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Corus Construction & Industrial

A corrosion protection guideFor steelwork exposed to atmospheric environmentsCorus Construction & IndustrialSpecifiers are advised to seek specialist advice for the protection of steelwork used in road or rail bridges, buriedin the ground or immersed in ) Environment Categories C3/C4/C5 above are based on those given in BS EN ISO 12944 and ISO ) There may be times or locations where the corrosivity category is higher than expected. For example, lighting columns that may be located in environment category C3 may be subjected to local conditions that may be equivalent to category C5M when salt is spread on the roads and pavements during of standardsBS EN ISO 12944: 1998 Paints and varnishes corrosion protection of steel structures by protective paint EN ISO 14713: 1999 protection against corrosion of iron and steel in structures Zinc and aluminium coatings EN ISO 1461: 1999 Hot dip galvanized coatings on fabricated iron and steel articles Specifications and test EN 10240: 1998 Coatings for steel tubes: Specification for hot dip galvanized 4628-3: 1982 Paints and varnishes Evaluation of degradation of paint coatings Des

A corrosion protection guide For steelwork exposed to atmospheric environments Corus Construction & Industrial

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1 A corrosion protection guideFor steelwork exposed to atmospheric environmentsCorus Construction & IndustrialSpecifiers are advised to seek specialist advice for the protection of steelwork used in road or rail bridges, buriedin the ground or immersed in ) Environment Categories C3/C4/C5 above are based on those given in BS EN ISO 12944 and ISO ) There may be times or locations where the corrosivity category is higher than expected. For example, lighting columns that may be located in environment category C3 may be subjected to local conditions that may be equivalent to category C5M when salt is spread on the roads and pavements during of standardsBS EN ISO 12944: 1998 Paints and varnishes corrosion protection of steel structures by protective paint EN ISO 14713: 1999 protection against corrosion of iron and steel in structures Zinc and aluminium coatings EN ISO 1461: 1999 Hot dip galvanized coatings on fabricated iron and steel articles Specifications and test EN 10240: 1998 Coatings for steel tubes: Specification for hot dip galvanized 4628-3.

2 1982 Paints and varnishes Evaluation of degradation of paint coatings Designation of intensity, quantity and size of common types of defect Part 3: Designation of degree of 7079: Part A1 Preparation of steel substrates before application of paints and related products Visual assessment of surface(ISO 8501-1)cleanliness Part 1: Rust grades and preparation grades of uncoated steel substrates and of steel substrates after overall removal of previous 9223: 1992 corrosion of metals and alloys Corrosivity of atmospheres EN 22063: 1994 Metallic and other inorganic coatings Thermal spraying Zinc, aluminium and their to table (overleaf)1. Coating system durability given in the table is based on practical experience. It is the expected life, in years, before first major maintenance (See MAINTENANCE below).

3 This is taken as degradation level Ri3 from ISO 4628 Part 3 (1% of surface area rusted). It should be noted that this does not imply a guarantee of life The durability of galvanized steelwork is derived from the figures in BS EN ISO Where painting of galvanized steelwork is required for aesthetic or other reasons; suitable systems from BS EN ISO 12944 may be The thickness values given for primers are the total thickness used and may include a pre-fabrication primer. For example 80 m can be in one coat or as 20 m pre-fabrication primer plus 60 m post-fabrication Costs given here are for guidance only. There will be considerable variation that may typically be +/- 50% for a variety of reasons. Quotations should be obtained before making the final selection of the protective treatment.

4 The indicative costs given are for 2004. They include estimates for material and labour but exclude taxes. The average surface area/tonne is assumed to be 25m2 It should be noted that the colour range of micaceous iron oxide (MIO) is In some countries, the use of sprayed zinc or alloys of zinc and aluminium may be preferred (BS EN 22063).8. The zinc rich primer applied at 80 m would increase the durability of the system by approximately 5 years and increase the cost by For steelwork 6mm thick or greater, the minimum average coating thickness is 85 protection guide for steelwork exposed toatmospheric environmentsExterior environmentsEnvironmentcategory (a) corrosion riskTypical steelwork location (b)C3 MediumMost rural and urban areas with low sulphur dioxide, acid, alkali and salt and Industrial atmospheres with moderate sulphur dioxide pollution and/or coastal areas with low highIndustrial areas with high humidity and aggressive and offshore areas with high corrosion protection guideFor steelwork exposed to atmospheric environmentsGeneral notesThis document gives details of corrosion protectionsystems for steelwork exposed to rate at which corrosion occurs largely depends onthe period of wetness.

5 Steelwork should, whereverpossible, be designed to shed rainwater andcondensation. Any details that collect or retain watershould be redesigned or incorporate adequatedrainage. Detailed advice may be obtained from BS EN ISO 12944 or BS EN ISO thicknessThe film thicknesses given in the table are nominal dryfilm values ( m = micron = ). Coatingthicknesses have been chosen in accordance with theprinciples of BS EN ISO is assumed that the quality of work and any repairs willbe to an acceptable professional standard and inaccordance with the coating preparationCorrect surface preparation is essential for satisfactoryperformance of coatings. Thorough removal of grease,dirt, rust and loose paint must be carried out beforeapplication of all systemsSteelwork fabricators process routes vary.

6 Thesequence may be a) Blast Fabricate Prime or b)Blast Prime Fabricate or c) Fabricate Blast choice of sequence depends on the facilitiesavailable to the fabricator or applicator, and the size ofthe structural members. A prefabrication primer may ormay not be needed, depending on the sequencechosen. Under certain circumstances, some of the coatsgiven in treatments as site-applied may be applied inthe shop if preferred. Similarly, some treatments givenas shop-applied may be applied on componentsThe weathering of zinc/iron alloy layers of thegalvanized coating can give the appearance ofsuperficial rusting many years before the durability limithas been reached. Where galvanized steelwork isaffected by white rust (wet storage stain) this shouldbe removed with a stiff brush and washed with waterbefore subsequent pre-treatment and C3 System equivalent BS EN ISO 12944 Surface preparation(BS 7079.

7 Part A1)Anticipated durability ofthe coating system inyears (notes 1 & 2) forenvironment categoryC340202030151515(C5I)/20(C5M)101 0 Blast clean to Sa 21 2 Blast clean to Sa 21 2 Hot dip galvanize toBS EN ISO 146185 m80 m100 mNone(note 3)Recoatable polyurethanefinishZinc phosphate epoxyprimer (note 4)High build epoxy MIO100 m100 mHigh solid epoxy zincphosphate primerHigh solid aliphaticpolyurethane finishC4C5 Coatings(note 4)ShopappliedCoatingsSiteappliedApproxim ate cost in /m2(note 5)60 mNoneA corrosion protection guide3 For steelwork exposed to atmospheric environmentsGalvanized or sherardized fasteners should be usedwith galvanized protectionCorrosion protection and fire protection are sometimesrequired together. If such an occasion arises, adviceshould be sought from the manufacturer of the fireprotection encasementStructural steel fully encased in concrete is not normallycoated.

8 It is suggested that the provisions of Eurocode 2and/or Eurocode 4 should be followed. The concreteshould have the correct composition and compactionwith a depth of cover appropriate for the guidance can be found in BS 8110, Part 1. As analternative to concrete encasement, steelwork incorrosive environments below ground level, can beprotected by the application of a high build epoxycoating to 450 m after suitable blast cleaning. Wheresteel is partially embedded in concrete in environmentsC3, C4 and C5, at column bases, extra protectionshould be provided at the steel/concrete junction bymeans of an alkali resistant paint at the junction or analkali resistant mastic at the issuesThe handling and application of all protective coatingsmust be carried out in accordance with themanufacturer's recommendations and comply with therequirements of relevant environmental and transportCare in handling to minimise mechanical damage isessential to the performance of the protective responsibility for the repair of damaged coatingsshould be clearly storageIncorrect storage on site before erection can acceleratethe deterioration of coatings.

9 Steelwork should besupported off the ground with items separated bywooden battens allowing free circulation of air. Avoid ponding (retention of standing water) by laying downsteelwork to ensure adequate sectionsIt is unnecessary to coat the interior of sealed hollow first major maintenance is recommended when thelevel of coating degradation reaches Ri3 as illustrated inISO 4628 Part 3 (1% of surface area rusted).Environmentcategory C4 Environmentcategory clean to Sa 21 240 m100 mHigh build epoxy MIO(note 6)Zinc rich epoxy primer High build epoxy MIO100 clean to Sa 21 240 m200 mHigh solid aliphaticpolyurethane finishZinc rich epoxy primer(note 8)High build epoxy MIO(one or two coats)80 +30+20+ 40 m100 mRecoatable polyurethanefinishHot-dip galvanize to BS EN ISO 1461 (note 9)Mordant washEpoxy primer High build epoxy MIO60 +20-2515 Blast clean to Sa 3150 m50 m100 mRecoatable polyurethanefinishSprayed aluminium to BS EN 22063 (note 7).

10 Zinc phosphate epoxy sealer coatHigh build epoxy MIO60 mA corrosion protection guide4 For steelwork exposed to atmospheric environmentsSome examples of detailing to minimise corrosionDetails should be designed to enhance durability by avoiding water entrapped dust and waterPay particularattention tocolumn basesDirt collectionSealing plateDrainage breakPrevention of retention ofwater and dirt at junctionplates by means of breaks Encourage air movementAvoid opencrevicesOther sources of adviceThe British ConstructionalSteelwork Association Ltd4 Whitehall Court Westminster London SW1A 2 EST 0207 839 8566F 0207 976 1634 Paint Research AssociationWaldegrave RoadTeddingtonMiddlesex TW11 8 LDT 0208 614 4800F 0208 943 4705 Galvanizers AssociationWren s Court 56 Victoria Road Sutton Coldfield West Midlands B72 1 SYT 0121 355 8838F 0121 355 8727 BestBadA corrosion protection guide5 For steelwork exposed to atmospheric environmentsExterior steelwork surface protectionThis document is intended toprovide guidance to engineers andarchitects concerned with thedesign of new structures.


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