large chunks of the liner you are weakening it structurally and often the joints either side of the junction would not be covered by the liner. The worst case scenario would be the liner partially covering the junction or the inversion hose finding its way out of the window and turning the remainder of the liner into one long channel pipe.

Robotic Cutters

Robotic cutters were designed so that junctions and lateral connections could be cut out in a controlled manner after the liner had cured, the video clip to the right is of an early model but it will give you an idea of the process. The modern cutters are far more superior and i would hope a lot faster.
  
Due to the popularity of the Drain Patch Repair method you are less likely to see a robotic cutter on a domestic system but there are occasions when they are invaluable, and there are plenty of contractors with an ancient rig sat in the corner of their lock up. They are however widely  used on larger diameter and deeper main line drainage systems.

Top Hat Liners 

In order to fully seal a relined system Top Hat Liners were developed as the connection from a branch line onto a main line is a weak spot, prone to fractures that can allow water loss into the sub-soil as well as root & ground water ingress into the system itself.

The majority of the liner sits within the lateral connection leaving a flange the moulds itself and adheres to the main line wall.

Typically the main line and the lateral connection will have been relined prior to the installation of the top hat but they can be installed on their own to cure specific faults such as root or ground water ingress.

Again you are very unlikely to find this method used on a domestic system due to the cost of the plant and machinery involved and the method is better suited to pipe work in excess of 150mm in diameter.

However on large sewer renovation projects it is a valuable part of the no-dig repair armoury with skilled installers saving major excavation works beneath our highways and roads.