Paint 4007-Tools for Maintenance Management

/13

STEEL PROTECTION

4007 Tools for maintenance management

SYSTEM

a thirteen page issue September 2005 revision of July 2005

GENERAL ASPECTS

A maintenance specification is more complex than a coating specification for a new fabrication. In this section a systematic approach is presented for checking objects which are due for maintenance painting in order to see if special measures have to be taken to extend the service life of the object to be protected by the maintenance coating system – NOTE FOR METALLIC SUBSTRATES

Steel Mill scale, corrosion, pitting corrosion. Cast iron Surface irregularities, porosity, corrosion. Corten steel Surface corrosion, very hard. Stainless steel Contact corrosion, smooth surface, chlorine/chloride contamination. Non ferrous metals Zinc, copper, aluminium, lead, contact corrosion, corrosion products. Zinc sprayed steel Surface irregularities, porosity, zinc salts, corrosion. Hot dipped galvanised steel Smooth surface, zinc salts, corrosion. Coil galvanised plate Smooth surface, zinc salts, corrosion. (Sendzimir) Aluminium Anodised, aluminium salts, pitting corrosion, contact corrosion. Aluminium sprayed steel Surface irregularities, porosity, aluminium salts. – NOTE FOR STRUCTURAL DETAILS

Weld spatters, rough welds, These cannot be protected properly and must be ground and/or tack (skip) welds, doublings, repaired by welding. intermittent welding Open connections, bolts and Moisture and dirt collects on these spots. nuts, crevices, sharp edges, Sharp edges must be rounded by grinding. wrong inclination See also “details prone to corrosion attack”. Combination of different Avoid contact corrosion by insulating properly. metals Inaccessable places Seal with caulking compounds.

/13

STEEL PROTECTION


SYSTEM

September 2005 – NOTE FOR ORIGINAL COATING SYSTEMS For each maintenance specification the compatibility of the maintenance paint with the existing paint system should be given or checked by a test patch. Main paint defects are corrosion, checking and cracking, blistering and detachment. Causes for paint defects should be detected, especially when the paint system did not perform well. See also “Paint Defects”. – NOTE FOR PHYSICAL AND/OR CHEMICAL ATTACK Extreme temperature changes, erosion, direct sunlight, UV radiation, rain, abrasion, humidity, moisture, chemicals, aggressive fumes, contact Corrosion, cathodic protection From practice it is known that in case of an early failure a wrong paint system was applied. If this has happened, the exposure conditions should be defined again another paint system should be considered Dry heat resistance of generic coating types

Continuous heat Intermittent heat (<5% of the time, max 24 hrs) bitumen 60°C (140°F) 60°C (140°F) chlorinated rubber 60°C (140°F) 75°C (165°F) vinyl 60°C (140°F) 75°C (165°F) alkyd 80°C (175°F) 100°C (210°F) tar epoxy* 120°C (250°F) 120°C (250°F) polyurethane 120°C (250°F) 120°C (250°F) epoxy, medium solids** 120°C (250°F) 150°C (300°F) epoxy, high solids 80°C (175°F) 90-100°C (194-210°F) epoxy, solvent free 80°C (175°F) 90-100°C (194-210°F) epoxy, phenolics 150°C (300°F) 150°C (300°F) zinc epoxy 180°C (355°F) 200°C (390°F) zinc silicate 400°C (750°F) 400°C (750°F) * Valid for SigmaCover 300 ** Discoloration at higher temperatures can occur

– NOTE FOR SURFACE PREPARATION

The methods for surface preparation in maintenance painting are often limited because interference with other works has to be avoided as well as damage to machines and equipment. Nevertheless when the cause of paint defects was related to poor surface preparation, this fault should not be repeated.

/13

STEEL PROTECTION


SYSTEM

September 2005 Full attention should be paid to the following points:

– Removal of weld spatters by power tool chiseling and grinding. – Structural repair by welding. – Pitting to be cleaned in depth and filled. – Sharp edges to be rounded by grinding preferably to a radius of 2 to 3 mm. – Smooth surfaces should be roughened, polished surfaces should be avoided. – Measurements to be taken to avoid contact (galvanic) corrosion by using proper sealing and insulation materials. – Removal of local rust by wire brushing and/or power tool disc cleaning. – Removal of rust and other corrosion products like zinc and aluminium salts is done by scrapers, blast cleaning (wet, dry, vacuum), power tool disc cleaning or scotch brite cleaning. – Contamination should be removed with detergents and/or high pressure fresh water cleaning. Solvent cleaning should be used only when this is unavoidable. – Old defective paint coats should be removed if the adhesion or the intercoat adhesion is insufficient. The edges of old intact paint coats should be feathered. – Old intact paint coats should be sanded lightly to achieve good adhesion. – SPECIFIC REMEDIAL ACTIONS

– CHALKING. A (high pressure) wash with solution of detergent and water, followed by thorough rinsing with fresh water will remedy chalking. – MILDEW. Remove mildew with proper material or by scrubbing with solution of one part of household bleach per three parts of water, followed by thorough rinsing with fresh water. – FLAKING and PEELING. Depending upon severity of atmospheric exposure and extent of flaking and peeling, minimum surface preparation is light blast cleaning, high pressure water cleaning, water abrasive blast cleaning, or power tool cleaning to remove all loosely adhering paint. – HARD, GLOSSY or TOUGH SURFACES. To provide satisfactory adhesion, the surface must be roughened by hand or power tool, or by wet or dry abrasive blasting. – BLEEDING. The surface should be sealed with a special coating (sealer). – UPGRADING of existing coating systems. Due to strong solvents (swelling) upgrading usually cannot be accomplished by direct application of high performance solvent based coatings. Recommended tiecoats should be applied first. Some water borne epoxies may be applied directly to the existing coating system. – BLISTERING or RUSTING. Minor blistering and/or rusting should be removed by power tool cleaning, high pressure water cleaning or spot blast cleaning. Where blistering and rusting is excessive, it is advised that the existing coating should be completely removed. – NOTE FOR PAINT APPLICATION

– Spraying of paint is often limited because interference with other works has to be avoided. So maintenance paints should be also fit for either roller or brush application. Very complex structures should be painted by brush or roller instead of by spraygun to avoid overspray, dry spray and extreme paint losses. – For brush or roller applied paints the specified dry film thickness should be reached for which extra coats might be needed. Sharp edges and complex structures should be stripe coated with each coat of the system. – The preceding (build) coat should be of a colour which allows the finishing coat to give good coverage.

/13

STEEL PROTECTION


SYSTEM

September 2005 – PAINT APPLICATION CONSIDERATIONS

– CONTAMINATION. The possibility of contamination of the substrate and the coating during application and curing or drying will influence the selection and future performance of the specific coating. – APPLICATION CONDITIONS. Specific information regarding temperature limitations is given in the product data sheets. A low temperature may inhibit curing while a high temperature may cause solvent popping and skin drying. A high wind velocity results in excessive paint consumption, dry spray and skin drying. – HUMIDITY. Best results for most coatings are obtained at a relative humidity, below 85%. The substrate temperature should be at least 3°C above dew point. – SOLVENT AND THINNER SELECTION. Follow the recommendations given in the product data sheets. – EXCESSIVE ZINC SALTS. Zinc salts may be removed by light blast cleaning, followed by fresh water rinsing to remove dust. High pressure water cleaning may be suitable as well as powertool cleaning using scotch brite. – CONTAMINATION. Suitable solvents or emulsifying agents should be used to remove surface or absorbed greasy contaminants.

/13

STEEL PROTECTION


SYSTEM

September 2005

SYMPTOM CORRECTION/ SURFACE IDENTIFICATION CONSEQUENCE PREPARATION

Aluminium Dull, greyish, smooth Insufficient adhesion Degrease, (disc)sand or soft surface. of coating. sweep blast with inert grit. Aluminium, Very smooth, (coloured) Insufficient adhesion Degrease, (disc)sand or anodised hard surface. of coating. sweep blast with inert grit. Aluminium, White aluminium Deposits are contaminated, (Disc)sand, wash corroded salts, pitting. corrosion will continue. thoroughly. Better: clean by water abrasive blast cleaning. Aluminium Very porous Absorption of contaminants. Overcoat within 4 hours, sprayed steel surface. Bubbles and pinholes if not, clean by water in the coating film. abrasive blast cleaning. Use correct sealer

Copper Metallic yellow or Insufficient adhesion of Degrease, (disc)sand. reddish-yellow sheen. coating. Very smooth soft surface. Copper Greenish-white copper Insufficient adhesion of (Disc)sand, wash corroded salts. coating. thoroughly.

Hot rolled Millscale. This has a Millscale is more noble Remove mill scale steel blueish black than steel leading to by blast cleaning. appearance. pitting corrosion in cracks. Steel/cold Rust. Rust deposits are Wash thoroughly. rolled steel, contaminated with salts, (Disc)sand, blast clean, corroded corrosion will continue. check surface for cleanliness. Better: clean by water abrasive blast cleaning. Cast iron, Rust-porosity. Absorption of contaminants. (Disc)sand, blast clean with corroded Rust deposits are fine abrasive. Better: clean difficult to remove from by water abrasive blast the pores. cleaning. Use correct sealer Stainless Very smooth. Insufficient adhesion Degrease, (disc)sand or steel of coating. blast clean with inert grit.

/13

STEEL PROTECTION


SYSTEM

September 2005

SYMPTOM CORRECTION/ SURFACE IDENTIFICATION CONSEQUENCE PREPARATION

Coil galvanised Thin plate with a very Insufficient adhesion Degrease, (disc)sand, plate(Sendzimir) smooth zinc layer. of coating. better: sweep blast the 15-50 µm zinc surface lightly with inert grit. Coil galvanised White zinc salts Corrosion deposits (Disc)sand, better: sweep plate corroded and rust. are contaminated. blast the surface lightly (Sendzimir) Insufficient adhesion with inert grit. of coating. Electrolytic Thin plate with a very No resistance to Degrease and sand lightly. zinc plate smooth very thin weathering. (Zincor) electrochemically Good coating adhesion. ± 5 µm zinc applied zinc layer. Electrolytic Rust and white Corrosion products (Disc)sand, better sweep: zinc plate, zinc salts. are contaminated. blast the surface lightly corroded Insufficient adhesion with inert grit. (Zincor) of coating. Hot dip Smooth, soft, Insufficient adhesion (Disc)sand, better sweep: galvanised greyish surface. of coating. blast the surface lightly steel with inert grit till a 50-200 µm zinc uniform matt appearance. (or zinc metal) Hot dip White dirty zinc All deposits are contaminated. (Disc)sand, better: galvanised salts, rust. Corrosion.will continue (sweep)blast the surface steel, Insufficient adhesion with inert grit. corroded of coating. Zinc sprayed Very porous Absorption of contaminants. Overcoat within4 hours, steel surface. Bubbles and pin holes if not, clean by water in the coating. abrasive blast cleaning. Use correct sealer. Zinc sprayed Porous surface Corrosion products are Blast clean with steel, with zinc salts contaminated. Insufficient inert grit. corroded and rust. adhesion of coating.

General: Prevent contact of metals (carbon) which can form a galvanic couple.

/13

STEEL PROTECTION


SYSTEM

September 2005

DETAILS PRONE TO CORROSION ATTACK Details of structures have an extremely big impact on the durability of a paint system and as a consequence on the maintenance cost.

Up to 15% of a structure is known as a critical part in respect of corrosion protection because of imperfect welds, sharp edges and areas where dirt and water can collect. Improvements of such details should be an integral part of maintenance jobs

Rivetted or bolted structures are difficult to protect. Often coating systems show cracks after a certain time due to the shrinkage of the coating around rivets, bolts or nuts or due to minor movements in the connections of the structure. Specially formulated coatings should be used for the protection of these areas, having a durable elasticity and low shrinkage. (Maintenance system 4111)

Prevent collection of dirt and water. Make drainage holes if necessary and ensure that the strength of the structure is not affected. Drainage of water should be done in a way that water does not collect where it can cause corrosion. Avoid openings where dirt and water can collect. Grind the welds and avoid breaks or tack welds. Avoid sharp edges and intermittent welding. Always attempt to have rounded shapes and complete welds. Structures composed of steel and concrete are frequently incompatible as far as protection and maintenance are concerned. At the design stage consideration should be given to the accessibility of the steel parts for painting during new fabrication and maintenance. Leakage between concrete floors and steel columns can be prevented by using synthetic rubber slabs and sealants. If these materials have to be coated the adhesion of the paint should be checked.

When installing tanks, equipment and pipelines, there must be sufficient space left in between to allow ventilation, cleaning and maintenance painting.

/13

STEEL PROTECTION


SYSTEM

September 2005 DETAILS PRONE TO CORROSION ATTACK

In a steel structure composed of several parts there are always places where moisture or dirt can collect. The connections between the sloping and vertical sections must always be constructed in a way that water can be drained off. The connection between round and flat surfaces always creates areas which are difficult to protect. These areas should be filled up by welding to improve the protection. The junction between facing plates also creates spots which will remain damp. Filling these spots with welding material or a flexible filler is necessary for a durable protection. Containers or process tanks should be constructed in a way that no liquid remains when emptied. Special attention should be paid to the couplings of the drain: the edge of the drain and coupling must not be higher than the bottom of the tank. Reinforcement in the shape of right-angled or U-profile must also be fitted in a way that painting is possible. Use a T-profile instead of 2 right-angled profiles or place the back to back angles so that the opening between them can be welded. Make sure that sharp edges of the profile are rounded by grinding. Reinforcement in the shape of tubes should be fitted to plate material in a way that all parts are accessible for coating, both during new fabrication and maintenance painting.

/13

STEEL PROTECTION


SYSTEM

September 2005

SUBSTRATE - PAINT SYSTEM MAINTENANCE AREA SYMPTOM - CORROSION IDENTIFICATION

The area to be repaired will be the scattered corroded area x 10 or the localised corroded area x 2. Re3 and below Re3 = spotrepair. above Re3 = total area to be repaired. The photos illustrating some degrees of rusting are a reduction in size. In practice the original European scale of degree of rusting should be used

European scale of degree of rusting ISO 4628/3 ASTM D610

POSSIBLE CAUSES MAINTENANCE CORRECTION

– Salt contamination. Check and if still present, wash with fresh water.

– Pinholes, porous film or damages. Feather off edges of damages.

– Deterioration. Abrade thoroughly.

– Mill-scale or remnants of rust. Abrade or blast clean mill scaled or rusty areas.

– Grit inclusions. Remove by chipping or abrading.

– Pitting. Investigate the cause. Pitting should be grinded and filled. It is impossible to coat pittings totally by spray application and sometimes even not by brush.

– Too low dry film thickness. Upgrade dft of maintenance system.

– Aggressive chemicals/solvents. Stop splash and spillage or change paint system.

/13

STEEL PROTECTION


SYSTEM

September 2005

SUBSTRATE - PAINT SYSTEM MAINTENANCE AREA SYMPTOM - CHECKING CRACKING IDENTIFICATION

Checked or cracked areas like No.8 and higher figures = spot repair. like No.6 and lower figures = total area to be repaired. The photos illustrating some degrees of checking and cracking are a reduction in size. In practice the original ASTM D 660 or ASTM D 661 should be used.

No. 8 No. 6

Intensity ratings are in accordance with ratings as per ASTM D 660 or D 661 ISO 4628/4 ISO 4628/5


– Hard coating on top of a soft coating. Check if still soft material is present underneath. (checking) Sometimes caused by a too short Abrade checked paint completely. overcoating interval or by the application Adjust paint system. of a too high film thickness.

– Hard coating on top of a soft old coating. Check if still soft material is present underneath. (cracking) Abrade cracked paint completely. Adjust paint system.

/13

STEEL PROTECTION


SYSTEM

September 2005

SUBSTRATE - PAINT MAINTENANCE AREA SYMPTOM - BLISTERS IDENTIFICATION

The area to be repaired will be the blistered area x 10. Below 2,5% blisters = spot repair. Above 2,5% blisters = total area to be repaired. The photos illustrating some degrees of blistering are a reduction in size. In practice the original ASTM D 714-56 should be used.

Area and Density degree according to ISO 4628/2 - ASTM D 714-56


– Soluble salts present under or in between the Check and if still present wash with fresh water. paintcoats.

– Cathodic over protection. Adjust CP and/or change paint system.

– Contamination or grease present under or Check, degrease and remove contamination. between coats.

– High temperature or temperature gradient. Change paint system and/or insulate.

– Contact with chemicals, solvents and water. Take preventive measures or change paint system. (condensation)

– Too low dry film thickness Upgrade dft of maintenance system.

– Too short overcoating time or application at The conditions during maintenance should be too low temperature. improved.

/13

STEEL PROTECTION


SYSTEM

September 2005

SUBSTRATE - PAINT SYSTEM MAINTENANCE AREA SYMPTOM - DETACHMENT IDENTIFICATION

The area to be repaired will be the detached area x 2. Below 15% detachment = spot repair. Above 15% detachment = total area to be repaired.


– Intercoat contamination within latest applied Check and remove defective paint. system or overcoating times too long.

– Incompatibility of paint coats within latest Check specification. applied system or with old system e.g. Change paint system. exudation.

– Attack by aggressive solvents to old system. Change paint system. (swelling) Remove all paint.

– Internal stresses leading to detachment from Check dft of total system. bare steel. Too thick coat or quick temperature Remove all paint. change see also causes blisters

– Detachment from bare steel initiated by cracks Check the extend of under creep. and moisture. Remove defective paint.

/13

STEEL PROTECTION


SYSTEM

September 2005

Limitation of Liability - The information in this data sheet is based upon laboratory tests we believe to be accurate and is intended for guidance only. All recommendations or suggestions relating to the use of the products made by Sigma Coatings, whether in technical documentation, or in response to a specific enquiry, or otherwise, are based on data which to the best of our knowledge are reliable. The products and information are designed for users having the requisite knowledge and industrial skills and it is the end-user's responsibility to determine the suitability of the product for its intended use.

Sigma Coatings has no control over either the quality or condition of the substrate, or the many factors affecting the use and application of the product. Sigma Coatings does therefore not accept any liability arising from loss, injury or damage resulting from such use or the contents of this data sheet (unless there are written agreements stating otherwise).

The data contained herein are liable to modification as a result of practical experience and continuous product development. This data sheet replaces and annuls all previous issues and it is therefore the user’s responsibility to ensure that this sheet is current prior to using the product.

Paint 4007-Tools for Maintenance Management

Documents

Transcript of Paint 4007-Tools for Maintenance Management