GALVANIZING WORK FOR POWER PROJECT CONTRACT

Hot-Dip Galvanizing

How Ensure Galvanizing the Steel Structure Correctly in Your Project

This article on the introduction and guide line for hot-dip galvanizing and zinc coating procedure followed by IEC and BS standard for underground power transmission cable line. In this power transmission project, the outdoor and indoor steel structure like cable termination and surge arrester support structure, cable supporting ladder, cable joint bay accessory, towers and others steel structure   galvanizing should be carried out by the hot dip process and unless otherwise specified, must conform in all respects with IEC standard.

Attention should be paid to the detail of members in accordance with IEC standard. Adequate provision for filling venting and draining must be made for assemblies fabricated form hollow sections. Of course vent holes be plugged suitably after galvanizing.

All surface defects in the steel, including cracks, surface laminations, laps and folds should be removed in accordance with IEC standard. All drilling cutting, welding, forming and final fabrications of unit members and assemblies should be completed before the structures are galvanized. The surface of the steelwork to be galvanized should be free from welding slag, paint, oil, grease and similar contaminants.

How Works Zinc Coating

The most effective and economical features of zinc coating or galvanizing engineering and technology on steel structure for any country may map up as below:
·        Increased strength;
·        Low cost;
·        More corrosion resistive;
·        Maximum recyclability;
·        Light weight.

Corrosion is a silent killer for steel structure, the industrialized country who have calculated the destruction of corrosion, it found a remarkable figure around 4% of country’s GDP, big amount.

Zinc Coating Technology and Environment
The zinc is an integral part of our environment, naturally it’s found in air, water, soil and rock.  Though zinc is essential micro-organism for animals and plants, then if its natural ratio is changed destructively then human and environment will experience hues impact.

Many expert think that hues zinc is required in our surrounding to biological process and technology able to maximize recycling steel and zinc from zinc coated steel, means negative impact is in acceptable.

Zinc coating or galvanizing steel recycling may happen in-
·        During galvanizing;
·        Manufacturing product;
·        Structure installation;
·        After life cycle of product.

Why is Used Zinc Coating
A perfect zinc coating may bring a lot of benefit for steel structure that emphasize industrial galvanizing. Here go some of the important factors of zinc coating:

·        Corrosion resistance- zinc coating resist the steel from corrosion and extend the life time;
·        Barrier protection- zinc coating acts like a physical barrier and protect moisture what is the main cause of corrosion for steel;
·        Cathodic Protection- zinc coated steel can protect corrode in scratch or cut edge due to cathodic protection, means adjacent zinc corrosion not happen;
·        Painted zinc coating- Zinc coating is used before painting that prevent steel even paint is damaged.
Zinc also may use as zinc-painting like metalizing, plating, sherardizing and zinc-rich paint etc.

How Ensure Proper Galvanizing Coating in Your Project

The Galvanizing Coating should be as specified in BS 720 or equivalent National standard. Structural steel items should initially grit blasted to BS 4232, second quality SA2.5 and the minimum average coating weight on steel sections 5 mm thick and over should be as specified in the table below:

THICKNESS OF STEEL        THICKNESS OF SIZE           MINIMUM AVERAGE
            SECTION                               COATING                  COATING WEIGHT
              mm                                       microns                                g/m²
               5                                           80 – 90                                600
             10                                          100 – 120                             750
             20                                          120 – 150                             900

Wit intermediate values will be on a pro rata basis.

On removal from the galvanizing bath the resultant coating should be smooth, continuous, and free from gross surface imperfections such as bare stops, lumps, blisters and inclusions of flux, ash or dross.

Galvanized contact surfaces to be joined by high strength friction grip bolts should be roughened before assembly so that the required slip factor as defined in BS 3294.

How Works Hot-Dip Galvanizing (HDG)
Hot-Dip galvanizing is a galvanizing process where steel galvanizing is perform in a vessel filled with molten zinc. During galvanizing steel in the vessel metallurgical react with molten zinc that formed a coating with tightly bonded on steel. This thick zinc coating acts like a strong physical barrier against forming corrosion on steel. The outdoor steel structure get a long life because of unique hot-dip galvanizing on it.

The hot-dip galvanizing standard defines minimum requirements for coating thickness and appearance. The galvanizing process has defined the minimum thickness standards based on the range of steel section thicknesses.

Practically hot-dip galvanizing ensure the materials long life time, sustainable structure, cost effective of the plant.

How Ensure in Your Project Hot Dip Galvanizing and BS Standard

Bolts, nuts and washers, including general grade high strength friction grip bolts as BS 3139 and BS 4395 part 1 should be hot dip galvanized and subsequently centrifuged in according to BS 729. Nuts should be tapped up to 0.4 mm oversize after galvanizing and the threads oiled to permit the nuts to be finger turned on the bolt for the full depth of the nut. No lubricant, applied to the projecting threads of a galvanized high strength friction grip bolt after the bolt has been inserted through the steelwork should be allowed to come into contact with the faying surfaces.

During off-loading and erection, nylon slings should be used to protect galvanized surfaces. Galvanized work which is to be stored in works on site should be stacked so as to provided adequate ventilation to all surfaces to avoid wet storage staining.

During erection the plant, small area galvanized coating may damage in any way should be brought to the attention of the Engineer who should authorize repair.

Cleaning the area of any weld slug and though wire brushing to give a clean surface. After fixing, bolt heads, washes and nuts should receive two coats zinc rich paint.

Chromium Plating
The chromium plating of those components of the plant where specified and where offered by the service provider should comply with the requirements of BS 1224 or equivalent national standard.

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