ISO 12991:2012 pdf free download.Liquefied natural gas ( LNG ) -Tank or on-board storage as a fuel for automotive vehicles.
ISO 12991 specifies the construction requirements for relilbblc fuel tanks For liquefied natural gas (L.NG) used in vehicles as well as the testing methods required to ensure that a reasonable level of protection from loss of life and property resulting from fire and explosion is provided.
ISO 12991 is .ipplicable to fuel tanks intended to be permanently attached to land vehicles but can be used as a guide for other mode of transport.
2 Normative references
The following documents, in whole or In part, are normatively referenced In ISO 12991 and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the btest edition of the referenced document (including any amendments) applies.
ISO 1176. Road vehicles — Masses — wicabulary and codes
ISO 14 31-1, Rubber, vulcanized or thermoplastic — Resistance to ozone cracking — Part I: Static and dynamic strain testing
ISO 2768-i, General tolerances — Part 1: Thlerances for linear and angular dimensions without individual tolerance indications
ISO 6957, Copper alloys — Ammonia test for stress corrosion resistance
ISO 9227, CorrosIon tests In artificial atmospheres — Salt spray tests
ISO 21013-3, Cryogenic vessels — Pressure-relief accessories for cryogenic service — Port 3: Sizing and capacity determination
ISO 21014. Cryogenic vessels — Cryogenic insulation performance
ISO 2102K-i, Cryogenic vessels — Toughness requirements for materials at cryogenic temperature — Part 1:
Temperatures below -80 degrees C
ISO 21029-1:2004. Cryogenic vessels — Transportable vacuum insulated vessels of not more than 1 000 litres volume — Part 1: Des&gn, fabrication, inspection and tests
ISO 23208, Cryogenic vessels — Cleanliness for cryogenic service
3 Terms and definitions
For the purposes of ISO 12991, the following terms and definitions apply.
accessory
device fixed directly to the inner tank or outer jacket of a fuel tank such as a pressure relief valve, shutoff valve, non-return valve or level gauge
3.2
boll-off management system
system that controls the boll-off olgas under normal conditions
4.3.2 Ambient temperature
The fuel tank shall be designed to withstand ambient temperatures ranging from —40°C to 85°C. If the fuel tank is to be installed in areas of internal heat sources such as the internal combustion engine compartment of a vehicle, the fuel tank shall be designed for an ambient temperature of 120°C, or a lower value if substantiated by calculations.
4.3.3 Operating temperature
The thermal stresses produced by the operating conditions shall be considered. The inner vessel and the other components that may be In contact with LNG shall be designed to operate at -196 °C.
4.4 MaterIals
The materials of the fuel tank and Its accessories shall be compatible, as applicable, with
a) LNG,and
b) other media and fluids found in a vehicle environment, such as coolants, brake fluid and battery acid.
Materials used at low temperatures shall meet the toughness requirements of ISO 21028-1. For nonmetallic materials, low temperature suitability shall be validated by an experimental method, taking Into account the service conditions.
The materials used for the outer jacket shall ensure the integrity of the insulation system and shall be made of austenitic stainless steel
For the inner vessel if materials other than austenitic stainless steels are used It shall be ensured that the materials will resist all the In service fatigue load
A corrosion allowance does not need to be added for the Inner tank. A corrosion allowance does not need to be added on other surfaces, if they are protected against corrosion.
For welded vessels, welds shall have properties equivalent to those specified for the parent material for all temperatures that the material may encounter.
4.5 DesIgn
4,5.1 DesIgn validation
Each type of vessel shall be validated in accordance with the design options specified in 10.1 of ISO 21029-1:2004 and In accordance with onc of options given in 4.5.1.1 and 43.1.2.
4.5.1.1 ValidatIon by calculation
This option requires calculation in accordance with 10.3 of ISO 21029.1:2004. Additional calculations are required to validate the design For accelerations In 4.2.2.
4.5.1.2 Validation by experiment method
This option requires validation In accordance with 10.4 of ISO 21029-1:2004 with the following modification: drop tests shall include a 9 m drop test of the fuel tank on the most critical area of the tank (other than the piping end) and a 3 rn drop test on the piping end.
4.5.2 Inner tank and outer lacket
For the design of inner and outer tank the only acceptable options are
— the design is validated as peroplion 10.1.3 of ISO 21029-1:2004, especially the requirements ofTable 3;
The pressure test shall be performed before the outer jacket Is mounted. The pressure In the Inner tank shall be increased at an even rate until the test pressure is reached. The Inner tank shall remain under the test pressure without the addition of test media for at least 10 mm to establish that the pressure is not decreasing.
After the test, the inner tank shall not show any signs of visible permanent deformation nor leaks. Inner tanks that do not pass the test because of perma nentdelormation shall be rejected and shall not be repaired, Inner tanks that do not pass the test because of leakage may be accepted alter repair and retesting.
Upon completion of the Lest, the inner tank shall be emptied, cleaned, and dried according to ISO 23208. A test report shall be drawn up and the inner tank shall be marked if accepted.
6.3 Leak test
After final assembly, the fuel tank shall be helium leak tested with a gas mixture containing a minimum of 10 % of helium using a mass spectrometer leak detector capable of detecting leaks ranging From I x 10- cm3/s at 20°C and 101,325 kPa to 1 x 10- cm3/s at 20 °C and 101,325 kPa. There shall be no detectable leak. The fuel tank accessories shall be leak tested in accordance with 8.2, exceptthat the test shall be performed only at 20°C ± S ‘C.
6.4 Verification of the dimensions
The following dimensions shall be verified at a frequency In accordance with the manufacturer quality system for each batch of no more than 50 tanks made from the same batch of Inner tank heads.
a) for cylindrical fuel tanks, the roundness of the inner tank shall be measured and not exceed the requirements specified In 11.5.4.2 of ISO 21029-1:2004:
b) departure from a straight line of the inner tank and outer jacket shall be measured and not exceed the requirements specified in 11.5.4.3 of ISO 21029-1:2004.
6.5 DestructIve and non-destructive tests of welded olnts
The destructive and non-destructive tests of welded joints shall be performed and meet the requirements specified In 12.2 to 12.4 of ISO 21029-1:2004.
All welded joints of the Internal pipe work between the Inner tank and the outer jacket shall be subjected to 100 % non-destructive inspection, When radiographs can be interpreted, radiographic inspection shall be used. When radiographs cannot be interpreted, ultrasonic inspection shall be used. When both.