S355J2H Galvanized Steel Tubes

Dimension Category

Symbol

Tolerance (Before Galvanizing)

Additional Tolerance for Hot-Dip Galvanizing

Total Tolerance (After Galvanizing)

Measurement Specifications

Outside Diameter (OD)

D

- OD ≤ 50mm: ±0.5mm
- 50mm < OD ≤ 100mm: ±0.8mm
- OD > 100mm: ±1.0% of nominal OD

Uniform zinc coating thickness: 70-100μm (adds 0.07-0.10mm to OD per side)

- OD ≤ 50mm: ±0.7mm
- 50mm < OD ≤ 100mm: ±1.0mm
- OD > 100mm: ±(1.0% of nominal OD + 0.2mm)

Measured with a digital caliper (accuracy ±0.01mm) at 3 cross-sections (1/4, 1/2, 3/4 of tube length); avoid weld seams (for welded tubes)

Inside Diameter (ID)

d

Same as OD tolerance (derived from OD - 2×WT)

Zinc coating does not affect ID (coating applied externally only)

Same as pre-galvanizing ID tolerance

Calculated as measured OD - 2×measured WT; verify with an internal caliper for ID > 80mm

Wall Thickness (WT)

t

- t ≤ 5mm: ±10% of nominal t
- 5mm < t ≤ 10mm: ±8% of nominal t
- t > 10mm: ±6% of nominal t

No impact on base metal thickness (zinc coating is external)

Same as pre-galvanizing WT tolerance

Measured via ultrasonic thickness gauge (UTG, accuracy ±0.05mm) at 4 points (90° apart) per cross-section; ensure probe coupling with galvanized surface

Tube Length (L)

L

- Random length (6-12m): +150mm / -0mm
- Fixed length (per order): +30mm / -0mm

No length change from galvanizing process

Same as pre-galvanizing length tolerance

Measured with a steel tape (accuracy ±1mm/m) from end face to end face; ensure ends are free of zinc drips

Zinc Coating Thickness

δ

N/A (applied post-manufacturing)

- Minimum: 70μm (per EN 10240)
- Average: 85-100μm

- Minimum: 70μm
- Average: 85-100μm

Measured with a magnetic coating thickness gauge (accuracy ±3μm) at 5 points per m² of tube surface; include flat, curved, and weld areas (for welded tubes)

Tolerance Type

Pre-Galvanizing Tolerance

Post-Galvanizing Tolerance

Testing Method

Out-of-Roundness

≤ 1.0% of nominal OD (max. 1.5mm for OD ≤ 100mm)

Same as pre-galvanizing (zinc coating is uniform)

Calculate as (max. OD - min. OD) at a single cross-section; test 3 cross-sections per tube

Straightness

≤ 1.5mm/m (total straightness: ≤ 1.5×L mm, L = tube length in meters)

Same as pre-galvanizing (galvanizing does not cause bending)

Place tube on 2 supports (1m from each end); measure maximum deflection with a dial gauge (accuracy ±0.01mm)

End Squareness

≤ 1.0mm/m (max. 2mm for tube ends with OD ≤ 150mm)

Same as pre-galvanizing (zinc drips may be removed to meet tolerance)

Place a precision square (class 0) against the tube end face; measure gap with a feeler gauge (0.01-1.0mm range)

Weld Seam Protrusion (Welded Tubes)

- External: ≤ 0.5mm
- Internal: ≤ 0.3mm

- External: ≤ 0.7mm (includes zinc coating)
- Internal: ≤ 0.3mm (no coating)

Use a weld gauge (type B) to measure protrusion at 3 points along the weld (start, middle, end)

Surface Flatness (Seamless Tubes)

No localized protrusions > 0.3mm

No localized protrusions > 0.5mm (includes zinc coating)

Run a straightedge (length ≥300mm, grade 1) along the tube surface; check for gaps with a feeler gauge

Coating Defect Type

Allowable Limit (Per EN 10240)

Rejection Criteria

Zinc Drips/Runs

Max. height: 1.0mm; max. length: 50mm; max. 2 drips per meter of tube length

Drips > 1.5mm in height; drips causing OD to exceed total tolerance

Bare Spots

Max. area: 25mm²; max. 2 spots per meter of tube length

Bare spots > 50mm²; contiguous bare spots > 100mm in length

Porosity

Isolated pinholes (≤ 0.5mm diameter) allowed; no clustered porosity

Clustered pinholes (≥3 in 100mm² area); pinholes > 1.0mm diameter

Adhesion

No flaking or peeling when tested with a sharp tool (scratch test: 90° angle, 5N force)

Visible flaking/peeling of coating; coating detachment during handling

Element

Content (Base Metal, per EN 10210-2:2006)

Note on Zinc Coating (Hot-Dip Galvanizing, per EN 10240:2009)

C (Carbon)

≤ 0.20

No carbon in zinc coating; coating does not alter base metal C content

Si (Silicon)

≤ 0.55

Silicon may slightly affect galvanizing reactivity (controlled to avoid uneven coating)

Mn (Manganese)

≤ 1.60

Enhances base metal strength; no impact on zinc coating adhesion

P (Phosphorus)

≤ 0.035

Strictly limited to prevent brittleness (critical for low-temperature performance)

S (Sulfur)

≤ 0.035

Minimized to reduce weld defects and improve ductility

Cr (Chromium)

≤ 0.30

Trace element; no negative effect on galvanizing process

Ni (Nickel)

≤ 0.30

Improves toughness; compatible with zinc coating

Cu (Copper)

≤ 0.30

May slightly increase coating thickness (controlled within range)

Mo (Molybdenum)

≤ 0.10

Trace element; enhances base metal corrosion resistance (supplementary to galvanizing)

V (Vanadium)

≤ 0.05

Refines grain structure; no impact on zinc coating properties

N (Nitrogen)

≤ 0.012

Stabilized with Ti/Nb to prevent aging brittleness

Ti (Titanium)

≤ 0.10

Grain refiner; improves base metal ductility

Nb (Niobium)

≤ 0.05

Works with Ti to stabilize nitrogen; no effect on galvanizing

Zinc (Zn, Coating)

N/A (coating composition: ≥ 98.5% pure Zn)

Zinc coating adds corrosion resistance; no diffusion into base metal

Property

Base Metal (Before Galvanizing, per EN 10210-2:2006)

Effect of Hot-Dip Galvanizing (Post-Galvanizing)

Test Standard/Method

Yield Strength (Rp0.2)

≥ 355 MPa

No significant change (galvanizing temp ~450℃; below base metal recrystallization temperature)

EN ISO 6892-1 (tensile test, transverse direction)

Tensile Strength (Rm)

470–630 MPa

±5% variation (max.) due to minor thermal stress relief; remains within EN 10210-2 range

EN ISO 6892-1 (tensile test on full tube or flat specimens)

Elongation After Fracture (A)

≥ 22% (for t ≤ 16mm); ≥ 20% (for 16mm < t ≤ 40mm)

No reduction (galvanizing does not induce embrittlement in S355J2H)

EN ISO 6892-1 (measured on gauge length L0 = 50mm)

Impact Absorption Energy (KV2)

≥ 34 J at -40℃ (low-temperature toughness requirement for J2 grade)

No degradation (zinc coating acts as barrier; base metal toughness preserved)

EN ISO 148-1 (Charpy V-notch test, transverse specimens)

Hardness (HV10)

≤ 230 HV (base metal)

Base metal hardness unchanged; zinc coating hardness: 70–90 HV (softer than base metal)

EN ISO 6507-1 (Vickers hardness test; base metal: 10kg load; coating: 1kg load)

Zinc Coating Adhesion

N/A (base metal property)

No flaking/peeling when bent 180° around mandrel (diameter = 3×tube OD) or when scratched with 5N force

EN 10240 (bend test and scratch test)

Zinc Coating Corrosion Resistance

N/A (base metal property)

≥ 500 hours of neutral salt spray (NSS) without red rust (per ASTM B117)

ASTM B117 (salt spray test); EN ISO 9227 (alternative)