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12.1.10.5.6. Lines, drains, and vents shall be separated or shielded from other high-energy systems; for example, heat, high voltage, combustible gases, and chemicals.
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12.1.10.5.7. Drain and vent lines shall not be connected to any other lines in any way that could generate a hazardous mixture in the drain/vent line or allow feedback of hazardous substances to the components being drained or vented.
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12.1.10.5.8. When lines are required for draining liquid explosive, flammable liquids or explosive waste, they shall be free of pockets or low spots so that a positive flow is achieved at all points in the drain line.
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12.1.10.5.9. The slope shall not be less than 1/4 inch per foot at any point on the drain line.
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12.1.10.6. Flight Hardware Pressure System Test Points
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12.1.10.6.1. If required, test points shall be provided so that disassembly for test is not required.
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12.1.10.6.2. The test points shall be easily accessible for attachment of ground test equipment.
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12.1.10.6.3. Common-plug test connectors for pressure and return sections shall be designed to require positive removal of the pressure connection before unsealing the return connections.
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12.1.10.6.4. Individual pressure and return test connectors shall be designed to positively prevent inadvertent cross-connections.
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12.1.11. Flight Hardware Pressure System and Pressurized Structure Supports and Clamps
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12.1.11.1. All rigid pipe and tubing assemblies shall be supported by a firm structure to restrain destructive vibration, shock, and acceleration.
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12.1.11.2. Components within a system shall be supported by a firm structure and not the connecting tubing or piping unless it can be shown by analysis that the tubing or piping can safely support the component.
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12.1.11.3. Pipe and tube accessories such as supports, anchors, and braces shall be compatible with hypergolic propellant vapors when installed in a hypergolic propellant system.
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12.1.11.4. All threaded parts in safety critical components shall be securely locked to resist uncoupling forces by acceptable safe design methods.
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Safety wiring and self locking nuts are examples of acceptable safe design.
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12.1.11.5. Torque for threaded parts in safety critical components shall be specified and documented.
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12.1.11.6. Friction-type locking devices shall be avoided in safety critical applications.
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12.1.11.7. Star washers and jam nuts shall not be used as locking devices.
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12.1.11.8. The design of internally threaded bosses shall preclude the possibility of damage to the component or the boss threads because of screwing universal fittings to excessive depths in the bosses.
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12.1.11.9. Retainers or snap rings shall not be used in pressure systems where failure of the ring would allow connection failures or blow-outs caused by internal pressure.
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12.1.11.10. Snubbers shall be used with all bourdon-type pressure transmitters, pressure switches, and pressure gauges, except air pressure gauges.
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12.1.12. Flight Hardware Pressure System Bonding and Grounding
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12.1.12.1. Hazardous pressure systems shall be designed so that the flight system being loaded or unloaded and the ground support loading system can be commonly grounded and bonded during transfer operations. When the flight system and the ground system are connected, maximum DC resistance from any flight system tubing or tanks to the nearest earth electrode plate shall be 1.0 ohm or less. See 11.2.1.8.
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12.1.12.2. Propellant system components and lines shall be grounded to metallic structures.
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12.1.12.3. All hazardous pressure systems shall be electrically bonded to the flight vehicle to minimize the DC resistance between the hazardous pressure system and the flight vehicle.
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12.1.13. Flight Hardware Pressure System and Pressurized Structure Material Compatibility and Selection
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12.1.13.1. Compatibility
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12.1.13.1.1. Materials shall be compatible throughout their intended service life with the service fluids and the materials used in the construction and installation of tankage, piping, and components as well as with nonmetallic items such as gaskets, seals, packing, seats, and lubricants.
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12.1.13.1.2. At a minimum, material compatibility shall be determined in regard to flammability, ignition and combustion, toxicity, and corrosion.
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12.1.13.1.3. Materials that could come in contact with fluid from a ruptured or leaky tank, pipe, or other components that contain hazardous fluids shall be nonflammable and non-combustible.
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12.1.13.1.4. Compatible materials selection shall be obtained from one of the following sources:
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12.1.13.1.4.1. T.O. 00-25-223.
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12.1.13.1.4.2. CPIA (Chemical Propulsion Information Agency) 394.
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12.1.13.1.4.3. MSFC-HDBK-527.
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12.1.13.1.4.4. KTI-5210, NASA/KSC Material Selection List for Oxygen and Air Services.
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12.1.13.1.4.5. The NASA Material and Process Technical Information System (MAPTIS).
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12.1.13.1.4.6. KTI-5212, NASA/KSC Material Selection List for Plastic Films, Foams, and Adhesive Tapes.
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12.1.13.1.4.7. 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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12.1.13.1.4.8. Other sources and documents approved by the PSWG and Range Safety.
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12.1.13.1.5. Compatibility Testing. When compatibility data cannot be obtained from a PSWG and Range Safety approved source, compatibility tests shall be performed. Test procedures, pass/fail criteria, and test results shall be submitted to the PSWG for PSWG and Range Safety review and approval.
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12.1.13.1.6. Compatibility Analysis. The payload project shall prepare a compatibility analysis containing the following information:
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12.1.13.1.6.1. List of all materials used in system.
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12.1.13.1.6.2. Service fluid in contact with each material.
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12.1.13.1.6.3. Source document or test results showing material compatibility in regard to flammability, toxicity, corrosion, and ignition and combustion.
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12.1.13.2. Selection
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12.1.13.2.1. Material "A" allowable values shall be used for pressure vessels and pressurized structures where failure of a single load path would result in loss of structural integrity.
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12.1.13.2.2. For redundant pressurized structures where failure of a structural element would result in a safe redistribution of applied loads to other load-carrying members, material "B" allowables may be used.
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12.1.13.2.3. The fracture toughness shall be as high as practical within the context of structural efficiency and fracture resistance.
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12.1.13.2.4. For pressure vessels and pressurized structures to be analyzed with linear elastic fracture mechanics, fracture properties shall be accounted for in material selection. These properties include fracture toughness; threshold values of stress intensity under sustained loading; sub-critical crack-growth characteristics under sustained and cyclic loadings; the effects of fabrication and joining processes; the effects of cleaning agents, dye penetrants, coatings, and proof test fluids; and the effects of inspection couplants or materials, temperature, load spectra, and other environmental conditions.
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12.1.13.2.5. Materials that have a low KISCC in the expected operating environments shall not be used in pressure vessels and pressurized structures unless adequate protection from the operating environments can be demonstrated by tests and reviewed and approved by the PSWG and Range Safety.
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12.1.13.2.6. If the material has a KISCC less than 60 percent of the plane-strain fracture toughness, KIC under the conditions of its application, it shall be mandatory to show, by a “worst case” fracture mechanics analysis, that the low KISCC factor will not precipitate premature structural failure.
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12.1.14. Flight Hardware Pressure System Contamination and Cleanliness Requirements
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12.1.14.1. 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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12.1.14.2. General contamination control requirements are as follows:
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12.1.14.2.1. Components and systems shall be protected from contaminants by filtration, sealed modules, clean fluids, and clean environment during assembly, storage installation, and use.
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12.1.14.2.2. Systems shall be designed to allow verification that the lines and components are clean after flushing and purging the system.
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12.1.14.2.3. Systems shall be designed to ensure that contaminants or waste fluids can be flushed and purged after fill and drain operations.
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12.1.15. Flight Hardware Pressure System Components Service Life and Safe-Life
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12.1.15.1. All hazardous pressure system components shall be designed for safe endurance against hazardous failure modes for not less than 400 percent of the total number of expected prelaunch cycles.
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12.1.15.2. The safe-life for pressure vessels and pressurized structures shall be established assuming the existence of pre-existing initial flaws or cracks in the vessel and shall cover the maximum expected operating loads and environments. The safe-life shall be at least four times the specified life for those pressure vessels not accessible for periodic inspection and repair.
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12.1.15.3. For those pressure vessels and pressurized structures that are readily accessible for periodic inspection and repair, the safe-life, as determined by analysis and test, shall be at least four times the interval between scheduled inspection and/or refurbishment.
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12.1.15.4. All pressure vessels and pressurized structures that require periodic refurbishment to meet safe-life requirements shall be recertified after each refurbishment by the same techniques and procedures used in the initial certification, unless an alternative recertification plan has been approved by the payload project and the PSWG and Range Safety.
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12.1.16. Flight Hardware Metallic Materials
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12.1.16.1. Selection. Metallic materials shall be selected on the basis of proven environmental compatibility, material strengths, fracture properties, fatigue-life, and crack growth characteristics consistent with the overall program requirements.
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12.1.16.2. Evaluation. Metallic material evaluation shall be conducted based on the following considerations:
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12.1.16.2.1. The metallic materials selected for design shall be evaluated with respect to material processing, fabrication methods, manufacturing operations, refurbishment procedures and processes, and other pertinent factors that affect the resulting strength and fracture properties of the material in the fabricated as well as the refurbished configurations.
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12.1.16.2.2. The evaluation shall ascertain that the mechanical properties, strengths, and fracture properties used in design and analyses shall be realized in the actual hardware and that these properties are compatible with the fluid contents and the expected operating environments.
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12.1.16.2.3. Materials that are susceptible to stress-corrosion cracking or hydrogen embrittlement shall be evaluated by performing sustained threshold stress intensity tests when applicable data are not available
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12.1.16.3. Characterization. Metallic material characterization shall be based on the following considerations:
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12.1.16.3.1. The allowable mechanical properties, strength and fracture properties of all metallic materials selected for pressure vessels and pressurized structures shall be characterized in sufficient detail to permit reliable and high confidence predictions of their structural performance in the expected operating environments unless these properties are available from reliable or other sources approved by the payload project, PSWG and Range Safety.
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Strength and fracture properties of metallic materials selected for pressure vessels and pressurized structures are available from references such as MIL-HDBK-5, ASTM Standards, the Air Force Damage Tolerant Design Handbook, military specifications, and the Aerospace Structural Metals Handbook.
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12.1.16.3.2. Where material properties are not available, they shall be determined by test methods approved by the payload project, and the PSWG and Range Safety.
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12.1.16.3.3. The characterization shall produce the following strength and fracture properties for the parent metals, weldments, and heat-affected zones as a function of the fluid contents, loading spectra, and the expected operating environments, including proof test environments, as appropriate:
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12.1.16.3.3.1. Tensile yield strength, Fy, and ultimate tensile strength, Fu.
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12.1.16.3.3.2. Fracture toughness, KIc, KIe, Kc, KISCC.
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12.1.16.3.3.3. Sustained-stress crack-growth data, da/dt versus Kmax.
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12.1.16.3.3.4. Fatigue crack growth data, da/dn versus KI and load ratio, R.
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12.1.16.3.4. Proven test procedures shall be used for determining material fracture properties as required. These procedures shall conform to recognized standards.
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Recognized standards include those developed by the ASTM.
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12.1.16.3.5. The test specimens and procedures used shall provide valid test data for the intended application.
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12.1.16.3.6. Sufficient tests shall be conducted so that meaningful nominal values of fracture toughness, fatigue data and crack growth rate data corresponding to each alloy system, temper, product form, thermal and chemical environments, and loading spectra can be established to evaluate compliance with safe-life requirements.
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12.1.16.3.7. If the conventional fatigue analysis is to be performed, the stress-life (S-N) or the strain-life (Se-N) fatigue data shall be generated in accordance with the standard test methods developed by ASTM.
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12.1.16.4. Fabrication and Process Control
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12.1.16.4.1. Proven processes and procedures for fabrication and repair shall be used to preclude damage or material degradation during material processing, manufacturing operations, and refurbishment.
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12.1.16.4.2. In particular, the melt process, thermal treatment, welding process, forming, joining, machining, drilling, grinding, repair and rewelding operations, and other operations shall be within the state-of-the-art and have been used on currently approved hardware.
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12.1.16.4.3. The fracture toughness, mechanical and physical properties of the parent materials, weldments and heat-affected zones shall be within established design limits after exposure to the intended fabrication processes.
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12.1.16.4.4. The machining, forming, joining, welding, dimensional stability during thermal treatments, and through-thickness hardening characteristics of the material shall be compatible with the fabrication processes to be encountered.
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12.1.16.4.5. Fracture control requirements and precautions shall be defined in applicable drawings and process specifications.
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12.1.16.4.6. Detailed fabrication instructions and controls shall be provided to ensure proper implementation of the fracture control requirements.
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12.1.16.4.7. Special precautions shall be exercised throughout the manufacturing operations to guard against processing damage or other structural degradation. In addition, procurement requirements and controls shall be implemented to ensure that suppliers and subcontractors use fracture control procedures and precautions consistent with the fabrication and inspection processes intended for use during actual hardware fabrication.
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12.1.17. Flight Hardware Pressure Vessel and Pressurized Structure Quality Assurance Program Requirements
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12.1.17.1. A quality assurance (QA) program shall be established to ensure that the necessary NDE and acceptance tests are effectively performed to verify that the product meets the requirements of this publication. The QA program shall be based on a comprehensive study of the product and engineering requirements, drawings, material specifications, process specifications, workmanship standards, design review records, stress analysis, failure mode analysis, safe-life analysis, and the results from development and qualification tests.
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12.1.17.2. The program shall ensure that materials, parts, subassemblies, assemblies, and all completed and refurbished hardware conform to applicable drawings and process specifications; that no damage or degradation has occurred during material processing, fabrication, inspection, acceptance tests, shipping, storage, operational use and refurbishment; and that defects that could cause failure are detected or evaluated and corrected.
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12.1.17.3. QA program Inspection Plan. At a minimum, the following considerations shall be included in structuring the quality assurance program:
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12.1.17.3.1. An inspection master plan shall be established before the start of fabrication.
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12.1.17.3.2. The plan shall specify appropriate inspection points and inspection techniques for use throughout the program, beginning with material procurement and continuing through fabrication, assembly, acceptance proof test, operation, and refurbishment, as appropriate.
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12.1.17.3.3. In establishing inspection points and inspection techniques, consideration shall be given to the material characteristics, fabrication processes, design concepts, structural configuration, and accessibility for inspection and detection of discontinuities or flaws.
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12.1.17.3.4. For metallic hardware, the flaw geometries shall encompass defects commonly encountered, including surface crack at the open surface, corner crack, or through-the-thickness crack at the edge of fastener hole, and surface crack at the root of intersecting prismatic structural elements.
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12.1.17.3.5. Acceptance and rejection standards shall be established for each phase of inspection and for each type of inspection technique.
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12.1.17.3.6. For COPVs and other composite hardware, laminate defects, such as delamination, fiber breakage, surface cuts, porosity, air bubbles, cracks, dents, and abrasions, shall be considered.
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12.1.17.3.7. All inspections shall be performed by inspectors qualified and certified in inspection techniques according to the American Society for Nondestructive Testing recommended practices (SNT-TC-1A) or PSWG and Range Safety approved equivalent.
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12.1.17.3.8. For COPVs, inspectors shall also be certified to American Society for Nondestructive Testing (ASNT) Level II (or PSWG and Range Safety approved equivalent) and shall be familiar with laminate production processes and composite shell defects. Inspectors shall be certified to inspect specific types of COPVs using specific inspection techniques in accordance with ASNT standards.
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12.1.17.4. Inspection Techniques. At a minimum, the following considerations shall be included in determining the appropriate inspection techniques:
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12.1.17.4.1. The selected NDE inspection techniques shall have the capability to determine the size, geometry, location, and orientation of suspect discontinuities; a flaw or defect; to obtain, where multiple flaws exist, the location of each with respect to the other and the distance between them; and to differentiate among defect shapes, from tight cracks to spherical voids.
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12.1.17.4.2. Two or more NDE methods shall be used for a part or assembly that cannot be adequately examined by only one method.
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12.1.17.4.3. The flaw detection capability of each selected NDE technique shall be based on past experience on similar hardware.
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12.1.17.4.4. Where this experience is not available or is not sufficiently extensive to provide reliable results, the capability, under production or operational inspection conditions, shall be determined experimentally and demonstrated by tests approved by the payload project on representative material product form, thickness, and design configuration.
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12.1.17.4.5. The flaw detection capability shall be expressed in terms of detectable crack length, crack depth, and crack area. For COPVs, the detection of laminate defects, such as delamination, fiber breakage, and air bubbles, shall also be addressed.
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12.1.17.4.6. The selected NDE should be capable of detecting allowable initial flaw size corresponding to a 90 percent probability of detection at a 95 percent confidence level.
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12.1.17.4.7. The most appropriate NDE technique(s) for detecting commonly encountered flaw types shall be used for all metallic pressure vessels, COPVs, pressurized structures, and other hardware based on their flaw detection capabilities.
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12.1.17.5. Inspection Data. At a minimum, inspection data shall be dispositioned as follows:
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12.1.17.5.1. Inspection data in the form of flaw histories shall be maintained throughout the life of the pressure vessel or pressurized structure. The inspection data shall be stored in the system certification file.
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12.1.17.5.2. These data shall be periodically reviewed and assessed to evaluate trends and anomalies associated with the inspection procedures, equipment and personnel, material characteristics, fabrication processes, design concept, and structural configuration.
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12.1.17.5.3. The result of this assessment shall form the basis of any required corrective action.
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12.1.17.5.4. For suspect COPVs, the payload project shall ensure a Material Review Board (MRB) is initiated to evaluate the NDE results and recommend disposition. Findings of the MRB shall be briefed to the payload project and the PSWG and Range Safety. The MRB shall use NDE comparison, past experience, additional NDE, and other qualitative and quantitative methods to recommend the acceptability of a suspect vessel. Data collected from the MRB process shall be input into the inspection database and system certification file.
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12.1.17.6. Acceptance Proof Test
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12.1.17.6.1. All pressure vessels, pressurized structures, and pressure components shall be proof pressure tested in accordance with the requirements of 12.2 through 12.5, as applicable, to verify that the hardware has sufficient structural integrity to sustain the subsequent service loads, pressure, temperatures, and environments.
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12.1.17.6.2. For pressure vessels, pressurized structures, and other pressurized components, the temperature shall be consistent with the critical use temperature; or, as an alternative, tests may be conducted at an alternate temperature if the test pressures are suitably adjusted to account for temperature effects on strength and fracture toughness.
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12.1.17.6.3. Proof test fluids shall be compatible with the structural materials in the pressure vessels and pressurized structures.
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12.1.17.6.4. Proof test fluids shall not pose a hazard to test personnel.
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12.1.17.6.5. If such compatibility data is not available, required testing shall be conducted to demonstrate that the proposed test fluid does not deteriorate the test article.
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12.1.17.6.6. Accept/reject criteria shall be formulated before the acceptance proof test.
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12.1.17.6.7. Every pressure vessel and pressurized structure shall not leak, rupture, or experience gross yielding during acceptance testing.
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12.1.18. Flight Hardware Pressure System and Pressurized Structure Operations and Maintenance
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12.1.18.1. Flight Hardware Pressure System and Pressurized Structure Safe Operating Limits
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12.1.18.1.1. Safe operating limits shall be established for each pressure vessel and each pressurized structure based on the appropriate analysis and testing used in its design and qualification in accordance with 12.2, 12.3, and 12.4.
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12.1.18.1.2. These safe operating limits shall be summarized in a format that provides rapid visibility of the important structural characteristics and capability.
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12.1.18.2. Flight Hardware Pressure System and Pressurized Structure Operating Procedures
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12.1.18.2.1. Operating procedures shall be established for each pressure vessel and pressurized structure.
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12.1.18.2.2. These procedures shall be compatible with the safety requirements and personnel control requirements at the facility where the operations are conducted.
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12.1.18.2.3. Step-by-step directions shall be written with sufficient detail to allow a qualified technician or mechanic to accomplish the operations.
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12.1.18.2.4. Schematics that identify the location and pressure limits of relief valves and burst discs shall be provided when applicable, and procedures to ensure compatibility of the pressurizing system with the structural capability of the pressurized hardware shall be established.
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12.1.18.2.5. Before initiating or performing a procedure involving hazardous operations with pressure systems, practice runs shall be conducted on non-pressurized systems until the operating procedures are well rehearsed.
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12.1.18.2.6. Initial tests shall then be conducted at pressure levels not to exceed 50 percent of the normal operating pressures until operating characteristics can be established and stabilized.
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12.1.18.2.7. Only qualified and trained personnel shall be assigned to work on or with high pressure systems.
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12.1.18.2.8. Warning signs with the hazard(s) identified shall be posted at the operations facility before pressurization.
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12.1.18.3. Flight Hardware Pressure System and Pressurized Structure Inspection and Maintenance
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12.1.18.3.1. The results of the appropriate stress and safe-life analyses shall be used in conjunction with the appropriate results from the structural development and qualification tests to develop a quantitative approach to inspection and repair.
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12.1.18.3.2. Allowable damage limits shall be established for each pressure vessel and pressurized structure so that the required inspection interval and repair schedule can be established to maintain hardware to the requirements of this volume.
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12.1.18.3.3. NDE technique(s) and inspection procedures to reliably detect characteristic discontinuities, defects and determine flaw size under the condition of use shall be developed for use in the field and at payload processing facilities.
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12.1.18.3.4. Procedures shall be established for recording, tracking, and analyzing operational data as it is accumulated to identify critical areas requiring corrective actions.
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12.1.18.3.5. Analyses shall include prediction of remaining life and reassessment of required inspection intervals.
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12.1.18.4. Flight Hardware Pressure System and Pressurized Structure Repair and Refurbishment
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12.1.18.4.1. When inspections reveal structural damage or defects exceeding the permissible levels, the damaged hardware shall be repaired, refurbished, or replaced, as appropriate.
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12.1.18.4.2. All repaired or refurbished hardware shall be recertified after each repair and refurbishment by the applicable acceptance test procedure for new hardware to verify their structural integrity and to establish their suitability for continued service.
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C
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12.1.18.5. Flight Hardware Pressure System and Pressurized Structure Storage Requirements
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I
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12.1.18.5.1. When pressure vessels and pressurized structures are prepared for transportation or storage, they shall be protected against exposure to adverse environments that could cause corrosion or other forms of material degradation.
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C
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12.1.18.5.2. Pressure vessels and pressurized structures shall be protected against mechanical degradation resulting from scratches, dents, or accidental dropping of the hardware.
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C
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12.1.18.5.3. Induced stresses due to storage fixture constraints shall be minimized by suitable storage fixture design.
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C
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12.1.18.5.4. In the event storage requirements are violated, recertification shall be required before acceptance for use.
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C
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12.1.18.6. Flight Hardware Pressure System and Pressurized Structure Reactivation
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I
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12.1.18.6.1. Pressure vessels and pressurized structures that are reactivated for use after an extensive period in either an unknown, unprotected, or unregulated storage environment shall be recertified to ascertain their structural integrity and suitability for continued service before commitment to flight.
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C
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12.1.18.6.2. Recertification tests for pressurized hardware shall be in accordance with the appropriate Recertification Test Requirement. (See 12.2.2.8.)
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C
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12.1.19. Flight Hardware Pressure System and Pressurized Structure Documentation Requirements
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I
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12.1.19.1. Inspection, maintenance, and operation records shall be kept and maintained throughout the life of each pressure vessel and each pressurized structure.
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C
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12.1.19.2. At a minimum, the records shall contain the following information:
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C
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12.1.19.2.1. Temperature, pressurization history, and pressurizing fluid for both tests and operations.
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C
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12.1.19.2.2. Number of pressurizations experienced as well as number allowed in safe-life analysis.
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C
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12.1.19.2.3. Results of any inspection conducted, including the inspector, inspection dates, inspection techniques employed, location and character of defects, defect origin, and cause.
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C
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12.1.19.2.4. Storage condition.
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C
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12.1.19.2.5. Maintenance and corrective actions performed from manufacturing to operational use, including refurbishment.
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C
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12.1.19.2.6. Sketches and photographs to show areas of structural damage and extent of repairs.
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C
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12.1.19.2.7. Acceptance and recertification tests performed, including test conditions and results.
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C
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12.1.19.2.8. Analyses supporting the repair or modification that may influence future use capability.
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C
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