galvanizing procedure

QUALITY SYSTEM PROCEDURE of 5

TITLE : HOT-DIP GALVANIZING PROCEDURE.

PROCEDURE NO : II/PR/LM6000/02

REVISION : 00 DATE: 15.06.2007.

PREPARED BY CHECKED BY

S.TAMIZH SELVAN, R. BALAMURUGAN,ENGINEER – QUALITY. MANAGER - QUALITY

II/PR/LM6000/02 REV.00 DATE 15.06.2007

HOT-DIP GALVANIZING PROCEDURE PAGE 2 OF 5

REVISION STATUS

REV DATE CHANGE

II/PR/LM6000/02 REV.00 DATE 15.06.2007


PROCEDURE FOR GALVANIZING & STEEL

1. SCOPE :This procedure deals with the galvanizing procedure of hot-dip galvanizing of iron & steel.

2. REFERENCE : ASTM A123-2001; ASTM A153; ASTM A143; ASTM B6; SSPC SP1 & SP11

3. PROCEDURE :

3.1 Preparation of Metal surface for Galvanizing.

3.1.1 Cleaning: Removing of Contamination like oil, grease or paint over the surface to be galvanized. Cleaning carried out by dipping the work in degreasing bath and should be raised and lowered in order to allow degreasing solution to enter inaccessible areas. Then immediately after degreasing the work should be rinsed in hot water (600C) followed by finding rinsing in cold running water.

3.1.2 Pickling: Removal of scale, patches and burnt-on on the surface to be galvanized by dipping the work in pickling bath (Diluted hydrochloric acid or sulphuric acid) with suitable inhibitor.

3.1.3 Rinsing: After pickling the work should be thoroughly rinsed in running water.

3.1.4 Fluxing: Work is dipped in a strong solution of zinc ammonium chloride.

Note: Pre fluxed & dried work should be galvanized without delay i.e. within an hour of fluxing

3.2 Galvanizing:

3.2.1 Galvanizing bath: Galvanizing bath should contain not less than an average of 98.0% zinc by weight. The zinc used in the bath should conform to Specification B6 (Slab zinc). Temperature of the bath is so critical to have consistency in product quality & to economically use zinc. Rate of immersion is as rapid as possible to reduce amount of dross & to have uniformity of coating.

3.3 Water Quenching: To remove flux residues, work is quenched in water.

II/PR/LM6000/02 REV.00 DATE 15.06.2007


3.4 Centrifuging: Small articles are handled in baskets. They are centrifuged to remove excess of zinc immediately after galvanizing while the coating is still in the molten condition. Threads on articles which are unsuited for centrifuging shall be cleaned with a rotating wire brush immediately after galvanizing before the coating sets.

3.5 Post-treatment: To avoid formation of ‘white rust’ or ‘wet storage stain’ on freshly galvanized surfaces post treatment like chromating is carried-out which will retard ‘white rust’ attack temporarily.

3.6 Stacking :To avoid flaking of coating articles are stacked immediately after quenching to allow the articles to dry before any further handling.

4. Testing and inspection:

4.1 Visual Appearance: Coating shall be adherent, smooth, reasonably bright, continuous & free from imperfections such as flux ash and dross insulation bare & black spots, pimples, lumpiness & runs, rust stains, bulky white deposits & blisters. No traces of solidified drop or sharp edges acceptable.

4.2 Coating thickness: Any one of the following method is used to determine the coating thickness:

4.2.1 Magnetic Thickness Measurement: Using magnetic thickness gauge the thickness of the coating is measured in accordance with Practice E 376. A minimum of five readings shall be taken at each location near the ends and in the middle of each piece being tested. For large products, the minimum of five readings in a location shall be taken peripherally about 4 in. (100 mm) from each end and in the approximate center of the member.

4.2.2 Stripping Method: The average weight of zinc coating may be determined by stripping test pieces from the sample at location approximately 4 in. (100mm) from each end and third from the approximate center of the member. The weight of coating is measured and should conform to the standard. Weight of coating per square foot of actual surface shall average not less than 3 ounces and no individual specimen shall show less than 2.5 ounces.

4.2.3 Weighing before and after galvanizing: The average weight of the zinc coating is determined by weighing the article before and after galvanizing.

II/PR/LM6000/02 REV.00 DATE 15.06.2007


4.3 Adhesion Test: The test is conducted on coated surface by cutting or prying with the point of a stout knife, applied with considerable pressure in a manner tending to remove a portion of the coating.

4.4 Embrittlement Test: The test is conducted in accordance with practice A 143

6. Repair of Galvanized surfaces:

All Galvanizing surfaces that require welding, cutting, drilling or other preparation and any galvanized surface that has been damaged shall be repaired with an approved coating repair system. Before application of repair coating surfaces shall be prepared in accordance with SSPC SP1, followed by SSPC SP11.

7. Records:

Sample Galvanizing test report form as in Annex A

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ANNEXURE - A

GALVANIZING - SUPPLIER NAME & ADDRESS

T.C. NO. : DATE :

TO M/s. INDIRA INDUSTRIES NO 6, SIPCOT INDUSTRIAL COMPLEX RANIPET – 632 403

YOUR PURCHASE ORDER No.

PROJECT :

TEST CERTIFICATE1. Reference Standard ASTM A123 - 2001

2. Name of the Zinc Used & Percentage

3. Component Description & Quantity

4. Test sample size

5. Magnetic Gauge reading

6. Stripe test result

7. Knife test

8. Visual Inspection

9. Others

Chemist : for

Date :

galvanizing procedure

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