TPT November 2012

Blasting and coating

The advantages of galvanising THE tube and pipe industries are, like many sectors worldwide, constantly looking for more efficient, effective and commercially viable ways of operating. As a process, galvanising is incredibly flexible, long-lasting and environmentally friendly, and one which can be incorporated into a variety of projects, both large and small-scale. So, how does the process work, what is the technology behind it and what sorts of projects within the industry is the process being used on? immersed in water to cool it, or allowed to cool in air. When the steel is dipped into the molten zinc, a series of zinc-iron alloy layers are formed. The main thickness of the coating is created at this time, after which the metallurgical reaction slows down so even if the steel remains in the galvanising bath for a considerable time, it will not form an overly thick protective layer. Typically items will be dipped for four to five minutes, and when they are removed a layer of pure molten zinc will be taken out on top of the alloy. It is this that cools to show the bright, shiny appearance generally associated with newly galvanising products.

Hot dip galvanising is essentially the process of coating clean steel with a layer of molten zinc to protect the item from corrosion and provide a long- lasting, durable covering. Because it forms a series of zinc alloy layers with the iron in the steel it is more robust than other coatings that only bond chemically or mechanically; it also has the added advantage of fully coating the steel, inside and out. The galvanising process starts with cleaning the steel to prepare it for galvanising. Cleaning involves the complete removal of light grease, scale and dirt using a variety of techniques. Commonly, the steel product is dipped into an alkaline or acidic degreaser and then rinsed before being dipped in a hydrochloric acid rinse at room temperature. After cleaning the product is rinsed and then usually dipped in a flux solution, which is typically made up from zinc ammonium chloride held in a temperature range between 65°C and 80°C. This final stage removes the last traces of oxide from the surface and coats the product with a thin film of flux. After the steel has dried, it is dipped into the molten zinc which is around 450°C. Finally the work may be

The cattle market

petrochemical giant BP’s (Floating Production Storage and Offloading) FPSO PSVM scheme in waters off the west coast ofAfrica. The galvanised pipes were installed as part of a system used by the offshore industry to receive and process hydrocarbons, which then store oil until it can be offloaded onto a tanker or transported via pipelines. The FPSO PSVM project is aiming to tap into four oil fields off Angola with waters ranging from 1,500 to 2,500m deep. Galvanising the steel was essential in helping reduce the risk of rust and corrosion. A project closer to home has seen the Wedge Group galvanise 120 tons of steel tubes, spanning almost 19 miles, as part of the production of more than 300 animal pens at the North West Auctions cattle market in Cumbria, which officially opened in August. A series of 48mm- wide tubes were manufactured to put together all the fences and gates needed to produce 2.7m² pens, which were then galvanised to ensure long-termprotection against the highly corrosive environment.

Zinc is an essential mineral, which is needed to sustain life and is found in many places including rocks and soil, as well as plants, animals and the air that we breathe. It’s widely abundant and can be indefinitely recycled. It reacts with air to create a surface film that is insoluble to rainwater and acts as a barrier to completely prevent moisture and oxygen reaching the steel itself. Not only does Zinc lengthen the lifespan of steel, but it is energy-efficient throughout its production and whole lifecycle. The galvanising process uses resources considerately to ensure a relatively low environmental burden, and galvanised steel can easily be recycled with steel scrap or it can be removed, re- galvanised and then reused. The past twelvemonths alone has seen Wedge Group Galvanizing undertake a number of national and international projects of all shapes and sizes. One such project involved the galvanising of steel used to create a number of pipe flanges connecting pipelines carrying oil as part of

Wedge Group Galvanizing – UK Website: www.wedge-galv.co.uk

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N ovember 2012