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ASTM A123 is a standard specification for hot-dip galvanized coatings of steel products formulated by the American Society for Testing and Materials (ASTM), with the core objective of ensuring the quality and durability of the hot-dip galvanizing process. This standard covers all kinds of steel products, including pipes, structural profiles, plates, etc.

1. Scope of application
It is applicable to steel products (such as steel pipes, structural components, bars, etc.) produced by rolling, forging and casting, and requires overall hot-dip galvanizing.
- Not applicable to galvanized thin steel plates (thickness <0.76mm), wire rods or threaded fasteners in continuous production lines (this category is subject to ASTM A153).

2. Requirements for coating thickness
Classified by material category and steel thickness, the minimum average coating thickness needs to meet the requirements of the following table :

Material category	Steel thickness range (mm)	Minimum average coating thickness (μm)
Pipes and conduits	<1.5	45
	1.5-3.0	45
	3.0-4.5	75
	4.5-6.0	75
Steel bars	Any thickness	100
Structural profiles/plates	>6.0	100

Special scenario requirements: For instance, the rectifier housing needs to be ≥610g/m² (approximately 85μm/ single-sided).

3. Pretreatment and process
- Degreasing and pickling: Thoroughly remove grease and rust to ensure the bonding strength of the zinc layer.
- Flux treatment: Use ammonium chloride/zinc chloride solution to prevent secondary rusting and promote the reaction between zinc and iron.
Galvanizing temperature: 435-450°C, and the time is adjusted according to the thickness of the component (the thicker the component, the longer the time).
- Structural design: For closed pipe fittings (such as box-type columns), zinc drainage holes (with a diameter of ≥φ20mm) should be reserved to prevent zinc liquid residue from causing an explosion (" zinc explosion phenomenon ").

4. Sampling and Testing
- Sampling plan: Samples are randomly selected from each batch. Pipe fittings with a surface area of ≤100,000mm² are regarded as single samples. Larger components need to be tested in three sections.
- Thickness measurement: Take ≥5 points for each sample and use the magnetic method (ASTM E376) or the microscopic method (ASTM B487).

ASTM A123 classifies products by form and application. It does not directly define "steel grade", but matches the coating grade based on the material category and the thickness of the substrate:
- Pipes and Tubes: Suitable for ordinary pipes and structural pipes, with medium coating requirements (45-75μm).
- Structural Shapes: Such as H-beams and I-beams, which require a high coating (75-100μm).
- Rebar: Concrete reinforcing component, uniformly required to be 100μm (corrosion resistance preferred).
- Plates: When the thickness is greater than 6mm, a 100μm coating is required.

Note: The base material needs to comply with supporting standards such as ASTM A105 (carbon steel forgings) to ensure mechanical properties.

1.Long-lasting anti-corrosion
The zinc coating isolates oxygen and moisture, with a lifespan of 30 to 50 years (particularly significant in humid or salt spray environments), and the salt spray test lasts for more than 500 hours.

2. High bonding strength
Zinc-iron metallurgical bonding (alloy layer thickness 50-80μm), resistant to mechanical impact and not easy to peel off.

3. Economy and environmental protection
The cost is lower than that of stainless steel, and the maintenance cost is low (only regular inspection is required). Zinc can be 100% recycled.

4. Convenient for construction
Galvanized pipes can be directly installed, eliminating the need for on-site anti-corrosion processes (such as painting) and shortening the construction period by more than 30%.

Field	Typical Scenarios	Cases/Advantages
Building structure	Steel structure beams and columns, bridge supports	Box columns filled with concrete + galvanizing to enhance seismic resistance/load-bearing capacity
Power facilities	Rectifier housing, cable tray	Land-based equipment requires a coating of ≥610g/m² (anti-electrochemical corrosion)
Water conservancy projects	Water supply pipelines and direct drinking water systems	Comply with NSF hygiene standards, with no risk of zinc ion leakage
Marine Engineering	Shipbuilding structural pipes, wharf supports	Replace traditional welded pipes, resistant to seawater corrosion
Industrial components	Flange joints (such as ASTM A105+ galvanized)	150psi low-pressure system, quick-release design

- Deformation control: Thin-walled tubes (<3mm) require a low-temperature slow zinc extraction process to prevent cooling deformation.

- Repair Specification: The damaged points shall be repaired in accordance with ASTM A780, using zinc-based coating + sealing agent.

- Contact with concrete: The steel bar assemblies need to be galvanized as a whole (ASTM A123), and the loose bars need to be treated in accordance with ASTM A767.

The hot-dip galvanized pipe certified by ASTM A123 integrates corrosion resistance, structural strength and economic benefits, and is an ideal choice for infrastructure in severely corrosive environments. When designing, it is necessary to strictly follow the requirements such as zinc drainage holes and coating classification to ensure the safety of the project.

ASTM A123 HOT DIP GALVANZIED PIPE

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