Showing posts with label Coating.products. Show all posts
Showing posts with label Coating.products. Show all posts

Monday, September 25, 2023

Cathodic protection of steel by Zinc Coating: What is the best anti-corrosive primer for steel? How does a Zinc coating works as anti-corrosive?

 

Cathodic protection of steel by Zinc Coating



SCOPE:   

Material: Stainless steel up to 120°C

Environment: Atmospheric

Exposure category C5 (high)

Standard ISO 12944 - 5

 

Abstract

According to AGA (American Galvanizers Association) explanation, Zinc is a natural, healthy and abundant element. Zinc metal has a number of characteristics that makes it a well suited corrosion protective coating for iron and steel products.

 

Zinc coating protect steel from corrosion due to it’s anodic properties where it will sacrificially corroded before the underlying steel.

 

Zinc Coating

The Film Galvanizing System ZINC coating contains 96% zinc in the dry film and provides cathodic protection of ferrous metals. Paint can be used as a unique system as an alternative to hot-dip galvanization or metallization, as primer in a duplex system (active + passive) or as a recharging system for hot-dip galvanization, metallization or zinced surfaces. Paint can be applied by brushing, rolling or spraying on a clean and rough substrate in a wide range of atmospheric circumstances.

 

Product physical & technical parameters

Components: - Zinc powder, Aromatic hydrocarbons, Binder

Density: 2.7kg/dm³

Volume Solids: 60 (±2%)

Solid content: 80% by weight (±2%) - 58% by volume (±2%) according to ASTM D2697

Color: Grey (color darkens after contact with humidity)

Zinc content: 96% (±1%) by weight, with a purity of 99,995%.

Special characteristics: Atmospheric temperature resistance of dry film

» Minimum: -40°C

» Maximum: 120°C with peaks up to 150°C

- pH resistance in immersion: 5,5 pH to 9,5 pH.

- pH resistance in atmospheric conditions: 3,5 pH to 12,5 pH.

- Excellent UV resistance

Non-toxicity:  A dry layer is not toxic. Have to test according to the standard AS/NSZ 4020.

Bellow table shows an overview of the steel preparation system

Step no.

Action

Method

Purpose

1

Pre-preparation

Visual inspection + wash down

Remove contamination

2

Salt Check

Conductivity Test

Check contamination

3

Preparation

Blast-clean all surfaces of the steelwork

Cleanliness / profile

4

De-dusting

By appropriate means

Cleanliness

 

Surface preparation

1.       Surface salt test: according with ISO 8502-6 and testing according to ISO 8502-9 (conductivity test).

2.       Blast cleaning:

Abrasive: all abrasives must comply with SSPC-AB1 grade 3

Abrasive salt contamination: test according with ISO 11127 or ASTM D 4940.

3.       Blast-profiles and cleanliness: All blast-profiles shall fall inside the range of 50 – 70 μm @110-130 PPI (peaks per inch) according to ISO 8503. Measurement according to ASTM 4417

The cleanliness of the overall surface must be in accordance with SA 2.5 standards - ISO 8501-1.

4.       De-dusting: The cleanliness should be class 1 (according to ISO 8502-3)

Surface Pre-preparation

Steam Clean @ 150 bar (min) @ 80°C or High Pressure Fresh Water Wash @ 150 bar (min)

 

Surface Preparation

Sa 2.5 (ISO 8501-1) SSPC-SP10 (Grit-blast or slurry blast. Also UHPAB to SSPC-SP12

Surface Profile

Rz 50 – 70µm (ISO 8503-2)

 

Surface Roughness

 Ra 12.5 – 15µm (ISO 8503-1)

 

Application:

Brush / Roller

Dilution is not required. Only when the product thickens, use thinner within 5% of paint weight.

Conventional spray

Use Gravity feed spray gun.

Nozzle size: 1.5 ~ 2.0 mm,

Pressure: 0.3 MPa Dilution: 0 ~ 5%, Paint strainer: #100

Air-less spray

Tip size: above 0.017 inches (e.g. 517)

Pressure: above 20 MPa,

Gun filter: #50 ~ 60 Dilution: 0 ~ 5%

 Application system:

Coats

Product

Application Type

Application Method

Required DRY Film Thickness (µm)

 

Coat-1

Zinc Coating

Full coat

Airless Spray, Conventional Spray & Brush

(60-120) µm

 

Coat-2

Zinc Coating

Full coat

Airless Spray, Conventional Spray & Brush

(60-120) µm

 


 

Properties

Test item

Methods

Result should be

Hardness

Pencil scratching (ISO/DIS 15184:1996)

Pencil B (minimum)

Adhesion

Peel off a sticky tape on 25 cells check pattern (square: 2mm x 25)- (ISO 2409:1992)

No abnormality

Heat resistance

Electrical constant temp. drier 170 °C, 24 hours

No abnormality

Cold resistance

Low temp. cycle test for 72 cycles <1 cycle>Left at -30 °C for 5 hours and Left at +10°C for 1 hour

No abnormality

 

 

Anti-corrosion performance

 

Test item

Testing method

Duration

Result Should be

Water immersion

Immersed in ion exchanged water

3 months

No abnormality other than white rust

Salt water immersion

Immersed in 3% salt water

3 months

No abnormality other than white rust

Salt spray

5% NaCl (pH6.5~7.2) Temp of spray chamber: 35±1°C (ISO 7253:1984)

1440 hours

No abnormality other than white rust

 



Image: Anti-corrosive Zinc Primer


Thanks

&

Regards

Sorwar Jahan

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