Steel grades of galvanized tubes
| EN 10305-1, EN 10305-4 | E235+N, E355+N |
Galvanized tubes
Zinc coated precision steel tubes (galvanized tubes) are destined for hydraulic and pneumatic pressure distribution (so called HPL tubes), production of automobile components, utility vehicles as well as for production of machine products such as fittings and joints.
Cold drawn precision tubes are used as the semi-finished product and they are made from rolled seamless tubes. Precision tubes HPL types are made from carbon and alloyed steel.
Dimensions of zinc coated tubes
| OUTER DIAMETER (OD) | 4,0 – 42,0 mm |
| WALL THICKNESS (WT) | 1,0 – 4,0 mm |
| EUROPEAN STANDARDS | EN 10305-1, EN 10305-4 |
Length of zinc coated tubes
| Length | Diameter |
|---|---|
| 6000 mm + 100 mm | 4 – 16 mm |
| 6000 mm + 50 mm | 18 – 42 mm |
Tubes testing and coat resistence testing
| Non specific or specifific testing. | flattening test or drift expanding test |
| leak tightness test (NDT) |
- eddy current (STN 01 5054, PRP 02-74, SEP 1925, ASTM E 309, EN 10246-3 Gr.E3),
- stray flux (STN 01 5047, ČSN 01 5047, SEP 1913, ASTM E 570, EN 10246-5 Gr.F3),
- ultrasound (STN 01 5028, ČSN 01 5028, SEP 1915, ASTM E 213, EN 10246-7 Gr.U3),
Other tests according to standard.
Zinc coated tubes ends
Ends of the tubes are smooth and are enclosed by plastic plugs
Tolerances of zinc coated tubes
Tolerances of the outside diameter:
| diameter between 4 – 30 mm | ±0,08 mm |
| diameter between 32 – 38 mm | ±0,15 mm |
| diameter between 32 – 38 mm | ±0,20 mm |
Tolerances of the inside diameter are according to EN 10305-4
Tolerance of the wall thickness ± 10%
Delivery condition of zinc coated tubes
Tubes are delivered as cold drawn and normalized NBK (acc. to DIN standard), +N (acc. to EN standard), N (acc. to ASTM standard). Overview of other conditions can be found here. Coarseness of the outer and inner surface (starting with 15 mm of the inside diameter) is Ra <= 4 micrometers (0.004mm).
Packaging of zinc coated tubes
(a) tubes bound with a steel band,
(b) tubes wrapped in plastic sheets, burlap,
(c) tubes in wooden crates.
Tube are supplied in packages with a circular or hexagonal outline with maximum weight of 2 000 kg
Marking of zinc coated tubes
The designation of metallic zinc coatings with additional Cr(VI)-free treatment is described in EN ISO 2081.
Since Cr(VI)-free passivations represent new systems, a new nomenclature has also been adopted.
Železiarne Podbrezová a.s. offers:
(a) Thick-layer passivation (iridescent – “rainbow”) with an iridescent appearance. It is designated with C.
(b) Surface without sealing has no code; a sealed surface is designated with T2.
Example of surface designation:
Fe / Zn8 / C / T2
(which means – base material steel / zinc layer of at least 8 micrometres / iridescent passivation / sealing).
Surface condition of zinc coated tubes
First layer: electrolitically leached zinc (Zn) – acts as anode and in a corrosive environment it corrodes first and the base metal is cathodically protected against corrosion. The zinc layer thickness may be in the range of 5 to 30 micrometers (µm).
Second layer: based on the valency of used chrome is called either: passivation or chromating. For chromating in the past the Cr+6 salts were used. Nowadays the term chromating is no longer used, but passivation, or based on the number of chromites (salts Cr3+) we are talking about chromiting.
Third layer: for the overall increase of coating resistance, we use as the last layer the layer of organic substances on the Si base that stabilizes the chrome layer. This process is called impregnation or sealing.
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