ASTM D1998-97

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D 1998 – 97
Standard Specification for
Polyethylene Upright Storage Tanks
This standard is issued under the fixed designation D1998; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope * D618 Practice for Conditioning Plastics and Electrical
Insulating Materials for Testing
1.1 This specification covers flat-bottom, upright, cylindri-
D883 Terminology Relating to Plastics
cal tanks molded in one-piece seamless construction by rota-
D1693 Test Method for Environmental Stress-Cracking of
tional molding. The tanks are molded from polyethylene for
Ethylene Plastics
above-ground, vertical installation and are capable of contain-
D2837 Test Method for Obtaining Hydrostatic Design
ingaggressivechemicalsatatmosphericpressure.Includedare
Basis for Thermoplastic Pipe Materials
requirements for materials, properties, design, construction,
D3892 Practice for Packaging/Packing of Plastics
dimensions, tolerances, workmanship and appearance. Tank
D4703 Practice for Compression Molding Thermoplastic
capacities are from 1900 L (500 gal) up.
Materials into Test Specimens, Plaques, or Sheets
1.2 This specification does not cover the design of vessels
E691 Practice for Conducting an Interlaboratory Study to
intended for use at pressures other than atmospheric pressure.
Determine the Precision of a Test Method
Furthermore, this specification does not cover the design of
F412 Terminology Relating to Plastic Piping Systems
portable tanks. It is also not for vessels intended for use with
2.2 OSHA Standard:
liquids heated above their flash points, or temperatures above
29 CFR 1910.106 Occupational Safety and Health Admin-
66°C (150°F) for Type I tanks and 60°C (140°F) for Type II
istration, Flammable and Combustible Liquids
tanks for continuous service. NFPA Standards 30 and 31
2.3 ANSI Standard:
should be consulted for installations which may be subject to
B-16.5 Pipe Flanges and Flanged Fittings
the requirements of these standards.
2.4 NFPA Standards:
1.3 Special design considerations not covered in this speci-
30 Flammable and Combustible Liquid Code
fication should be given to vessels subject to superimposed
31 Installation of Oil Burning Equipment
mechanical forces, such as seismic forces, windload or agita-
tion;tovesselssubjecttoservicetemperatureinexcessof23°C
3. Terminology
(73.4°F);andvesselssubjecttosuperimposedpressureexceed-
−3 3.1 Definitions: Definitions are in accordance with Termi-
ing 25.4 cm (10 in.) of water or 2.5 310 MPa (0.36 psi).
nologies D883 and F412 and the Association of Rotational
1.4 The values stated in SI units are to be regarded as the
Molders (ARM) Glossary of Terms, unless otherwise indi-
standard. The values given in parentheses are for information
cated.
only.
3.2 Definitions of Terms Specific to This Standard:
NOTE 1—There is no similar or equivalent ISO standard.
3.2.1 impact failure, n—any crack in the test specimen
resulting from the impact and visible in normal room lighting
1.5 The following precautionary caveat pertains only to the
test methods portion, Section 11, of this specification: This to a person with normal eyesight.
3.2.2 rotational molding, n—a three-stage commercial pro-
standard does not purport to address all of the safety concerns,
if any, associated with its use. It is the responsibility of the user cess consisting of loading the mold with powdered resin,
of this standard to establish appropriate safety and health
practices and determine the applicability of regulatory limita-
tions prior to use. 2
Annual Book of ASTM Standards, Vol 08.01.
Annual Book of ASTM Standards, Vol 08.04.
2. Referenced Documents
Annual Book of ASTM Standards, Vol 08.02.
Annual Book of ASTM Standards, Vol 08.03.
2.1 ASTM Standards:
Annual Book of ASTM Standards, Vol 14.02.
Available from OSHA, 2900 Newton St., NE, Washington, DC 20018.
Available from American National Standards Institute, 11 W. 42nd St., 13th
Floor, New York, NY 10036.
1 9
This specification is under the jurisdiction of ASTM Committee D-20 on Available from National Fire Protection Association, Batterymarch Park,
Plastics and is the direct responsibility of Subcommittee D20.12 on Olefin Plastics. Quincy, MA 02269.
Current edition approved Nov. 10, 1997. Published April 1998. Originally Available fromAssociation of Rotational Molders, 435 North MichiganAve.,
published as D1998–91. Last previous edition D1998–96. Suite 1717, Chicago, IL 60611-4067.
*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.
D1998–97
fusing the resin by heating while rotating the mold about more 6. Design Requirements for Both Type I and Type II
than one axis, and cooling and removing the molded article. Tanks
3.2.3 service factor, n—anumberlessthan1.0(whichtakes
6.1 Cylinder Shell (Unsupported Portion of Tanks)—The
into consideration all the variables and degrees of safety
minimumrequiredwallthicknessofthecylindricalshellatany
involved in a polyethylene storage tank installation) which is
fluid level shall be determined by the following equation, but
multiplied by the hydrostatic design basis to give the design
shall not be less than 4.7 mm (0.187 in.) thick. The tolerance
hoop stress.
indicated in 9.1.2 applies to these dimensions.
T 5 P 3 OD/2 SD (1)
4. Classification
where:
4.1 Tanksmeetingthisspecificationareclassifiedaccording
T = wall thickness, mm (in.),
to type as follows, and it is the responsibility of the purchaser
P = pressure,MPa(0.0098MPa/m-H O 3SG 3H(m)),
to specify Type I or Type II:
or psi (0.433 psi/ft-H O 3 SG 3 H (ft)),
4.1.1 Type I—Tanks molded from cross-linkable polyethyl-
SG = specific gravity of fluid,
ene.
H = fluid head, m (ft),
OD = outside diameter of tank, mm (in.), and
4.1.2 Type II—Tanks molded from noncross-linkable poly-
SD = hydrostatic design stress, MPa (psi).
ethylene.
6.1.1 The hydrostatic design stress that is used to determine
5. Materials theminimumwallthicknessatanyfluidlevelmustbebasedon
hoopstressdatafortheresin.Thehoopstressdata,obtainedin
5.1 This specification is based upon the use of 100% virgin
accordance with the procedures of Test Method D2837,
polyethylene intended for the rotational molding process.Any
provide a hydrostatic-design-basis for the resin. The
use of regrind, recycled or reprocessed materials, or combina-
hydrostatic-design-basismustbereducedbyaservicefactorto
tions of such materials, shall not rely upon the performance
determine the actual hydrostatic design stress. The maximum
data of their original constituents, but must meet the require-
servicefactorshallbe0.5forwallthicknesseslessthan9.5mm
ments of this specification in its own right.
(0.375 in.). For thicknesses equal to or greater than 9.5 mm
5.1.1 The polyethylene shall have a stress-cracking resis-
(0.375 in.), the maximum service factor shall be 0.475. For
tance of 500 h minimum F50 in accordance with Test Method
example, if the hydrostatic-design-basis for the resin is 8.7
D1693, Condition A, full-strength stress-cracking agent. The
MPa (1260 psi), the hydrostatic design stress for a tank with
test specimens may be compression molded or rotational
wall thickness greater than 9.5 mm (0.375 in.) is
molded. If compression molded, Procedure C ofAnnexA1 of
0.475 38.7=4.1 MPa (or 0.475 31260=600 psi).
Practice D4703 shall be followed for both types of polyethyl-
6.1.2 All tank hoop stress shall be derated for service above
enewithaminimumplatentemperatureof177°C(350°F).Ifit
23°C (73.4°F).
is a crosslinkable polyethylene the temperature shall be 197°C
6.2 Cylinder Shell (Externally Supported Tanks)—The
(390°F) and the platen shall be kept closed under full pressure
minimumrequiredwallthicknessforthecylinderstraightshell
for 5 min at the specified temperature in order to bring about
must be sufficient to support its own weight in an upright
the crosslinking reaction. If the test specimens are rotational
positionwithoutanyexternalsupport,butshallnotbelessthan
molded, the conditions for rotational molding shall be similar
4.7 mm (0.187 in.) thick. The tolerance indicated in 9.1.2
to the conditions used for molding a tank from this polyethyl-
applies to these dimensions.
ene.
6.3 Top Head—Mustbeintegrallymoldedwiththecylinder
NOTE 2—The stress-cracking test is not used as an indicator of general
shell.The minimum thickness of the top head shall be equal to
chemical resistance of a polyethylene. The polyethylene supplier’s or
the top of the straight wall.
molder’s chemical-resistance chart should be referred to for information
6.4 Bottom Head—Must be integrally molded with the
on the resistance of the polyethylene to specific chemicals or products, or
testing of specific products or chemicals should be conducted. cylinder shell. The minimum thickness for a full-supported
flat-bottom head shall be 4.7 mm (0.187 in.).The radius of the
5.2 All tanks used for outdoor installation shall contain an
bottomknuckleofaflat-bottomtankshallnotbelessthan25.4
ultraviolet stabilizer at a level adequate to give protection for
mm (1 in.) for tanks with a diameter less than 1.8 m (6 ft) and
the intended service life of the tanks. This stabilizer shall be
38.1 mm (1.5 in.) for a diameter greater than 1.8 m (6 ft). The
compounded in the polyethylene.
minimum thickness of the radius shall not be less than the
5.3 Pigments may be added at the purchaser’s request and
maximum thickness of the cylinder wall.
must be compatible with the polyethylene, but should not
6.5 Open-Top Tanks—The top edge of open tanks shall be
exceed0.5%dryblended,and2%compoundedin,ofthetotal
reinforced by design to maintain its shape after installation.
weight.
NOTE 3—The use of dry-blended pigments may result in an effect on 7. Fittings
physical properties, that is, impact strength.
7.1 Fabricatednozzles,gaskets,andotherfittingaccessories
5.4 Each resin used in designing tanks covered by this
must be chemically compatible with the materials to be
specification shall have hydrostatic-hoop-stress data available. handled in the tanks.
D1998–97
7.2 Openings that are cut in tanks to install fittings must not air bubbles, pinholes, pimples, crazing, cracking and delami-
have sharp corners. Holes should have minimum clearance to nations that will impair the serviceability of the vessel. Fine
insure best performance of fittings. bubbles are acceptable with Type II tanks to the degree to
7.3 The size, location, and specification, etc., for manways whichtheydonotinterferewithproperfusionoftheresinmelt.
andfittingsshallbeagreeduponbetweenthepurchaserandthe 10.2 Becauseofthedifferencesinvariousresinsusedinthis
manufacturer. application and the molding conditions used, the interior
7.4 The vents must comply with OSHA 1910.106 (F) (iii) surface characteristics may vary.The acceptable finish shall be
(2) (IV) (9) normal venting for atmospheric tanks, or other predetermined by agreement between the molder and the
accepted standard, or shall be at least as large as the filling or buyer.
withdrawal connection, whichever is larger but in no case less
11. Test Methods
than 25.4 mm (1 in.) nominal inside diameter.
11.1 TestSpecimens—Testspecimensshallbetakenfroman
7.5 Fittings installed in tanks shall be of appropriate
area that is representative of the bottom side wall. If no
strength to meet manufacturer and purchaser specifications.
representative sample cut-out area in the tank is available, test
7.6 Bolts securing mechanical fittings must be manufac-
specimens may be molded in a test mold. In either case, prior
tured of materials compatible with tank contents.
testing shall verify that the tank wall and the test specimen
7.7 Provisionsshallbemadetoattachhold-downdevicesto
have equal impact resistance.
the tanks for outdoor service.
11.1.1 The test mold shall be constructed of the same type
7.8 For all flanged connectors, the flange drilling and
material and have the same wall thickness as the tank mold.
bolting shall be in accordance with ANSI/ASME B-16.5 for
The thickness of the specimen from a test mold shall be the
150 psi (1 MPa) pressure class straddling the principal center-
same as the thickness of the bottom side wall within the
line of the vessel.
tolerances as defined in 9.1.2. The test mold shall be molded
8. Performance Requirements
with each tank.
8.1 The following performance requirements shall be met
11.2 Conditioning—If requested, test specimens may be
by Type I and Type II tanks:
conditionedat23 62°C(73.4 63.6°F)and50 65%relative
8.1.1 Low-Temperature Impact—Low-temperature impact
humidity for not less than 40 h prior to testing in accordance
shall be determined using the test method described in 11.3.
with Procedure A of Practice D618.
The requirements for Type I and Type II tanks are as follows:
11.3 Low-Temperature Impact Test:
Impact energy, 11.3.1 Scope—This test method is for the determination of
Wall thickness, mm (in.)
min. J (ft-lb)
the impact property of rotational-molded polyethylene tanks at
lowtemperature.Thetestmethodisusedontanksmoldedfrom
4.7 mm (0.187 in.) to and including 6.4 mm (0.25 in.) 122.0 (90)
6.6 mm (0.26 in.) to and including 12.9 mm (0.50 in.) 135.5 (100) both crosslinked and non-crosslinked polyethylenes.
12.9 mm (0.51 in.) to and including 19.3 mm (0.75 in.) 203.2 (150)
11.3.2 Summary of Test Method—Test specimens are cut
19.3 mm (0.76 in.) to and including 25.4 mm (1.00 in.) 271.0 (200)
from available areas on the tank and conditioned at −29°C
greater than 25.4 mm (1.00 in.) 271.0 (200)
(−20°F) for a specified period of time. A suitable type of test
8.1.2 Percent Gel, for Type I Tanks Only—The percent gel
apparatus is shown in Fig. 1 and Fig. 2. The specimens are
level shall be determined using the test method described in
placed, inside-surface down, in the sample holder and imme-
11.4. The percent gel level for Type I tanks on the inside 3.2
diately impacted with a dart of specified weight, from a
mm (0.125 in.) of the wall shall be a minimum of 60%.
prescribed height with a specified radius on the tip. The
9. Dimensions and Tolerances specimen is observed for failure on both surfaces. The test
prescribes a minimum impact value which the specimen must
9.1 General—All dimensions will be taken with the tank in
pass.
the vertical position, unfilled. Tank dimensions will represent
11.3.3 Significance and Use:
the exterior measurements.
11.3.3.1 The dart impact test at−29°C (−20°F) produces a
...