Hot Dip Galvanized Pipe

Properties of Galvanized Steel

Galvanized steel is produced by coating the steel in zinc. The properties of galvanized steel are a unique combination that make it ideal for use in interior and exterior applications such as car bodies, appliances, nuts and bolts, roofs, and rebar.

Corrosion Resistance

According to the American Galvanizers Association, galvanized steel resists corrosion up to 100 times better than uncoated steel.

Surface Appearance

All galvanized steel has a matte-gray appearance. Zinc coating applied by using electrogalvanizing is smoother than galvanized steel made with batch or continuous galvanizing and allows for a higher quality finish when painted.

Formability

The zinc coating on galvanized steel is resistant to cracking and loss of adhesion when the steel is formed into a product.

Durability

The zinc coating does not require special handling to protect it during transport or use. It is extremely durable and resistant to scratches from abrasion.

Recyclable

Steel is by far the most recycled material in North America. Galvanized steel is as recyclable as other types of steel.

What Is the Difference in Black Steel Pipe & Galvanized Steel Pipe?

Water and gas require the use of pipes to carry them into residential homes and commercial buildings. Gas supplies power to stoves, water heaters and other devices, while water is essential for other human needs. The two most common types of pipes used to carry water and gas are black steel pipe and galvanized steel pipe.

Galvanized Pipe

Galvanized pipe is covered with a zinc material to make the steel pipe more resistant to corrosion. The primary use of galvanized pipe is to carry water to homes and commercial buildings. The zinc also prevents the buildup of mineral deposits that can clog the water line. Galvanized pipe is commonly used as scaffolding frames because of its resistance to corrosion.

Black Steel Pipe

Black steel pipe is different from galvanized pipe because it is uncoated. The dark color comes from the iron-oxide formed on its surface during manufacturing. The primary purpose of black steel pipe is to carry propane or natural gas into residential homes and commercial buildings. The pipe is manufactured without a seam, making it a better pipe to carry gas. The black steel pipe is also used for fire sprinkler systems because it is more fire-resistant than galvanized pipe.

Problems

The zinc on galvanized pipe flakes off over time, clogging the pipe. The flaking can cause the pipe to burst. Utilizing galvanized pipe to carry gas can create a hazard. Black steel pipe, on the other hand, corrodes more easily than galvanized pipe and allows minerals from water to build up inside it.

Cost

Galvanized steel pipe costs more than black steel pipe because of the zinc coating and manufacturing process involved in producing galvanized pipe. Galvanized fittings also cost more than the fittings used on black steel. Galvanized steel pipe must never be joined with black steel pipe during the construction of a residential home or commercial building.

Quite simply, galvanizing a metal gives it anti-corrosion properties. Without the protective zinc coating, the metal would remain exposed to the elements and potentially oxidize and corrode much faster. Galvanized Steel is a cost effective alternative to using materials such as austenitic stainless steel or aluminum in order to prevent corrosion.

How Does It Work?

Galvanizing can protect metal is a number of ways. Firstly, it creates a protective coating that shields the metal from the surrounding environment. The layer of zinc prevents water and moisture and other elements in the air from corroding the steel underneath. Should the zinc coating be scratched deep enough, the metal would become exposed and susceptible to corrosion.

Galvanizing can also protect metal through a process called "galvanic corrosion". Galvanic corrosion occurs when two metals of a different electrochemical make up are placed into contact with one another with an electrolyte present, such as salty water. Depending on the atomic structure of the two metals, one metal is the anode and the other is the cathode. The anode corrodes more rapidly than it would by itself and the cathode corrodes at a slower pace than it would by itself. The reason zinc is used for galvanizing is because it has an affinity towards being the anode when in contact with many different types of metals. Since the zinc coating in contact with the base metal is usually the anode, it slows the corrosion of the base metal, or the cathode.

Different methods of galvanizing

There are several different processes for galvanizing metal:

As the name implies, this method involves dipping the base metal into a molten pool of zinc. First, the base metal must be cleaned either mechanically, chemically, or both to assure a quality bond can be made between the base metal and the zinc coating. Once cleaned, the base metal is then fluxed to rid it of any residual oxides that might remain after the cleaning process. The base metal is then dipped into a liquid bath of heated zinc and a metallurgical bond is formed.

The advantages of this method are that it is economical; it can be performed quickly and to complex shapes. However, the final coating can be inconsistent relative to other galvanizing processes.

This method is very similar to hot-dip galvanizing but is performed at the steel mill, usually on materials that already have a specific shape. Pre-galvanizing involves rolling metal sheet through a similar cleaning process to that of the hot-dip galvanizing process. The metal is then passed through a pool of hot, liquid zinc and then recoiled.

An advantage of this method is that large coils of steel sheet can be rapidly galvanized with a more uniform coating compared to hot-dip galvanizing. A disadvantage is that once fabrication of the pre-galvanized metal begins, exposed, uncoated areas will become present. This means that when a long coil of sheet is cut into smaller sizes, the edges where the metal is cut are left exposed.

Unlike the previous processes, electrogalvanizing does not use a molten bath of zinc. Instead, this process utilizes an electrical current in an electrolyte solution to transfer zinc ions onto the base metal. This involves electrically reducing positively charged zinc ions to zinc metal which are then deposited on the positively charged material. Grain refiners can also be added which helps to ensure a smooth zinc coating on the steel. Similar to the pre-galvanizing process, electrogalvanizing is typically applied continuously to a roll of sheet metal.

Some advantages of this process are a uniform coating and precise coating thickness. However, the coating is typically thinner than the coating of zinc achieved by the hot-dip galvanizing method which can result in reduced corrosion protection.

Threaded end steel pipe

Typically used on pipe 3" and smaller, threaded connections are referred to as screwed pipe. With tapered grooves cut into the ends of a run of pipe, screwed pipe and screwed fittings can easily be assembled without welding or other permanent means of attachment. In the United States, the standard pipe thread is National Pipe Thread (NPT).

The reason for this is that as NPT connections are assembled, they become increasingly more difficult for the process to leak. The standard taper for NPT pipe is 3/4" for every foot. Threaded End is abbreviated on drawings as TE.

Threaded fittings have threads that are either male or female. Male threads are cut into the outside of a pipe or fitting, while female threads are cut into the inside of the fitting. As screwed pipe and fittings are assembled, two pieces are pulled together. The distance that is pulled together is called the thread engagement.

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