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Low carbon stainless steels such as type 304L or 316L should be used for welded parts.
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11.2.2.11.13. For liquid systems, the use of glass-faced or radiation source emitting liquid level indicators is prohibited. Other prohibited types include capacitance, conductive, and pressure/density types due to historical operational failures and continuous maintenance problems.
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11.2.2.11.14. Liquid system sight glasses used for liquid level indicators shall be protected from physical damage.
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11.2.2.11.15. As required, pressure gauges shall allow for precision cleaning and verification of cleanliness by particle analysis and non-volatile residue analysis; for example, a bourdon tube tip bleeder or equivalent.
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11.2.2.11.16. Each pressure-indicating device shall be provided with an isolation valve and a test connection (test port) between the isolation valve and the pressure-indicating device. Trapped volume between the isolation valve and the pressure-indicating device shall not exceed 1 inch3.
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11.2.2.11.17. The operating range-of-pressure transducers used for monitoring pressures during hazardous operations shall not be less than 1.2 and not more than 2.0 times the system MOP.
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11.2.2.12. Ground Support Pressure System Flexible Hoses
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11.2.2.12.1. Flexible hoses shall be used only when required for hookup of portable equipment or to provide for movement between interconnecting fluid lines when no other feasible means is available.
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11.2.2.12.2. 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.
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In applications where stringent permeability and leakage requirements apply, hoses with a metal inner pressure carrier tube should be used. Where these hoses are used in a highly corrosive 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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11.2.2.12.3. Hoses shall be provided with 300-series stainless steel end fittings of the coupling nut, 37-degree flared type or with fittings to mate with the appropriately sized ANSI B16.5 flange or KC159 hub. Other end fittings may be used for unique applications, with prior PSWG and Range Safety approval.
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11.2.2.12.4. Flexible hoses shall not be interchanged among incompatible service media. Permeation is not totally negated by any cleaning process. Hoses shall be dedicated to a service media.
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11.2.2.12.5. Hoses over 2 feet long pressurized to 150 psig or greater shall meet the following restraint requirements:
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11.2.2.12.5.1. Flexible hoses shall have safety chains or cables securely attached across each union or splice and at intervals not to exceed 6 feet. Flexible hose installations that are 6 feet long or longer shall be configured so that restraint is provided on both the hose and adjacent structure at no greater than 6-foot intervals and at each end to prevent whiplash in the event of a failure.
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11.2.2.12.5.2. Hose end restraints shall be securely attached to the structure in a manner that does not interfere with the hose flexibility.
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11.2.2.12.5.3. Flexible hose restraint devices shall be capable of withstanding not less than 6 times the open line pressure force. See Table 11.2 below.
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11.2.2.12.5.4. The design safety factor for restraint devices shall not be less than 3 on material yield strength.
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11.2.2.12.5.5. Temporary flexible hose installations may be weighted with 50-pound sand bags, lead ingots, or other suitable weights at intervals not to exceed 6 feet.
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11.2.2.12.5.6. Hose clamp-type restraining devices shall not be used.
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Table 11.2 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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1.0
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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 the right-hand column by the source pressure (psi)
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11.2.2.12.6. Flexible hose installation shall be designed to avoid abrasive contact with adjacent structures or moving parts.
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11.2.2.12.7. 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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11.2.2.12.8. Flexible hose shall not be supported by rigid lines or components if excessive loads from flexible hose motion can occur.
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11.2.2.12.9. Flexible hose between two components may have excessive motion restrained where necessary but shall never be rigidly supported by a tight rigid clamp around the flexible hose.
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11.2.2.12.10. Flexible hoses shall not be exposed to temperatures that exceed the rated temperature of the hose.
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11.2.2.12.11. Flexible hoses that are permitted to pass close to a heat source shall be protected with a fireproof boot metal baffle.
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11.2.2.12.12. Designs using convoluted, unlined bellows, or flexible metal hoses shall be analyzed to verify premature failure caused by flow-induced vibration is precluded.
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11.2.2.12.13. Acoustic coupling that can intensify the stresses caused by flow-induced vibration shall be avoided by ensuring that normal fluid flow requirements do not exceed a velocity of Mach 0.2.
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A guidance document for performing the flow-induced vibration analysis is MSFC 20MO2540, Assessment of Flexible Line and Flow-Induced Vibration.
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11.2.2.12.14. The bend radius of flexible hoses shall be designed to be no less than the safe minimum bend radius recommended in authoritative specifications for the particular hose and in no case less than five times the outside diameter of the hose.
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11.2.2.12.15. A means of plugging or capping flexible hoses shall be provided when the hose is not in use.
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11.2.2.12.16. Ground Support Cryogenic System Flexible Hoses:
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11.2.2.12.16.1. Flexible hoses shall be used only when required to isolate vibration and piping movement and for hookup of portable and mobile equipment.
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11.2.2.12.16.2. Flexible hoses shall be of the single-wall, double-wall, or double-wall vacuum-jacketed type.
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11.2.2.12.16.3. All convoluted portions of flexible hoses shall be covered with stainless steel wire braid.
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11.2.2.13. Ground Support Pressure System Relief Devices
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11.2.2.13.1. All fixed pressure vessels shall be protected against overpressure by means of at least one conventional safety relief valve or pilot-operated pressure relief valve in accordance with ASME Code, Section VIII, Division 1. Rupture disks alone shall not be used to protect against overpressure.
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11.2.2.13.2. A rupture disc may be installed between the pressure relief valve and the vessel provided that the limitations of ASME Code, Section VIII, Division 1, Paragraphs UG-127(a)(3)(b) and UG 127(a)(3)(care met.
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11.2.2.13.3. Particular care shall be taken to monitor and/or vent the space between the rupture disc and the relief valve as required. The space between a rupture disc and a relief valve shall be designed to allow annual testing for leakage and/or contamination.
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11.2.2.13.4. All rupture discs installed in hazardous fluid systems shall be replaced every two years.
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Providing a screen between the rupture disc and the valve to prevent rupture disc contamination of the relief valve should be considered.
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11.2.2.13.5. Installation of the pressure relief devices shall be in accordance with ASME Code, Section VIII, Division 1.
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11.2.2.13.6. The flow capacity for all relief devices shall be certified in accordance with ASME Code, Section VIII, Division 1, Paragraph UG-127, UG-129, UG-131, and UG-132, as applicable.
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11.2.2.13.7. The total relieving capacity of pressure relief devices shall be determined in accordance with ASME Code, Section VIII, Division 1, Paragraph 9.1, as applicable. The required relieving capacity shall be provided by a single valve where possible.
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11.2.2.13.8. Pressure relief devices shall be set to operate at a pressure not to exceed the MAWP of the vessel. See ASME Code, Section VIII, Division 1, Paragraphs UG-134(A), UG-134(b), UG-134(c), and UG-134(d)(1).
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11.2.2.13.9. The relieving capacity of the relief valve shall be equal to or greater than the maximum flow capability of the upstream pressure reducing device or pressure source and shall prevent the pressure from rising more than 20 percent above the system MOP or that allowed by ASME B31.3, whichever is less.
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11.2.2.13.10. Pressure relief valves shall be set to operate at a pressure not to exceed 110 percent of the system MOP or that allowed by ASME B31.3, whichever is less.
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11.2.2.13.11. Negative pressure protection shall be provided for vessels not designed to withstand pressures below one atmosphere.
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Negative pressure protection may be accomplished by the use of check valves or negative pressure relief devices.
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11.2.2.13.12. Pressure vessel relief devices shall be located so that other components cannot render them inoperative except as specified in ASME Code, Section VIII, Division 1, Paragraphs UG-135(d)(1), UG-135de)(2), and Appendix M, Installation and Operations, Paragraphs M-5 and M-6. When a shutoff valve is allowed in accordance with ASME Code, the valve type shall have provisions for being locked in the open or closed position.
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Safety wiring is an acceptable means of locking shutoff valves in the open or closed position.
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11.2.2.13.13. The shutoff valve associated with the relief device shall have permanent marking clearly identifying its position (OPEN or CLOSED).
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The body and other pressure containing parts for pressure relief devices should be 300-series stainless steel. Exception: DOT cylinders or trailer relief devices may contain parts of brass or bronze.
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11.2.2.13.14. A pressure relief valve shall be installed downstream of the last GSE regulator before flight hardware interface and before entering a container and/or black box purge system.
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11.2.2.13.15. All relief valves and piping shall be structurally restrained to eliminate any thrust effects from transferring moment forces to the vessel nozzles or lines.
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