Plastic Jacketing for Steel Pipe
A plastic jacket is used to provide protection against corrosion for steel pipe laid in the open air, underground and under water. To protect this corrosion-inhitibiting jacket from mechanical damage when the pipe is being transported and laid, the jacketed pipe are enclosed with an additional protective covering. However, pipe with such mulitlayer jackets has certain drawbacks. If, for instance, a crack in the outer jacket is created by mechanical action, the adhesive bond with the underlying layer can alow the crack to propagate and ultimately reach the steel underneath. Under unfavorable conditions, corrosion of the steel pipe takes place.
A recently published patent proposes a pipe jacket that can withstand the shear forces encountered during processing and laying, but does not allow a crack to propagate to the underlying jacketing layer. The proposed pipe jacket consists of at least two layers of thermoplastic applied to the pipe separately. The individual layers are bonded to one another in the course of jacketing only via friction. A special surface coating incrases the adhesive friction of the two materials. This prevents actual material bonding between the layers. The coating that increases the adhesive friction consists of material particles that are applied to the surface of the jacketing layer. These particles may be plastic, inorganic granules or sand. Since the jacket layer still proviees adequate shear resistance, shifting of the jacket layers with respect to each other during processing or laying of the pipe is prevented.