Galvanized steel pipes were once widely used in water supply, fire protection, and HVAC systems, relying primarily on their zinc coating for corrosion protection. However, in actual use, many users encounter a typical problem: after a few years of use, the pipes begin to clog, water pressure drops, and even serious corrosion leaks occur.
The reason behind this is not a single factor, but rather the result of the combined effects of material properties, water quality, usage environment, and time.
I. Why do galvanized steel pipes corrode?
- The “sacrificial protection” of zinc plating is limited.
The essence of zinc plating is based on the principle of electrochemical corrosion:
- Zinc (Zn) is more reactive than iron (Fe).
- In a corrosive environment, zinc is preferentially oxidized (“sacrificial anode”),
- thus protecting the internal steel from corrosion.
The problem is that zinc will eventually be depleted.
Once the zinc layer is exhausted:
- the exposed steel substrate is in direct contact with water and oxygen,
- and the corrosion rate will accelerate significantly.
- Water and oxygen are “catalysts” for corrosion.
When water is transported inside a pipe for a long time, the following processes continuously occur:
- Dissolved oxygen participates in the reaction
- Electrolytes (salts, ions) in the water accelerate corrosion
- Rust (Fe₂O₃) forms
Results:
- The pipe wall gradually thins
- The inner wall becomes rough
II. Why does “internal blockage” occur?
- Continuous accumulation of corrosion products
Substances produced by corrosion include:
- Red rust (iron oxide)
- Black rust (magnetic iron oxide)
- Zinc corrosion products (white rust)
These substances will:
- Adhere to the pipe wall
- Gradually thicken
Ultimately leading to:
- A smaller pipe diameter
- A decrease in flow rate
- Scale Deposition (especially in hard water areas)
If the water contains a high amount of calcium and magnesium ions (hard water):
- Scale (CaCO₃) forms after heating or prolonged flow.
- Scale adheres to rough, corrosive surfaces.
- Corrosion + Scale = Double Blockage
- Localized Corrosion Leading to Particle Shedding
The following may occur inside the pipeline:
- Pitting (localized corrosion)
- Localized spalling
These fragments will:
- Be carried away by water flow
- Clog valves, nozzles, and terminal equipment
III. What factors accelerate the failure of galvanized steel pipes?
- Water quality issues
| Water Quality Type | Impact |
|---|---|
| High dissolved oxygen water | Accelerates oxidation |
| High chloride (Cl⁻) content | Damages the zinc coating |
| Acidic water (low pH) | Accelerates corrosion |
| Hard water | Prone to scaling and blockage |
- Temperature Factors
- High temperatures (>60°C) accelerate zinc plating dissolution.
- This significantly reduces the lifespan of galvanized pipes in hot water systems.
- This is why many standards do not recommend the use of galvanized pipes in hot water systems.
- Flow Rate and Erosion
- High flow rate → Accelerates zinc plating wear.
- Low flow rate → Easily deposits impurities.
- Installation and Construction Issues
- Lack of anti-corrosion treatment after cutting.
- Welding damages the galvanized layer.
- Residual impurities inside the pipe.
- IV. Typical Problem Manifestations
Many clients encounter the following issues in actual projects:
- Increasingly low water pressure
- Weak or even interrupted water flow
- Yellowish water with a rusty taste
- Frequent clogging of valves and sprinklers
- Leaking or even bursting pipes
Root Cause: Internal corrosion + buildup and blockage
V. How to effectively prevent or solve this problem?
- Optimize material selection
| Application Scenario | Recommended Alternative Solutions |
|---|---|
| Drinking water systems | Stainless steel pipe / PPR pipe |
| Industrial fluids | Carbon steel pipe + internal coating |
| Highly corrosive environments | Epoxy-coated steel pipe |
- Water Quality Control
- Install filters
- Reduce hardness (soft water treatment)
- Control pH level
- Regular Maintenance
Pipe flushing
Descaling
Endoscopic inspection
- Corrosion Protection Upgrade
- If galvanized steel pipes must be used:
- Choose hot-dip galvanizing (thick zinc layer)
- Add inner coating protection
- Use cathodic protection (high-end projects)