Galvanized Steel Pipe: Welded Pipe vs. Seamless Pipe

Galvanized steel pipe (GI pipe) is a broad concept encompassing not only galvanized welded pipe but also various other types. Based on the steel base material, galvanized steel pipes are divided into galvanized welded pipe and galvanized seamless pipe. We will now explore these two types of galvanized steel pipe in detail.

Galvanized Welded Pipe:

1. Production Process
Galvanized welded pipe is made by rolling and welding steel plates or strips, followed by galvanizing. The process is simple and low-cost. First, steel plates or strips are rolled and welded into pipes, usually showing a visible weld seam, followed by galvanizing.

2. Weld Seam and Pressure
The weld seam is the most significant difference between galvanized seamless pipe and seamless pipe. Upon close inspection, a longitudinal weld seam can be found on both the inside and outside of the pipe wall. This is a significant feature that affects its pressure-bearing capacity; relatively speaking, welded pipe has a lower pressure resistance. Due to the presence of the weld seam, its pressure-bearing capacity is lower than that of seamless pipe, making the weld seam a weak point.

3. Precision and Applications
Welded pipes offer high dimensional accuracy and uniform wall thickness, making them suitable for low-pressure fluid transportation. They are commonly used for transporting low-pressure fluids, such as water, gas, and heating pipes (exposed) in buildings, scaffolding, and guardrails.

Galvanized Seamless Pipes:

1. Manufacturing Process and Characteristics
Seamless pipes are manufactured by piercing a solid tube blank, resulting in a compact structure without welds. The manufacturing process involves piercing a solid tube blank and then galvanizing it.

2. Performance and Cost
Due to the absence of welds, galvanized seamless pipes have a uniform and compact structure. This gives them excellent pressure resistance under high-pressure conditions. Although the wall thickness distribution of seamless pipes may not be as uniform as that of welded pipes, their precision requirements are often higher. Consequently, they have higher pressure resistance, higher precision requirements, and higher costs and prices than welded pipes. Because the manufacturing process is relatively complex, the cost and price of galvanized seamless pipes are also relatively high.

3. Applications and Uses
Seamless pipes are commonly used in high-pressure environments, such as boilers and chemical equipment. Commonly used for fluid transportation in high-pressure environments, such as boiler pipes, high-pressure oil pipes, chemical equipment pipes, and pipes for mechanical structures.

Galvanizing Process Classification:

1. Hot-dip galvanizing
Immersing the steel pipe in molten zinc. It offers excellent corrosion resistance and strong adhesion, but is more expensive. Hot-dip galvanizing is the most common method, where the steel pipe is immersed in molten zinc to uniformly coat its surface with a zinc layer, thus enhancing its corrosion resistance.

2. Electroplating and spray galvanizing
Electroplating is a process where zinc ions are deposited onto the surface of a steel pipe through an electrolytic reaction. Its characteristic is a relatively thin zinc layer, resulting in relatively poor corrosion resistance. Depositing zinc in an electrolyte solution or spraying zinc powder onto the steel pipe is low-cost but slightly less corrosion resistant. Spray galvanizing involves spraying zinc powder onto the surface of the steel pipe to form a protective layer. These different galvanizing processes each have their own characteristics; the choice of method depends mainly on specific application requirements and cost considerations.

Read more: Seamless vs Welded pipe