Requirements in this section may already be covered as part of a broader overall quality assurance program levied on the program. It is highly recommended that the requirements in this section be reviewed for duplication against existing program requirements. In cases where there is duplication, it is recommended to apply tailoring to this NASA Technical Standard and not apply some or all of the requirements of this section.
4.8.1 Design Documentation
[TFSR 26] The engineering documentation shall specify:
- a. The part or identifying numbers of fastening system hardware, and
- b. Required lubricants, coatings, or sealants used in threaded fastening systems, the area to which they are applied, as well as their application processes, and
- c. Dimensions and tolerances necessary to manufacture and assemble the fastened joint and its constituent parts, and
- d. The types, locations, and allowable quantities of washers, and
- e. The installation methods and parameters for achieving preload, and
- f. The installation torque range or applicable standard that defines the installation torque range, and
- g. Whether the specified torque is total torque or the torque above running torque.
[Rationale: Engineering documentation such as drawings, analysis, and process specifications are important to verify that the design, analysis, and assembly are consistent.]
Lubrication of fasteners prior to assembly is often desirable and sometimes necessary to prevent galling or to reduce preload variation when using torque control. For a given applied torque, use of lubricants, coatings, or sealants can increase the preload and reduce variation in preload compared to an unlubricated joint. The surfaces on which lubricants, coatings, or sealants are applied, or the surfaces to which they migrate, influence preload as well. Lubricants also reduce wear, inhibit fretting, and improve ease of installation and removal of fasteners.
Lubricants used in sensitive applications such as fluid wetted components, optical systems, and some external spacecraft surfaces can result in system contamination and performance degradation. Application of lubricant in excess of the amount necessary to achieve the design performance should be avoided, even in non-sensitive applications.
When engineering documentation does not specify “above running torque,” the specified torque is understood to be the final torque indicated by the torque instrument. Running torque does not generate preload. Specifying torque above a measured running torque provides tighter control of preload.
The engineering documentation should specify whether torque is to be applied to the fastener head or the nut because the relationship between torque and preload is different depending upon which part is torqued. Whenever possible, torque should be applied to the nut. When torque is applied to the fastener head, the fastening system should be designed to ensure no binding occurs between any parts of the rotating shank and its clearance hole.
When it is important for joints with multiple fasteners to have an evenly distributed clamp load, an appropriate torque sequence along with incremental torqueing should be specified on the engineering drawing or hardware-specific installation procedure. Example procedures for multi-fastener preloading can be found in MIL-HDBK-60, Threaded Fasteners-Tightening to Proper Tension, Section 5.7: Flange Joint Bolt Tensioning.
4.8.2 As-Built Documentation
[TFSR 27] Records documenting the as-built procedures and configuration of each assembly shall be created and maintained by the hardware developer and provided for review upon request by the delegated NASA Technical Authority.
[Rationale: As-built records show evidence that the hardware was assembled using parts and procedures in conformance with the approved design and that as-built variances are noted. As- built records are necessary for physical configuration audits.]
4.8.3 Training
[TFSR 28] Personnel installing fastening system hardware shall be trained per program-, project-, or organization-specific quality process.
[Rationale: Training ensures that technicians have the proper knowledge and skills for effectively performing the tasks associated with installing threaded fastening systems on spaceflight hardware. Fastener installation with insufficiently trained personnel can result in as-built non-conformances resulting in critical and catastrophic hazards.]
4.8.4 Tools and Instruments
- a. [TFSR 29] Tools and instruments used to install fastening system hardware shall be verified to be in calibration prior to use and used within their design and calibration ranges.
[Rationale: Improperly calibrated tools lead to uncertainty in the amount of initial preload in the system.]
If, during use of a tool or instrument there is a condition where the calibration may be invalidated such as dropping, impact, or other damage, it should be confirmed that the calibration is still valid.
- b. [TFSR 30] Torque instruments shall conform to ASME B107.300-2010, Torque Instruments, or a NASA-approved alternative.
[Rationale: This NASA Technical Standard provides performance and safety requirements for manually operated torque instruments.]
Torque instruments should be chosen so the torque (running or final assembly) being measured or controlled is between 20 and 90 percent of the instruments’ full-scale torque.
4.8.5 Threaded Fastening System Hardware Inspection
[TFSR 31] Threaded fastening system hardware shall be inspected prior to installation to verify that part number(s), cleanliness, and orientation are in accordance with the engineering documentation.
[Rationale: Improperly installed fastening system hardware can lead to functional or structural integrity issues not considered in the design of the system hardware.]
4.8.6 Fastening System Hardware Procurement, Inspection, and Storage
[TFSR 32] Procurement, receiving inspection, and storage of threaded fastening system hardware that joins or retains components or structural elements shall meet the requirements of NASA-STD-8739.14, NASA Fastener Procurement, Receiving Inspection, and Storage Practices for NASA Mission Hardware.
Examples of fastening system hardware that are subject to this requirement include, but are not limited to, bolts, screws, nuts, nut plates or anchor nuts, rivets, shear pins, helical or cylindrical inserts, setscrews, washers, safety wire, and cotter pins.
Adherence to NASA-STD-8739.14 is mandatory for threaded fastening system hardware whose failure or disengagement could result in a critical hazard, catastrophic hazard, or generate foreign object debris that can credibly and negatively affect the functional performance of unrelated systems. For all other fastening system hardware, adherence to NASA-STD-8739.14 is recommended but not mandatory.
[Rationale: This NASA Technical Standard establishes requirements, responsibilities, and practices to ensure that threaded fastening system hardware meets quality assurance requirements deemed necessary by NASA for safe and reliable performance.]