At the renovation site of urban water supply pipe networks, silver-gray pipes are being laid in an orderly manner; at coastal wind power project bases, pipes soaked in seawater for years remain intact—these "corrosion-resistant experts" are exactly hot-dip galvanized seamless pipes.

I. Raw Material Refining: Seamless Base Material Lays the Foundation for Quality

"The 'confidence' of hot-dip galvanized seamless pipes starts accumulating from the raw material stage," said Engineer Zhang, the production director, pointing to the round steel billets in the workshop. The enterprise selects high-quality carbon structural steels such as Q235B and 20# as raw materials. After being heated at a high temperature of 1200℃, the materials are rolled into seamless steel pipes with an outer diameter of 10-630mm and a wall thickness of 1.5-50mm via a piercing mill.

"During the piercing process, we adopt the 'three-roll cross-rolling' technology to ensure the wall thickness deviation of the steel pipe is ≤10% and the ovality is controlled within 0.5mm, laying a uniform base material foundation for subsequent anti-corrosion treatment," Engineer Zhang added.

In the flaw detection workshop, the reporter saw that the initially formed seamless pipes were undergoing a dual "physical examination"—eddy current testing and ultrasonic testing. The detection accuracy for each meter of pipe reaches 0.1mm; if defects such as inner wall cracks or laminations are found, the pipes will be directly sent for rework. "The integrity of seamless pipes is the prerequisite for anti-corrosion; any tiny flaw may become a 'breakthrough point' for corrosion in the later stage," emphasized Li Na, a quality inspection engineer.

II. Core Hot-Dip Galvanizing Process: Applying "Corrosion-Resistant Armor" at 480℃

After pre-treatment, the seamless pipes immediately enter the core hot-dip galvanizing process. On the fully automated production line:

The pipes first pass through a degreasing tank to remove surface oil stains;

Then they are immersed in a pickling tank (15% hydrochloric acid solution) for 30-40 minutes to completely remove oxide scales;

Next, they go through a fluxing tank (zinc chloride-ammonium chloride solution) for surface activation;

Finally, they are slowly immersed in molten zinc liquid at 480℃, held for 2-5 minutes, and then lifted out at a constant speed—forming a zinc coating with a thickness of 60-100μm.

"Temperature and time are key parameters," Engineer Zhang demonstrated the zinc liquid temperature control system on site, where the screen showed real-time temperature fluctuations controlled within ±5℃. "Too low a temperature will lead to poor adhesion of the zinc coating, while too high a temperature will cause the zinc coating to be too thick and crack."

For long pipes exceeding 12 meters in length, the enterprise adopts the "segmented galvanizing + intermediate supplementary plating" process to ensure uniform coverage of the zinc coating, making the anti-corrosion effect at both ends consistent with that of the pipe body.

III. Performance Testing: A "Corrosion-Resistant Champion" Under Strict Challenges

Before leaving the factory, hot-dip galvanized seamless pipes must pass a number of "extreme tests" to verify their quality. In the laboratory, the reporter witnessed the salt spray test: pipe samples were placed in an atomized environment of 5% sodium chloride solution; after 500 hours of continuous testing, the corrosion rate of the zinc coating was only 0.002mm/year, far lower than the national standard of 0.005mm/year.

In the bending test, after the pipe was bent to 120°, the zinc coating showed no peeling or cracking, demonstrating excellent adhesion and toughness. "We also conduct zinc coating thickness testing for each batch of products," Li Na measured different positions of the pipe with a magnetic thickness gauge, and the data showed that the thickness was consistently between 80-90μm. "Pipes used in municipal engineering require a zinc coating thickness of no less than 85μm, and all our products exceed this standard."

In addition, during the water pressure test, the pipes must maintain pressure at 1.5 times the working pressure for 30 minutes without leakage or deformation to be qualified.

IV. Wide Applications: Empowering "Longevity" for Infrastructure in Multiple Fields

With its outstanding anti-corrosion performance, hot-dip galvanized seamless pipes have become the "main force" in the infrastructure field. According to industry data, their application proportion in fields such as municipal water supply, gas transmission, petrochemical engineering, and power communication exceeds 65%.

In the underground comprehensive pipe gallery project of Xiong'an New Area, the water supply pipes made of this material have a designed service life of 50 years; in the Putian offshore wind power project in Fujian Province, hot-dip galvanized seamless pipes have withstood the erosion of a high-salt spray environment and remained stable after 3 years of operation.

"Compared with ordinary steel pipes, hot-dip galvanized seamless pipes do not require frequent maintenance, which can reduce the whole-life cycle cost by more than 30%," said Professor Wang, an expert from the China Pipeline Engineering Association. "With the advancement of new urbanization and new energy projects, the demand for hot-dip galvanized seamless pipes will continue to grow, and the market scale is expected to exceed 30 billion yuan by 2025."

From urban underground pipe networks to offshore projects, hot-dip galvanized seamless pipes are using their "corrosion-resistant armor" strength to build a solid safety barrier for various infrastructure projects and safeguard the "lifeline" of urban operation and energy transmission.