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11.2.1. Generic Ground Support Pressure System Requirements
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11.2.1.1. Generic Ground Support Pressure System Service Life. All pressure system components shall operate safely and reliably during their intended period of service (service life). Components shall not fail at operating conditions in a time period that is four times the service life of the components. Normal preventive maintenance and calibration shall be performed to maintain the service life in accordance with NASA-STD-8719.17, NASA Requirements for Ground-Based Pressure Vessels and Pressurized Systems (PVS). The source documents for the service life are the ASME Boiler and Pressure Vessel Code, API (American Petroleum Institute), etc.
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11.2.1.1.2. Other components shall be designed to have a service life of not less than 5,000 cycles.
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11.2.1.2. Generic Ground Support Pressure System Safety Factor. Safety factor for pressure systems is the ratio of design burst pressure over the maximum allowable working pressure or design pressure, whichever is greater. The safety factor can also be expressed as the ratio of tensile strength over the maximum allowable stress for the material. ASME or DOT codes are specified as compliance documents for various components such as pressure vessels and piping throughout this part. Acceptable safety factors have already been incorporated into the specified code. If an ASME or DOT code is not specified in this part as a compliance document for a component (applicable code does not exist), the minimum safety factor for the component shall be 4.
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11.2.1.3. Generic Ground Support Pressure System Failure Tolerance
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11.2.1.3.1. Ground support pressure systems shall be designed to ensure that no two failures can result in a catastrophic event and no single failure (component fails to function or human operator error) can result in a critical event.
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11.2.1.3.2. Single-failure tolerant systems shall have at least two, PSWG and Range Safety approved, independent and verifiable inhibits in place during all periods when the critical hazard exists. The structural failure of tubing, piping, welded fittings, or pressure vessels are not to be considered single failure.
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11.2.1.3.3. Dual-failure tolerant systems shall have at least three, PSWG and Range Safety approved, independent and verifiable inhibits in place during all periods when the catastrophic hazard exists.
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11.2.1.4. Generic Ground Support Pressure System Material Selection and Compatibility
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11.2.1.4.1. Materials shall be compatible throughout their intended service life with the service fluids and the materials such as supports, anchors, and clamps used in construction and installation of tankage, piping, and components as well as nonmetallic items such as gaskets, seals, packing, seats, and lubricants.
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11.2.1.4.2. At a minimum, material compatibility shall be determined in regard to the following criteria: permeability, flammability, ignition and combustion, functional and material degradation, contamination, toxicity, pressure and temperature extremes, shock, oxidation, and corrosion.
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11.2.1.4.3. Brittle materials shall not be used for pressure system components. The nil-ductility transition temperature of materials shall be below the service temperatures.
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Material properties should be selected in accordance with reputable government and industry sources such as MAPTIS (Materials and Processing technical Information Systems) or material test results when testing was done in accordance with Range Safety approved testing methods. Reliable sources include MIL-HDBK-5, Metallic Materials and Elements for Aerospace Vehicle Structures, MIL-HDBK-17, Plastic for Aerospace Vehicles, Part 1, Referenced Plastics, American Society for Testing Materials (ASTM) standards, and the Air Force Damage Tolerant Design Handbook should be used to verify material is not crack sensitive.
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11.2.1.4.4. Materials that could come in contact with fluid from a ruptured or leaky tank, pipe, or other components that store or transfer hazardous fluids shall be compatible with the fluid so that they do not create a flammable, combustible, or toxic hazard.
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11.2.1.4.5. Compatible materials selection shall be obtained from one of the following sources:
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11.2.1.4.5.1. Integrated Pressure Systems and Components (Portable and Installed) T.O. 00-25-223.
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11.2.1.4.5.2. Chemical Propulsion Information Agency (CPIA) 394, Hazards of Chemical Rockets and Propellants.
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11.2.1.4.5.3. Marshall Space Flight Center Handbook (MSFC-HDBK)-527, Material Selection for Space Hardware, Volume 1.
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11.2.1.4.5.4. KTI-5210, NASA/KSC Material Selection List for Oxygen and Air Services.
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11.2.1.4.5.5. The NASA Material and Process Technical Information System (MAPTIS).
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11.2.1.4.5.6. KTI-5212, NASA/KSC Material Selection List for Plastic Films, Foams, and Adhesive Tapes.
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11.2.1.4.5.7. MSFC-STD-3029, NASA/MSFC Guidelines for the Selection of Metallic Materials for Stress Corrosion Cracking Resistance in Sodium Chloride Environments.
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11.2.1.4.5.8. Others approved by PSWG and Range Safety sources and documents.
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11.2.1.4.6. Compatibility Testing
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11.2.1.4.6.1. Materials shall be tested for compatibility if data does not exist.
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11.2.1.4.6.2. If compatibility testing is performed, the test plan shall be submitted to the PSWG for PSWG and Range Safety review and approval.
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11.2.1.4.7. Compatibility Analysis. A compatibility analysis containing the following information shall be prepared:
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11.2.1.4.7.1. List of all materials used in system.
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11.2.1.4.7.2. Service fluid in contact with each material.
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11.2.1.4.7.3. Materials that may come in contact with leaking fluid.
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11.2.1.4.7.4. As requested, source document or test results showing material compatibility in regard to permeability, flammability, ignition and combustion, functional and material degradation, contamination, toxicity, pressure and temperature extremes, shock, oxidation, corrosion, and environmental conditions.
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11.2.1.4.8. Metallic components for pressure vessels, pipes, valves, and fittings shall be fabricated from low carbon stainless steel or other alloys that provide adequate strength, corrosion resistance, and material compatibility. See Table 11.1.
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PSWG and Range Safety approved materials that provide adequate strength and material compatibility may be used for metallic components of pressure vessels, pipes, valves, and fittings.
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Table 11.1. Sheet/Plate Material Stainless Steel Properties.
Property
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Requirement
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Tensile strength
Yield strength (0.2 percent offset)
Minimum elongation in 2 inches
Minimum elongation in 2 inches
C maximum
Mn maximum
P maximum
S maximum
Si
Ni
Cr
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Minimum 75 ksi
Minimum 25 ksi
Longitudinal 35 percent
Transverse 25 percent
0.03 percent for 304L, 316Land 0.08 percent for 304
2.00 percent
0.045 percent
0.03 percent
0.75 percent to 1.00 percent
8.00 percent to 16.00 percent
16.00 percent to 20.00 percent
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11.2.1.5. Generic Ground Support Pressure System Corrosion Control. Although corrosion control is primarily the responsibility of the maintainer of the equipment, the designer is responsible for providing hardware that cannot present safety problems caused by corrosion. As a minimum, the following potentially critical areas shall be evaluated and appropriately protected:
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A Range Safety approved corrosion control standard, such as NASA-STD-5008, Protective Coating Of Carbon Steel, Stainless Steel, And Aluminum On Launch Structures, Facilities, And Ground Support Equipment, or NACE RP0285-latest version, Corrosion Control of Underground Storage Tank Systems by Cathodic Protection (published by the National Association of Corrosion Engineers), should be used as guidance for corrosion control. Corrosion protection of fixed outdoor pressure systems includes supports, anchors, and clamps. Avoid use of 17-4PH stainless steel wherever possible due to its susceptibility to stress corrosion cracking at low heat treatment levels. Any 17-4PH stainless steel specified should be heat treated to condition H1025 or higher. Where 300-series stainless steels are specified, type 303 should be avoided wherever possible due to susceptibility to stress corrosion cracking.
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11.2.1.5.1. Carbon steel surfaces exposed to atmospheric corrosion shall be protected by the application of zinc coatings (inorganic zinc or hot dip galvanizing) or equivalent means.
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11.2.1.5.2. Stainless steel surfaces exposed to rocket engine exhaust impingement or acid deposits from solid rocket motor exhaust shall be coated with inhibitive poly amide epoxy primer and aliphatic polyurethane topcoat in accordance with NASA-STD-5008, Protective Coating of Carbon Steel, Stainless Steel, and Aluminum on Launch Structures.
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Nitrile, rubber-based, aluminum-pigmented coating (AR-7) is no longer recommended for coating stainless steel surfaces because it has a high volatile organic compound content and is generally unavailable through commercial suppliers.
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11.2.1.5.3. Exterior stainless steel surfaces of pressure systems with potential exposure to hypergolic fuel shall be coated with a compatible inhibitive coating applied in accordance with NASA-STD-5008 unless usage, storage, care, and maintenance processes are in place to prevent any surface corrosion.
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Where exterior stainless steel surfaces of GSE pressure systems could be exposed to hydrazine, the surfaces could be coated with inhibitive polyamide epoxy primer and aliphatic polyurethane topcoat that is hydrazine compatible per NASA-STD-6001, Flammability, Offgassing, and Compatibility Requirements and Test Procedures, and applied in accordance with NASA-STD-5008.
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11.2.1.5.6. Dissimilar metals shall be protected through mutual isolation.
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11.2.1.6. Generic Ground Support Pressure System Contamination Control
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11.2.1.6.1. To avoid a hazardous failure, adequate levels of contamination control shall be established by relating the cleanliness requirements to the actual needs and nature of the system and components.
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KSC-C-123, Surface Cleanliness of Fluid Systems, Specifications for, or T.O. 42C-1-11, Cleaning and Inspection Procedures for Ballistic Missile Systems, should be used as guidance in relating cleanliness requirements to the actual needs and nature of the system and components.
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11.2.1.6.2. Materials and fluids used in the design shall be selected to reduce internally generated contamination caused by rate of wear, friction, and fluid decomposition.
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11.2.1.6.3. Systems shall have acceptable contamination tolerance levels. The tolerance level of the system and/or components shall be based on considerations of the overall functional requirements and service life.
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11.2.1.6.4. The system shall be designed to verify, through sampling, that the lines and components are clean after flushing and purging of the system.
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11.2.1.6.5. Each component or section of a system shall be cleaned to the appropriate level before installation. Immediately following cleaning, all components or sections of a system shall be protected to prevent contamination.
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11.2.1.6.6. Equipment designed to be cleaned or recleaned in place without significant disassembly shall be provided with high point bleeds and low point drains to facilitate introduction and removal of cleaning fluid.
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11.2.1.6.7. Filters shall be installed immediately downstream of all interfaces where control of particulate matter is critical and at other appropriate points as required to control particulate migration.
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