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
Limite d'élasticité	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.

There are mainly the following cutting methods for anti-corrosion steel pipes:

Mechanical cutting

External installation cutting: Using the principle similar to that of a lathe, the cutting equipment is installed on the outside of the steel pipe, and the pipe mouth is cut and beveled by a turning tool. This method has a large span for a single machine, a wide range of steel pipe thicknesses that can be processed, less waste, basically no pollution, and no high temperature during processing, so it will not affect the pipe material, which is beneficial to subsequent welding work. It is often used for cutting large-diameter anti-corrosion steel pipes, such as in the construction of long-distance oil and natural gas pipelines, when cutting and cutting 3PE anti-corrosion steel pipes with larger diameters.

Internal installation cutting: The cutting tool is placed inside the steel pipe for cutting operations, which is also based on the principle of turning tool processing. It is suitable for some occasions where it is not convenient to cut from the outside, or where there are special requirements for the cutting quality of the internal steel pipe, such as after the construction of the internal anti-corrosion layer of some chemical pipelines, precise cutting is required inside to meet the process requirements.

Flame cutting

Oxygen-acetylene flame cutting: By adjusting the oxygen valve and acetylene valve, changing the mixing ratio of oxygen and acetylene, three different flames can be obtained: neutral flame, oxidizing flame and carburizing flame. Neutral flame is suitable for cutting general carbon steel anti-corrosion steel pipes; oxidizing flame has a higher temperature and can be used to cut some thicker steel pipes, but it may increase the degree of metal oxidation at the cut; carburizing flame is suitable for cutting high-carbon steel and other steels that are prone to hardening, which can reduce the hardening phenomenon at the cut. At the construction site, oxygen-acetylene flame cutting is a common method for cutting ordinary anti-corrosion steel pipes used for fire protection pipelines.

Plasma cutting: With different working gases, it can cut various metals that are difficult to cut with oxygen cutting, especially for non-ferrous metals such as stainless steel, aluminum, copper, titanium, nickel, etc., and the cutting effect is better. When cutting metals with small thickness, plasma cutting speed is fast. For example, when cutting ordinary carbon steel thin plates, the speed can reach 5-6 times that of oxygen cutting method. The cutting surface is smooth, the thermal deformation is small, and the heat affected zone is also small. Plasma cutting is often used for the processing of some stainless steel anti-corrosion steel pipes that require high cutting accuracy and quality.

Water cutting

High-pressure water is generated by a high-pressure pump, mixed with abrasives such as corundum, and sprayed onto the surface of the steel pipe through a nozzle for cutting. Its incision is clean, the thermal impact on the steel pipe is almost zero, and it will not change the material properties of the steel pipe. The processing span is also large, and it can adapt to the cutting of steel pipes of different diameters. However, the efficiency of water cutting is relatively low, and the processing thickness is limited by factors such as the pressure of the high-pressure pump and the performance of the abrasive. It is generally suitable for the cutting of anti-corrosion steel pipes with high cutting accuracy requirements, strict requirements on material properties, and small cutting volume, such as in the installation of anti-corrosion pipelines in some precision instrument production workshops.

Sawing

Metal saw cutting: General anti-corrosion steel pipes can be cut with metal saws, and small-diameter pipes can be cut with manual or electric metal saws. They are easy to operate, low cost, and can meet general cutting accuracy requirements. For example, in small-scale building decoration projects, manual metal saws can be used to complete a small amount of cutting of anti-corrosion steel pipes below DN50.

Sawing machine cutting: Large diameter pipes should be cut by sawing machine, which has high cutting accuracy, relatively flat cutting surface, and can ensure that the cross section of the pipe is perpendicular to the axis of the pipe. In pipe processing factories, sawing machines are often used when cutting batches of large diameter epoxy resin powder anti-corrosion steel pipes.

Galvanized steel pipes rely on their own high toughness, good bending and welding properties, but are mainly made of important parts that require extremely high wear resistance and crack resistance. The thickness of the wear-resistant layer of wear-resistant alloy pipes varies, generally controlled between 3-120mm, so their hardness grades are also different.

Compared with ordinary alloy wear-resistant pipes or other materials, alloy wear-resistant steel pipes have much stronger wear resistance, and are much higher than the wear resistance obtained by spray welding and thermal spraying. The wear-resistant layer of the wear-resistant pipe is metallurgically bonded to the substrate, and the bonding strength is high.

Even if it is impacted, it can absorb energy during the impact process, and the wear-resistant layer will not fall off. If it can be applied to working conditions with strong vibration and impact, this is unattainable for cast wear-resistant materials and ceramic materials.

Although the surface strength of ordinary galvanized steel pipes can be improved after heat treatment or surface carburizing, nitriding and other treatments, if the hardness of this wear-resistant alloy pipe is too high, it may peel off quickly, which is not conducive to wear resistance, and some softer materials may also be more wear-resistant.

Alloy wear-resistant pipes are wear-resistant mainly because they not only have hard particles but also a soft matrix. Generally, during the wear process, some detached materials will be integrated into the soft matrix and will not cause much damage to the surface. If the hardness of the pipe matrix structure is also relatively high, the falling abrasives or other materials will grind against each other during the mutual movement, which will destroy the matrix structure faster. For galvanized steel pipes, hardness is only one of the parameters, and it is also related to its chemical composition, but as a key parameter to measure pipeline performance, it should be paid more attention.

The function of the pipeline is mainly to transport liquids or other solids. It can be said to be the most commonly used equipment in our lives. 3 treatment methods for pipeline anti-corrosion.

1. What are the treatment methods for pipeline anti-corrosion?

1. Pipeline external anti-corrosion design Petroleum asphalt is the oldest pipeline anti-corrosion layer, which is well used in most dry areas. At present, epoxy coal tar, zinc-rich coatings, etc. have replaced petroleum asphalt as anti-corrosion coatings for steel water pipelines, and epoxy coal tar series coatings have excellent anti-corrosion performance and low prices.

2. The anti-corrosion coating on the outer wall of the pipeline is evenly and densely applied on the surface of the rust-removed metal pipeline to isolate it from various corrosive media. It is one of the most basic methods for pipeline anti-corrosion. Since the 1970s, laying pipelines in harsh environments such as polar regions and oceans, and heating and transporting oil products to increase the temperature of the pipeline, have put forward more requirements on the performance of the coating.

3. Pipeline inner wall anti-corrosion coating Surface treatment of the inner wall of the pipe can ensure that the coating is firmly bonded to the pipe wall. Since the 1970s, the trend has been to use the same material for the inner and outer wall coatings of the pipe so that the inner and outer wall coatings can be carried out simultaneously. Before the pipeline is treated for corrosion, the surface of the pipeline substrate must be treated to remove moisture, oil, dirt, pollutants, rust and scale on the surface of the substrate. There are many methods for surface treatment, and manual rust removal, sandblasting or chemical rust removal are generally used. When removing rust manually, the quality standard should reach St3 level; when sandblasting or chemical rust removal, the quality standard should reach Sa2.5 level, and the surface roughness of 30 to 50µm is more appropriate. The treated surface should be primed within 4 hours.

2. What is the role of pipeline anti-corrosion?

1. Prevent the pipeline from being corroded by soil, air, medium, etc. Nowadays, pipelines are mostly used to transport gasoline, natural gas and other substances. These substances have a very large corrosive effect on the soil of the environment, and pipelines can effectively prevent the environment from being polluted by these substances, and greatly improve the transportation efficiency.

2. Pipeline anti-corrosion can prevent the leakage of natural gas, oil, etc., and has a very good protection and prevention effect on fire and the environment.

3. What are the precautions during pipeline anti-corrosion construction?

1. The ambient temperature should be higher than 5℃ and the air humidity should be lower than 80% during the construction of the anti-corrosion layer.

2. The diluent ratio is 5%, the glass cloth is pressed 20-25mm, and the overlap length of the cloth head is 100-150mm.

3. Anti-corrosion layer voltage inspection: ordinary level 2000V; reinforced level 2500V; extra reinforced level 3000V.

4. Anti-corrosion layer inspection: every 10km leakage point ≯5, use a low-voltage audio signal leak detector to measure.

The buried pipeline uses plastic-coated steel pipe for the transmission line tower, which is composed of towers connected by tower pole devices. The pole tower is made of steel. The surface of the tower pole steel and the inner and outer surfaces of the tower pole are hot-dipped with a modified polyethylene plastic layer. The plastic-coated steel pipe is a steel pipe coated with red modified epoxy resin powder inside and outside. It is a new type of steel pipe made on the basis of steel pipe, through sandblasting chemical pretreatment, preheating, inner and outer coating, curing, post-treatment and other processes.

It successfully solves the problems of burial, rust, scaling and other problems of plastic-coated steel pipe. There will be no pipe blocking and spray blocking, which improves the service life of fire water supply pipelines. The plastic-coated steel pipe mainly focuses on the excellent mechanical properties of steel and the excellent chemical corrosion resistance of polymer materials. The product has excellent anti-static, high-pressure and flame-retardant properties, and can withstand harsh use environments. Its super corrosion resistance greatly improves the service life of the pipeline.

This steel pipe has good pressure resistance and thermal insulation properties. It mainly protects the wires, so leakage will not occur at all. So far, plastic-coated steel pipe manufacturers are changing these advantages. The pipe wall is relatively smooth and burr-free. It is suitable for crossing cables or wires during construction.

Fire buried pipe plastic-coated steel pipe has the advantages of smooth wall thickness, good drainage performance, low fluid resistance, and no scaling, which can greatly reduce losses compared with other pipes. At the same time, the linear expansion coefficient of large-diameter plastic-coated pipes is very small, making it very advantageous as a main pipeline, greatly overcoming the defects of other plastic pipes and ordinary pipes with large linear expansion coefficients.

Plastic-coated steel pipe is an upgraded product of traditional steel-plastic pipes and galvanized pipes. It has comprehensive properties such as high strength, high elongation, good low-temperature brittleness, low expansion coefficient, corrosion resistance, wear resistance, and low fluid resistance. It belongs to a new type of water supply and drainage, anti-corrosion green large-diameter pipeline, which is more and more widely used in domestic industry.