Corrosion Protection & Coatings Repair. DN Issue 001

Transcription

1 DN Issue 001

2 Document Designation: Document Title: Language: Region: DN EN All Issue: Issue 001 Download the latest version of this document from this link: Or scan the QR code on the right. Disclaimer While all care has been taken to ensure that information contained in this document is true and correct at the time of publication, Mechatron reserves the right to make any changes without any notice. Copyright 2016 Mechatron ABEE. Reproduction, distribution, or public release of any information contained within this document is prohibited.

3 CONTENTS Document Information... 4 Scope... 4 Units Corrosion Protection... 5 Guidelines... 5 Mechatron Coating Specifications... 6 Structural Steel Components... 6 Continusly Galvanized Components (Purlins)... 6 Other Coatings... 6 ISO Standards On Hot Dip Galvanizing... 7 ISO 9223 Environment Corrosivity Categories... 7 ISO Corrosion Rates for Zinc and Steel... 8 Life to First Maintenance of Hot Dip Galvanized Steel Hot-Dip GalvanizeD Coatings Site Repair Repair Methods Zinc Metal Sprayed Coatings Zinc Rich Epoxy or Zinc Rich Paint... 10

4 Document Information Scope DOCUMENT INFORMATION SCOPE This document was written to help Mechatron s EPCs and clients understand how they can calculate the life expectancy of products against corrosion, until a maintenance is required to continue normal operation. Also there is a brief description of the repair procedures for zinc coatings in cases that this is deemed necessary. UNITS This document follows the The International System of Units. A coma (,) is used as a decimal mark. A period (.) is used as a thousand separator. In some points of the document, Imperial units are given in addition to S.I. units, in order to help readers understand the content easier. 4

5 Corrosion Protection Guidelines 1 CORROSION PROTECTION GUIDELINES To determine the lifespan of corrosion protection of a Mechatron product you have to follow 3 steps: Step 1 Determine the corrosivity category of the environment that the product is going to be installed in by using the data given in paragraph Step 2 Consult the data given in paragraph & 1.2.2, to find out what coating thicknesses are used throughout the product s components. Step 3 Go to the table in paragraph and use the data from the previous 2 steps to find out the expected life of the corrosion protection until the first maintenance is needed. Step 4 If the Life to First Maintenance that derives from the table in paragraph is not acceptable for a given project, the client can specify different coating thicknesses and designations by following the information given in paragraph

6 Corrosion Protection Mechatron Coating Specifications MECHATRON COATING SPECIFICATIONS All weather exposed steel components hot dip galvanized to protect against corrosion, following the methods below: STRUCTURAL STEEL COMPONENTS All weather exposed components made of steel (except the purlins), are hot-dip galvanized according to: EN ISO 1461:2009, with mean zinc coating thickness of 85 μm and minimum local zinc coating thickness of 75 μm. CONTINUSLY GALVANIZED COMPONENTS (PURLINS) All purlins are Z275 (G90 for North America) continuously hot-dip galvanized according to EN 10346:2009. Nominal mass of coating is 275 g/m 2 including both surfaces (see table below). Coating designation Minimum total coating mass, both surfaces Equivalent coating thickness, single side Triple Spot Test [TST] Single Spot Test [SST] Triple Spot Test [TST] Z g/m g/m 2 19,3 μm (0, 76 mils) G90 0,90 oz/ft 2 (equiv. to: g/m 2 ) 0,80 oz/ft 2 (equiv. to: 244,12 g/m 2 ) 0,76 mils (19,3 μm) OTHER COATINGS For projects on very hostile environments products with higher coatings can be supplied. COATINGS FOR CONTINUSLY GALVANIZED PRODUCTS AS PER ASTM-A653 & EN ASTM A653 Designation International EN Typical produced coating weight both sides oz/ft 2 Typical produced coating weight both sides g/m 2 Typical produced coating thickness per side mils G30 Z90 0, ,34 9 G40 Z120 0, ,40 10 G60 Z180 0, ,55 14 G90 Z275 0, ,81 20 G115 Z350 1, ,03 26 G140 Z450 1, ,26 32 G165 Z500 1, ,48 38 G185 Z550 1, ,66 42 G210 Z600 2, ,89 48 G235 Z700 2, ,13 54 G300 Z900 3, ,73 69 G360 Z1100 3, ,28 83 Typical produced coating thickness per side μm COATINGS FOR HOT-DIP GALVANIZED PRODUCTS AS PER ASTM-A123 & EN-ISO-1461 Any thickness of hot dip galvanized coating can be achieved according to clients specifications. 6

7 Corrosion Protection ISO Standards On Hot Dip Galvanizing ISO STANDARDS ON HOT DIP GALVANIZING ISO 9223 ENVIRONMENT CORROSIVITY CATEGORIES Corrosivity category Corrosivity Indoor Typical environments Outdoor C1 Very Low Heated spaces with low relative humidity and insignificant pollution, e.g. offices, schools, museums Dry or cold zone, atmospheric environment with very low pollution and time of wetness, e.g. certain deserts, Central Arctic/Antarctica C2 Low Unheated spaces with varying temperature and relative humidity. Low frequency of condensation and low pollution, e.g. storage, sport halls Temperate zone, atmospheric environment with low pollution (SO2 < 5 μg/m 3 ), e.g. rural areas, small towns Dry or cold zone, atmospheric environment with short time of wetness, e.g. deserts, subarctic areas C3 Medium Spaces with moderate frequency of condensation and moderate pollution from production process, e.g. food-processing plants, laundries, breweries, dairies Temperate zone, atmospheric environment with medium pollution (SO2: 5 μg/m3 to 30 μg/m3) or some effect of chlorides, e.g. urban areas, coastal areas with low deposition of chlorides Subtropical and tropical zone, atmosphere with low pollution C4 High Spaces with high frequency of condensation and high pollution from production process, e.g. industrial processing plants, swimming pools Temperate zone, atmospheric environment with high pollution: 30 μg/m 3 < SO2 < 90 μg/m 3 or substantial effect of chlorides, e.g. polluted urban areas, industrial areas, coastal areas without spray of salt water or, exposure to strong effect of de-icing salts Subtropical and tropical zone, atmosphere with medium pollution C5 Very High Spaces with very high frequency of condensation and/or with high pollution from production process, e.g. mines, caverns for industrial purposes, unventilated sheds in subtropical and tropical zones Temperate and subtropical zone, atmospheric environment with very high pollution 90 μg/ m 3 < SO2 < 250 μg/m 3 and/or significant effect of chlorides, e.g. industrial areas, coastal areas, sheltered positions on coastline CX Extreme Spaces with almost permanent condensation or extensive periods of exposure to extreme humidity effects and/or with high pollution from production process, e.g. unventilated sheds in humid tropical zones with penetration of outdoor pollution including airborne chlorides and corrosion-stimulating particulate matter Subtropical and tropical zone (very high time of wetness), atmospheric environment with very high SO2 pollution (higher than 250 μg/ m 3 ) including accompanying and production factors and/or strong effect of chlorides, e.g. extreme industrial areas, coastal and offshore areas, occasional contact with salt spray Deposition of chlorides in coastal areas is strongly dependent on the variables influencing the transport inland of sea salt, such as wind direction, wind velocity, local topography, wind sheltering islands outside the coast, distance of the site from the sea, etc. Extreme effect by chlorides, which is typical of marine splash or heavy salt spray, is outside of the scope of this Chart. Corrosivity classification of specific service atmospheres, e.g. in chemical industries, is outside of the scope of this Chart. Surfaces that are not sheltered or rain-washed in marine atmospheric environments where chlorides are deposited can experience a higher corrosivity category due to the presence of hygroscopic salts. In environments with expected CX category, it is recommended that the atmospheric corrosivity classification from one-year corrosion losses be determined. One-year exposure tests should start in the spring or autumn. In climates with marked seasonal differences, a starting time in the most aggressive period is recommended. The concentration of sulfur dioxide (SO2) should be determined during at least one year and is expressed as the annual average. However, SO2 is so low in most environments that it is generally considered that It can be ignored, other than for specific industrial applications or extreme traffic examples. Coastal areas are normally defined as between 50 m to 1 Km inland from sheltered seas and between 1 Km and Km from surf beaches depending upon prevailing winds and topography. 7

8 Corrosion Protection ISO Standards On Hot Dip Galvanizing ISO CORROSION RATES FOR ZINC AND STEEL Corrosivity category C1 C2 C3 C4 C5 CX Comparative corrosion rates for steel and zinc from ISO 9223 r corr Unit Carbon Steel Zinc g/(m 2 a) r corr 10 r corr 0,7 μm/a r corr 1,3 r corr 0,1 g/(m 2 a) 10 < r corr 200 0,7 < r corr 5 μm/a 1,3 < r corr 25 0,1 < r corr 0,7 g/(m 2 a) 200 < r corr < r corr 15 μm/a 25 < r corr 50 0,7 < r corr 2,1 g/(m 2 a) 400 < r corr < r corr 30 μm/a 50 < r corr 80 2,1 < r corr 4,2 g/(m 2 a) 650 < r corr < r corr 60 μm/a 80 < r corr 200 4,2 < r corr 8,4 g/(m 2 a) 1500 < r corr < r corr 180 μm/a 200 < r corr 700 8,4 < r corr 25 The classification criterion is based on the methods of determination of corrosion rates of standard specimens for the evaluation of corrosivity (see ISO 9226). The corrosion rates, expressed in grams per square metre per year [g/(m 2 a)], are recalculated in micrometres per year (μm/a) and rounded. Corrosion rates in category CX are considered extreme. Corrosivity category CX refers to specific marine and marine/industrial environments. Specific calculation models, guiding corrosion values and additional information on long-term corrosion behaviour, are given in ISO

9 Corrosion Protection ISO Standards On Hot Dip Galvanizing LIFE TO FIRST MAINTENANCE OF HOT DIP GALVANIZED STEEL The LFM range for a particular hot dip galvanizing coating thickness and each corrosivity zone can be read from the chart. For example, the LFM range for a hot dip galvanized article with an 85 μm thickness and located in the C4 (High) corrosivity zone is 20 to 40 years. 50 C1 C2 C3 C4 Coating life to first maintenance (years) µm 55 µm 70 µm 85 µm 125 µm C5 CX Coating thickness (μm) 9

10 Hot-Dip GalvanizeD Coatings Site Repair Repair Methods 2 HOT-DIP GALVANIZED COATINGS SITE REPAIR The zinc coating of hot-dip galvanized steel is difficult to damage, and field fabrication that requires removal of the coating should be minimized as much as possible. However, sometimes due to improper handling or abrasion after years in service, small voids are found in the coating. To maintain uniform barrier and cathodic protection and ensure longevity, it is best practice to touch-up and repair the coating. When it comes to touching-up galvanized steel in the field, there is no limitation to the size that can be repaired. The preferred method of repair is by zinc metal spraying. Due to the remoteness of most sites, however, and the unavailability of metal spraying equipment, repairs by zinc rich epoxy or zinc rich paint have to date generally been more popular. Should excessive amounts of grease or oil be present at the affected area, it shall be removed by means of an approved solvent. As far as possible, all residues are to be thoroughly removed by washing with clean water. REPAIR METHODS Any repairs made to galvanized products must follow the requirements of ISO 1461 or ASTM A780, which define the acceptable materials and the required procedures. Materials used to repair hot-dip galvanized products include zinc-based solder, zinc-rich paint, and zinc spray metallizing. ZINC METAL SPRAYED COATINGS The damaged area is to be lightly blasted using preferably a pencil blasting nozzle or the surrounding coating should be masked in order to limit damage. A zinc metal sprayed coating is then applied to the abrasively blasted surface to a thickness at least 30 μm greater than the minimum specified zinc coating thickness, or equal to the surrounding coating thickness, whichever is the greater. The repaired area is then wire brushed (preferably stainless steel) to remove loosely adhering over sprayed zinc. Wire brushing provides the added benefit of sealing the pores that may be present in the sprayed coating. ZINC RICH EPOXY OR ZINC RICH PAINT The defective area shall be blasted as above or abraded with abrasive paper (roughness 80 grit). All dust and debris must be completely removed. In the event of moisture being present, all surfaces are to be properly dried. A zinc rich paint or epoxy containing not less than 90% of zinc in the dry film (60% by volume), should be applied to a thickness, 30 μm greater than the minimum specified for the galvanized coating or equal to that of the surrounding galvanized coating, whichever is greater. The paint coating should overlap the surrounding zinc by at least 25 mm. The preferred product is a two or three component zinc rich epoxy. Single pack zinc rich paints are good materials and can easily be applied. They, however, require several coats to achieve a reasonable repair. Multiple coats will also necessitate longer drying times between coats. 10