ASTM D4097-19

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D4097 − 18 D4097 − 19 An American National Standard
Standard Specification for
Contact-Molded Glass-Fiber-Reinforced Thermoset Resin
Corrosion-Resistant Tanks
This standard is issued under the fixed designation D4097; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This specification covers cylindrical tanks fabricated by contact molding for above-ground vertical installation, to contain
aggressive chemicals at atmospheric pressure, and made of a commercial-grade polyester or vinyl ester, resin. Included are
requirements for materials, properties, design, construction, dimensions, tolerances, workmanship, and appearance.
1.2 This specification does not cover the design of vessels intended for pressure above atmospheric or under vacuum conditions,
except as classified herein, or vessels intended for use with liquids heated above their flash points.
1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are provided for
information purposes only.
1.4 Special design consideration shall be given to tanks subject to environmental and/or mechanical forces such seismic, wind,
ice, agitation, or fluid dynamic forces, to operational service temperatures greater than 180°F (82°C) and to tanks with unsupported
bottoms.
1.5 The following safety hazards caveat pertains only to the test method portion, Section 11, of this specification: This standard
does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this
standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory
limitations prior to use.
NOTE 1—There is no known ISO equivalent to this standard.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C581 Practice for Determining Chemical Resistance of Thermosetting Resins Used in Glass-Fiber-Reinforced Structures
Intended for Liquid Service
C582 Specification for Contact-Molded Reinforced Thermosetting Plastic (RTP) Laminates for Corrosion-Resistant Equipment
D618 Practice for Conditioning Plastics for Testing
D638 Test Method for Tensile Properties of Plastics
D790 Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
D883 Terminology Relating to Plastics
D2150 Specification for Woven Roving Glass Fabric for Polyester-Glass Laminates (Withdrawn 1987)
D2583 Test Method for Indentation Hardness of Rigid Plastics by Means of a Barcol Impressor
D2584 Test Method for Ignition Loss of Cured Reinforced Resins
D2996 Specification for Filament-Wound “Fiberglass” (Glass-Fiber-Reinforced Thermosetting-Resin) Pipe
This specification is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.23 on Reinforced Plastic Piping
Systems and Chemical Equipment.
Current edition approved Aug. 1, 2018Aug. 1, 2019. Published August 2018August 2019. Originally approved in 1982. Last previous edition approved in 20102018 as
D4097 - 01D4097 - 18.(2010). DOI: 10.1520/D4097-18.10.1520/D4097-19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4097 − 19
D2997 Specification for Centrifugally Cast “Fiberglass” (Glass-Fiber-Reinforced Thermosetting-Resin) Pipe
D3892 Practice for Packaging/Packing of Plastics
D4024 Specification for Machine Made “Fiberglass” (Glass-Fiber-Reinforced Thermosetting Resin) Flanges
D5421 Specification for Contact Molded “Fiberglass” (Glass-Fiber-Reinforced Thermosetting Resin) Flanges
F412 Terminology Relating to Plastic Piping Systems
2.2 ANSI Standards:
B 16.1 Cast Iron Pipe Flanges and Flanged Fittings, Class 25, 125, 250, and 800
B 16.5 Steel Pipe Flanges, Flanged Valves and Fittings
3. Terminology
3.1 Definitions—Definitions are in accordance with Terminologies D883 and F412, unless otherwise indicated.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 contact molding—includes the “hand lay-up” or a combination of the “hand lay-up” and the “spray-up” manufacturing
processes.
4. Classification
4.1 Tanks meeting this specification are classified according to type. It is the responsibility of the purchaser to specify the
requirement for Type II tanks, the operating pressure or vacuum levels, and the safety factor required for external pressure. Absence
of a designation of type required shall imply that Type I is adequate.
4.1.1 Type I—Atmospheric pressure tanks vented directly to the atmosphere, designed for pressure no greater or lower than
atmospheric.
4.1.2 Type II—Atmospheric pressure tanks vented directly into a fume conservation system, and designed to withstand, the
specified positive and negative pressure not to exceed 14 in. of water (355.6 mm) when all tie-down lugs are properly secured,
in accordance with the fabricator’s recommendations for flat-bottom tanks.
4.2 Tanks meeting this specification are classified according to type as follows:
4.2.1 Grade 1—Tanks manufactured with a single generic type of thermoset resin throughout.
4.2.2 Grade 2—Tanks manufactured with different generic types of thermoset resin in the barrier and the structural portion.
NOTE 2—The external corrosive environment due to spillage or corrosive vapors should be considered when specifying Grade 2 tanks (see 7.1.3.3).
5. Materials and Manufacture
5.1 Resin—The resin used shall be a commercial grade, corrosion-resistant thermoset that has either been evaluated in a
laminate by test in accordance with 11.3, or that has been determined by previous documented service to be acceptable for the
service conditions. Where service conditions have not been evaluated, a suitable resin may also be selected by agreement between
fabricator and purchaser.
5.1.1 The resin shall contain no pigment, dyes, colorants, or filler, except as follows:
5.1.1.1 A thixotropic agent that does not interfere with visual inspection of laminate quality, or with the required corrosion
resistance of the laminate, may be added for viscosity control.
NOTE 3—The addition of a thixotropic agent may reduce the resistance of many resin systems to certain corrosive chemical environments. It is the
responsibility of the fabricator, using a thixotropic agent in the resin required for 7.1.1 and 7.1.2, to ascertain its compatibility with the corrosive
environment when this has been reported by the purchaser.
5.1.1.2 Resin pastes used to fill crevices before overlay shall not be subject to the limitation of 5.1.1.
5.1.1.3 Resin may contain pigment, dyes, or colorants when agreed upon between fabricator and purchaser.
NOTE 4—The addition of pigment, dyes, or colorants may interfere with visual inspection of laminate quality.
5.1.1.4 Ultraviolet absorbers may be added for improved weather resistance if agreed upon between the fabricator and the
purchaser.
5.1.1.5 Antimony compounds or other fire-retardant agents may be added to halogenated resins for improved fire resistance, if
agreed upon between the fabricator and the purchaser.
NOTE 5—Because the addition of fire-retardant agents may interfere with visual inspection of laminate quality, they should not be used in the inner
surface (7.1.1) or interior layer (7.1.2), unless their functional advantages would outweigh the loss of visual inspection.
5.2 Reinforcement:
5.2.1 Chopped-Strand Mat—Chopped-strand mat shall be constructed from chopped commercial-grade E-type glass strands
bonded together using a binder. The strands should be treated with a sizing that is chemically compatible with the resin system
used.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
D4097 − 19
NOTE 6—The selection of the particular chopped-strand mat is dependent upon the performance characteristics required of the finished product and
upon the processing techniques to be used.
5.2.2 Nonwoven Biaxial or Unidirectal Fabric—These products shall be a commercial grade of E-type glass fiber with a sizing
that is chemically compatible with the resin system used.
5.2.3 Woven Roving—Woven roving shall be in accordance with Specification D2150.
5.2.4 Surface Mat—The reinforcement used for the inner surface (7.1.1) shall be either a commercial-grade chemical resistant
glass surface mat or an organic-fiber surface mat. In environments that attack glass, the use of an organic-fiber surface mat is
required.
6. Design Requirements
6.1 Straight Shell—The minimum required wall thickness of the cylindrical straight shell at any fluid level shall be determined
by the following equation, but shall not be less than ⁄16 in.:
t 5 PD/2S 5 0.036 γ HD/2S or 0.2489 γ HD/2S
~ !
H H H
where:
t = wall thickness, in. (mm),
S = allowable hoop tensile stress (not to exceed ⁄10 of the ultimate hoop strength), psi (kPa) (see 11.8),
H
P = pressure, psi (kPa),
H = fluid head, in. (mm),
γ = specific gravity of fluid, and
D = inside diameter of tank, in. (mm).
NOTE 7—The use of an accepted analytical technique, such as laminated plate theory (LPT), for design and analysis of composite vessels may predict
stresses, strains, and strength on a ply-by-ply basis, given some basic lamina properties.
NOTE 8—The calculation is suitable for the shell design of elevated dished-bottom tanks that are mounted or supported below the tangent of the
dished-bottom head. Special consideration must be given to the loading on the straight shell at the support when tank has mounting supports located above
the tangent line.
NOTE 9—Table X2.1, Appendix X2, illustrates minimum straight-shell wall thicknesses.
6.2 Design for External Pressure:
0.5
6.2.1 Cylindrical Shells—For cylindrical shells, compute the value 1.73 (D /t) . If the result is less than L/D of the cylinder,
o o
compute P as follows:
a
2.5
P 5 2.6~E/F! D /L ~t/D !
~ !
a o o
If the result is greater than L/D of the cylinder, compute P as follows:
o a
2.5
2.6 E/F D /L t/D
~ !~ !~ !
o o
P 5
a 0.5
~L/D ! 2 0.45~t/D !
o o
where:
D = outside diameter, in.,
o
E = hoop tensile modulus of the filament wound structural laminate, psi (kPa),
t
F = design factor = 5,
L = design length, in. (mm), of a vessel section, taken as the largest of the following: (a) the distance between head tangent
lines plus one-third the depth of each formed head, if there are no stiffening rings (excluding conical heads and sections);
(b) the distance between cone-to-cylinder junctions for vessels with a cone or conical heads if there are no stiffening rings;
(c) the greatest center-to-center distance between any two adjacent stiffening rings; (d) the distance from the center of the
first stiffening ring to the formed head tangent line plus one-third the depth of the formed head (excluding conical heads
and sections), all measured parallel to the axis of the vessel; (e) the distance from the first stiffening ring in the cylinder
to the cone-to-cylinder junction,
P = allowable external pressure, psi (kPa), and
a
t = wall thickness, in. (mm) (nominal).
6.2.2 Torispherical Heads—For torispherical heads, compute the allowable external pressure, P , as follows:
a
P 5 0.36~E/F! t/R
~ !
a o
where:
R = outside crown radius of head, in. (mm).
o
For toruspherical heads subject to internal loading, the knuckle radius shall be externally reinforced in accordance with Fig. 1.
The reinforcement thickness shall be equal to the thickness of the head as calculated above. The thickness of a joint overlay near
the knuckle radius tangent line of dished head contributes to the knuckle reinforcement.
6.2.3 Stiffening Rings—The required moment of inertia, I , of a circumferential stiffening ring for cylindrical shells under
s
external pressure or internal vacuum shall not be less than that determined by the following:
D4097 − 19
FIG. 1 Jointed Head Detail
(Sketch A)
I 5 PL D F/24E
s s h
where:
D = shell outside diameter, in. (mm),
o
E = hoop tensile modulus, psi (kPa),
h
F = design factor = 5,
4 4
I = moment of inertia, in. (mm ), of stiffener for the effective length of shell, L ,
s s
L = one-half of the distance from the centerline of the stiffening ring to the next line of support on one side, plus one-half of
s
the centerline distance to the next line of support on the other side of the stiffening ring, both measured parallel to the axis
of the cylinder, in. A line of support is the following: (a) a stiffening ring that meets the requirements of this paragraph;
(b) a circumferential line on a head at one-third the depth of the head from the head tangent line; (c) a cone-to-cylinder
junction,
P = actual external pressure, psi (kPa).
Typical half-round stiffener sizes and dimensions for different values of I are shown in Fig. 4. Other stiffener profiles meeting
s
the required moment of inertia may be used.
6.3 Top Head—The top head, regardless of shape, shall be able to support a 250-lb (113.4 kg) load on a 4 by 4-in. (100 by 100
mm) area without damage and with a maximum deflection of ⁄2 % of the tank diameter.
6.3.1 The minimum thickness of the top head shall be ⁄16 in. (4.8 mm).
NOTE 10—Support of auxiliary equipment, snow load, or operating personnel, may require additional reinforcement or the use of stiffening ribs, or both,
sandwich construction, or other stiffening systems.
6.4 Bottom Head:
6.4.1 The minimum thickness for a fully supported flat-bottom head shall be as follows:
⁄16 in. (4.8 mm) for 2 to 6-ft (0.6 to 1.8-m) diameter,
⁄4 in. (6.4 mm) for over 6 to 12-ft (1.8 to 3.7-m) diameter, and
⁄8 in. (9.5 mm) for over 12-ft (3.7-m) diameter.
6.4.2 Bottom heads may be molded integrally with the straight-shell, or may be molded separately with a straight flange length
for subsequent joining to shell.
6.4.3 The radius of the bottom knuckle of a flat-bottom tank shall be not less than 1 in. (25 mm) on tanks 4 ft or smaller in
diameter and 1.5 in. (38 mm) on tanks larger than 4 ft in diameter. The minimum thickness of the radiused section shall be equal
to the combined thickness of the shell wall and the bottom. The reinforcement of the knuckle-radius area shall taper so that it is
tangent to the flat bottom, and shall not extend beyond the tangent line onto the tank bottom, unless methods of manufacture are
used that maintain flat-bottom configuration, and shall extend up the vertical tank wall a minimum of length “L” of 8 in. (203 mm)
on tanks up to 4 ft (1219 mm) in diameter, and 12 in. (304 mm) on tanks over 4 ft (1219 mm) in diameter. The reinforcement shall
then taper into the side wall over an additional length “ M” of 4 in. (102 mm) (see Fig. 2). Methods of manufacture that incorporate
stiffening bands as a means of knuckle stabilization, are permissible alternatives by agreement between purchaser and fabricator,
provided that the fabricator can document the validity of design.
6.4.4 The tank bottom shall not have variations from a nominally flat plane that would prevent uniform contact of the entire
bottom surface with a properly prepared support surface when the tank is filled with liquid. The bottom laminate surface shall be
D4097 − 19
FIG. 2 Flat-Bottom Tank Corner Detail
a hand-work finish and shall have no excessive laminate projections that would prevent uniform contact with a properly prepared
flat support surface when the tank is filled with liquid.
NOTE 11—This requirement is not intended to exclude the use of drain nozzles, which are commonly used at the bottom of the side shell. However,
foundation cut-outs are required of the appropriate dimensions for nozzle type and size.
6.4.5 The thickness of an elevated torispherical dished bottom, suitable for supporting the weight of the fluid head, shall be
determined by the following equation, but shall not be less than ⁄16 in. (4.8 mm):
t 5 0.885 PR/S 5 0.885 ~0.036 γ HR!/Sor ~0.885 ~0.2489 γ HR!/S!
where:
t = thickness, in. (mm),
S = allowable stress (not to exceed ⁄10 of ultimate strength), psi (kPa) (see 11.8),
γ = specific gravity of fluid,
P = pressure, psi (kPa),
R = inside radius of dished head, in. (mm), and
H = distance from the top of the fluid to the deepest portion of the bottom, in. (mm).
NOTE 12— An alternate method for design of an elevated toruspherical dished bottom is shown in Appendix X3.
6.4.5.1 Minimum thickness of ellipsodial heads, (2:1) shall be calculated as follows:
PD
t 5
2S
6.4.5.2 Minimum thickness of conical heads shall be calculated as follows:
PD
t 5
2S· cos ~}!
where:
} = ⁄2 of APEX angle of the cone at the centerline of the head (not to exceed 30°).
D4097 − 19
6.4.6 The torispherical dished-bottom head shall have a radius of curvature that is equal to or less than the inside diameter of
the tank straight shell, and a minimum knuckle radius of at least 6 % of the diameter of the head.
6.4.7 Deflection of the flat bottom when the tank is empty, commonly known as “oil canning,” is permissible as long as the
requirements of 6.4.4 are met.
6.5 Open-Top Tanks—The top edge of open-top tanks shall have a horizontal reinforcing flange or other means of reinforcement
sufficiently rigid to maintain the shape of the tank after installation. The flange shall be in accordance with Table 1. See Table 2.
6.6 Joints:
6.6.1 The cured resin surfaces to be overlayed shall be roughened using 36 or coarser grit abrasive media. The roughened area
shall extend beyond the lay-up area so that no reinforcement is applied to an unroughened surface. Surfaces shall be clean and dry
before lay-up. The entire roughened area shall be coated with paraffinated resin after the joint lay-up is made.
6.6.2 The secondary laminate joints are used to join hoop segments of the straight shell, or to join the bottom or top head to
the shell. The thickness of the structural joint overlay shall be equal to the shell thickness as determined in 6.1.
6.6.3 The minimum width of the structural joint overlay for bottom supported tanks is shown in Table 3.
6.6.4 The corrosion-resistant barrier component of the joint shall be formed in the same manner as the inner surface and the
interior layer (7.1.1 and 7.1.2) and shall not be considered a structural element in determining joint thickness. The minimum
overlay width shall be 4 in. (100 mm).
6.6.5 The thickness of a joint near the bottom tangent line shall not be considered to contribute to the knuckle reinforcement
of 6.4.3, but shall be additive thereto.
6.7 Fittings:
6.7.1 The more common method of fabricating nozzles is by contact molding both the nozzle neck and flange to the dimensions
shown in Table 4. The corrosion-resistant barrier of the nozzle shall be at least equivalent to the inner surface and interior layer
(7.1.1 and 7.1.2) and shall be fabricated from the same resin as the tank head or shell to which it is attached.
6.7.2 Acceptable alternative methods are the use of contact-molded pipe, filament-wound pipe in accordance with Specification
D2996, or centrifugally cast pipe in accordance with Specification D2997, joined to a suitable contact-molded (Specification
D5421), compression-molded, or filament-wound flange (Specification D4024). The corrosion-resistant barrier of the contact
molded portions of such nozzles shall be equivalent to the inner surface and interior layer (7.1.1 and 7.1.2) and shall be fabricated
from the same resin as the tank head or shell to which it is attached.
6.7.3 Nozzles 4 in. (102 mm) and smaller shall be supported by a suitable gusseting technique using plate gussets or conical
gussets, as shown in Fig. 3 and Fig. 4. Plate gussets, where needed, shall be evenly spaced around the nozzle and are to be added
after complete assembly of nozzle on shell. Larger nozzles, subject to superimposed mechanical forces, require special
consideration.
6.7.4 Manways installed in top heads may be of the flanged design or of a nonflanged design, as agreed upon between the
fabricator and purchaser.
6.7.4.1 Side-shell manways shall be in accordance with 7.3.2 and 7.3.3.
6.7.4.2 Typical manway dimensions are shown in Table 5.
NOTE 13—Tanks over 6 ft (1.8 m) straight-shell may need both top- and side-shell opening manways for safety and maintenance considerations.
6.7.5 Vents:
6.7.5.1 Vents that discharge freely into the atmosphere shall be provided in all Type I closed-top tanks. Minimum vent size shall
be sufficient to handle the flow displacement of all combined inlet or outlet nozzles without creating any pressure above
atmospheric pressure, or any vacuum condition.
NOTE 14—Special vent sizing consideration should be given to the numerous operating situations that could otherwise cause a positive or a negative
pressure in a closed tank. Since overfilling a closed tank with a top vent can cause it to be overpressurized, a suitably sized overflow or other appropriate
protection may be required to prevent overpressuring the tank.
6.7.6 Type II tanks shall be designed to withstand the specified positive or negative pressures not to exceed 14 in. of water
(355.6 mm). Special design consideration shall be given to buckling of tank wall and heads, the hold-down lug system, and top
and bottom knuckle requirements. Fluid level in the tank is an important consideration in the analysis.
6.7.6.1 Flat-bottom tanks shall have all hold-down lugs properly secured to the foundation, in accordance with the tank
fabricator’s recommendation for the design of the lugs used and for the tank installation and operation.
TABLE 1 Minimum Acceptable Contact Molded Laminate Physical Properties
Property Thickness, in. (mm)
1 3 1 5 3
⁄8 to ⁄16 (3.2 to 4.8) ⁄4 (6.4) ⁄16 (7.9) ⁄8 and up (9.5 and up)
Ultimate tensile strength, min, psi (kPa) 9 000 (620.5) 12 000 (827.4) 13 000 (930.8) 15 000 (1 034)
Flexural strength, min, psi (kPa) 16 000 (1 103) 19 000 (1 310) 20 000 (1 399) 22 000 (1 517)
Flexural modulus for elasticity (tangent), psi (kPa) 700 000 (48 263) 800 000 (55 158) 900 000 (62 053) 1 000 000 (68 948)
D4097 − 19
TABLE 2 Standard Tank Inside Diameters
in. (mm) in. (mm) in. (mm)
24 (610) 54 (1372) 96 (2438)
30 (762) 60 (1524) 108 (2743)
36 (914) 66 (1676) 120 (3048)
42 (1067) 72 (1829) 132 (3353)
48 (1219) 84 (2134) 144 (3658)
6.8 Hold-Down Lugs—Hold-down lugs shall be a requirement on all tanks for outdoor service, on all Type II tanks, and on tanks
subject to seismic loads or vibrations. The design number and attachment of such lugs is the responsibility of the fabricator, based
on the wind, seismic, and other loads specified by the purchaser.
6.8.1 Hold-down lugs shall be placed on the tank in such a way that they do not protrude below the bottom surface of the tank.
6.9 Lifting Lugs—Lifting lugs or other provisions for lifting tanks (see Appendix X1) shall be provided for tanks over 500 lb
(227 kg) in weight.
7. Laminate Construction Requirements
7.1 Structural Tank—The laminate comprising the structural tank (bottom, cylindrical shell, top head) shall consist of a
corrosion-resistant barrier comprised of an inner surface, interior layer, and a structural layer.
7.1.1 Inner Surface—The inner surface exposed to the chemical environment shall be a resin-rich layer 0.010 and 0.020 in.
(0.254 to 0.508 mm) thick, reinforced with a suitable chemical-resistant glass-fiber surfacing mat or with an organic-fiber surfacing
mat, in accordance with 5.2.4.
NOTE 15—This resin-rich inner surface will usually contain less than 20 % by weight of reinforcing material.
7.1.2 Interior Layer—The inner surface layer exposed to the corrosive environment shall be followed with a layer composed
of resin, reinforced only with noncontinuous glass-fiber strands applied in a minimum of two plies of chopped-strand mat
2 2
equivalent to a total of 3 oz/ft (0.92 kg/m ). As an alternative, a minimum of two passes of chopped roving of minimum length
0.5 in. (13 mm) to a maximum length of 2.0 in. (50.8 mm), shall be applied uniformly to an equivalent weight. Each ply of mat
or pass of chopped roving shall be well rolled prior to the application of additional reinforcement. The combined thickness of the
inner surface and interior layer shall not be less than 0.10 in. (2.5 mm).
7.1.2.1 Glass content of the inner liner and the interior layer combined shall be 27 6 5 % by weight, when tested in accordance
with 11.4.
7.1.2.2 The degree of cure of the laminate shall be such as to exhibit a Barcol hardness on the inner surface of at least 90 %
of the resin manufacturer’s minimum specified hardness for the cured resin, when tested in accordance with 11.7 and Note 18, Note
19, and Note 20.
7.1.3 Contact Molded Structural Layer in Top and Bottom Heads—Subsequent reinforcement shall be comprised of 1.5 oz/ft
(0.46 kg/m ) chopped strand mat or equivalent weight of chopped roving or shall be comprised of chopped strand mat or chopped
2 2 2 2
roving and such additional number of alternating plies of 24 oz/yd (0.81 kg/m ) woven roving or 18 oz/yd (0.61 kg/m )
nonwoven biaxial fabric to a thickness as required to meet the physical properties that are used for the design. The use of woven
roving is optional. The designations of these specific weights of glass reinforcement are for reference only and may be comprised
of other weight combinations of reinforcement materials, when agreed to between the fabricator and purchaser. Each successive
ply or pass of reinforcement shall be well rolled prior to the application of additional reinforcement. Where woven roving or
nonwoven fabric is used, chopped strand glass reinforcement shall be used as alternating and final layers. All woven roving and
nonwoven fabric, surfacing mat shall be overlapped. Laps in subsequent layers shall be staggered at least 2.25 in. (60 mm) from
laps in the preceding layer.
7.1.3.1 When the outer surface of this structural layer is to be subject to spillage or a corrosive environment, a resin-rich layer
in accordance with 7.1.1 shall be applied over the final layer of reinforcement.
7.1.3.2 Where air-inhibited resin is exposed to air, full surface cure shall be obtained by coating such surface with a coat of resin
containing 0.2 to 0.6 % paraffin with a melt point of 122 to 126°F (50 to 52°C). Other techniques such as sprayed, wrapped, or
overlaid films are also acceptable methods to attain surface cure. The acetone sensitivity test may be used to check surface cure
(see Note 19).
7.1.3.3 Tanks used for outdoor service or subject to ultraviolet exposure shall incorporate provisions to minimize ultraviolet
degradation. Suitable methods include use of ultraviolet absorbers, incorporation of pigment of sufficient opacity in the outer
surface of the resin rich layer, or use of resins inherently resistant to ultraviolet degradation. Since pigmentation makes inspection
difficult, it shall be added after inspection or otherwise by agreement between the purchas
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