Corrosion never sleeps, get it galvanized.

HDG Process Flow

01 Material Unloading and Inspection

The following pre-galvanized requirements are checked visually before acceptance of goods.

  • Proper fabrication according to the requirements for good galvanizing.
  • Rust condition
  • Paint Inclusions
  • Oil
  • Welding Slag, spatters
  • Welding Condition

02 Pre-Preparation

Pre-preparation works are done for the items that should be cleaned for oil/paint and items that need provisions for hanging on frames.

Sandblasting is done to remove heavy corrosion, thick oil layers, or paint on goods.

Holes are made to have provisions for excess Zn draining and for trapped air removal.

Hooks are attached to the hanging of items on frames.

03 Pickling

Surface cleaning and removal of scales using Hydrochloric acid is used as the pickle liquor.

  • The average Acid concentration is 10%. (w/v) or higher.
  • Temperature range 20oC – 40oC
  • Iron Content of each bath is less than130 g/l
  • The aim of the pickling is to remove the scale but not to attack the underlying steel. It is strongly concerned about the pickling duration by considering the acid bath concentration and the rust level of the items

04 Rinsing

After removing the scales from the articles, the remaining acid and iron particles should be removed by washing using the rinsing tank. This will prevent the introduction of Iron, acid, and other chemicals to the flux bath.

05 Fluxing

Double salt of Zinc ammonium chloride is used as the fluxing reagent to:

  • Prevent oxide film from forming on the highly reactive steel surface,
  • Remove iron salts and acid carried over on articles from the rinsing bath.
  • Obtain a better and more consistent finish.
  • As a temporary protection until the dipping activity.

The following parameters are controlled in the flux bath.

  • Temperature at room temperature
  • Specific gravity of the flux bath remains at 1.20
  • pH between 4 – 5
  • Iron Content < 1 g/l

06 Drying

The items are dried thoroughly to prevent explosion hazards during galvanizing and to prevent spatters on galvanized articles.

There is a double-chamber drying furnace to facilitate the drying of 02 frames simultaneously.

It operates with indirect heating by using the heat of the waste gases. Indirect heating helps to reduce natural resource depletion by reducing electricity consumption.

07 Galvanizing – Steel Bath (Dipping in molten Zinc)

Galvanizing Bath is 7 m in length, 2.1 m in depth, and 1.3 m in width. Zinc used for galvanizing is LME-approved, 99.995% pure Special High-Grade Zn ingots. The following parameters are controlled during the process.

  • Temperature of the bath: 445oC - 450oC
  • Duration of immersion
  • Speed of withdrawal

08 Galvanizing – Ceramic Bath

The ceramic bath is 3 m in length, 1.2 m in depth, and 0.8 m in width. This bath is used to galvanize small items followed by centrifugation.

Both the steel bath and the ceramic bath are manufactured by LOI Thermprocess of Germany.

09 Quenching and Passivation

Quenching is done by immersing in a freshwater tank to stop the Fe-Zn intermetallic reaction and to cool down the article quickly. Passivation is done to prevent wet storage stain.

10 Cleaning and Quality Inspection

Cleaning is done to remove ash, Zinc spikes, and other stains on the galvanized article. After cleaning, the thickness of the Zinc layer is measured and compared with the requirements specified in the BS 1461:2022 standard.

11 Effluent Treatment

Spent pickle liquor is treated in the effluent treatment plant by using a filter press and disposed of in a 100% environmentally friendly manner.

12 Specification and Quality Inspection

Hot Dip Galvanizing processes meet the requirements of company standards and the BS EN ISO 1461:2009 international standard. Coating thickness of the galvanized steel exceeds the minimum requirements specified in tables 3 & 4 of the above standard.

Table 3 - Minimum coating thickness and mass on samples that are not centrifuged

Articles and their thicknesses Local coating thickness
(min) µm
Local coating mass (min)
Mean coating thickness
(min) µm
Mean coating thickness mass (min)
Steel > 6mm 70 505 85 610
Steel > 3mm to 6mm 55 395 70 505
Steel ≥ 1.5mm to 5.3mm 45 325 55 395
Steel < 1.5mm 35 250 45 325

Table 4 - Minimum coating thickness and mass on samples that are centrifuged

Articles and their thicknesses Local coating thickness
(min) µm
Local coating mass (min)
Mean coating thickness
(min) µm
Mean coating thickness mass (min)
Articles with threads:
> 6mm diameters 40 285 50 360
≤ 6mm diameters 20 145 25 180
Other articles (including casting):
≥ 3mm 45 325 55 395
< 3mm 35 250 45 325

LTL Galvanizers has a strong technical collaboration agreement with the American Galvanizers Association (AGA) and LTL Galvanizers is also a member of AGA.

The Integrated Management System of LTLGalvanizers is certified to ISO 9001:2015, ISO 14001:2015, and ISO 45001:2018 by internationally acclaimed certifying agency, Det Norske Veritas (DNV) Netherlands.

13 Packing and Delivery

All fabricated and galvanized goods are inspected for quality compliance and packaged in accordance with the standards and specifications of the customer. To ensure the products arrive at their final destinations safely, they are loaded onto pallets with space left over to prevent moisture build-up. The pallets are then secured with PVC strapping. Packing lists are created and each package is numbered and recorded in a delivery document before shipping.