Galvanized Steel Pipe, Galvanized Seamless Steel Pipe

What is Galvanized Steel Pipe?

Galvanized steel pipe (GI Pipe) is the surface with hot-dip galvanized or electro-galvanized layer. Galvanized steel can increase corrosion resistance and prolong life. Galvanized steel pipe is widely used, except for water, gas, oil, generally low-pressure fluid line pipe, also used oil heater oil industry in particular, marine oil wells pipes, pipelines, chemical coking equipment, condensing coolers, washing coal distillate oil exchange used tubes, as well as the bridge piles, mine tunnel support frame with a pipe.

Types of galvanized steel pipes:

Galvanized steel pipe is divided into cold galvanized pipe and hot galvanized pipe, among which hot-dip galvanized steel pipes are more widely used. Hot galvanized steel is widely used in construction, machinery, mining, chemical, railway vehicles, the automotive industry, roads, bridges, container, sports facilities, agricultural machinery, petroleum machinery, prospecting machinery and other manufacturing industries. 

Hot-dip galvanized steel pipe is molten metal reacting with the iron matrix alloy layer, so that the substrate and coating combination of both. Galvanized pipe is first pickled, the steel surface in order to remove iron oxide, after pickling, cleaning tank by mixing an aqueous solution of ammonium chloride or zinc chloride and zinc chloride or ammonium chloride solution, and then into hot dip tank. Galvanized with coating uniformity, strong adhesion, long life and other advantages. Hot dip galvanized steel substrate with molten bath complicated physical, chemical reactions, the formation of corrosion-resistant zinc-iron alloy structure closely layer. Alloy layer and layer of pure zinc, steel base blend. Therefore it resistant to corrosion.

Cold-dip galvanized steel pipes (electro-galvanized steel pipes) are still used in specific scenarios, but the overall frequency of use is not as common as hot-dip galvanized steel pipes, mainly in low-cost, short-term or indoor scenarios. In most industrial and construction fields, hot-dip galvanizing or other anti-corrosion processes are more mainstream.

Electro-galvanized steel is designed to prevent corrosion of the object, which to improve the corrosion resistance and service life of steel, but also to increase the decorative appearance of the product, steel growth over time will be weathering, water, or soil erosion. Annual domestic steel corroded steel accounts for almost one-tenth of the entire amount, so in order to protect the life or steel parts are generally used galvanized steel to be processed. Because zinc is not easy to change in dry air, and in a humid environment to produce a more basic zinc carbonate film that will be able to protect the internal parts without being corrosion damage, even if the zinc layer is destroyed some factors case, after a period of zinc and steel combination will form a micro-cell, leaving the cathode and the steel substrate to be protected.

Galvanizing process:

Hot dip galvanizing process:
Workpiece degreasing → washing → pickling → washing → drying solvent dip fluxing preheated hot dip galvanized → cooling → finishing → rinsing → drying → passivation test

Electro-galvanized process:

Chemical degreasing → washing → hot water hot water electrolysis degreasing → washing → washing → strong corrosive galvanized iron alloy → washing → washing → light → → washing → drying passivation

Galvanized means that the surface of the steel pipe has been galvanized, and it may be a welded pipe or a seamless pipe. 

There are two types of galvanized seamless pipes (GI seamless pipe), hot-dip galvanizing (hot-dip galvanizing) and cold-dip galvanizing (electro-galvanizing). Hot-dip galvanizing has a thick galvanized layer, which has the advantages of uniform coating, strong adhesion, and long service life. However, the cost of electro-galvanizing is low, the surface is not very smooth, and its corrosion resistance is much worse than that of hot-dip galvanized pipes. 

Selection suggestions:
1. High pressure/high stress environment: choose galvanized seamless pipe (such as ASTM A106).
2. General construction, low pressure fluid: choose galvanized welded pipe (such as ASTM A53).
3. Large diameter (>Φ500mm): only welded pipe can be selected (seamless pipe is subject to process restrictions).
4. Limited budget: welded pipe is preferred, but the quality of the weld needs to be ensured (such as hot-dip galvanized welded pipe).

Read more: Galvanized ERW pipe or Guide for Selecting the Thickness of Galvanized Steel Pipe