Jemena, agrees that it is often third-party construction crews that cause damage but then neglect to report it. “We've had a contractor digging a trench to install a water pipe that damaged large sections of the coating on a steel pipe and then thought it would be OK to simply place back the damaged coating and secured it with gaffer tape,” he says. Mr Galanos says that the pipelines for which his company is responsible are the high pressure, high volume supply lines that traverse both country and urban areas carrying petroleum, gas, water and other products. “Beneath Sydney, for example, there are hundreds of kilometres of steel pipes in a range of diameters “Some of these have been safely in place for decades but urban sprawl is now threatening them.” Most pipes lie beneath public spaces such as roads and parklands, but some do cross private property. Mr Dragar added that the coating on the buried pipelines was the primary way his company mitigates corrosion thereby maintaining the structural integrity of its assets. The weakest points in the network, however, are the field joints where lengths of pipe are laid and welded together on site and then recoated. “We could have the best design and materials being used for a project, but the effectiveness of the coating over the a joint comes down to the abilities of the applicators applying it.” An example of this is where the instructions for applying a heat-shrink sleeve to a pipe joint say that the pipe surface has to be heated to more than 80 degrees Celsius. However, some applicators may heat the metal to an even higher temperature but then take too long putting the sleeve in place during which the temperature has dropped to around 70 degrees which means the sleeves do not adhere properly. “As a result, we have mandated that all construction is to be carried out to a higher level than that required by the relevant Standard,” Mr Dragar says. Another corrosion control method used on pipelines is cathodic protection (CP). This is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded "sacrificial metal" to act as the anode. The sacrificial metal then corrodes instead of the protected metal. “Where current is applied to a pipeline, it provides protection, but where the current leaves a pipe it causes corrosion,” adds Brian Martin, a consulting engineer specialising in CP systems. The shortest time I've seen for a hole to appear in a steel pipeline because of stray current interference, is six weeks.” According to Mr Martin, the effectiveness of a CP system of a pipeline is dependent on the quality of the coating applied to a pipe, the age of the pipe and to some extent the pipe diameter. “Up until the 1980s it was very difficult to get a good coating on a pipe large than 20 inches.” In Sydney, many pipelines are quite old and have poor coatings, whereas most modern (post-1980) non-urban, large diameter pipes have very good coatings. The thousands of kilometres of buried steel pipelines across Australia mostly have some form of cathodic protection associated with them. Older Impressed Current Cathodic Protection systems used to consist of a small number of high-capacity anode groundbeds spaced along the pipeline. Galanos said that the design of newer cathodic protection systems now incorporate larger numbers of smaller capacity systems located much closer to the pipeline. The main reason for this revolves around urban development and interference effects of foreign buried metallic structures. “The designs incorporate a great deal of redundancy because it has been found that adding lots of extra connections and test points when a pipeline is constructed is far cheaper than having to dig up sections of pipeline to add them at a later date,” Mr Dragar says. Town planners in the 1950s and '60s did not expect the rapid and extensive growth of the major Australian cities. “It is not just in the capital cities either,” says Mr Galanos. “The construction costs associated with effectively isolating the rail lines of new DC-powered Light Rail systems or installing stray current mitigation devices post construction can be in the order of millions of dollars. These costs include ongoing monitoring to ensure the stay current effects on nearby foreign buried metallic structures remain within acceptable limits." Mr Martin explains that there is a wealth of experience with the @all HYDRAULIC specialists: No Piston Drilling Necessary! NEW ABSOLUTE POSITION SENSOR TO MEASURE THE STRIKE OF HYDRAULIC & TELESCOPIC CYLINDERS! Measurement Systems: -Linear/Rotary Movement -Pressure -Temperature -Shock/Accereleration -Tilt/Angle 463 Mount Eden Road Mount Eden, Auckland 09 630 7871 WWW.MANDENO.CO.NZ EN248 www.engineeringnews.co.nz 27
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