Patent Description:
Suitable pressure vessel shell materials include metals, such as steel; or composites which may include laminated layers of wound fiberglass filaments or other synthetic filaments bonded together by a thermal-setting or thermoplastic resin. The fiber may be fiberglass, aramid, carbon, graphite, or any other generally known fibrous reinforcing material. The resin material used may be epoxy, polyester, vinyl ester, thermoplastic, or any other suitable resinous material capable of providing fiber-to-fiber bonding, fiber layer-to-layer bonding, and the fragmentation resistance required for the particular application in which the vessel is to be used. The composite construction of the vessels provides numerous advantages such as lightness in weight and resistance to corrosion, fatigue and catastrophic failure. These attributes are due to the high specific strengths of the reinforcing fibers or filaments. In this case, "composite" means a fiber reinforced resin matrix material, such as a filament wound or laminated structure.

A polymeric or other non-metallic resilient liner or bladder is often disposed within the composite shell to seal the vessel and prevent internal fluids from contacting the composite material. The liner can be manufactured by compression molding, blow molding, injection molding, or any other generally known technique. Alternatively, the liner can be made of other materials, including steel, aluminum, nickel, titanium, platinum, gold, silver, stainless steel, and any alloys thereof. Such materials can be generally characterized as having a high modulus of elasticity. In one embodiment, the liner <NUM> is formed of blow molded high density polyethylene (HDPE).

<FIG> illustrates an elongated pressure vessel <NUM>, such as that disclosed in <CIT>, entitled "Pressure vessel with damage mitigating system". Vessel <NUM> is generally a tank defining a cavity for holding fluids and has in some embodiments a main body section <NUM> and substantially hemispherical or dome-shaped end sections <NUM>. A boss <NUM>, typically constructed of aluminum, is provided at one or both ends of the vessel <NUM> to provide a port for communicating with the interior of the vessel <NUM>. As shown in <FIG>, vessel <NUM> may be formed with an inner liner <NUM> covered by a shell <NUM>. In an example, the shell <NUM> can be a filament-wound composite shell. In such cases, the composite shell <NUM> resolves structural loads on the vessel <NUM>.

<FIG> illustrates a partial cross-sectional view, taken along line <NUM>-<NUM> of <FIG>, of a typical end section <NUM> including a composite shell <NUM> liner <NUM> and a boss <NUM>, such as that disclosed in <CIT>, entitled "Boss for a filament wound pressure vessel". The boss <NUM> typically has a neck <NUM>, a port <NUM> allowing fluid communication with the interior of vessel <NUM>, and an annular flange <NUM> extending radially from port <NUM>. Boss <NUM> is fit to outer shell <NUM> and liner <NUM> such that port <NUM> extends between the interior and exterior of pressure vessel <NUM>. Typically, shell <NUM> abuts neck <NUM>, and flange <NUM> is sandwiched between the liner <NUM> and the shell <NUM>. This construction secures the boss <NUM> to the vessel <NUM> and provides a seal at the interfaces between the boss <NUM>, shell <NUM>, and liner <NUM>.

A method of forming a pressure vessel <NUM> includes mounting a boss on a mandrel and allowing a fluid polymer material for liner <NUM> to flow around flange <NUM> of boss <NUM>. The liner material then solidifies; liner <NUM> is thereby mechanically interlocked with boss <NUM>. Accordingly, even under extreme pressure conditions, separation of liner <NUM> from boss <NUM> is prevented.

In an exemplary embodiment, outer shell <NUM> is formed from wound fibers and surrounds the liner <NUM> and at least a portion of flange <NUM> of boss <NUM>. In an exemplary method, a dispensing head for the fibers moves in such a way as to wrap the fiber on the liner <NUM> in a desired pattern. If the vessel <NUM> is cylindrical, rather than spherical, fiber winding is normally applied in both a substantially longitudinal (helical) and circumferential (hoop) wrap pattern. This winding process is defined by a number of factors, such as resin content, fiber configuration, winding tension, and the pattern of the wrap in relation to the axis of the liner <NUM>. Details relevant to the formation of an exemplary pressure vessel are disclosed in <CIT>, entitled "Filament Winding Process and Apparatus".

<CIT>, entitled "Damage indicator for a composit pressure tank", discloses a composite fuel tank formed by winding filaments or strips around a plastic liner and binding the material with a curable binder. The filaments or strips are embedded within the wrapped material at predetermined depths from the surface to provide a color indication of the level of damage to the tank.

French Patent application No. <CIT>, entitled "Composite gas conditioning vessel comprising a plurality of superimposed envelopes", discloses a composite gas conditioning vessel comprising a hollow cylindrical body for receiving gas, a filament winding coiled around the body and a plurality of envelopes superimposed one over the other. A first envelope is arranged directly around, and in contact with, the filament winding, and a second envelope arranged directly around, and in contact with, said first envelope. At least one of said envelopes is designed to show a visual change in the event of a potentially critical mechanical impact or in the event of exposure to a flame or to a temperature higher than <NUM>.

Composite pressure vessels are increasingly being used for general commercial and transport applications, such as, for example, fuel storage (e.g., natural gas or hydrogen) in passenger and commercial vehicles, hydraulic systems, and large-scale gas transportation. Use of pressure vessels in these and other uncontrolled environments increases the potential that a vessel be dropped, scraped, subjected to impact, or otherwise damaged. Such damage may not be readily apparent upon visual examination of the vessel, but may be severe enough to render the vessel unfit for continued use. Alternatively, damage to the shell <NUM> may be visible, but the severity of the damage may not be able to be determined through visual inspection. In other words, an operator may see damage, such as a scrape or dent, on the shell <NUM> and remove the vessel from service when the damage is not severe enough to render the vessel unfit for use. Approaches to preventing damage to a vessel include adding protective layers, materials, coatings, end caps, or other sacrificial pieces to the exterior of the vessel. However, no approach is able to entirely prevent damage to a vessel, so there exists a need for a visual indication of the existence and severity of vessel damage.

A pressure vessel for holding fluids is disclosed herein, the vessel including a tank and a coating disposed on an outer surface of the tank. The tank defines a cavity for holding fluids, and an outer surface of the tank includes a first visual characteristic. The coating includes an indicator layer, an outer layer, and a first intermediate layer. The indicator layer is disposed on the outer surface, the indicator layer including a second visual characteristic that visually contrasts with the first visual characteristic. The outer layer is disposed over the indicator layer, the outer layer including a third visual characteristic that visually contrasts with the second visual characteristic. The first intermediate layer is positioned between the indicator layer and the outer layer, the first intermediate layer being visually transparent or translucent.

In one aspect, the disclosure describes a coating configured for application to a substrate including a first visual characteristic. The coating includes an indicator layer, an outer layer, and a first intermediate layer. The indicator layer is disposed on the substrate, the indicator layer including a second visual characteristic that visually contrasts with the first visual characteristic. The outer layer is disposed over the indicator layer, the outer layer including a third visual characteristic that visually contrasts with the second visual characteristic. The first intermediate layer is positioned between the indicator layer and the outer layer, the first intermediate layer being visually transparent or translucent.

This disclosure, in its various combinations, either in apparatus or method form, may also be characterized by the following:.

This summary is provided to introduce concepts in simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the disclosed or claimed subject matter and is not intended to describe each disclosed embodiment or every implementation of the disclosed or claimed subject matter. Specifically, features disclosed herein with respect to one embodiment may be equally applicable to another. Further, this summary is not intended to be used as an aid in determining the scope of the claimed subject matter. Many other novel advantages, features, and relationships will become apparent as this description proceeds. The figures and the description that follow more particularly exemplify illustrative embodiments.

The disclosed subject matter will be further explained with reference to the attached figures, wherein like structure or system elements are referred to by like reference numerals throughout the several views.

While the above-identified figures set forth one or more embodiments of the disclosed subject matter, other embodiments are also contemplated, as noted in the disclosure. In all cases, this disclosure presents the disclosed subject matter by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this disclosure.

The figures may not be drawn to scale. In particular, some features may be enlarged relative to other features for clarity. Moreover, where terms such as above, below, over, under, top, bottom, side, right, left, etc., are used, it is to be understood that they are used only for ease of understanding the description. It is contemplated that structures may be oriented otherwise.

The present disclosure describes various embodiments of a protective multilayer for a pressure vessel that provides a visual indication that the coating has been damaged. Additionally, the coating provides a visual indication of the severity of the damage so that an operator may keep a vessel in service if the damage does not render the vessel unfit for use. An operator may remove a vessel from service if damage to the vessel compromises the effective use of the vessel. Damage such as a scrape, scratch, or gouge exposes at least one inner layer of the multilayer coating, which provides a visual indicator of the severity of the damage. In exemplary embodiments, the visual indicator may be due to contrasting visual characteristics between layers of the coating, including contrasting colors, differing reflectivity properties, or differing refraction properties, for example. Additionally, an exemplary embodiment of the coating acts to protect the pressure vessel against damage such as, for example, abrasion and impacts.

<FIG> shows an exemplary embodiment of a multi-layer indicator coating <NUM> on shell <NUM>. In some embodiments, coating <NUM> is an ultraviolet (UV)-curable coating, with one or more layers thereof provided in a form such as a UV-curable liquid or powder. However, coating <NUM> may be of any material or type that exhibits properties such as adherence to a substrate such as shell <NUM> (on its own or via an intermediate binding layer, not shown), abrasion and impact resistance, and color retention to allow for visual perception of damage to vessel <NUM>, for example. <FIG>, <FIG> are enlarged partial cross-sectional views of exemplary embodiments of a portion of the pressure vessel and protective multilayer coating of <FIG>, oriented so that an inside of the pressure vessel is shown on the left and the outside of the pressure vessel is shown on the right. While these are cross-sectional views, cross-hatching of the components of indicator coating <NUM> have been omitted for clarity of illustration.

<FIG> shows an enlarged partial cross-section of an exemplary coating 28a on a pressure vessel having shell <NUM> and liner <NUM>. In an exemplary embodiment, coating 28a includes an indicator layer <NUM> disposed on shell <NUM>, a middle or intermediate layer <NUM> disposed on indicator layer <NUM>, and an outer layer <NUM> on middle layer <NUM>. Thus, middle layer <NUM> is positioned intermediate indicator layer <NUM> and outer layer <NUM>. In exemplary embodiments of coating <NUM>, respective coating layers <NUM>, <NUM>, <NUM> adhere to each other on their own or via one or more intermediate binding layers, not shown.

In an exemplary embodiment, any of the layers of multiple-layer coating <NUM> includes a material that can be applied to an underlying vessel shell <NUM> or an underlying layer. Suitable materials include urethane, polyurethane, epoxy, acrylic, and compressible and/or collapsible foams, for example. Particularly suitable materials are curable by ultraviolet (UV) radiation. The use of UV curable materials can decrease the time needed for coating and curing the various layers of multiple-layer coating <NUM>, compared to materials that require more curing time. The specific compositions of the materials of any of the layers of multiple-layer coating <NUM> can be tailored to provide desired adhesion and environmental resistance properties such as temperature and moisture resistance, fade resistance, strength, abrasion resistance, and impact resistance, for example.

In the illustrated embodiment, indicator layer <NUM> is disposed on shell <NUM>. In an exemplary embodiment, indicator layer <NUM> is a UV-curable paint of a color that contrasts with the color of shell <NUM> so that shell <NUM> is readily visually discernable from indicator layer <NUM>. For example, if shell <NUM> is black, a suitable color for indicator layer <NUM> may be gold, red, orange, or a neon color. However, any contrasting colors are suitable for adjacent layers of multiple-layer coating <NUM>. Indicator layer <NUM> is applied to shell <NUM> by rolling, spraying, brushing, flow coating or any useful application method. In an exemplary embodiment, indicator layer <NUM> is applied in two coats to a total thickness of between and including about <NUM> inch (<NUM>) and about <NUM> inch (<NUM>) to provide adequate coverage of shell <NUM> and visually present a solid (as opposed to translucent or uneven) color to a user. In other embodiments, indicator layer <NUM> may be applied in any number of coats of any thickness, so long as the layer is readily visible when portions of the middle and/or outer layers <NUM>, <NUM> are removed.

In an exemplary embodiment, middle layer <NUM> is a substantially transparent or translucent UV-curable coating applied onto indicator layer <NUM>, and through which the color of indicator layer <NUM> can be seen. When middle layer <NUM> in an exemplary embodiment is visually transparent or translucent, middle layer <NUM> does not serve as a visual damage indicator alone. Rather, its primary role is as a protective layer, accepting gouges, scratches, and other damage and preventing the damage from reaching indicator layer <NUM> or shell <NUM>. Moreover, when middle layer <NUM> is transparent or translucent, it provides an early indication of damage, as indicator layer <NUM> can be viewed through the transparent middle layer <NUM> when merely outer layer <NUM> has been included, even if middle layer <NUM> is essentially intact.

Middle layer <NUM> is applied to indicator layer <NUM> by rolling, spraying, brushing, flow coating, or any useful application method. In some embodiments, middle layer <NUM> is thicker than a combined thickness of indicator layer <NUM> and outer layer <NUM>. In an exemplary embodiment, middle layer <NUM> has a thickness of between and including about <NUM> inch (<NUM>) and about <NUM> inch (<NUM>). In some embodiments, middle layer <NUM> may make up about <NUM>% of the total thickness of multi-layer coating <NUM>. In an exemplary embodiment, middle layer <NUM> may be made of a material that can absorb impact forces, thereby providing additional damage resistance. The material may be a flexible or collapsible foam, and may be a polyurethane foam, for example.

In an exemplary embodiment, outer layer <NUM> is a UV-curable material in the form of a paint of a color that contrasts with the color of indicator layer <NUM> so that indicator and outer layers <NUM>, <NUM> can be readily discerned from each other. Outer layer <NUM> adheres to middle layer <NUM> and to any layer(s) that may be added to outer layer <NUM>, such as, for example, base layers onto which labelling may be adhered or otherwise attached. Outer layer <NUM> is applied to middle layer <NUM> by rolling, spraying, brushing, flow coating, or any useful application method. In an exemplary embodiment, outer layer <NUM> is applied in two or three coats to a thickness of between and including about <NUM> inch (<NUM>) and about <NUM> inch (<NUM>). In other embodiments, outer layer <NUM> may be applied in any number of coats of any thickness. In vessels <NUM> having a thicker outer layer <NUM>, deeper gouges may be made in multi-layer coating <NUM> without breaking through to the middle layer <NUM> to expose indicator layer <NUM> to view.

<FIG> show a first exemplary embodiment of multi-layer coating <NUM>. <FIG> shows an exemplary embodiment of an undamaged multi-layer coating 28a on vessel <NUM>. In each respective <FIG>, a gouge <NUM> of a different depth has caused damage of differing levels of severity. This disclosure refers to a "gouge" to describe any scrape, scratch, flaw, abrasion, crack or other feature that breaks the outer surface of coating <NUM>. <FIG> shows that multi-layer coating 28a has been subjected to minor damage by gouge 36i that is not severe enough to compromise the use of vessel <NUM>. In <FIG>, the damage to outer layer <NUM> has caused a gouge 36i that does not extend through outer layer <NUM> to middle layer <NUM>. Only the color of the outer layer <NUM> is visible, indicating that vessel <NUM> is fit for use.

In <FIG> and <FIG>, the gouge 36ii, 36iii does not extend through the entire thickness of multilayer coating <NUM>. Instead, in <FIG>, gouge 36ii extends partially into middle layer <NUM> so that indicator layer <NUM> can be seen through transparent (or translucent) middle layer <NUM>. In <FIG>, gouge 36iii extends through middle layer <NUM>, thereby exposing indicator layer <NUM>.

<FIG> and <FIG>, the visibility of the color of indicator layer <NUM> (visible either directly as in <FIG> or indirectly through middle layer <NUM> as in <FIG>) indicates that vessel <NUM> has been subjected to damage such as an impact or abrasion but may not be damaged to the extent that use of vessel <NUM> is contraindicated. Vessel <NUM> may be inspected at the site of damage during, for example, routine maintenance instead of being immediately removed from service.

In <FIG> and <FIG>, damage has caused a gouge 36iv that has removed the total thickness of a portion of multi-layer coating 28a. Shell <NUM> of vessel <NUM> is exposed to view, indicating that severe damage has occurred and in some cases that vessel <NUM> is ready for removal from service or other corrective action. In this case, at least a portion of the gouge 36iv is the color of shell <NUM>, this portion being surrounded by a portion of the gouge <NUM> that is the color of the indicator layer <NUM>, which in an exemplary embodiment visually contrasts with the color of shell <NUM>. When middle layer <NUM> is transparent, the portions of walls 40a through middle layer <NUM> and indicator layer <NUM> appear to be the color of indicator layer <NUM>, and the demarcation between the layers <NUM>, <NUM> is not readily discernable. In an exemplary embodiment, the color of outer layer <NUM> visually contrasts with the color of indicator layer <NUM>.

The relative sizes and shapes of the colored portions revealed by a gouge or flaw depend on the size and shape of the gouge, and on the angles of the gouge walls <NUM> relative to the exterior surface of shell <NUM>. Reference number <NUM> refers to a gouge of any configuration, while 36i refers to the configuration of a gouge shown in <FIG>; 36ii refers to the configuration of a gouge shown in <FIG>; 36iii refers to the configuration of a gouge shown in <FIG>; 36iv refers to the configuration of a gouge shown in <FIG> and <FIG>; and 36c refers to the configuration of a gouge shown in <FIG>. Reference number <NUM> refers to gouge walls of any configuration, while 40a refers to the configuration of gouge walls shown in <FIG> and <FIG>; 40c refers to the configuration of gouge walls in <FIG>.

As apparent in <FIG> and <FIG>, gouge walls <NUM> oriented nearly perpendicularly to the shell <NUM> reveal little of the indicator color of layer <NUM>, while gouges with walls <NUM> oriented relatively obliquely to the shell <NUM> will reveal more of the indicator color. Relatively wide gouges <NUM> with gently-sloping walls are characterized by relatively large portions of indicator layer <NUM> being visible around the exposed portion of shell <NUM>. Gouges <NUM> with steeply-sloping walls are characterized by relatively small or narrow portions of indicator layer <NUM> being visible around the exposed portion of shell <NUM>. The appearance of the exposed layers allows for a rough determination of the size, shape, type, and/or severity of the damage to vessel <NUM>. In an exemplary embodiment, the outer layer <NUM>, indicator layer <NUM>, and shell <NUM> all have mutually contrasting colors. In that case, even if gouge walls <NUM> are steep (and even undercut), the gouge 36iv may be visually perceived by the detection of the color of shell <NUM>, which contrasts with the color of outer layer <NUM>, even if the color of indicator layer <NUM> is not easily seen.

The total thickness of multilayer coating <NUM> may be theoretically or experimentally derived. An exemplary thickness of multilayer coating <NUM> is inclusive and between about <NUM> inch (<NUM>) and about <NUM> inch (<NUM>). The total thickness of multi-layer coating <NUM>, the thickness of each layer, the color of each layer, and the protective characteristics of each layer can be chosen and calibrated to provide the desired indications. For example, the composition and structure of multi-layer coating <NUM> may be selected so that visible exposure of shell <NUM> indicates the lowest severity of damage that is likely to render a vessel <NUM> unsuitable for operation, but the composition and structure of multi-layer coating <NUM> may be chosen to indicate any level of damage useful for a given application.

For instance, in applications requiring response to slight vessel damage, the total thickness of multi-layer coating <NUM> may be chosen to be small, such that a relatively shallow gouge <NUM> removes a total thickness of a portion of coating <NUM>, indicating that vessel <NUM> be removed from service or otherwise attended to after relatively light damage. Alternatively, in applications requiring response to slight vessel <NUM> damage, the total thickness of multi-layer coating <NUM> may be chosen to be large, while the thickness of outer layer <NUM> is chosen to be small. A relatively shallow gouge <NUM>, such as gouge 36ii of <FIG> removes a section of outer layer <NUM>, thereby revealing the color of indicator layer <NUM> through transparent middle layer <NUM>. A user may remove the vessel <NUM> from service or attend to the vessel <NUM> at that point, after relatively light damage. Thus, the multi-layer coating <NUM> can be used in a manner that offers an early indication of damage while at least some layers or portions of multi-layer coating <NUM> are still intact to offer continued damage protection.

In an exemplary embodiment, at least some layers of multi-layer coating <NUM> serve not only as visual indicators, but also function to protect shell <NUM> against abrasions, scuffs, minor impacts, and the like. As such, for a given material, a thinner coating <NUM> or respective layer provides less protection. In any case, the relative thicknesses of the respective layers may be chosen with regard to the materials used for the layers and the requirements of the vessel <NUM> application.

<FIG> shows an exemplary embodiment of multi-layer coating 28b having no middle layer <NUM>. In this embodiment, outer layer <NUM> is applied directly onto indicator layer <NUM>, so the removal of a small amount of coating 28b (relative to embodiments in which multi-layer coating <NUM> includes middle layer <NUM>) indicates that vessel <NUM> is damaged. In an exemplary embodiment, the total thickness of a coating 28b having no middle layer <NUM> is between about <NUM> inches and about <NUM> inches. The coating 28b with no middle layer <NUM> renders an indicator that is sensitive to damage, in that small abrasions or impacts are indicated as damage. Such a coating 28b is cost efficient and light-weight because of the reduced use of coating materials compared to thicker coatings.

<FIG> shows an exemplary embodiment of multi-layer coating 28c on a vessel <NUM> having several intermediate indicator layers <NUM> between indicator layer <NUM> and outer layer <NUM>. Individual intermediate indicator layers <NUM> may have different colors, may be transparent/translucent, or a combination of colored and clear layers <NUM>. A gouge 36c in coating 28c exposes indicator layers along the walls 40c of the gouge 36c so that the depth of the gouge 36c may be determined by, for instance, counting the number of exposed layers or by noting the color of the deepest exposed layer, where each layer has a known thickness. In an exemplary embodiment, shell <NUM> has a first color, for example, black. Indicator layer <NUM> has a second color that contrasts with the first color, for example gold. Outer layer <NUM> has a third color that contrasts with both the first and second colors, for example red. At least one of intermediate layers <NUM> is substantially clear. And at least one of intermediate layers <NUM> has a fourth color that contrasts with both the first, second, and third, colors - for example, green. While this example uses different colors for each layer, it is also contemplated that fewer colors may be used, as long as contrasting colors are used in adjacent layers.

Moreover, the structure of multi-layer coating 28c may place colored layers <NUM>, <NUM> at known, discrete depth measurements from outer layer <NUM>. Thus, exposure of a particular color readily alerts a user to the depth of gouge 36c. Multiple intermediate indicator layers <NUM> may also be used to determine the topographical characteristics of a gouge <NUM>, in an embodiment where all areas of a given color exposed on the gouge <NUM> walls are at substantially the same depth from outer layer <NUM>.

Claim 1:
A coating (<NUM>) configured for application to a substrate including a first visual characteristic, the coating (<NUM>) including:
an indicator layer (<NUM>) disposed on the substrate, the indicator layer (<NUM>) including a second visual characteristic that visually contrasts with the first visual characteristic;
an outer layer (<NUM>) disposed over the indicator layer (<NUM>); and
a first intermediate layer (<NUM>) positioned between the indicator layer (<NUM>) and the outer layer (<NUM>), the first intermediate layer (<NUM>) being visually transparent or translucent, wherein the first intermediate layer (<NUM>) is thicker than a combined thickness of the indicator layer (<NUM>) and the outer layer (<NUM>);
the coating (<NUM>) characterised by:
the outer layer (<NUM>) including a third visual characteristic that visually contrasts with the second visual characteristic.