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ASTM A252 standard specifies steel pipes for welded or seamless steel pipe piles. This standard mainly classifies different steel grades based on the minimum yield strength of steel pipes.

The latest version of ASTM A252 (such as A252/A252M-19) classifies steel pipe piles into the following three steel grades: Grade 1 (GR 1), Grade 2 (GR 2), and Grade 3 (GR 3)

Grade 1 (GR 1):

Strength level: This is the steel grade with the lowest strength requirement in the ASTM A252 standard. Its minimum yield strength is 205 MPa (30 ksi), and the minimum tensile strength is 345 MPa (50 ksi).

Material properties: Usually made of carbon steel or low alloy steel. The relatively low strength means that it usually has better ductility and weldability.

Typical applications:

Pile foundation projects with relatively low bearing capacity requirements.

In situations where the soil conditions are relatively good (such as dense sandy soil or hard clay), and the lateral earth pressure or end resistance requirements are not high.

When the long-term ultimate bearing capacity requirement for temporary support structures (such as foundation pit support) is not high.

Projects that are cost-sensitive and whose strength requirements can be met by GR1.

Advantages: The cost is usually the lowest, and processing (such as cutting and welding) is relatively easy.

Grade 2 (GR 2):

Strength level: Medium strength steel grade. The minimum yield strength is 240 MPa (35 ksi), and the minimum tensile strength is 415 MPa (60 ksi). Compared with GR1, the yield strength has increased by approximately 17%, and the tensile strength has increased by approximately 20%.

Material properties: Also made of carbon steel or low alloy steel. Strike a balance between strength and solderability.

Typical applications:

The most commonly used and widely applied steel grade. It is applicable to most conventional permanent pile foundation projects.

Foundations of buildings, Bridges, docks and other structures with medium load-bearing capacity requirements.

The soil conditions are medium (such as common sandy soil, silt, and clay).

Projects that need to take into account both economy and carrying capacity.

Advantages: It has excellent comprehensive performance in terms of strength, solderability, cost and availability.

Grade 3 (GR 3):

Strength level: The steel grade with the highest strength requirements in the ASTM A252 standard. Its minimum yield strength has been significantly increased to 310 MPa (45 ksi), and the minimum tensile strength is the same as that of GR2, which is 415 MPa (60 ksi). The yield strength is approximately 29% higher than that of GR2 and approximately 51% higher than that of GR1.

Material properties: Generally, it is necessary to use low-alloy steel with higher strength or undergo specific processing techniques (such as controlled rolling, microalloying). High yield strength is its most prominent feature, but its ductility and weldability may be relatively lower than those of GR1/GR2, and more stringent welding process control is required.

Typical applications:

Pile foundation projects with extremely high load-bearing capacity requirements.

The foundations of super high-rise buildings, large industrial facilities, heavy Bridges, offshore platforms, etc.

Poor or complex soil conditions (such as soft soil, deep water, and areas with high seismic intensity) require the pile body to have extremely high strength to resist huge axial loads, bending moments, lateral earth pressure or dynamic loads (such as earthquakes, ship impacts).

In situations where the pile diameter or wall thickness needs to be reduced to meet specific spatial limitations while ensuring high bearing capacity (by taking advantage of its high yield strength).

Advantages: It offers the highest yield strength, capable of withstanding extremely heavy loads and complex stress states, and helps optimize the design of piles (such as reducing cross-sectional dimensions).

Manufacturing process: ASTM A252 covers welded steel pipe piles (straight seam welded or spiral welded) and seamless steel pipe piles. Welding is the main process.

Dimensional specifications: The standard specifies the range of outer diameter and wall thickness of steel pipe piles and their allowable deviations. Wall thickness is one of the key factors affecting bearing capacity and should be selected based on the design load.

Chemical composition: Although the standards mainly classify based on mechanical properties, there are also upper limit restrictions on chemical composition (such as carbon, manganese, phosphorus, sulfur, etc.) to ensure the weldability, toughness and overall quality of the material. GR3 may have higher requirements for alloy elements to meet high strength.

Process requirements:

Welding: All weld seams must be continuous and meet non-destructive testing requirements (usually ultrasonic testing or radiographic testing). High steel grades (especially GR3) have higher requirements for welding process qualification and welder skills.

End treatment: The ends of the steel pipes need to be cut flat to ensure the quality of butt welding or installation of pile boots.

Straightness: Steel pipes need to meet certain straightness requirements.

Marking: The manufacturer's name or trademark, standard number (ASTM A252), steel grade (GR 1, GR 2, GR 3), size specifications (outer diameter and nominal wall thickness), furnace number/batch number, etc. must be clearly marked on the steel pipe. Usually, the pipe ends are also colored (such as yellow for GR2) for auxiliary identification.

Testing and Certification: Manufacturers are required to provide material test reports to prove that the products meet the standard requirements, including mechanical property tests (tensile tests) and chemical analysis results.

Design and selection: The choice of steel grade depends on the design load of the pile foundation (axial pressure/tension, bending moment, shear force), geological conditions (soil parameters, groundwater, seismic risk), environmental factors (corrosiveness), construction methods and economy. Structural engineers will make calculations and choices based on these factors. GR2 is a commonly used choice, GR3 is used in high-demand situations, and GR1 is used in less demanding or temporary projects.

Anti-corrosion: For steel pipe piles, anti-corrosion measures usually need to be considered based on the service environment, such as coating, cathodic protection or increasing the corrosion margin (increasing the wall thickness).

GR 1: Low foundation strength, low cost, good ductility and weldability, and is used for projects with low loads or temporary ones.

GR 2: The most commonly used medium strength grade, with good comprehensive performance and suitable for most permanent pile foundations.

GR 3: Maximum yield strength, used in critical projects subject to extremely large loads and complex stresses (super high-rise buildings, heavy loads, harsh geological/environmental conditions), but attention should be paid to the requirements for welding and ductility.

When choosing and using, it is essential to refer to the specific design requirements of the project and the detailed provisions of the latest valid version of ASTM A252 corresponding to the purchased products.

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