The final treated product was tested The works included the blasting Lemonthyme for “cleanliness” before discharging and painting of the spiral casing in to the local river system. The at the station. Works in this area Penstock Internal Corrosion Coating Replacement treatment plant was designed to had to fit within a two-week remove Aromatic Hydrocarbons, window whilst the turbine was Lemonthyme Power Station is a areas of the penstock as the interior and quality considerations Chlorobenzene, Polychlorinated removed from the station for 51MW power station located on the was very slippery and the steeper contributed to this decision. Biphenyls and similar contaminants. refurbishment works. The exact in the central north sections (45°) were too dangerous The treatment plant proved so window dates were not known until An outage of the Lemonthyme Power west of Tasmania. to inspect. The inspection of these successful the treated water was a week before and were dependent Station was approved between areas revealed random areas of “cleaner” than the water in the on critical path activities for other Commissioned in 1969, the station is January and April 2008 with the existing stream. contractors in the station; pitted corrosion with some of the Settling ponds under construction supplied with water from Parangana works estimated to take 12 weeks. pitting having caused up to 4mm of . The storage is fed from the No treatment facilities existed within The penstock is in rugged steel loss. In late 2007 the tender for the works discharge of Rowallan and Fisher Tasmania to deal with the solid Tasmanian bush and out of was awarded to Lothway TBS Pty Power Stations and subsequently Analysis of the potential failure waste from this project. Lothway TBS site of the public and tourists. Ltd. Tenders were assessed on the then flows on to Cethana, Devil’s mechanisms of the penstock indicated subcontracted Tox Free Solutions This created issues for safety basis of proposed methodology, Gate and Paloona Power Stations. that further loss of thickness of the Limited to address this issue and at the site and even issues with safety, environment and proposed Water flow to the station is via a steel could result in failure of the the waste was transported to curious wildlife wanting to enter timeframes. Lothway TBS offered 6.5 km long tunnel and a 1.6 km long penstock as a result of negative Wedgefield, Port Hedland, Western the penstock. an innovative proposal that met all surface penstock with a diameter pressures that might occur during Australia, for incineration. safety, environmental and quality Although the prime aim of this varying between 2.9m and 3.81m. water hammer effects resulting requirements whilst providing value As soon as existing coatings work was to reinstate the corrosion from a station trip and sudden The station contributes for money and a timeframe of only were completely removed from protection for the penstock, it has stop to the flow of water. It was discreet sections of the penstock, been estimated that reduced head approximately three per cent of eight weeks. Upstream “flat” section of the penstock therefore determined that removal ’s annual revenue. dehumidification was put in place loss effects were achieved by the low of the existing internal coating and Throughout the project, SICC The station is placed within the and a final whip blast carried out. friction co-efficient characteristic replacement with a new corrosion Services provided technical advice of Interline 975 corrosion protection Mersey Forth chain of stations The new coating system was protection system was necessary to and inspection services as well as system. This has resulted in an that then contributes a further immediately applied. This consisted sustain the asset for the future. 24/7 supervision of the works on estimated benefit of $0.25M per eight per cent of revenue to the of a primer coat and one coat of behalf of, and in conjunction with, annum to Hydro Tasmania. Hydro business (Refer Figure 1). The An added benefit of a new coating Interline 975 from International Hydro Tasmania. ® ® Tasmania was very impressed with passage of water through the system was an expected efficiency Protective Coatings with a total dry all aspects of the Lothway TBS station, as opposed to by-passing gain in delivery of water to the Removal of the existing coal tar film thickness (dft) of 500 microns. work and International Protective the generator, is a key component of station due to reduced friction losses enamel and epoxy system was Application was predominantly ® Coatings’ support on this project. delivering maximum revenue from from the coating system. carried out with the use of Ultra High carried out by robotics providing run of river systems that do not have Water Pressure (UHWP) robotics. Nearly two years on there have been The existing coating was made consistent coating thickness and large storage reservoirs. Removal in such a manner resulted no issues identified with the works. Painting robot up of coal tar enamel and epoxy minimal OH&S issues. in the need to treat both solid and An inspection in 2002 identified the measuring over 6mm in thickness liquid waste. Coarse solids were The work was completed two days beginning of corrosion issues. The in some areas. Ultra high pressure removed directly from the penstock. ahead of schedule and over four coating was failing and warranted water-blasting was specified as Liquids were pumped to a purpose- weeks ahead of Hydro Tasmania’s replacement at the earliest planning the preferred methodology for made settling pond to remove original estimate. opportunity. A more detailed removal, mainly because of OH&S additional solids, then treated in Other challenges faced during this inspection inside the Lemonthyme issues related to removal of these a purpose-built onsite treatment project were: Penstock was conducted in February materials using more traditional grit plant, before emptying the treated 2005. This was limited to the flatter blasting methods. Environmental Lothway TBS was able to offer a Lemonthyme water in to storage tanks. Penstock shortened timeframe by running shifts 24/7; The site is located approximately one hour from the nearest township, Sheffield. Lothway transported staff to and from the site using a bus in order to minimise the likelihood of accidents resulting from fatigue at the end of shifts;

Examples of some of the more sever rust nodules On-site treatment plant Completed section of penstock with butterfly Figure 1: Schematic showing Lemonthyme in the Mersey-Forth Power Scheme created by failure of the corrosion system valve in background

24 Corrosion & Materials Vol 34 No 6 December 2009 25