COMMENT
A fresh coat can extend plant life
The need to extend the life of equipment calls for a strategic approach to coatings, says Dan Macdonald, managing director, Repair Protection & Maintenance
he cost of corrosion in the UK is around 4% of GDP per annum, but these are costs that can be cut when it is realised that not everything that is corroded necessarily needs replacing. In the current climate of financial constraint it is essential to preserve and extend the life of plant and equipment for as long as possible, putting off, or indeed negating, the need to find the heavy capital cost of replacements.
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An additional bonus is the fact that a longer warranty period can often be obtained for something that has been repaired and lined than the manufacturer will offer on brand new equipment. A typical manufacturer’s warranty will be two to three years at most, where coatings companies can offer up to 10 years, depending on the operational environment. It is no longer the case that a corroded tank, pipe or other equipment, needs to be replaced; even ones with severe corrosion pitting or actual holes. One way of achieving this is rebuilding corroded or damaged areas with appropriate repair compounds and lining the vessel to protect and extend its service life.
Anyone who has ever repaired a boat or car bodywork will be familiar with the basic principle. You use some suitable resin material and GRP to repair the hole and then use further GRP layers and other coatings, until the boat is not only water tight but also looks as good as new. For industrial applications the principle is the same; only the resin binder is specifically selected to suit the chemicals being handled.
These lining methods are a very effective alternative solution to replacement in terms of costs, time and environmental impact. For example, there is no necessity to dispose of contaminated equipment, to to dig anything up or knock anything down to deal with the problem. The use of repair compounds and linings can also enhance safety by allowing in-situ cold work with VOC free materials.
The same methodology can also be employed to extend the service life of new plant and equipment and older equipment can be updated to comply with new legislation.
Water storage tanks in buildings are, in many instances, put in place and the building constructed around them; some even form part of the structure. This means that to replace or renew them when they corrode or start to leak is difficult and, in some instances, impossible. The answer is to repair and, in some cases, even re-build the tank using a GRP laminate system, effectively forming a tank within a tank. If required the tank thus formed can then be lined with a Drinking Water Inspectorate (DWI) approved coating allowing it to be used for potable water. A typical example of this methodology was the repair and lining of six large water tanks, each 6.25m diameter by 4m high at Anglian Water’s Elsham water treatment works (WTW) which was completed earlier this year. Two of the tanks were holed due to corrosion pitting and the logistics and cost of replacing these tanks was considerable.
wwtonline.co.uk Before and after – coating gives new life to a corroded strainer
The manager in charge of this project remembered having a similar problem with DAF tanks at the Sladen Valley WTW back in 2002. The solution then was to grit blast the tanks and build a self-supporting GRP laminate tank within the existing tanks. Once formed the laminate tank was then lined with a Water Regulations Advisory Scheme/DWI approved two-pack, solvent-free epoxy coating. After repair the tanks were tested and sampled to prove the water quality.
On checking that these tanks were still operational a decade after the original repair, he had no hesitation in adopting the same repair method for Elsham. The repair proved very cost effective and, with little over a week to repair and line each tank, the time-frame for the project was also reduced.
The effective use of coatings can also be employed when a change of service conditions in a tank would be advantageous. For example, redundant diesel tanks can, through the use of coatings, change the service duty to a water tank. This effectively recycles the tank, reduces carbon footprint and saves on the cost of a new tank and removal of the old tank. Large fuel storage tanks can also have their life extended in a similar way. The bottom of the tank and walls, up to around 300mm above the floor, suffer from various forms of corrosion, mainly due to the water content in the fuel; the environmental fall-out along with the subsequent associated costs should a leak occur are immense. A cost effective and environmentally friendly solution is to line the floor with a suitable coating and, if required, reinforced it with a laminate system to strengthen the floor.
It is a wise precaution to implement a regular programme of inspections to monitor the condition of plant, tanks, pipework and equipment so that damage and wear and tear can be identified early and rectified before it causes a major problem, costly down-time and either replacement or expensive repairs.nnn
August 2013 Water & Wastewater Treatment 17
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