GB2428429A

GB2428429A - Method and apparatus for treating the internal surface of a hollow vessel

Info

Publication number: GB2428429A
Application number: GB0509134A
Authority: GB
Inventors: Frank Morris
Original assignee: STAINLESS RESTORATION Ltd
Current assignee: STAINLESS RESTORATION Ltd
Priority date: 2005-05-03
Filing date: 2005-05-04
Publication date: 2007-01-31
Anticipated expiration: 2025-05-04
Also published as: GB0508933D0; GB0509134D0; GB2428429B

Abstract

A method and apparatus for treating the internal surface(s) (2, Fig 1) of a generally closed, hollow stainless steel vessel 1 having first (3, Fig 1) and second (4, Fig 1) apertures that are spaced along the length of the vessel comprises: <SL> <LI>(i) locating the vessel on a first moveable support frame (11, Fig 6) in an orientation such that said first aperture is the upper of the two apertures and providing the vessel with a removable internal spray head (7, Fig 2) located through the first aperture, <LI>(ii) moving the support frame to a treatment station, <LI>(iii) at the treatment station, introducing treatment liquid containing hydrofluoric acid into the spray head such that the liquid issues from the spray head to treat the inner surface(s) of the vessel and continuously draining treatment liquid from the vessel via the second aperture, <LI>(iv) moving the frame away from the treatment station and demounting the vessel from the frame, and <LI>(v) repeating steps (i)-(iv) for a further vessel. </SL> The method can be used to treat the internal surfaces of hot water cylinders.

Description

* 2428429

I

Method and Apparatus for Treating Internal Surface(s) of a Hollow Vessel The present invention relates to a method and apparatus for treating the internal surface(s) of a generally closed, hollow vessel and more particularly such a vessel having first and second apertures that are spaced along the length of the vessel.

An example of such a vessel is a cylindrical vessel intended for use as a hot water cylinder in a domestic or commercial water supply.

For many years, hot water cylinders have been made of copper. There is however now a trend to produce such cylinders from stainless steel, e.g. a 2304 duplex grade of stainless steel. During manufacture, the cylinder undergoes a fusion welding process (e.g. using tungsten inert gas welding) . This process can affect the corrosion resistant properties of the material, particularly in the areas adjacent to the weld. It is important that the corrosion resistant properties be restored particularly in view of the fact that the interior of the cylinder will come into contact with hot water that may contain relatively high levels of chloride. Thus an acid treatment ("pickling") is used to restore the corrosion resistant properties of the material. The treatment liquid generally contain hydrofluoric acid, usually in conjunction with either nitric acid or a mixture of nitric acid and sulphuric acid. The treatment liquid will generally be to ASTM A380 and contain 1-8% hydrofluoric acid and 15-20% nitric acid, the balance being water.

According to a first aspect of the present invention there is provided a method of treating the internal surface(s) of a generally closed, hollow stainless steel vessel having first and second apertures that are spaced along the length of the vessel, the method comprising: (i) locating the vessel on a first moveable support frame in an orientation such that said first aperture is the upper of the two apertures and providing the vessel with a removable internal spray head located through said first aperture, (ii) moving the support frame to a treatment station, (iii) at the treatment station, introducing treatment liquid containing hydrofluoric acid into the spray head such that the liquid issues from the spray head to treat the inner surface(s) of the vessel and continuously draining treatment liquid from the vessel via the second aperture, (iv) moving the frame away from the treatment station and demounting the vessel from the frame, and (v) repeating steps (i)-(iv) for a further vessel.

According to a second aspect of the present invention there is a provided an apparatus for treating the internal surface(s) of a generally closed, hollow stainless steel vessel having first and second apertures spaced along the length of the vessel, the apparatus comprising (a) a moveable support frame for locating the vessel in an orientation such that said first aperture is the upper of the two apertures.

(b) a spray head for location through the first aperture of the vessel for issuing treatment liquid to treat the inner surface(s) of the vessel, (c) a treatment station including a tank for holding a treatment liquid to be supplied through said spray head and drain means for returning liquid discharged from the second aperture to the tank, said support frame being moveable to and from the treatment station, and (d) means for supplying treatment liquid from the tank to the head.

The invention therefore provides a continuous method for the treatment of the internal surface(s) of generally closed hollow vessels. More particularly, the method is effected by spraying the treatment liquid containing hydrofluoric acid from a spray head located through a first aperture which (in the "treatment orientation" of the vessel) is at a higher level than a second aperture from which the treatment liquid is contmuously drained.

The invention is applicable particularly to the treatment of vessels in which the first aperture is provided in the vessel wall towards one end of the vessel and the second aperture is provided centrally in the opposite end of the vessel. It is however possible for the second aperture to be provided along the vessel wall rather than in the end of the vessel.

The invention has particular application to the treatment of cylindrical vessels made of stainless steel which are intended for use as cylinders in domestic or commercial hot water systems. The invention is particularly applicable to stainless steel vessels (e.g. formed using a welding operation such as that described above) intended for use as domestic or commercial hot water cylinders. The treatment will improve the corrosion resistance at the interior of the vessel, particular adjacent to any weld lines.

By providing the vessels on a moveable support frame which may be moved towards and away from a treatment station, it is possible to effect the treatment of the interior surface(s) of the vessel and then move the support frame away from the treatment station for further processing, e.g. rinsing of the interior surface(s) of the vessel. The rinsing may be effected by spraying water through the spray heads that were provided in the vessel. Alternatively these spray heads may be removed prior to rinsing and a high-pressure hose inserted through the first aperture, the water being drained through the second aperture.

Preferably, in step (i) of the method, a plurality of vessels are located on the support frame in the orientation as defined.

It is particularly preferred that the method and apparatus of the invention incorporate two or more of said moveable frames so that the vessel(s) located on one of the frames may be subjected to treatment at the treatment station while the other support frame is subjected to a number of other operations. These may, for example, involve washing of the interior surface(s) of the vessel(s) located on this support frame, demounting of the treated vessel(s) from the frame, and mounting further vessel(s) on the frame for subsequent location at the treatment station. Thus the support frames may be positioned alternately at the treatment station to make maximum use thereof.

The two or more support frames may be moveable along, and guided by, a track (preferably a floor-mounted track). The apparatus may incorporate first and second washing stations and, for the purposes of steps (ii)-(iv) of the method, one of the frames is moved between the first washing station and the treatment station and the other is moved between the second washing station and the treatment station.

An alternative possibility is for the two support frames to be mounted on a carousel arrangement.

The treatment liquid contains hydrofluoric acid, usually in combination with either nitric acid or a mixture of nitric acid and sulphuric acid. The treatment liquid may, for example, comprising 1-8% hydrofluoric acid, preferably in combination with 15-20% nitric acid, the balance of the treatment liquid being water.

In the apparatus of the invention, the tank will be of a material that is capable of resisting the aggressive nature of hydrofluoric acid and will generally be polypropylene.

The spray head may be of PVC since this is easily machined into the required configuration. The spray head may be supported on a lance which may for example be formed of polypropylene.

In operation of the method, it is preferred that at least a portion of the treatment liquid issuing from the spray head is directed at the interior surface at the end of the vessel adjacent the first aperture. That (internal) end is thus treated by the spray and the walls of the vessel may be treated by a combination of being contacted by spray and liquid draining down the walls under gravity.

In a particular preferred embodiment of the invention, the spray head is spherical and has a plurality of apertures for directing treatment liquid in a number of different radial directions, preferably to provide a 360 spray pattern.

It is particularly preferred that treatment liquid discharged from the cylinders is re-circulated for further use. Thus, for example, the apparatus may be effected using an apparatus having a holding tank for the treatment liquid. In this case, the treatment liquid is supplied from the tank (e.g. by means of a pump such a centrifugal pump or a diaphragm pump) to the spray head and treatment liquid discharged from the vessel is returned via a drain or a diaphragm air driven pump to the tank.

Conveniently the method of the invention may be effected simultaneously on two or more vessels using an apparatus having a plurality of vessel treatment stations.

In a preferred embodiment of the apparatus of the second aspect of the invention which is particularly applicable to the treatment of vessels in which the first aperture is provided in an end of the vessel, the or each support frame includes a support element for supporting a lower end of the vessel (i.e. the end provided with the first aperture) whilst allowing liquid to be discharged from the first aperture. The support element may, for example, be in the form of a fork (e.g. Y-shaped) or a ring.

In such an arrangement, a draw pipe of a cylinder (associated with the first aperture) may project through the support element. The support frame may be adapted to locate the support element above a drain provided at the treatment station, the drain serving to return treatment liquid to the tank.

The invention will be further described by way of example only with reference to the accompanying drawings, in which: Fig. I schematically illustrates a domestic hot water cylinder to be treated in accordance with the method of the invention; Fig. 2 schematically illustrates the method of the invention; Fig. 3 is a detail (to an enlarged scale) of a spray unit employed in the process depicted in Fig. 2; Fig 4 is a photograph of one embodiment of apparatus in accordance with the invention; Fig 5 is a similar photograph but taken from the opposite end of the apparatus; Fig 6 illustrates a moveable support frame for use in an apparatus in accordance with the invention; Fig. 7 is similar to Fig. 6 but illustrates cylindrical vessels to be treated in position in the apparatus; Figs. 8 and 9 are details of the apparatus shown in Fig. 6; and Fig 10 schematically illustrates the treatment station of the apparatus of Figs 3 and 4.

Reference is initially made to Fig I which illustrates a stainless steel domestic hot water cylinder 1 whereof the interior surface 2 is to be acid treated (i.e. pickled) by use of an apparatus in accordance with the invention as described more fully below with reference to Figs 2-10. The illustrated cylinder 1 is a generally closed vessel which, in use in a domestic hot water supply system, will be orientated as shown in Fig 1. Provided in a lower region of the cylindrical wall is an aperture 3 in which an immersion heater will ultimately be located. Additionally, the top of cylinder 1 has a water outlet port defined by a hot water draw pipe 4 projecting from a dished end 5 of the cylinder 1.

Although not illustrated in the drawing, the cylinder 1 may incorporate (as conventional) a heat-exchanger coil.

For the purposes of treating the cylinder 1, a spray head unit 6 is mounted therein (see also Figs 2 and 3). This unit comprises a generally spherical spray head 7 mounted on a lance 8 having a boss 9 that is screwed into aperture 3 such that the boss seals the aperture against egress of acid. The spray head may be fabricated from PVC and the lance from polypropylene. As shown particularly in Figure 3, spherical spray head 7 has a plurality of apertures 7a to which are orientated in a number of different radial directions to provide a 360 spray pattern.

The interior surfaces of the cyiinders 1 are acid treated either by virtue of being contacted directly be spray from the head 7 or by virtue of passage of acid along the interior walls of the cylinder. Acid drains from the cylinders 1 via their hot water draw pipes 4.

Cylinders 1 will generally incorporate apertures additional to those referenced as 3 and 4 in the drawings. In this case, any such additional apertures will be "plugged" before effecting the process of acid treatment which is described more fully below.

As shown in the photographs of Figs 4 and 5 (when considered in conjunction with Figs 6 to 9), the apparatus comprises a plurality (four shown) of moveable support frames 11 which at each end have wheels 12 running on parallel tracks 13.

The frames 11 each serve to support a plurality of cylinders I for treatment with a "pickling" liquid containing hydrofluoric acid at a treatment station 14 (see Figs 5 and 10). For convenience, the two support frames shown in the foreground of Fig 4 are designated herein as I Ia and 1 lb and are intended to be moved between the treatment station 14 and a wash station 15 (again shown in the foreground of Fig 4). The other two moveable support frames are designated 1 ic and lid and are intended to move to-and-fro between the treatment station 14 and a further wash station 16 (see Fig 5) which is at the opposite end of the tracks 13 to the wash station 15.

A support frame 11 is illustrated in more detail in Figs 6 and 7 and is designed for the simultaneous treatment of a total of ten cylinders I that are arranged in two rows of five cylinders each. Fig 6 shows the apparatus without the cylinders I whereas Fig 7 shows the ten cylinders in position.

The support frame 11 comprises lower end frame members 21 connected by a longitudinal rail 22 and an upper frame structure comprised of spaced uprights 23 which are connected at their lower ends on the rail 22 and which at their upper ends are connected by a further rail 24. The wheels 12 are provided at the lower ends of the frame members 21, as illustrated.

As will be appreciated from Figs 6 and 7, the two rows of five cylinders 1 are arranged one on each side of the upper frame structure. For this purpose, five of the uprights 23 are provided at their lower ends and on each side with a horizontally projecting spar 25 (see also Fig. 8) terminating in a V-shaped fork 26 whereof the inner sides converge to a radiussed portion 27 (see Fig 9).

Additionally each of those uprights 23 provided with a pair of forks 26 are further provided (on each side) with a generally semi-circular location bracket 28 associated with a chain 29.

Although not illustrated in Figs 6 and 7, the support frame 11 incorporates a manifold that runs along (and generally parallel to) the rail 24. This manifold has one inlet connection and ten outlet connections (one for each cylinder 1 mounted on the frame).

In use of the frame structure illustrated in Fig 6, each cylinder is located in an inverted position such that its dished end 5 is supported on the fork 26 with the hot water draw pipe 4 locating in the radiussed portion 27 of the fork 26. It will be appreciated that the bracket 28 partially encircles the outer surface of the cylinder 1 which can then be retained in position by virtue of the chain 29 extending between (and being fastened to) the free ends of the bracket 28.

The treatment station 14 is illustrated in more detail in Fig 10 and comprises a sub-terranean acid-holding tank 40 which is made of polypropylene or other material that is not degraded by hydrofluoric acid. Although not illustrated in the drawings, tank 40 incorporates a heater (for heating the acid) and a thermostat to ensure that the correct temperature is maintained. Generally, the acid will be maintained at a temperature of 40 to 60 C. The tank 40 is part of an acid re-circulation system incorporating a pump 41 for supplying acid to the manifold on the support frame 11 and a drain system 42 (provided above ground) including spaced upright inlet pipes 43 for returning acid to the tank 40. The upper ends of inlet pipes 43 converge downwardly in the form of a funnel. The rails 13 are provided at opposite ends of the drain system 42.

Although Fig 10 only illustrates one drain system 42 and five inlet pipes 43 there will in fact be four drain systems 42 each associated with five such pipes 43, for reasons which will be explained below.

Use of the illustrated apparatus will now be described.

Consider a situation in which the moveable support frames 11 a and 11 b are located at the wash station 15 and the moveable support frames 11 c and lid are located at the wash station 16.

The frames ila and 1 lb may each be loaded with ten cylinders whereof the inner surfaces are to be "pickled". Each cylinder 1 is provided with an assembly of lance 6 and spray head 7 (in the manner illustrated in Fig 2), each lance 6 being connected by a hose (not shown) to the manifold on the support frame 11.

The support frames ha and lib are now moved along the tracks 13 to the treatment station 14 and positioned such that the hot water draw pipes 4 of the cylinders 1 each locate above a respective one of the inlet pipes 43. The pump 41 is now connected to the manifolds on the support frames 11 a and 11 b. Operation of the pump 41 causes treatment liquid to be sprayed into the interior of each cylinder 1.

Subsequently, the pump 41 is disconnected from the manifolds on support frames 11 a and 1 lb which are then moved back to the wash station 15. At this station, the manifolds on the support frames I Ia and ilb are connected to a high pressure water system which serves to rinse the interior of the cylinders I. Water discharged from the draw pipes 4 passes through a floor-level grid for discharge to drain.

Whilst cylinders mounted on support frames 1 la and 1 lb are being treated at the wash station 15, the support frames lic and lid (loaded with cylinders 1 each provided with the internal spray head 7) are moved to the treatment station 14 for processing as described above. During the time that cylinders 1 mounted on support frames Ii a and 11 b spend at the treatment station 14, the cylinders 1 on support frames 11 a and 11 b may be washed and demounted from the apparatus. Additionally new cylinders 1 may be located on the frames 11 a and 1 lb (and provided with internal spray heads 7).

Once treatment of the cylinders 1 on support frames 11 c and lid has been completed at the treatment station 14, these frames may be moved back to washing station 16 where the procedure is generally as described for washing station 15. The support frames ii a and 1 lb may now be moved from wash station 15 back to treatment station 14.

Therefore the apparatus allows one set of twenty cylinders I to be treated at the treatment station 14 whilst twenty cylinders that have already been treated are washed and demounted and twenty further cylinders are prepared ready for treatment.

This ensures effective and economical use of the treatment station 14.

The Y-shaped forks 26 may be replaced by supports of other configuration that allow the cylinder to be supported by its end with the draw pipe 4 projecting downwardly through the support. Thus, for example, the support may be in the form of a partial or complete ring.

The washing procedure may be modified whereby the spray head 7 are removed and washing effected by introducing a high-pressure hose through the aperture 2.

Although the invention has been illustrated with reference to a cylinder having a draw pipe 4 projecting from a domed-end of the cylinder, the invention is also applicable to the treatment of cylinders in which the draw-pipe 4 is provided along the vessel wall (rather than in the vessel end).

It should be appreciated that a number of amendments may be made to the illustrated embodiments. Thus, for example, the frame 11 may be constructed so as to accommodate a greater or lesser number of cylinders. Thus, for example, such a modified apparatus might accommodate only one row of cylinders. Alternatively or additionally there may be less than or more than five cylinders for each row supported by the apparatus.

It should also be appreciated that the apparatus may be used for treating different sizes of cylinders, e.g. 90 litre cylinders or 300 litre cylinders. At any one time, the cylinders being treated may be of the same or different sizes.

Claims

1. A method of treating the internal surface(s) of a generally closed, hollow stainless steel vessel having first and second apertures that are spaced along the length of the vessel, the method comprising: (i) locating the vessel on a first moveable support frame in an orientation such that said first aperture is the upper of the two apertures and providing the vessel with a removable internal spray head located through said first aperture, (ii) moving the support frame to a treatment station, (iii) at the treatment station, introducing treatment liquid containing hydrofluoric acid into the spray head such that the liquid issues from the spray head to treat the inner surface(s) of the vessel and continuously draining treatment liquid from the vessel via the second aperture, (iv) moving the frame away from the treatment station and demounting the vessel from the frame, and (v) repeating steps (i)-(iv) for a further vessel.

2. A method as claimed in claim 1 wherein in step (i) a plurality of said vessels are located on the support frame in the orientation such that the first of their two apertures is uppermost and said vessels are each provided with a spray head.

3. A method as claimed in claim I or 2 wherein in step (iv) the frame is moved to a washing station where water is introduced into the vessel via the first aperture and continuously drained via the second aperture.

4. A method as claimed in claim 3 wherein the water is introduced into the vessel through the removable internal spray head.

5. A method as claimed in claim 3 wherein the spray head is removed and the water is introduced through the first aperture via a hose.

6. A method as claimed in any one of claims 1 to 5 wherein two or more of said moveable frames are provided so that movement of one frame in accordance with step (iv) allows the other frame to be moved to the treatment station for effecting step (iii).

7. A method as claimed in any one of claims 1 to 6 wherein the or each support frame is moveable along, and guided by, a track.

8. A method as claimed in claim 7 when directly or indirectly dependent to claim 3 wherein first and second washing stations are provided and, for the purposes of steps (ii)-(iv) one of said frames is moved between the first washing station and the treatment station and the other frame is moved between the second washing station and the treatment station.

9. A method as claimed in any one of claims 1 to 6 wherein the or each support frame is mounted on a carousel.

10. A method as claimed in any one of claims 1 to 9 wherein the treatment liquid comprises 1-8% hydrofluoric acid.

11. A method as claimed in any one of claims 1 to 10 wherein the treatment liquid further comprises either nitric acid or a mixture of nitric acid and sulphuric acid.

12. A method as claimed in any one of claims I to 11 wherein the first aperture is provided in the vessel wall towards one end of the vessel and the second aperture is provided centrally in the opposite end of the vessel.

13. A method as claimed in claim 12 wherein the vessel is cylindrical.

14. A method as claimed in claim 13 wherein the vessel is intended for use as a hot water cylinder.

15. A method as claimed in any one of claims 11 to 14 wherein at least a portion of the liquid issuing from the spray head is directed at the interior surface at that end of the vessel adjacent the first aperture.

16. A method as claimed in any one of claims 1 to 15 wherein the spray head is spherical and has a plurality of apertures for directing treatment liquid in a number of different radial directions.

17. A method as claimed in any one of claims Ito 16 wherein the treatment liquid is held in a tank and the liquid is supplied to the spray head by means of a pump.

18. A method as claimed in claim 17 wherein the pump is centrifugal pump or a diaphragm air driven pump.

19. A method as claimed in claim 17 or 18 wherein treatment liquid discharged from the vessel via a second aperture is returned to the tank.

20. The apparatus for treating the internal surface(s) of a generally closed, hollow stainless steel vessel having first and second apertures spaced along the length of the vessel, the apparatus comprising (a) a moveable support frame for locating the vessel in an orientation such that said first aperture is the upper of the two apertures.

21. Apparatus as claimed in claim 20 wherein said support frame is adapted to support a plurality of vessels.

22. Apparatus as claimed in claim 20 or 21 which is provided with at least two of said support frames, each support frame being moveable to and away from the treatment station.

23. Apparatus as claimed in any one of claims 20 to 22 additionally comprising at least one washing station, said support frame being moveable between a washing station and said treatment station.

24. Apparatus as claimed in any one of claims 20 to 23 wherein said support frame is moveable along, and guided by, a track.

25. Apparatus as claimed in claim 24 when directly or indirectly dependent from claim 23 wherein first and second washing stations are provided and one of said support frames is moveable between the treatment station and the first washing station and the other of said support frames is moveable between the treatment station and the second washing station.

26. Apparatus as claimed in any one of claims 20 to 23 wherein the support frames are mounted on a carousel.

27. Apparatus as claimed in any one of claims 20 to 26 wherein the tank is of polypropylene.

28. Apparatus as claimed in any one of claims 20 to 27 wherein the spray head is spherical and has a plurality of apertures for directing treatment liquid in a number of different radial directions.

29. Apparatus as claimed in any one of claims 20 or 28 including a pump for supplying treatment liquid from the tank to the spray head.

30. Apparatus as claimed in any one of claims 20 to 29 wherein the or each support frame includes a support for supporting a lower end of the vessel at the treatment station.

31. Apparatus as claimed in any one of claims 20 to 30 incorporating a drain for returning treatment liquid discharged from the second aperture of the vessel to the tank.

32. Apparatus as claimed in claim 31 wherein the drain has an inlet provided at each treatment station below the support at the station.

33. A method as claimed in any one of claims 1 to 19 when carried out on the apparatus of any one of claims 20 to 32.

34. A method of treating the internal surface(s) of a generally closed, hollow vessel substantially as hereinbefore described with reference to the accompanying drawing.

35. Apparatus for treating the internal surface(s) of a generally closed hollow vessel substantially as hereinbefore described with reference to the accompanying drawings.