8.48 the pressure test is conducted first. This also allows checking for large leaks by monitoring all compartments for any pressure loss during the test. The hull is then depressurized and undergoes a spin test. Plate failures during operations are detected by monitoring pressure differences between adjacent compartments and between individual compartments and the main inner volume. This also allows detection of leaks from causes other than structural component failures. (Quality control in materials processing is assumed to be internal to the processing system, and so is not considered separately here.) VIII.8.2: Inspection Methods VIII.8.2.1: Comparisons of NDE Methods: Various nondestructive evaluation techniques usable in space are listed below with some advantages and disadvantages given for each. The list is essentially a condensation of material in references (8.14), (8.15), (8.16), (8.17); other references are given where applicable. 1. Visual/Optical --greatest operational flexibility --rapid scan and interpretation --detects surface flaws only --low reliability and accuracy 2. Radiography --permanent visual record --requires operator to interpret record --not very accurate (misses some flaws entirely) --requires access to both sides of item being inspected --very slow (complicated setup and film development) --radiation hazard 3. Ultrasonics --can be very accurate and sensitive --excellent depth penetration from one side --ultrasonic beam can be reflected or refracted to look sideways and around corners --easily adapted to manual or automatic inspection --small search area per transducer --usually requires mechanical coupling to surface
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