Setting, insulating, anti sea spray icing coating and a marine structure coated with a setting, insulating anti sea spray icing coating
The present invention relates to a setting, insulating, anti sea-spray icing coat. The anti sea-spray icing coat presents a passive protection against marine icing or any icing caused by discontinuous water spray. The insulating coating has a heat transfer coefficient in the range from 10 to 100 W/m2j(-
Marine icing is a known problem in the marine industry and poses a great threat for offshore and coastal structures and vessels. Marine icing may result in a considerable weight increase and resulting instability due to the shift of a centre of gravity of a vessel. Marine icing is the cause of slippery decks that endangers human health, increased maintenance, falling ice, breaking equipment or reduced functionality of equipment, reduced access, blocked exits, ventilation and emergency equipment. Conditions where marine icing is a problem are well covered in the literature.
Icing on vessels and structures is caused by two different sources of water droplets: atmospheric (rain, snow, fog) and sea spray. Freezing sea spray causes typically 80-90% of all icing events in marine environment. The main cause of sea spray is the wave interaction with the vessel, or any sort of offshore or coastal structure.
The problems associated with marine icing has led to a great focus in the industry and academia over several decades, but no robust and cost effective technology has been developed and implemented for this market. In spite of considerable efforts and a long felt need within the area, does no prior art solution completely solve the problem of marine icing from sea-spray.
The research and development in this field has focused mainly on solutions to reduce sea-spray icing through heated surfaces, hydrophobic coatings and spray with de-icing chemicals. Use of chemicals, mechanical removal and heating is
costly and time consuming. A technology preventing marine icing should be robust and exhibit a permanent or at least a long lasting effect.
Use of chemicals is harmful to the environment and requires storage and equipment for applying the chemicals. In severe conditions must chemicals be applied frequently.
Hydrophobic coatings represent the only passive method against marine icing that has undergone extensive testing and use. This method considers physical processes of steady state ice accretion common for atmospheric icing.
Hydrophobic anti-icing coatings stop working completely when a small amount of ice is formed. Hydrophobic properties also tend to deteriorate in time. Hydrophobic coatings cannot be coated with an extra layer to of additional functionality
(abrasion resistance, flame resistance, anti-fouling paint etc.).
Insulating coatings have several uses both in marine environments and on shore, and are well known within the technical field of coating.
Another solution that have been tested but not utilized beyond testing includes applying anti-icing mats on parts of a ship exposed to marine icing. The anti-icing mats were made of polystyrene foam covered in rubber sprayed canvas. During testing, the anti-icing mats reduced icing problems but proved difficult and labour intensive to apply onto a surface reliably. Anti-icing mats are unsuited for complex surfaces and increase the weight. Covered surfaces typically maintain moisture and promotes corrosion. During testing, it was an occasion where the anti-icing mats loosened and peeled off completely in a single voyage. Furthermore, the mats where found to absorb water and freeze.
The solution proposed in the present invention reduces marine icing. The physics causing marine icing differs from atmospheric icing. In atmospheric icing, the heat conduction of a structure is less important for the icing as the water constantly impinging on the structure is colder than ambient conditions and the temperature of the structure. In addition, the amount of cooling from airflow is sufficient to
freeze all the water. This is quite the opposite of sea-spray icing. During sea-spray icing, the water is considerably warmer then the ambient conditions and the structure because it takes at least 50 seconds for a sea spray droplet to cool down to air temperature. Additionally, the water intermittently impinges on the structure. The result is variation of the ice accretion temperature and variations of water film salinity on the surface of the ice. This increases the importance of the heat flux between the structure and accreted ice. The present solution utilizes the physical processes of unsteady ice accretion due to interaction generated sea spray or any icing caused by discontinuous spray with a temperature higher or close to its freezing temperature.
The present invention is based on the acknowledgement of the cooling effect of the structure on the ice and thereby the ice accretion. In traditional methods for preventing ice accretion, the effect of the cooling of the ice due to heat conduction by the structure is considered negligible, as it is the case for atmospheric icing. It has been thought that the ice, in particular spongy ice created by freezing spray, has low heat conductivity and act as an insulator towards the exposed structure. Assumption of low heat conductivity is valid for fresh water. This assumption is not valid for saline ice created by saline sea spray. The present invention is based on the acknowledgement that the cooling of the ice from the structure facilitates the ice accretion from sea-spray. The assumption that insulation has little effect on sea spray icing, or that insulation in addition to soft rubber sprayed canvas is needed to provide an icing as taught by the prior art is teaching away from the present invention.
The invention includes a coating a the total heat transfer coefficient in the range from 10 to 100 ^ '/ ' 2 v on the surface of marine vessels, offshore structures, coastal structures, or fish farms exposed to sea spray to prevent icing.
Typically, the heat transfer coefficient of a paint is higher than 700 W/m2 j(- Reduction of the heat transfer coefficient of the coating to the values that are typical for the air heat transfer during icing (e.g., 20 - 100 ^ lmi v) facilitates
reduction of the cooling during spray impinging, and therefore reduces the ice growth. Reduction of the heat transfer coefficient of the coating down to 100 W/m2j( will result in avoiding the most severe icing events. Further decrease of the heat transfer coefficient of the coating will further reduce the thickness of accreted ice. The present invention is based on the acknowledgement that reduction of the heat transfer coefficient below 10 W/m2 j( will not give any additional benefit except unnecessary increase of the coating thickness. This also acknowledges that mats of thick polystyrene foam covered in rubber sprayed canvas are not needed.
The solution slows down accretion rate even when some ice already is formed or the water temperature is lower than its freezing point. Furthermore the solution of the present invention facilitates melting and breaking of the existing ice if the spray is warmer than its freezing temperature.
The solution of the present invention is passive, permanent and thereby cost and resource efficient. Furthermore, the solution of the present invention has uniform structure in contrast to hydrophobic surfaces, and therefore, does not lose its anti- icing properties due to mechanical damage or environmental exposure, is relatively quick to apply even to complex surfaces, has low weight (due to low density) and is mechanically rigid.
By providing an insulating coating with a thickness that is just sufficient to prevent accretion of ice, the required increase of cost and weight is kept to a minimum. Furthermore, such an insulating coating is easy to retrofit on existing structures and most structures can maintain their original functionality without any
modifications. Furthermore, the solution of the present invention can be utilized without accumulating moisture or increase corrosion problems.
The present invention relates to a setting anti sea spray icing coating for coating sea-spray exposed surfaces on a structure, said setting anti sea spray icing coating having a thermal conductivity in the range from 0,05 to 0, 1 W/mK and a
set coating with a total heat transfer coefficient in the range from 10 to 100
W/m2j(, whereby a cooling effect of the structure on the ice and thereby ice accretion is reduced and whereby heat from the sea spray is sufficient to melt and break the ice when the sea spray is warmer than the freezing temperature of the sea spray.
The setting anti sea spray icing coating for coating sea-spray exposed surfaces such that a thermal conductivity of a set coating is in the range of 0,05 to 0, 1 W/mK. The thickness of the coating is chosen to achieve the total heat transfer coefficient in the range from 10 to 100 W/m2 j(■ This will lead to a 0,5-10 mm thick coating when the thermal conductivity of the coating is in the range 0,05 to
0, 1 W/mK. The setting anti sea spray icing coating is typically sprayed or rolled onto the sea-spray exposed surfaces before it sets.
The setting anti sea spray icing coating may include a setting matrix and a thermal conductivity reducing filler material.
The setting matrix may be a solvent based paint.
The setting matrix may be a water based paint
The setting matrix may be a thermosetting paint.
The setting matrix may be a chemically cured paint
The setting matrix may be a UV-setting paint.
The setting matrix may include an epoxy material.
The setting matrix may include a resin material
The coating may include reinforcing fibers for additional strength.
The thermal conductivity reducing filler material may be any porous or hollow filler, beads, particles or granules and so on, which has sufficient mechanical strength but the thermal conductivity and density are reduced by existence of voids. Such materials can be for example porous silica, porous glass, ceramic or carbon beads.
The setting matrix may include corrosion inhibitors.
Furthermore, the invention relates to setting anti sea spray icing composition comprising a setting matrix and a thermal conductivity reducing filler material with a thermal conductivity in the range from 0,05 to 0, 1 W/mK, whereby the setting anti sea spray icing composition can be applied to sea-spray exposed surfaces on a structure to thereby reduce a cooling effect from the structure on the ice and whereby heat from the sea spray is sufficient to melt and break the ice when the sea spray is warmer than the freezing temperature of the sea.
The setting anti sea spray icing composition comprise a setting matrix and a thermal conductivity reducing filler material with a thermal conductivity in the range from 0,05 to 0, 1 W/mK.
Furthermore, the present invention relates to a marine structure exposed to sea spray including at least one sea-spray exposed surface, said surface further comprising at least one layer of set sea spray icing reducing coating to reduce sea spray icing, said coating having a thermal conductivity in the range from 0,05 to 0, 1 W/mK, said at least one layer of coating having a heat transfer coefficient in the range from 10 to 100 W/m2j(, whereby the at least one layer of set sea spray icing reducing coating reduce a cooling effect from the marine structure on the ice and whereby heat from sea spray is sufficient to melt and break ice when the sea spray is warmer than the freezing temperature of the sea spray.
The marine structure exposed to sea spray include at least one sea-spray exposed surface. The surface includes at least one layer of anti-icing coating with thickness in the range 0,5mm and 10mm including a setting matrix and a thermal
conductivity reducing filler material which has thermal conductivity in the range 0,05 to 0, 1 W/mK.
To get the maximal effect in most applications the recommended range of the coating heat transfer is 10-50 W/m2 j(- To reduce the paint weight such range can be limited to 20-50 W/m2 j(- The mass per unit area of such coating will be approximately equal to (in the case of 50 W/m2 j() mass per unit area of standard
0.45-mm-thick coating for splash zone recommended by NORSOK. The mass per unit area of such coating will be approximately 2.5 times greater (in the case of 20 W/m2j() than the mass per unit area of standard 0.45-mm-thick coating for splash zone recommended by NORSOK. In application where the coating weight is an issue, an insulating layer with a heat transfer coefficient in the range from 50 to 100 W/m2 j( can be applied. Such layer would reduce severe icing growth rate to the values typical for moderate growth rate (<6 cm/day).
"A marine structure exposed to sea spray" is in the context of this specification intended to cover any floating or fixed structure exposed to sea spray. Examples of marine structures exposed to sea spray include but are not limited to offshore installations used in the oil and gas industry, seagoing vessels, farms for marine organisms, seaside installations, railings, posts, offshore or seaside windmills, lighthouses etc.
"Setting" in the content of the application also intended to cover "curing". The hardening process will depend on the substance used as an insulated coating, and the term "setting" is not intended to limit the invention to a specific process for solidification.
The coating can be applied by spraying, brushing, rolling or any other well-known coating method.
Fig. 1 is a schematic representation of a cross section of a marine structure of the invention exposed to sea spray with a surface of metal, plastic or wood (to the left
on fig. 1 ). The surface is coated with a primer (in the center). The primer is a suitable primer for improving corrosion properties, improve adhesion, decrease water penetration etc. A coating of the invention (to the right) with a thickness in the range 0,5mm to 10mm is applied to the primed surface. The coating of the invention includes a setting matrix and porous or hollow beads.
Fig. 2 corresponds to fig 1 , but includes an additional coating on top of the coating of the invention. Fig. 2 is included to highlight that the invention not prevents the application of further coats or layers to achieve additional functionality. Additional functionality can include color, improvement of anti-fouling properties,
improvement of abrasion resistance, improvement of hydrophobic properties, to provide a specific surface finish, to make the surface electrically conducting, to achieve a specific friction or lack of friction, to promote surface turbulence, to improve temperature or fire resistance, to provide adhesion, to provide a layer serving visual effects etc.
Fig. 3 shows ice accretion rate simulation for a surface with the coating of the invention and non-coated metal surfaces in typical icing conditions. The example compares a surface with no surface coating and a surface with a heat transfer coefficient of 33 ^ J l 2 v in similar conditions.