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TECHNICAL INFORMATION DURAGAL EASY PAINTING & CORROSION PROTECTION GUIDE TECHN

TECHNICAL INFORMATION DURAGAL EASY PAINTING & CORROSION PROTECTION GUIDE TECHNICAL INFORMATION DuraGal® Easy Painting & Corrosion Protection Guide February 2001 Page 1 I N D E X PAGE Introduction 2 Environments Atmospheric classifications 3 Warnings About Especially Harsh Corrosion Conditions General Warnings 5 Salt, acid rain, farming, animal husbandry & other corrosion causes 5 Special precautions 5 Salt spray contamination 5 Animal or bird urine or faeces 6 Soot from burning sugar cane 6 If regularly dowsed with highly mineralised water 6 Columns, stumps, posts, etc in buried in concrete or in contact 6 with soils Chemical attack 7 The Corrosion Life of DuraGal Corrosion life of unpainted DuraGal 7 The corrosion life of painted DuraGal 7 Zinc coating comparison 8 Protection of the bore of DuraGal hollow sections 8 White Rust or Zinc Storage Stain Avoiding white rust 9 Preventative actions 9 Remedial treatment 10 Warning to powder-coaters 10 Painting Hints Surface preparation 11 Paint preparation 11 Painting conditions 11 Paint application 11 Quick drying finishes 12 Recommended Paint Systems Corrosion protection for DuraGal - powder coating 12 Painting fabrications welded from DuraGal with black steel attachments 12 Protection of bolts and bolt holes 13 Corrosion protection for DuraGal - design tables Table 1 - Protection for atmospheric classifications up to 14 and including AS/NZS 2312 tropical Table 2 - Protection for atmospheric classifications up to 15 and including AS/NZS 2312 marine Table 3 - Point of sale decoration for factory manufactured items 16 - Protection for dry mild internal environments in buildings Table 4 - Protection for wet internal environments in buildings 16 - Protection for harsh wet internal environments in buildings Corrosion protection for DuraGal - substitution tables. 17 to 21 Coating Systems – Paint Manufacturers nominated systems for DuraGal. 22 to 27 DuraGal® Easy Painting & Corrosion Protection Guide February 2001 Page 2 INTRODUCTION Cost Effective High Tensile Steel Products with a Fully Prepared Surface DuraGal steel hollow sections have been developed to provide cost effective corrosion resistance, as well as a smooth, easy to use surface finish. The advantages of the DuraGal prepared surface are now available in a full range of DuraGal cold- formed open profiles - angles, channels and flats. Extending the DuraGal Family of Products®. Architecturally Decorative Finish which is Kind to the Environment The steel surface, prepared in a closely controlled factory environment, eliminates or significantly reduces the need for messy open air blasting, chemical, hand or power tool cleaning and its effect on the environment. DuraGal sections are mechanically cleaned to AS1627.4 Class 3 and then chemically cleaned prior to hot dip galvanising. A zinc coating weight of 100gms/m2 (14.3 microns) is applied. A surface conversion coating is then applied to help prepare the surface for later painting and to assist prevent white rust during transport and storage. Then, in the case of equal angles (greater than 50 x 50), channels and flats, a clear barrier polymer coat is applied. Cost Effective The most cost effective way to use DuraGal products is unpainted, touching up any welds. The Table on page 7, called “Corrosion life of Unpainted DuraGal in AS/NZS 2312 Atmospheric Environments”, indicates which combinations of environment and expected life to first maintenance that unpainted DuraGal can cover. However, if painting is required the result is an even better surface protection. By teaming the hot dip zinc coating with paint a synergistic effect occurs, ie the corrosion life of the duplex coating system is higher than the sum of the corrosion lives of the zinc and the paint coatings used separately. Research has shown that the increase can be from 1.5 to 2.3 times the sum of the lives of the zinc coating and the paint system, used separately. When superior corrosion life before first maintenance is required, the DuraGal hot dip galvanized coating will eliminate or considerably reduce the cost of surface preparation and may allow a more cost effective paint coating system to be used, reducing the cost of your project. The total cost of a product fabricated from a DuraGal profile or hollow section can be considerably less than that of other steel shapes. There can be savings in both the cost of steel and the cost of applying the corrosion resistant coatings. The high tensile DuraGal shapes and hollow sections and their structural advantages can save steel and often dollars. About This Guide This guide is designed to cover, in a practical and concise form, paint systems for a wide range of environments, performance levels, pre-treatments and application methods. On pages 22 to 27 of this guide you will find the recommended coating systems from several leading coatings manufacturers. These coatings manufacturers have carried out their own evaluation for the DuraGal Family of Products® and the exposure categories listed within AS/NZS 2312:1994. For further information on the coatings listed, OneSteel recommends you contact the coatings manufacturer directly to discuss the details of your application, and obtain detailed data sheets on surface preparation, application and safe use of their products. OneSteel Direct can assist you by providing the nearest location and contact details for the nominated coatings manufacturers listed in this guide. Freecall: 1800 065 415 Freefax: 1800 800 744 e-mail: onesteeldirect@onesteel.com DuraGal® Easy Painting & Corrosion Protection Guide February 2001 Page 3 ENVIRONMENTS Atmospheric Environments General The following classifies atmospheric zones in Australia and New Zealand, which affect the corrosion of steel and the life of a coating system. This information was taken from Section 2 of AS/NZS 2312:1994 (with some additions) and is included in this publication with the permission of Standards Australia. When selecting an appropriate protective coating system, the overall atmospheric conditions in the location of the intended structure require consideration. A structure situated in an aggressive environment will require a much higher standard of corrosion protection than one in a benign environment. The environment can affect both the steel and the paint system. Of prime importance is the effect the environment has on the corrosion of steel. The effect the environment has on the life of the paint system is also important. It should be appreciated that corrosive environments described do not necessarily affect coatings in the same way as they affect bare steel. Environments that would not be considered to be particularly corrosive to steel, such as hot dry climates with a high amount of ultraviolet (UV) radiation, can cause early breakdown of some coatings. Tropical environments, with high humidity, rainfall, and which promote mould and fungal growth, are far more aggressive to organic coatings than the corrosion rate would suggest. Furthermore, the colour of the paint may influence its performance in some environments. In addition to climatic effects, the local environment effects (or microclimate) produced by the erection of a structure or installation of equipment need to be taken into account. Such on-site factors require additional consideration because a mildly corrosive atmosphere can be converted into an aggressive environment by microclimatic effects. A significant acceleration of corrosion rate can occur in the following circumstances:- (a) At locations where the metal surface remains damp for an extended period, such as where surfaces are not freely drained or are shaded from sunlight. (b) On unwashed surfaces, ie surfaces exposed to atmospheric contaminants, notably coastal salts, but protected from cleansing rain. (c) Where the surface is in contact with animal urine or faeces, prolonged intimate contact with very slightly contaminated hay or straw will rapidly remove the zinc coating and initiate rusting. Other microclimatic effects which may accelerate the corrosion of the substrate or the deterioration of its protective coating include acidic or alkaline fallout, industrial chemicals and solvents, airborne fertilisers and chemicals, prevailing winds which transport contamination, hot or cold surfaces and surfaces exposed to abrasion and impact. These effects can outweigh those of the macroclimatic zones described below. Microclimatic effects can make it very difficult, if not impossible, to predict accurately the aggressiveness of a given environment and a certain amount of educated judgement is required to assess its influence on the coating life. Atmospheric Classifications (a) Mild A mild environment will corrode mild steel at a rate of up to 10 microns per year and includes all areas remote from the coast, industrial activity and the tropics. Sparsely settled regions such as outback Australia are typical examples, but the category also includes rural communities other than those on the coast. The only areas in New Zealand in this category are sheltered inland areas. Corrosion protection required for this category is minimal. DuraGal® Easy Painting & Corrosion Protection Guide February 2001 Page 4 (b) Moderate A moderate environment will cause a first year corrosion rate of mild steel of 10 microns to 25 microns and includes areas with light industrial pollution or very light marine influence, or both. Typical areas are suburbs of cities on sheltered bays such as Melbourne, Adelaide and Hobart (except those areas near the coast) and most inland cities. Most of New Zealand, other than sheltered inland areas and areas near the coast, is in this uploads/Geographie/ painting-guide.pdf