Common protection systems

The protection systems detailed in this section (see Tables 12.2 and 12.3) are based on those which are currently recommended by Corus

for various environments. The system numbers are those allocated by Corus and the recommended paint thicknesses are the dry film thickness. These thicknesses may vary between manufacturers.

Systems have been chosen which are suitable for the following environments:

— low risk: where there is a low risk of condensation, exhibition halls, workshops, sports halls

— medium risk: production buildings, or those with potentially high humidity and some risk of pollution.

— medium risk: most rural and urban areas, with low sulphur dioxide, acid, alkali and salt pollution

— high risk: urban and industrial atmospheres with moderate sulphur dioxide and/or coastal areas with low salinity

— very high risk: industrial areas with high humidity and aggressive atmospheres. Coastal and offshore areas with high salinity.

The tables show both interior hidden and interior visible, to facilitate the choice of one system in structures where parts of the steelwork are hidden and parts are visible.

The tables do not cover the following:

— very low risk: with a dry atmosphere (e.g. offices, shops, schools, etc.) as, generally, no protection system is required, except for decorative reasons.

Table 12.2 Recommended corrosion protection systems for interior environments47 (|xm = 10 6 m)

Environment

Interior low risk

Interior medium risk

Table 12.2 Recommended corrosion protection systems for interior environments47 (|xm = 10 6 m)

Environment

Interior low risk

Interior medium risk

Hidden

Visible

Hidden

Visible

Hidden

Visible

Hidden

Visible

Visible

Structure life in years'1'

55+

55 +

Unknown

Unknown

60+

60+

55 +

45+

40+

Coating life in years'2'

N/A

15

N/A

Unknown

N/A

20+

N/A

25

20

BS system number

B3

BIO

B4

Bit

B6

B13

B7

B14

B15

Shop applied surface preparation

Blast clean to SA 2.5

Blast clean to SA 2.5

Blast clean to SA 2.5

Blast clean to SA 2.5

Blast clean to SA 2.5

Blast clean to SA 2.5

Coating

Zinc

Zinc

Water-based

Water-based

Hot-dip

Hot-dip

High solid

High solid

High solid

phosphate

phosphate

acrylic or

acrylic or

galvanize to

galvanize to

epoxy zinc

epoxy zinc

epoxy zinc

epoxy primer (80 |xm)'3'

epoxy primer (80 |xm)'3'

epoxy zinc

epoxy zinc

BS 729 (85 |xm)'5'

BS 729 (85 |xm)'5'

phosphate

phosphate

phosphate

phosphate

phosphate

primer

primer

primer

(2 x 60 |xm)'4'

primer

(2 x 60 |xm)'4'

(80 |xm)

(80 |xm)

(100 |xm)

High build recoatable epoxy MIO (120 |xm)

High build recoatable epoxy MIO (120 |xm)

High build aliphatic Polyurethane finish (120 |xm)

Surface

None

Wash free of

None

Wash free of

None

Mordant

None

Wash free of

None

preparation

contamination

contamination

wash

contamination

Structure life — the number of years of freedom of severe corrosion that might lead to weakening of the structure.

The expected number of years to first maintenance of the coating.

Can be applied as a 20 |xm prefabrication primer plus 60 |xm post-fabrication primer.

Water-based technology is still developing and advice should be obtained from the manufacturer.

A thickness of 85 |xm can be achieved on steel over 6 mm thick without grit-blasting.

Table 12.3 Recommended corrosion protection systems for exterior environments47 (|xm = 10 6 m)

Environment

Exterior — medium risk

Exterior — medium risk

Exterior — very high risk

Coating life in years'1'

20+

20

20

25

25

20

25

BS system number

B12

B14

B15

E6

E9

E9

E10

Shop applied surface preparation

Blast clean to SA 2.5

Blast clean to SA 2.5

Blast clean to SA 2.5

Blast clean to SA 2.5

Blast clean to SA 2.5

Blast clean to SA 2.5

Hot-dip galvanize to BS 729 (85 |xm) High-build epoxy MIO (100 |xm)

Zinc phosphate epoxy primer (80 |xm) High-build epoxy MIO (100 |xm)

High solid epoxy phosphate primer

High solid aliphatic polyurethane finish

(100 |xm)

Zinc-rich epoxy primer (100 |xm) High-build epoxy MIO (100 |xm)

Zinc-rich epoxy primer (100 |xm) High-build epoxy MIO (200 |xm)

Zinc-rich epoxy primer (100 |xm) High-build epoxy MIO (200 |xm)

Zinc-rich epoxy primer (100 |xm) High-build epoxy MIO (200 |xm)

Surface preparation

None

Wash free of contamination

None

Wash free of contamination

Wash free of contamination

Wash free of contamination

Wash free of contamination

Coating

None

Recoatable polyurethane finish (60 |xm)

None

High-build epoxy MIO (100 |xm)p)

High solid aliphatic polyurethane finish (60 |xm)

High solid aliphatic polyurethane finish (60 |xm)

Recoatable polyurethane finish (60 |xm)

Coating system durability is based on experience and is the expected life in years before major maintenance. It is not a guaranteed life expectancy. It should be noted that the available colours are limited.

Interior:

— high risk: buildings with high humidity and corrosive atmospheres, e.g. chemical plants, swimming pools, paper manufacturing plants, etc. In these cases, it is recommended that specialist advice is sought.

For steelwork in contact with a masonry outer skin it is recommended that the steel is galvanized or, alternatively, it is blast-cleaned and one coat of solvent-free epoxy (dry film thickness of 450 |xm) is applied. If the steelwork is galvanized, two coats of heavy duty bitumen (total dry film thickness of 200 | m) should be applied.

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