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 A detailed interpretation of the specific requirements for Hot Formed Steel pipes in the EN 10210 standard.

EN 10210-1 and EN 10210-2 are European standards that specify the technical requirements for hot-formed welded hollow sections of non-alloy and fine-grained structural steel used in load-bearing structures. These requirements are very comprehensive, ensuring the safety and reliability of steel pipes in key structures such as buildings and Bridges.

The following are the core requirements for steel pipes in this standard, which are mainly divided into several aspects:

• Manufacturing method:

The steel pipe must be hot-formed. This usually refers to bending steel plates or steel strips at high temperatures (typically above the recrystallization temperature) and welding them (usually using continuous welding processes such as submerged arc welding (SAW)), then flattening the weld seam through mechanical, thermal or combined methods and shaping the entire cross-sectional dimensions.

• Steel grade:

The standard specifies specific grades of non-alloy and fine-grained structural steel. These grades are identified by their minimum yield strength. The most common ones include:

◦ S235J2H, S235J0H

◦ S275J2H, S275J0H, S275N/NH, S275M/MLH

◦ S355J2H, S355J0H, S355K2H, S355K0H, S355N/NH, S355M/MLH (these are the most widely used grades)

◦ S420N/NH, S420M/MLH

◦ S460N/NH, S460M/MLH, S460Q/QL/QL1H

◦ Grade meaning: For example, S355J2H

▪ S: Structural steel

▪ 355: The minimum yield strength is 355 N/mm²

▪ J2, K2, J0, K0: represent impact toughness grade (quality grade)

▪ J: 27J impact energy, test temperature 0°C

▪ K: 40J impact energy, test temperature 0°C

▪ J0: 27J impact energy, test temperature +20°C (lower toughness requirement)

▪ N: Normalized rolling state

▪ M: Hot mechanical rolling state

▪ H: Hollow profile

The standard has strict upper limit regulations on the chemical composition (smelting analysis) of each steel grade, mainly including:

• Carbon (C) :

The content is strictly controlled to ensure good weldability and toughness.

• Manganese (Mn) :

Enhances strength.

• Sulfur (S) and phosphorus (P) :

As harmful impurities, their contents are restricted to very low levels (for example, P≤0.030%, S≤0.025%) to enhance the purity of steel and prevent hot brittleness and cold brittleness.

• Carbon equivalent (CEV) :

This is a crucial indicator used to assess the weldability and hardening tendency of steel. The carbon equivalent has a clear calculation formula and upper limit value based on the strength grade of the steel. For instance, the CEV of S355J2H is typically required to be ≤0.45%. The lower the CEV, the smaller the risk of cold cracking during steel welding.

This is the core to ensuring structural safety. The standard stipulates the minimum performance requirements for each grade.

• Yield strength (ReH) :

Unit N/mm². This is the stress value at which the material begins to undergo obvious plastic deformation. For instance, the yield strength of S355 steel pipes must be no less than 355 N/mm².

• Tensile strength (Rm) :

Unit N/mm². This is the maximum stress that the material can withstand before being pulled apart. The standard also stipulates the range of tensile strength (for example, S355J2H is 470-630 N/mm²), which not only ensures the strength but also prevents the decline in toughness caused by excessive strength.

• Elongation after fracture (A) :

Expressed as a percentage. This represents the ductility of the material, that is, how much it can elongate before breaking. The minimum value is clearly specified according to the type and thickness of the sample, ensuring that the material has good plastic deformation capacity.

• Impact energy (KV) :

Unit joule (J). This is a key indicator for measuring the toughness of materials, especially important for preventing brittle fracture at low temperatures. The standard specifies the minimum Charpy V-notch impact energy value (such as 27J or 40J) at a specific temperature according to the quality grade (J2, K2, etc.).

The standard has extremely detailed regulations on the allowable deviations of the external dimensions of steel pipes to ensure the assembly accuracy of the structure.
• The tolerance of the outer diameter (D) and the side length (A, B)

• Tolerance of wall thickness (t) : Generally ±10% of the nominal wall thickness.

• Tolerance of length (L)

• Ellipticity: The maximum difference limit of the outer diameters of the two opposite sides of the cross-section of a circular pipe.

• Straightness: The curvature (arc) limit of the entire length of the steel pipe.

The verticality (right-angle deviation) and concavity and convexity (flatness) of the square rectangular tube.

• Weight tolerance: The allowable deviation between the actual weight per meter and the theoretical weight.

• Surface condition:

The steel pipe should have no defects that are harmful to its use. Minor surface irregularities, thin layers of oxide scale or rust caused by manufacturing processes (such as hot rolling and hot expanding) are allowed, provided that their depth does not exceed half of the negative dimensional tolerance.

• Weld seams:

Weld seams should be continuous and uniform. Weld seam clearance can exist, but it usually cannot exceed the specified height (for example, for pipes with t≥3mm, if the clearance is ≤3mm or 10%t, the smaller value is taken).

• Defect treatment:

Surface defects can be removed by grinding, but the wall thickness after grinding must not be less than the minimum allowable wall thickness. Welding repair is not allowed.

Manufacturers must conduct the following tests to prove that their products comply with the standards and provide the corresponding inspection certificates:
• Tensile test: Verify yield strength, tensile strength and elongation.

• Impact test: Verify impact energy (toughness).

• Chemical analysis: Verify the chemical composition.

• Geometric measurement: Verify dimensional and shape tolerances.

• Visual inspection: Verify surface quality.

• Non-destructive testing: such as ultrasonic testing (UT), can be used to detect internal defects in welds and base materials. The standard stipulates the scope of testing and the acceptance criteria.

• Marking: Each steel pipe or bundle shall be clearly marked in a durable manner, and the content shall at least include: manufacturer's name or trademark, standard number (EN 10210), steel grade, size specification, production batch number, etc.

• Documentation: The manufacturer must provide with the goods inspection certificates in compliance with EN 10204 standards, for example:

3.1 Certificate: Declare that the product complies with the standard requirements and attach the manufacturer's own test results.

3.2 Certificate: A certificate issued by an inspection agency independent of the manufacturer, which is more authoritative.

The requirements of EN 10210 for hot-formed steel pipes are a comprehensive quality assurance system. It has been strictly regulated from four dimensions: the source (chemical composition), process (manufacturing technology), result (mechanical properties, size and shape), and verification (testing and inspection).

1. Choosing steel pipes that comply with the EN 10210 standard means you have obtained:
Predictable and reliable mechanical properties (strength, toughness).
2. Excellent weldability reduces the risks of welding construction.
3. Precise geometric dimensions facilitate structural design and installation.
4. Complete quality traceability documents, meeting the strict quality requirements of modern engineering projects, especially large-scale infrastructure and construction projects.

These strict requirements have made EN 10210 steel pipes the preferred material for heavy and critical structural fields such as high-rise buildings, sports venues, Bridges, and port cranes.