Pipeline spacers are a non-metallic spacer used in pipeline rehabilitation and new construction. The main type used with PE pipes is a "Bow Spring Type". such as the HD series pipe spacer. If the liner pipe is heavier (such as steel, DI pipes or very large PE pipes) then a stronger "Casing Spacer" such as the HDX or HDXT may be required.
Pipe Spacers are used in applications where a smaller diameter liner pipe is being hosted in a new or existing host pipe. This may be due to rehabilitation of an old host pipe or installing a PE liner pipe inside a jacked steel pipe that provides a sacrificial host pipe for construction purposes. The purpose of the spacer pipe is to
- Centre the liner pipe inside the host pipe to ensure even grouting of the annulus and maintain gradient if necessary.
- Withstand grout pressure up force on the PE pipe to maintain an annulus around the PE pipe for grout to flow into.
- Reduce pulling or jacking friction during the installation process
- Prevent damage and wear to the PE pipes outer surface as it is pulled into the host pipe
Spacers come in various formats and materials, some have wheels, runners or skids. They can contain multiple pipes in a single host pipe, however, most common is a low-cost sacrificial spacer manufactured from engineering plastic. These clamp onto the pipe surface with a given spacing between each spacer both along and around the pipe. The spacings are determined by the mass of the liner pipe and the expected wear rate based on the length of the pull.
Key requirements for pipeline rehabilitation spacer are:
- Ability to grip onto the surface of the pipe and not slip or ‘stack up’ during the pull – features such as rubber pads to grip to the pipe surface and mechanical banding through the spacer onto the pipe may be required where frictions loads are expected to be high where the annulus gap is small.
- Non-rigid design so the spacer can deflect to allow passage of the pipe through tight areas but has sufficient rebound strength to recover to its original spacer height under static load in order to maintain an even grouting annulus
- Provide load sharing between runners – as the liners mass is focused onto a small radial area during the pull (around bends), the deflection of the spacer must allow the excessive load on one spacer skid to deflect so it is shared between the adjacent skids when required and then recover its normal height.
- Offers various wear resistance options for the runner surfaces such as POM (acetal or polyacetal) and UHMWPE (Ultra-high-molecular-weight polyethylene) to allow tailoring of wear on the spacers given the host pipe condition and respective pull lengths.
- Allow rapid installation on-site around the circumference of the liner pipe in the pit as it is being pulled in to the host pipe, to avoid construction delays.