ASTM D6041-23

Standard Specification for Contact-Molded “Fiberglass” (Glass-Fiber-Reinforced Thermosetting Resin) Corrosion Resistant Pipe and Fittings

SCOPE
1.1 This specification covers pipe and fittings fabricated by contact molding, for pressures to 150 psi and made of a commercial-grade polyester resin. Included are requirements for materials, properties, design, construction, dimensions, tolerances, workmanship, and appearance.  
1.2 This specification does not cover resins other than polyester, reinforcing materials other than glass fibers or fabrication methods other than contact molding.
Note 1: For the purposes of this specification, the term polyester resin will include both polyester and vinylester resins.  
1.3 This specification does not cover the design of pipe and fittings intended for use with liquids heated above their flash points.  
1.4 The values stated in inch-pound units are to be regarded as the standard. The SI units given in parentheses are provided for information purposes only.  
1.5 The following precautionary caveat pertains only to Section 10, the test methods portion, 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 2: 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.

General Information

• Status: Published
• Publication Date: 31-Jul-2023
• ICS: 23.040.20 - Plastics pipes
• ICS: 23.040.45 - Plastics fittings
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.23 - Reinforced Thermosetting Resin Piping Systems and Chemical Equipment

Relations

• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM F412-20 - Standard Terminology Relating to Plastic Piping Systems
• Effective Date: 01-Apr-2020
• Refers: ASTM C581-20 - Standard Practice for Determining Chemical Resistance of Thermosetting Resins Used in Glass-Fiber-Reinforced Structures Intended for Liquid Service
• Effective Date: 15-Feb-2020
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM F412-19 - Standard Terminology Relating to Plastic Piping Systems
• Effective Date: 01-Jan-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM D2584-18 - Standard Test Method for Ignition Loss of Cured Reinforced Resins
• Effective Date: 15-Sep-2018
• Refers: ASTM D1599-18 - Standard Test Method for Resistance to Short-Time Hydraulic Pressure of Plastic Pipe, Tubing, and Fittings
• Effective Date: 01-Sep-2018
• Refers: ASTM D648-18 - Standard Test Method for Deflection Temperature of Plastics Under Flexural Load in the Edgewise Position
• Effective Date: 01-Apr-2018
• Refers: ASTM D1600-18 - Standard Terminology for Abbreviated Terms Relating to Plastics (Withdrawn 2024)
• Effective Date: 01-Jan-2018

Overview

ASTM D6041-23 is the standard specification developed by ASTM International for contact-molded “fiberglass” (glass-fiber-reinforced thermosetting resin) corrosion-resistant pipe and fittings, covering products fabricated for pressures up to 150 psi. This specification details the requirements for materials, physical properties, design, construction, dimensions, tolerances, workmanship, and appearance of corrosion-resistant pipes and fittings constructed using commercial-grade polyester or vinylester resin and glass fiber reinforcement by contact molding processes.

Pipes and fittings built to ASTM D6041-23 are widely used in industries requiring robust corrosion resistance, including chemical processing, water treatment, and industrial fluid conveyance, due to their reliable performance in harsh environments where metallic piping systems may fail.

Key Topics

• Scope and Applicability

  • Covers contact-molded fiberglass pipes and fittings for pressures up to 150 psi.
  • Applies specifically to products made from polyester or vinylester resin and glass-fiber reinforcements.
  • Excludes resins, reinforcements, or manufacturing methods outside this scope.

• Material and Construction Requirements

  • Mandates use of commercial-grade, corrosion-resistant polyester or vinylester resin.
  • Requires glass fiber reinforcement for structural strength and long-term durability.
  • Permits limited use of additives, pigments, and flame retardants if agreed upon between manufacturer and purchaser.

• Design and Performance

  • Provides calculation methods for minimum wall thickness and pressure class based on design pressure and allowable stress.
  • Details laminate construction for corrosion barrier, structural layer, and surface finish to achieve targeted chemical resistance and mechanical strength.
  • Specifies requirements for joints, fittings, elbows, reducers, tees, and flanges to ensure structural integrity and dimensional compatibility.

• Dimensions, Tolerances, and Marking

  • Lists standard internal diameters and specifies tolerances for out-of-roundness, wall thickness, squareness of ends, and sizing of fittings.
  • Requires clear and durable product marking, including standard reference, size, pressure rating, manufacturer, and traceability data.

• Testing and Quality Assurance

  • Outlines mandatory proof of design by pressure testing, barcol hardness measurement for degree of cure, and chemical resistance testing.
  • References other recognized ASTM standards for testing methodologies and terminology.

Applications

ASTM D6041-23 fiberglass-reinforced thermosetting resin pipes and fittings are suitable for use in:

• Chemical Processing: Handling aggressive chemicals where corrosion resistance is critical
• Water and Wastewater Treatment: Piping for conveyance of treated water, wastewater, and corrosive sludges
• Industrial Piping Systems: Transporting process fluids, cooling water, brine, or corrosive effluents
• Potable Water Systems: When certified in line with applicable health and safety requirements (referencing NSF Standard 61)
• Underground and Outdoor Installations: Where exposure to soil chemicals, moisture, or UV radiation demands enhanced durability

Proper handling and installation procedures are recommended, as highlighted in the standard’s appendices, to maximize performance and maintain the integrity of the pipe system throughout its service life.

Related Standards

Several key standards are referenced within ASTM D6041-23 for consistency in testing and terminology, including:

• ASTM C581: Practice for Determining Chemical Resistance of Thermosetting Resins
• ASTM C582: Specification for Contact-Molded Reinforced Thermosetting Plastic Laminates
• ASTM D638: Test Method for Tensile Properties of Plastics
• ASTM D648: Test Method for Deflection Temperature of Plastics
• ASTM D1599: Test Method for Resistance to Hydraulic Pressure
• ASTM D5421: Specification for Contact-Molded “Fiberglass” Flanges
• NSF Standard 61: Drinking Water System Components – Health Effects

Adhering to ASTM D6041-23 ensures compatibility and safety across a wide range of demanding industrial applications requiring corrosion-resistant fiberglass piping systems.

Standards Content (Sample)

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.
Designation: D6041 − 23
Standard Specification for
Contact-Molded “Fiberglass” (Glass-Fiber-Reinforced
Thermosetting Resin) Corrosion Resistant Pipe and
Fittings
This standard is issued under the fixed designation D6041; 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.
1. Scope* 2. Referenced Documents
2.1 ASTM Standards:
1.1 This specification covers pipe and fittings fabricated by
C581 Practice for Determining Chemical Resistance of
contact molding, for pressures to 150 psi and made of a
Thermosetting Resins Used in Glass-Fiber-Reinforced
commercial-grade polyester resin. Included are requirements
Structures Intended for Liquid Service
for materials, properties, design, construction, dimensions,
C582 Specification for Contact-Molded Reinforced Thermo-
tolerances, workmanship, and appearance.
setting Plastic (RTP) Laminates for Corrosion-Resistant
1.2 This specification does not cover resins other than
Equipment
polyester, reinforcing materials other than glass fibers or
D618 Practice for Conditioning Plastics for Testing
fabrication methods other than contact molding.
D638 Test Method for Tensile Properties of Plastics
NOTE 1—For the purposes of this specification, the term polyester resin D648 Test Method for Deflection Temperature of Plastics
will include both polyester and vinylester resins.
Under Flexural Load in the Edgewise Position
D883 Terminology Relating to Plastics
1.3 This specification does not cover the design of pipe and
D1599 Test Method for Resistance to Short-Time Hydraulic
fittings intended for use with liquids heated above their flash
Pressure of Plastic Pipe, Tubing, and Fittings
points.
D1600 Terminology for Abbreviated Terms Relating to Plas-
1.4 The values stated in inch-pound units are to be regarded
tics
as the standard. The SI units given in parentheses are provided
D2583 Test Method for Indentation Hardness of Rigid Plas-
for information purposes only.
tics by Means of a Barcol Impressor (Withdrawn 2022)
D2584 Test Method for Ignition Loss of Cured Reinforced
1.5 The following precautionary caveat pertains only to
Resins
Section 10, the test methods portion, of this specification: This
D3567 Practice for Determining Dimensions of “Fiberglass”
standard does not purport to address all of the safety concerns,
(Glass-Fiber-Reinforced Thermosetting Resin) Pipe and
if any, associated with its use. It is the responsibility of the user
Fittings
of this standard to establish appropriate safety, health, and
D3681 Test Method for Chemical Resistance of “Fiberglass”
environmental practices and determine the applicability of
(Glass–Fiber–Reinforced Thermosetting-Resin) Pipe in a
regulatory limitations prior to use.
Deflected Condition
NOTE 2—There is no known ISO equivalent to this standard.
D5421 Specification for Contact Molded “Fiberglass”
1.6 This international standard was developed in accor-
(Glass-Fiber-Reinforced Thermosetting Resin) Flanges
dance with internationally recognized principles on standard-
F412 Terminology Relating to Plastic Piping Systems
ization established in the Decision on Principles for the
2.2 ANSI Standards:
Development of International Standards, Guides and Recom-
B16.1 Cast Iron Pipe Flanges and Flanged Fittings
mendations issued by the World Trade Organization Technical
B16.5 Pipe Flanges and Flanged Fittings
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
This specification is under the jurisdiction of ASTM Committee D20 on Standards volume information, refer to the standard’s Document Summary page on
Plastics and is the direct responsibility of Subcommittee D20.23 on Reinforced the ASTM website.
Thermosetting Resin Piping Systems and Chemical Equipment. The last approved version of this historical standard is referenced on
Current edition approved Aug. 1, 2023. Published August 2023. Originally www.astm.org.
approved in 1996. Last previous edition approved in 2018 as D6041 – 18. DOI: Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/D6041-23. 4th Floor, New York, NY 10036, http://www.ansi.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6041 − 23
approached carefully. It is not uncommon for specified operating condi-
B18.22 Type “B” Narrow Washers
tions to be overstated in an attempt to achieve a higher safety margin.
2.3 National Sanitation Foundation Standard:
NSF Standard 61 Drinking Water System Components— 4.1.1.1 The use of one resin in the corrosion barrier and a
Health Effects different resin in the structural layer (see Section 6) is permit-
ted with the acceptance of the purchaser.
3. Terminology
4.1.2 Additives, such as additional styrene, fillers, dyes,
pigments, or flame retardants may be used when agreed upon
3.1 Definitions:
between the manufacturer and purchaser. Thixotropic agents
3.1.1 General—Definitions are in accordance with Termi-
may be added to the resin for viscosity control.
nology D883 and Terminology F412 and abbreviations are in
accordance with Terminology D1600, unless otherwise indi-
NOTE 6—The addition of fillers, dyes, pigments, flame retardants, and
cated. The abbreviation for reinforced thermosetting resin pipe
thixotropic agents may interfere with visual inspection of laminate quality.
is RTRP.
NOTE 7—Chemical resistance can be affected by the catalyst/promoter
system, diluents, dyes, fillers, flame retardants, or thixotropic agents used
3.2 Definitions of Terms Specific to This Standard:
in the resin.
3.2.1 contact molding, n—a process for molding reinforced
NOTE 8—Antimony compounds or other fire-retardant agents may be
plastics in which reinforcement and resin are placed on an open
added to halogenated resins for improved fire resistance, if agreed upon
mold or mandrel by either the “hand lay-up”(where resin and between the manufacturer and the purchaser. These compounds do not
improve the flame retardancy of non-halogenated resins.
glass mat are applied by hand), or the “spray-up” manufactur-
ing processes (where resin and chopped glass fibers are sprayed
4.1.3 Ultraviolet Absorbers may be added for improved
under pressure), or a combination of the two. The resulting
weather resistance when agreed upon between the manufac-
laminate is then consolidated by rolling and cured without the
turer and the purchaser.
application of pressure.
4.1.4 Resin Putty, used where necessary to fill crevices at
joints prior to applying the joint laminate shall not be subject
3.2.2 fiberglass pipe, n—a tubular product containing glass
to the limitations of 4.1.3. Putty shall be made with resin and
fiber reinforcements embedded in or surrounded by cured
fillers. The resin used in the putty must be compatible with the
thermosetting resin. The composite structure may contain
resin used in the pipe and fittings.
granular or platelet fillers, thixotropic agents, pigments, or
dyes. Thermoplastic or thermosetting liners may be included.
4.2 Fiber Reinforcements:
3.2.3 polyester, n—resins produced by the polycondensation
4.2.1 Surfacing Mat (Veil) is a thin mat of fine fibers used
of dihydroxy glycols and dibasic organic acids or anhydrides,
primarily to produce a smooth and corrosion–resistant resin-
wherein at least one component contributes ethylenic unsatu-
–rich surface on a reinforced plastic laminate.
ration yielding resins that can be compounded with styrol
4.2.1.1 Veils are made from chemical resistant (type “C”)
monomers and reacted to give highly crosslinked thermoset
glass or organic fiber. The use of an organic-fiber surface mat
copolymers.
is recommended for environments that attack glass. The veil
3.2.4 vinyl ester, n—resins characterized by reactive unsatu- used in a laminate shall be determined to be acceptable for the
ration located predominately in terminal positions that can be chemical service either by Practice C581 or by verified case
compounded with styrol monomers and reacted to give highly history.
crosslinked thermoset copolymers. 4.2.1.2 The veil shall be a minimum of 10 mils in dry
thickness and produce a thickness of 0.010 to 0.020 in. (0.25 to
4. Materials and Manufacture
0.50 mm) when saturated with resin.
NOTE 3—Specification C582 provides additional information on the
materials and manufacturing of contact–molded laminates.
NOTE 9—The primary chemical resistance of the RTR pipe is provided
NOTE 4—Fiberglass pipe intended for use in the transport of potable by the resin. In combination with the cured resin, the surfacing veil helps
water should be evaluated and certified as safe for this purpose by a testing
determine the thickness of the resin-rich layer, and reduces micro
agency acceptable to the local health authority. The evaluation should be cracking.
in accordance with requirements for chemical extraction, taste, and odor
4.2.2 Chopped-strand Reinforcements shall be “E”-type or
that are no less restrictive than those included in National Sanitation
“ECR”-type glass fibers 1 to 2 in. (25 to 50 mm) long applied
Foundation (NSF) Standard 61. The seal or mark of the laboratory making
the evaluation should be included on the fiberglass pipe.
in a uniform layer with random orientation. The fibers shall
have a sizing compatible with the selected resin. Chopped
4.1 Resin System:
strand reinforcements may be purchased and applied as a mat
4.1.1 The resin used shall be a commercial grade, corrosion-
or as continuous strand roving which is chopped into short
resistant polyester that has been determined to be acceptable
lengths and sprayed onto the laminate in a process known as
for the service either by test, (see Practice C581), or by
“spray up.” Either form is most commonly applied in layers
previous documented service. Where service conditions have
2 2
weighing 1 ⁄2 oz/ft (450 g ⁄m ) although other weights are
not been evaluated a suitable resin may also be selected by
available and may be used.
agreement between manufacturer and purchaser.
4.2.3 Woven Roving, shall be “E”-type or “ECR”-type glass
NOTE 5—The use of “previous documented service” needs to be
roving, woven into a fabric. The sizing on the roving shall be
compatible with the selected resin. The most common woven
roving has a 5 by 4 weave and a weight of 24 oz/yd (832
Available from NSF International, P.O. Box 130140, 789 N. Dixboro Rd., Ann
Arbor, MI 48113-0140, http://www.nsf.org. g/m ).
D6041 − 23
4.2.4 Non-woven Roving “E type or “ECR” glass reinforc- supports should also be considered. The minimum wall thick-
ing fabrics such as biaxials and uni-directionals may be used in ness shall be the greater of 0.18 in. (4.5 mm) or 1 % of the pipe
special applications such as reinforcing tees and other fittings inside diameter.
or to improve the physical properties of the laminate in a
P*ID
~ !
t 5
specific direction.
2*S 2 P
~ !
4.2.5 Multiple Layer Reinforcements are fabrics composed
where:
of two or more layers of reinforcement combined into one
t = calculated wall thickness, in. (mm) (see 6.1.2.3),
fabric. A common form is one layer of 1 ⁄2 oz/ft chopped
P = design pressure, psi (kPa),
strand mat combined with one layer of 24 oz/yd woven
ID = inside diameter of the pipe, in. (mm),
roving. The pipe manufacturer must use extra caution to ensure
S = allowable stress (not to exceed ⁄10 of the Class A
proper laminate quality is maintained when using multiple
design basis per 5.1.1 or ⁄6 of the Class B design basis
layer reinforcements.
per 5.1.2), psi (kPa).
5.3 Standard pressure classes are 25, 50, 75, 100, 125, and
5. Design
150 psi, however, custom classes are allowed.
5.1 Design Basis:
NOTE 12—Special design consideration should be given to pipe and
5.1.1 Class A (Design by Rules)—For pipe to be manufac-
fittings subject to vacuum or superimposed mechanical forces, or both,
such as earthquakes, wind load, or burial loads, and to pipe and fittings
tured using Type I or Type II laminates as described in
subject to service temperature in excess of 180°F (82°C).
Specification C582, the Ultimate Tensile Strengths shown in
Specification C582 may be used for the design basis.
6. Laminates
5.1.2 Class B (Design by Testing)—For pipe manufactured
6.1 Laminate Construction—The laminate comprising the
with other than Type I or Type II laminates (in accordance with
pipe wall shall consist of a corrosion barrier comprised of an
Specification C582), or for Ultimate Tensile Strengths to be
inner surface and interior layer, a structural layer, and an outer
determined by destructive tests, testing in accordance with 10.5
surface.
or 10.6 is required to establish a design basis for each laminate
6.1.1 The Corrosion Barrier, consisting of the inner surface
type used by the pipe manufacturer. Testing shall be performed
and interior layers, shall be included in the total thickness for
on a sample laminate or pipe of the same type and construction
all design calculations unless otherwise specified.
as will be used on the actual pipe and fittings. The thickness of
6.1.1.1 Inner Surface—The inner surface exposed to the
the laminate sample will be ⁄8 in. (9.5 mm) or the maximum
chemical environment shall be resin-rich and reinforced with at
thickness to be provided in the pipe and fittings, whichever is
least one layer of a suitable surfacing veil in accordance with
less. If testing in accordance with 10.6, testing is required in
4.2.1. Some chemical environments may warrant the use of a
both directions if the reinforcement is not applied equally in
second layer of surfacing veil. This resin-rich inner surface will
both directions. The laminate sample shall not include a
contain less than 20 % by weight of reinforcing material and
corrosion barrier. Laminates greater than ⁄8 in. (9.5 mm) thick
have a thickness between 0.010 and 0.020 in. (0.25 to 0.50
are to be constructed with standard repeating sequences of
mm)
reinforcement such as those described in Specification C582.
6.1.1.2 Interior Layer—The inner surface layer shall be
Results from previously tested laminates may be used provided
followed with a layer composed of resin reinforced only with
that such laminates were manufactured with the same resin,
non-continuous glass-fiber strands. This reinforcement shall be
laminate type, and thickness within the previous five years.
applied as chopped strand mat or as chopped roving (spray up
2 2
NOTE 10—Reinforcements such as 24 oz/yd (832 g/m ) produced with
process) (either in accordance with 4.2.2) resulting in a
a 5 by 4 weave are considered equal in both directions for the purpose of
2 2
minimum reinforcement weight of 1 ⁄2 oz/ft (459 g/m ). The
5.1.2.
combined thickness of the inner surface and interior layer shall
5.1.3 Temperature Limits—Service temperature shall be
not be less than 0.05 in. Depending on the chemical
2 2
considered in the design of RTRP pipe unless the service
environment, multiple 1 ⁄2 oz/ft (459 g/m ) layers of chopped
temperature is the lower of 150°F (65°C) or 35°F (19°C) below
strand applied as mat or spray up may be required. Two layers
the resin Heat Deflection Temperature (HDT) in accordance
are most commonly used with as many as four or five layers
with Test Method D648. When the service temperature exceeds
occasionally used in severe environments. When multiple
these limits, testing in accordance with 10.4 shall be performed
layers are used, each ply of mat or pass of chopped roving shall
at the service temperature with samples conditioned in accor-
be well rolled to eliminate all trapped air prior to the applica-
dance with Practice D618.
tion of additional reinforcement. Glass content of the inner
surface and the interior layer combined shall be 27 6 5 % by
NOTE 11—The use of ambient temperature property values for elevated
weight, when tested in accordance with 10.4.
temperature service when using polyester resins should be considered
carefully. Some combinations of temperature, chemical environment and
6.1.2 Structural Layer—Subsequent reinforcement shall be
laminate stress(strain) may result in the need to use reduced properties or
Type I or Type II or “other” as described below. Types I and II
increased safety factors to achieve the desired performance.
are described in further detail including laminate sequences
5.2 Wall Thickness—The required wall thickness due to and thicknesses in Specification C582.
internal pressure shall be determined by the following formula. 6.1.2.1 Type I laminates consist of multiple layers of 1.5
2 2
Other loads such as thermal expansion and bending between oz/ft (0.46 kg/m ) chopped strand mat or equivalent weight of
D6041 − 23
chopped roving as required to achieve the thickness as calcu- 6.2.2 The minimum width of the first layer of joint overlay
lated according to Section 5. Each successive ply or pass of shall be 3 in. (76 mm). Successive layers shall increase in
reinforcement shall be well-rolled prior to the application of width to form a uniform taper. The total width of the joint
additional reinforcement. The exterior surface shall be rela- laminate shall be at least twelve times the joint thickness plus
tively smooth with no exposed fibers or sharp projections and the width of the first layer and shall be centered on the joint.
enough resin shall be pres
...

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: D6041 − 18 D6041 − 23
Standard Specification for
Contact-Molded “Fiberglass” (Glass-Fiber-Reinforced
Thermosetting Resin) Corrosion Resistant Pipe and
Fittings
This standard is issued under the fixed designation D6041; 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.
1. Scope*
1.1 This specification covers pipe and fittings fabricated by contact molding, for pressures to 150 psi and made of a
commercial-grade polyester resin. Included are requirements for materials, properties, design, construction, dimensions, tolerances,
workmanship, and appearance.
1.2 This specification does not cover resins other than polyester, reinforcing materials other than glass fibers or fabrication
methods other than contact molding.
NOTE 1—For the purposes of this specification, the term polyester resin will include both polyester and vinylester resins.
1.3 This specification does not cover the design of pipe and fittings intended for use with liquids heated above their flash points.
1.4 The values stated in inch-pound units are to be regarded as the standard. The SI units given in parentheses are provided for
information purposes only.
1.5 The following precautionary caveat pertains only to Section 10, the test methods portion, 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 2—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:
This specification is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.23 on Reinforced Plastic
Thermosetting Resin Piping Systems and Chemical Equipment.
Current edition approved Nov. 1, 2018Aug. 1, 2023. Published November 2018August 2023. Originally approved in 1996. Last previous edition approved in 20112018
as D6041 – 11.D6041 – 18. DOI: 10.1520/D6041-18.10.1520/D6041-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6041 − 23
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
D648 Test Method for Deflection Temperature of Plastics Under Flexural Load in the Edgewise Position
D883 Terminology Relating to Plastics
D1599 Test Method for Resistance to Short-Time Hydraulic Pressure of Plastic Pipe, Tubing, and Fittings
D1600 Terminology for Abbreviated Terms Relating to Plastics
D2583 Test Method for Indentation Hardness of Rigid Plastics by Means of a Barcol Impressor (Withdrawn 2022)
D2584 Test Method for Ignition Loss of Cured Reinforced Resins
D3567 Practice for Determining Dimensions of “Fiberglass” (Glass-Fiber-Reinforced Thermosetting Resin) Pipe and Fittings
D3681 Test Method for Chemical Resistance of “Fiberglass” (Glass–Fiber–Reinforced Thermosetting-Resin) Pipe in a Deflected
Condition
D5421 Specification for Contact Molded “Fiberglass” (Glass-Fiber-Reinforced Thermosetting Resin) Flanges
F412 Terminology Relating to Plastic Piping Systems
2.2 ANSI Standards:
B16.1 Cast Iron Pipe Flanges and Flanged Fittings
B16.5 Pipe Flanges and Flanged Fittings
B18.22 Type “B” Narrow Washers
2.3 National Sanitation Foundation Standard:
NSF Standard 61 Drinking Water System Components—Health Effects
3. Terminology
3.1 Definitions:
3.1.1 General—Definitions are in accordance with Terminology D883 and Terminology F412 and abbreviations are in accordance
with Terminology D1600, unless otherwise indicated. The abbreviation for reinforced thermosetting resin pipe is RTRP.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 contact molding, n—a process for molding reinforced plastics in which reinforcement and resin are placed on an open mold
or mandrel by either the “hand lay-up”(where resin and glass mat are applied by hand), or the “spray-up” manufacturing processes
(where resin and chopped glass fibers are sprayed under pressure), or a combination of the two. The resulting laminate is then
consolidated by rolling and cured without the application of pressure.
3.2.2 fiberglass pipe, n—a tubular product containing glass fiber reinforcements embedded in or surrounded by cured
thermosetting resin. The composite structure may contain granular or platelet fillers, thixotropic agents, pigments, or dyes.
Thermoplastic or thermosetting liners may be included.
3.2.3 polyester, n—resins produced by the polycondensation of dihydroxy glycols and dibasic organic acids or anhydrides, wherein
at least one component contributes ethylenic unsaturation yielding resins that can be compounded with styrol monomers and
reacted to give highly crosslinked thermoset copolymers.
3.2.4 vinyl ester, n—resins characterized by reactive unsaturation located predominately in terminal positions that can be
compounded with styrol monomers and reacted to give highly crosslinked thermoset copolymers.
4. Materials and Manufacture
NOTE 3—Specification C582 provides additional information on the materials and manufacturing of contact–molded laminates.
NOTE 4—Fiberglass pipe intended for use in the transport of potable water should be evaluated and certified as safe for this purpose by a testing agency
acceptable to the local health authority. The evaluation should be in accordance with requirements for chemical extraction, taste, and odor that are no
less restrictive than those included in National Sanitation Foundation (NSF) Standard 61. The seal or mark of the laboratory making the evaluation should
be included on the fiberglass pipe.
The last approved version of this historical standard is referenced on www.astm.org.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from NSF International, P.O. Box 130140, 789 N. Dixboro Rd., Ann Arbor, MI 48113-0140, http://www.nsf.org.
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4.1 Resin System:Resin System:
4.1.1 The resin used shall be a commercial grade, corrosion-resistant polyester that has been determined to be acceptable for the
service either by test, (see Practice C581), or by previous documented service. Where service conditions have not been evaluated
a suitable resin may also be selected by agreement between manufacturer and purchaser.
NOTE 5—The use of “previous documented service” needs to be approached carefully. It is not uncommon for specified operating conditions to be
overstated in an attempt to achieve a higher safety margin.
4.1.1.1 The use of one resin in the corrosion barrier and a different resin in the structural layer (see Section 6) is permitted with
the acceptance of the purchaser.
4.1.2 Additives, Additives,such as additional styrene, fillers, dyes, pigments, or flame retardants may be used when agreed upon
between the manufacturer and purchaser. Thixotropic agents may be added to the resin for viscosity control.
NOTE 6—The addition of fillers, dyes, pigments, flame retardants, and thixotropic agents may interfere with visual inspection of laminate quality.
NOTE 7—Chemical resistance can be affected by the catalyst/promoter system, diluents, dyes, fillers, flame retardants, or thixotropic agents used in the
resin.
NOTE 8—Antimony compounds or other fire-retardant agents may be added to halogenated resins for improved fire resistance, if agreed upon between
the manufacturer and the purchaser. These compounds do not improve the flame retardancy of non-halogenated resins.
4.1.3 Ultraviolet Absorbers Ultraviolet Absorbersmay be added for improved weather resistance when agreed upon between the
manufacturer and the purchaser.
4.1.4 Resin Putty, Resin Putty,used where necessary to fill crevices at joints prior to applying the joint laminate shall not be subject
to the limitations of 4.1.3. Putty shall be made with resin and fillers. The resin used in the putty must be compatible with the resin
used in the pipe and fittings.
4.2 Fiber Reinforcements:Fiber Reinforcements:
4.2.1 Surfacing Mat (Veil) Surfacing Mat (Veil)is a thin mat of fine fibers used primarily to produce a smooth and
corrosion–resistant resin–rich surface on a reinforced plastic laminate.
4.2.1.1 Veils are made from chemical resistant (type “C”) glass or organic fiber. The use of an organic-fiber surface mat is
recommended for environments that attack glass. The veil used in a laminate shall be determined to be acceptable for the chemical
service either by Practice C581 or by verified case history.
4.2.1.2 The veil shall be a minimum of 10 mils in dry thickness and produce a thickness of 0.010 to 0.020 in. (0.25 to 0.50 mm)
when saturated with resin.
NOTE 9—The primary chemical resistance of the RTR pipe is provided by the resin. In combination with the cured resin, the surfacing veil helps determine
the thickness of the resin-rich layer, and reduces micro cracking.
4.2.2 Chopped-strand Reinforcements shall be “E”-type or “ECR”-type glass fibers 1 to 2 in. (25 to 50 mm) long applied in a
uniform layer with random orientation. The fibers shall have a sizing compatible with the selected resin. Chopped strand
reinforcements may be purchased and applied as a mat or as continuous strand roving which is chopped into short lengths and
sprayed onto the laminate in a process known as “spray up.” Either form is most commonly applied in layers weighing 1 ⁄2 oz/ft
(450 g ⁄m ) although other weights are available and may be used.
4.2.3 Woven Roving, shall be “E”-type or “ECR”-type glass roving, woven into a fabric. The sizing on the roving shall be
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compatible with the selected resin. The most common woven roving has a 5 by 4 weave and a weight of 24 oz/yd (832 g/m ).
4.2.4 Non-woven Roving “E type or “ECR” glass reinforcing fabrics such as biaxials and uni-directionals may be used in special
applications such as reinforcing tees and other fittings or to improve the physical properties of the laminate in a specific direction.
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4.2.5 Multiple Layer Reinforcements are fabrics composed of two or more layers of reinforcement combined into one fabric. A
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common form is one layer of 1 ⁄2 oz/ft chopped strand mat combined with one layer of 24 oz/yd woven roving. The pipe
manufacturer must use extra caution to ensure proper laminate quality is maintained when using multiple layer reinforcements.
5. Design
5.1 Design Basis:
5.1.1 Class A—A (Design by Rules)—For pipe to be manufactured using Type I or Type II laminates as described in Specification
C582, the Ultimate Tensile Strengths shown in Specification C582 may be used for the design basis.
5.1.2 Class B—B (Design by Testing)—For pipe manufactured with other than Type I or Type II laminates (in accordance with
Specification C582), or for Ultimate Tensile Strengths greater than those shown into be determined by destructive C582,tests,
testing in accordance with 10.5 or 10.6 is required to establish a design basis for each laminate type used by the pipe manufacturer.
Testing shall be performed on a sample laminate or pipe of the same type and construction as will be used on the actual pipe and
fittings. The thickness of the laminate sample will be ⁄8 in. (9.5 mm) or the maximum thickness to be provided in the pipe and
fittings, whichever is less. If testing in accordance with 10.6, testing is required in both directions if the reinforcement is not applied
equally in both directions. The laminate sample shall not include a corrosion barrier. Laminates greater than ⁄8 in. (9.5 mm) thick
are to be constructed with standard repeating sequences of reinforcement such as those described in Specification C582. Results
from previously tested laminates may be used provided that such laminates were manufactured with the same resin, laminate type,
and thickness within the previous five years.
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NOTE 10—Reinforcements such as 24 oz/yd (832 g/m ) produced with a 5 by 4 weave are considered equal in both directions for the purpose of 5.1.2.
5.1.3 Temperature Limits—Service temperature shall be considered in the design of RTRP pipe unless the service temperature is
the lower of 150°F (65°C) or 35°F (19°C) below the resin Heat Deflection Temperature (HDT) in accordance with Test Method
D648. When the service temperature exceeds these limits, testing in accordance with 10.4 shall be performed at the service
temperature with samples conditioned in accordance with Practice D618.
NOTE 11—The use of ambient temperature property values for elevated temperature service when using polyester resins should be considered carefully.
Some combinations of temperature, chemical environment and laminate stress(strain) may result in the need to use reduced properties or increased safety
factors to achieve the desired performance.
5.2 Wall Thickness—The required wall thickness due to internal pressure shall be determined by the following formula. Other
loads such as thermal expansion and bending between supports should also be considered. The minimum wall thickness shall be
the greater of 0.18 in. (4.5 mm) or 1 % of the pipe inside diameter.
P*ID
~ !
t 5
~2*S 2 P!
where:
t = calculated wall thickness, in. (mm) (see 6.1.2.3),
P = design pressure, psi (kPa),
ID = inside diameter of the pipe, in. (mm),
1 1
S = allowable stress (not to exceed ⁄10 of the Class A design basis per 5.1.1 or ⁄6 of the Class B design basis per 5.1.2), psi
(kPa).
5.3 Standard pressure classes are 25, 50, 75, 100, 125, and 150 psi, however, custom classes are allowed.
NOTE 12—Special design consideration should be given to pipe and fittings subject to vacuum or superimposed mechanical forces, or both, such as
earthquakes, wind load, or burial loads, and to pipe and fittings subject to service temperature in excess of 180°F (82°C).
6. Laminates
6.1 Laminate Construction—The laminate comprising the pipe wall shall consist of a corrosion barrier comprised of an inner
surface and interior layer, a structural layer, and an outer surface.
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6.1.1 The Corrosion Barrier, consisting of the inner surface and interior layers, shall be included in the total thickness for all
design calculations unless otherwise specified.
6.1.1.1 Inner Surface—The inner surface exposed to the chemical environment shall be resin-rich and reinforced with at least one
layer of a suitable surfacing veil in accordance with 4.2.1. Some chemical environments may warrant the use of a second layer
of surfacing veil. This resin-rich inner surface will contain less than 20 % by weight of reinforcing material and have a thickness
between 0.010 and 0.020 in. (0.25 to 0.50 mm)
6.1.1.2 Interior Layer—The inner surface layer shall be followed with a layer composed of resin reinforced only with
non-continuous glass-fiber strands. This reinforcement shall be applied as chopped strand mat or as chopped roving (spray up
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process) (either in accordance with 4.2.2) resulting in a minimum reinforcement weight of 1 ⁄2 oz/ft (459 g/m ). The combined
thickness of the inner surface and interior layer shall not be less than 0.05 in. Depending on the chemical environment, multiple
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1 ⁄2 oz/ft (459 g/m ) layers of chopped strand applied as mat or spray up may be required. Two layers are most commonly used
with as many as four or five layers occasionally used in severe environments. When multiple layers are used, each ply of mat or
pass of chopped roving shall be well rolled to eliminate all trapped air prior to the application of additional reinforcement. Glass
content of the inner surface and the interior layer combined shall be 27 6 5 % by weight, when tested in accordance with 10.4.
6.1.2 Structural Layer—Subsequent reinforcement shall be Type I or Type II or “other” as described below. Types I and II are
described in further detail including laminate sequences and thicknesses in Specification C582.
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6.1.2.1 Type I laminates consist of multiple layers of 1.5 oz/ft (0.46 kg/m ) chopped strand mat or equivalent weight of chopped
roving as required to achieve the thickness as calculated according to Section 5. Each successive ply or pass of reinforcement shall
be well-rolled prior to the application of additional reinforcement. The exterior surface shall be relatively smooth with no exposed
fibers or sharp projections and enough resin shall be present to prevent fiber show.
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6.1.2.2 Type II laminates consist of multiple layers of 1.5 oz/ft (0.46 kg/m ) chopped strand mat or equivalent weight of chopped
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roving alternating with layers of 24 oz/yd (814 g/m ) woven or non-woven roving as required to achieve the thickness as
calculated according to Section 5. Each successive ply or pass of reinfo
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