Galvanized Pipe

Galvanized steel can be made into a strong plumbing or tubing material — one that resists corrosion from exposure to water or the elements. It has been used used for water-supply pipes or as a strong tubing for outdoor applications.

It is most commonly used for outdoor construction like fences and handrails, or for some interior plumbing. It is also sometimes called galvanized iron pipe. Galvanized steel pipe has been coated with a layer of zinc. The zinc provides a barrier against corrosion so that the pipe may be exposed to the outdoor environmental elements. The protective barrier proves equally effective against damage from indoor humidity.

Galvanized steel pipe is covered with a zinc material to make the steel pipe more resistant to corrosion.

The process of galvanization was first discussed by scientists in the 1770s, nearly 60 years before it was finally introduced in the 1830s. French engineer Stanislaus Tranquille Modeste Sorel took out the first patent for the process in 1937, and began manufacturing it soon after. By the 1850s, Europe was producing galvanized steel out of manufacturing plants located around the continent. The United States followed shortly thereafter, opening its first plant in the 1870s.

To create galvanized steel pipe, steel materials are placed into a molten bath of zinc. This process is also called hot dip galvanization. The two metals are chemically bound to one another in this process, and will therefore never separate, resulting in a more resistant and longer lasting version of steel.

Galvanized Steel Pipe is used in a variety of settings. Until about 30 years ago, galvanized steel was utilized for water supply pipes in construction. It is used in outdoor applications wherever the strength of steel is desired, such as fence posts and rails, scaffolding and as protective railings.

• Galvanized steel clamp connection technology applications

When used as water pipe, the zinc barrier coating tends to react to the minerals in the water, often causing plaque to build up inside of the pipe. This impedes the water flow and, in severe cases, may lead to burst pipes. Galvanized piping is connected with threaded fittings that may also introduce leaks into the plumbing if not properly fitted.

There are a number of methods of applying zinc coatings and each will determine the coating’s thickness and its ultimate durability in a specific environments The most commonly encountered types of zinc coatings are:

• Zinc electroplating
• Mechanical plating
• Continuously galvanized sheet
• Continuously galvanized wire
• Galvanized pipe and tube
• General or hot dip galvanizing

Hot-dip galvanizing (HDG), as referenced is the process of dipping fabricated steel into a kettle or vat of molten zinc. While the steel is in the kettle, the iron metallurgically reacts with the molten zinc to form a tightly-bonded alloy coating that provides superior corrosion protection to the steel.

Hot-dip galvanizing is a form of galvanization. It is the process of coating iron, steel or aluminum with a thin zinc layer, by passing the metal through a molten bath of zinc at a temperature of around 860 °F (460 °C).

Galvanized pipe welding processes can be divided into spiral welded and straight seam welded, and galvanized spiral welding process is relatively wider number of applications, but also more complex.

Galvanized spiral pipe welding method is first out of the forward end portion of the electrode about 5 ~ 7mm, without leaving a blunt edge technology for centralized control to ease the industry needs to pay attention to seriously handle groove dimensions and near-plated zinc layer.

For penetration, undercut the tendency will be very small, If the front and rear of the round-trip transportation technology is used, generally 1.5 ~ 2.5mm; to reduce zinc weld penetration, with a focus on playing groove industry downturn, such as the use of short welding slag such as J427, to leave some space sector is expected to greatly reduce the liquid zinc remain in the weld, when welding fillet welds, you can get no defects of welding quality.

Advantages of galvanized spriral welding: the welding precision can not be compared for the straight seam welding, large diameter pipes or some special pipes are all used the spiral welded pipe, because spiral welding welding density is big, welding up is very flexible, welded together can form a variety of changes.

But straight seam welding can only weld one line, the curve of straight seam welding completely couldn’t play the advantages, therefore, The use of spiral welded is the best choice.

Mild steel pipes and is one of the low carbon steel pipes with low carbon content and the lesser hardness.

Galvanized mild steel pipe is cheap and anticorrosive performance is relatively better related stainless steel pipes. 

Galvanized pipe in the design and production of an important form of full use of the standard design, galvanized mild steel pipe is generally pipe joints, mainly for low domestic water pipes, low cost, good corrosion resistance, connections are made using British Elbow, tee, short sections to achieve, and generally do not have the means to connect welding, welding will destroy the zinc coating, welding slag prone plus, porosity phenomenon and the impact of anti-corrosion effect.

Galvanized mild steel pipe is to use the principle of electrochemical corrosion, cathodic protection and consumed mainly in the steel and zinc anode contact, carbon steel a cathode, zinc as the anode, thus ensuring that the steel from corrosion. Generally used for process instrumentation or process water piping is threaded connections for multi-temperature low-pressure pipeline medium without danger. Galvanized mild steel pipe are generally after surface treatment on its surface coated with a layer of protective film, with hot dip and cold-plated to prevent corrosion.

Galvanized mild steel pipe because of high potential than iron, zinc corrosion first, so it protected the iron pipe, and if not threaded connection, you can also use welding methods, welding room ventilation must be good, because zinc oxide is toxic to humans with acid electrode J422 can be welded.

Manufacturing process difference: galvanized steel refer to a galvanized surface, there may be welded pipe, it could be seamless, seamless steel pipe manufacturing process means welded and seamless points.

Seamless pipes are extensively applied for the nuclear device, gas, petrochemical, ship building and boiler industries. seamless pipes dominates 65% of market share in Chinese boiler industry.

Seamless steel pipe is very widely used, except for water, gas, oil, general low pressure fluid line pipe, also used as heating oil oil industry in particular, marine oil field oil well pipes, pipelines, chemical coking equipment, a condensate cooler, coal distillation of wash oil exchange Used pipe, and trestle piles, mine tunnel support frame with a pipe. Galvanized pipe generally is utilized to make make fences, fence, fence, balcony guardrail. Commonly used in municipal projects, roads, factories, schools, development zones, gardens, squares, residential and other places.

Hot-dip galvanizing, it is at high temperatures the zinc ingots melt, being placed in the auxiliary material, then the metal structure is immersed in a zinc plating bath, so that the metal member attached to a layer on the zinc layer.

The hot galvanized advantage depend on its preservative ability, the better the adhesion and hardness of the galvanized layer.

Cold galvanizing is a zinc salt solution by electrolysis, to the plating on the coating, in general, which do not have heating, the amount of zinc rarely encountered humid environment is very easy to fall off. The cold galvanizing physical treatment, just in the surface brush a layer of zinc, zinc coating so easy to fall off the use of hot-dip galvanized construction.

Hot dip galvanized is immersed in liquid zinc dissolved workpiece degreasing, pickling, dipping, drying a certain period of time and put forward.

Cold galvanizing, also called electro-galvanized, is the use of electrolysis device to the workpiece into the composition of the zinc salt solution, after degreasing, pickling, and connecting the negative electrode of the electrolytic device; zinc plate placed at the opposite side of the workpiece is connected in the electrolytic device the positive electrode, the power is turned on, a current from the positive electrode to the negative directional movement, it will be deposited on the workpiece with a layer of zinc.

Cold galvanizing looks more smooth, bright, color passivation process plating layer is yellow-green in color, was colorful. Plating layer was bluish-white or white with white passivation process was green, white coating passivation process and the sun was significant Colorful angle. The complex workpiece angular edges parts prone to “electrical burning” from gloomy, the parts of the zinc layer thick. Yin corner site is easy to form a current dead undercurrent gray area and the area zinc layer is thinner. The workpiece overall zinc tumor, caking phenomenon.

Hot dip galvanized look a little rough compared to the electro-galvanized, silvery white, look prone process waterlines and a few drops of tumor is more obvious, especially in the one end of the workpiece. Hot dip galvanized zinc layer than a few times of the electro-galvanized thick corrosion protection is several times that of the electro-galvanized.

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.

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.

There are several different processes for galvanizing metal:

HOT-DIP GALVANIZING

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.

PRE-GALVANIZING

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.

ELECTRO-GALVANIZING

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.

In recent years, with the surface quality continuous improvement of hot dip galvanized, the coating quality of the galvanized sheet has also been greatly improved.

However, as cars and appliances of the two industries need high-grade galvanized steel sheet, which still have to solve the substrate surface contamination and uncoated points affect the quality of the galvanized coating.

Composition and source of a substrate surface contaminants

Hot dip galvanized substrate surface covered with a layer of black sludge pollutants. A mixture of contaminants from solids such as oil and iron particles, which about 30% to 50% iron and non-metallic solids. The hot rolled strip in a high-speed cold rolling process, part of the iron off from the surface of the roll and strip surface into the emulsion, contamination of the emulsion, the other part is stuck in the strip surface. In the strip rolling process, in addition to the emulsion due to the formation of high-temperature emulsion breaking film lubricant, as well as a small amount of oil residues in the strip surface and iron powder mixed pollutants, firmly glued to the strip surface. exports were unlikely to be blowing in the mill washed off.

Set layer type of quality defects

The types of defects that affect the coating quality can be broadly divided into:

• surface contamination;
• growth between the bump and metal compounds;
• uncoated point;
• embedded in people coating of zinc slag particles;
• pit;
• zn-Fe crystal growth in the coating.