The Difference between Galvanized Seamless Pipes and Galvanized Welded Pipes

Jane

Galvanized seamless pipes are the product of seamless pipes after galvanizing, and galvanized welded pipes are the product of welded pipes after galvanizing. They are all galvanized pipes. The galvanized pipe is a general term, including pipes that are galvanized by different forming methods (seamless or seamed), the purpose of which is to use the zinc layer to improve the corrosion resistance of the pipe. So what is the difference between them?

1. Manufacturing process

A galvanized seamless pipe is a seamless steel pipe made by seamless processes such as perforation. The common manufacturing method is hot rolling or cold rolling. The solid steel billet is heated and perforated, and then goes through multiple rolling processes to make the size accuracy and performance of the pipe meet the requirements. After that, it is galvanized, which mainly includes hot-dip galvanizing and electro-galvanizing. Hot-dip galvanizing is to immerse the seamless steel pipe in molten zinc liquid so that a layer of zinc is attached to the surface of the steel pipe; electro-galvanizing uses the principle of electrolysis to deposit a zinc layer on the surface of the steel pipe.

Galvanized welded pipes are first formed by rolling the strip steel, and then the joints are welded together using welding processes such as high-frequency welding to form a steel pipe with a seam. The welded steel pipe is then galvanized, which can be done by hot-dip galvanizing or electro-galvanizing. However, since the welded pipe itself has a weld seam, special attention should be paid to the galvanizing quality at the weld seam during the galvanizing process to ensure the anti-corrosion performance of the entire pipe.

2. Structural features

The biggest feature of galvanized seamless pipes is that the pipe wall is seamless, which makes the pipe more advantageous in strength and pressure resistance. The seamless structure can effectively avoid the stress concentration problem caused by the weld, and has better stability when it is subjected to high-pressure fluid transportation or large external pressure. And because there is no weld, it is smoother and more regular in appearance.

A galvanized welded pipe has a longitudinal weld, which is a distinct structural feature. Although modern welding technology can make the weld quality higher, the weld is still a relatively weak link. When subjected to greater pressure or impact, the weld may become the starting point of rupture. However, welded pipes are relatively more flexible in the selection range of pipe diameter and wall thickness, and can produce pipes of various sizes by adjusting the welding process and the specifications of the strip steel.

3. Corrosion resistance

Due to the seamless structure of galvanized seamless pipes, the galvanized layer can be more evenly covered on the surface of the pipe, providing good anti-corrosion protection. Under the same galvanized layer thickness and quality, the corrosion resistance of seamless pipes is relatively more stable, especially in some harsh corrosive environments or application scenarios with high requirements for pipe integrity.

If the galvanizing quality of the galvanized welded pipes is not well controlled, the zinc layer may be uneven or partially fall off, thus affecting the overall corrosion resistance. However, as long as the galvanizing process is qualified, it can also provide good anti-corrosion effect in general environment, such as being widely used in water supply and drainage systems of ordinary buildings.

4. Strength and pressure resistance

Galvanized seamless pipes have high strength and pressure resistance and can be used to transport high-pressure liquids or gases. For example, in oil and natural gas pipelines, some galvanized seamless pipes are used to ensure the safe operation of the pipelines under high pressure.

The strength and pressure resistance of galvanized welded pipes are relatively low, and they are generally suitable for low-pressure fluid transportation or structural applications with low pressure requirements, such as building fences, ordinary ventilation ducts, etc.

5. Application areas

Galvanized seamless pipes are mainly used in fields that require high quality, strength and corrosion resistance of pipes, such as corrosive fluid pipelines in the chemical industry, high-pressure oil and natural gas pipelines (parts), and high-precision structural components in machinery manufacturing.

Galvanized welded pipes are widely used, but they are mainly used in places that do not require high pressure but are more sensitive to cost, such as ordinary water supply and drainage pipes, heating pipes, building scaffolding, decorative guardrails, etc. in the construction industry.