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Paint Coating Stainless Steel




Stainless steel are used because of its corrosion resistance properties in a wide variety of service environments, usually without additional coatings. In certain circumstances, however, stainless steel components or structures may require a coated paint finish. Examples of this may include company colour schemes or logos, environmental blending and compatibility, and general aesthetic requirements.

Coating systems for stainless steel must be carefully selected to provide sufficient durability to meet the requirements of the service environment and its associated operating conditions. The combination of surface preparation and formulation of the paint system are key factors in meeting these objectives. In certain environments, localised breakdown of the coating can lead to corrosion, which may be more severe than that experienced with un-coated surfaces and may result in high, localised, rates of attack.

In general, stainless steel have flatter and smoother surfaces than carbon steel. This applies particularly to thin cold-rolled products (sheet and coil) and may adversely affect adhesion between the metal surface and the coating system. Roughening of stainless steel surfaces prior to coating is essential and can usually be achieved by abrasive blasting, light hand abrasion or chemical etching.

Abrasive Blasting

Abrasive blasting can be accomplished by using clean, fine, hard non-metallic abrasive particles (e.g. alumina or silicon carbide). The abrasive medium must be iron-free to avoid contamination, which can result in rust staining on the surface prior to coating and the compressed air carrying the abrasive medium must be free of compressor oil.

Abrasive blasting may be readily confined to specific areas by masking. Support should be given to thin sections or cold-rolled material to avoid distortion or damage during blasting.
Stainless steel surfaces should be prepared to give a surface roughness Ra of approximately 50 micron and a minimum cleanliness of grade 2 in accordance with BS 7079:Part 1A.

Light Hand Abrasion

To avoid distortion to light sections light hand abrasion is an alternative method to blasting. Iron-free, 320 to 400 grit abrasive media are usually satisfactory. Chemical etching treatments can also be considered. Certain paint manufacturers have special primers designed for such applications and it is recommended that details of the surface to be coated are specified when seeking advice on an appropriate coating system.

Final Cleaning

Prior to coating, all stainless steel surfaces must be dry and free from rust, other foreign materials, oil and grease. The presence of such contaminants may lead to failure of the coating system. Oil and grease may be removed organic solvents, for example acetone and final drying done with a hot air blower.

Coating application and systems

The table below gives details of paint systems suitable for coating stainless steels and, in accordance with ISO 12944 and ISO 9223, classifies them in terms of the severity of the envisaged service environment.

Exterior Environment Coating System
Category Corrosion Risk Location .
C3 Medium Rural and urban areas with low sulphur dioxide, acid, alkali and salt pollution Two pack epoxy or polyurethane primer suitable for stainless steel at 30-50 micron dry, FOLLOWED BY High solids polyurethane finish at 100 micron dry
C4 High Urban and industrial areas with moderate sulphur dioxide and/or coastal areas with low salinity Two pack epoxy or polyurethane primer suitable for stainless steel at 30-50 micron dry, FOLLOWED BY High build epoxy MIO* at 100 mm dry, FOLLOWED BY Re-coatable polyurethane finish at 60 micron dry
C5I Very High Industrial areas with high humidity and aggressive atmospheres Two pack epoxy or polyurethane primer suitable for stainless steel at 30-50 micron dry, FOLLOWED BY High build epoxy MIO* at 200 micron dry (one or two coats), FOLLOWED BY Re-coatable polyurethane finish at 60 micron dry
C5M Very High Coastal and offshore areas with high salinity Two pack epoxy or polyurethane primer suitable for stainless steel at 30-50 micron dry, FOLLOWED BY High build epoxy MIO* at 200 micron dry (one or two coats), FOLLOWED BY Re-coatable polyurethane finish at 60 micron dry

MIO = Micaeous Iron Oxide

Cleanliness is extremely important in the successful application of paint coatings to stainless steels surfaces. Paint coatings should be applied in clean, dust-free conditions to clean, dry stainless steel surfaces.

If the correct precautions are taken, the complete coating systems suggested in the table can be applied in 'on-site'.

It may be preferable for some or all of the components of coating systems to be applied under paint shop conditions, where site conditions cannot be carefully controlled. Provided the initial coating stages are done under these conditions, then the final coat can be applied 'on-site' or after final assembly.

The first primer coat can be followed by subsequent coats in strongly contrasting colours to ensure complete coverage of the component or structure by the full coating system. The paint manufacturer's instructions concerning drying times should be followed and coatings must be fully dry before the application of subsequent coats.

Before applying new coatings to painted stainless steel, the original coating system should be identified and advice on surface preparation obtained from the paint system manufacturer. This should help ensure compatibility between the new and existing coating systems.

Paints that contain metallic zinc should not be used on stainless steel as embrittlement of the stainless steel substrate can occur in the event of severe fire damage.

Before commencing any task ensure that you have received the appropriate health and safety literature from the supplier and fully understand it. If in doubt seek advice

Stainless Steel Tubing, Nickel Alloy Tubing, Brass Alloy Tubing, Copper Nickel Pipe Material Grades


Related References:
Paint Coating Stainless Steel
Zinc Coatings-Galvanized|Electrogalvanized|Galvanneal|Galfan
Physical Properties of HDG Hot-Dip Galvanized
HDG Hot-Dip Galvanized Abrasion Resistance Resistance to Mechanical Damage
Hot-Dip Galvanized Corrosion Protection and the Zinc Patina
HDG Hot-Dip Galvanized High Temperature Exposure
HDG Hot-Dip Galvanized Surface Reflectivity
Painting Hot-Dip Galvanized Steel
Painting Hot-Dip Galvanized Steel Chemical Cleaning Surface Preparation
Paint Selection Painting Hot-Dip Galvanized Steel
Cost of Galvanized Steel


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Stainless Steel Tubing Pipe

304 Stainless Steel Pipe
304L Stainless Steel Pipe
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304/304L Stainless Steel Tubing
309S Stainless Steel Pipe
310S Stainless Steel Pipe
316L Stainless Steel Tubing
316Ti Stainless Steel Tube
317L Stainless Steel Pipe
321 321H Stainless Steel
347 347H Stainless Steel
904L N08094 Seamless Tubes
17-4 PH 630 UNS S17400 Stainless Steel
253MA S30815 Stainless Steel Tube
S31254 254 SMO Pipe
S31803 Stainless Steel
2205 Duplex Pipe Tubing
S32101 Stainless Steel
S32304 Stainless Steel
2507 Super Duplex Pipe
S32750 Super Duplex Pipe
S32760 Super Duplex Steel
1.4462 Stainless Steel Pipe
ASTM A213 | ASTM A269
ASTM A312 | ASTM A511
ASTM A789 | ASTM A790
ASTM B161 / ASME SB 161 | ASTM B111
EN 10216-5
ASTM A789 ASME SA 789 S31803 S32205 S32101 S32750 S32760 S32304 S31500 S31260 Seamless Tubes
EN 10216-5 1.4462 1.4362 1.4162 1.4410 1.4501 Seamless Tubes
Nickel Alloy Tubing:

UNS N08020 Alloy 20 Tubing
UNS N02200 Alloy 200 Tube
UNS N02201 Alloy 201 Pipe
UNS N04400 Monel 400 Tubing
N06600 Inconel 600 Tube
N06601 Inconel 601 Tubing
N06625 Inconel 625 Tubes
N08800 Incoloy 800 Tube
N08810 Incoloy 800H Tube
N08811 Incoloy 800HT Tubing
UNS N08825 Incoloy 825 Pipe
ASTM B622 N10276 C276 Tubing
ASTM B622 N06022 Hastelloy C-22 Alloy Tubes
C28000 Brass Seamless Tubes C44300 Brass Seamless Tubes
C68700 Brass Seamless Tubes
C70600 Copper Nickel Tubes
C71500 Copper Nickel Tubes
DIN 2391 Seamless Precision Steel Tubes
EN 10305-1 E215 E235 E355 Seamless Precision Steel Tube Tubing Tubes
DIN 2393 St28 St34.2 St37.2 St44.2 St52.3 Welded Precision Steel Tubes
EN 10305-2 E195 E235 E355 Welded Cold Drawn Precision Steel Tube