ASTM C581 - 20

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Designation: C581 −20
Standard Practice for
Determining Chemical Resistance of Thermosetting Resins
Used in Glass-Fiber-Reinforced Structures Intended for
Liquid Service
1
This standard is issued under the ﬁxed designation C581; 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 practice is designed to evaluate, in an unstressed
state, the chemical resistance of thermosetting resins used in
the fabrication of reinforced thermosetting plastic (RTP) lami-
nates. This practice provides for the determination of changes
in the properties, described as follows, of the test specimens
and test reagent after exposure of the specimens to the reagent:
hardness of specimens, weight change thickness, appearance of
specimens, appearance of immersion media, and ﬂexural
strength and modulus.
1.1.1 This practice is also useful to evaluate other factors,
such as surfacing veils and the effect of resin additives, on the
chemical resistance of the resin.
1.2 The values stated in inch-pound units are to be regarded
as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only
and are not considered standard.
NOTE 1—There is no known ISO equivalent to this standard.
1.3 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 appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
2
D790 Test Methods for Flexural Properties of Unreinforced
and Reinforced Plastics and Electrical Insulating Materi-
als
D883 Terminology Relating to Plastics
D2563 Practice for Classifying Visual Defects in Glass-
Reinforced Plastic Laminate Parts
D2583 Test Method for Indentation Hardness of Rigid Plas-
tics by Means of a Barcol Impressor
D2584 Test Method for Ignition Loss of Cured Reinforced
Resins
3. Terminology
3.1 Deﬁnitions of Terms:
3.1.1 For deﬁnitions of terms associated with plastic
materials, see Terminology D883.
4. Signiﬁcance and Use
4.1 The results obtained by this practice shall serve as a
guide in, but not as the sole basis for, selection of a thermo-
setting resin used in an RTP structure. No attempt has been
made to incorporate into the practice all the various factors that
will potentially affect the serviceability of an RTP structure
when subjected to chemical environments. These factors will
potentially include stress, different resin-to-glass ratios, and
multiple veils.
5. Apparatus
5.1 Hardness Testing Instrument—This shall be as described
in Test Method D2583.
1
This practice 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 Feb. 15, 2020. Published March 2020. Originally
approved in 1965. Last previous edition approved in 2015 as C581 – 15. DOI:
10.1520/C0581-20.
2
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.
*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
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.

5.2 Flexural Properties Testing Apparatus, in accordance

with Test Methods D790.

5.3 Thickness Measurement—A micrometer suitable for

measurement to 0.001 in. (0.025 mm).

5.4 Containers, of sufficient size, capacity, and inertness to

allow total immersion of reinforced thermosetting plastic

specimens in the speciﬁc corrosives chosen for testing. These

containers shall, when necessary, be capable of maintaining

liquid levels of volatile solutions, that is, solvents. This can be

accomplished by the use of reﬂux condensers.

5.5 Heating Apparatus—A constant temperature oven, heat-

ing mantle, or liquid bath capable of maintaining temperature

within range of 64.0°F (62.2°C). Take proper precautions if

the corrosives selected are ﬂammable liquids.

5.6 Analytical Balance, suitable for accurate weighing to

0.001 g.

6. Reagents

6.1 The test media shall consist of the reagents or solutions

to which the RTP laminates are to be exposed.

7. Test Specimens

7.1 Standard Laminates—Prepare standard ﬁber-reinforced

laminates using identical reinforcement in all of the laminates.

The laminates shall be constructed of the following materials:

7.1.1 Surfacing Mat (Veil)—A thin mat of ﬁne ﬁbers used

primarily to produce a smooth, resin-rich surface on a rein-

forced plastic. The surfacing veil helps determine the thickness

of the resin-rich layer, reduces microcracking and provides a

non-wicking chemically–resistant layer. The surfacing veil

shall be compatible with the resin and manufactured with

uniform ﬁber distribution and non-bundled ﬁbers. The dry veil

layer(s) shall be a minimum 10 mils in thickness and produce

a 10 to 15 mil resin-saturated veil layer per 10 mils of dry veil.

To eliminate the surfacing veil as a variable in corrosion tests,

prepare each laminate within a test group with the same

surfacing veil.

7.1.2 Chopped Strand Mat—Type E glass ﬁber with sizing

and binder compatible with the resin. It is acceptable to use

other glass ﬁber compositions, but using such alternate com-

positions shall be considered as variables for comparison to the

standard.

7.1.2.1 Note that this practice applies to E-CR glass ﬁber,

which is a type of E glass ﬁber. If the E glass ﬁber material is

of the E-CR type that information shall be identiﬁed in the test

report.

7.1.3 Resin—Catalyzed and promoted in accordance with

the resin manufacturer’s recommendation.

NOTE 2—It is acceptable to add ﬁllers, such as antimony trioxide for

improved ﬁre performance or thixotropes for viscosity control, but it is

possible that this will detract from the corrosion resistance of the test

laminate.

7.2 Dimensions and General Properties—The laminates

shall conform to the required dimensions and general proper-

ties of 7.2 and be fabricated in accordance with 7.3.

7.2.1 Laminate Size—A suitable laminate size has been

found to be 26 by 33 in. (660 by 838 mm) after trimming. This

laminate size is not restrictive and other dimensions are

acceptable.

7.2.2 Thickness—The thickness of the cured standard lami-

nate shall be between 0.120 and 0.140 in. (3.05 and 3.56 mm).

7.2.3 Reinforcement Content—The glass ﬁber and binder

shall be 4.73 60.47 oz/ft

(three layers of 1.5 oz/ft

chopped

strand mat 4.5 oz/ft

having a nominal binder content of 3.5 %

and two layers of 10 mil surfacing mat 0.23 oz/ft

having a

nominal binder content of 7 %)—determined by pre-weighing

the materials prior to construction of the laminate. This is

equivalent to 23.6 weight % (12.5 volume %) glass ﬁber when

using a resin having a cured speciﬁc gravity of 1.15. Such a

laminate will have a thickness of 0.125 in. (3.18 mm). The use

of resins having different speciﬁc gravities will result in

different weight percentages of glass ﬁber, but the volume

percentage of glass ﬁber will remain the same. When using

synthetic organic ﬁber surfacing veil, the glass content shall be

4.50 60.45 oz/ft

(three layers of 1.5 oz/ft

chopped strand

mat having a nominal binder content of 3.5 %).

7.2.4 Hardness—The hardness shall be at least 90 % of that

of a fully-cured clear casting of the resin, or of a similarly

constructed laminate as deﬁned by the resin manufacturer.

Hardness shall be determined in accordance with s5.1. Note

that the use of synthetic veil will result in signiﬁcantly lower

hardness values. The hardness value will vary with the type of

resin and number of plies of synthetic veil. The resin manu-

facturer needs to be contacted for the allowable Barcol

hardness value of a laminate containing synthetic veils with the

speciﬁc resin.

7.2.5 Laminate Condition—The laminate shall meet Accep-

tance Level I of Table I of Practice D2563.

7.3 Fabrication of Standard Laminate—The sequence of

lay-up shall be as follows:

7.3.1 Apply catalyzed resin and a 10-mil (0.25-mm) surfac-

ing mat on a ﬂat surface covered with plastic release ﬁlm or

treated with a suitable release agent and roll to distribute resin.

NOTE 3—Use the following formula as a guide to determine the total

weight of resin to be used. This is equivalent to 12.5 volume % glass ﬁber

in the laminate. Grams resin equals grams glass ﬁber material per 7.2.3

times 2.82 G. Where Gequals speciﬁc gravity of cured resin. It is

acceptable to use excess resin due to loss by adhering to mixing

containers, rollers, and other factors. A suggested amount of excess resin

is 10 to 15 % by weight.

7.3.2 Follow with three plies of 1.5 oz/ft

chopped strand

mat and resin. Roll after each ply to distribute and wet-out the

chopped strand mat. Rolling with a serrated roller is acceptable

after each ply to remove entrapped air but it shall be done in

accordance with 7.3.4. The mat weight shall be within 65%of

1.5 oz/ft

upon weighing the full 26 by 33-in. cut (660 by

838-mm) piece, (or other full dimension used, 7.2.1.).

NOTE 4—Cut chopped strand mat so that the 26-in. dimension is across

the width of the roll and the 33-in. dimension is along the machine

direction of the mat. Mat weight variation will most commonly occur

across the width of the mat. If a wide roll of mat, 52 in. (1320 mm) or

greater, is used, place the two plies of mat in the laminate such that the

center cut of one ply is placed over the outside edge of the second ply. If

narrower width mat is used, reverse the second ply 180° in the machine

C581 − 20

direction and lay it on top of the ﬁrst ply to minimize weight variations.
7.3.3 Follow with a 10-mil (0.25-mm) surfacing mat as in
7.3.1.
7.3.4 Remove the air by rolling over the surface with a
serrated metal or plastic roller. Take care not to expel enough
resin to raise the glass content above the permissible maxi-
mum. The laminate is considered within the range of allowable
levels of resin and glass if the thickness of the laminate is
within 0.120 and 0.140 in. (3.05 and 3.56 mm), as described in
7.2.2.
7.3.5 After the lay-up is completed, cover the laminate with
a plastic release ﬁlm to prevent air inhibition or to provide a
uniform smooth glossy surface, or both. Carefully smooth
down to remove entrapped air.
NOTE 5—It is acceptable to use any convenient method for the
application of the release ﬁlm. Regardless of how it is applied, it is critical
that any entrapped air between the ﬁlm and the laminate be entirely
removed. One method of application is done by previously wrapping the
ﬁlm around a metal rod. Starting at one edge of the laminate, slowly unroll
the ﬁlm from the rod, keeping a bead of resin ahead of the rod as you cross
the laminate. Any entrapped air remaining can be removed by rubbing a
tongue depressor across the release ﬁlm surface. Carefully pull the ﬁlm
taut and fasten at the edges to prevent wrinkling of the ﬁlm. Placing stops
(neoprene has been found to be suitable) around the edges of the laminate
and passing a heavy metal roller over the laminate helps to insure uniform
controlled thickness.
7.3.6 Cure as recommended by the resin manufacturer. The
cure schedule shall be reported.
7.3.7 Trim edges as required.
7.4 Record of Standard Laminate Construction—Record the
properties of the standard laminate as follows:
7.4.1 Hardness—Determine Barcol hardness on the strip as
described in 7.2.4 in accordance with Test Method D2583.
7.4.2 Laminate Conditions—Visually examine the laminate.
The laminate shall meet Acceptance Level I of Table 1 of
Practice D2563.
7.4.3 If the laminate meets the requirements of this
speciﬁcation, retain the laminate sections for preparation of test
specimens.
NOTE 6—The major criteria for accepting a laminate is thickness and
not glass content. If glass content is desired, cut eight 1 by 1 in. specimens
from the center of the laminate and test in accordance with Test Method
D2584.
7.5 Individual Test Specimens:
7.5.1 Specimens for immersion in test solutions shall be
approximately 4 by 5 in. (101.6 by 127 mm), cut from the
standard laminate.
7.5.2 Identity of specimens shall be maintained by suitable
means.
7.5.3 Cut edges and drilled holes, if used for suspension,
shall be sanded smooth and coated with paraffinated resin.
7.5.4 The number of specimens required is dependent on the
number of test solutions to be employed, the number of
different temperatures at which testing is performed, and the
number of test intervals. In addition, at least two 4 by 5 in.
(101.6 by 127 mm) specimens shall be available for test (see
8.4) following the curing period, prior to immersion.
8. Procedure
8.1 Measurement of Specimens—Immediately following the
curing period, measure the thickness of the specimens to the
nearest 0.001 in. (0.025 mm) at the geometric center of each of
the intended 1 by 3 in. (25.4 by 76.2 mm) specimens that will
be cut for ﬂexural tests after the completed exposures. Measure
the weight of the specimens to the nearest 0.01 g. These
thickness and weight measurements shall also be used for
comparison against thickness and weight measurements after
the completed exposures.
8.2 Exposure—Following the curing period, as speciﬁed in
7.3.6, prior to immersion, record a brief description of the color
and surface appearance of the coupons and the color and the
clarity of the test solution. The total number of coupons per
container is not limited except by the ability of the container to
hold the coupons without touching each other or the container.
The coupons must always be completely immersed. Coupons
shall be vertical, parallel, and spaced a minimum of 0.25 in.
(6.35 mm) apart. There shall be a minimum of 0.50 in. (12.7
mm) between coupon edges and the container or the liquid
surface. Place the closed container in a constant temperature
oven adjusted to the required temperature or in a suitably
adjusted liquid bath. Examine the coupons after 30, 90, 180
days, and one year of immersion or other time intervals as
required to determine the rate of attack.
8.2.1 Discard the test solution and replace it with fresh
solution as often as necessary to maintain original composition
and concentration. As a minimum, solutions known to be stable
need to be replaced at the end of each test period.
8.3 Cleaning and Examination After Exposure—Clean the
coupon and dry by blotting with a paper towel. Cold tap water
is normally used for specimen cleaning. If other cleaning
agents are used, verify that they do not attack the resin being
tested.
8.3.1 Note any indication of surface attack on a coupon, any
discoloration of the test solution, and the formation of any
sediment.
8.3.2 After ﬁnal blotting, immediately measure the coupon
thickness to the nearest 0.001 in. (0.025 mm) in the geometric
center of each intended 1 by 3 in. (25 by 76.2 mm) specimen.
Measure the coupon to the nearest 0.01g. The Barcol hardness
can then be checked, taking an average of ten readings on each
coupon, a minimum of 0.50 in. (12.7 mm) from the edge.
8.3.3 After washing and measuring thickness, weight, and
Barcol hardness, place the coupons in an air-tight polyethylene
bag for conditioning or shipping as described in 8.4.1.
8.4 Flexural Testing—Determine the ﬂexural strength and
modulus for: (1) two sets of three specimens immediately
following the curing period, and (2) one set of three specimens
after each inspection, for each solution, and each test tempera-
ture. Calculation of ﬂexural strength and modulus after expo-
sure shall use the coupon thickness determined at the time of
ﬂexural testing as measured in 8.3.2. The two pretested sets
shall be taken from the center of the laminate as described in
7.2.1. The ﬂexural strengths for these two sets shall be
averaged together for use in calculating the retained ﬂexural
C581 − 20
3

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摘要：

ASTM C581 - 20 是一项由美国材料与试验协会发布的标准测试方法，专门用于评估玻璃纤维增强塑料（FRP）在化学环境中的耐腐蚀性能。该标准通过将层压板材浸泡在特定化学介质中，并测量其在不同时间点的弯曲强度保持率、外观变化及重量变化，从而判断材料的长期耐化学侵蚀能力。ASTM C581 - 20 广泛应用于化工储罐、管道及船舶结构等对防腐性要求高的工业领域，帮助工程师和制造商筛选适用于特定腐蚀性环境的复合材料，确保设备在恶劣工况下的安全性与使用寿命。该标准的最新版本（2020年发布）在测试

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