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12.1.10.1.1. The design of hypergolic propellant systems shall take into consideration limitations imposed on individuals dressed in SCAPE or other approved propellant handling ensembles during fill and drain operations.
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C
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12.1.10.1.2. Sufficient clearances are needed for the insertion of assembly tools.
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C
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12.1.10.1.3. Redundant pressure components and systems shall be separated from main systems to decrease the chance of total system failure in case of damage, fire, or malfunction.
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12.1.10.1.4. Pressure systems shall be shielded from other systems to protect against hazards caused by proximity to combustible gases, heat sources, and electrical equipment.
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12.1.10.1.5. Any failure in any such adjacent system shall not result in combustion, explosion, or release of pressure fluids.
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12.1.10.1.6. Safety critical pressure systems shall be designed so that special tools are not required for removal and replacement of components unless it can be shown that the use of special tools does not create additional hazards and the special tools will be made available throughout testing, ground processing and launch.
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12.1.10.2. Flight Hardware Pressure System components and Fixtures
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12.1.10.2.1. Fixtures for safe handling and hoisting with coordinated attachment points in the system structure shall be provided for equipment that cannot be hand carried and attached with fixtures and attachment points being included in the flight structures analyses.
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12.1.10.2.2. Components shall be designed so that, during the assembly of parts, sufficient clearance exists to permit assembly of the components without damage to seals, O-rings, or backup rings where they pass over threaded parts or sharp corners.
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12.1.10.2.3. Handling and hoisting loads shall be in accordance with 29 CFR 1910 requirements, Chapter 6 of this volume, Chapter 6 of Volume 6 and NASA-STD 8719.9.
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12.1.10.2.4. All incompatible propellant system connections shall be designed to be physically impossible to interconnect.
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Incompatible propellant system connections should be keyed, sized, or located so that it is physically impossible to interconnect them.
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12.1.10.2.5. Quick Disconnect Couplings
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The quick disconnect assembly consists of both the ground-half and air-half couplings.
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12.1.10.2.5.1. All quick disconnect couplings shall be designed with a factor of safety of not less than 2.5.
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12.1.10.2.5.2. Quick disconnect coupling bodies and appropriate parts shall be constructed of 304, 304L, 316, or 316L series stainless steel. All parts that contact the fluid shall be compatible with the fluid.
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12.1.10.2.5.3. The quick disconnect ground-half coupling shall withstand being dropped from a height of six feet on to a metal deck/grating or concrete floor without leaking or becoming disassembled.
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12.1.10.2.5.4. When uncoupled, the quick disconnect shall seal the air-half and ground-half couplings and shall not permit external leakage. Both halves of the coupling shall seal under both low and high pressure. In cryogenic systems only, quick disconnects used in vent coupling assemblies shall allow gaseous cryogenic flow through the coupling whether connected or disconnected.
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12.1.10.2.5.5. When coupled, the quick disconnect shall permit fluid flow in either direction.
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12.1.10.2.5.6. The quick disconnect shall not permit external leakage during any phase of coupling or uncoupling.
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12.1.10.2.5.7. The quick disconnect shall be designed so that coupling and uncoupling can be performed with simple motions.
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12.1.10.2.5.8. The quick disconnect coupling shall contain a positive locking device that will automatically lock the connection of the coupling halves. It shall be possible by visual inspection to determine that the quick disconnect is completely coupled and locked. The quick disconnect shall not have any partially coupled unlocked position in which the coupling can remain stable and permit fluid flow.
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12.1.10.2.5.9. Special care shall be taken in the quick disconnect design to ensure that the possibility of inadvertent uncoupling and/or coupling external leakage due to side and axial loads is minimized.
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12.1.10.2.5.10. The quick disconnect shall be designed to couple/uncouple without imparting adverse loads on fluid lines that could cause flight hardware damage.
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12.1.10.2.5.11. Quick disconnects shall be designed to ensure that all incompatible fuel and oxidizer couplings cannot be inadvertently connected, causing mixing of propellants.
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12.1.10.2.5.12. All quick disconnect ground half couplings shall be identified in accordance with the requirements of 11.2.1.7.6 of this volume.
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12.1.10.2.6. Pressure fluid tanks shall be shielded or isolated from combustion apparatus or other heat sources.
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12.1.10.3. Flight Hardware Pressure System Tubing and Piping
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12.1.10.3.1. In general, tubing and piping shall be located so that damage cannot occur due to being stepped on, used as handholds, or by manipulation of tools during installation.
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12.1.10.3.2. Straight tubing and piping runs shall be avoided between two rigid connection points.
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12.1.10.3.3. Where such straight runs are necessary, provisions shall be made for expansion joints, motion of the units, or similar compensation to ensure that no excessive strain is applied to the tubing and fittings.
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12.1.10.3.4. Line bends shall be used to ease stresses induced in tubing by alignment tolerances and vibration.
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12.1.10.4. Flight Hardware Pressure System Flexible Hose Requirements
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Guidance for the handling and installation of flexible hoses can be found in KSC specification 80K51846, Flex Hose Handling and Installation Requirements.
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12.1.10.4.1. Flexible hoses shall be used only when required to provide movement between interconnecting fluid lines when no other means are available.
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12.1.10.4.2. Flexible hose systems shall be designed to prevent kinking, avoid abrasive chafing from the restraining device, and avoid abrasive contact with adjacent structure or moving parts that may cause reduction in strength.
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12.1.10.4.3. Flexible hoses shall not be supported by rigid lines or components if excessive loads from flexible hose motion can occur.
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12.1.10.4.4. Flexible hose assemblies shall not be installed in a manner that will place a mechanical load on the hose or hose fittings to an extent that will degrade hose strength or cause the hose fitting to loosen.
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12.1.10.4.5. Flexible hoses shall be designed such that the bend radius is not less than the minimum bend radius recommended in authoritative specifications for the particular hose.
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12.1.10.4.6. Flexible hoses shall not be exposed to internal temperatures that exceed the rated temperature of the hose.
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12.1.10.4.7. Flexible hoses shall not be permitted to pass close to a heat source unless approved by the PSWG and Range Safety and sufficiently protected from the heat source.
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12.1.10.4.8. All flexible hoses that are not lined shall be subjected to a flow-induced vibration analysis.
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MSFC 20MO2540 provides guidance for performing flow-induced vibration analysis.
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12.1.10.4.9. Flexible hoses shall consist of a flexible inner pressure carrier tube (compatible with the service fluid) constructed of elastomeric [typically poly-tetrafluoroethylene (PTFE) for hypergolic fluid] or corrugated metal (typically 300-series stainless steel) material reinforced by one or more layers of 300-series stainless steel wire and/or fabric braid. Flexible hoses used shall be verified to be within acceptable shelf life requirements.
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In applications where stringent permeability and leakage requirements apply, hoses with a metal inner pressure carrier tube should be used. If these hoses will be used in a highly erosive environment, consideration should be given to the use of Hastalloy C-22 in accordance with ASTM B575 for the inner pressure carrier tube and C-276 material for the reinforcing braid.
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12.1.10.4.10. Flexible hose restraining devices shall be designed and demonstrated to contain a force not less than 1.5 times the open line pressure force (see Table 12.1).
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12.1.10.4.10.1. The restraint design safety factor shall not be less than 3 on material yield strength.
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12.1.10.4.10.2. Hose clamp-type restraining devices shall not be used.
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12.1.10.4.11. Flexible hose installations shall be designed to produce no stress or strain in the hard lines or components. Stresses induced because of dimensional changes caused by pressure or temperature variations or torque forces induced in the flexible hose shall be included in the analysis.
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Table 12.1. Open Line Force Calculation Factor.
Diameter Opening (inch)
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Calculated Force Factor for Each psi of Source Pressure (psi)
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1/8
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0.18506
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1/4
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0.28320
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3/8
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0.38140
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1/2
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0.47960
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5/8
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0.57770
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3/4
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0.67590
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7/8
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0.77410
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1
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0.87230
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To calculate the force acting on line opening, select the applicable diameter opening and multiply he right-hand column by the source pressure (psi)
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12.1.10.5. Flight Hardware Pressure System Valves, Vents, Vent Lines, and Drains
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12.1.10.5.1. Manually operated valves shall be located to permit operation from the side or above to prevent spillage of “hazardous” service fluid on the operator due to leak or failure of the valve seals.
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12.1.10.5.2. For remotely controlled non-pyrotechnically actuated valves, positive indication of actual valve position shall be displayed at the control station.
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Indication of valve stem position or flow measurement is an acceptable indication. Indication of an electrical control circuit actuation is not a positive indication of valve position.
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12.1.10.5.3. Vent lines for flammable and combustible vapors shall be extended away from work areas to prevent accidental ignition of vapors and/or injury to personnel.
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12.1.10.5.4. Vent outlets shall be located far enough away from incompatible propellants systems and incompatible materials to ensure no contact is made during vent operations.
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12.1.10.5.5. Safety valves and burst diaphragms shall be located so that their operation cannot cause injury to personnel standing close by or damage to the installation or equipment, or they shall be equipped with deflection devices to protect personnel and equipment.
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