The base materials are different: PPGI (polytetrafluoroethylene) is the abbreviation for pre-painted galvanized steel, while PPGL is the abbreviation for pre-painted galvanized steel. As the name suggests, PPGI uses galvanized sheet (with a coating of zinc) as the base metal. PPGL is based on a galvanized steel sheet, which is coated with 55% aluminum, 43.3% zinc and 1.6% silicon. This is the main difference between PPGI and PPGL, which further impacts their functions and applications.

Different lifespans: Both zinc and aluminum-zinc layers are used to protect metal from rusting, thereby extending its service life. For galvanized steel sheets, when the galvanized layer is completely corroded, the base material will be damaged. Generally speaking, the service life of galvanized sheet can reach 10 to 15 years. The aluminum and zinc alloys form microscopic grain regions. The zinc-rich phase corrodes preferentially, while the aluminum-rich phase corrodes very slowly. Therefore, Al-Zn coating is more corrosion-resistant than galvanized steel sheet. According to data, the service life of polylactic acid is 3 times longer than that of PPGI.

Appearance Difference: The surface of PPGL sheets is smoother than that of PPGI sheets. This is because aluminum adheres better than zinc. For the same reason, PPGL sheets can be painted directly without pre-treatment. However, PPGI sheets require pre-treatment.

When selecting steel pipe coatings, the following factors must be comprehensively considered:
Operating Environment: Indoor/outdoor, buried/above-ground, land/marine, dry/humid
Medium Properties: Temperature of conveyed substances, chemical composition, corrosiveness
Design Life: Short-term temporary use or long-term permanent project
Budget Constraints: Balance between initial investment and total lifecycle costs
Construction Conditions: Factory prefabrication or field application, technical capability requirements

As a critical infrastructure material, steel corrugated steel culvert pipes require crucial corrosion protection, directly impacting their service life and safety. Currently, the following corrosion protection methods are available for steel corrugated steel culvert pipes:

1. Coating: Coating is one of the most common corrosion protection methods. By coating the surface of the steel corrugated steel culvert pipes with various anti-corrosion coatings, such as epoxy resin, polyurethane and other high-performance coatings, a dense protective film is formed, which effectively isolates the direct contact between air, moisture and corrosive media and the steel, thereby preventing the steel from rusting. The thickness, uniformity and adhesion of the coating have a decisive influence on the anti-corrosion effect, so the construction process and coating quality need to be strictly controlled.

‌2. Galvanizing anti-corrosion‌: Galvanizing treatment is to immerse the steel corrugated pipe in molten zinc liquid so that the zinc layer is evenly attached to the surface of the steel, forming a corrosion-resistant zinc layer. The zinc layer not only has good corrosion resistance, but also can protect the steel from mechanical damage to a certain extent. There are two main galvanizing methods: hot-dip galvanizing and electro-galvanizing. Hot-dip galvanizing has better anti-corrosion effect, but the cost is relatively high.

‌3. Cathodic protection‌: Cathodic protection is an electrochemical corrosion protection method that uses an auxiliary anode to make the steel below a cathode, forming an electrochemical corrosion cell in the electrolyte solution, thereby inhibiting the corrosion reaction of the steel. Cathodic protection can be divided into sacrificial anode protection and impressed current protection. The sacrificial anode protection method uses a metal that is more active than steel as a sacrificial anode to provide electrons for the steel; the impressed current protection method provides current to the steel through an external power supply, making it a cathode.

‌4. Composite anti-corrosion‌: Composite anti-corrosion is the combination of multiple anti-corrosion treatment methods to achieve better anti-corrosion effect. For example, galvanizing can be performed first and then anti-corrosion paint can be applied, or rust inhibitors can be added to the coating. This treatment method can give full play to the advantages of various anti-corrosion methods and improve the comprehensive anti-corrosion performance of steel bellows.

Common Anti-corrosion Treatment Techniques
Coating Anti-corrosion
This is a relatively common method. Common coating materials include epoxy resin and polyethylene. Taking epoxy resin coating as an example, it can form a dense protective film on the surface of steel bellows, effectively isolating water, oxygen and corrosive media from contact with steel. Moreover, the epoxy resin coating has strong adhesion, can remain stable for a long time, and is not easy to fall off, providing reliable protection for the steel corrugated pipe.

Galvanizing Anti-corrosion: A layer of zinc is applied to the surface of the steel corrugated pipe by hot-dip galvanizing or electro-galvanizing. Zinc is more chemically active than iron. In a corrosive environment, zinc will corrode first, thus protecting the steel. The hot-dip galvanized zinc layer is thicker and has a better anti-corrosion effect. It is suitable for some occasions with high anti-corrosion requirements, such as underground drainage pipes.

Cathodic protection is an electrochemical protection method that applies an electric current to the steel bellows, making it the cathode and thus inhibiting the corrosion of the steel. The sacrificial anode method is usually used to connect metals that are more active than steel (such as magnesium, zinc, etc.) to the steel bellows. The active metal acts as the anode and continuously dissolves, protecting the steel bellows as the cathode.