Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

In-Service Inspection
The methods described above are applied in the course of and immediately
after the production process and are therefore called production tests. To
survey highly stressed parts, especially in power plants, repeated tests or inservice
inspections are becoming more and more important. In these
inspections any defects identified earlier but not being a cause for rejection
can be observed for any changes caused by the service conditions. In
addition service-produced defects must be detected, these being mainly
cracks caused by thermal shock, fatigue or creep, or by corrosion attack.