EP3870731B1 - Method of providing a zinc alloy coating on a steel tube in a continuous processing line - Google Patents

Method of providing a zinc alloy coating on a steel tube in a continuous processing line Download PDF

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Publication number
EP3870731B1
EP3870731B1 EP19784101.8A EP19784101A EP3870731B1 EP 3870731 B1 EP3870731 B1 EP 3870731B1 EP 19784101 A EP19784101 A EP 19784101A EP 3870731 B1 EP3870731 B1 EP 3870731B1
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EP
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Prior art keywords
zinc alloy
alloy coating
steel tube
magnesium
coating
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EP19784101.8A
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German (de)
French (fr)
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EP3870731A1 (en
Inventor
Petrus Cornelis Jozef Beentjes
Arjen Kamp
Arno Harold René HARMSEN
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Tata Steel Nederland Tubes BV
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Tata Steel Nederland Tubes BV
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc
    • C22C18/04—Alloys based on zinc with aluminium as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/38—Wires; Tubes
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
    • C23C28/023—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only
    • C23C28/025—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only with at least one zinc-based layer

Definitions

  • the invention relates to a method of providing a zinc alloy coating on a steel tube in a continuous processing line wherein the steel tube is passing through a liquid zinc alloy bath. It also relates to a steel tube provided with a zinc alloy coating according to the method.
  • Zinc alloy coated, or galvanised steel tubes are well known in the art and are used in a wide range of applications, for instance in central heating systems, industrial packaging, automotive parts, greenhouse constructions, roof constructions, recreational equipment, fencing systems and household appliances.
  • the corrosion resistance of zinc or zinc alloy coated steel is considered sufficient for many applications. However, it has appeared in practice that, in particular in saline environments, the corrosion resistance sometimes does not meet the quality requirements of the customer.
  • a method of providing a zinc alloy coating on a steel tube in a continuous processing line wherein the liquid zinc alloy bath comprises 0.20 to 0.35 % (w/w) magnesium, 0.05 to 0.14 % (w/w) aluminium and unavoidable impurities, the remainder being zinc.
  • the corrosion resistance is increased considerably and at the same time the staining or colouration of the coating over time and / or when exposed directly to open air remains at a low level.
  • the normally applied upper limit of the magnesium content could be lowered to 0.20 to 0.35 % (w/w), without severely affecting the corrosion resistance.
  • the aluminium content is in the range of 0.10 to 0.14 % (w/w) aluminium. More preferably the aluminium content is 0.10 % (w/w) aluminium.
  • the zinc alloy coating comprises 0.20 to 0.35 % (w/w) magnesium, and with a zinc alloy coating that comprises 0.25 to 0.35 % (w/w) magnesium.
  • a lower amount of magnesium has the added benefit, whilst still protecting against corrosion, that the hardness of the coating layer increases compared to magnesium-free coatings. This results in better scratch and wear resistance when used in practice.
  • the zinc alloy coating comprises 0.30 % (w/w) magnesium.
  • the zinc alloy coating has a thickness in a range of 4 to 25 ⁇ m.
  • the thickness is in a range of 6 to 25 ⁇ m and a thickness in a range of 12 to 25 ⁇ m is suitable for most applications. This gives enough corrosion protection while still giving a good appearance.
  • the zinc alloy coating is provided only on the outside of the steel tube.
  • these tubes should not have a zinc containing coating on the inside.
  • a top coating layer is provided on top of the zinc alloy coating.
  • a top coating can either be a transparent layer or a coloured layer, wherein the top coating layer is an organic coating layer.
  • a urethane, acrylate or epoxy based organic coating layer is used as top coating layer.
  • the organic coating can be applied as a dispersion of small particles of non-water soluble organic polymer binders in water (having a pH between 4 and 5) to steel tubes in-line by spraying, dipping or wiping. After applying the organic coating, the organic coating layer is cured and / or dried in-line before the steel tube is cut to length, for instance by means of an induction or infrared heating device.
  • the organic coating is applied with a thickness that is typically in a range of 1 to 5 ⁇ m and preferably in a range of 1 to 3 ⁇ m and is also referred to as thin organic coating, or TOC.
  • each bath chemistry at least 5 samples were produced.
  • one sample of each bath chemistry was chosen having the best properties, i.e. one side a layer thickness between 9 and 11 ⁇ m and free of bare spots.
  • samples were chosen having a uniform surface. Coating thickness was not considered to be of importance.
  • This measurement method measures all light reflected from the substrate, including the light reflected at the angle of incidence.
  • a decrease of the SCI L-value is an indication that less light in total has reflected from the surface after exposure of the acid covered samples to humid atmosphere, i.e. darkening has occurred during the exposure. This darkening is thought to be due to local chemical erosion of the surface by electrochemical corrosion, leading to surface roughening. The corrosion products formed are not black, but the roughening of the metal surface is thought to prevent reflection of light that enters the pits, increasing light absorption.
  • Table 2 shows the results of staining, percentage red rust after 504 hrs of salt spray testing and appearance of white rust after 1008 hrs VDA 233-102 cyclic testing (a cyclic corrosion test of materials and components).
  • Light colour “yes” means the sample has not darkened appreciably as seen by the naked eye, whereas light colour “no” means that the sample showed a clear darkening as seen by the naked eye.
  • “Coarse” means large amounts of porous white rust deposits and "fine” means whitewash type of appearance having a low amount of deposit. Table 2.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Coating With Molten Metal (AREA)
  • Paints Or Removers (AREA)

Description

  • The invention relates to a method of providing a zinc alloy coating on a steel tube in a continuous processing line wherein the steel tube is passing through a liquid zinc alloy bath. It also relates to a steel tube provided with a zinc alloy coating according to the method.
  • Zinc alloy coated, or galvanised steel tubes are well known in the art and are used in a wide range of applications, for instance in central heating systems, industrial packaging, automotive parts, greenhouse constructions, roof constructions, recreational equipment, fencing systems and household appliances.
  • The corrosion resistance of zinc or zinc alloy coated steel is considered sufficient for many applications. However, it has appeared in practice that, in particular in saline environments, the corrosion resistance sometimes does not meet the quality requirements of the customer.
  • The addition of magnesium to a zinc based coating in order to improve corrosion resistance is known in the art and trials with such a zinc-magnesium based coating showed improved results with respect to zinc based coatings without magnesium. For these trials a zinc based coating alloy was used with a 1.4 to 1.8 % (w/w) magnesium content and a 1.4 to 1.8 % (w/w) aluminium content, with the remainder being zinc and unavoidable impurities. The addition of aluminium also contributes to the increase of the corrosion resistance of the coating. This is a well-known coating alloy composition which e.g. is used in the automotive industry and has excellent anti-corrosion properties. Other coating alloy compositions known to improve the corrosion resistance are further described in documents EP 3 179 146 A1 , JP 2004 277839 A , JP 2004 091879 A and JP 2006 188724 A .
  • Although the corrosion resistance improved considerably compared to the zinc based coating alloys without magnesium, the use of magnesium in the coating composition gives rise to another problem. These coatings show a certain degree of darkening, staining or discolouration of the coating over time. This is a problem, in particular for applications wherein the steel tubes are clearly visible, such as in household appliances or use in automotive parts where aesthetic properties play an important role.
  • The inventors, who do not wish to be called superficial in any sort of way, tried to find solutions for both problems. It is therefore an objective of the present invention to provide a steel tube with a coating with improved anti-corrosion properties. It is another objective to provide a steel tube with a coating that shows no or minimal staining or discolouration over time.
  • Accordingly, a method of providing a zinc alloy coating on a steel tube in a continuous processing line is provided wherein the liquid zinc alloy bath comprises 0.20 to 0.35 % (w/w) magnesium, 0.05 to 0.14 % (w/w) aluminium and unavoidable impurities, the remainder being zinc. With this zinc coating alloy applied, the corrosion resistance is increased considerably and at the same time the staining or colouration of the coating over time and / or when exposed directly to open air remains at a low level. In the trials it appeared that the normally applied upper limit of the magnesium content could be lowered to 0.20 to 0.35 % (w/w), without severely affecting the corrosion resistance. With an aluminium content in a range of 0.05 to 0.14 % (w/w) aluminium it appeared that for most applications together with the magnesium content of the alloy, a sufficient corrosion resistance is provided and at the same time a minimal degree of staining or colouration is achieved. Therefore these results were considered to have an optimal balance between the two requirements. Preferably the aluminium content is in the range of 0.10 to 0.14 % (w/w) aluminium. More preferably the aluminium content is 0.10 % (w/w) aluminium.
  • Good results have also been realised by providing a zinc alloy coating that comprises 0.20 to 0.35 % (w/w) magnesium, and with a zinc alloy coating that comprises 0.25 to 0.35 % (w/w) magnesium. A lower amount of magnesium has the added benefit, whilst still protecting against corrosion, that the hardness of the coating layer increases compared to magnesium-free coatings. This results in better scratch and wear resistance when used in practice. Preferably the zinc alloy coating comprises 0.30 % (w/w) magnesium.
  • Preferably the zinc alloy coating has a thickness in a range of 4 to 25 µm. Typically the thickness is in a range of 6 to 25 µm and a thickness in a range of 12 to 25 µm is suitable for most applications. This gives enough corrosion protection while still giving a good appearance.
  • Preferably the zinc alloy coating is provided only on the outside of the steel tube. When used for sanitary piping or the like these tubes should not have a zinc containing coating on the inside.
  • If the steel tubes provided with the coating are used in very corrosive conditions, it could happen that despite the zinc alloy coating, after some time, red rust occurs. According to a preferred embodiment, to prevent corrosion and / or colouration in such harsh conditions, a top coating layer is provided on top of the zinc alloy coating. Such a top coating can either be a transparent layer or a coloured layer, wherein the top coating layer is an organic coating layer. Preferably, a urethane, acrylate or epoxy based organic coating layer is used as top coating layer.
  • The organic coating can be applied as a dispersion of small particles of non-water soluble organic polymer binders in water (having a pH between 4 and 5) to steel tubes in-line by spraying, dipping or wiping. After applying the organic coating, the organic coating layer is cured and / or dried in-line before the steel tube is cut to length, for instance by means of an induction or infrared heating device.
  • Such coatings deliver increased corrosion protection, no white rust due to storage, protection against colouration / staining, better tube bendability (less tooling friction) and finger print resistance. The organic coating is applied with a thickness that is typically in a range of 1 to 5 µm and preferably in a range of 1 to 3 µm and is also referred to as thin organic coating, or TOC.
  • To optimise the investigation of corrosion resistance together with staining resistance a matrix of different coating samples were prepared in the laboratory with a Rhesca zinc hot dip simulator with varying concentrations of both aluminium and magnesium. See table 1 below. Table 1.
    Code % aluminium % magnesium
    Zn0.1Al 0.1 0.0
    Zn0.1Al0.1Mg 0.1 0.1
    Zn0.1Al0.2Mg 0.1 0.2
    Zn0.1Al0.3Mg 0.1 0.3
    Zn0.1Al0.6Mg 0.1 0.6
    Zn0.1Al0.9Mg 0.1 0.9
    Zn0.5Al 0.5 0.0
    Zn0.5Al0.2Mg 0.5 0.2
    Zn0.5Al0.5Mg 0.5 0.5
    Zn0.5Al1.0Mg 0.5 1.0
    Zn1.6Al 1.6 0.0
    Zn1.6Al0.2Mg 1.6 0.2
    Zn1.6Al0.5Mg 1.6 0.5
    Zn1.6Al1.0Mg 1.6 1.0
    Zn1.6Al1.6Mg 1.6 1.6
    Zn5.0Al 5.0 0.0
    Zn5.0Al0.2Mg 5.0 0.2
    Zn5.0Al0.5Mg 5.0 0.5
    Zn5.0Al1.0Mg 5.0 1.0
  • For each bath chemistry, at least 5 samples were produced. For corrosion testing, one sample of each bath chemistry was chosen having the best properties, i.e. one side a layer thickness between 9 and 11 µm and free of bare spots. For staining tests, samples were chosen having a uniform surface. Coating thickness was not considered to be of importance.
  • All samples were exposed to a staining test, by dipping into a 0.1 M solution of acetic acid at room temperature for 20 seconds. All samples were drawn out of the solution with minimal drag-out and rapidly dried by a blast of cold air, avoiding stray droplets as much as possible. That way, the surface retained its uniformity (no dried droplets). No staining occurred during this procedure. Exposure of the dried but not rinsed samples to humid and warm atmosphere (80 % relative humidity at 40 °C) for 4 days (96 hours) and 15 days (360 hours) caused a decrease of L-values measured with the Specular Component Included (SCI) method using a Minolta CM2002 spectrophotometer. This measurement method measures all light reflected from the substrate, including the light reflected at the angle of incidence. A decrease of the SCI L-value is an indication that less light in total has reflected from the surface after exposure of the acid covered samples to humid atmosphere, i.e. darkening has occurred during the exposure. This darkening is thought to be due to local chemical erosion of the surface by electrochemical corrosion, leading to surface roughening. The corrosion products formed are not black, but the roughening of the metal surface is thought to prevent reflection of light that enters the pits, increasing light absorption.
  • Table 2 shows the results of staining, percentage red rust after 504 hrs of salt spray testing and appearance of white rust after 1008 hrs VDA 233-102 cyclic testing (a cyclic corrosion test of materials and components). Light colour "yes" means the sample has not darkened appreciably as seen by the naked eye, whereas light colour "no" means that the sample showed a clear darkening as seen by the naked eye. "Coarse" means large amounts of porous white rust deposits and "fine" means whitewash type of appearance having a low amount of deposit. Table 2.
    %Al %Mg sci L-value sci L-value sci L-value light colour %RR SST WR 1008 hrs results combined
    0 days 4 days 15 days 15 days VDA
    Zn0.1Al 0.1 0.0 92 92 91 yes 90 coarse --
    Zn0.1Al0.1Mg 0.1 0.1 92 88 87 yes 20 coarse -
    Zn0.1A10.2Mg 0.1 0.2 90 85 84 yes 5 coarse -
    Zn0.1Al0.3Mg 0.1 0.3 89 84 82 yes 0 fine ++
    Zn0.1Al0.6Mg 0.1 0.6 86 80 74 no 0 fine 0
    Zn0.1Al0.9Mg 0.1 0.9 80 75 68 no 0 fine 0
    Zn0.5Al 0.5 0.0 92 92 91 yes 80 coarse - -
    Zn0.5Al0.2Mg 0.5 0.2 90 89 88 yes 10 coarse -
    Zn0.5Al0.5Mg 0.5 0.5 88 85 84 yes 0 fine ++
    Zn0.5Al1.0Mg 0.5 1.0 88 81 77 no 0 fine 0
    Zn 1.6Al 1.6 0.0 92 92 91 yes 70 coarse - -
    Zn1.6Al0.2Mg 1.6 0.2 91 85 86 yes 0 coarse +
    Zn1.6Al0.5Mg 1.6 0.5 88 81 82 yes 0 fine ++
    Zn1.6Al1.0Mg 1.6 1.0 88 78 76 no 0 fine -
    Zn1.6Al1.6Mg 1.6 1.6 82 68 69 no 0 fine -
    Zn5.0Al 5.0 0.0 92 92 91 yes 5 coarse -
    Zn5.0Al0.2Mg 5.0 0.2 92 87 87 yes 0 coarse +
    Zn5.0Al0.5Mg 5.0 0.5 91 88 84 yes 0 fine ++
    Zn5.0Al1.0Mg 5.0 1.0 91 85 78 no 0 fine 0
  • In this test, it is clear that the L-value of those samples not containing any Mg hardly decrease in this test, indicating no staining with time. The L-values decrease with more magnesium and longer exposure times to humid atmosphere (before and right after dipping all samples did not show any decrease of L-value). The high aluminium grades were seen to be less sensitive to staining with the addition of magnesium than the other samples.
  • The values in table 2 show clearly that magnesium leads to staining, and more magnesium leads to more staining. Probably, a higher amount of aluminium (5 %) makes the coating less sensitive to staining (more gloss retention in case of high magnesium content). Even a minor addition of magnesium is strongly beneficial, which is very fortunate in the light of reducing staining issues.
  • The VDA-test after 1008 hours of testing (6 weeks), shows some red rust specks on the Zn1.6AI sample only. All samples acquire a whitish appearance, But all samples not containing any magnesium show coarse and repulsive deposits of white oxide.

Claims (13)

  1. Steel tube provided with a zinc alloy coating, characterised in that the zinc alloy coating comprises 0.20 to 0.35 % (w/w) magnesium, 0.05 to 0.14 % (w/w) aluminium and unavoidable impurities, the remainder being zinc, and wherein the zinc alloy coating is provided only on the outside of the steel tube.
  2. Steel tube provided with a zinc alloy coating according to claim 1, characterised in that the zinc alloy coating comprises 0.10 to 0.14 % (w/w) aluminium.
  3. Steel tube provided with a zinc alloy coating according to claim 1 or 2, characterised in that the zinc alloy coating comprises 0.25 to 0.35 % (w/w) magnesium.
  4. Steel tube provided with a zinc alloy coating according to anyone of the claims 1 to 3, characterised in that the zinc alloy coating comprises 0.30 % (w/w) magnesium.
  5. Steel tube provided with a zinc alloy coating according anyone of the claims 1 to 4, characterised in that the zinc alloy coating has a thickness in a range of 4 to 25 µm.
  6. Steel tube provided with a zinc alloy coating according to any of the claims 1 to 5 , characterised in that a top coating layer is provided on top of the zinc alloy coating.
  7. Steel tube provided with a zinc alloy coating according to claim 6 , characterised in that the top coating layer is a transparent or coloured organic coating layer.
  8. Method of providing a zinc alloy coating on a steel tube in a continuous processing line wherein the steel tube is passing through a liquid zinc alloy bath, characterised in that the liquid zinc alloy bath comprises 0.20 to 0.35 % (w/w) magnesium, 0.05 to 0.14 % (w/w) aluminium and unavoidable impurities, the remainder being zinc, and wherein the zinc alloy coating is provided only on the outside of the steel tube.
  9. Method of providing a zinc alloy coating according to claim 8 , characterised in that the liquid zinc alloy bath comprises 0.10 to 0.14 % (w/w) aluminium.
  10. Method of providing a zinc alloy coating according to claim 8 or 9, characterised in that the liquid zinc alloy bath comprises 0.25 to 0.35 % (w/w) magnesium.
  11. Method of providing a zinc alloy coating according to claim 8 or 9, characterised in that the liquid zinc alloy bath comprises 0.30 % (w/w) magnesium.
  12. Method of providing a zinc alloy coating according to anyone of the claims 8 to 10, characterised in that the zinc alloy coating has a thickness in a range of 4 to 25 µm.
  13. Method of providing a zinc alloy coating according to anyone of the claims 8 to 12, characterised in that a top coating layer is applied after applying the zinc alloy coating.
EP19784101.8A 2018-10-25 2019-10-16 Method of providing a zinc alloy coating on a steel tube in a continuous processing line Active EP3870731B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
EP18202470 2018-10-25
EP19196741 2019-09-11
PCT/EP2019/078073 WO2020083722A1 (en) 2018-10-25 2019-10-16 Method of providing a zinc alloy coating on a steel tube in a continuous processing line

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EP3870731A1 EP3870731A1 (en) 2021-09-01
EP3870731B1 true EP3870731B1 (en) 2024-06-19

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ES (1) ES2983204T3 (en)
WO (1) WO2020083722A1 (en)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004091879A (en) * 2002-09-02 2004-03-25 Nippon Steel Corp Zinc-based metal-coated steel with excellent corrosion resistance at the end face and scratches
JP2004277839A (en) * 2003-03-18 2004-10-07 Nippon Steel Corp Zinc-based metal-coated steel
JP4564361B2 (en) * 2005-01-04 2010-10-20 新日本製鐵株式会社 Flux composition for hot dip Zn-Al-Mg alloy plating and method for producing hot dip Zn-Al-Mg alloy plating steel using the same
JP6477709B2 (en) * 2014-08-06 2019-03-06 Ａｇｃ株式会社 Resin-coated metal tube and manufacturing method thereof

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ES2983204T3 (en) 2024-10-22
EP3870731A1 (en) 2021-09-01

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