Tank or pipe having a coating system

Abstract

A tank or a pipe having an internal steel surface, at least a portion of the internal steel surface comprising a coating system. The coating system being formed of an overcoat layer and an overcoat-enhancing layer, the overcoat-enhancing layer being interposed between the steel surface and the overcoat layer. In use, the overcoat-enhancing layer enhances the chemical resistance of the overcoat layer to aggressive cargo types.

Claims

1. A tank or a pipe having an internal steel surface, wherein at least a portion of the internal steel surface comprises a coating system, the coating system comprising: a. an overcoat layer comprising epoxy, silicate, polyurethane, polyurea, and/or vinyl esters; and b. an overcoat-enhancing layer having a thickness between 10 nm to 2 ?m, the overcoat-enhancing layer comprising a composition based on a group IIIB or IVB metal compound from the periodic table of elements, silane compound, metal alkoxide, zinc phosphate or mixtures thereof; wherein at least a portion of the internal steel surface has a surface roughness prior to the application of the coating system of 20 ?m to 150 ?m; the overcoat-enhancing layer being interposed between the internal steel surface and the overcoat layer, wherein the internal steel surface comprising the coating system is flat compared to an internal steel surface having the overcoat layer but not the overcoat-enhancing layer following exposure of the internal steel surface comprising the coating system and the internal steel surface having the overcoat layer but not the overcoat-enhancing layer to methyl ethyl ketone (40? C., 2 weeks).

2. The tank or pipe according to claim 1, wherein the tank or pipe is configured to hold a liquid, solid or semi-solid.

3. The tank or pipe according to claim 1, wherein the overcoat layer is formed from a single coat of an overcoat composition.

4. The tank or pipe according to claim 1, wherein the overcoat layer is formed from a substantially volatile organic solvent free overcoat composition.

5. The tank or pipe according to claim 1, wherein the steel surface has a level of cleanliness prior to coating of Sa3, Sa2?, Sa2 or Sa1.

6. A tank or pipe coating system for application to at least a portion of an internal steel surface of a tank or pipe, the coating system comprising: a. an overcoat layer comprising epoxy, silicate, polyurethane, polyurea, and/or vinyl esters; and b. an overcoat-enhancing layer having a thickness between 10 nm to 2 ?m, the overcoat-enhancing layer comprising a composition based on a group IIIB or IVB metal compound from the periodic table of elements, silane compound, metal alkoxide, zinc phosphate or mixtures thereof; wherein at least a portion of the internal steel surface has a surface roughness prior to the application of the coating system of 20 ?m to 150 ?m; the overcoat-enhancing layer being interposed between the internal steel surface and the overcoat layer, wherein the internal steel surface comprising the coating system is flat compared to an internal steel surface having the overcoat layer but not the overcoat-enhancing layer following exposure of the internal steel surface comprising the coating system and the internal steel surface having the overcoat layer but not the overcoat-enhancing layer to methyl ethyl ketone (40? C., 2 weeks).

7. A method of increasing the chemical resistance of an overcoated steel surface, the method comprising interposing an overcoat-enhancing layer comprising a composition based on a group IIIB or IVB metal compound from the periodic table of elements, silane compound, metal alkoxide, zinc phosphate or mixtures thereof and having a thickness between 10 nm to 2 ?m between a steel surface and an overcoat coating layer comprising epoxy, silicate, polyurethane, polyurea, and/or vinyl esters, wherein at least a portion of the steel surface has a surface roughness prior to the interposing of the overcoat-enhancing layer of 20 ?m to 150 ?m.

Description

(1) For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the following experimental data and figures, in which:

(2) FIG. 1 shows a photograph of two coated panels, the left-hand coated panel comprising a comparative coating system and the right-hand coated panel comprising a coating system according to the present invention.

(3) FIG. 2 shows a photograph of two coated panels, the left-hand coated panel comprising a comparative coating system and the right-hand coated panel comprising a coating system according to the present invention.

EXAMPLES

(4) The following materials and coating compositions were prepared, applied and tested as follows.

(5) The substrates used were steel panels (Ympress? Laser E250C from Tata Steel) that had been grit blasted to Sa2? with a roughness of Rz=50-65 ?m.

(6) The composition used to form the overcoat enhancing layers was Zircobond? 4200SM (from PPG Industries).

(7) Application Method of the Overcoat Enhancer Layer:

(8) The steel panels were placed into spray cleaning tank and alkaline cleaned by spraying for 1 minute at 60? C. using UTEC 812 at 2% by volume. The panels were then subjected to a deionized water immersion dip followed by a deionized water immersion spray. The panels were then placed immediately into a overcoat enhancing composition containing spray tank whilst still wet. The panels were then sprayed for 2 minutes at 26.6? C. with the overcoat enhancing composition. The panels were then subject to a deionized water spray rinse, followed by several minutes of forced hot air drying.

(9) Application method for the SigmaGuard 720 (straight epoxy/amine cured solvent based tank coating system, from PPG industries) overcoat layer:

(10) The overcoat enhancing layer treated panels were subjected to air spray application of the overcoat layer at 20-23? C. Two overcoats of 125 ?m dry film thickness were applied with an overcoating interval of 2 days. The overcoat layers were cured for 3 weeks at 20-23? C. The non-treated panels of the comparative examples were overcoated in the same manner.

(11) Application method for the SigmaGuard CSF650 (straight epoxy/amine cured solvent based tank coating system, from PPG Industries) overcoat layer:

(12) The overcoat enhancing layer treated panels were subjected to air spray application of the overcoat layer at 20-23? C. The base paint was pre-heated to 60? C. to facilitate spray application. A one coat system of 375-450 ?m dry film thickness was applied. The overcoat layers were cured for 2 weeks at 20-23? C. The non-treated panels of the comparative examples were overcoated in the same manner.

(13) Tests

(14) The coated panels were continuously exposed to methyl ethyl ketone (technical grade, available from Acros Organics (article number 444170050) at 40? C. for 6 months. The lower parts of the panels were exposed to methyl ethyl ketone in liquid form, and the upper part of the panels were exposed to methyl ethyl ketone in vapour form.

(15) Results

(16) TABLE-US-00001 TABLE 1 Results after 6 months continuous chemical resistance testing Overcoat Example enhancing Overcoat Methyl ethyl ketone Number layer layer 40? C. Example 1 Zircobond? SigmaGuard OK, no defect 4200SM 720 Example 2 Zircobond? SigmaGuard OK, no defect 4200SM CSF650 Comparative None SigmaGuard Fail, severe blistering in example 1 720 2 weeks, mainly in liquid exposed area Comparative None SigmaGuard Fail, severe blistering in example 2 CSF650 2 weeks

(17) Referring firstly to FIG. 1, there is shown two coated panels after testing. The left-hand coated panel (labelled 528-1) comprises a comparative coating system according to comparative example 1 and the right-hand coated panel (labelled 529-1) comprises a coating system according to example 1. The panels were tested according to the abovementioned testing procedure. The left-hand panel suffered from blistering within 2 weeks, as shown by the plurality of raised domes on the surface of the panel exposed to the liquid. The panel also suffered from rippling on the surface of the panel that was exposed to the vapour. In contrast, the surface of the right-hand panel remained intact for 6 months, as shown by the flat surface of the panel.

(18) Referring now to FIG. 2, there is shown two coated panels after testing. The left-hand coated panel (labelled 530-2) comprises a comparative coating system according to comparative example 2 and the right-hand coated panel (labelled 531-2) comprises a coating system according to example 2. The panels were tested according to the abovementioned testing procedure. The left-hand panel suffered from severe blistering within 2 weeks in both the liquid and vapour exposed region of the panel, as shown by the plurality of raised domes across the surface of the panel. In contrast, the surface of the right-hand panel remained intact for 6 months, as shown by the flat surface of the panel. The small non-coated region on the right hand panel, located toward the centre of the bottom half of the panel was intentionally removed by hand using a knife after testing.

(19) The above experimental results show chemical immersion testing of an overcoat enhancement layer in combination with different types of overcoat, resulting in improved chemical resistance. As shown in table 1 and the figures, inventive examples 1 and 2 show improved resistance when exposed to methyl ethyl ketone.

(20) It has further been found that the inventive coating system also shows improved chemical resistance to a range of cargo types. The inventive coating system has also shown improved performance after cycling, and after cycling with varying cargo temperatures.

(21) Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

(22) All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

(23) Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

(24) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.