7.5. Service SCC in segments A1 and A2
The crack tips of service SCC in segments A1 and A2 were shown in Figs. 5, 7 and 8. Most of the crack surface was covered by an obvious oxide film except for the crack tip. Between the oxide film and the tearing structure, there was a narrow region that showed a feature similar to the narrow IGSCC area in the JQ2 sample. It indicates that the crack tip in the service pipe is not very old at all. If the crack is dormant as type III, there would not be any region between the crack surface covered by an oxide film and the tearing structure. From the above observation and comparison of the crack tip between service pipe and the laboratory samples, it can be concluded that the cracks in segments A1 and A2 are most likely active.
7.6. Small cut—v- coupons
This study indicated that examination of the very crack tip was indeed the critical aspect needed for a decision on whether or not the service SCC was likely to be active. It is thus a logical deduction that any sampling technique is adequate as long as the sampling technique can guarantee extraction of the very crack tip. Cutting a sample from the service pipe is indeed one way to guarantee extraction of the very crack tip. It is also possible to imagine a trepanning procedure whereby the crack is extracted from the service pipe.
8. Conclusions
To judge whether the crack in the service pipe is active or dormant, it is reasonable to compare the very crack tip of the service pipe crack and the fresh crack in the laboratory sample. If the crack tip of the active laboratory sample is similar to that of the service pipe, it means that it is wise to deduce that the crack in the service pipe is active.