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Federal Motor Vehicle Safety Standards; Compressed Natural Gas Fuel Containers Publication: Federal Register Agency: National Highway Traffic Safety Administration Byline: Ricardo Martinez Date: 24 July 1995 Subject: American Government  • Safety
Topic: Federal Motor Vehicle Safety Standards |
[Federal Register Volume 60, Number 141 (Monday, July 24, 1995)]
[Rules and Regulations]
[Pages 37835-37844]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-18109]
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[[Page 37836]]
DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration
49 CFR Part 571
[Docket No. 93-02; Notice 10]
RIN 2127-AF47
Federal Motor Vehicle Safety Standards; Compressed Natural Gas
Fuel Containers
AGENCY: National Highway Traffic Safety Administration (NHTSA),
Department of Transportation (DOT).
ACTION: Final rule, petitions for reconsideration.
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SUMMARY: This document responds to petitions for reconsideration of the
final rule that established performance requirements for compressed
natural gas (CNG) fuel containers. The final rule specified burst test
safety factors of up to 3.33 for use in evaluating the strength of
carbon fiber containers. In an initial notice responding to the
petitions, a single, lower safety factor of 2.25 was adopted, subject
to further consideration of that issue. This final rule reaffirms that
decision. Today's document also responds to the other issues raised in
the petitions.
DATES: Effective Date: August 23, 1995.
Petitions for Reconsideration: Any petition for reconsideration of
this rule must be received by NHTSA no later than August 23, 1995.
ADDRESSES: Petitions for reconsideration of this rule should refer the
Docket number referenced at the beginning of this document and should
be submitted to: Administrator, National Highway Traffic Safety
Administration, 400 Seventh Street, S.W., Washington, D.C. 20590.
FOR FURTHER INFORMATION CONTACT: Mr. Gary R. Woodford, NPS-01.01,
Special Projects Staff, Office of Safety Performance Standards,
National Highway Traffic Safety Administration, 400 Seventh Street SW.,
Washington, D.C. 20590 (Telephone 202-366-4931) (FAX 202-366-4329).
SUPPLEMENTARY INFORMATION:
I. Final Rule Establishing FMVSS No. 304
II. Petitions for Reconsideration
III. December 1994 Final Rule Responding to Petitions for
Reconsideration
IV. Further Response to Petitions for Reconsideration
A. Carbon Fiber Safety Factors
B. Other Issues
1. Burst Pressure Definition
2. Container and Material Requirements
a. NASA Computer Program
b. Autofrettage Requirement
c. Reference to S5.7.3
d. Container Liner Burst Test
e. Check Analysis Tolerances for Materials
f. Wall Stress Formula
g. Service Pressure vs. Hydrostatic Pressure in Stress Formula
3. Performance Requirements
a. Hydrostatic Test
b. Burst Pressure vs. Fiber Stress Ratio
c. Fiberglass Stress Ratios: Type 2 Containers
4. Labeling Requirements
a. Letter Height
b. Container Label Permanency
c. Fill Pressure
d. Service Pressure
e. ``DOT'' Symbol
f. Service Life
g. Qualification/Batch Test Requirements
5. Test Conditions
a. Diesel Fuel in Bonfire Test
b. More Detail In Bonfire Test
c. Complete Venting of Container During Bonfire Test
d. Burst and Pressure Cycling Test Procedures
6. Miscellaneous
a. Withdraw or Delay the Effective Date of FMVSS 304
b. Flexibility and Adaptability of Final Rule
c. Chemical Compositions
V. Rulemaking Analysis
I. Final Rule Establishing FMVSS No. 304
On September 26, 1994, NHTSA published a final rule addressing the
safe performance of compressed natural gas (CNG) containers 1 (59
FR 49010). The final rule established a new Federal motor vehicle
safety standard (FMVSS) FMVSS No. 304, Compressed Natural Gas Fuel
Container Integrity, that specifies pressure cycling, burst, and
bonfire tests for the purpose of ensuring the durability, initial
strength, and venting of CNG containers. The pressure cycling test
evaluates a container's durability by requiring a container to
withstand, without any leakage, 18,000 cycles of pressurization and
depressurization. This requirement helps to ensure that a CNG container
is capable of sustaining the cycling loads imposed on the container
during refuelings over its entire service life. The burst test
evaluates a container's initial strength and resistance to degradation
over time. This requirement helps to ensure that a container's design
and material are appropriately strong over the container's life. The
bonfire test evaluates a container's ability to relieve internal
pressure, primarily pressure due to temperature rise. In addition, the
final rule specifies labeling requirements for CNG fuel containers.
FMVSS No. 304 took effect on March 27, 1995.
\1\ When used as a motor fuel, natural gas is stored on-board a
vehicle in cylindrical containers at a pressure of approximately
20,684 kPa (3,000 psi). Among the terms used to describe CNG fuel
containers are tanks, containers, cylinders, and high pressure
vessels. The agency will refer to them as ``containers'' throughout
this document.
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The new FMVSS is patterned after the American National Standards
Institute's (ANSI's) voluntary industry standard known as ANSI/NGV2.
ANSI/NGV2 and FMVSS No. 304 specify detailed material and other
requirements for four different types of containers. A Type 1 container
is a metallic noncomposite container. A Type 2 container is a metallic
liner over which an overwrap such as carbon fiber or fiberglass is
applied in a hoop wrapped pattern over the liner's cylinder sidewall. A
Type 3 container is a metallic liner over which an overwrap such as
carbon fiber or fiberglass is applied in a full wrapped pattern over
the entire liner, including the domes. A Type 4 container is a non-
metallic liner over which an overwrap such as carbon fiber or
fiberglass is applied in a full wrapped pattern over the entire liner,
including the domes.
For each type of container, ANSI/NGV2 and FMVSS No. 304 specify a
unique safety factor for determining the internal hydrostatic pressure
that the container must withstand during the burst test. The safety
factors range from 2.25 to 3.50, depending on the material and design
involved. The higher the safety factor, the more material is needed to
comply with the requirement. To satisfy this aspect of ANSI/NGV2 and
FMVSS No. 304, a container must meet the applicable material and
manufacturing requirements as well as the burst test.
While FMVSS No. 304 followed ANSI/NGV2 in most respects, it
departed from ANSI/NGV2 in requiring that carbon fiber containers
comply with the burst tests based on higher safety factors.
Specifically, the final rule establishing FMVSS No. 304 specified a
safety factor of 2.50 for Type 2 containers and 3.33 for Type 3 and
Type 4 containers. In contrast, ANSI/NGV2 specifies a safety factor of
2.25 for all carbon fiber containers.
II. Petitions for Reconsideration
NHTSA received 133 petitions for reconsideration of the final rule
that established FMVSS No. 304. The petitions were submitted by CNG
container manufacturers, vehicle manufacturers, natural gas utilities,
research and testing laboratories, and Canada and several of its
provincial governments.
Most of the petitioners addressed the carbon fiber safety factors.
Many of them stated that the levels specified by the agency in the
final rule are higher
[[Page 37837]]
than warranted by safety considerations. They further stated that the
higher safety factors will unduly increase the cost of carbon fiber
containers and make them noncompetitive with other technologies. Some
petitioners stated that NHTSA's safety factors are not harmonized with
the Canadian Standards Association (CSA) standard (Canadian B51 Part
II) or with the 1993 draft International Standards Organization (ISO)
standard (ISO/TC 58/SC 3/WG 17), both of which specify a 2.25 safety
factor for carbon fiber containers. On the other hand, only one
commenter supported the 3.33 safety factor.
While the carbon fiber safety factors were the most controversial
issue raised by petitioners, some petitioners requested changes to
other aspects of the final rule. For example, some petitioners
expressed concern that FMVSS No. 304 prohibits certain materials, such
as new or different aluminum and steel alloys or other new materials.
Some petitioners wanted FMVSS No. 304 to include additional safety
requirements found in ANSI/NGV2. A number of petitioners requested the
agency to delay or withdraw FMVSS No. 304 until the current revision of
ANSI/NGV2 is completed. Petitioners also raised questions about the
need for certain technical amendments to FMVSS No. 304.
NHTSA has responded to the petitions for reconsideration by issuing
two different notices. The two-step approach to responding to the
petitions was necessary to provide immediate regulatory relief by
allowing the manufacture of carbon fiber containers, subject to a
single safety factor of 2.25. This approach also provided NHTSA an
opportunity to review and analyze all the information presented in the
petitions for reconsideration.
III. December 1994 Final Rule Responding to Petitions for
Reconsideration
In an initial notice responding to petitions for reconsideration
published on December 28, 1994, the agency established a burst test
safety factor of 2.25 for carbon fiber containers, and indicated that
it would issue a final determination about the appropriate burst test
safety factor pending completion of the reconsideration process. (59 FR
66773) That notice also responded to several other technical issues
whose resolution did not necessitate extensive review or consideration.
In today's notice, the agency sets forth a final determination about
the safety factor for carbon fiber containers and responds to the
balance of the issues in the petitions for reconsideration.
IV. Further Response to Petitions for Reconsideration
A. Carbon Fiber Safety Factors
In the September 1994 final rule, NHTSA departed from ANSI/NGV2 and
established higher safety factors for carbon fiber containers. The
agency made this determination because at that time the agency was not
aware that these containers were being used extensively in motor
vehicle applications. The agency stated that adopting more stringent
safety factors is consistent with the longstanding approach taken by
the Research and Special Programs Administration (RSPA) 2 to
initially adopt conservative requirements in response to the uncertain
level of risk posed by new technologies and subsequently modify the
requirements if further real-world safety data become available
supporting less stringent regulations. The agency indicated that it
would consider reducing the safety factors for carbon fiber containers
if data supporting a reduction ``are developed and become available on
the use of carbon fiber containers in motor vehicle applications.''
\2\ RSPA is an administration within the United States
Department of Transportation whose functions include regulating the
transportation of hazardous materials.
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In response to the final rule, CNG container manufacturers and
other petitioners have submitted new test data and information
indicating that carbon fiber containers at the lower 2.25 safety factor
can provide a level of performance equal to that of other materials
built to higher safety factors. This information also indicated that
implementing higher safety factors for carbon fiber would make carbon
fiber containers noncompetitive because of the higher costs associated
with adding additional material to meet the higher safety factors. The
data include information on tests and analyses of carbon fiber
containers, the number of containers in use in motor vehicle
applications, and cost and weight information.
Several petitioners, particularly Brunswick Technical Group and EDO
Corp., submitted test data which indicate that carbon fiber containers
that comply with ANSI/NGV2 are safe. Brunswick stated that it has
qualified 26 different configurations of its carbon fiber containers
under ANSI/NGV2 requirements and has destructively tested 500 carbon/
fiberglass CNG containers.3 That manufacturer further stated that
there is no information indicating that carbon fiber containers that
comply with ANSI/NGV2 requirements have failed in the field or that
test data would indicate the likelihood of such failure. To illustrate
its claim, Brunswick provided the results of tests recently performed
by British Gas on its containers.
\3\ Brunswick's design uses carbon as the major load carrying
fiber with a small layer of fiberglass outside.
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EDO also provided extensive testing information and analyses about
its carbon fiber containers built to the 2.25 safety factor. EDO
submitted an analysis showing how its container meets the requirements
of a draft industry-wide guideline for the performance of CNG
containers used in a motor vehicle environment. The guideline, which
was developed by General Motors (GM) following failures of CNG
containers on two GM pickup trucks in 1994, includes requirements for
performance relative to contaminants, corrosives, crashworthiness, leak
integrity, fire resistance, reliability, dependability, and accelerated
aging. The results of the analysis indicate that EDO's carbon fiber
containers built to the 2.25 safety factor comply with these
requirements.
EDO also provided a detailed analysis, known as a Failure Modes and
Effects Analysis (FMEA),4 which it performed to determine the
safety risks of its carbon fiber containers built to ANSI/NGV2
requirements. This analysis led EDO to conclude that no significant
safety risk could be identified for the carbon fiber containers.
Specifically, EDO cited the significantly long fatigue life and high
resistance to stress rupture of carbon fiber, which are evaluated by
the burst test. EDO also cited additional test data that it believes
indicate that no further requirements are needed with respect to
container strength.
\4\ A FMEA sets out in writing each failure mode that is
possible with a product along with the potential cause for the
failure and the design control in place to counter the failure. RSPA
sometimes requires a FMEA to be submitted when it evaluates a
manufacturer's particular container design. NHTSA believes that FMEA
is a valid technique for assessing the adequacy of a particular
design, provided that other supporting information is presented.
Several petitioners supplied information favorably comparing the
performance (under both real world and laboratory test conditions) of
carbon fiber containers subject to the 2.25 safety factor with
fiberglass containers. Based on an evaluation that Powertech conducted
for Transport Canada, Powertech concluded that carbon fiber resists
stress rupture, and
[[Page 37838]]
environmental and fire effects better than fiberglass.
Several petitioners stated that carbon fiber containers subject to
the 2.25 safety factor are being used safely in real world situations.
Thomas Built Buses, Inc., reported that there have been several
thousand carbon fiber CNG containers built to ANSI/NGV2 requirements,
i.e., subject to a safety factor of 2.25. Brunswick and EDO stated that
they have built over 5,000 carbon fiber containers to ANSI/NGV2
requirements (2,600 Brunswick and 2,500 EDO.) According to Brunswick,
many of these containers have been in service for at least 18 months,
including carbon fiber containers that have been used in buses in
Sweden for over five years.
Petitioners further stated that the higher carbon fiber safety
factors in FMVSS No. 304 are not harmonized with the standards being
set by others. For instance, Canada's CSA standard for CNG vehicle fuel
containers uses a 2.25 safety factor. Similarly, the draft ISO standard
for CNG containers incorporates the 2.25 safety factor. Moreover,
several organizations and States have incorporated ANSI/NGV2 into their
standards for CNG vehicles, including the National Fire Protection
Association, New York Department of Transportation, California Highway
Patrol, Texas Railroad Commission, and the State of Nebraska.
Many petitioners contended that the higher safety factors for
carbon fiber containers required by FMVSS No. 304 will make these
containers noncompetitive by unnecessarily increasing their cost and
weight, thereby inhibiting the growth of the natural gas vehicle
market. They noted that for a CNG container of a given size, the
increased safety factor not only increases the cost and weight, because
of the increased carbon fiber needed, but also reduces container
interior volume. The American Gas Association (AGA), the National Gas
Vehicle Coalition (NGVC), Brunswick, EDO, and Thomas each indicated
that these results have a significant impact on the motor vehicle
applications, particularly for buses and small passenger vehicles,
which are particularly weight sensitive.
These petitioners provided specific data on the cost and weight
impacts. AGA and NGVC stated that the higher safety factors in FMVSS
No. 304 will increase the cost of carbon fiber containers by 25 to 40
percent 5 and eliminate their weight advantage. EDO stated that
the higher safety factor for one of its carbon fiber containers would
result in a 38 percent (or $395) selling price increase and 32 percent
weight increase (approximately 25 pounds) for the same container
interior volume. EDO added that for a bus using 12 such containers,
this would result in a price increase of $4,740 for the containers
(excluding other costs such as OEM markup and changes to the mounting
brackets). Similarly, Brunswick stated that the agency's Final
Regulatory Evaluation (FRE) significantly understated the cost impact
of the higher safety factors, particularly for buses. That manufacturer
estimated that the incremental cost impact of the higher safety factors
would be $5,461 per bus, not $1,240 to $2,483 as estimated by the
agency. Thomas Built stated that the high strength, light-weight carbon
fiber container has made its bus applications more practical by
increasing passenger capacity by six persons over what is possible with
steel/fiberglass containers, since a smaller carbon fiber CNG container
has approximately the same internal capacity as a larger steel/
fiberglass container.
\5\ Assuming that each CNG carbon fiber container built to the
2.25 safety factor costs approximately $1,000, costs would increase
between $250 and $400.
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Based on the information submitted in the petitions for
reconsideration and other available information, NHTSA has determined
that a 2.25 safety factor is more appropriate than the factors
originally established in September 1994 for carbon fiber CNG
containers. After analyzing this information, the agency believes that
the lower safety factor adopted in December 1994 is adequate to ensure
that carbon fiber CNG containers will have sufficient strength to
perform in a motor vehicle environment. The test data and information
on real-world experience supplied by the petitioners appear to support
the agency's determination that a 2.25 safety factor is appropriate.
During that time, there have been no known failures. NHTSA further
notes that the 2.25 safety factor harmonizes with the value specified
in ANSI/NGV2 and in the CSA standard. The agency also agrees with the
petitioners that the higher safety factor adopted in the final rule
would have significantly increased the cost and weight associated with
carbon fiber containers, even though the 2.25 safety factor now appears
adequate to ensure their safety. In conclusion, NHTSA has determined
that adopting the 2.25 safety factor is sufficient to ensure safety.
Thus, the safety factor or stress ratio, for each fiber material in a
fuel container will be as defined in FMVSS No. 304 for that fiber, with
the stress ratio for carbon fiber being 2.25.
B. Other Amendments
In the petitions for reconsideration, ten petitioners--Ford,
Pressed Steel Tank (PST), Norris, Structural Composites Industries
(SCI), Compressed Gas Association (CGA), NGV Systems, the Flxible Corp,
Powertech Labs, Brunswick, and Chrysler--requested a variety of
amendments to FMVSS No. 304. Each requested modification, along with
the agency's analysis of the desirability of the requested
modification, is discussed below.
1. Definitions for Burst Pressure
SCI recommended that the reference to temperature in the definition
of burst pressure be in terms of ambient temperature, rather than 70
deg.F, since the current reference implies to the petitioner that the
burst test must be performed at 70 deg.F. Section S4 defines burst
pressure as ``* * * the highest internal pressure reached in a CNG fuel
container during a burst test at a temperature of 21 deg.C (70
deg.F).''
NHTSA has decided not to adopt SCI's request to modify the
definition for burst pressure. Neither NHTSA nor NGV2 specifies the
temperature at which the burst test needs to be conducted. The agency
further notes that SCI provided no other rationale to justify this
modification, and no other petitioner commented that the definition was
inappropriate. Further, the definition for burst pressure in S4 is
consistent with that of ANSI/NGV2, which represents a consensus of the
natural gas vehicle industry. Therefore, adopting the requested
modification might cause confusion for manufacturers.
2. Container and Material Requirements
a. NASA computer program. NGV Systems, SCI, Powertech, and PST
petitioned the agency to correct the name and statement about the
availability of the National Aeronautics and Space Administration
(NASA) computer program referenced in S5.5.1 and Part 571.5(b)(9).
NHTSA has adopted the requested amendments to S5.5.1 and Part
571.5(b)(9), since the agency, in the final rule, used an incorrect
title and erroneously stated that it was available from NASA. The
computer program's correct title is ``Computer Program for the Analysis
of Filament-Reinforced Metal-Wound Pressure Vessels.'' The program is
available from the National Technical Information Service,
[[Page 37839]]
Springfield, Virginia as N67-12097 (NASA CR-72124).
b. Autofrettage requirement. Norris Cylinder Co. (Norris)
petitioned the agency to amend FMVSS No. 304 to include an autofrettage
6 requirement. Norris stated that composite containers are usually
produced by volumetric expansion (autofrettage) of the liner wrapped
with continuous filament windings.
\6\ Autofrettage is a manufacturing process for composite
containers in which the container is pressurized to the point where
the metal liner begins to yield, thereby placing the liner in
compression and the fiber overwrap in tension once pressure is
released.
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NHTSA has decided not to adopt Norris' request to include a
requirement addressing autofrettage. The agency believes that the
current requirements in FMVSS No. 304 such as the material designation
requirements in S5.2 and the manufacturing processes for composite
container requirements in S5.3 adequately ensure the safe performance
of a CNG container. The agency further believes that this manufacturing
process should be left to the discretion of the container manufacturer.
Moreover, no other manufacturer raised this issue, and Norris offered
no convincing rationale for amending FMVSS 304 to include such a
requirement.
c. Reference to S5.7.3. SCI stated that S5.4.3 refers to a
nonexistent S5.7.3, and therefore suggested that this reference be
deleted or defined. NHTSA notes that SCI's statement is incorrect;
there is a section S5.7.3, Tensile Strength.
d. Container liner burst test. SCI petitioned the agency to amend
FMVSS No. 304 to add a new section S5.4.2.4 which would state that
``Wall thickness of a liner shall be such that the burst pressure of
the liner without overwrap is at least 1.25 times the service pressure
of the container.'' SCI stated compliance with this new requirement
should be demonstrated by the addition of a liner burst test in S8. SCI
further stated that these requirements are needed since the safety
factors for Type 2 containers are based on the premise that the liner
without the fiber overwrap will maintain service pressure without
failure.
NHTSA has decided not to amend FMVSS No. 304 to add a wall
thickness performance requirement. While SCI's assertion is true that
the liner alone is to maintain service pressure, this fact is not
relevant to its request for a new test. Moreover, SCI provided no
compelling safety rationale as to why these new requirements should be
added. Section S5.4.2 of the final rule currently specifies liner wall
thickness based on liner stress requirements at various container
pressures, which is consistent with ANSI/NGV2, the voluntary industry
standard. The agency believes that there is no need to add these new
requirements for the liner only, since the rule has burst, pressure
cycling, and bonfire requirements which test the container as a whole
after manufacturing.
e. Check analysis tolerances for materials. PST stated that the
requirements for chemical analysis in S5.2, Material designations, are
unreasonable unless the agency allows normal check analysis tolerances
in addition to the stated chemical composition ranges. Normal check
analysis tolerances are the slight variations found when verifying a
metal's chemical composition. PST added that this is not seen as a
problem with the rule, but only in the definition of NHTSA enforcement
tests. According to the petitioner, since metal analysis is not
absolutely precise, some allowance for non-repeatability in the
analyses is necessary.
NHTSA has decided not to amend FMVSS No. 304 with respect to the
chemical analysis of materials. The agency notes that the requirements
specified in S5.2 already provide ranges for the chemical compositions
of various elements. For example, copper is allowed to be between 0.15
to 0.60 percent in certain aluminum containers. Manufacturers seeking
to ensure compliance could aim to hit the mid-point in each range. PST
provided no data to support its claim that the specified ranges for
chemical compositions, which are consistent with the ranges specified
in NGV2, are inadequate. Moreover, no other manufacturer informed the
agency that these chemical composition ranges posed a problem. NHTSA
believes that absent a compelling reason to provide otherwise, FMVSS
No. 304 should be consistent with ANSI/NGV2 since the manufacturers
already comply with the industry standard. Moreover, the agency
believes that it should not consider amending the requirement absent
input from other manufacturers. Based on the above considerations,
NHTSA has decided that it is not appropriate for the Standard to
specify check analysis tolerances.
f. Wall stress formula. PST and Norris petitioned NHTSA to change
the units which refer to pressure in the wall stress formula to make
the units consistent. The petitioners state that the units are not
consistent: on the left side of the equation, wall stress is in units
of MPa (psi); while, on the right side of the equation, minimum
hydrostatic test pressure is in Bar (psig). The equation is referenced
in S5.4.1(b), Wall thickness, Type 1 containers. The petitioners state
that this is also an error in ANSI/NGV2.
NHTSA has decided to amend FMVSS No. 304 to incorporate this change
in the wall stress formula. The agency notes that the petitioners are
correct that the minimum hydrostatic test pressure should be in units
of MPa, and not in Bar (psig). This change will make the units in the
formula consistent. The agency has docketed a memorandum describing a
telephone conversation between agency personnel and a representative of
the AGA in which AGA stated that this is a typographical error in ANSI/
NGV2. AGA is serving as the secretariat for the Natural Gas Vehicle
Fuel Cylinder Task Group, which is the industry group currently
revising and updating ANSI/NGV2.
g. Service pressure vs. Hydrostatic pressure in stress formula. PST
stated that the wall stress formula in S5.4.1(b) should be modified to
refer to service pressure. The formula currently uses, as part of the
equation, hydrostatic test pressure rather than service pressure to
calculate wall stress. The petitioner also stated that the rule does
not define test pressure.
NHTSA has decided not to adopt PST's request to amend the wall
stress formula in S5.4.1(b). The agency notes that the petitioner
provided no rationale as to why service pressure should be used in the
formula rather than hydrostatic test pressure.7 The agency notes
that ANSI/NGV2, which represents the consensus of the natural gas
vehicle industry, uses hydrostatic test pressure. Regarding the
definition of hydrostatic pressure, the rule specifies the definition
for hydrostatic pressure in S4, which is also consistent with the
definition in ANSI/NGV2.
\7\ The agency notes that the terms ``hydrostatic pressure,''
``hydrostatic test pressure,'' and ``test pressure'' are all
synonymous.
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3. Performance Requirements
a. Hydrostatic test. CGA and Norris petitioned the agency to
specify a hydrostatic test and test pressure. CGA stated that test
pressure is commonly 1.5 times the service pressure, and that all
similar containers worldwide are required to be tested to this level to
establish that each one will withstand such pressure at the time of
manufacture. CGA added that unsafe containers might enter the market if
they are not tested at the time of manufacture.
[[Page 37840]]
NHTSA has decided not to adopt the petitioner's request to include
a hydrostatic test. While ANSI/NGV2 requires a hydrostatic pressure
test be performed on each container, FMVSS No. 304 does not require
such a test. Instead, the agency requires each manufacturer to certify
that its containers comply with the burst test requirement. That test
is based on the level of pressure reached at the safety factors, or
stress ratios, specified in FMVSS No. 304. Further, since the burst
test is more stringent than the hydrostatic test, the hydrostatic test
would not provide any additional information about a container's
strength, and therefore is not necessary.
b. Burst pressure vs. Fiber stress ratio. NGV Systems, Ford, PST,
Brunswick, CGA, SCI and Chrysler petitioned the agency to amend FMVSS
No. 304 to correct what they viewed as a conflict in the wording of
S7.2.2. Specifically, the last sentence in S7.2.2 states that ``Burst
pressure is calculated by multiplying the service pressure by the
applicable fiber stress ratio set forth in Table Three.'' The
petitioners claimed that this requirement is in error since burst
pressure is not always directly proportional to fiber stress ratio,
particularly for Type 2 and Type 3 containers where the liner carries
some of the load. The petitioners further indicated that this statement
is not in keeping with the intent of ANSI/NGV2 requirements or industry
practice. Ford and PST suggested that the last sentence of S7.2.2 be
deleted. SCI suggested other changes, such as changing the term
``stress ratio'' to ``pressure ratio'' in S7.2.2, and making other
similar wording changes in the rule to reflect the last sentence in
S7.2.2.
After reviewing the petitions, NHTSA has decided to amend FMVSS No.
304 by deleting the last sentence of S7.2.2. The agency agrees with the
petitioners that the final rule did not reflect the fact that the liner
carries some of the load. Today's modification recognizes the methods
used to manufacture CNG containers and therefore makes the requirement
more practicable than the requirement that was specified in the final
rule. This modification corrects the wording conflict and makes FMVSS
No. 304 consistent with ANSI/NGV2, which was the agency's intent. The
agency has decided not to adopt SCI's suggested wording changes, which
are not necessary given the agency's decision to delete the last
sentence in S7.2.2. The agency further notes that SCI's requested
modification would have made the final rule inconsistent with ANSI/
NGV2.
c. Fiberglass stress ratios: Type 2 containers. Norris petitioned
the agency to revise the safety factors for E-Glass and S-Glass Type 2
containers. Section S7.2.2 of Standard 304 specifies these at 2.65.
Norris stated that considerable safe experience exists with the similar
DOT FRP-2 cylinder design at a safety factor of 2.5, and that this
should not be arbitrarily changed to 2.65. In addition, the CGA
commented more generally that the stress ratios in Table 3 of S7.2.2
for some cylinder types are different from those used in industry
practice, and suggested an open forum at NHTSA to discuss these points.
NHTSA has decided not to adopt Norris' request to lower the safety
factor for E-Glass and S-Glass containers to 2.5. The agency believes
that it would be inappropriate to make such a change based on DOT FRP-
2, which is a RSPA requirement that regulates cylinders used in
transport. In contrast, FMVSS No. 304 is a Federal motor vehicle safety
standard that regulates the manufacture of CNG containers for use in
motor vehicle applications. Although cylinders made to FRP-2 are
similar in design to Type 2 containers, they are subject to a much
different operating environment. For example, Type 2 containers, being
in the automotive environment, are subject to many more pressurization
cycles due to refueling. Based on these different applications, NHTSA
believes the higher safety factor of 2.65 is justified. More generally,
the fiber stress ratios which NHTSA has currently set in FMVSS No. 304
are the same as those of ANSI/NGV2, which represents a consensus of the
CNG vehicle industry.
4. Labeling Requirements
a. Letter height. Ford, SCI, and Chrysler petitioned the agency to
reduce the height of the required lettering on the container label
specified in S7.4. Ford requested the lettering height be changed from
12.7 mm to 4 mm, stating that 4 mm is the same height required for VIN
lettering. Ford stated that using letters 12.7 mm high will result in a
label so large that, when it is applied to the container, not all parts
of the label will be visible due to the label's wrapping around the
container surface. SCI petitioned the agency to reduce the lettering
height to 6.35 mm. SCI stated that if the lettering were 12.7 mm in
height, the label might be so large that it could be impossible to read
all the necessary information once the fuel container is installed.
Chrysler stated that typical labeling uses a combination of 3 mm and 6
mm characters.
After reviewing these petitions for reconsideration, NHTSA has
decided to amend FMVSS No. 304 to reduce the required lettering height
since the lettering height in the final rule is too large to enable
manufacturers to provide labels that fit appropriately on the CNG
containers. Specifically, the agency has decided to amend S7.4 to
specify that the lettering height be 6.35 mm (0.25 inch), which is
consistent with the comments of Chrysler and SCI. The agency believes
that Ford's request to reduce the lettering height still further, to 4
mm (0.157 inch), would be inappropriate since lettering of that height
could be too small to be readily visible at various locations on CNG
vehicles.
b. Container label permanency. SCI requested that NHTSA clarify how
S7.4 should be interpreted, claiming that it is difficult for a
container manufacturer to guarantee label permanency. That provision
states that ``Each CNG fuel container shall be permanently labeled * *
*.''
By ``permanent,'' NHTSA means that the label should remain in place
and be legible for the manufacturer's recommended life of the
container. For instance, a metal tag with embossed or raised letters
riveted in place would be considered permanent. Similarly, a mylar
label that is subsurface printed and is made of a material that is
resistant to fade, heat, moisture and abrasion would typically be
considered permanent (see Standard No. 129, section S5.4.3). To carry
out this intent, NHTSA has modified section S7.4 to state that ``Any
label affixed to the container in compliance with this section shall
remain in place and be legible for the manufacturer's recommended life
of the container.''
c. Fill pressure. Norris petitioned the agency to require that the
container label indicate the maximum allowed fill pressure during
refueling. Norris stated, without explanation, that information about
fill pressure would be more useful than service pressure.
NHTSA has decided not to adopt Norris's request to include the fill
pressure on the label. Section S7.4 of FMVSS No. 304 requires that the
service pressure be specified on the container label. This is the
pressure at which the container is designed to operate under normal
conditions. At present, there are two basic service pressures for CNG
containers: 3,000 psi and 3,600 psi. NHTSA did not propose and does not
now believe there is a compelling reason to specify maximum fill
pressure. The agency notes that Norris provided no safety rationale to
justify such a requirement and that the current labeling requirement to
specify service pressure is consistent with ANSI/NGV2,
[[Page 37841]]
which represents a consensus of the CNG fuel container industry.
d. Service pressure. SCI petitioned the agency to specify that
``Service pressure'' be on the container label, rather than ``Maximum
service pressure'' as required by S7.4(c). Since ``Service pressure''
is defined in FMVSS No. 304, not ``Maximum service pressure,'' SCI
stated that this revision to the label would retain consistent
terminology.
NHTSA has decided to adopt SCI's request to specify ``service
pressure'' on the container label. The agency notes that the term
``maximum service pressure,'' as required to be on the container label
in FMVSS No. 304, was intended to mean the same as ``service
pressure.'' Thus, the agency was using the two terms interchangeably,
even though FMVSS No. 304 defines ``service pressure'' but not
``maximum service pressure.'' The agency believes that use of the two
different terms in FMVSS No. 304 could be confusing. Specifically, the
term ``maximum service pressure'' could be construed to mean a higher
pressure than what was intended in FMVSS No. 304. Therefore, S7.4(c)
has been revised to read:
``Service Pressure ________ kPa (________ psig).''
e. Symbol ``DOT''. Section S7.4(d) requires the symbol ``DOT'' to
be placed on the container label as the manufacturer's certification
that the container complies with all requirements of FMVSS No. 304. SCI
stated that the container label symbol ``DOT'' is not meaningful and
should be expanded to include the standard and effective date, ``DOT
FMVSS-304-0395.''
NHTSA has decided not to adopt SCI's request to modify the labeling
requirement related to the symbol ``DOT.'' The agency believes that the
information requested by SCI would create additional confusion. The
agency further notes that the use of the symbol ``DOT'' in FMVSS No.
304 is readily understood in the motor vehicle industry and is
consistent with its use in other FMVSSs for items of motor vehicle
equipment, such as FMVSS No. 106, Brake Hoses, and FMVSS No. 109, New
pneumatic tires. The agency decided not to specify the version of the
standard, since the agency typically does not reissue standards en toto
every few years. Rather, at most, it periodically amends specific
provisions in a standard. Therefore, the agency does not refer to its
standards as the 1995 version of a particular standard.
f. Service life. SCI petitioned the agency to specify a 15 year
service life for CNG containers since FMVSS No. 304's pressure cycling
test of 18,000 cycles is based on 15 years (four refuelings per day,
300 days per year for 15 years).
NHTSA does not have the authority to regulate the length of time
that the public uses an item of motor vehicle equipment, such as a CNG
container. The agency does have authority to specify labeling
requirements that address a CNG container's service life. The agency is
currently reviewing comments on this matter in response to a December
1994 supplemental notice of proposed rulemaking (SNPRM) that proposed a
container label requirement specifying a container life of 15 years or
a time period specified by the manufacturer. (59 FR 65299, December 19,
1994). If the agency determines that labeling CNG containers with a
service life is appropriate, it will do so in the context of that
rulemaking.
g. Qualification/batch test requirements. Norris requested that
FMVSS No. 304 define ``design family.'' It also stated that neither
qualification nor batch test requirements are spelled out. Such a
requirement would be consistent with RSPA's method of regulating CNG
containers.
Norris' request for FMVSS No. 304 to include information about
``design family'' and other manufacturing considerations would be
inconsistent with how Federal motor vehicle safety standards are
generally promulgated. The manufacturer typically must certify that
each container it manufactures complies with the standard. Therefore,
to comply with FMVSS No. 304, each container must be capable of meeting
the applicable requirements, such as the burst test, and be certified
to meet them. In rare situations such as the flasher requirements in
FMVSS No. 108, Lamps, reflective devices, and associated equipment,
establishing compliance to the standard through batch testing is
permitted.
Given that a batch testing requirement is typically disfavored by
the agency and that the consequences for a failed CNG container are
likely much more dangerous than a failed flasher, NHTSA believes that
it is necessary for a CNG container manufacturer to certify the
compliance of each CNG container.
NHTSA notes that in contrast to NHTSA's framework, RSPA authorizes
batch testing so that each container need not be certified as complying
with its requirements. Terms such as design family, qualification
testing, or batch are used in ANSI/NGV2, and RSPA requirements for DOT
cylinders. For example, ANSI/NGV2 requires qualification tests, such as
the burst test, only when certain design changes are made to a
particular design of CNG containers. In addition, manufacturer tests
are sometimes done on batches or lots of 200 cylinders. Based on the
above considerations, it would be inappropriate to require the
information requested by Norris.
5. Test Conditions
a. Diesel fuel in bonfire test. NHTSA received two petitions for
reconsideration to amend S8.3.6, which addresses the bonfire test's use
of diesel fuel. Flxible petitioned the agency to allow the use of a
wood-fueled bonfire test rather than diesel fuel. It stated that fire
marshals and other authorities have placed restrictions on the use of
diesel fuel. SCI stated that the use of diesel fuel would adversely
affect the environment, but offered no alternative.
NHTSA has decided not to amend FMVSS No. 304 with respect to the
bonfire test's fuel in today's notice. Instead, the agency is currently
reviewing comments on this matter in response to a SNPRM that included
a proposal to amend the bonfire test to allow alternative types of fuel
given the potential environmental problems with using diesel fuel. If
the agency determines that the bonfire test's fuel needs to be changed,
it will do so in the context of that rulemaking.
b. More detail in bonfire test. PST requested that NHTSA define the
bonfire test in more detail. Paragraph S8.3.10 states that, during the
bonfire test, ``[t]he average wind velocity at the container is not to
exceed 2.24 meters per second (5 mph).'' The petitioner stated that in
some conditions, a 2.24 meters per second wind might preclude the
container from being totally engulfed in flames. This consideration led
PST to recommend that this requirement should instead read ``* * * 5
mph or less if necessary to achieve full impingement and engulfment.''
PST indicated that it uses a system of wind shields during its testing
to assure full impingement or engulfment.
NHTSA has decided not to amend the bonfire test in FMVSS No. 304.
The agency notes that since S8.3.2 and S8.3.3 specify full flame
impingement or engulfment of the container during testing, allowing a
wind speed of up to 2.24 meters per second will not preclude total
flame impingement or engulfment. The agency notes that a manufacturer
is not precluded from using wind shields to assure that full flame
impingement or engulfment is achieved.
c. Venting of container during bonfire test. Section S7.3 specifies
that during the bonfire test, the CNG container shall
[[Page 37842]]
either completely vent its contents through a pressure relief device or
shall not burst while retaining its entire contents. PST stated that
this requirement is unreasonable because it is difficult to verify and
unnecessary. PST offered no alternative language, but stated that under
certain conditions a small amount of gas can escape through seals
around the pressure relief devices and leak small quantities of gas
during the test. According to PST, this leakage is not harmful and
should be allowed. PST further stated that if the intent of S7.3 is
that the container vent completely through the pressure relief device,
incidental leaks should be of no concern.
NHTSA believes that it would be inappropriate to amend FMVSS No.
304 based on PST's unsupported claim that under certain conditions a
small amount of gas can leak through seals around the pressure relief
device. PST provided no information showing that the burst requirement
is inappropriate or that leakage around the seal is a problem in a
properly constructed CNG container. The agency further notes that no
other petitioner believed that this requirement is inappropriate or
raised practicability problems. If such additional information is
provided, NHTSA would consider whether further rulemaking is
appropriate. As an alternative to seeking an amendment to the standard,
PST could file a petition requesting the agency determine that such a
noncompliance with the standard is inconsequential as it relates to
safety under Part 556, Exemption for Inconsequential Defect or
Noncompliance.
d. Burst and pressure cycling test procedures. PST stated that the
allowable range of pressurization rates for the burst test is
unreasonable, and that NHTSA should draft and publish methods for
compliance testing which set a minimum pressurization rate of 100 psi
per second. S8.2.2 specifies that pressurization throughout the burst
test shall not exceed 200 psi per second. PST indicated that test
results are a function of pressurization rate, and that very low rates
can make the test overly stringent. Similarly, PST stated that the
absence of a minimum cycling rate or test duration in the pressure
cycling test, S8.1.3, is unreasonable, since fatigue cycle life is
known to be sensitive to the cycling rate and test duration. Section
S8.1.3 specifies a maximum cycling rate of 10 cycles per minute. PST
stated that a minimum cycling rate of 5 cycles per minute is
reasonable, or alternatively, a test duration of 60 hours. PST stated
that it had previously commented on these issues.
NHTSA has decided not to adopt PST's request to modify the
pressurization rates in the burst test. While PST is correct that
pressurization rates do affect the test's severity, the agency notes
that it is appropriate to specify the range because CNG containers in
the real world will experience a variety of pressurizations. Therefore,
it is in the interest of safety to specify such rates. In addition,
specifying maximum pressurization and cycling rates in FMVSS No. 304
without specifying minimums is consistent with the voluntary industry
standard, ANSI/NGV2. The agency specifically asked CGA and the NGVC
about minimum pressurization and cycling rates, but neither
organization was able to provide adequate rationale to include them in
the final rule. PST has offered no new data to support the inclusion of
a minimum rate for pressurization or cycling. Based on the above
considerations, the agency believes that the rule should remain the
same as those in NGV2 with no minimum pressurization and cycling rates.
6. Miscellaneous
a. Withdraw or delay the effective date of FMVSS 304. Several
petitioners asked that the final rule be withdrawn, or delayed for a
year or more. A number of them stated the rule does not reflect all of
the safety requirements contained in ANSI/NGV2, and therefore is not
comprehensive from a safety standpoint. They also stated that ANSI/NGV2
is currently being revised and updated by the industry, and indicated
that a delay would allow incorporation of these new revisions.
NHTSA has determined that it would be inappropriate to withdraw the
effective date of the September 1994 final rule, which took effect
March 27, 1995. Even though the rule does not contain all of the
requirements of ANSI/NGV2, NHTSA believes that it is better to have
some requirements in place rather than none at all. Further, the agency
is moving toward adding more requirements through the SNPRM that was
published in December 1994. That notice proposes additional performance
requirements, consistent with those in ANSI/NGV2, to evaluate a CNG
fuel container's internal and external resistance to corrosion and
acidic chemicals, brittle fracture, fragmentation, and external damage
caused by incidental contact with road debris or mechanical damage
during the vehicle's operation.
With regard to the revisions currently being made to ANSI/NGV2,
NHTSA believes that it would be inappropriate for the same reason to
delay the rule.
b. Flexibility and adaptability of final rule. Chrysler supported
earlier comments submitted by the American Automobile Manufacturers
Association (AAMA) which included the statement that the ANSI/NGV2
voluntary industry standard ``* * * lacks the flexibility and
adaptability that should be part of a regulatory requirement * * *''
Those earlier comments were submitted by AAMA in response to the
December 1993 SNPRM.
NHTSA notes that in the December 1993 SNPRM, the agency announced
that it was considering the adoption of many of the requirements in
ANSI/NGV2 for its final rule on CNG containers. The agency also laid
out its rationale for this approach. After considering all of the
comments, the agency based the rule on the voluntary industry standard,
ANSI/NGV2. Chrysler offered no new arguments which the agency has not
already considered and responded to in promulgating the rule.
c. Chemical compositions. NHTSA has decided to revise S5.2.2 to
reflect new information provided by AGA in a telephone conversation
with NHTSA staff members. The AGA advised the agency that there is a
typographical error in S5.2.2 concerning the amount of magnesium in
6061 alloy aluminum. While FMVSS No. 304 specifies ``0.60 to 1.20
percent,'' AGA stated that the correct numbers are 0.80 to 1.20. The
error is also present in the current version of ANSI/NGV2.
NGVSys submitted a letter dated February 16, 1995, requesting that
the percent limits for lead and bismuth in aluminum alloy 6061 be
revised. S5.2.2 of Standard 304 currently specifies these each at 0.003
percent maximum. NGVSys requested that the limits be revised to 0.01
percent maximum, indicating that the industry group currently revising
ANSI/NGV2 has accepted this change for its 1995 revision. NGVSys
enclosed with its request a copy of a letter from Alcoa, an aluminum
supplier. The letter indicates that Alcoa's current limit for lead and
bismuth in aluminum alloy 6061 is 0.010 percent each, and that further
reductions in this limit would impact cost.
NHTSA has decided to deny NGV System's request. NGV Systems has
provided no rationale to justify its request, nor has it provided any
information on the safety implications of allowing the increased
amounts of lead and bismuth. The agency notes that FMVSS No. 304's
specifications for lead and bismuth are consistent with both
[[Page 37843]]
the current version of ANSI/NGV2 and the draft ISO standard for CNG
containers.
IV. Rulemaking Analyses
A. Executive Order 12866 and DOT Regulatory Policies and Procedures
NHTSA has considered this rulemaking action in connection with
Executive Order 12866 and the Department of Transportation's regulatory
policies and procedures. This rulemaking document was not reviewed
under E.O. 12866, ``Regulatory Planning and Review.'' This action has
been determined to be ``nonsignificant'' under the Department of
Transportation's regulatory policies and procedures. In conjunction
with the September 1994 final rule, NHTSA prepared a Final Regulatory
Evaluation (FRE) in which it estimated the rulemaking's costs. Today's
rule simply reaffirms the December final rule in which the agency
concluded that ``specify(ing) a 2.25 safety factor for carbon fiber
containers would negate this cost increase to container manufacturers,
as they currently manufacture containers to this value.'' As a result,
manufacturers will not have to depart from current manufacturing
practices and thus not incur additional costs. Most of the performance
requirements in the standard are already being met by CNG fuel
container manufacturers, who produce and test containers in accordance
with ANSI/NGV2. The agency's reaffirmation of its December 1994
decision to specify a 2.25 safety factor for carbon fiber containers
negates the cost increase faced by container manufacturers as a result
of the higher factor in the September 1994 final rule. The
manufacturers already manufacture containers to the lower factor. Since
the agency has decided to adopt the same safety factor as that
currently met by container manufacturers, there is no need to perform a
new regulatory evaluation. The agency further notes that the various
minor amendments being made in today's notice will collectively have
only a negligible effect on costs.
B. Regulatory Flexibility Act
NHTSA has also considered the effects of this rulemaking action
under the Regulatory Flexibility Act. Based upon the agency's
evaluation, I certify that this rule will not have a significant
economic impact on a substantial number of small entities. Information
available to the agency indicates that businesses manufacturing CNG
fuel containers are not small businesses. Further, as noted above, the
amendments made in today's document will have a negligible effect on
costs of compliance.
C. Executive Order 12612 (Federalism)
NHTSA has analyzed this rulemaking action in accordance with the
principles and criteria contained in Executive Order 12612. NHTSA has
determined that the rule will not have sufficient Federalism
implications to warrant the preparation of a Federalism Assessment.
D. National Environmental Policy Act
In accordance with the National Environmental Policy Act of 1969,
NHTSA has considered the environmental impacts of this rule. The agency
has determined that this rule will have no adverse impact on the
quality of the human environment. On the contrary, because NHTSA
anticipates that ensuring the safety of CNG vehicles will encourage
their use, NHTSA believes that the rule will have positive
environmental impacts. CNG vehicles are expected to have near-zero
evaporative emissions and the potential to produce very low exhaust
emissions as well.
E. Civil Justice Reform
This final rule does not have any retroactive effect. Under 49
U.S.C. 30103, whenever a Federal motor vehicle safety standard is in
effect, a State may not adopt or maintain a safety standard applicable
to the same aspect of performance which is not identical to the Federal
standard, except to the extent that the State requirement imposes a
higher level of performance and applies only to vehicles procured for
the State's use. 49 U.S.C. 30161 sets forth a procedure for judicial
review of final rules establishing, amending or revoking Federal motor
vehicle safety standards. That section does not require submission of a
petition for reconsideration or other administrative proceedings before
parties may file suit in court.
List of Subjects in 49 CFR Part 571
Imports, Incorporation by reference, Motor vehicle safety, Motor
vehicles.
PART 571--[AMENDED]
In consideration of the foregoing, 49 CFR Part 571 is amended as
follows:
1. The authority citation for Part 571 continues to read as
follows:
Authority: 49 U.S.C. 322, 30111, 30115, 30117 and 30166;
delegation of authority at 49 CFR 1.50.
Sec. 571.5 [Amended]
2. Section 571.5 is amended by removing paragraph (b)(9).
Sec. 571.304 [Amended]
3. Section 571.304 is amended by revising S5.2.2, S5.4.1(b),
S5.5.1, S7.2.2, S7.4, S8.1.3, S8.2.2, and S8.3.10 to read as follows:
* * * * *
S5.2.2 Aluminum containers and aluminum liners. (Type 1, Type 2 and
Type 3) shall be 6010 alloy, 6061 alloy, and T6 temper. The aluminum
heat analysis shall be in conformance with one of the following grades:
Table Two.--Aluminum Heat Analysis
------------------------------------------------------------------------
Grade: Element 6010 alloy percent 6061 alloy percent
------------------------------------------------------------------------
Magnesium.............. 0.60 to 1.00........... 0.80 to 1.20.
Silicon................ 0.80 to 1.20........... 0.40 to 0.80.
Copper................. 0.15 to 0.60........... 0.15 to 0.40.
Chromium............... 0.05 to 0.10........... 0.04 to 0.35.
Iron................... 0.50 max............... 0.70 max.
Titanium............... 0.10 max............... 0.15 max.
Manganese.............. 0.20 to 0.80........... 0.15 max.
Zinc................... 0.25 max............... 0.25 max.
Bismuth................ 0.003 max.............. 0.003 max.
Lead................... 0.003 max.............. 0.003 max.
Others, Each \1\....... 0.05 max............... 0.05 max.
Others, Total \1\...... 0.15 max............... 0.15 max.
Aluminum............... Remainder.............. Remainder.
------------------------------------------------------------------------
\1\ Analysis is made only for the elements for which specific limits are
shown, except for unalloyed aluminum. If, however, the presence of
other elements is indicated to be in excess of specified limits,
further analysis is made to determine that these other elements are
not in excess of the amount specified. (Aluminum Association Standards
and Data--Sixth Edition 1979).
* * * * *
S5.4.1 Type 1 Containers.
(a) * * *
(b) For minimum wall thickness calculations, the following formula
is used:
[GRAPHIC][TIFF OMITTED]TR24JY95.004
Where:
S = Wall stress in MPa (psi).
P = Minimum hydrostatic test pressure in Mpa (psi).
D = Outside diameter in mm (inches).
d = Inside diameter in mm (inches).
* * * * *
S5.5.1 Compute stresses in the liner and composite reinforcement
using National Aeronautics and Space Administration (NASA), Computer
Program for the Analysis of Filament Reinforced Metal-Wound Pressure
[[Page 37844]]
Vessels, N67-12097 (NASA CR-72124) (May 1966), or its equivalent.
* * * * *
S7.2.2 Each Type 2, Type 3, or Type 4 CNG fuel container shall not
leak when subjected to burst pressure and tested in accordance with
S8.2. Burst pressure shall be no less than the value necessary to meet
the stress ratio requirements of Table 3, when analyzed in accordance
with the requirements of S5.5.1.
Table Three.--Stress Ratios
------------------------------------------------------------------------
Material Type 2 Type 3 Type 4
------------------------------------------------------------------------
E-Glass................................... 2.65 3.5 3.5
S-Glass................................... 2.65 3.5 3.5
Aramid.................................... 2.25 3.0 3.0
Carbon.................................... 2.25 2.25 2.25
------------------------------------------------------------------------
* * * * *
S7.4. Labeling. Each CNG fuel container shall be permanently
labeled with the information specified in paragraphs (a) through (d).
Any label affixed to the container in compliance with this section
shall remain in place and be legible for the manufacturer's recommended
life of the container. The information specified in paragraphs (a)
through (d) of this section shall be in English and in letters and
numbers that are at least 6.35 mm (0.25 inch).
(a) The statement: ``If there is a question about the proper use,
installation, or maintenance of this container, contact ____________.''
inserting the CNG fuel container manufacturer's name, address, and
telephone number.
(b) The statement: ``Manufactured in ____________.'' inserting the
month and year of manufacture of the CNG fuel container.
(c) Service Pressure ________ kPa (________psig).
(d) The symbol DOT, constituting a certification by the CNG
container manufacturer that the container complies with all
requirements of this standard.
* * * * *
S8.1.3 The cycling rate for S8.1.1 and S8.1.2 shall be any value
up to and including 10 cycles per minute.
* * * * *
S8.2.2 The pressurization rate throughout the test shall be any
value up to and including 1,379 kPa (200 psi) per second.
* * * * *
S8.3.10 The average wind velocity at the container is any velocity
up to and including 2.24 meters/second (5 mph).
* * * * *
Issued on July 18, 1995.
Ricardo Martinez,
Administrator.
[FR Doc. 95-18109 Filed 7-19-95; 2:09 pm]
BILLING CODE 4910-59-P