scope:

This document specifies the requirements for the design and acceptability of all convoluted metal bellows and flexhoses located in both flight and Support Equipment hardware in order to prevent failure from flow-induced vibrations. Flow charts are presented in Figure 3.1-1 and Figure 3.2-1 depicting the process for acceptability.

The following exclusions from this specification shall apply:

a. Metal bellows and flexhoses with full flow liners that preclude flow-induced vibration are excluded from this specification.

b. Metal bellows and flexhoses with steady-state flow of less than one second duration are excluded from this specification.

c. Metal bellows and flexhoses which experience an operating flow environment that is different than the FIV phenomena described in MSFC-DWG-20M02540 or also beyond the capability of MSFC-DWG-20M02540 to predict are excluded from Paragraphs 3.1 and 3.2 of this specification but shall be compliant with Paragraph 3.4. This exclusion should be carefully reviewed and receive approval from the appropriate NASA organization.

The two documents, MSFC-DWG-20M02540 and MSFC-SPEC-626, shall be used in conjunction with this document.

The MSFC-DWG-20M02540 document provides the method for analyzing a design for susceptibility to flow-induced vibrations. In determining the acceptability of the design, the analytical procedures found in MSFC-DWG-20M02540 shall be considered of having two phases.

Phase I - Use MSFC-DWG-20M02540 to calculate the flow range at which FIV of the bellows or flexhose will occur.

Phase II - If Phase I predicts FIV, use MSFC-DWG-20M02540 to calculate the flow-induced stress at the critical flow velocity and use it as the FIV load input in assessing the overall fatigue life of the bellows or flexhose. In addition to loads from FIV, this overall fatigue life assessment shall take into account all other static and dynamic load sources (see paragraph 3.0 in MSFC-DWG-20M02540).

The MSFC-SPEC-626 document provides the methods and criteria for conducting resonant flow tests of bellows or flexhoses.

This document, herein, applies the following: all mandatory actions (i.e., requirements) are denoted by statements containing the term "shall." The following terms also apply: "may" or "can" denote discretionary privilege or permission, "should" denotes a good practice and is recommended, but not required; "will" denotes expected outcome, and "are/is" denotes descriptive material.