Method for coating pipes

Abstract

A method for coating a pipe (1) in the interior thereof, wherein the method has at least the following method steps: (i.) providing an immersion basin (2) which is filled with a coating liquid (3); (ii.) first immersion of the pipe (1) to be coated into the coating liquid (3); (iii.) first removal of the pipe (1) to be coated from the coating liquid (3) ensuring an angle () between the central axis (M) and the surface of the coating liquid (3) with 1<()<30; (iv.) second immersion of the pipe (1) to be coated into the coating liquid (3); (v.) second removal of the pipe (1) to be coated from the coating liquid (3) ensuring an angle () between the central axis (M) and the surface of the coating liquid (3) where 30<()<1.

Claims

1. A method of coating a pipe (1) in its interior, wherein the pipe (1) to be coated in its interior has an outside (a) and an inside (b), a first outer end (e.sub.1) at the first end of the pipe (1) and a second outer end (e.sub.2) at the second end of the pipe (1), a length (L), a first inside diameter (D.sub.1) at the first outer end of the pipe (1) and a second inside diameter (D.sub.2) at the second outer end of the pipe (1), and a central axis (M), wherein the method according to the disclosure is characterised in that the method has at least the following method steps: (i.) providing an immersion basin (2) which is filled with a coating liquid (3) up to a filling level (h), the coating liquid containing FeF.sub.3iron fluoride and paint particles in dispersion and is suitable for receiving over its full length (L) the pipe (1) to be coated, (ii.) first immersion of the pipe (1) to be coated into the coating liquid (3) in a chemical-based process, (iii.) first removal of the pipe (1) to be coated from the coating liquid (3) ensuring an angle () between the central axis (M) .[.and.]..Iadd., .Iaddend.the surface of the coating liquid (3).Iadd., and the second outer end (e2) .Iaddend.with 1<()<30, (iv.) second immersion of the pipe (1) to be coated into the coating liquid (3) in a chemical-based process, (v.) second removal of the pipe (1) to be coated from the coating liquid (3) ensuring an angle () between the central axis (M) .[.and.]..Iadd., .Iaddend.the surface of the coating liquid (3).Iadd., and the second outer end (e2) .Iaddend.with 30<()<1, and (vi.) ensuring a filling level of the coating liquid (3) in the immersion basin (2) with (h)>(L).Math.sin() and (h)>(L).Math.sin().

2. A method of coating a pipe (1) in its interior according to claim 1, wherein a plurality of pipes (1) are simultaneously subjected to method steps (ii.) to (vi.).

3. A method of coating a pipe (1) in its interior according to claim 1, wherein the four method steps (ii.) first immersion, (iii.) first removal, (iv.) second immersion and (v.) second removal are repeated with a repetition frequency of between 1 and 7.

4. A method of coating a pipe (1) in its interior according to claim 1, wherein the four method steps (ii.) first immersion, (iii.) first removal, (iv.) second immersion and (v.) second removal are repeated with a repetition frequency of between 1 and 3.

5. A method of coating a pipe (1) in its interior according to claim 1, wherein the angle () is within the range of 1.8 and 5.5.

6. A method of coating a pipe (1) in its interior according to claim 1, wherein the angle () is within the range of 1.8 and 3.5.

7. A method of coating a pipe (1) in its interior according to claim 1, wherein the angle () is within the range of 1.8 and 5.5.

8. A method of coating a pipe (1) in its interior according to claim 1, wherein the angle () is within the range of 1.8 and 3.5.

9. A method of coating a pipe (1) in its interior according to claim 1, wherein the angles () and (.Iadd..Iaddend.) within the four method steps (ii.) first immersion, (iii.) first removal, (iv.) second immersion and (v.) second removal are identical.

10. A method of coating a pipe (1) in its interior according to claim 1, wherein the first inside diameter (D.sub.1) at the first end of the pipe (1) and the second inside diameter (D.sub.2) at the second end of the pipe (1) are identical.

11. A method of coating a pipe (1) in its interior according to claim 1, wherein the coating liquid (3) is kept in motion in the immersion basin (2) by means of a circulating device (6).

12. A method of coating a pipe (1) in its interior according to claim 1, wherein the immersion speed (v.sub.1) for first immersion, the speed (v.sub.2) for the first removal, the immersion speed (v.sub.3) for the second immersion, and the speed (v.sub.4) for the second removal are respectively in a range of 6 to 12 m/min.

13. A method of coating a pipe (1) in its interior according to claim 12, wherein the filling level (h) is so selected to ensure internal wetting over the entire periphery with the coating liquid (3) over the entire pipe length (L) of the pipe (1) to be coated during an entire immersion and removal cycle (ii., iii., /// iv., v.) having regard to the speeds (v.sub.1, v.sub.2, v.sub.3, v.sub.4) over a period of 60 sec to 210 sec.

14. A method of coating a pipe (1) in its interior according to claim 12, wherein the filling level (h) is so selected to ensure internal wetting over the entire periphery with the coating liquid (3) over the entire pipe length (L) of the pipe (1) to be coated during an entire immersion and removal cycle (ii., iii., /// iv., v.) having regard to the speeds (v.sub.1, v.sub.2, v.sub.3, v.sub.4) over a period of 85 sec to 105 sec.

15. A method of coating a pipe (1) in its interior according to claim 1, wherein the pipe (1) is of a nominal width (n) in a range of DN 32 to DN 65.

16. A method of coating a pipe (1) in its interior according to claim 1, wherein the pipe (1) is in the form of a mild steel metal pipe of a length (L) in a range of 7 m to 12 m.

.Iadd.17. A method of coating a pipe (1) in its interior according to claim 1, where the coating liquid containing FeF.sub.3 iron fluoride and paint particles forms a layer containing iron and paint particles bonded to the outside and the inside of the pipe having a thickness on the inside of at least of 12.8 m..Iaddend.

Description

DRAWINGS

(1) Following FIGS. 1 to 3 are intended to describe the present disclosure in greater detail.

(2) FIG. 1 shows a pipe (1) to be coated with the method proposed here, which is pivoted through an angle () with 1<()<30 with respect to the horizontal which extends parallel to the surface (not shown) of the coating liquid (3). The pipe (1) which is considered here as a longitudinally welded metal pipe has: an outside (a) as the outwardly disposed surface of the pipe (1), an inside (b) as the inside wall of the pipe (1), and a length (L), and at its first outer end (e.sub.1) which here is placed lower, it is of a first inside diameter (D.sub.1) which is identical to the second inside diameter (D.sub.2) at the second end (e.sub.2) of the pipe (1), that here is placed higher.

(3) FIG. 2 showsviewed from the same positionthe same pipe (1) as was already shown in FIG. 1, with the difference that the pipe (1) is now pivoted through an angle () with 30<()<1 relative to the horizontal which extends parallel to the surface (not shown) of the coating liquid (3). What is decisive here is that, in contrast to the situation shown in FIG. 1, and where the one end of the pipe (1)here the first outer end (e.sub.1)is placed at a lower position, now the other end of the pipe (1)here the second outer end (e.sub.2)is placed at the lower position while the respective other end of the pipe is placed at the correspondingly higher position.

(4) FIG. 3 shows a scenario during method step (iii.) in which the pipe (1) to be coated, after first immersion in the coating liquid (3) according to method step (ii.) issues again from the coating liquid (3), ensuring an angle () between the central axis (M) and the surface of the coating liquid (3) with 1<()<30 and is removed. In that case the pipe which was already shown in greater detail in FIG. 1 is used, in which the second end (e.sub.2) of the pipe (1) is higher by the amount (L).Math.sin() in comparison with the first end (e.sub.1) of the pipe (1). In FIG. 3 the pipe is in part already outside the coating liquid (3) which evidently within the immersion basin (2) is of a filling level (h), with (h)>(L).Math.sin (). To promote a preferably turbulent flow in the pipe (1) during the coating operation in the illustrated case a propeller for circulating the coating liquid (3) is provided at the side wall of the immersion basin (2).

DETAILED DESCRIPTION

(5) The disclosure will be illustrated in greater detail by means of the Examples hereinafter. For that purpose longitudinally welded metal pipes which are each 9 m in length and which have a continuous nominal width (n) in a range of DN 15 and DN 32 respectively are placed on numerous Teflon-coated bar-like support holders of an immersion frame which is also Teflon-coated. The immersion frame is carried from above by means of a travelling carriage crane which is capable of individually lowering and raising both the front part and also the rear part of the immersion frame individually, wherein the respective first ends of the pipes (1), carried by the immersion frame with the support holders, and the respective second ends of the pipes (1) can be individually raised and lowered. The pipes (1) themselves are set up and oriented in space as shown in FIGS. 1 and 2.

(6) In a plurality of successively connected immersion basins the pipes (1) are degreased and subjected to intermediate rinsing. In a further immersion basin (2) set up as shown in FIG. 3 the pipes (1) which have been pre-treated as described and which are supported as described are acted upon in their interior with a coating, for which purpose the immersion basin (2) is filled with a coating liquid (3) over a filling level (h) with (h)>(L).Math.sin() and (h)>(L).Math.sin (). In that case the coating liquid (3) is an epoxy/acrylic-based Aquence coating material of the 900 series from Henkel in Dsseldorf, Germany. The individual DN nominal widths (n) of the pipes (1), the immersion angles and the removal angles which are identical here (=), the repetition frequency over the four method steps (ii.) of first immersion, (iii.) of first removal, (iv.) of second immersion and (v.) of second removal, the conveyor speeds (v.sub.1=v.sub.2=v.sub.3=v.sub.4) for immersion and removal, the residence times and the coating thicknesses achieved are to be found in Table 1 hereinafter. The coated pipes (1) are finally rinsed and dried.

(7) The Examples as results of the tests performed confirm the recognitions of the present disclosure in an extremely vivid fashion. Below , =1 the coating on the inside wall (b) of the pipes (1) turns out to be too thin and with flaws and cracks to be noted, the same applies for ranges above , =30. Within the claimed angle range of 1<()<30 and 30<()<1 the coatings are uniform and homogeneous and at least in a range above 12.8 m with a calculated value of C=125 as the constant for type and condition of the pipe in the Hazen-Williams formula. Within the preferred angle ranges of 1.8<()<5.5 and 5.5<()<1.8 it is also possible to achieve coating thicknesses of more than 21 m with a calculated value of C130. The coatings are absolutely uniform and homogeneous and free from any flaws, so that water cannot infiltrate under them even after years. Thus the basic problem of providing pipes (1) in general, which are free from corrosion even after a prolonged period of use and which thus permit a monetary improvement in the design and operation of fire protection installations is completely solved.

(8) TABLE-US-00001 TABLE 1 Repetition Residence time frequency per dip operation Pipe over the Conveyor in accordance (1)-DN- four method speeds with method steps Ex- Nominal Angle steps (ii.), (v.sub.1 = v.sub.2 = (ii.) with (iii.) and -coating Comments/ ample width (n) ( = ) (iii.), (iv.), (v.) v.sub.3 = v.sub.4) (iv.) with (v.) thickness assessment 1 32 0 1 9 m/min 90 sec 8.5 m Pipes (1) partly float up during immersion, no continuous and flaw-free coating 2 32 2.5 2 9 m/min 80 sec 28.0 m Excellent uniform coating; C = 140 3 15 2.5 1 9 m/min 90 sec 12.8 m Uniform coating; C = 125 4 15 4.5 3 9 m/min 60 sec 25.5 m Excellent uniform coating; C = 140 5 15 10 2 9 m/min 80 sec 13.5 m Uniform coating; C = 125 6 32 4.5 2 9 m/min 80 sec 21.5 m Excellent uniform coating; C = 130 7 32 10 4 9 m/min 60 sec 25.5 m Excellent uniform coating; C = 130 8 32 20 2 9 m/min 80 sec 15.5 m Uniform coating; C = 125 9 32 40 3 9 m/min 60 sec 10.0 m Cracks and flaws in the coating; C = 105 10 32 45 2 9 m/min 80 sec 8.5 m Cracks and flaws in the coating; C = 100