ASTM D6990-20

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: D6990 − 20
Standard Practice for
Evaluating Biofouling Resistance and Physical Performance
of Marine Coating Systems
This standard is issued under the fixed designation D6990; 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 Thispracticeestablishesapracticeforevaluatingdegree
of biofouling settlement on and physical performance of RecommendedASTM Methods and Practices for evaluation
of antifouling coatings via panel exposure under a variety of
marine coating systems when panels coated with such coating
systems are subjected to immersion conditions in a marine exposure conditions:
D3623 Test Method for Testing Antifouling Panels in Shal-
environment. Guidance for preparation or exposure and han-
dling of test specimens can be found in related ASTM low Submergence
D4938 Test Method for Erosion Testing of Antifouling
standards as noted below (see Section 2).
Paints Using High Velocity Water
1.2 This practice and related exposure methodologies are
D4939 TestMethodforSubjectingMarineAntifoulingCoat-
designed as tools for the relative assessment of coating
ing to Biofouling and Fluid Shear Forces in Natural
performance, and in no way are to be used as an absolute
Seawater
indicator of long-term performance under all conditions and in
D5479 Practice for Testing Biofouling Resistance of Marine
all environments. There can be high variability among and
Coatings Partially Immersed
within exposure sites with respect to water quality and popu-
D5618 Test Method for Measurement of BarnacleAdhesion
lation or species of fouling organisms, and coating perfor-
Strength in Shear (Withdrawn 2020)
mance may vary with these and other properties.
G141 Guide for Addressing Variability in Exposure Testing
1.3 The values stated in SI units are to be regarded as the
of Nonmetallic Materials
standard. The values given in parentheses are for information
only.
3. Terminology
1.4 This standard does not purport to address all of the
3.1 Definitions of Terms Specific to This Standard:
safety concerns, if any, associated with its use. It is the
3.1.1 biofilm, n—matrix-enclosed populations of microor-
responsibility of the user of this standard to establish appro-
ganisms adherent to each other or to surfaces, or both, or
priate safety, health, and environmental practices and deter-
interfaces.
mine the applicability of regulatory limitations prior to use. A
3.1.2 biofouling adhesion, n—qualitative or quantitative
specific hazard statement is given in Section 6.
force required for the successful and complete removal of
1.5 This international standard was developed in accor-
marine fouling attached to the antifouling coating surface (for
dance with internationally recognized principles on standard-
example, reference Test Method D5618 for barnacles).
ization established in the Decision on Principles for the
3.1.3 corrosion eruptions, n—build up of oxides, exiting
Development of International Standards, Guides and Recom-
through protective paint film.
mendations issued by the World Trade Organization Technical
3.1.4 damage, n—limited destruction of portions of paint
Barriers to Trade (TBT) Committee.
film due to impact with a foreign article.
This practice is under the jurisdiction of ASTM Committee D01 on Paint and
Related Coatings, Materials, and Applications and is the direct responsibility of For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Subcommittee D01.45 on Marine Coatings. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Sept. 1, 2020. Published September 2020. Originally Standards volume information, refer to the standard’s Document Summary page on
approved in 2003. Last previous edition approved in 2011 as D6990 – 05 (2011) the ASTM website.
which was withdrawn in January 2020 and reinstated in September 2020. DOI: The last approved version of this historical standard is referenced on
10.1520/D6990-20. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6990 − 20
3.1.5 digging, n—a term used to describe hard fouling exposure to be valid, the surface of the negative control should
macroorganisms that are growing “into” the coating. That is, show heavy fouling relative to the standard system(s).
where its calcareous shell penetrates/breaks through the coat-
5.4 Marine coating systems that produce positive results
ing surface causing physical damage to the coating.
relevant to the standard system(s) show potential for use in
3.1.6 macroorganism, n—organismslargeenoughtobeseen
protecting underwater marine structures.
with the naked eye and thus would be noted when growing on
5.5 The format can be utilized independent of exposure
submerged surfaces.
protocol and coating type, and provides the end user with a
3.1.7 microorganism, n—organisms too small to be seen
consistent practice and format for reporting of performance
with the naked eye, which generally include bacteria, protozoa,
rating.
fungi and microalgae (sometimes collectively called “slime”).
3.1.8 peeling, n—the phenomenon manifested in paint films
6. Safety Precautions
where a portion of a film, when pulled, can be removed in
6.1 Warning—Certain marine coating systems contain
strips or relatively large intact pieces, or both.
toxicmaterials(biocides)thatmaycauseskinandeyeirritation
3.1.9 silt, n—sedimentary material consisting especially of
on contact as well as adverse physiological effects if ingested
mineral particles intermediate in size between those of sand
or inhaled. In the preparation, application, and general han-
and clay.
dling of panels coated with various types of marine paints, the
3.1.10 softness, adv—the phenomenon manifested by paints use of appropriate protective clothing and equipment is re-
in transferring some of its pigmentation to a foreign item or
quired consistent with local, state, federal government regula-
substance, upon encountering friction on its surface. tions and recognized industrial and technical standards.
3.1.11 wearing, n—gradual loss of the paint film caused by
7. Procedure—Evaluation of Fouling Present on Test
use or exposure to the environment.
Surface
4. Summary of Practice
7.1 Controls should be exposed and assessed at the same
4.1 Test specimens or panels are coated with marine coating
time as the test materials. More information about the use of
systems and exposed to marine immersion conditions for a
control materials in weathering tests can be found in Guide
specified amount of time and under specific sets of conditions
G141. (See also 5.3.)
as agreed upon by the producer and user. See 2.1 for published
7.2 Retrieve test panels and any negative controls and
ASTM standard methods and practices that provide guidance
reference coatings from immersion site. Note and record the
for exposure of coating systems.
visual percentage coverage by biofilm or silt, or both, or lack
4.2 Coating systems are evaluated in terms of fouling rating
thereof in accordance with the guidelines provided below.
(percent of coverage of the coating system by biofouling
7.3 Prior to inspection, it is recommended that panels be
organisms), and physical deterioration rating (percent area of
rinsed (see below and 7.3.2 for more information) in order to
the coating system affected by physical coating failure(s)).
remove silt (may interfere with observation of attached forms)
These data are useful in assessing and comparing effectiveness
and unattached forms. Alternatives to rinsing such as either
of antifouling coating systems.
gentle agitation of the panels or not rinsing the panels at all
may be done but must be specified in the final reports.
5. Significance and Use
Whichever preparation is chosen, it must be documented and
5.1 This practice is designed to provide guidance to a panel
performed on all panels equally and at each inspection. If
inspector for quantitative and consistent evaluation of coating
rinsed, the test panel surface is to be wetted using low-pressure
performance from test panels coated with marine antifouling
water. For example, use household water pressures from
coating systems. The practice assesses performance of coating
3 1
garden hose sized-nozzles measuring 9.5 to 13 mm ( ⁄8 to ⁄2
systems based on both antifouling and physical properties.
in.) in the form of a gentle shower spray or non-forceful flow
5.2 The user is cautioned that the results are representative
to allow for a reliable inspection of what is attached to the
for the specific region and time of year in which the specimens
coating/panel.Nozzlesthatcausewatertobeforcefullyapplied
areimmersed.Itshallbenotedthatinterpretationofresultswill
to the panel shall not be used. Warning—Risk in rinsing
depend on the geographical location where the test is
panels is that subsequent biofouling attachment may be af-
conducted, whether the coated specimens are exposed either
fected.Alternatively, panels may be gently agitated in water to
totally or partially immersed, under static or dynamic
remove loose/unattached bacterial biofilm or silt deposits, or
conditions, and position and orientation.
both. Warning—Risk in not rinsing panels is that silt or slime,
or both, may interfere with assessment of biofouling attach-
5.3 Simultaneous testing of a proven standard antifouling
ment on complete panel surface.
coating system (known to minimize fouling accumulation, for
7.3.1 Test panels shall not be allowed to dry during the
example, containing biocide or active agent(s) to prevent
entire inspection period. A holding tank is useful for accom-
fouling settlement/growth) in the specific marine environment
plishing this.
shall be included as a reference to assist in interpretation of
results.Inaddition,anegativecontrol(inertsurfacesusceptible 7.3.2 Rinse water and holding tank water, shall be taken
to heavy fouling) shall be included on a regular basis. For the from the immersion site.
D6990 − 20
7.3.3 Efforts shall be made to minimize the length of time 8.2 Evaluate individual physical performance failure, quali-
panels remain removed from the normal immersion site, and to tatively and quantitatively, for each test specimen. Observa-
not touch the coated surfaces. tions of erosion, wearing, blistering, alligatoring, checking,
cracking, chipping, peeling, flaking, and damage shall be
7.4 Populations and types of organisms will vary by test
made. For additional information and guidance for evaluating
site. Some examples of biofouling microorganisms include
any of the previous physical deteriorations, refer to Sections 2
barnacles, oysters, mussels, bryozoans (arborescent and
and 3. Record the percent surface area affected by each
encrusting), hydroids, tubeworms, tunicates, sponges, and
physical parameter.
various types of algae. Each type of fouling organism directly
8.2.1 Observations of physical deterioration shall be per-
attached to the test surface shall be reported by (1) the
formed for each coat visible to the inspector (for example,
estimated percentage of the panel area covered by all of the
topcoat, intermediate, primer). The percent surface area af-
same type of biofouling (for example, colonial forms), (2) the
fected by each physical parameter shall be estimated based on
frequency (number of individuals for the larger and solitary
the visible area of each coat.
organisms; for example, barnacles, mussels, oysters, tube
worms, and some tunicates), and (3) the range of size for the 8.3 Discount any physical failures within 13 mm ( ⁄2 in.)
from all edges of the test panel.
individual organisms (for larger, solitary organisms). See
Appendix X1 for guidance on estimating percent cover and
8.4 Observations of physical deterioration cannot be per-
Fig. X2.1 for a suggested sample antifouling inspection report
formed on panel surface areas covered by hard fouling. At the
form.
time of inspection do not count this area in the generation of
7.4.1 Make a note of any fouling organisms found to be
the physical deterioration rating (PDR); see also 11.2. At the
growing into the paint film, also referred to as “digging.”
end of the panel test period, a final evaluation of physical
7.4.2 Note that percentage cover of algae and arborescent
deterioration rating can be performed after removal of hard
bryozoansshallbebasedontheareacoveredbythe“holdfast”
fouling in order to determine whether physical deterioration
and not the area covered by the “strands” or colony. The type
has occurred under areas that had been covered by hard
ofalgae(forexample,brown,red,green)shallalsoberecorded
fouling.
if known.
9. Procedure—Evaluation of “Softness” of Marine
7.4.3 Only attachment of primary biofouling settlement
Coating System
(that is, biofouling attached directly to the coating system)
shall be recorded. Notes on secondary fouling (biofouling
9.1 Evaluation of “softness” is intended for marine coating
attachedtootherfoulingorganisms)canbemadeifdesired,but
systems (excluding silicone coating systems), and is an indi-
shall not factor into the generation of a “fouling rating.”
cator of a coating’s pigment erosion characteristics. It is
7.4.4 Percent cover by mud tube-building amphipods shall measuredonasubjectivescaleof10to0(see9.2.1),dependent
bereportedasafootnoteinFig.X2.1,butshallNOTfactorinto on the amount of pigment transferred from the coating to a
the generation of a “fouling rating.” cotton swab.
7.4.5 Partial Immersion Test Panels Only—Panels exposed
9.2 After rinsing the test panels (see 7.2), rub a wet cotton
in accordance with Practice D5479 are partially immersed.The
swab, exactly 10 strokes in a back and forth motion, over the
non-immersed area will be subject to splash and may show
wet test surface.The cotton swab is held at one of its ends with
some fouling attachment, but the area is not included in the
the thumb and index finger. The cotton swab is positioned at
determination of a fouling rating. Therefore, the fouling rating
45° to the coating surface and sufficient pressure is applied so
is calculated based on the fully immersed surface area, count-
that the cotton swab stem just starts to bend. The strokes shall
ing the immersed surface area as 100 %.
be made continuously in a back and forth motion, in the same
7.4.6 In addition, antifouling performance of coating sys-
linear pattern, approximately 50 mm (2 in.) in length. Use of
tems is often different in the immediate waterline vicinity.
proper protective equipment, such as gloves, is recommended.
Therefore,anestimateofcoveragealongthefirst50mm(2in.)
9.2.1 Softness shall be evaluated on the following subjec-
of the test panel shall also be made and can then be contrasted
tive scale, where:
with the overall coverage. Fouling occurring in the “above the
10 = no pigment transferred to a cotton swab,
waterline” area, if any, is not considered when generating a
8 = trace amount of pigment tran
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