◇Outer diameter tolerance: Steel pipes of different specifications have different outer diameter  tolerance requirements.

◇Wall thickness size: There is a specified range of thickness sizes. For example, for a steel pipe with a certain outer diameter, its wall thickness has a corresponding allowable deviation range.

◇Length tolerance: usually implemented according to the order contract or agreement between the supplier and the buyer, and the general tolerance is 0 - 10mm.

◇Curvature: The curvature is required to be ≤1mm/m.

◇Ovality: The ovality of the inner hole of the stainless steel round tube is less than 0.05mm. 

◇Surface defects: The surface should be bright and uniform, the weld should be full and free of damage.   

The national standard for the composition of stainless steel pipes mainly includes the content ranges of elements such as carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), chromium (Cr), nickel (Ni) and molybdenum (Mo).‌

The national standard for the composition and content of stainless steel pipes is as follows:

Carbon (C): Content ≤ 0.030%, reduces carbon content and improves welding performance.‌

Silicon (Si): Content ≤ 1.00%, helps maintain the crystal structure.‌

Manganese (Mn): Content ≤ 2.00%, affects mechanical properties and hardness.‌

Phosphorus (P): Content ≤ 0.045%, helps to improve corrosion resistance.‌

Sulfur (S): content ≤ 0.030%, affects processing performance.‌

Chromium (Cr): Content ranges from 16.00% to 18.00%, providing corrosion resistance.

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Nickel (Ni): The content is between 10.00% and 14.00%, which increases corrosion resistance.‌

Molybdenum (Mo): The content is between 2.00% and 3.00%, which improves the resistance to sensitized intergranular corrosion.

◊Tensile Strength: The tensile strength of stainless steel is generally between 500 and 700 MPa, which can be increased to greater than or equal to 650 MPa after heat treatment.

◊Yield Strength: In the annealed state, the yield strength of welded pipe stainless steel is usually between 200 and 250 MPa, depending on the heat treatment conditions and material thickness. After heat treatment, its yield strength can be increased to greater than or equal to 280 MPa‌.

◊Elongation after fracture: Welded pipe stainless steel has good plasticity, and its elongation is usually greater than 40%, which ensures the deformation ability of the material when subjected to stress.

◊Hardness: Its hardness range is usually between 150 and 220 HB, and the specific value is affected by heat treatment conditions.

Food grade stainless steel pipe standards:

◊Migration of heavy metals: Refer to GB/T 31604.24 - 2016, GB/T 31604.25 - 2016, GB/T 31604.33 - 2016, GB/T 31604.34 - 2016, GB/T 31604.38 - 2016 and other standards, which have specific limits on the migration of heavy metals such as cadmium, nickel, lead and arsenic.

◊Surface roughness: The surface roughness Ra value of the surface in contact with food is less than or equal to 0.8μm, the Ra value of other surfaces is less than or equal to 2.5μm, and the Rz value of the weld surface is less than or equal to 12.5μm.

◊Air tightness test: For steel pipes with an outer diameter not exceeding 50.8mm, underwater air tightness tests can be performed one by one instead of hydraulic tests. The test pressure should be no less than 1.0MPa, and the test medium should be compressed air. Under the test pressure, the steel pipe should be completely immersed in water, and the pressure stabilization time should be no less than 10s. The steel pipe should not leak.