BACKGROUND OF THE INVENTION

This invention relates to the chemical arts. In particular, it relates to fire-resistant, filament-wound structural members, such as fiberglass pipes, and to methods for making such fire-resistant structural members.

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Fire-resistant pipe, especially fire-resistant pipe for carrying fire-extinguishing sprinkler valve water, has typically been constructed of metal. Certain environments, however, pose a threat to metal pipe in the 0 form of corrosion. Corrosion of metal pipe can lead to either structural failure, or blockage from metal oxide buildup within the pipe.

One environment particularly prone to corrosion 5 is found on an off-shore oil rig. The off-shore oil rig is built on a platform surrounded on all sides by ocean water. The remoteness of the off-shore oil rig makes a built-in fire-extinguishing system of water pipes and sprinkler valves the first line of defense in case of an outbreak of 0 a fire. The volatility of the oil being pumped through the rig increases the danger to life and property should a fire on such a structure occur.

The remote location of the oil rig has led to the 5 practice of using the surrounding sea-water, which is abundant, available, and free, for the fire-extinguishing water, or at least for the testing of the fire- extinguishing pipe system. Frequent testing, by running deluge volumes of sea-water through the pipe system, is 0 necessary to ensure the readiness and operability of the system at the crucial instant of an outbreak of fire. After testing and draining the system, however, the interior of the pipe system will usually retain enough sea-

water and moisture, of corrosive salinity, that oxidation of a metal pipe begins almost immediately.

In addition to the danger to life and property in the event of a fire, the high economic cost associated with repairing or rebuilding a damaged rig, and the loss of operation during the time needed to undertake such activities, bodes well for having a reliable means for utilizing sea water to fight fire.

Accordingly, there exists a great need to avoid the inevitable corrosion associated with metal pipe. Fiberglass pipe is an attractive choice for carrying high salinity water, because it is not as susceptible as metal to degradation by water, oxygen, and salt. One drawback, however, to using fiberglass pipe in applications requiring a fire-resistant pipe, has been the inability of fiberglass to withstand the high temperature associated with a raging blaze. Over a certain temperature, depending on the particular composition of the fiberglass, a fiberglass structure may lose its structural integrity, melt, or ignite.

Fiberglass pipe has, nonetheless, been rendered somewhat immune from the damage which high temperature and fire can cause, by the use of relatively thick, fire- resistant coatings. Such coatings include intumescent coatings, which upon exposure to heat, swell and take on ceramic characteristics, to form an insulating layer that prevents the underlying fiberglass from heating to a temperature at which it would fail.

Typically, such coatings are made from a paste¬ like material, sometimes termed a mastic, because of its highly viscous consistency. The consistency of a mastic, intumescent material has necessitated that it be applied by spraying or by trowelling directly onto an underlying structure. Both of these application methods, however, allow significant variation in the thickness of the fire-

resistant coating. Variation in thickness leaves uncertainty as to its effectiveness. Variation in the thickness can result in uneven insulation of the underlying fiberglass pipe and the possibility of hot spots developing during a fire which can undermine the effectiveness of the coating.

Spraying and trowelling of intumescent materials also can produce voids within the coating and between the coating and the underlying fiberglass pipe. Such voids undermine the effectiveness of the coating by reducing the thickness of the coating at that point, and by leaving portions of the fiberglass pipe unprotected. It is another drawback of intumescent coatings applied by spraying or trowelling that the coatings have poor impact resistance, so that they can be susceptible to mechanical failure due to normal maintenance and cleaning.

Further, the thickness of a spray or trowel applied coating can give rise to problems. The relative thickness of the coating increases the outer diameter of the pipe to which it is applied, which in turn increases its weight. Often, especially aboard off-shore oil rigs where space and weight are at a premium, a heavy, large diameter pipe is difficult to install or replace.

Additionally, a pipe having a coating produced by spraying or trowelling is likely to have variations in its overall diameter leading to additional installation difficulties.

Moreover, variations in the pipe's dimensions can undermine the strength of the pipe and lead to premature structural failure.

Spraying and trowelling methods also have economic drawbacks. Both have a relatively high waste factor, being inefficient techniques for applying a coating. Moreover, both are labor intensive, requiring extra equipment and additional labor steps to be performed after the fabrication of the original fiberglass pipe. For

example, with spraying, it is not uncommon that as much as 50% of the spray material is lost.

Thus, the need exists for a means of producing a fiberglass pipe having a relatively lightweight and thin fire-resistant coating of uniform thickness which remains structurally bound to the underlying pipe after repeated maintenance and cleaning and which maintains the integrity of the fiberglass pipe even under exposure to fire and high pressure water. The need further exists for a fiberglass pipe which can be made fire-resistant during its fabrication as well as afterwards, with voidless fire- resistant protection, and which can be so produced economically without the expenditure for additional capital or labor. The present invention satisfies these and other needs and provides further related advantages.

SUMMARY OF THE INVENTION

The invention is directed to an improved fire- resistant, filament-wound structural member made of a fibrous carrier, such as fiberglass, impregnated with a curable resin, such as an epoxy resin, containing a fire- resistant material, such as an intumescent material. I n some embodiments, the fire-resistant, filament-wound structural member has a filament-wound core that is overwrapped with a filament-wound, fire-resistant outerlayer formed of the fire-resistant material containing curable resin impregnated carrier.

The fire-resistant structural member is made using an underlying structure, e.g. either a mandrel or a filament-wound core, and a resin bath containing a combination of a curable resin and a fire-resistant material and having a predetermined viscosity, preferably from about 400 to about 15,000 cps. A fibrous carrier is drawn through the resin bath, wound around the underlying form and then cured to form the fire-resistant filament- wound structural member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial elevational view of a fire- resistant pipe in accordance with the invention.

FIG. 2 is a cross-sectional view of the fire- resistant pipe of FIG 1 taken along line 2-2.

FIG. 3 is a cross-sectional view of another embodiment of a fire-resistant pipe in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now there has been found a structural member having improved fire-resistance properties. The structural member can be of any filament-windable shape. Representative structural members include filament-wound pipes and pipe fittings.

Referring to the embodiment shown in FIGS. 1 and 2, there is shown a structural member 10 having a core 12 and a fire-resistant outerlayer 14. The core is formed from a wound fiber impregnated or coated with a curable resin.

The fire-resistant outerlayer 14 is made from a wound, fibrous carrier impregnated or coated with a curable resin. The outerlayer is made fire-resistant by the introduction of a suitable material into the resin prior to impregnating the carrier.

Thus, as shown in FIG. 1, the structural member 10 has at least two separately wound layers of resin-impregnated fiber. The first layer 12 is a core, or primary layer of resin-coated fiber. This layer serves as the interior, structural portion of the structural member. The second layer 14 is an exterior fire-resistant layer, formed of the fibrous carrier impregnated with a curable

resin containing a fire-resistant material. In the embodiment shown in FIG. 2, the structural member 20 is formed of a single layer 22 entirely of wound fiber impregnated or coated with the fire-resistant aterial- containing curable resin and the structural member does not contain a separate core.

Turning first to the manufacture of the filament- wound core, the core is formed by methods conventional in the art. A mandrel is chosen as a temporary skeleton upon which filaments impregnated or coated with a curable resin are wound. To coat or impregnate the filament with the curable resin, the filament is passed through a bath of the resin prior to winding around the mandrel.

The coated filament is then wound upon the mandrel to form the core. Thus, the inside dimensions of the filament-wound core approximate the outside dimensions of the mandrel. Therefore, a mandrel of a particular size and dimension is chosen to permit the winding of a structural member of desired interior dimension. As is known in the art, use of a hollow mandrel aids in curing the resin of the structural member by allowing the introduction of hot oil or heated gas, such as steam, within the mandrel to heat the structural member from the inside.

The core is made from a windable filament coated or impregnated with a curable resin. The filament is of any suitable fibrous material, with fiberglass filaments being preferred.

The filament can be in the form of a single strand, rovings of multiple strands, a mat, or a veil of individual filaments. The particular configuration of the filament can be varied according to the requirements of the desired structural member and the choice will be readily apparent to one skilled in the art. A structural member requiring a high tensile strength is achieved by using a

mat or veil configuration to form the core. A structural member having an intricate contour is formed most easily by forming the core from a roving or single filaments.

The filament, in whatever configuration is chosen, is impregnated or coated with a curable resin. Suitable resins are known in the art and the particular resin chosen will depend on the ultimate characteristics desired in the structural member. Representative resins include thermosetting epoxy, polyester, melamineformaldehyde, urea-formaldehyde, phenol- formaldehyde resins and the like. Epoxy and phenol- formaldehyde resins are preferred, with epoxy resins being most preferred.

Turning next to the second, fire-resistant layer, the core is overwrapped with a carrier that has been impregnated or coated with the fire-resistant material containing curable resin by passing the carrier through a resin bath containing a mixture of the curable resin and the fire-resistant material. In some embodiments, the fire-resistant layer is applied in a secondary manufacturing step, after the production of a core. Accordingly, it is an advantage of the process in accordance with the invention, that a core, such as a conventional fiberglass pipe or pipe fitting, can be manufactured and the fire-resistant outerlayer only applied to such structural members on an as-needed basis. Alternatively, the second layer can be wrapped around the core, as an in-process step, after the core has been partially cured. In those embodiments not containing a separate core, the impregnated filament is directly wound around a mandrel of the desired configuration.

To ensure the carrier is impregnated as it is drawn through the resin bath, the viscosity of the resin mixture in the bath must be controlled. The viscosity of the resin mixture is preferably maintained in the range of from about 400 to about 15,000 cps, more preferably in the

δ range of from about 1,000 cps to about 5,000 cps, so that the filament to resin ratio of the impregnated carrier is from about 70:30 to about 30:70, more preferably about 45:55 based on the weight of the components. It should be appreciated that while lower viscosities would permit easier passage of the carrier through the bath, they would also shorten the pot-life of the resin mixture. Greater viscosities would make passage through the bath difficult and would prevent the carrier from being adequately impregnated with the resin mixture.

A movable bath unit holds the resin mixture. The bath unit is moved to allow coating of the carrier at a point close to where the carrier is wrapped upon the pipe or other underlying form receiving the fire-resistant outerlayer. As the carrier is pulled through the bath and wound upon the underlying form, the bath unit is moved by a computer controlled mechanical assembly, to follow the winding location of the carrier.

The movement of the bath is precisely controlled to traverse the winding location of the underlying form so that the carrier coated with the fire-resistant material- containing resin is still wet as it is wound upon the form. In this manner, an outerlayer of a desired shape and thickness can be accurately produced. Preferably, a circular or circumferential pattern is maintained in winding the fire-resistant material-containing resin-coated filament. However, if structural strength is of concern for a particular structural member being produced, a helical winding pattern can be used in which the helix forms an angle of approximately 45° with the longitudinal axis of the structural member. The impregnated filament is wound back and forth along the core until an outerlayer having a thickness preferably from about 3 mm to about 12 mm, more preferably from about 4 mm to about 8 mm is obtained. In those embodiments not having an underlying core, the impregnated filament is wound around the mandrel, until member having a desired diameter is obtained.

Following winding of the underlying form with the fire-resistant material coated or the fire-resistant material impregnated carrier, the newly wound layer is cured. Curing can either be partial (B-staged) or complete. The mandrel can be heated to apply heat to the inside of the pipe. Typically, the mandrel is heated by hot oil or steam. Alternatively, radiant or convective heat can be applied to the outside of the new layer. A further post-cure can be done in an oven ensure that the entirety of the newly formed pipe has been cured.

It is another advantage in accordance with the invention that the overlayer need only be from about 3 mm to about 12 mm, preferably only from about 4 mm to about 8 mm, in order to achieve a significant enhancement in the fire-resistance of the core.

The fibrous carrier can be made of the same or of a different material than the filament used to form the core. Fiberglass is the preferred fibrous carrier. As with the core, the filament can be in the form of a single strand, rovings of multiple strands, a mat, or a veil of individual filaments. The choice of filament and of filament configuration to be used in any given application will depend of the particular requirements of the application and will be apparent to one skilled in the art.

The curable resin can be the same or different resin as is used to form the core. Consequently, suitable resins include thermosetting epoxy, polyester, melamineformaldehyde, urea-formaldehyde, phenol- formaldehyde resins and the like. Epoxy and phenol- formaldehyde resins are preferred, with epoxy resins being most preferred.

The fire resistant material can be any material that imparts fire-resistant properties to the outerlayer, so long as it is compatible with the curable resin. The preferred fire-resistant materials are intumescent

materials. Such materials swell upon exposure to a specified level of heat, and thereupon form a ceramic-like char. The resin to which the intumescent is added will take on such intumescent qualities itself upon the introduction of the sufficient quantities of intumescent material per quantity of resin. Preferably, a ratio of from about 10 parts per hundred to about 110 parts per hundred, more preferably from about 80 parts per hundred to about 100 parts per hundred, based on the weight of resin to the weight of fire-resistant material is used.

Intumescent substances are known and have been used as additives to epoxy resins. A typical intumescent component comprises a mixture of materials which act as suppliers of phosphorous, zinc, boron and an expansion gas. The expansion gas creates the bubbling and expansion actions characteristic of intumescent materials when heated to their intumescent temperature point. The gas can be carbon dioxide, or a nitrogen gas, and thus a substance which releases one of these gases upon exposure to flame or heat is included in the mixture to serve as a source for the expansion gas. The particular combination of epoxy resin and intumescent material chosen will depend on the environment the pipe is destined and the temperatures that the pipe must withstand to survive a fire in that environment.

The phosphorous, zinc, and boron are believed to aid in the formation of a char layer, which is a layer of partially burned charcoal or carbon, and which serves to insulate the underlying unburned structure. It is believed that the phosphorous functions as a char promoter, that the zinc functions as an aid to the formations of small cellular structures within the char, and that the boron acts as a fluxing agent to promote a uniform char layer. Numerous substances can be used to supply these elements, and a single substance can be incorporated into the epoxy to supply more than one of these elements as well as the expansion gas. For example, mela ine pyrophosphate itself

can serve to supply both phosphorous as well as expansion gas. Intumescent materials for use in this invention are not limited to materials containing these substances.

A reinforcing filler can be added to the intumescent resin, and it is believed that such addition promotes controlled expansion of the fire-resistant layer prior to and during the formation of the char layer formed at the outer extremity of the fire-resistant layer upon exposure to sufficient heat. In this manner, the use of reinforcing filler promotes the formation of a compact and uniform char layer. Glass filaments or ceramic filaments function well as reinforcing fillers. It should be appreciated, however, that other fibrous substances or platelet type reinforcing fillers may be used.

A curing agent is typically provided into the epoxy to enable curing of the epoxy into a thermoset solid.

A curing agent containing an alkyl substituted phenol is believed to promote char expansion of the intumescent epoxy when the cured material is subjected to sufficient heat.

Combinations of curable resins and fire-resistant materials are commercially available. For example, combinations of epoxy resins and intumescent materials are manufactured by PPG Industries under the trademark Pitt Char and by Textron under the trade name CHAR TEC. However, the viscosities of such materials are too high to be suitable to make fire-resistant products in accordance with the invention.

The viscosities can be lowered and the commercially available products used to form the fire- resistant outerlayer, by adding a non-reactive diluent. Representative non-reactive diluents include dibutyl phthalate, such as 3 M-FC 430. Alternatively, the viscosity of the resin mixture can be reduced by adding a suitable curing agent. Representative curing agents include ethyl-glycidyl ether, such as Lindride 600. Yet

another method for reducing the viscosity of commercially available intumescent-containing curable resin mixtures involves maintaining the resin bath at an elevated temperature in order to achieve the desired low viscosity during application of the resin to the glass fiber.

Thus, by using a low viscosity combination of curable resin and fire-resistant material to impregnate a fibrous carrier it is now possible to produce a fiberglass pipe or other structural member having a relatively thin and voidless fire-resistant coating of uniform thickness which remains structurally bound to the underlying pipe after repeated maintenance and cleaning and which maintains the integrity of the fiberglass pipe even under exposure to fire and high pressure water. Moreover, the process by which such structural members are made fire-resistant can be employed either during fabrication of the structural member, as well as after fabrication is complete.

While reference has been made to off-shore oil rig fire-extinguishing systems, it should be appreciated that the invention may be used advantageously for creating fire-resistant fiberglass pipe for other fire-extinguishing systems, such as those used in refineries and high-rise buildings. Moreover, the invention provides a fire- resistant fiberglass pipe or structural member which can be used in many applications in building and construction.

Although the invention has been described with respect to specific embodiments, it will be appreciated that modifications that would be obvious to a person of ordinary skill in the pertinent art may be made without departing from the invention defined in the following claims.