Mechanical Properties Analysis Of Galvanized Steel Pipes

The mechanical properties analysis of galvanized pipes requires a comprehensive evaluation based on material properties, galvanizing process and application scenarios. The following is a detailed analysis based on the latest industry standards and research data:

I. Basic materials of galvanized pipes

1. Substrate type

1. Carbon steel: commonly used Q195, Q215, Q235 (corresponding to American standard ASTM A53 Grade B), yield strength 195-235MPa, tensile strength 315-430MPa.

2. Low alloy steel: such as Q345 (corresponding to ASTM A106 Grade B), yield strength ≥345MPa, tensile strength 470-630MPa.

3. Stainless steel: 304/316 stainless steel galvanized pipe, yield strength ≥205MPa, tensile strength ≥515MPa, corrosion resistance significantly improved.

2. Galvanizing layer parameters

1. Hot-dip galvanizing: zinc layer thickness 85-150μm (GB/T 3091-2015), zinc layer weight ≥500g/m² (ASTM A53/A53M-21).

2. Electrogalvanizing: zinc layer thickness 8-15μm, suitable for thin coating demand scenarios.

2. Core indicators of mechanical properties

1. Strength and plasticity

Indices	Test standards	Typical value range	Influence mechanism of galvanizing
Streckgrenze	GB/T 228.1	Q235: 235-265MPa	May lift 5-10% after galvanizing(work hardening)
Tensile strength	GB/T 228.1	Q235: 375-500MPa	No significant change
Elongation after fracture	GB/T 228.1	Q235: ≥26%	2-5% reduction (zinc layer brittleness effect)
Reduction of area	GB/T 228.1	Q235: ≥50%	Down about 10%

2. Hardness and toughness

Surface hardness: zinc coating HV (Vickers hardness) is about 50-70, significantly lower than the steel itself (Q235 HBW≈120).

Impact toughness: -20℃ Charpy V-notch impact energy ≥27J (GB/T 18984-2016), low-temperature toughness may decrease by 10-15% after galvanizing.

3. Fatigue performance

Fatigue limit: The fatigue limit of smooth specimens is about 35-45% of the tensile strength. Defects in the galvanized layer (such as microcracks) may reduce the fatigue life by 15-20%.

III. Effect of process on performance

1. Hot-dip galvanizing

Advantages: The zinc layer and the substrate form a Fe-Zn alloy layer (thickness 5-15μm), and the bonding force is ≥35N/cm (GB/T 2694-2018).

Disadvantages: High temperature (450℃) treatment may cause grain coarsening and a decrease in elongation of 5-8%.

2. Electrogalvanizing

Advantages: No high temperature effect, maintaining the original mechanical properties of the substrate.

Disadvantages: The zinc layer has weak adhesion (cross-cut test ≥4B level), and the corrosion resistance is only 1/3-1/2 of hot-dip galvanizing.

4. Performance requirements for typical application scenarios

Application fields	Key indicators	Recommended Materials	Performance requirements
Construction scaffolding	Yield strength, Welding performance	Q235 hot dip galvanized pipe	Yield strength ≥ 235 MPa, weld tensile strength ≥ 375 MPa
High-pressure water transmission pipe	Corrosion resistance, internal pressure resistance	Q345B Hot-dip Galvanized Pipe	Burst pressure ≥ 5 times the working pressure
Electric power threading pipe	Hardness, Impact resistance	20# steel electric galvanized pipe	Rockwell hardness HRB ≥ 70
Automotive drive shaft	Fatigue strength, surface wear resistance	40Cr Galvanized Seamless Steel Pipe	Fatigue life ≥ 10⁶ cycles

5. Standards and test methods

1. International standards

ASTM A53: The yield strength of galvanized steel pipes is ≥250MPa (Grade B) and the minimum elongation is 18%.

EN 10217-1: The thickness of the hot-dip galvanized layer is required to be ≥85μm, and the impact test temperature is -20℃.

2. Chinese standards

GB/T 3091-2015: The uniformity test of the galvanized layer is ≥5 times of copper sulfate immersion without red rust.

GB/T 13793-2016: The flattening test of the straight seam electric welded steel pipe is pressed to 1/3 of the outer diameter without cracks.

6. Performance optimization direction

1. Alloying treatment

Adding 0.1-0.3% Al can refine the grains of the galvanized layer and improve the toughness by 10-15%.

The use of Zn-Al-Mg coating (such as Zn-55% Al-1.6% Si) can improve corrosion resistance by 3-5 times without reducing mechanical properties.

2. Surface treatment

Phosphating pretreatment can enhance the adhesion of the zinc layer, and the cross-cut test can reach 5B level.

Coating epoxy resin (300-500μm) can simultaneously improve corrosion resistance and wear resistance.

VII. Summary and suggestions

1. Performance characteristics

The comprehensive mechanical properties of hot-dip galvanized pipes are slightly lower than those of the substrate, but the corrosion resistance is improved by 5-10 years.

Electro-galvanized pipes maintain the performance of the substrate, but require regular maintenance.

2. Selection suggestions

Select hot-dip galvanized Q345B for high corrosion environments, and select calm steel (such as Q235D) for low-temperature toughness requirements.

Precision mechanical parts should preferably select electro-galvanized seamless steel pipes.

3. Data limitations

The softening of the weld heat affected zone (HAZ) needs to be considered in actual engineering (hardness decreases by 15-20%).

The mechanical properties of girth welds of large diameter steel pipes (DN ≥ 300) need to be verified.