The principal metals and alloys used for aircraft and aerospace tubing applications are 21-6-9, Type 304 stainless to MIL-T-6845 and commercially pure and alloyed (3A1-2.5V) titanium. Specifications covering this tubing require high quality with very tight defect levels. Very careful workmanship in processing and rigid inspection practices must be followed in order to meet the requirements.
Many kinds of defects can befall the tubing. during processing. Some of these are common to all grades of tubing, while others are peculiar to individual alloys. Welded tubing is subject to more defects than seamless. Tubing in general is subject to more defects than almost any other kind of wrought steel product.
Inspection practices include every kind of destructive and nondestructive tests applicable to tubing. Each test has certain capabilities and limitations. A combination of tests is required to give best assurance for critical applications.