Hot Dipped Galvanized Seamless Steel Pipe

Hot dipped galvanized seamless steel pipe

Hot dipped galvanized seamless steel pipe

Hot dipped galvanizing process:

The galvanizing process consists of three basic steps: surface preparation, galvanizing and inspection.

SURFACE PREPARATION

Surface preparation is the most important step in the application of any coating. Any failures or

inadequacies in surface preparation will immediately be apparent when the steel is withdrawn

from the molten zinc because the unclean areas will remain uncoated and immediate corrective

action must be taken.

Caustic Cleaning - A hot alkali solution often is used to remove organic contaminants such as dirt, paint markings, grease and oil from the metal surface. Epoxies, vinyls, asphalt or welding slag must be removed before galvanizing by grit-blasting, sand-blasting or other mechanical means.

Pickling - Scale and rust normally are removed from the steel surface by pickling in a dilute solution of sulfuric acid (5-15% by volume) or ambient temperature hydrochloric acid.

Fluxing - Fluxing is the final surface preparation step in the galvanizing process. Fluxing removes

oxides and prevents further oxides from forming on the surface of the metal prior to galvanizing.

GALVANIZING

In this step, the material is completely immersed in a bath consisting of a minimum of 98% pure molten zinc. The bath temperature is maintained at about 840 F (449 C). Fabricated items are immersed in the bath until they reach bath temperature. The zinc metal then reacts with the iron on the steel surface to form a zinc/iron intermetallic alloy.

INSPECTION

A variety of simple physical and laboratory tests may be performed to determine thickness, uniformity, adherence and appearance. Products are galvanized according to longestablished, well-accepted, and approved standards of ASTM A123/A123M, AS/NZS 4680, and BS EN ISO 1461.

ASTM Standards Hot-Dip Galvanizing

ASTM A123/A123M: Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products

ASTM A143: Practice for Safeguarding Against Embrittlement of Hot-Dip Galvanized Structural Steel Products and Procedure for Detecting Embrittlement

ASTM A153/A153M: Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware

ASTM A384: Practice for Safeguarding Against War page and Distortion During Hot-Dip Galvanizing of Steel Assemblies

ASTM A385: Practice for Providing High-Quality Zinc Coatings (Hot-Dip)

ASTM A767/A767M: Specification for Zinc Coated (Galvanized) Steel Bars for Concrete Reinforcement

ASTM A780: Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings

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