NL2006349C2 - Method to detect and locate liquid water in an insulation composition. - Google Patents

Description

METHOD TO DETECT AND LOCATE LIQUID WATER IN AN INSULATION

COMPOSITION

FIELD OF THE INVENTION

5 The invention is directed to a method to detect and locate liquid water in an

insulation composition positioned around a metal transport conduit. BACKGROUND OF THE INVENTION

Corrosion under insulation (CUI) is corrosion that develops over time beneath thermal insulation used on pipes, tanks and other manufacturing and process 10 equipment. Wherever piping, tanks or equipment are thermally insulated, there is potential for CUI. It is usually caused by condensation, rainwater, cleaning fluids, etc., that permeate into the insulation and attack the metal surface of the above equipment. Regardless of how securely insulation materials are applied to a substrate material, there will inevitably be areas where water can seep in, 15 thereby creating conditions that subsequently causes corrosion and damage to the metal surface. As a consequence of the above, CUI may occur at any location and time, even at locations or under conditions which are initially regarded as less likely or even non-likely to experience corrosion.

Various publications are directed to insulation compositions or methods which 20 aim at reducing the content of water in said insulation composition.

JP2002181280 describes a method wherein through the insulation material wound around a pipe a gas of a temperature different from ordinary temperature in the inner part is passed. This gas picks up the water which is discharged at another point.

25 WO 91/18237 describes an insulation system comprising a layer of a heat insulating material for a conduit or container having a surface temperature below the dew point of the ambient air and in particular an insulating system for insulating cold pipes and conduits and containers for the transportation or storage of cooling media. The insulating system has layers of a hygroscopic 30 wicking material on both sides of a thermally insulating material which is adapted to be arranged round a pipe. The two layers communicate with each other 2 through an opening in the thermally insulating material, whereby condensate by capillary action can be transported from the inner layer to the outer layer.

WO 95/19523 describes an insulation around a pipe wherein strips of an hydroscopic material are equidistantly spaced from each other along the length 5 of the pipe. The strips extend from a direct contact with the metal surface to the outside of the insulation where it is exposed to the ambient air and forms an evaporation surface.

A common feature of the prior-art solutions exemplified by WO 91/18237 and WO 95/19523 to the problem with removing of condensate is that a hygroscopic ίο material is arranged on the metal surface on which condensate is formed.

Another common feature is that the hygroscopic material is brought into direct contact with the ambient air.

A problem with the above insulation compositions is that either water is only removed locally in case strips are used. In case a wicking layer totally covers the 15 metal layer corrosion may still take place, especially when the metal surface has a relatively high temperature. Such high temperature metal surfaces are for example encountered in transport conduits for steam. Although water is removed corrosion may still occur.

Detection of CUI (Corrosion under insulation) in industrial plants has been 20 identified as a significant problem, which can affect the integrity of tanks and pipes and lead to a shortening of the lifespan or even outright failure of expensive industrial infrastructure. Lengthy inspections and equipment failures often lead to manufacturing facility downtime, and consequently a loss of efficiency and increase in associated costs. One insidious aspect of CUI is that 25 the corrosion is hidden from view by the thermal insulation. Typically, plants have miles of piping and thousands of square feet of insulation covered equipment. It is neither practical nor economical to remove the insulation at all locations for direct inspection. For the assessment of CUI a wide range of non-destructive techniques have been proposed, as described by Michael Twomey, NDTnet 30 1998 February, Vol.3 No.2, INSPECTION TECHNIQUES FOR DETECTING

CORROSION UNDER INSULATION. Examples of techniques are eddy current 3 measurements to measure the wall thickness, radiography techniques, guided wave techniques and the use of hand-held thermal imaging cameras to identify locations of wet thermal insulation. The known methods are however not optimal because of their costs, their complexity, the requirement to remove the insulation 5 before inspection and/or the highly laborious character of the method. Other disadvantages are that most methods are not suited to measure on a continuous basis and/or that some methods are not distinctive.

There is, therefore, a widespread but presently unmet need for an efficient and accurate detection system capable of identifying likely CUI corrosion sites in 10 a variety of industrial manufacturing and processing environments.

Examples of the above methods will be briefly discussed. W0201050617 describes an inspection method for inspecting corrosion under insulation, in piping to which a heat insulator is provided, the method comprising: providing a fiber optical Doppler sensor to the piping; and inspecting the corrosion in the 15 piping by using the fiber optical Doppler sensor. A disadvantage of this method is that first corrosion has to occur before it can be detected.

W0201053813 describes a method of detecting corrosion under insulation. The method utilizes infrared imaging video cameras to detect characteristic signatures of wet thermal traits on process equipment and communicating said 20 corrosion related data to an operator. This method detects wet areas in the insulation. This is advantageous because it will identify areas where the risk of corrosion may be significant. This method enables maintenance of the equipment based on risk based inspection. This is advantageous because insulation needs to be removed less for an actual inspection and only the locations, where 25 corrosion may be expected, are inspected. A disadvantage of the method is that an operator has to scan the entire length of the pipe with a camera.

WO-A-2010/143948 describes a system wherein the local temperature and humidity values are measured in the insulation surrounding a pipeline. These values are said to be an indication related to local corrosion and degradation of 30 the pipeline. A high humidity and a certain temperature may indicate that 4 corrosion can occur locally. Applicants however believe that this system will still give rise to many falls calls.

The object of the present invention is to provide a method which enables the user to locate areas where CUI may have occurred.

5

SUMMARY OF THE INVENTION

The invention is directed to a method to detect and locate liquid water in an insulation composition positioned around a metal transport conduit wherein the insulation composition comprises of a layer of wicking material and wherein the 10 layer of wicking material comprises measuring means to measure the presence of liquid water.

Applicants believe that the presence of liquid water is a better indicator that corrosion is taking place locally and that this method will give far less falls calls than the method described in WO-A-2010/143948. A further advantage is that 15 the method is more simple in that it measures less properties in the insulation than the prior art method which is based on the measurements of temperature, humidity and in some cases also the chloride, ammonia and nitride contents.

BRIEF DESCRIPTION OF DRAWINGS

20 Figure 1 is an insulation composition.

Figure 2 is a insulation composition.

Figure 3 is a insulation composition.

Figure 4 is a transport conduit and an insulation composition Figure 5 is a transport conduit and an insulation composition having means 25 to add a transport gas.

Figure 6 is a cross-sectional view of an insulated transport conduit provided with a means to detect liquid water.

DETAILED DESCRIPTION OF THE INVENTION

30 The invention shall be described in more detail and preferred embodiments will be discussed and their specific advantages.

5

Wicking layer is suitably composed of a woven, non-woven or knit fabric, preferably a non-woven fabric and even more preferably a non-woven fabric made from a hydrophilic fiber such as cotton, viscose, for example Rayon, or polyamide, or surface treated fabrics, such as a polypropylene. An even more 5 preferred non-woven fabric is a non-woven nylon as obtainable from companies like Fiberweb or Freudenberg. Other examples of suitable materials for the wicking layer are the hydroscopic materials described in WO-A-2005/038330, which publication is hereby incorporated by reference and/or the filler material as described in WO-A-99/09346, which publication is hereby incorporated by 10 reference. The wicking layer preferably has a weight of 30 to 300 grams per square meter (gsm) and more preferably about 25 gsm to 50 gsm. The fabric will have a fiber size from 0.1 to 100 microns. The fabric is preferably made from a polymer that is dimensionally stable from about -5 to 175 °C. The thickness of layer will depend on the type of material, the method to discharge water from this 15 layer and the expected volume of water which is to be removed locally.

Embodiments with more than one layer of wicking material as described above on top of each other are within the scope of the present invention. Applicants believe that one layer is sufficient but it is not excluded to use more than one layer.

20 The means to detect liquid water can be those known to the skilled person.

Examples of suitable means are water sensible coatings. Water sensible coatings are preferably used in combination with a single thin waveguide. In such use the presence of liquid water will change the colour of the coating. By passing light through the waveguide a change of colour will be detected. Since the speed 25 of light in the waveguide is known the position of the colour change and thus the presence of liquid water can be determined.

Another means to detect liquid water is by measuring the local electrical conductivity in the wicking layer. This detector suitably comprises an ohm-meter and a pair of electrodes. A minimum amount of water present between the two 30 measuring electrodes will close the so-called electrical bridge and allow a small current to run between the two electrodes. Suitably the detector is operated in a 6 so-called I/O mode allowing detection of either presence or absence of liquid water. The number of pairs of electrodes in the wicking material will be dependant on the desired accuracy. The output of the ohm-meter can be sent to an electronic device for triggering action, data acquisition and/or storage.

5 Communication of the numerous measurements along a transport conduit to a central data processing unit may for example be performed by applying a multiplex technique to the various signals and communicating the collected signals via one single coaxial cable to said central data processing unit.

The electrodes of the detector suitably comprises of a non-corroding 10 electrical guiding material, e.g. a silver wire and length; but also include electrical guiding components printed on flexible, non-electrical guiding materials such as poly ethylene. The electrodes are suitably directly applied to, or interwoven in the various wicking layers of the insulation composition. Preferably the local electric conductivity is measured at more than one location along the insulated metal 15 transport conduit in an axial direction. The detection limit of this detection system will depend on a number of typical detector dimensional parameters allowing the system to be tuned towards the application needs. Such detectors are known to the skilled person. For example the detectors may be the same as the detectors used in a so-called Protimeter, a commercially available moisture meter.

20 The intrinsic dispersion of liquid water in the wicking layer leads to significant lowering of the minimum volume of detectable water. When applied to a transport conduit the detectors are suitably uniformly distributed in the wicking material. The pairs of electrodes of one detector may be spirally wrapped around the axis of the transport conduit for a certain length of the insulated conduit.

25 Other models of wrapping may be applicable for achieving adequate spatial resolution in e.g. non-linear, non uniform applications such as flanges and pumps, reactors and /or other process equipment.

Because water will accumulate in the wicking layer any liquid water which is present in the insulating composition can be effectively detected without having 30 to use a large array of measuring means across the entire insulating composition. If no water is detected in the wicking layer it can be safely 7 concluded that no water is or has been present on the metal surface and that therefore the corrosion risk at that location can be considered to be low. Thus locations of corrosion risk can be identified and maintenance based on risk based inspection can be performed in a more simple manner.

5 The invention is thus also directed to an insulated metal transport conduit having a layered insulation composition placed around said conduit, wherein the insulating composition comprises a wicking layer and wherein the wicking layer comprises a means to measure the local electrical resistance in said layer. The wicking layer may as described for wicking layer (b) above. The insulation 10 composition is preferably an insulation composition as described in the present specification.

Preferably the insulation composition comprises of the following layers (a) a hydrophobic, moisture permeable layer composed of a woven, non-woven, or knit fibrous material, 15 (b) the layer of hydrophilic wicking material, and (c) an insulation material layer.

Applicants found that by using such a preferred insulation composition water is less likely to accumulate on the surface of the metal transport conduit and as a consequence corrosion of the metal surface is further avoided. This preferred 20 insulation composition comprises a layer (a) composed of a woven, non-woven or knit fibrous material. The function of this layer is to separate the wicking layer, which may contain water, off a metal surface of the conduit or vessel which is to be insulated. This layer (a) should be sufficiently porous and thin as to ensure that any water on said surface is physically pressed up into the wicking layer 25 (b). The meaning of the terms hydrophobic and hydrophilic as used to describe layer (a) and layer (b) is only to indicate that layer (a) is less hydrophilic than the wicking layer (b). The hydrophilic property of the layer will be defined by the material of the layer and the structure. For the present invention a more hydrophilic material will more quickly take up a volume of water per volume of 30 layer material. The result of the fact that layer (a) is less hydrophilic than the wicking layer (b) is that any water which may be present on the surface of the 8 metal object to be insulated is readily transported away from said surface and into the wicking layer. The material of layer (a) may, optionally, be treated with a surfactant or otherwise processed to impart a desired level of wettability and hydrophilicity. The layer (a) should be sufficiently porous to water such that water 5 can readily penetrate through its thickness. Layer (a) may suitably be composed of the same material used as topsheet in sanitary products such as diapers and sanitary napkins, wherein the topsheet is the sheet is made of a synthetic fiber and which is in contact with the skin of the user. Suitable fibrous materials for layer (a) are synthetic fibers, for example, carbon, polyester, polyether, 10 polyethylene (PE) or polypropylene (PP) fibers. The material of layer (a) is suitably present as a spunbonded web or as a bonded-carded web because they are more easy to manufacture. An example of a suitable layer (a) is a non-woven, spunbond, polypropylene fabric. For applications wherein the temperatures can vary between -4 and 175 °C, for example when the insulation 15 is used around a transport conduit in a refinery, it is preferred to use a material which is dimensionally stable under these conditions. Examples of suitable materials for such applications are polyethylene terephthalate or polyether sulphone.

The layer (a) will suitably have a weight of 10 to 100 grams per square meter 20 (gsm) and preferably from 25 gsm to 50 gsm. The fiber size of the fibres used in the woven, non-woven or knit material is suitably from 0.1 to 100 microns. Embodiments wherein more than one of the above described layer (a) are positioned on top of each other are within the scope of the present invention. Applicants believe that one layer (a) is sufficient but it is not excluded to use 25 more than one layer (a).

Layer (b) is the wicking layer. The function of this layer is to accumulate liquid water as described above and in addition to quickly transport water away from layer (a) and thus away from the insulated metal surface and to remove the water to suitably a discharge point or to a preferred next void layer (b1). The wicking 30 layer should be sufficiently hydrophilic and porous so as to ensure that any water in layer (a) is easily and quickly drawn into the wicking layer by hydrophilic and 9 capillary forces. The wicking layer should be sufficiently thick to avoid complete saturation with water of said layer. Complete saturation is to be avoided because wicking layer (b) would then loose its ability to remove any water from layer (a). Intake of water from layer (a) is suitably performed within seconds or minutes 5 while the subsequent discharge of water from layer (b) can proceed more slowly from the larger volume of wicking layer (b).

In a preferred embodiment of the present invention a layer (b1) of a high void material is present between wicking layer (b) and insulation layer (c). The high void material layer (b1) is advantageous because it provides a drain which can 10 take in water from the wicking layer (b) and/or the insulation layer (c) and subsequently provide a transport channel to discharge of said water from the insulation. Transportation can be passive transport or more preferably by means of a transport gas, for example hot air, preferably hot and dry air, which is supplied to layer (b1) at a first point. At a second point spaced away from said 15 first point the gas is subsequently discharged from layer (b1) and from the insulation composition. Along the way evaporated water is picked up in the high void layer and an efficient and quick method to dry an insulation composition is obtained. This method of discharging water from an insulation composition is more effective than the prior art method described in the earlier referred to 20 JP2002181280 because the pressure drop will be lower and because water will concentrate in this layer making the pick up by means of the transport gas much more effective.

The high void material is suitably structurally strong such to maintain the high void properties when applied as part of an insulation composition. The material is 25 an open structure that allows for easy movement of a gas, for example the transport gas. The high void space is furthermore advantageous because of the resulting low pressure drop over the distance between the spaced away first and second points described above.

The detection of water by means of the above method can trigger an 30 inspection of the insulation at the location where water is detected or can be used as a trigger to start providing a transport gas as described above to a high 10 void layer (b1), if present. The supply of transport gas can be terminated once the measurement of the local conductivity indicates that the water has been removed or when the content of water in the transport gas as it leaves the insulation reached a certain minimum value. The transport gas and its use as 5 described above can also be advantageously used to detect leakage of the insulated process pipelines. Such leaks may be caused by damaged seals between flanges or by, illegal, tapping. The method comprises supplying a transport gas to the high void material layer at one position and discharging the transport gas at a second location and analyzing the composition of the transport 10 gas as it leaves the insulation composition for components which are present in the insulated pipelines. This method is suited to measure small leaks of for example hydrogen or other flammable components. Thus the invention is also directed to a method to detect leakage of an insulated metal transport conduit comprising a metal transport conduit and an insulation composition, wherein the 15 insulation composition comprises of a layer (b1) of a high void material, by supplying a stream of gas to the layer of high void material at a first point and discharging a stream of the gas and any leaked components from the insulated transport conduit from the high void material at a second point and analyzing said discharged stream for such a component.

20 The different elements of the insulation composition comprising the high void material layer (b1) may be combined when applying the composition to a surface to be insulated. In a preferred embodiment an intermediate composition, comprising layers (a), (b) and (b1), are combined with insulation material layer (c) when positioning the insulation composition on the metal surface to be insulated. 25 The invention is thus also directed to such an intermediate composition comprising the following layers (a) a hydrophobic, moisture permeable layer composed of a woven, non-woven, or knit fibrous material, (b) a hydrophilic wicking layer comprising the means to detect liquid water, and a layer (b1) of a high void material. This intermediate composition can be used to manufacture 30 the insulation composition according to the invention. In addition the composition can also be used to keep metal surfaces dry in situations where insulation is not 11 the primary objective of the use. In this use no insulation layer (c) is present. When used in this other, non-insulating, application the composition can also comprise a cover sheet of a polymer or metal material. Polymer cover sheets may be a poly-olefin sheet, e.g. a PE or PP sheet and examples of a metal sheet 5 are for example aluminum foil or sheet also referred to as aluminum cladding.

The high void material layer (b1) of this composition is advantageous for the same reasons as described earlier for the insulation composition in that it provides a drain which can take in water from the wicking layer (b) and subsequently provide a transport channel to discharge of said water from the 10 composition. Transportation can be passive transport or more preferably by means of a transport gas, for example hot air, which is supplied to layer (b1) at a first point. At a second point spaced away from said first point the gas is subsequently discharged from layer (b1) and from the composition. Along the way evaporated water is picked up in the high void layer and an efficient and 15 quick method to dry the composition is obtained.

The high void material can be a knit fibrous material, sometimes also referred to as Spacer 3D, or a so-called three dimensional fiber network. An example of a suitable knit fibrous material is Spacetec as obtainable from Heathcoat Fabrics Ltd. A suitable three dimensional fiber network is a so-called embossed material 20 comprised of one or more sheets of woven fibers which are spaced away from each other by means of projections as for example described in US5364686. The projections are portions of the sheet of woven fiber which rise above the base plane of the sheet. Such a network can be obtained by molding a textile fabric impregnated with a thermoplastic or more preferably by molding a thermoplastic 25 fabric, wherein the mold is shaped such that the above projections are formed when molding. The projections can have many designs and rise about between 2 and 20 mm above the base plane of the sheet. The fabric which may be woven or knit and should be sufficiently permeable for water and/or water vapor. The thermoplastic is preferably a hydrophobic fiber with a diameter of 0.02 mm to 0.2 30 mm, preferably 0.05 mm. The thermoplastic is preferably dimensionally stable from about -5 to 175 °C. Preferred thermoplastic materials are polyethylene 12 terephthalate or polyether sulphone. The layer preferably has a void ratio e of between 5 and 50 wherein void ratio is defined as the Vv/Vs in which Vv is the volume of void and Vs is the volume if solid material in the high void material.

The bulk density will suitably be between 0.02 g/cc and 0.2 g/cc. The thickness of 5 the high void material layer (b1) should be sufficient to transport water away from the insulating composition in combination with an acceptable pressure drop. Suitably the layer (b1) is at least 2 mm and more preferably at least 5 mm thick. The upper limit is less critical, but in order to avoid a very thick insulation composition layer (b1) is preferably at most 20 mm thick, ίο The three dimensional fiber network materials which may be used for layer (b1) may be the same three dimensional fiber networks used for mattresses in hospital beds and car seats as for example described in US6701556. Because for the present application the ‘feel’ for the patient or car driver is less important also three dimensional fiber networks can be used which are not optimal for 15 these applications but have the desired high void and structural strength properties as suited for the presently invented application.

The insulation material present in insulation material layer (c) may be any known type of insulating material. The insulating material may be of the open or closed cell type. Examples of closed cell type insulating materials are foamed 20 rubber or foamed plastic. Examples of open cell insulating materials are mineral wool as for example glass wool, rock wool or slag wool obtainable from Rockwool International A/S, foamed open-cell plastic and polyurethane foam, or may further alternatively comprise combinations of the materials mentioned above. The thickness of the layer will depend on the required insulation. For 25 example one to four layers of commercially available insulation material may be combined wherein each individual layer may have a thickness of between 25 and 150 mm.

In a preferred embodiment a second high void material layer (d) is present on the insulation material layer (c). This second high void material layer (d) is 30 present at the side of layer (c) not facing earlier referred to wicking layer (b) or high void material layer (b1). This second high void layer can effectively remove 13 any water entering the insulation from the exterior before it reaches the insulation material layer (c). Possible high void materials for use in layer (d) are as described for layer (b1), wherein for an insulation composition the high void material in layer (b1) may be the same or different from the high void material of 5 layer (d). The thickness of layer (d) may be between 2 and 20 mm.

The insulation composition is suitably used to insulate a metal vessel, metal apparatus, and more preferably a metal transport conduit. Examples of vessels are heat-exchangers, storage tanks and reactors. The temperature of the metal surface facing the insulation may be below or above the dew point of water. The ίο insulation may have the function to avoid heating or avoid cooling of the metal surface by the ambient air present at the metal surface. Preferably the insulation is present to avoid cooling of the metal surface. The temperature of the metal surface to be insulated is suitably from 30 to 175 °C. The metal may be stainless steel and especially carbon steel and the so-called 300 series stainless steels. It 15 is especially such surfaces and temperature conditions wherein corrosion in the presence of liquid water can readily occur. On the carbon steels it manifests as generalized or localized wall loss. With the stainless pipes it is often pitting and corrosion induced stress corrosion cracking (CISCO). Such corrosion can now be avoided by using the insulation composition according to the present invention.

20 The invention is especially directed to refinery, LNG, GTL and chemical processing pipelines and steam pipelines in general which pipelines are made of steel piping and insulated with an insulating composition according to the invention and protected with an aluminum cover. Pipelines and transport conduits have the same meaning in the context of the present invention. Unfortunately, 25 moisture cannot be completely excluded from the insulation of such a pipeline and, by the natural hot/cold cycles of the day, vapor condenses in the insulation and collects against the pipe. Over time, this condensation can cause, through electro-chemical reactions, the corrosion of the pipe. In the extreme, this can cause leakage/release from liquids, gases and slurries. This may lead to loss of 30 production yield, unintended shut-downs and hazardous situations. Moreover the 14 presence of water in the insulation material reduces its insulating value and forces the frequent replacement of insulation.

The invention is thus especially directed to an insulated metal transport conduit comprising a metal transport conduit and an insulation composition as 5 described above, wherein the moisture permeable sheet of layer (a) contacts the outer surface of the metal transport conduit and wherein a cover (e) is present at the exterior of the insulation composition. The cover (e) is a diffusion proof layer at the outside of the insulation composition relative to the inner positioned conduit to be insulated. The diffusion proof layer may suitably be a plastic or 10 metal foil, e.g. an aluminium foil or sheet also referred to as aluminium cladding.

The insulation composition described above is not only suitable for insulating the actual transport conduit, but also for mounting on valves, flanges, fittings and the like, which are built into or attached to the conduit. Although cover (e) is substantially diffusion proof water nevertheless can enter the insulation 15 composition where the cover (e) is damaged or at locations where different parts of the insulation composition connect. Because of this unavoidable ingress of water into the insulation composition liquid water cay accumulate on the metal surface to be insulated. By using the insulating composition according to the present invention the presence of liquid water can be avoided or at least the time 20 at which the liquid water is present on the surface can be reduced. This reduces the accumulation of corrosion.

The insulated metal transport conduit preferably has a layer (b1) of a high void material between wicking layer (b) and insulation layer (c). Preferably layer (b1) is fluidly connected to a means to discharge water from said layer (b1) to the 25 exterior of the insulated metal transport conduit. Such a discharge can be a drain pipe as for example described in WO-A-2007061311. Water as present in the insulation composition can for example evaporate into high void layer (b1) and be subsequently transported by passive transport to said means to discharge water. In addition the insulated transport conduit preferably also has an supply means to 30 add a transport gas to layer (b1) such that evaporated water can be picked up between said inlet means and outlet means in layer (b1) as described above.

15

DETAILED DESCRIPTION OF THE FIGURES

The absolute and relative dimensions of the layers in the Figures are chosen to more clearly illustrate the composition and are not necessarily the most optimal dimensions.

5 Figure 1 shows an insulation composition (1) having a moisture permeable layer (2), a wicking layer (3) and insulation material layer (4).

Figure 2 shows an insulation composition (5) and part of a metal surface (16) of a conduit to be insulated. Figure 2 further shows a hydrophobic layer (6), also referred to as the drying layer, as a thin hydrophobic fabric that separates ίο the metal surface (16) from a wicking layer (7). The wicking layer (7) draws water off the surface of the metal surface (16), through the drying layer (6) and quickly distributes it throughout a large region of the wicking layer (7). Once distributed through the wicking layer (7), the water evaporates in a layer (8) of a high void material. On the other side of the high-void layer (8) and facing away 15 from the wicking layer (7) is an insulation material layer (9) is present. When wet, this insulation layer (9) is also dried by the natural evaporation of the water from the insulation material layer (9) or accelerated by air forced through the high-void layer (8). Optionally a water impenetrable polymer film (8a) may be used to isolate the insulation layer (9) from the high-void layer (8).

20 Figure 3 shows an insulation composition (10) comparable to insulation composition (5), having a hydrophobic layer (11), a wicking layer (12), a layer (13) of a high void material and an insulating material layer (14). In addition an additional layer (15) of a high void material is present at the side of the insulation material (14) which does not face layer (13).

25 Figure 4 shows a cross-sectional view of an insulated metal transport conduit (17) comprising a metal transport conduit (18), an insulation material layer (19) and a cover sheet (20). Between insulation composition (19) and cover sheet (20) a layer (21) of high void material is present. Between layer (21) and insulation material layer (19) a water impenetrable polymer film (21a) may be 30 present avoid water entering the insulation material layer (19) from the layer (21) of high void material. Water will as a result flow due to gravity to the lower end of 16 the insulated transport conduit (17) and can subsequently be discharged from said conduit via discharge opening (22).

Figure 5 shows an insulated transport conduit as in Figure 2 provided with an optional layer (23) of a high void material. The cover sheet, which is typically 5 present, is not shown in this figure. In figure 5 layer (8) of high void material is fluidly connected to a means (24) to supply a stream of gas to said layer (8) at a first position (25). Layer (8) is fluidly connected to a means (26) to discharge gas from said layer (8) at a second position (27). As shown in Figure 5 first (25) and second position (27) are axially spaced away along the axis (28) of the insulated ίο metal transport conduit.

The means to supply a transport gas and the means to discharge the gas loaded with water can be added to the insulated transport conduit at a later moment in time. For example, when after some years the water problem becomes apparent for a section of the insulated transport conduit such means 15 may be added. This may be advantageous in order to minimize the initial investment and complexity of the system.

Figure 6 shows a cross-sectional view of an insulated transport conduit (18) according to the present invention. In wicking layer (7) (layer (b)) two pairs of electrodes (29, 30) are present and spirally run along a section (31) and (32) 20 respectively along the longitudinal axis (28) of the transport conduit (18). If water is detected by a pair of electrodes (29) or (30) one will know at which section water is detected by reference to the pair of electrodes that detect the liquid water. By having multiple pairs of electrodes, like pairs (29) and (30), along the axis of the transport conduit a system results which can simply detect and locate 25 said water. The accuracy can be varied by varying the length of the section for each individual pairs of electrodes.

EXAMPLES

The invention will be illustrated by means of the following non-limiting 30 examples.

17

Comparative Experiment A

A flat plate was heated to 65 °C to simulate the surface of an oil pipeline. Onto this plate a pair of thin electrodes separated by a gap of 0.5 mm was affixed. The resistance between these electrodes was measured by an ohm 5 meter. Below 100 kQ resistance waterwas considered to be present. At or above 2,000 kQ resistance the surface was considered dry. To confirm that the detector worked, a single drop of water placed on the exposed electrodes. The resistance dropped from a value greater than 2,000 kQ to less than 100 kQ.

When the water evaporated the resistance rose to a value greater than 2000 kQ.

ίο On the plate with the electrodes a layer of wicking material composed of a thin, woven, polyester fabric was placed. 5 drops of water were added to the layer at the location of the electrodes. The electrodes detected a dry surface in 90 seconds.

15 Example 1

Comparative Experiment A was repeated except that between the wicking layer and the surface with the electrodes a flat, thin, knit polypropylene fabric was placed between the electrodes and the wicking layer. After the 5 drops of water were added a dry surface was detected in 30 seconds.

20

Comparative Experiment B

A fiberglass insulation material having the dimensions of 10cm x 10cm x 5cm was placed directly onto the plate with the electrodes of Experiment A. 15 ml of water were injected at the center of the fiberglass insulation at 0.5 mm above 25 the electrodes. The entire volume was absorbed by the insulation. The resistance immediately dropped to <100 kQ and only rose as the surface approached dry. Although only about 3 ml of water evaporated from the system (the remainder trapped in the insulation) the electrodes and the surface were dry in 9 minutes.

30 18

Example 2

On the surface of a horizontal mounted pipe surface a detector 1 was placed consisting of two blank iron wires of 0.5 mm spaced apart by 2.5 cm. The wires or electrodes were connected to a voltmeter, type ELRO M300, capable of 5 measuring electrical resistance up to 2000 kQ between the two electrodes at timed intervals. Subsequently a layer of polypropylene (layer (a)) was placed over the electrodes. The polypropylene layer had the following properties:

Fiber Diameter: 15pm Fiber Length: continuous 10 Fiber Shape: 32 projection winged fiber

Fabric Construction: hydro-entangled nonwoven spunbond Basis weight: 65 gsm

On top of layer (a) a layer of Switch, Nedac Sorbo(art. # 76348) (55% Polyester; 25% Polyamide; 20% Polyurethane) as wicking material was placed 15 having a thickness of 1 mm. At the exterior of the wicking material another set of electrodes (detector 2) as above was placed. Subsequently a layer (b1) of 10 mm of a high void material was placed on top of layer (b) consisting of knitted PES having a void ratio e of 20. A next layer of 4 cm of standard fiberglass insulation material as obtained from Rockwool (Rockwool 850) was placed. On 20 top of the insulation material a sheet of polyethylene was placed and on top of said sheet a next layer (d) of a high Void 3D material being Dacron non-woven sheet (100 gsm) having a thickness of 10 mm was placed The entire pipe and insulation was covered with a sheet of aluminum foil.

The aluminum foil was perforated at the top end of the insulation with 1 25 perforation and at the bottom end of the insulation with a row of 3 perforations just below the upper perforation. Each perforation had a surface area of 1 cm2.

Through the top perforation, 20 ml of water was injected into the high void material of layer (d). After about 3 seconds, water was pouring out through the bottom holes and 95% of the water was removed from the holes at the lower end 30 of the pipe within one minute.

19

No liquid water was detected by detector 1 or detector 2 system (measuring a resistance R of greater than 2000 kOhm during the entire experiment). After removing the aluminium sheet, only very little water was observed in the high void material layer (d). After inspection no water could be detected to have 5 entered the thermal insulation material as measured by a protimeter.

Example 3

An insulated pipe of Example 2 was made except that layer (b1) now was composed of 5 mm of a ‘embossed black 3-D material. The 3-D material is an ίο embossed material made from knit PET fibers having a fiber diameter of 0.1 mm and a pore size opening of between 0.5 and 1 mm wherein the knit fibers are molded with a mold shape having single sided cylindrical projections of 0.5 cm by 0.5 cm cylinders which are regularly spaced with 1 projection per cm.

To this layer (b1) air of 35 °C and a relative humidity of 35% can be supplied 15 at one end of the pipe and discharged at the other end of the pipe along its longitudinal axis.

1 ml of water was injected into layer (b) (the wicking layer). After 600 seconds the flow of air was turned on for 150 seconds. The results for detector 1 and detector 2 are summarized in Table 1.

20

Table 1

Time (seconds) Detector 1 signal Detector 2 signal Action (kOhm) (kOhm) 0 >2000 >2000 Injection water ~30 >2000 35 "3ÖÖ >2000 ÏÏ 600 >2000 24 Air flow on 750 >2000 >2000 Air flow off 20

Example 4

Example 3 was repeated except that 2 ml of water was injected into layer (b) (the wicking layer). After 90 seconds the flow of air was turned on for 450 seconds. The results for detector 1 and detector 2 are summarized in Table 2.

5

Table 2

Time (seconds) Detector 1 signal Detector 2 signal Action (kOhm) (kOhm) 0 >2000 >2000 Injection water 90 110 10 Air flow on "3ÖÖ 275 90 ~540 >2000 >2000 Air flow off

Example 5

Example 3 was repeated except that 10 ml of water was injected into layer ίο (b) (the wicking layer). After 30 seconds the flow of air was turned on for 1050 seconds. The results for detector 1 and detector 2 are summarized in Table 3.

Table 3

Time (seconds) Detector 1 signal Detector 2 signal Action (kOhm) (kOhm) 0 >2000 >2000 Injection water 30 115 0 Air flow on "3ÖÖ 170 Ö “9ÖÖ >2000 TÏ6 1080 >2000 >2000 Air flow off 15 The above examples illustrate that liquid water can be detected and removed within a relatively short period of time from an insulated transport conduit. Imagine a situation wherein liquid water can be present on the metal surface of a transport conduit unnoticed for e.g. a year and can cause 4 mm of 21 corrosion accumulation (at a rate of e.g. 4 mm/year). With the present invention liquid water can be detected and removed within an hour reducing the accumulation of corrosion by a factor of 8000.

Claims (19)

1. Method for detecting and locating liquid water that may be present in an insulating assembly arranged around a metal transport line, the insulating assembly being provided with a layer consisting of a wick material, and wherein the wick material is provided with measuring means to measure the presence of liquid water. Method according to claim 1, wherein the measuring means measure the local electrical conductivity in the wick material. 3. Method according to claim 2, wherein the local electrical conductivity is measured in more than one location along the insulated metal transport line, and this in an axial direction. The method of any one of claims 2-3, wherein the local electrical conductivity in the wick material is measured using a pair of electrodes provided in the wick material. 20 5. Method as claimed in any of the claims 1-4, wherein the insulating whole comprises the following layers: a. A hydrophobic, moisture-impermeable layer which is formed from a woven, non-woven, or knitted fibrous material, b. the layer with the hydrophilic wick material, and c. a layer that consists of an insulating material. The method according to claim 5, wherein, between the wick layer (b) and the insulating layer (c), a layer (b1) is provided that consists of a material with a high pore content. 30 A method according to claim 6, wherein water is drained from the insulating whole by supplying a gas stream in a first point along the line to the layer consisting of the material with the high pore content, and in a second point, axially at a away from the first point, a flow of the gas, possibly accompanied by water taken from the material with the high pore content, can be discharged. 8. Method according to claim 7, wherein water is discharged from a part of the insulating whole in which liquid water was detected in the wick material, and wherein the method according to claim 6 is not applied to parts of the insulating whole in which no water was detected. 9. Method for carrying out risk assessment based maintenance of an insulated metal transport line, by carrying out the method according to any of claims 1-8, and wherein the insulation is inspected more frequently at places where liquid water is detected than at places where no or less water is detected. 10. Insulating unit provided with a layer of insulating material and with a layer of wick material, the layer of wick material comprising means for detecting liquid water. The insulating whole according to claim 10, wherein the means for detecting liquid water uses the measurement of the local electrical conductivity. 25 The insulating assembly of claim 11, wherein the local electrical conductivity in the wick material is measured by a pair of electrodes provided in the wick material. An insulating whole according to any one of claims 10-12, wherein the whole is formed by the following layers: a. A hydrophobic, moisture-permeable layer formed by a woven, non-woven, or knitted fibrous material, b. the layer consisting of wick material, and c. the layer consisting of the insulating material. 5 An insulating whole according to claim 13, wherein, between the wick layer (b) and the insulating layer (c), there is a layer (b1) consisting of a material with a high pore content. The insulating whole according to claim 14, wherein the material with the high pore content has a pore number e which is between 5 and 50. The insulating whole according to any one of claims 14-15, wherein the material (b1) with the high pore content has a thickness that is between 2 and 20 mm. 15 The insulating whole of any one of claims 13-16, wherein the layer (a) consisting of the fibrous material is polyethylene terephthalate or polyether sulfone. 18. Insulated metal transport line, comprising a metal transport line as well as an insulating whole according to any one of claims 10-17. 19. Insulated metal transport line, comprising a metal transport line as well as an insulating whole according to any one of claims 14-17, wherein the layer (b1) consisting of the material with the high pore content is in fluid communication with means for transferring a gas to the layer (b1) in a first position, and wherein the layer (b1) is in fluid communication with means for removing gas from the layer (b1) in a second position, the first and second positions mutually spaced apart at an axial distance are located along the insulated metal transport line. 30