Steel water pipelines coated with coal tar enamel were dominant in most of the last century, but the coating failed in various ways. Disbondment, cracking, and holidays, places where the coating cracked and allowed moisture to come into contact with the steel pipe and initiate the corrosion process, were some of the problems associated with the coating in service. The Australian water utility companies realised the need for coating systems that could bond differently and more consistently and should also be applied under consistent factory conditions.
Thereafter, a research programme was developed in conjunction with the water utility agency in Australia that aimed at coming up with a coating system that would be effective in all the possible soil and moisture conditions in Australia. Sintakote steel pipeline systems came out in the early 1970s and the coating used was fusion-bonded medium density polyethylene. By the end of the 1980s, it had become the standard coating system for steel water pipelines in Victoria and continued to spread throughout Australia.
What the Fusion Bonding Process Actually Produces?
Fusion bonding is actually a process that results in a product. The pipe surface is cleaned by grit-blasting and then the pipe is coated with a fluidised bed of medium density polyethylene powder after heating. The powder is fused directly to the heated steel surface hence giving a coating with no interfaces at which moisture can get underneath and no bare steel. The coating covers not only the external part of the pipe but also covers the internal side, overlapping the cement mortar lining. Thus, the coating extends to cover the spigot and socket ends of the pipes and covers the whole pipe surface continuously.
The end result of such coating is that the ferrous material will not be exposed either to the soil or to the water being transported.
The Internal Lining and What It Contributes
External coating solves one side of the corrosion problem. The internal surface needs its own protection, both from the chemical action of the conveyed water and from the roughness growth that unlined steel develops over time, reducing hydraulic efficiency as the pipeline ages. Centrifugally spun cement mortar lining addresses both. The spinning process during application compresses the mortar, producing a dense, smooth surface that is chemically resistant and maintains hydraulic efficiency across the design life of the pipeline.
Different cement types serve different environments. General-purpose cement suits standard potable water applications. Sulphate-resistant cement applies in ground conditions where sulphate levels are elevated. Calcium aluminate cement is used in highly aggressive or industrial wastewater environments. Each is manufactured to Australian Standard AS 1281 for cement mortar lining of steel pipes and fittings.
The Joint System as Part of the Envelope
Historically, the joint has always been the most vulnerable part of the pipeline. The Push-In jointing system compatible with this coating system is one where the polyethylene coating covers the joining of individual lengths of pipe. The rubber ring seals the joint hydraulically, while the polyethylene coatings applied to the spigot and socket provide for corrosion protection throughout the joint area. Welded joints are protected with field-applied wrap systems that provide comparable levels of protection.
The pipeline system is available in diameters ranging from 100mm to 2500mm, encompassing all ISO and AS dimensions, pipe lengths ranging from 6.0m to 13.4m, and wall thicknesses from 4.5mm to 20mm.
A Track Record Measured Across Decades and Conditions
This pipeline system has been installed over thousands of projects since the early 1970s in Australia, from the tropical north of Queensland, to the semi-arid areas of Western Australia, to the reactive clays of Victoria, and even in ground-level applications in mining site infrastructure exposed to ultraviolet rays. The formulation of the polyethylene is resistant to UV degradation, allowing installation of the pipes in above-ground applications without any further coating.
