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12.9.1. Flight Hardware Cryogenic System General Design Requirements
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12.9.1.1. Propellant systems shall have low point drain capability.
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12.9.1.1.1. Low point drains shall be accessible and located in the system to provide the capability of removing propellant from the tanks, piping, lines, and components.
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12.9.1.1.2. In addition, the LH2 system shall be designed to be purged with inert fluids.
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12.9.1.2. Bi-propellant systems shall have the capability of loading the fuel and oxidizer one at the time.
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12.9.1.3. For prelaunch failure modes that could result in a time-critical emergency, provision shall be made for automatic switching to a safe mode of operation. Caution and warning signals shall be provided for these time-critical functions.
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12.9.1.4. Pneumatic systems servicing cryogenic systems shall comply with the pneumatic pressure system requirements of 12.6.
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12.9.1.5. Cryogenic systems shall be designed to control liquefaction of air.
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12.9.1.6. For systems requiring insulation, nonflammable materials shall be used in compartments or spaces where fluids and/or vapors could invade the area.
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12.9.1.7. Vacuum-jacketed systems shall be capable of having the vacuum verified.
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12.9.1.8. Purge gas for LH2 and cold GH2 lines should be gaseous helium (GHe).
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12.9.1.9. Precautions shall be taken to prevent cross-mixing of media through common purge lines by use of check valves to prevent back flow from a system into a purge distribution manifold.
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12.9.1.10. Titanium and titanium alloys shall not be used where exposure to GOX (cryogenic) or LO2 (LOX) is possible.
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12.9.2. Flight Hardware Cryogenic System Vessels and Tanks. Cryogenic vessels and tanks shall be designed in accordance with the requirements in 12.2.
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12.9.3. Flight Hardware Cryogenic System Piping and Tubing
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12.9.3.1. The amount and type of thermal insulation (insulation material or vacuum-jacketed) shall be determined from system thermal requirements.
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12.9.3.2. The use of slip-on flanges shall be avoided.
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12.9.3.3. Flanged joints in LH2 systems shall be seal welded.
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12.9.3.4. Flanged joint gaskets shall not be reused.
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12.9.3.5. Cryogenic systems shall provide for thermal expansion and contraction without imposing excessive loads on the system.
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Bellows, reactive thrust bellows, or other suitable load relieving flexible joints may be used.
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12.9.3.6. All pipe and tube welded joints shall be 100 percent radiographically inspected. All joints shall be inspected by surface NDE techniques after system acceptance pressure testing. Where post-proof test surface NDE is impractical, visual inspection will be allowed with justification and PSWG and Range Safety approval.
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12.9.3.6.1. Welded connections shall meet the requirements of AWS D17.1, Specification for Fusion Welding for Aerospace Applications, as prescribed by NASA-STD-5006, General Fusion Welding Requirements for Aerospace Materials Used in Flight Hardware.
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12.9.3.6.2. Tube and fitting welded joints shall meet the inspection requirements of AIAA/NAS 1514-72, Radiographic Standard for Classification of Fusion Weld Discontinuities, and ASTM E 1742, Standard Practice for Radiographic Examination, and be visually inspected using appropriate mechanical aids as needed to ensure compliance with weld specifications and requirements in accordance with aerospace industry practices. Surface inspection, if applicable, shall meet the requirements of ASTM E 1417, Standard Practice for Liquid Penetrant Inspection.
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12.9.4. Flight Hardware Cryogenic System Valves
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12.9.4.1. Cryogenic systems shall be designed to ensure icing does not render the valve inoperable.
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12.9.4.2. Remotely controlled valves shall provide for remote monitoring of the open and closed positions.
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12.9.4.3. Remotely operated valves shall be designed to be fail-safe if pneumatic or electric control power is lost during prelaunch operations.
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12.9.4.4. All electrical control circuits for remotely actuated valves shall be shielded or otherwise protected from hazardous stray energy.
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12.9.4.5. Manually operated valves shall be designed so that overtorquing the valve stem cannot damage seats to the extent that seat failure occurs.
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12.9.4.6. Valve stem travel on manual valves shall be limited by a positive stop at each extreme position.
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12.9.4.7. The application or removal of force to the stem positioning device shall not cause disassembly of the pressure containing structure of the valve.
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12.9.4.8. Manual or remote valve actuators shall be operable under maximum design flow and pressure.
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12.9.4.9. Valves that are not intended to be reversible shall be designed or marked so that they cannot be connected in a reverse mode.
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12.9.4.10. Stem position local or remote indicators shall sense the position of the stem directly, not the position of the actuating device.
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12.9.4.11. All electromechanical actuator electrical wiring shall be sealed to prevent fluid ignition.
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12.9.5. Flight Hardware Cryogenic System Pressure Indicating Devices
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12.9.5.1. A pressure indicating device shall be located on any cryogenic vessel and/or tank and on any section of the system where cryogenic liquid can be trapped.
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12.9.5.2. These pressure indicating devices shall be designed to be remotely monitored during prelaunch operations.
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12.9.6. Flight Hardware Cryogenic System Flexible Hoses. Flexible hose requirements are specified in 12.1.10.4 in addition to the following:
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12.9.6.1. Flexible hoses used in cryogenic system shall be of the single-wall, double-wall, or double-wall, vacuum-jacketed type.
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12.9.6.2. All convoluted portions of flexible hoses shall be covered with stainless steel wire band.
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12.9.7. Flight Hardware Cryogenic System Pressure Relief Devices
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12.9.7.1. All cryogenic vessels and tanks shall be protected against overpressure by means of at least one pressure relief valve.
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12.9.7.2. Minimum design requirements are as follows:
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12.9.7.2.1. The pressure relief device shall be installed as close as practical to the cryogenic vessel or tank.
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12.9.7.2.2. Pressure relief valves shall be set to operate at pressures determined on a case-by-case basis by the payload project.
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12.9.7.2.3. The relieving capacity of the relief valve shall be determined on a case-by-case basis by the payload project.
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12.9.7.3. All pressure relief devices shall be vented separately unless the following can be positively demonstrated:
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12.9.7.3.1. The creation of a hazardous mixture of gases in the vent system and the migration of hazardous substances into an unplanned environment is impossible.
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12.9.7.3.2. The capacity of the vent system is adequate to prevent a pressure rise more than 20 percent above MOP when all attached pressure relief devices are wide open and the system is at full pressure and volume generating capacity.
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12.9.7.4. All relief devices and associated piping shall be structurally restrained to eliminate any deleterious thrust effects on cryogenic system vessels or piping.
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12.9.7.5. The effects of the discharge from relief devices shall be assessed and analyzed to ensure that operation of the device shall not be hazardous to personnel or equipment.
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Items to be analyzed are thrust loads, impingement of high velocity gas or entrained particles, toxicity, oxygen enrichment, and flammability.
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12.9.7.6. No obstructions shall be placed downstream of the relief valves.
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12.9.7.7. Relief valves shall be located so that other components cannot render them inoperative.
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12.9.8. Flight Hardware Cryogenic System Vents
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12.9.8.1. GH2 shall be vented to atmosphere through a burner system.
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12.9.8.2. Cryogenic systems shall be designed so that fluids cannot be trapped in any part of the system without drain or vent (relief valve or vent valve) capability.
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12.9.8.3. Each line venting into a multiple-use vent system shall be protected against back pressurization by a check valve if the upstream system cannot withstand the back pressure or where contamination of the upstream system cannot be tolerated.
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12.9.8.4. Vents shall be placed in a location normally inaccessible to personnel and at a height or location where venting is not normally deposited into habitable spaces.
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12.9.8.5. Each vent shall be conspicuously identified using appropriate warning signs, labels, and markings.
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12.9.8.6. Vent outlets shall be located far enough away from incompatible propellant systems and incompatible materials to ensure no contact is made during vent operations.
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12.9.8.7. Incompatible fluids shall not be discharged into the same vent or drain system.
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12.9.8.8. Fuel vent systems shall be equipped with a means of purging the system with an inert gas to prevent explosive mixtures.
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12.9.8.9. Vent outlets shall be protected against rain intrusion and entry of birds, insects, and animals.
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12.9.8.10. Special attention shall be given to the design of vent line supports at vent outlets due to potential thrust loads.
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12.9.9. Testing Flight Hardware Cryogenic System Components Before Assembly
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12.9.9.1. All cryogenic vessels and tanks shall be qualification tested in accordance with 12.2.2.6 and acceptance tested in accordance with 12.2.2.7.
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12.9.9.2. Flight hardware cryogenic system components shall meet the test requirements of 12.5.1.17.1 before assembly.
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12.9.10. Testing Flight Hardware Cryogenic Systems After Assembly
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12.9.10.1. Flight hardware cryogenic systems shall meet the test requirements of 12.5.1.17.2 after assembly.
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12.9.10.2. All newly assembled cryogenic systems shall be leak tested.
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12.9.10.3. The system shall be pressurized to the system MOP using gaseous helium for LH2 systems and GN2 for LO2 (LOX) systems.
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12.9.10.4. Following the leak test, all newly assembled cryogenic systems shall have a system validation test performed at system MOP before first operational use at the payload processing facility and launch site area.
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12.9.10.5. Minimum test requirements are as follows:
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12.9.10.5.1. The intended service fluid (LO2[LOX], LH2) shall be used as the validation test fluid.
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12.9.10.5.2. The functional capability of all components and subsystems shall be validated.
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12.9.10.5.3. All prelaunch operational sequences for the system shall be exercised, including emergency shutdown, safing, and unloading procedures.
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12.9.10.5.4. Vacuum readings of all vacuum volumes shall be taken and recorded before, during, and after the test.
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12.9.10.5.5. No deformation, damage, or leakage is allowed.
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12.9.11. Testing Modified and Repaired Flight Hardware Cryogenic Systems
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12.9.11.1. Any cryogenic system element, including fittings or welds, that have been repaired, modified, or possibly damaged before the system leak test shall be retested.
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12.9.11.2. The component retest sequence shall be as follows:
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12.9.11.2.1. The component shall be hydrostatically proof tested at ambient temperature to 1.5 times the component MAWP or MEOP.
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12.9.11.2.2. The component shall be reinstalled into the cryogenic system and a leak check performed at system MOP or MEOP.
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12.9.11.2.3. The functional capability of the modified and/or repaired component shall be revalidated using the intended service fluid at system MOP or MEOP.
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12.9.11.3. If any cryogenic system elements such as valves, regulators, gauges, or pipes have been disconnected or reconnected for any reason, the affected connection shall be leak checked at MOP.
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