Steel grades for piling pipe

Pipe piling is a steel pipe used as a structural component for supporting foundations in buildings. It has various steel grades. The following is a detailed introduction to the common steel grades of pipe piles, including different standards such as ASTM A252, API 5L/ISO 3183, European EN10219, etc.

ASTM A252 standard
It is most commonly used in pipe pile construction and has three grades:

ASTM A252 Grade 1: minimum yield strength approximately  205 MPa (≈30 ksi), tensile strength approximately  345 MPa, elongation ~30%.
ASTM A252 Grade 2: Yield ≥ 240 MPa, tensile strength ≥ 415 MPa, elongation ~25%.
ASTM A252 Grade 3 (most commonly used) : yield ≥ 310 MPa, tensile strength ≥ 455 MPa, elongation ~20%. Due to its higher strength, it is more suitable for pile foundation engineering with strict bearing requirements.

The chemical composition of each grade is similar: C ≤ 0.26%; Si ≤ 0.45%; Mn ≤ 1.60%; P ≤ 0.050%; S ≤ 0.030  (Grade 2, 3 the same). OD tolerance ±1%; Minimum wall thickness -12.5%; Appearance defects must be less than 25% of the wall thickness or can be repaired by welding. A water pressure test is not required.

API 5L/ISO 3183 (tubing for oil and gas transportation)
Although these standards originated from transportation pipelines, they can also be used as steel pipe piles in pile foundations, especially in high-strength, long piles and Marine environments.

Common grades: Grade B, X42, X46, X52, X56, X60, X65, X70
The typical mechanical properties of each grade are approximately as follows (taking API B/X60 as an example) :
Grade B: Yield ~245 MPa, tensile strength ~415 MPa, elongation ~23%
X52: ≈360 MPa, 460 MPa, 21%
X60: ≈415 MPa, 520 MPa, 18%
X70: ≈485 MPa, 570 MPa, 17%

This standard steel pipe has restrictions on chemical composition, with carbon ≤0.26%, and limits on elements such as manganese, phosphorus, and sulfur. Some grades allow trace alloying elements like Ni, V, and Nb to enhance strength and toughness.

European EN10219 / EN10220 (formed or welded pipe structure)
It can also be used as pipe piles. Common grades when used as pipe piles:

Typical EN10219 grades: S355, S420MH, S460MH

The corresponding performance is roughly as follows (taking S355J0H as an example) :
Yield of S355 ≈355 MPa, tensile strength ≈480 MPa, elongation ~20%
The yield of S420MH is approximately 420 MPa, the tensile strength is approximately 500-660 MPa, and the elongation is approximately 19%
The yield of S460MH is approximately 460 MPa, the tensile strength is approximately 530-720 MPa, and the elongation is approximately 17%

Such standards have relatively strict control over chemical composition, such as strictly controlling parameters like CEV (carbon equivalent) and nitrogen content to ensure toughness and weldability.

The function of steel pipe piles

Deep bearing and load transfer: Steel pipe piles can transfer the loads they bear to the deep soil layer underground. Through the combined effect of end bearing force and side friction force, the stability and safety of the structure are ensured.
It can form a stable structure: Steel pipe piles themselves have structural properties. If concrete and steel bars are filled inside them, they will become composite piles, significantly enhancing their load-bearing capacity and rigidity.
As a retaining wall structure: In scenarios such as ports, foundation pit support, and bridge construction, pipe piles can be combined with sheet piles to form interlocking walls, which not only bear weight but also prevent soil or water from intruding, and have the dual functions of water and soil retention.

The advantages of steel pipe piles

High axial load-bearing capacity: Large-diameter structures can provide a larger end bearing area and side friction area, enhancing the overall load-bearing performance.
High bending stiffness and strong resistance to lateral loads: Suitable for conditions such as bridge piers and retaining walls that are subjected to lateral ground pressure or wind loads.
Convenient for construction and transportation: It can be installed by welding or direct socket connection, and the transportation is simple. It can be transported by various means of transportation.
High strength: Steel pipe piles have a very high tensile strength and can withstand considerable pressure.

Green and environmentally friendly: Steel can be recycled and reused, reducing carbon dioxide emissions.

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