Quality Control of Pressure Hoses

Stress cracking is the main reason that high pressure overbraided hoses fail. The variables include mechanical stress at fittings, the type of chemical environment, process variables and the polymer type. A number of industrial and military aerospace specifications have addressed themselves to the questions of testing and requirements of pressure hoses. An example is MIL-H-25579, which is used by the United States Air Force for military aircraft hose specification. The types of measurements required by such specifications are lengthy and time consuming. There are a number of rapid tests which simplify the task of assessment of hose quality. 

A tube which meets requirements of the simplified tests is highly likely to meet formal specifications  

A high quality aerospace hose should meet the following criteria  

The tests to measure these indices are described in the following paragraphs. 

Stretch void index (SVI). SVI provides an indication of the number voids in the part. It indicates how well the sintering and coalescence have eliminated small voids, which can be present because of the processing technique orthe properties ofthe resin. Voids directly affect the performance of a tube in the end-use. For example, a void free or low void content part will have a longer flex life and greater flex fatigue resistance than a part containing more voids. 

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