GB2250225A - Abrasive cleaning apparatus - Google Patents

Abstract

An abrasive cleaning apparatus is in the form of a transportable module (20) and serves to mix abrasive particles with liquid and gaseous conveying media and to discharge a liquid/gaseous abrasive stream towards a target surface to be cleaned. The apparatus comprises a mixing chamber (21), means for supplying abrasive particles to the mixing chamber, means for supplying liquid to the chamber to mix with and to thoroughly wet the particles and the liquid being supplied in sufficient amount to provide a minimum volumetric ratio of liquid to solid of about 3:1, a discharge outlet arranged to discharge a liquid/solid abrasive mixture slurry from the chamber (21) when the chamber contains thoroughly wetted abrasive particles, a discharge line (22) connected to the outlet and having a discharge nozzle (23) at one end which is able to discharge a gas/liquid borne stream of wetted abrasive material towards the target surface, and means for supplying a gaseous driving pressure medium to the discharge line (22) in order to convey the slurry. <IMAGE>

Description

ABRASIVE CLEANING APPARATUS This invention relates to an abrasive cleaning apparatus which comprises a mixing chamber to which abrasive particles can be supplied. means for supplying a driving gaseous pressure medium to operate the apparatus.

an outlet from the chamber for discharging the abrasive particles. a delivery line connected to the outlet, and a discharge nozzle at one end of the delivery line for directing a stream of abrasive particles towards a target surface which is to be cleaned.

Many different abrasive cleaning apparatus have been developed over the years. in order to direct streams of abrasive particles towards target surfaces which are to be cleaned. but generally they fall into two categories. A first category provides delivery of a high pressure gas / abrasive stream and a second category provides a liquid / abrasive stream. There are also known combined systems, in which an abrasive stream is formed which uses liquid and gas to convey the abrasive material.

One particularly demanding environment where periodic cleaning of surfaces is required is the underwater cleaning of metal surfaces. such as oil or gas pipelines on the seabed, and the support legs of oil production platforms which are secured to the seabed, or other underwater surfaces such as drilling rigs and platforms.

The necessity to carry out cleaning underwater of these surfaces requires the pressure delivery head to the discharge nozzle to be sufficient to overcome the hydrostatic pressure prevailing at the depth of any particular cleaning operation. and also to enable the abrasive stream discharged from the nozzle to have sufficient kinetic energy upon impact with the surface to be cleaned, despite inevitable speed reduction as the abrasive stream passes from the nozzle through the water before making impact with the surface.

In the case of an apparatus which provides a purely gaseous-borne abrasive stream, this necessitates the use of high pressure gas supply to the apparatus. in order that the abrasive stream can have sufficient kinetic energy to pass through the water and to carry out a satisfactory cleaning operation upon impact with the surface.

Apparatus which provides a purely liquid conveying abrasive stream can have a higher kinetic energy, by reason of the fact that the abrasive particles will be wetted and therefore have a greater mass than gas driven particles.

but also the mass flow rate of the liquid can be much higher than that of a gaseous stream (at the same pressure). Despite this, pressures of as high as 9 to 16,000 psi are normally required for a purely liquid-borne abrasive stream, in order to carry out a satisfactory cleaning operation.

However, in an underwater environment, the most effective cleaning can be carried out using a mixture of gas and liquid (usually air and water) in order to convey the abrasive particles in an abrasive stream towards the particular target surface.

The handling of abrasive particles presents some significant problems, whether in a purely gas-borne, a liquid-borne, or a gas / liquid-borne system, in that the abrasive particles must normally be stored in a dry state before supply to the apparatus, and also must be maintained in a dry state in the apparatus before mixture with gas and / or liquid takes place. and subsequent discharge from the apparatus. This is necessary with all existing apparatus, because moist particles can easily clog-up or block any outlets or passages through which the particles are forced to travel prior to, during or after admixture with the conveying fluids (gas and / or liquid).

This necessity to maintain the particles in a substantially dry state imposes practical difficulties in maintaining stores of the abrasive particles in a dry environment immediately prior to use, which is particularly difficult during storage e.g. on a deck of a vessel, and also presents difficulties in excluding as far as possible air-borne moisture from coming into contact with the particles when held or temporarily stored in a mixing chamber of the existing apparatus.

The invention seeks to solve this problem in a novel way, by accepting that in practice it will be inevitable for the abrasive particles to become at least moisture laden, and therefore to take steps to ensure that the particles are brought into contact with and maintained in contact with a substantial volume of liquid in a mixing chamber, before being exposed to the action of a gaseous driving pressure supply to discharge a liquid / gas conveying stream of abrasive particles from the chamber.

According to the invention there is provided an abrasive cleaning apparatus for mixing abrasive particles with liquid and gaseous conveying media and to discharge a liquid / gaseous abrasive stream towards a target surface to be cleaned, said apparatus comprising: a mixing chamber; means for supplying abrasive particles to the mixing chamber; means for supplying liquid to the chamber to mix with and to thoroughly wet the particles, the liquid being supplied in sufficient amount to provide a minimum volumetric ratio of liquid to solid of about 3:1; a discharge outlet arranged to discharge a liquid / solid abrasive mixture slurry from the chamber when the chamber contains thoroughly wetted abrasive particles; a discharge line connected to the outlet; means for supplying a gaseous driving pressure medium to the discharge line in order to convey the slurry; and, a discharge nozzle at one end of the discharge line to discharge a gas / liquid-borne stream of wetted abrasive particles.

Therefore, in carrying out the invention. the abrasive particles are thoroughly wetted before any attempt is made to discharge the particles under gas pressure (or can be maintained in this form between successive operations), and usually there will be a considerably greater volume of liquid in the chamber than of abrasive solid particles. so that the particles (usually sand type abrasive particles) are thoroughly wetted and can be discharged as a slurry from the chamber thereby eliminating the risk of blockages or restrictions occuring.

Preferably, in addition to means for supplying liquid to the chamber, there is also means for supplying pressurising gas to the chamber.

Advantageously. the discharge outlet includes a device for ensuring a consistent concentration of liquid / solid in the slurry.

The slurry particles have considerably increased bulk density as compared with dry particles, and therefore when driven under gaseous pressure, can have substantial kinetic energy which is dissipated upon impact with the target surface.

The discharge line will be of a length corresponding with the depth of the target surface, and can be up to e.g.

700 feet in the North Sea environment. The gas supply pressure must be sufficient to overcome this hydrostatic head, but it has been found in practice that an embodiment of the invention can operate very effectively with only a small super pressure e.g. about 30 to 80 psi above the prevailing pressure at the nozzle.

Indeed, with a suitably designed nozzle, an abrasive stream can be formed which is capable of cleaning metal surfaces very effectively, but also can cut through and remove strongly adhereing material, even including material such as the usual concrete mantle which is provided on oil pipelines on the seabed. With such an effective performance, other types of material adhereing to underwater structures e.g. barnacles and other marine growth can easily be removed.

Underwater structures have to be cleaned on a regular basis, and particularly oil drilling rigs, and production platforms, so that the surfaces can be inspected and tested on a routine basis, to ensure that the structural integrity of the structure is maintained.

In a particularly preferred construction, the apparatus has a twin chamber arrangement. with each chamber being arranged to be operated independently via its own discharge line in one arrangement. Alternatively, a single run of discharge line to the discharge nozzle may be arranged to be capable of being coupled-up with the discharge outlet of either of the chambers in sequence.

This can enable a diver operating on the seabed to carry out cleaning operations using at first one of the chambers, and then the supply can readily be switched to the other chamber by operation of suitable valves which are accessible from a surface vessel, or an oil rig platform, on which the main operating components of the apparatus are arranged.

The apparatus is preferably arranged in the form of a readily transportable module which is provided with all that is required to operate the apparatus, so that it is only necessary to couple-up the discharge line and extend it down to the target surfaces to be cleaned, before operation of the apparatus is commenced.

If it is required to provide for separate operation of two discharge nozzles and respective discharge lines, each being supplied from a respective one of the twin chambers, it may be desirable to provide a third chamber which can be operated on a stand-by basis. This can be coupled-up with the two main chambers, and be brought into operation selectively to replenish any particular one of the main chambers when the latter has delivered all of its abrasive material contents.

The particular effectiveness of the apparatus according to the invention is derived by means of the very thorough wetting of the abrasive particles which takes place prior to discharge of the water-borne slurry under gaseous driving pressure action, and which can have substantial kinetic energy by reason of the additional mass of the particles. In addition, the discharge nozzle may be shaped in such a way as to apply a rotating vortex motion to the gas / liquid abrasive particle slurry, which applies a particularly effective cleaning action on the target surface.

One embodiment of abrasive cleaning apparatus according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic illustration of the apparatus; Figure 2 is a schematic illustration of further operation components of the apparatus; Figure 3 is a detail view of an alternative arrangement for discharging slurry from a twin chamber arrangement.

Referring first to Figure 1 of the drawings, there is disclosed an abrasive cleaning apparatus for mixing abrasive particles with liquid and gaseous conveying media and to discharge a liquid / gaseous abrasive stream towards a target surface to be cleaned, such as an underwater pipeline on the seabed, or the support leg of an oil production platform. The apparatus will normally be provided in a transportable module 20, which can be loaded onto the deck of a ship, or a platform, and which is provided with its own power source and all operating components, and only requires the discharge lines to be lowered down through the water to bring the outlet nozzles within reach of a diver at the target surfaces.

In the illustrated embodiment, the apparatus comprises a twin chamber arrangement of separate mixing chambers 21, in which solid abrasive particles. usually sand type particles, are mixed with water to form a slurry, prior to discharge from the chambers to the discharge lines.

However, while the illustrated arrangement has twin chambers 21, it is within the scope of the invention for the apparatus to be provided with a single mixing chamber.

Means is provided to supply abrasive particles to each mixing chamber 21, and also to supply liquid to the chamber, usually water, in order to mix with and to thoroughly wet the particles. Usually, the liquid will be supplied in a sufficient amount to provide a minimum volumetric ratio of liquid to solid of about 3:1. This liquid content of each chamber is provided, before any discharge of the particles takes place.

By this means, the solid particles are thoroughly wetted, and therefore when subsequently a gaseous driving pressure medium is supplied to operate the apparatus, the solid particles can be discharged from the outlet of the chamber in the form of a liquid slurry. Therefore, this minimises the risk of clogging or blocking of any of the passages of the apparatus to take place.

Each chamber therefore has a discharge outlet which is arranged to discharge a liquid / solid abrasive mixture in the form of a slurry from the chamber via a discharge line 22 connected to each discharge outlet and having a discharge nozzle 23 at one end which is able to discharge a gas / liquid borne stream of wetted abrasive material towards the target surface.

The gaseous pressure supply will be sufficient to overcome the hydrostatic head prevailing at the depth at which the nozzles 23 are employed, and will also provide a super pressure of perhaps 30 to 80 psi above this prevailing pressure. With a suitably shaped nozzle, an abrasive stream can be formed which is capable of cleaning metal surfaces very effectively, but which also can cut through and remove strongly adhereing material. The nozzle may be shaped so as to impart a rotating vortex motion to the gas / liquid abrasive particle slurry, which is able to apply a particularly effective cleaning action on the target surface.

As shown in Figure 1. each nozzle 23 is associated with a respective one of the chambers 21 via its discharge line 22. and this arrangement provides for independent operation of each nozzle from a single supply chamber.

However. as shown in dashed outlines. a switchable arrangement may be provided. whereby one nozzle only is provided. but which can be supplied initially with gas driven liquid slurry material from one chamber until the chamber is empty, and can then be readily switched over to the other chamber. While the first chamber is being recharged, the second chamber discharges until it is empty, and then the first chamber is switched in while the second chamber is recharged, and so on for as long as is required.

This can enable the diver to operate for indefinite periods of time in a practically non-stop operation.

Typically, in a practical construction, cleaning can take place for about one hour and forty minutes from each mixing chamber.

Alternatively, as shown in Figure 3, the chambers can be constructed as to allow continuous discharge without the need to alternate the delivery hose from chamber to chamber. This is accomplished by coupling two chambers one on top of the other. The water and abrasives are laoded into the vessels via the top chamber which in turn fills the bottom chamber to a required charge. The bottom chamber is then pressurised and is isolated from the top chamber by way of a pop-up mushroom valve. Once the top chamber has been isolated it can be filled with an appropriate charge in readiness for the depletion of the lower chamber. When this occurs the top chamber is pressurised to equal the pressure of the lower chamber.

Upon equalisation of the two chambers the mushroom valve of the lower chamber falls both by its own weight and that of the wetted sand above it. The wetted sand then falls into the lower chamber replenishing its charge. Once the top chamber has emptied, it is decompressed through its exhaust valve. The lower chamber while making up the loss of gas injects more air through its pressurisation valve and in turn pushes up the mushroom valve to seal and isolate itself from the upper chamber. The upper chamber when fully decompressed allows for re-charging when the mushroom valve drops under its own weight. In this way the lower chamber can be charged continuously without the need for stopping the gas or abrasive flow to the discharge nozzle.

Returning against to Figure 1, the gaseous driving pressure medium is supplied to the discharge line 22, in order to convey the liquid / solid slurry discharged from the outlet of the chamber 21 into the line 22, and as shown in Figure 1, each chamber 21 has a grit regulating discharge valve 14. In order to assist the discharge of the liquid slurry via each valve 14, it is preferred that a by-pass 24 applies discharge pressure to each chamber 21 after the latter has been filled with a sufficient amount of sand and liquid, in order to assist the discharge downwardly under gravity through each valve 14, and to compensate for the progressive loss of material.

In Figure 1, the gaseous driving pressure medium comprises compressed air supplied along supply lines 25, and valves 1, 2, 3, 4, 5, 7, 8 are isolating valves which are operable to control the supply of compressed air to the discharge lines 22, and in order to pressurise the mixing chambers 21, and to isolate certain sections when necessary. Reference 6 designates a pressure and flow regulator, valve 9 serves to admit grit particles to each chamber 21, and valves 12 serve to admit liquid to each chamber.

As indicated above, each discharge line 22 may be coupled-up with a respective one of the chambers 21, for independent operation. or alternatively can be switched to discharge the chambers successively.

In the event of separate discharge from each chamber via its own output nozzle, a stand-by chamber or pot 26 may be provided. containing reserve material. which can be switched to fill either one of the chambers 21 when the latter have been exhausted. to replenish the exhausted chamber and allow continued operation by the diver under water.

The system therefore basically comprises two air receivers (21) known as "blast pots" which are filled with a specific amount of water, which can be fresh water or salt water. plus any suitable abrasive material. The simple procedure ensures that the abrasives are fully saturated and will flow under gravity through a grit regulation valve (forming the discharge valve) into an air stream which is directed down a hose and exhausted through a nozzle. Because the abrasives are fully saturated, the previous problems met with existing apparatus of dry abrasive particles becoming damp in the pots, and with consequent clogging, can be eradicated.

The system allows for continuous blasing through a simple cross over "whip" (as shown in dashed outline), which can be attached to either pot and relocated to the other once each pot has exhausted its charge.

To prevent the back pressure created by the depth of the nozzle returning up the hose, while changing over the whip, a stop valve is located between the pot and the blast hose to the diver nozzle. By shutting this valve, the system can be depressurised without the need to bleed down the entire blast line.

Also, as mentioned above, each pot can be used independently and at different pressures from the other, thus allowing two diving operations to be carried out at equal or different depths to each other. However, upon exhaustion of one unit, this does mean that a certain amount of time is wasted in stopping and recharging the pot prior to restarting. However, as indicated above, to overcome this problem. as an optional feature the third pot (26) may be provided in the apparatus to allow continuous blasting to take place. The third pot therefore serves as a back-up which can be charged in readiness for either of the main chambers being exhausted.

Figure 1 shows diagrammatically one embodiment of the apparatus. and Figure 2 shows in more detail the control valves which control the supply of air, water and abrasive particles to a single chamber.

Figure 2 of the drawings shows in schematic form the manner by which the supply of gas, liquid and abrasive particles is controlled. The system comprises a main air and blast line A and a pneumo line B. In the main air and blast line A there is a blast line stop valve 101, a choke valve 102, a dome loader 103 which controls the supply of grit to the mixing chamber. a grit regulator 104 which discharges the liquid slurry into the line A, and a blast line pressure gauge 105. Tapping off the line A there is the dome loader 103, a quick release on / off valve 106, a dome loader regulator 107, and a primary pressure gauge 108.

A water inlet check valve 110 controls the supply of water to the mixing chamber. and a water overflow 109 also is connected at a lower level to the chamber. A water inlet check valve 110 controls the supply to the chamber.

In addition, a pressurisation valve 112 can control the supply of a discharge pressure to the mixing chamber, and a pressure release valve 113 can enable the pressure in the chamber to be discharged. There is also an exhaust valve 114, and an exhaust muffler 115 connected with the upper end of the mixing chamber. 116 comprises a purge valve and 117 comprises a pneumo gauge nozzle.

Claims (9)

1. An abrasive cleaning apparatus for mixing abrasive particles with liquid and gaseous conveying media and to discharge a liquid / gaseous abrasive stream towards a target surface to be cleaned. said apparatus comprising: a mixing chamber: means for supplying abrasive particles to the mixing chamber; means for supplying liquid to the chamber to mix with and to thoroughly wet the particles, the liquid being supplied in sufficient amount to provide a minimum volumetric ratio of liquid to solid of about 3:1; a discharge outlet arranged to discharge a liquid / solid abrasive mixture slurry from the chamber when the chamber contains thoroughly wetted abrasive particles; a discharge line connected to the outlet; means for supplying a gaseous driving pressure medium to the discharge line in order to convey the slurry; and, a discharge nozzle at one end of the discharge line to discharge a gas / liquid-borne stream of wetted abrasive particles.

2. Apparatus according to Claim 1, including means for supplying pressurising gas to the mixing chamber.

3. Apparatus according to Claim 1 or 2, in which the discharge outlet includes a device for ensuring a consistant concentration of liquid / solid in the slurry.

4. Apparatus according to any one of Claims 1 to 3, and having a twin chamber arrangement. with each chamber being arranged to be operated independently via its own discharge line.

5. Apparatus according to any one of Claims 1 to 3, and having a twin chamber arrangement, and a single run of discharge line to the discharge nozzle which is arranged to be capable of being coupled-up with the discharge outlet of either of the chambers in sequence.

6. Apparatus according to any one of Claims 1 to 5 and arranged in the form of a transportable module.

7. Apparatus according to Claim 4 or 5, including a third chamber operable on a stand-by basis, and which can be coupled-up with the two main chambers, and be brought into operation selectively to replenish any particular one of the main chambers when the latter has delivered all of its abrasive material contents.

8. Apparatus according to any one of Claims 1 to 7.

in which the discharge nozzle is shaped in such a way as to apply a rotating vortex motion to the gas / liquid abrasive particular slurry.

9. Apparatus according to Claim 1 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.