Note: Descriptions are shown in the official language in which they were submitted.
2110221
Case 1025CIP GB117000576
REINFORCEMENT 8YSTEM FOR MASTIC INTUME8CENT FIRE PROTECTION
COATINGS
This invention relates generally to mastic fire protection
coatings and more particularly to reinforcement systems for such
coatings.
Mastic fire protection coatings are used to protect
structures from fire. One widespread use is in hydrocarbon
processing facilities, such as chemical plants, offshore oil and
gas platforms and refineries. Such coatings are also used around
hydrocarbon storage facilities such as LPG (liquified petroleum
gas) tanks.
The coating is often applied to structural steel elements
and acts as an insulating layer. In a fire, the coating retards
the temperature rise in the steel to give extra time for the fire
to be extinguished or the structure evacuated. Otherwise, the
steel might rapidly heat and collapse.
Mastic coatings are made with a binder such as epoxy or
'0 vinyl. Various additives are included in the binder to give the
coating the desired fire protective properties. The binder
adheres to the steel.
One particularly useful class of mastic fire protective
coatings is termed "intumescent". Intumescent coatings swell up
'5 when exposed to the heat of a fire and convert to a foam-like
21 10221
char. The foam-like char has a low thermal conductivity and
insulates the substrate. Intumescent coatings are sometimes also
calIed "ablative" or "subliming" coatings.
Though the mastic coatings adhere well to most substrates,
it is known to embed mesh in the coatings. The mesh is
mechanically attached to the substrate. U.S. patents 3,913,290
and 4,069,075 to Castle et al. describe the use of mesh. In
those patents, the mesh is described as reinforcing the char once
it forms in a fire. More specifically, the mesh reduces the
chance that the coating will crack or "fissure". Fissures reduce
the protection provided by the coating because they allow heat to
more easily reach the substrate. When fissures in the material
do occur, they are not as deep when mesh is used. As a result,
the mastic does not need to be applied as thickly. Glass cloth
has also been used to reinforce fire protective mastics. U.S.
3,915,777 describes such a system. Glass, however, softens at
temperatures to which the coating might be exposed. Once the
glass softens, it provides no benefits. Though the glass is
partially insulated by the fire protective coating, we have
recognized that intumescent systems also often contain boron or
other materials which are glass fluxing agents. The fluxing
agents lower the softening point of the glass reinforcement. As
a result, the glass does not provide adequate reinforcement in
some fire situations to which the material might be exposed.
Examples of two widely used types of glass fibers are E-
glass and S-glass sold by Owens-Corning. E-glass loses 25% of
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its tensile strength when heated 343~C. S-glass, while
slightly stronger, loses 20~ of its tensile strength at the
same temperature. When heated to temperatures of 732~C and
849~C, E-glass and S-glass, respectively, have softened
appreciably and by 877~C and 970~C, E-glass and S-glass
respectively, have softened so much that fibers made of
these materials cannot support their own weight. These low
softening temperatures are a drawback of using glass
reinforcement.
Use of mesh in conjunction with mastic coatings has
been criticized because it increases the cost of applying
the material. It would be desirable to obtain the benefits
of mechanically attached wire mesh without as much added
cost.
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SUMMARY OF THE lNv~,.llON
With the foregoing background in mind, it is an object to
provide a fire protection coating system with relatively low
manufacturing cost, low installation cost and good fire
protection.
The foregoing and other objects are achieved with a mesh
made of a combination of fibers. Non-melting, non-flammable,
flexible fibers with a high softening point are interwoven with
fibers with a relatively low softening point.
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BRIEF DESCRIPTION OF THE DR~WINGS
The invention will be better understood by referenee to the
following more detailed description and accompanying drawings in
which:
FIG. 1 shows a eoating with yarn mesh embedded in it; and
FIG. 2 is a sketch of a hybrid woven mesh according to an
embodiment of the invention;
FIG. 3 is a sketeh of a hybrid knitted mesh aeeording to an
embodiment of the invention; and
FIG. 4 is a sketeh of a eoated beam with a hybrid mesh
aeeording to an embodiment of the invention.
2 ~ 1 0 2 2 1
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a column 100 such as might be used for
structural steel in a hydrocarbon processing facility. A
column is illustrated. However, the invention applies to
beams, joists, tubes or other types of structural members
or other surfaces, such as walls, floors, decks and
bulkheads, which need to be protected from fire. Coating
102 is applied to the exposed surfaces of column 100.
Coating 102 is a known mastic intumescent fire protection
coating. Chartek~ coating available from Textron Specialty
Materials in Lowell, MA USA is an example of one of many
suitable coatings.
Coating 102 has a hybrid mesh 104 embedded in it.
Hybrid mesh 104 contains a flexible, noninflammable fibrous
material which maintains in excess of 80~ of its room
temperature tensile strength at temperatures in excess of
343~C. Preferably, the fibrous material retains in excess
of 80~ of its room temperature strength as temperatures
above 849~C and more preferably above 1200~C. Examples of
suitable fibrous materials are carbon, boron and graphite
fibers. Fibers containing carbides, such as silicon carbide
or titanium carbide; borides, such as titanium diborides;
oxides, such as alumina or silica; or ceramic might be
used. The fibers can be used in the form of monofilaments,
multifilaments, tows or yarns. If yarns are used, they may
be either continuous filament yarns or discontinuous
filament yarns such as stretch broken or spun yarn. Herein-
after, such materials are referred to generally as "high
temperature fiber". Such high temperature fibers offer
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the advantage of being light and flexible in comparison to welded
wire mesh. In addition, they do not burn, melt or corrode and
withstand many environmental effects.
Carbon yarn is the preferred high temperature fiber. Carbon
yarns are generally made from either PAN (poly acrylic nitride)
fiber or pitch fiber. The PAN or pitch is then slowly heated in
the presence of oxygen to a relatively low temperature, around
450~F. This slow heating process produces what is termed an
"oxidized fiber". Whereas the PAN and pitch fibers are
0 relatively flammable and lose their strength relatively quickly
at elevated temperatures, the oxidized fiber is relatively
nonflammable and is relatively inert at temperatures up to 300~F.
At higher temperatures, the oxidized fiber may lose weight, but
is acceptable for use in some fire protective coatings in some
fire environments. Oxidized fiber is preferably at least 60%
carbon.
Carbon fiber is made from the oxidized fiber by a second
heat treating cycle according to known manufacturing techniques.
This second heat treating step will not be necessary in some
0 cases since equivalent heat treatment may occur in a fire. After
heat treating, the fiber contains preferably in excess of 95%
carbon, more preferably in excess of 99%. The carbon fiber is
lighter, stronger and more resistant to heat or flame than the
precursor materials. The carbon is, however, more expensive due
to the added processing required. Carbon fiber loses only about
1~ of its weight per hour at 500~C in air. Embedded in a fire
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protection coating, it will degrade even less.
Hybrid mesh contains a low temperature fiber. The low
temperature fiber helps hold the high temperature fiber together
into a handleable mesh. We have discovered that more fibers are
needed to provide a handleable mesh than are needed to provide
adequate reinforcement in a fire. As a result, low temperature
fibers are interwoven with high temperature fibers. The low
temperature fibers are selected to be of relatively low cost and
to provide good handleability to the mesh. Examples of suitable
lo low temperature fibers are glass fibers, Kevlar fibers (trademark
of DuPont for aramid), mineral fibers, basalt, organic fibers, or
nylon, polyester or other synthetic fibers. Combinations of
fibers mights also be used.
Glass fibers are preferred. Such fibers are relatively low
cost and make a handleable material. Moreover, when hybrid mesh
is used in an intumescent coating, glass fibers have a high
enough softening temperature to provide some desirable effects
during the early stages of intumescence.
FIG. 2 shows the construction of a hybrid mesh 204. Here, a
lino weave is used. Fill yarns 206 are carbon yarn. Carbon fill
yarns 206 alternate with glass fill yarns 208. The warp yarns
are made by alternating glass yarns 210 and a combined glass and
carbon yarn 212.
The end result is an open fabric with a major cell having a
dimension Ml which is bounded by high temperature fiber. The
major cell is filled with minor cells having a dimension M2 which
2 ~ 2 2 1
is defined by low temperature fiber. Preferably, a dimension M
is below four inches, more preferably M~ will be below one inch
and most preferably approximately one half inch. The dimension
M2 is preferably less than two inches and more preferably below
one half inch. Most preferably M2 is approximately one quarter
inch. Mesh with these spacings provides adequate strength and
reduces fissuring when used in intumescent materials. The
spacing is large enough, though to allow easy incorporation into
a mastic coating.
In FIG. 2, hybrid mesh 204 is shown with major and minor
cells both being square. It is not, however, necessary that the
cells be square. The cells could be rectangular or of any shape
resulting from the construction of the mesh.
For example, in FIG. 3, a hybrid mesh 304 is shown with high
temperature warp fibers 312 which are not straight. As a result,
the major and minor cells are not rectangular.
The hybrid mesh 304 of FIG. 3 is a knitted mesh which
provides the advantages of easily expanding in the warp
direction, W. Expansion of the mesh is desirable when used an
reinforcement of intumescent fire protecting coatings. As the
coating intumesces, it pushes outwards as it expands to provide a
thick blanket of insulation. If the mesh expands, it will allow
the coating to intumesce more and therefore provide greater
insulation.
This added expansion is particularly important at edges or
on small diameter objects, such as pipes, where the expanded
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coating has a greater surface area than the unexpanded coating.
Fissures are most likely to occur in the intumescent coating at
these places. To achieve full benefit from an expandable mesh,
though, it is necessary that hybrid mesh 304 be oriented with
S warp direction, W, perpendicular or tangential to the direction
of expansion. In FIG. 1, for example, the warp direction W is
shown to be around the flange edges of column 100. In this way,
as the radius of the coating around the flange edges increases in
a fire, the mesh reinforcement will increase also. As a result,
less fissuring of the intumescent coating on the flange edges is
likely.
A second advantage of an expandable mesh is that less
intumescent fire protective material is needed. We have observed
that with the use of mesh, when fissures do occur, they are not
as deep. In general, the fissure does not penetrate into the
coating any deeper than the mesh. With expandable mesh, the mesh
moves further from the substrate as the material intumesces. As
a result, a thicker insulating material is between the mesh and
the substrate. Thus, when fissures form, down to the mesh, the
substrate is better insulated. This effect is particularly
important for thin coatings, say less that 0.35".
Returning now to FIG. 3, the construction of the hybrid mesh
is described in greater detail. Hybrid 304 is a fabric
characterized as a 2-bar marquisette with warp layin and weft
insertion. Amoco T-300 3,000 filament carbon yarn was used as
the high temperature fiber. Owens-Corning ECC150 glass yarn was
-- 2110221
used as the low temperature fiber. Warp carbon fibers 312 and
weft carbon fibers 314 define major cells which have corners
spaced apart 1/2" in each direction. Minor cells are defined by
warp glass yarn 316 and weft glass yarns 318. The glass yarns
5 make squares which are approximately 1/2" x 1/4". Since these
squares are offset by 1/4" from the squares formed by the carbon
yarns, they are bisected along the long axes by the weft carbon
yarns 314 to form two 1/4" x 1/4" minor cells.
Hybrid mesh 304 was made on a Raschel knitting machine
10 equipped with weft insertion. Stitches running in the warp
direction W are made by knitting two glass yarns in a pillar
stitch, four pillar stitches per inch. These stitches are spaced
apart 1/4". Every other pillar stitch 316B encompasses a single
carbon yarn 312.
The weft carbon fibers 314 are added by weft insertion. The
weft glass fibers 318 are produced by "laying in" every 1/2".
Laying in means that a yarn from one pillar is transferred to the
adjacent stitch.
Warp yarns 316B are not straight. The serpentine shape of
20 these fibers results from the fact that, due to the inclusion of
carbon yarn 312 in stitches 316B, the tension is different in
yarns 316A and 316B. This serpentine shape is desirable because
it allows the mesh to stretch.
Sizing may be used on the hybrid mesh to improve the
25 handleability of the mesh.
Returning to FIG. 1, column 100 is coated according to the
2110~1
following procedure. First, a layer of mastic intumescent coating
is applied to column 100. The mastic intumescent may be applied
by spraying, troweling or other convenient method. Before the
coating cures, the hybrid mesh 104 is rolled out over the
surface. It is desirable that mesh 104 be wrapped as one
continuous sheet around as many edges of column 100 as possible.
Mesh 104 is pressed into the coating with a trowel or roller
dipped in a solvent or by some other convenient means.
Thereafter, more mastic intumescent material is applied.
Coating 102 is then finished as a conventional coating. The
carbon mesh is thus "free floating" because it is not directly
mechanically attached to the substrate.
EXAMPLE I
A steel pipe of roughly 18"-circumference was coated with
8mm of intumescent fire proofing material. A hybrid mesh as
shown in FIG. 3 was embedded in the coating approximately 5mm
from the surface of the pipe. The pipe was placed in a 2,000~F
furnace.
After testing, the glass portions of the hybrid mesh were
not observable. The carbon portions of the hybrid mesh were
found approximately 9-lOmm from the surface of the pipe. The
circumference of the hybrid mesh had increased approximately 1
3/4" from approximately 18 1/3". Qualitatively, the coating was
observed to have less severe fissures than similar substrates
protected with intumescent fireproofing material reinforced with
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metal mesh.
EXAMPLE II
A hybrid mesh as shown in FIG. 3 was embedded in a mastic
intumescent fire protective coating applied to a section of a
lOWF49 beam. The coating was applied at an average thickness of
5mm. The hybrid mesh was embedded 3mm from the surface at the
flange edges of the beam. When placed in a furnace which was
already heated to 2,000~F, the average temperature of the beam,
as measured by thermocouples embedded in the beam, was 1,000~F
after 48 minutes. For a second beam segment coated with 7mm of
fire protective material with the same type mesh, the time to
1,000~F was 63 minutes.
For comparison, a similarly tested beam without mesh reached
1,000~F after 30 minutes.
While not directly comparable, a lOWF49 column was coated
with 0.27 inches of intumescent fire protective material. Metal
mesh was embedded in the coating at the flange edges. The column
was placed in a furnace which was then heated to 2,000~F
according to the UL 1709 protocol. The column reached an average
temperature of 1,000~F after 60 minutes. If scaled to a
thickness of 5mm, this time is equivalent to only 44 minutes.
Turning now to FIG. 4, an alternative hybrid 404 mesh is
shown embedded in a fire protective coating 402. As shown, mesh
404 has carbon yarns 406 running in only one direction around
flange edges of a column. Carbon yarns 406 are held together by
low temperature fibers 408. In this way, the amount of high
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temperature fibers is reduced.
Having described the invention, it will be apparent that
other embodiments might be constructed. Different types or
combinations of fibers might be used. The hybrid mesh as
S described herein might also be used to reinforce fire protective
coatings on a variety of substrates, such as beams, columns,
bulkheads, decks, pipes, tanks and ceilings. The invention
should, thus, be limited only by the spirit and scope of the
appended claims.
14
