Galvanized vs black steel pipe

Galvanized steel pipes and black steel pipes are the two most common types of products. All of them are based on carbon steel, but due to different surface treatment methods, their performance and applications vary significantly. Galvanized steel pipes are coated with a layer of zinc on the outside, which makes them have excellent anti-corrosion performance and a long service life. They are often used in water supply, outdoor projects and agricultural irrigation. Black steel pipes, on the other hand, are not treated for protection and have a lower cost. However, they have poor corrosion resistance and are more suitable for the transportation of media such as natural gas and steam or for indoor use.

1. Definition and Manufacturing process

What is galvanized steel pipe?
Galvanized steel pipes are usually made of carbon steel pipes as the base material, with a layer of zinc plated on its surface to enhance the corrosion resistance of the steel pipes. Common methods include:
Hot-dip galvanizing: Steel pipes are immersed in molten zinc to form a thick zinc layer.
Cold galvanizing: By electroplating or other methods, a thin layer of zinc is attached to the surface of steel pipes. It has a relatively low cost, but the zinc layer is prone to damage and has limited corrosion resistance.

What is black steel pipe?
Black steel pipes refer to those that have not undergone galvanization or other coating treatments. Their surfaces appear black or dark gray due to the natural film of iron oxide, and they are usually made of hot-rolled steel.

2. The differences between galvanized steel pipes and black steel pipes

(1) In terms of appearance: The zinc coating on galvanized steel pipes adheres to carbon steel pipes, presenting a silver-white or grayish white color, while the surface of black steel pipes appears black or dark gray. The main reason for this color is the iron oxide layer on the surface of the steel pipes.
(2) In terms of performance: The corrosion resistance of galvanized steel pipes is significantly higher than that of black steel pipes. The main reason is that the zinc layer can form a protective film, preventing the steel pipe from direct contact with air or moisture. Moreover, the oxidation of zinc will also form an oxide film, further enhancing the anti-corrosion performance of the steel pipe. The surface of black steel pipes is only covered with a thin film of iron oxide, which is highly prone to oxidation and rusting. They can only be used indoors or in dry environments.
(3) In terms of cost: Galvanized steel pipes are relatively more expensive due to the addition of the galvanizing process, while black steel pipes have not undergone complex treatments, resulting in lower production costs and better economic performance, making them suitable for large-scale production.
(4) In terms of application fields: Galvanized steel pipes are generally used in water supply and drainage systems and other water transportation systems, while black steel pipes are mostly used in natural gas and liquefied gas transportation pipelines and as building structural components, steel frames, etc.

Frequently Asked Questions (FAQ)

Can galvanized steel pipes be used to transport natural gas?
Q: Generally not recommended. Because the galvanized coating may peel off during long-term use, it may clog pipes or affect the safety of gas transportation. Natural gas pipeline networks mostly use black steel pipes or dedicated gas pipelines.

Can black steel pipes be used to transport drinking water?
Q: Not recommended. Black steel pipes are prone to corrosion and rusting. Long-term use can lead to water pollution. Therefore, galvanized steel pipes or stainless steel pipes are usually chosen for drinking water pipelines.

How long is the service life of galvanized steel pipes?
Q: Under normal conditions, it can be used for 30 to 50 years. The specific lifespan depends on the thickness of the galvanized layer and the usage environment.

Which is better for galvanized steel pipes, hot-dip galvanizing or cold galvanizing?
Q: Hot-dip galvanized steel pipes have stronger corrosion resistance and longer service life, and are widely used in construction and water supply and drainage projects. Cold galvanizing has a low cost, but the coating is thin and prone to peeling off. It is less used in engineering nowadays.

Read more：Hot-dip vs Cold galvanized pipe or Schedule 40 galvanized steel pipe