[0001] The present invention relates to a method for preventing or reducing corrosion of concrete.

BACKGROUND ART

[0002] It is well known that anaerobic wastewater in sewers leads to the generation of H ₂ S by sulfate-reducing bacteria residing in the sewer biofilms/sediments below the water surface. The H ₂ S generated is then transferred into the gas phase under turbulent conditions. In this regard it will be understood that sewers frequently operate under conditions where the sewer pipes are not entirely filled with wastewater, generally leading to a lower liquid phase a sewer- air phase or gaseous phase above the liquid phase. In the presence of oxygen in sewer air, sulphide-oxidizing bacteria (SOB) develop on the concrete surface exposed to sewer air, and oxidize H ₂ S to sulfuric acid. The reactions between sulfuric acid and cement lead to concrete corrosion with gypsum and ettringite as the primary products. Although chemical oxidation of hydrogen sulphide also occurs at the concrete surface, recent studies have shown that this reaction is believed to be relatively slow in comparison to microbial sulphide oxidation. Therefore, microbial processes are the key driving force for concrete corrosion.

[0003] The currently used strategies for reducing sewer corrosion can be divided into three categories:

[0004] Liquid phase technologies: with liquid phase technologies chemicals are dosed to wastewater to reduce the formation of H ₂ S in wastewater and/or its transfer to sewer air. This is a commonly used method both in Australia and worldwide. The most commonly used chemicals include: oxygen and nitrate as oxidants to oxidise sulphide, magnesium hydroxide as an alkali to reduce the H ₂ S fraction of dissolved sulphide and its transfer to sewer air, iron salts to precipitate sulphide, and caustic shocking to deactivate sewer biofilms. However, in order to use such technologies large amounts of chemicals are needed due to the large volume of wastewater to be treated, incurring high operational costs, typically between $0.05-0.50 per m ³ of sewage treated. While these technologies are highly suitable for controlling H ₂ S at corrosion and odour hot spots, it is cost prohibitive to apply these technologies to achieve network-wide corrosion control. [0005] Gas phase technologies: in gas phase technologies, sewer air is collected through active ventilation and treated with gas treatment units. The treatment technologies include activated carbon adsorption of H ₂ S (and other odorous compounds), chemical scrubbing for H ₂ S detention in an alkali solution, and biotrickling filters for the biological oxidation H ₂ S (and other odorous compounds). These technologies also have proven effectiveness. However, like liquid phase technologies, they are also more suitable for H ₂ S control at corrosion and odour 'hot spots' . Once again it is cost-prohibitive to achieve network-wide corrosion control using these technologies.

[0006] Sewer rehabilitation: such rehabilitation requires corroded concrete surfaces to be repaired, coated or lined. These passive approaches, as the last resort, are all capital intensive and more expensive than the above two options. For example, the cost to rehabilitate a 10 km large trunk sewer is of the order of approximately $100 million. Pipe lining is one effective way of making sewer resistant to corrosion. Whilst being effective, pipe relining also requires very large capital investment. Similarly, coating with plastic or epoxy resins is also expensive. Also, the long-term performance could be undermined due to imperfect coating in practice.

[0007] In a previously published patent application PCT/AU2011/000481, the applicant reported the inhibitory and biocidal effects of intermittently dosing waste water streams with Free Nitrous Acid (FNA). This process requires a large quantity of additives to be added to the waste water for producing the required amount of FNA in the waste water pipes or vessels. The FNA in the waste water contacts the surface of the pipe or vessel and results in killing SRB and other organisms. However, such treatment is restricted to the parts of the inner walls of the pipe which contacts the waste water. Thus, the inhibitory or biocidal effect of the FNA is restricted to lower levels of the pipe which at or below the liquid phase of the water as shown in Figure 1. This treatment leads to reduced sulphide formation in the liquid phase, and consequently reduced transfer of H ₂ S from the liquid to the gas phase, and thus reduced corrosion. As a result, this treatment does not affect the biofilm on the pipe surface that is above the water line, where SOB reside and oxidize any sulphide in the air, transferred from the liquid phase or transported from other locations in sewer air due to air movement, causing pipe corrosion. Therefore, there is at least a commercial need to further address the issue of concrete corrosion in sewer pipes and vessels.

[0008] It will be clearly understood that prior art referred to herein does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

BRIEF DESCRIPTION OF INVENTION

[0009] With the foregoing in view, the present invention in one form, resides broadly in a method for controlling or inhibiting corrosion of any pipe or vessel, said vessel or pipe comprising an inner wall defining an internal volume for receiving fluid, the method comprising applying to or coating or lining at least a part of the inner wall of the vessel or the pipe with a nitrite containing material or nitrite forming material or a free nitrous acid (FN A) precursor material or FNA such that during use at least a part of the coating forms free nitrous acid (FNA) on at least a part of the inner wall of the vessel or pipe.

[0010] In one embodiment, the nitrite containing material or nitrite forming material or a free nitrous acid (FNA) precursor material or FNA is applied to a part of the inner wall that, in use, is exposed to a gaseous atmosphere.

[0011] It is to be understood that any references to "inner wall" in the present specification generally refers to an in use configuration of the pipe or vessel. It would be understood that "inner wall" encompasses within its scope surfaces including fluid contacting surface and/or an air contacting surface. The inner wall is no way limited to wall portions which actually contact the fluid but generally refers to the wall that defines the internal volume of the pipe or vessel described herein.

[0012] Throughout this specification, references to "FNA precursor" include any starting materials which may be reacted to form free nitrous acid. Such FNA precursor materials include (but are not limited to) nitrites (N0 ₂ ^" ) such as sodium nitrites (NaN0 ₂ ) or nitrite forming materials.

[0013] Without wishing to be bound by theory, it is believed that conduction of fluids such as anaerobic wastewater in pipes such as sewer pipes leads to the generation of H ₂ S by sulfate - reducing bacteria residing in the sewer biofilms/sediments below the water surface as shown in Figure 1. The H ₂ S generated is then transferred into the gas phase under turbulent conditions. In the presence of oxygen in sewer air, sulphide-oxidizing bacteria (SOB) develop on the concrete surface exposed to sewer air, and oxidize H ₂ S to sulfuric acid. Therefore, concrete surfaces that are not in direct contact with water are susceptible to corrosion due to the formation of the sulfuric acid in the presence of SOB and oxygen. Typically, the reactions between sulfuric acid and cement lead to concrete corrosion. Although chemical oxidation of hydrogen sulphide also occurs at the concrete surface, the applicant has discovered that this reaction is relatively slow in comparison with microbial sulphide oxidation as described above. Typically in a sewer pipe, a relatively small part of the internal walls of the pipe are in constant contact with water. A substantial part of the inner wall of the pipe or vessel remains exposed to sewer air and hence is particularly susceptible to sewer corrosion due to the action of SOB as explained above. The applicants have surprisingly discovered that directly coating or lining the internal walls of the pipe or vessel with a nitrite containing or nitrite forming or an FNA precursor material is highly advantageous to prevent or reduce such corrosion. The present inventor believes that the lining or the coating forms FNA on the inner walls or the internal walls of the pipe or vessel including the walls of the pipe or vessel which is not constantly in contact with water. For example, formation of a coating or a lining comprising a nitrite such as Sodium Nitrite under optimal environmental conditions such as acidic pH (less than 7.0) results in the formation of free nitrous acid (FNA). As a result of FNA formation, the activity of SOB is reduced which acts to reduce corrosion of the inner walls of the pipe or vessel. Such a method is highly efficient because it assists in applying the corrosion inhibiting lining or coating at specific or localised sections of areas of the inner walls (including water contacting and air contacting surfaces) of the pipe/vessel which have been affected by localised corrosion thereby alleviating the need for dosing or flushing large quantities of additives through the fluid stream which may not necessarily have a significant effect on localised corrosion on the inner wall of the pipe or sewer.

[0014] The method of the first aspect is particularly advantageous for treating corrosion of sewer pipes or vessels comprising cementitious material such as concrete.

[0015] In an embodiment, the method may be utilised for inhibiting corrosion in pipes or vessels with at least some prior corrosion damage or prior use. For example at least a part of the contacting surface may comprise a layer of biofilm formed on the contacting surface such that during the step of coating or lining the inner wall surfaces, the coating/lining is at least partially formed on the biofilm thereby disrupting or weakening the biofilm by forming FNA on the biofilm. Disrupting or weakening a pre-existing biofilm on an internal wall surface of the pipe or vessel also assists in inhibiting, preventing or treating corrosion of the vessel or pipe.

[0016] In some embodiments, the nitrite containing or nitrite forming material may be applied onto the inner wall of the pipe or vessel by spraying the nitrite containing or nitrite forming or the FNA precursor material or the FNA onto the inner wall.

[0017] The method may further comprise the step of controlling the pH of the coated or lined inner wall in the range of 1.0 to 7.0 and more preferably in the range of 2.0-4.0. Controlling the pH to maintain an acidic environment on the lined or coated inner wall further assists in formation of FNA. In some embodiments, the environment of the inner wall may itself be acidic (for example, due to the activity of SOB living on the inner wall), thereby leading to the formation of FNA on the inner wall. In other embodiments, the surface of the coated or lined inner wall may be acidified.

[0018] In some embodiments, the step of coating or lining the inner wall with the nitrite containing compound comprises applying a composition comprising an effective amount of water soluble nitrite. This composition may be applied by way of spraying the composition onto a surface of the inner wall in the form of an aqueous solution comprising the water soluble nitrite.

[0019] In some embodiments, the method may further comprise the step of coating or lining or applying hydrogen peroxide (H ₂ O ₂ ) or a hydrogen peroxide forming precursor material to the inner wall of the vessel or pipe.

[0020] The hydrogen peroxide may be coated or lined or applied simultaneously with the nitrite containing or the nitrite forming or the free nitrous acid (FNA) precursor material or the free nitrous acid (FNA).

[0021] Alternatively or additionally the hydrogen peroxide may be coated or lined or applied before or after the step of coating or lining or applying of the nitrite containing or the nitrite forming or the free nitrous acid (FNA) precursor material or the free nitrous acid (FNA).

[0022] The applicants have found that synergistic use of H ₂ O ₂ with FNA in a manner as described in some of the embodiments provides an effective method for inhibiting or controlling corrosion. Directly application or lining or coating of H ₂ O ₂ and FNA (directly or sequentially) to the inner walls of the pipe or vessel body (which may comprise a concrete surface coated with a biofilm) assists in mitigating SOB. It is envisaged that in at least some applications, the synergistic use of H ₂ O ₂ with FNA may be more effective in addressing the build-up of SOB in comparison with the use of FNA alone.

[0023] In a second aspect, the invention provides a pipe or a vessel for use in conducting or treating a fluid, the pipe or vessel comprising a pipe or vessel body formed from a cementitious material, an inner wall defining an internal volume for receiving fluid, the inner wall being formed by the pipe or the vessel body wherein the cementitious material comprises a nitrite containing material or a nitrite forming material or an FNA precursor material such that during use at least a part of the cementitious material is adapted to form FNA thereby inhibiting corrosion of the pipe or the vessel body.

[0024] The second aspect enables the provision of a pipe or a vessel that is at least resistant to corrosion. Such an advantageous effect is provided by the incorporation of the nitrite containing or nitrite forming material incorporated in the cementitious material forming the pipe body. During use, formation of FNA assists in controlling microbial activity of bacteria particularly SOB thereby inhibiting corrosion of the body.

[0025] In one embodiment, the nitrite containing or nitrite forming or the FNA precursor material may form an intermediate layer of the pipe body such that the use wearing or corrosion of an inner wall of the pipe results in the nitrite containing material or the nitrite forming material or the FNA precursor material being exposed for contact with water, such as a film or layer of condensed water, thereby preventing or minimising further corrosion of the pipe body. Corrosion causing biofilm containing SOB often grows on the film or layer of condensed water. For example, any wearing or corrosion of the inner lining or inner wall (such as a sacrificial lining) of the pipe or vessel may expose the intermediate layer comprising the nitrite containing or nitrite forming material. As a result, the exposed part of the intermediate layer may act as a corrosion inhibiting layer forming the FNA. As discussed earlier, FNA prevents or inhibits the growth of SOB which often forms a part of a biofilm. This, in turn, prevents or inhibits the formation of sulphuric acid by the SOB, thereby reducing corrosion. Exposing the intermediate layer that contains the nitrites or the nitrite forming material or the FNA precursor material to an acidic environment also results in the formation of FNA that inhibits or reduces SRBs present in the water phase, which results in a reduction of H ₂ S being formed which, in turn, reduces the amount of H ₂ S available for formation of sulphuric acid by oxidation. Reducing the formation of sulphuric acid directly results in reducing or inhibiting concrete corrosion. The FNA also has an inhibitory effect on the activity of (SOB) present in the air phase in the sewer, which also acts to reduce the amount of sulphuric acid formed by the microbial activity of SOB, thereby reducing corrosion. For example, if the intermediate layer contacts with the biofilm, the biofilm would get weakened or disrupted thereby preventing any further corrosion of the body. This would also result in the intermediate layer arresting or preventing corrosion in localised regions of the inner wall surfaces of the vessel or pipe affected by corrosion.

[0026] In another embodiment, the nitrite containing or nitrite forming material may form at least a part of the inner wall such that the free nitrous acid is formed on the said at least part of the inner wall during use. Unlike the previously described embodiment, the present embodiment relies on continuous formation of FNA throughout the inner wall of the pipe or vessel inhibits corrosion of the pipe body and does not require any wearing of the inner walls or inner lining for the formation of FNA. Therefore, such a configuration allows for sustained release of FNA across the inner walls of the vessel/pipe thereby providing a sustained corrosion inhibiting effect across the internal wall of the pipe or vessel body.

[0027] In some further embodiments, the first and second embodiments may be combined to arrive at a third advantageous embodiment. For example, a very low concentration of FNA precursor material such as a nitrite material may be incorporated into the inner wall of the vessel or pipe body and a comparatively higher concentration of FNA precursor material may be incorporated into the intermediate layer of the body. Such a configuration may provide a combination of continued release of low concentration of FNA across the inner wall surface and high concentration of FNA in regions of localised corrosion due to exposure of the intermediate layer (where the lining of the pipe or the vessel is compromised due to corrosion).

[0028] The nitrite containing material may comprise sodium nitrite and/or potassium nitrite and/or any other suitable nitrite that is capable of forming FNA. Furthermore, the pipe or vessel body may further comprise one or more of additives including transition metallic oxides, zeolites, catalysts, reinforcing agents.

[0029] In some embodiments, the pipe or vessel may further comprise hydrogen peroxide or a hydrogen peroxide forming precursor forming a part of the cementitious material such that during use hydrogen peroxide is formed thereby inhibiting corrosion of the pipe or vessel body.

[0030] Preferably, the hydrogen peroxide or a hydrogen peroxide forming precursor is incorporated into the intermediate layer such that formation of the hydrogen peroxide on said at least exposed portion of the intermediate layer prevents further weathering of the pipe or vessel body.

[0031] The synergistic use of Η ₂ 0 ₂ with FNA for forming a part of the cemetitious material in a manner as described above in some of the embodiments provides an effective method for inhibiting or controlling corrosion by mitigating SOB. Once again it is envisaged that in at least some applications, the synergistic use of H ₂ O ₂ with FNA may be more effective in addressing the build-up of SOB in comparison with the use of FNA alone. Exposing the intermediate layer that results in the formation of FNA and Η ₂ 0 ₂ is useful in addressing the reduction of SRB's as well as SOBs. Any contact of the FNA and H ₂ 0 ₂ in the exposed concrete or cementitious material with fluids such as wastewater inhibits or reduces SRBs present in the water phase, which results in a reduction of H ₂ S being formed which, in turn, reduces the amount of H ₂ S available for formation of sulphuric acid by oxidation. Reducing the formation of sulphuric acid directly results in reducing or inhibiting concrete corrosion.

[0032] The FNA and H ₂ 0 ₂ also have a combined (synergistic) inhibitory /biocidal effect on the activity of (SOB) present in the air phase in the sewer, which also acts to reduce the amount of sulphuric acid formed by the microbial activity of SOB, thereby reducing corrosion. For example, if the intermediate layer containing the FNA and H ₂ 0 ₂ contacts with the biofilm, the biofilm would get weakened or disrupted thereby preventing any further corrosion of the body. This would also result in the intermediate layer arresting or preventing corrosion in localised regions of the inner wall surfaces of the vessel or pipe affected by corrosion.

[0033] In a third aspect, the invention provides a method of repairing a pipe, the method comprising the application of a coating comprising a nitrite containing or nitrite forming material on to at least a part of an inner wall of the pipe or vessel defining an internal volume for receiving fluids to form a coated surface on the inner wall.

[0034] Corroded section or portions of a sewer pipe can be repaired by applying the coating to one or more corroded portions of the inner wall of the pipe. Coating the corroded portions directly with a nitrite containing or nitrite forming material or the FNA precursor material is highly advantageous because FNA formed on the corroded portion of the pipe as a result of the applied coating prevents or inhibits corrosion. Corrosion may be inhibited particularly on the air contacting surfaces of the pipe and vessel. Such a method is highly efficient because it assists in applying the corrosion inhibiting lining or coating at specific or localised sections of areas particularly inner walls of the pipe/vessel which are not usually in contact with fluids passing through the pipe/vessel for example wastewater and contact the sewer air directly above the liquid phase of the pipe/vessel. This method preferably alleviates the need for dosing or flushing large quantities of additives through the fluid stream which may not necessarily have a significant effect on localised corrosion on the inner walls of the pipe that are usually not in contact with the fluid flowing through the pipe/vessel.

[0035] In an embodiment, the step of applying the coating includes applying the coating to a corroded portion of the inner walls to form FNA on the coated corroded portion of the pipe or vessel. The coating layer that contains the nitrites or the nitrite forming material or the FNA precursor material results in the formation of FNA (when contacted with an acidic solution) on the surface of the inner walls. The FNA has an inhibitory effect on the activity of SOB present in the air contacting part of the corroded portion of the walls of the pipe. The FNA formation reduces the amount of sulphuric acid formed by the microbial activity of SOB, thereby reducing corrosion. Reducing the formation of sulphuric acid directly results in in reducing or inhibiting concrete corrosion. The FNA also has an inhibitory effect on the water contacting part of the sewer. Specifically, the FNA formation on the corroded portion of the walls that contact water inhibits or reduces SRBs present in the water phase, which results in a reduction of H ₂ S being formed which, in turn, reduces the amount of H ₂ S available for formation of sulphuric acid by oxidation. In some further embodiments, the step of coating comprises spraying the nitrite containing or nitrite forming material onto the contacting surface.

[0036] The method may further comprise the step of controlling pH of coated surface in the range of 1.0 to 7.0 and more preferably in the range of 2.0-4.0. In other embodiments, the environment of use of the pipe or vessel may result in the coating being exposed to an aqueous solution having an acid pH, which results in the formation of FNA.

[0037] The method may involve coating the inner wall with the coating comprises applying a composition comprising an effective amount of water soluble nitrite, wherein the effective amount is in the range of 0.001 to 95.5 weight percent. The coating may be applied by spraying the nitrite or nitrite forming compound onto the inner wall.

[0038] In other embodiments, the coating may comprise a coating of a cementitious material, the cementitious material including a nitrite containing material or a nitrite forming material or an FNA precursor material. This embodiment has the advantage that corroded or eroded parts of the pipe or vessel are also filled with cementitious material. The cementitious material can release FNA when exposed to the environment of the pipe or vessel, thereby resulting in a reduction or minimisation of corrosion of the cementitious material.

[0039] In a fourth aspect, the invention provides a method of inhibiting corrosion in a vessel or pipe, said vessel or pipe comprising one or more inner walls defining an internal space for receiving fluid, the method comprising introducing an influent steam of liquid comprising a nitrite containing or a nitrite forming material or an FNA precursor material or FNA into the vessel or pipe such that a substantial part of the inner wall contacts the influent stream of liquid such that FNA is formed on at least a part of the inner walls thereby inhibiting corrosion of the inner wall.

[0040] The invention of the fourth aspect may for example involve, introducing an influent stream of water such as a waste water stream dosed with a nitrite material such as a water soluble nitrite. The method may involve introducing the stream at a relatively high pressure or high flow rate to ensure that a substantial surface area of the inner walls comes into contact with the influent stream dosed with nitrite material. In some embodiments, flow of the influent stream of water may be temporarily suspended to retain dosed water in the vessel or pipe for a specific residence time to further ensure that FNA is formed at the inner walls thereby preventing or inhibiting corrosion of the inner walls.

[0041] In some embodiments, the method of the third aspect may further comprise the step of coating or lining or applying to the inner wall of the vessel or pipe with hydrogen peroxide (H ₂ O ₂ ) or a hydrogen peroxide forming precursor material.

[0042] The hydrogen peroxide may be coated or lined or applied simultaneously with the nitrite containing or the nitrite forming or the free nitrous acid (FNA) precursor material or the free nitrous acid (FNA).

[0043] Alternatively or additionally the hydrogen peroxide may be coated or lined or applied before or after the step of coating or lining or applying of the nitrite containing or the nitrite forming or the free nitrous acid (FNA) precursor material or the free nitrous acid (FNA).

[0044] It is important to appreciate that a large part of the inner walls of the sewer pipe is exposed to air and is not in direct contact with the water flowing through the sewer pipe. Therefore, directly contacting such inner walls of the pipe with the hydrogen peroxide and the FNA provides an effective method of controlling the SOB in the air phase of the sewer pipe or the vessel.

[0045] The applicants have found that synergistic use of H ₂ 0 ₂ with FNA in a manner as described in some of the embodiments provides an effective method for inhibiting or controlling corrosion. It is envisaged that in at least some applications, the synergistic use of H ₂ O ₂ with FNA may be more effective in addressing the build-up of SOB in comparison with the use of FNA alone.

[0046] In some embodiments, the method of the third aspect may further comprise a step of dosing the influent stream with hydrogen peroxide (H ₂ O ₂ ). The step of dosing with H ₂ O ₂ may be carried out simultaneously with the step of introducing the influent steam of water comprising a water soluble nitrite or a nitrite forming or an FNA precursor material. Alternatively, the step of dosing with H ₂ O ₂ may be carried out after the step of introducing the influent steam of water comprising a water soluble nitrite or a nitrite forming or an FNA precursor material. [INSERT] It is important to appreciate the step of dosing the influent stream differs significantly from the previously described step of applying or lining or coating hydrogen peroxide onto the inner wall. Dosing the influent stream with H ₂ O ₂ results in the liquid phase of the sewer phase being contacted by the dosed H ₂ O ₂ and therefore the dosing step addresses the SRB but does not address SOB.

[0047] The method may further comprise controlling the pH on the inner wall contacting the influent stream in a range of 1.0 to 7.0 and more preferably 2.0 to 4.0.

[0048] In a fifth aspect, the invention provides a method for forming a pipe or a vessel adapted for conducting fluid, the process comprising casting or forming a pipe or vessel body from a cementitious material such that an inner wall formed by the pipe body defines an internal space for receiving fluid during use; wherein a nitrite containing material or a nitrite forming material or an FNA precursor material is incorporated into the cementitious material such that during use at least a part of the cementitious material is adapted to form FNA thereby inhibiting corrosion of the pipe body.

[0049] Incorporation of the nitrite containing or nitrite forming material or the FNA precursor material into the cementitious material forming the pipe or vessel body is highly advantageous. During use, at least some of the nitrite material of the pipe body may form FNA on the inner wall of the pipe or vessel. The FNA as formed has an inhibitory effect on the activity of SOB present in the air contacting part of the corroded portion of the walls of the pipe. The FNA formation reduces the amount of sulphuric acid formed by the microbial activity of SOB, thereby reducing corrosion. Reducing the formation of sulphuric acid directly results in reducing or inhibiting concrete corrosion. The FNA also has an inhibitory effect on the water contacting part of the sewer. Specifically, the FNA formation on the corroded portion of the walls that contact water. Presence of FNA also assists in controlling microbial activity of bacteria particularly sulphate reducing bacteria or methanogenic archaea (or both) thereby inhibiting corrosion of the pipe or vessel body that contacts the fluid flowing therethrough (such as the wastewater). In one embodiment, the method comprises forming an intermediate layer of the pipe body such that the intermediate layer comprises the nitrite containing or nitrite forming or the FNA precursor material incorporated into the pipe or vessel body wherein during use wearing or corrosion of the inner wall of the pipe body results in at least a part of the intermediate layer being exposed, whereby formation of the FNA on said at least part of the intermediate layer prevents or reduces or controls further wearing of the pipe body.

[0050] In an alternative embodiment, the method comprises incorporating the nitrite containing or nitrite forming or the FNA precursor material into at least a part of the inner wall such that the FNA formed on the said at least part of the inner wall during use inhibits corrosion of the pipe or the vessel body.

[0051] The nitrite containing material may comprise sodium nitrite and/or potassium nitrite and/or any other FNA precursor material. Further additives may also be incorporated into the cementitious material, the additives being preferably selected from transition metallic oxides, zeolites, catalysts, reinforcing agents.

[0052] The fluid that passes through or into the pipe or vessel may comprise a gas or a liquid, or a gas containing liquid.

[0053] In one embodiment, the fluid comprises a gas containing some H ₂ S and moisture.

[0054] In at least some embodiments of the method aspects, the fluid may comprise waste water.

[0055] The invention described herein is in no way limited to inhibiting corrosion in pipes conducting waste water. For example, in at least some embodiments, the invention may be directed to treatment corrosion in pipes conducting fluids such as oils and gases.

[0056] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

[0057] The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.

BRIEF DESCRIPTION OF DRAWINGS

[0058] Various embodiments of the invention will be described with reference to the following drawings, in which:

[0059] Figure 1 is a schematic illustration of concrete sewer corrosion; and

[0060] Figure 2 is a schematic illustration of a testing arrangement for testing the corrosion of concrete in accordance with a method embodiment of the present invention.

[0061] Figure 3 is a schematic illustration of a reactor arrangement for testing suspension solutions of products obtained from concrete corrosion.

[0062] Figure 4 is typical profile of Hydrogen Sulphide Uptake rates for concrete samples treated in accordance with a method embodiment of the present invention and a comparative example.

[0063] Figure 5 illustrates confocal laser scanning microscope images of stained bacteria separated from corrosion biofilms (A) before treating concrete in accordance with a method embodiment of the present invention; and (B) after treating concrete in accordance with a method embodiment of the present invention.

[0064] Figure 6 is a comparison of Sulphide Uptake Rates (SUR), Adenosine Triphosphate (ATP) concentration and ratio of viable bacteria for concrete before and after treatment in accordance with a method embodiment of the present invention.

DETAILED DESCRIPTION

[0065] It should be understood that whilst the detailed embodiment described herein refers to prevention of corrosion in pipes and vessel conducting waste water, the present invention is in no way limited to waste water related applications. In alternative embodiments, the present invention may be directed to preventing corrosion in pipes or vessels conducting other fluids including gases and oils.

[0066] In an exemplary experiment in accordance with one or more aspects of the present invention, sodium nitrite material was sprayed onto corroding concrete surfaces. Such surfaces typically have a pH in the range of 2.0-4.0 that results in an acidic or acidified environment. Spraying of the nitrite material results in formation of FNA on the corroding surfaces treated with the sprayed nitrite material. As a result of the formation of FNA at a level substantially above the biocidal threshold (ppm level) results in reducing or killing the corrosion-causing organisms (typically SOB).

[0067] A corrosion chamber was designed and set up in a laboratory experimental to achieve a controlled environment similar to real sewers to incubate the prepared concrete coupons as illustrated in Figure 1. The chamber was constructed of glass panels (4 mm thick) with dimensions of 550 mm (length) x 450 mm (width) x 250 mm (height). Concrete coupons were prepared from corroded concrete slabs, previously part of a sewer wall for about 70 years. The dimensions of the concrete coupons were approximately 100 mm (length) x 70 mm (width) x 70 mm (thickness). The concrete of the coupons had about 2-4 mm of pre-existing corrosion layer on an internal surface. The coupons were obtained by cutting by a water-cooled saw, the concrete coupons were removed of the corrosion product by fresh water, dried in an oven (Thermotec 2000, Contherm oven) at 60 °C for 3 days and then weighed. The previously exposed internal surface of the slabs was designed as the experimentally exposed surface of the coupons. After cutting, the coupons were embedded in stainless steel frames using epoxy (FGI R180 epoxy & HI 80 hardener) with the steel frame providing a reference point for determining the change in thickness due to corrosion. The corrosion chamber was sized to contain approximately 2.5 L of domestic sewage collected from a pumping station, which was replaced every 14 days. The coupons were arranged in a manner such that a first part of the coupons is exposed to a gas phase of the chamber with the exposed surface facing downwards about 100 mm above the sewage. This arrangement of the coupons simulates the sewer pipe crown where is highly susceptible to sulfide induced corrosion and is usually exposed to air.

[0068] Specifically 5 mL of a sodium nitrite solution (8 g/L) was applied to the corroding concrete surface of one of the coupons (pH: -3.0; being exposed to 50 ppm H ₂ S for ~3 years prior to the test), denoted by Coupon 1 in Table 1. The recovery of the corrosion biofilm was monitored after the application of the sodium nitrite solution. As explained in earlier sections, applying the sodium nitrite onto the coupons under acidic pH conditions results in formation of FNA. Figure 2 shows that the biological sulphide uptake rate (which is theoretically proportional to corrosion rate) of the sprayed coupon was reduced substantially after the FNA treatment to a level that is believed to be mainly related to chemical sulphide oxidation. It is clear that the pre-corroded concrete coupon in the comparative example (denoted by "control" in Figure 3) (dominated by microbially induced corrosion) barely changed its activity in the following 300 days. Also, the surface pH in the FNA treated coupon increased to above 7, confirming that the biological sulfuric acid production was stopped or substantially reduced. This result demonstrates that applying or forming FNA on a corroding concrete surface has great potential as an inhibitory /biocidal agent for the microbes involved in sewer corrosion.

[0069] The gas phase environment inside the chamber was controlled to be 50 ppm of H ₂ S, 22 - 25 °C and 100% relative humidity. The gaseous level of H ₂ S in the chamber was achieved by dosing Na ₂ S stock solution (80 g L-l) into a container partially filled with HC1 (16% HC1) using a solenoid pump (Bio-chem fluidics, model: 120SP1220-5TP) with a dispense volume of 20 The gaseous mixing in the chamber was achieved by a fan and the gaseous H2S concentration was monitored through a H ₂ S sensor (App-Tek OdaLog® Logger L2, range of detection is 0-200ppm). The gaseous level of H ₂ S was controlled at around 50 ppm through controlling the pumping events based on the real time reading of H ₂ S concentration by a programmable logic controller. The gas phase temperature of the chamber was controlled at 22 - 25 °C by placing the chamber in a cabinet arranged in a temperature controlled lab. The liquid phase temperature of the chamber was controlled by re-circulating temperature controlled water from a water bath through two glass tubes submerged in the liquid. Through this way, the gas phase relative humidity in the chamber was controlled at about 100% and was computed through the reading from a wet bulb and dry bulb.

[0070] At the start of the experiment, the concrete coupons were allowed to develop active corrosion by H ₂ S exposure in the chamber for 34 months. Obvious corrosion biofilm was observed on the coupon surface and the surface pH of concrete biofilm ranged between 2.5 to 3.9.

[0071] Among the six concrete coupons (Table 1), coupon No. 1 (FN AO) was treated with nitrite spray on Day 0. Six months following the nitrite spray, coupon No. 2 (FNA176) with corrosion activity higher than coupon No. 1 was also treated with nitrite spray. The nitrite spray procedures applied on the two coupons were the same (described in the next paragraph). The concrete coupon 3, 4 and 5 without any spray, served as control (CTL) or comparative examples. To determine the bactericidal effect of FNA on microorganisms of corrosion biofilm, nitrite spray was performed on another coupon (CV) exposed in the corrosion chamber and the corrosion layer was scraped to determine the percentage of viable microorganisms prior to and 39 hours after the nitrite spray. [0072] Table 1 - The coupons used for various purposes in this study.

Coupons Label Treatment

1 FNA0 FNA @ day 0

2 FNA176 FNA @ day 176

3 CTL Control

4 CTL Control

5 CTL Control

6 CV Cell viability

[0073] For each spray treatment, sodium nitrite solution (8.3 g NaN0 ₂ -N L-l) stored in a mist sprayer was evenly sprayed (5 mL) onto the surface of the concrete coupon 1 and 2 by retrieving the coupon from the corrosion chamber and arranging the coupon in a hood with the exposure side facing upward (the exposure side previously faced downward towards sewage in corrosion chamber). The time of the spray on coupon No. 1 was named Day 0. Due to the low pH level of corrosion biofilm, FNA was formed through the reaction between nitrite and H ⁺ within the corrosion biofilm. To ensure sufficient penetration of FNA into deep corrosion biofilm and eliminate loss of moisture of corrosion biofilm, the coupon was stored in a hood and covered with a plastic case for 1 h. The concentration of FNA in the corrosion biofilm was estimated to be between 100 and 1000 mg-HN0 ₂ -N L-l due to the low liquid volume in concrete and corrosion biofilm (water content 31.52% + 0.90%). Then, the coupon was put back into the corrosion chamber for re-exposure.

[0074] H ₂ S uptake rate measurement was also performed intermittently on 3 control coupons without FNA treatment and 2 experimental coupons before and after nitrite spray to assess the effect of FNA treatment on the H ₂ S uptake activity of coupons. To measure the Sulfide Uptake Rate (SUR) for each coupon, the coupons were retrieved from the corrosion chamber and then immediately setup on the H ₂ S uptake reactor with the relative humidity controlled at 100%. Gaseous H ₂ S produced in a H ₂ S generating bottle was injected into the reactor to the level of 65 ppm and the H ₂ S uptake profile of the coupon was monitored by a H ₂ S detector (App-Tek OdaLog® Logger L2, range of detection is 0-200ppm). The SUR of the coupon at 50 ppm of H ₂ S (i.e. the historical exposure level of H ₂ S in the corrosion chamber) was calculated using the monitored H ₂ S profiles. To repeatedly measure the SUR, the injection of gaseous H ₂ S into the reactor was performed when the monitored H ₂ S level in gas phase of reactor decreased to 40 ppm. The SUR of coupon at 50 ppm measured in each batch test was the averaged SUR at 50 ppm measured from the 3 - 5 replicates.

[0075] For coupon with nitrite spray on day 0 (FN AO), the SUR was intermittently measured over 4 months before the spray and over more than 10 months after spray. For the other sprayed coupon (FNA176), the SUR was intermittently measured over 10 months before spray and 4 months after spray.

[0076] To identify the effect of FNA on corrosion biofilm scraped from the concrete coupons, further tests were carried out. Referring to Figure 2 the testing set up is schematically illustrated. The tests were conducted in a 330 ml glass bottle reactor with 330 ml working volume in a temperature controlled room (24 + 0.5 °C) (Figure 2). The tests used 5.80 g of corrosion biofilm with pH at 2.7 + 0.2 scraped from coupon No.6 after 40 months exposure. The corrosion biofilm scraping was transferred into the reactor. The nutrient solution consisted of 400 mg L-1 of KH ₂ P0 ₄ , 400 mg L-1 of MgS0 ₄ .7H ₂ 0, 400 mg L-1 of (NH ₄ ) ₂ S0 ₄ (Franzmann et al., 2005) and 588 mg L-1 of NaHC0 ₃ and with the pH adjusted to 2.7 by titration of 1 M H ₂ S0 ₄ was filled into the reactor. To monitor the levels of H ₂ S and dissolved oxygen (DO), a H ₂ S microsensor (H ₂ S-50, Unisense, Denmark) and a dissolved oxygen (DO) sensor (LDO101, HQ40d, Hach) were mounted through the lids of the reactor and sealed by Teflon tape (Oxygen tape, Unasco Pty Ltd, Sydney, Australia). The tests were carried out with no headspace in the reactor and under stirring generally at 100 rpm to avoid high disturbance of the H ₂ S microsensor.

[0077] Dissolved Oxygen level was maintained between 35-40% and 90-95% air saturation by flushing compressed air from the aeration inlet near the bottom to the outlet on top of the reactor connecting a 50 mL extension pipe. Background DO consumption profiles were monitored over 2 days prior to intermittent dosing of Na ₂ S stock solution (7.2 g L-1) into the reactor through the rubber stopper using a needle connected syringe. The reactor solution was treated by about 550 mg-HN0 ₂ -N L-1 of FNA after 22 days incubation. The SUR, adenosine triphosphate (ATP) concentration and live/dead cell ratio (5 ml reactor solution per sample) were monitored prior to, 2 h, and 700 h after FNA treatment.

[0078] Surface pH of the coupons was measured by placing a flat surface pH electrode (PH150-C, ExStikTM Concrete pH Kit) on the coupon surface after being wetted with 0.5 mL of milliQ water. To obtain a steady reading, the pH electrode was allowed to stay on the coupon surface for 1 - 2 mins. The average surface pH of each coupon was calculated from four independent measurements performed at different locations on the coupon. To eliminate the disturbance of surface pH measurement on corrosion activity, minimum times of surface pH measurement were performed over the 18 months. The surface pH measurements were performed twice and three times prior to and after FNA treatment or Day 0, respectively.

[0079] The ATP level of the suspension solution of corrosion biofilm was determined. 300 μΐ, of reactor solution was trapped to a well of the 96 well plate (96 well LUMITRAC 200 white immunology plate, Greiner Bio-One, Germany) and mixed with 50 μΐ _^ of BacTiter- GloTM Reagent (G8230, Promega Corporation, USA). The relative light unit of the sample was determined by DTX 880 Multimode Detector (Beckman coulter, USA) using LUM_560 ATP 0.2 s protocol (Luminescence mode, 38 °C, moyen orbital shaking for 20 s, integration time of 0.2 s per well and no filter). The obtained relative light unit of each sample was converted to ATP according to a calibration curve generated with ATP standard (PI 132, Promega Corporation, USA). The ATP measurement of the reactor solution after autoclaving at 121 °C for 30 mins was served as control and all tests were performed in triplicates.

[0080] The viability of bacterial cells in corrosion biofilm scraped from concrete coupon and in the suspension solution of corrosion biofilm was determined by the LIVE/DEAD BacLightTM bacterial viability kits (L7012, Molecular probes). The kits utilized the green fluorescent nucleic acid stain, i.e. SYTO 9, and the red-fluorescent nucleic acid stain green- fluorescent nucleic acid stain, i.e. propidium iodide (PI). When used alone, SYTO 9 stain labels bacteria with either intact or damaged membranes. In contrast, PI penetrates bacteria with damaged membranes and thus reduces the SYTO 9 stain fluorescence when both dyes are used.

[0081] To extract the bacteria from corrosion particles, sterile sodium pyro -phosphate solution (0.2%, pH adjusted to 2.8 by titration of 1M H ₂ SO ₄ ) was filled to a 50 mL falcon tube containing 3 g of corrosion scraping or 5 mL of the reactor solution to 25 mL and then treated by sonication at 65 kHz (Branson Sonifier 250) for 60 s with the falcon tube partially submerged in ice bath. The solution was carefully layered onto 25 ml of sucrose solution (1330 g L-l) and centrifuged (Eppendorf, Centrifuge 5810R) at 5500 xg, 4 °C for 2 mins with slow acceleration (3) and deceleration (3). The upper sodium pyro -phosphate solution containing the bacteria was transferred into a new falcon tube and centrifuged at 18, 000 xg, 4 °C for 5 min. The sediment (bacteria) was washed away of sucrose twice by NaCl solution (0.8%, pH 2.7), re-suspended into 0.5 ml of NaCl solution (0.8%, pH 2.7) and mixed by vortex for 15 s. [0082] The solution containing the bacteria was transferred into a 2-mL plastic centrifuge tube with 1.5 μΐ _^ of SYTO-9 and PI mixture solution and mixed with vigorous shaking. The solution was incubated for 15 min under dark condition at the room temperature (22 °C). 5 μΐ _^ of the prepared solution was trapped to the microscope slide and photographed using a confocal laser scanning microscope (Ziess LSM 510 MET A), equipped with a Krypton-Argon laser (488 nm) and two He-Ne lasers (543 and 633 nm). 20 photographs of randomly chosen field of stained bacteria sample were taken. Quantitative analysis of live and dead cells was performed through determining the relative abundance of green and red pixels of the 20 photos using DAIME.

[0083] Before applying the nitrite spray (sodium nitrite as discussed in previous sections), the SUR of both experimental coupons and control coupons was relatively constant over the 4 months of measurement as illustrated in Figure 4. Particularly, experimental coupon No. 1 (FNA sprayed on Day 0) and the 3 control coupons have similar level of SUR and the averaged SUR of those 4 coupons fluctuated between 54 and 83 mg-S m-2 h-1 over the 4 months of measurement prior to FNA treatment (Figure 4). The surface pH of the 4 coupons ranges between 3.6 and 3.9 and no obvious change was found between the two measurements. It suggests that the corrosion activity of coupons were at relatively steady levels. In comparison, the other experimental coupon (i.e. coupon No.2) has a higher SUR, i.e. 107 + 6 mg-S m-2 h-1, and lower surface pH level, i.e. 2.7 + 0.2, suggesting that it has a higher corrosion activity probably due to the higher microbial activity than the other coupons.

[0084] A gradual decrease of SUR in the following 15 days (data not shown) and then remaining at relative low SUR in the following months were seen on both experimental coupons. The maximum decrease of SUR of the coupon with FNA spray on Day 0 (i.e. coupon No. 1) and 176 (coupon No. 2) were 84% and 92%, respectively. It indicates that the FNA formed on the experimental coupon significantly suppressed/inhibited the sulfide uptake activity of concrete coupons. It is noteworthy that although the 2 experimental coupons had different levels of SUR before nitrite spray, they got similar and lower SUR after nitrite spray. It indicates that the remaining low SUR after nitrite spray may be mainly contributed by physical adsorption of sulfide, chemical oxidation of sulfide or reaction between sulfide and alkaline compounds in corrosion layer. In addition, the sulfide uptake process follows an order of about 0.5 and 1 before and after nitrite spray, respectively.

[0085] In contrast, over the 18 months, barely any increase of SUR of coupons without nitrite spray (the control coupons) was observed (Figure 4). Given that the coupons with FNA treatment have similar and relative high SUR compared to the coupons without FNA treatment at the start of the experiment, the results implicated that FNA formation can effectively mitigate the H ₂ S uptake rate by coupons having an active corrosion layer.

[0086] Referring to Figures 5(a) and (b), two confocal laser scanning microscope images of suspension solutions of bacteria extracted from corrosion biofilm prior to and after FNA treatment are illustrated. The percentage of viable microbes was calculated by determining the percentage of areas in green to the total area of both green and red in the 20 microscope images. For the corrosion biofilm prior to and after FNA treatment, the percentage of viable microbes was 84.6% + 8.3% and 10.7% + 4.3%, respectively. The results suggest that the FNA formation effectively inactivated most of the microbes within 39 h.

[0087] Referring to Figure 5, graphical illustration of the levels of SUR and microbial activities (i.e. ATP levels and ratio of viable microbes) of the reactor solution is depicted. The reactor solution comprises the suspension solution of corrosion biofilm scraped from concrete coupon, prior to and after 2 h and 700 h of FNA treatment. Prior to FNA treatment, the SUR was recorded at 4.8 + 0.1 mg-S L-l h-1 and the ATP level was recorded as 6.3 + 0.2 nM, indicating the active microbial activity including the sulfide oxidizing activity. In addition, the percentage of viable microbes was determined to be 79.7 + 6.2%. SUR sharply decreased to 0 immediately after the FNA treatment and the ATP level and the percentage of viable microbes also decreased to 0.7 + 0.1 nM and 42.2 + 6.6%, respectively, after 2 h of the FNA treatment. These results further suggest that the sulfide uptake activity was completely inhibited and microbial activity was also inhibited within short-term of FNA treatment. No recovery of SUR was observed 700 h after FNA treatment and the ATP level was found to be further decreased to 0.03 + 0.005 nM. It suggests that long-term FNA treatment of microbes of corrosion biofilm can completely inhibit sulfide uptake activity, possibly due to the strong bactericidal effect of FNA on microbes.

[0088] This study demonstrated for the first time that spraying nitrite solution onto the acidic concrete corrosion biofilm resulted in strong bactericidal effect of FNA (formed by the reaction between nitrite and H ⁺ in acidic corrosion biofilm) on sulfide oxidizing microbes. This was experimentally demonstrated through comparing the sulfide uptake activity and microbial activity of both intact corrosion biofilm and suspension solution of corrosion biofilm prior to and after FNA treatment. For the intact corrosion biofilm, SUR decreased by 84 - 92% 1 - 2 months after nitrite spray and the viable bacteria decreased by about 74% within two days after nitrite spray. For the suspension solution of corrosion biofilm scraped from concrete coupon, the sulfide uptake activity was completely inhibited immediately after nitrite addition and the ATP level and viable bacteria decreased by about 89% and 38% within a few hours after nitrite addition.

[0089] Without wishing to be bound by theory, the inventors hypothesize that the formation of FNA is likely to be an important factor that results in the recorded decrease in microbial activity of the acidic corrosion biofilm ion the coupons. Calculations in accordance with the Henderson - Hasselhalch equation suggest that more than 99% of the nitrite applied on the coupons existed as FNA on the coupons in view of the pH levels of corrosion biofilms that generally ranges between 2.5 and 3.9 as discussed in previous sections.

[0090] It is also noted that the sulfide uptake activity of suspension solution of corrosion biofilm was completely inhibited before the complete decrease of ATP. This may occur because the biological sulfide oxidizing activity is inhibited before the deactivation of sulfide oxidizing microbes by FNA.

[0091] For intact corrosion biofilms, although H ₂ S uptake was largely suppressed, the SUR did not decrease to 0 as that in suspension solution of corrosion biofilm. It could be due to non- microbial processes such as physical adsorption and/or chemical sulfide oxidation.

[0092] In this study, no obvious recovery of H ₂ S uptake rates after FNA treatment was observed for up to 11 months. As the recovery of SUR requires re-growth of SOB, the results indicate that FNA treatment caused long-lasting bactericidal effect on bacteria of corrosion biofilm. Similarly, no re-growth of bacteria was observed in the suspension solution of corrosion biofilm was observed over 1 month. The results clearly demonstrated that sulfide uptake activity can be largely inhibited for nearly one year and possibly even longer due to the bactericidal effect of FNA on sulfide oxidizing microbes.

[0093] As durability is one of the key factors that determine the applicability potential of the method for corrosion control, the long-lasting bactericidal effect of FNA treatment on SOB can be used to effectively control microbial induced concrete corrosion. To assess the potential economic cost of the FNA-based technology, the potential chemical cost of nitrite spray on a gravity pipe with diameter of 2 m was evaluated as follows. Assuming half of the concrete surface is exposed to gas phase and subject to corrosion. The chemical cost is about AU$ 33 per kilometre, assuming the price of sodium nitrite is $500/tonne. This indicates that the chemical costs for the nitrite spray process in accordance with the present invention is negligible. Several methods may be used for delivering the FNA in a cost-effective manner. (Gunderson 1997; Sydney et al., 1996).

ADVANTAGES OF THE INVENTION

[0094] Compared to previously reported methods to control microbial induced concrete corrosion, there are multiple advantages for the presently described invention. Firstly, FNA formed on concrete surfaces has a long lasting effect in deactivating the sulfide oxidizing microbes and thus does not require to be applied as frequent as those required through dosing chemicals into sewage water to inhibit sulfide build up. Secondly, the present invention is relatively inexpensive compared to other crown spray methods (e.g. mixture of magnesium hydroxide and titanium dioxide) due to the cheaper chemicals, or coating methods (e.g. epoxy, zeolite and polymers) due to the unnecessary step of surface cleaning/preparation. Thirdly, the method utilises an environmentally friendly chemical (i.e. a nitrite) which the applicants believe is not harmful to the environment. The environmental consequences of nitrite spraying on sewer pipe exposed to gas phase could mainly be from the potential impacts of residual FNA being introduced into the sewage thereby increasing the total nitrogen-load in the downstream wastewater treatment plant (WWTP). However, due to the fact that the amount of nitrite sprayed to concrete is small and part of nitrite that could be dropped to the sewage can be easily degraded through denitrification, and the effect on the downstream WWTP would be negligible. In addition, the usage of FNA will not lead to additional N ₂ 0 emission and probably even help reduce the methane production in sewers.

[0095] In the present specification and claims (if any), the word 'comprising' and its derivatives including 'comprises' and 'comprise' include each of the stated integers but does not exclude the inclusion of one or more further integers.

[0096] Reference throughout this specification to 'one embodiment' or 'an embodiment' means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases 'in one embodiment' or 'in an embodiment' in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations. [0097] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.