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Long life and the good performance characteristics of Flowtite pipe can only be achieved by proper handling and installation of the pipe. It is important for the owner, engineer and contractor to understand that glass-reinforced plastic (GRP) pipes are designed to utilize the recommended installation procedures.

The information described below is only a partial review of installation procedures; it is not intended to replace separate installation instructions which are available and must be followed for any project.

Belowground - Buried

For most cases, the most economical pipeline installation is a buried Flowtite pipe. The soil will provide the support that the pipe needs, avoids vandalism and damage. Since the pipes are not designed to resist full end-thrust, all unbalanced thrusts resulting from change in direction, tees, reducers, wyes etc. need to be resisted by thrust blocks or lock-joints for transfer of these loads to stable ground.

The trench bed, of suitable material, should provide uniform and continuous support for the pipe. To ensure a satisfactory pipe-soil system, correct backfill material must be used. Most coarse grained soils are acceptable bedding and pipe zone backfill material.

After installation of each pipe, the maximum diametrical vertical deflection must be checked. The maximum allowable initial diametrical deflection (typically vertical) is 2.5% for pipes equal/smaller than 250 mm. The maximum allowable long term diametrical deflection is 5% for diameters 300 mm and larger, and 4% for smaller diameters. These values apply to all stiffness classes.

More information on buried installation acc. to AWWA and ATV is available in the "Download" section.

Aboveground - Aerial

For above ground installations Flowtite GRP pipes are laid on supports or cradles and fastened with straps to ensure stability. The supports are usually concrete or steel; the fastening straps are made of steel. We differentiate both thrust-bearing pipe systems and non-thrust bearing systems.

Non-thrust bearing installation

Non-thrust bearing pipe systems carry the fluid pressure, but they are not designed to transfer thrust forces generated at any direction change or geometry change / change in cross sectional area. Therefore the systems require thrust blocks or other supports to resist unbalanced thrust. Thrust blocks are usually made of reinforced concrete. They need to encase the fitting completely and transfer the thrust safely to solid ground. Non-thrust bearing pipe systems need carefully analysed and water pressure needs being included when stability is checked.

Thrust-bearing installation

Thrust-bearing pipe systems, also called biaxial pipes and joints, restrained joints or self-anchoring system, carry the fluid pressure and also transfer longitudinal forces or bending moments. Both pipes and joints have axial load bearing capacity. Unbalanced thrust is thus be resisted by the piping system and no thrust blocks are necessary. The careful placement of supports ensure that axial stresses are below given limits. Thrust-bearing piping systems require a careful 3D dimensional structural analysis. Specialised computer software determines all stresses and displacements, as well as support forces. Axial stresses generated in such a system usually make a higher pressure class of pipes and joints necessary than the operating pressure. Due to the fact that Flowtite pipes have lower E-moduli than e.g. steel, the force on components are quite often of lower value.

More information on aboveground installation is available in the "Download" section.


Slip lining - Rehabilitation

With the ability to make custom diameters, Flowtite GRP pipes can be manufactures with optimum pipe size to match the inside diameter of existing pipelines. This will provide the maximum flow capabilities while still permitting ease of installation.

Also standard Flowtite pipes can be assembled outside the deteriorated pipe and then pushed into place. This can be done even with low flows, if the old pipeline is less than 1/3 full.

For pushing long distances, thrust rings can be built onto the spigot ends of the pipe, allowing the force transfer through the joint without effecting the sealing capability. This is especially important for rehabilitating pressure lines. For large diameters the pipe can easily be carried using a light weight frame cart and assembled at it’s final position. The ability to manufacture variable lengths also helps to reduce installation time.

Slip lining with flush joints, which allow a close match of the internal diameter to the existing pipe and the external spigot diameter of the slip-lining, is also possible. Slip lining with flush joints is available in SN5000 and SN10000 with diameters ranging from 600 to 1,900 mm.


GRP pipes are often installed under water especially for intake and outfall lines. It is often convenient that the pipes are joined together and towed to the position to be installed. The installation procedure is usually using the following types of joints .

  • Double bell coupling joints with marine harness lugs
  • Key lock joints
  • Laminated/ Lay-up joints
  • Flanged joints.

In addition to these joints, various other types of joints are available and need to be selected based on project requirements. Depending on project requirements and site or weather conditions different installation techniques are used. These are:

  • Single pipe installation - With this method the pipes are lowered to water and joined under water one by one
  • Multiple pipe installation - Two or three section of pipes are preassembled on land or barge then lowered to water and joined under water
  • Multiple pipe installation, providing pipe strings (towing)

Your supplier will provide specific installation instructions for any particular project.

More details are available in our Flowtite product brochure for subaqueous applications which can be downloaded here.