Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Slip-Plane Outerwrap

Last updated: August 31, 2017

What Does Slip-Plane Outerwrap Mean?

A slip-pane outerwrap is a strong, tightly woven, geotextile membrane that is wound around pipes to reduce soil stresses while providing non-shielding coating properties. The outerwrap is made of a strong, non-woven, polypropylene textile, engineered to provide low elongation and tensile properties in addition to a high bursting strength. The slip-plane outerwrap prevents the destructive effect of the pressure created by the swelling and shrinking of the surrounding soil due to variations in the groundwater conditions.


Corrosionpedia Explains Slip-Plane Outerwrap

Pipe systems in expansive soils are subjected to pressures created by the swelling and shrinking of the surrounding soil caused by variations in water levels in the soil. The soil expands or shrinks depending on the moisture content and therefore varies with seasons.

The wrapping is usually installed prior to the laying of the pipes inside the trench. The plastic-like cushion layer provides a longitudinal slip plane between the pipe and the moving surrounding soil. The wrapping provides protection to the pipe system against any movements that may occur. The slip-plane outerwrap prevents damage to the pipe and joints, in addition to protecting the corrosion protection system from breaking.

The fabric wrapping allows for a slip plane between the outer surface of the pipe and the surrounding shrinking and swelling soil. The fabric is porous and therefore permits the cathodic protection currents and water to pass through it. The outerwrap thus provides a high soil stress resistance while protecting the wrapped pipelines against corrosion.

The outerwrap does not adhere to the corrosion protection coating on the pipe and is often free to move freely without interfering with the quality of the coating. It is designed not to adhere to the coatings and has the freedom to move when subjected to the sources from the soil stresses. The slip-plane outerwrap is independent of the surface coating of the pipeline; otherwise, if the fabric is bonded to the coating, the soil stresses would be transferred to this protective coating and end up damaging the coating, hence reducing the corrosion protection capacity.

The slip-plane outerwrap provides soil-stress resistance in expansive soils, are non-shielding, and often used over other corrosion protection coating systems.


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