ERW BLACK Pipes. Electric Resistance Welded (ERW) Pipes are manufactured from Hot Rolled Coils / Slits. All the incoming coils are verified based on the test certificate received from steel mill for their chemistry and mechanical properties. ERW pipe is cold-formed into a cylindrical shape, not hot-formed. 

ERW black pipe is a type of welded steel pipe that is black in color and is used for a variety of industrial and structural applications: 

What it's used for

ERW black pipes are used in a variety of applications, including: 

Oil and gas pipelines 

Oil and water well casing 

Chilled water 

Fire fighting 

Construction applications 

Mining industry to transport materials and equipment.

Water supply and drainage systems in mining operations 

How it's made

ERW pipes are manufactured by rolling metal and then welding it longitudinally across its length. The welding process is called electric resistance welding (ERW), which involves heating metal parts in contact with an electric current to permanently join them. 

Pre-galvanized pipe is a steel pipe that has been galvanized before it is formed into a tube. The galvanization process involves coating the steel with zinc to protect it from corrosion and rust. 

Here are some characteristics of pre-galvanized pipes:

Appearance

Pre-galvanized pipes can have a shiny, spangled, matte grey, or shiny and dull appearance. 

Thickness
The coating thickness of pre-galvanized pipes can vary by grade and strand diameter, but is typically around 20–30 μm. 

Uses
Pre-galvanized pipes are used in a variety of products, including conduit, lip, and open channels. 

Comparison to hot-dipped galvanized steel
Hot-dipped galvanized steel is generally more effective than pre-galvanized steel because the coating covers the joins and seams where parts connect. The coating used for hot-dipped galvanized steel is also thicker and more durable. 

Hot-dip galvanizing (HDG) is a process that coats steel with a zinc alloy to protect it from corrosion. The process involves immersing the steel into a bath of molten zinc, where the iron in the steel reacts with the zinc to form a protective coating. 

HDG has many benefits, including:

Corrosion protection: 

The zinc coating provides barrier and cathodic protection, as well as a zinc patina that helps resist corrosion. 

Maintenance-free: 

Galvanized steel can last for decades with little to no maintenance. 

Environmental sustainability: 

Zinc is abundant in the environment and is essential for life. Galvanized steel is 100% recyclable and has little impact on the environment. 

The HDG process involves several steps, including:

Inspection:

 Ensuring the steel meets drainage and venting requirements 

Cleaning: 

Removing paint, grease, and other contaminants from the steel 

Pickling:

 Removing mill scale and rust from the steel with sulfuric acid 

Fluxing: 

Applying a zinc ammonium chloride solution to remove any remaining oxides and create a protective layer 

Galvanizing: 

Immersing the steel in the molten zinc bath 

The surface of galvanized steel has a crystallized pattern called a "spangle".