Through-wall defects

Leak Testing Location of through wall defects and flaws while under pressure or vacuum. Various fluids and gases are used for pressure testing several types of leak detectors are used to locate a leak. 

Type A The defect is within the steel but is not leaking and is not expected to become a through-wall defect during the extended life of the repaired pipe. The defect can be internal or external. In Type A, the depth of defect is the only design parameter which in both codes is considered to be fully circumferential with a constant remaining pipe wall thickness. 

For this defect type, the designer has to design the repair based on one of the methods mentioned for defect Type A in addition to designing it as a through-wall defect. The results are to be compared and the stronger chosen. 

By definition, a defect within the pipe is through-wall if the remaining pipe wall thickness at any point is 1 mm or less or if it is expected to be so at the end of the (after repair) extended design life of the pipe. Design of repair then varies based on the defect shape. ISO 24817 has considered three different shapes of defects, which are circular or near circular, axial slots, and circumferential slots. The design for a through-wall defect is experimentally based and requires performance test data. The equations are long and not to be repeated here. As an introduction only, ISO equations for circular or near-circular defects are presented below. 

In the design of through-wall defects, the following differences are apparent. Firstly, the service factor, /perf, is set to 0.333 or as per Table 10.5 if the performance data are available. This factor has also been used instead so ASME does not define a different derating... 

ASME PCC-2 does not offer any solutions for the circumferential through-wall defect. 

Based on a 55 °C IW cure, it can be seen from Table 12.3 that the Tg of the composite is approximately 23 °C higher than that of the equivalent OOW cure case, hence meeting both wall thinning and through-wall defect requirements immediately upon curing. This shows that ProAssure Wrap Extreme has an added advantage when used IW. 

The method for determining the repair laminate/substrate interface toughness parameter (energy release rate) for pipes with through-wall defects is briefly described... 

Table 12.6 Type A pressure containment capacity as a function of through-wall defect size for the OOW and IW conditions (Djukic et al., 2014a)...

Figure 12.16 Subsea repairs, in this case to rectify a through-wall defect, could be carried out with a system like ProAssure Wrap Extreme.

Figure 12.17 Installing a composite repair clamp onto a pipe with a through-wall defect.

Most of the AHoy 600 outer diameter tube corrosion has occurred in the region of the upper tubesheet near the open lane, ie, an untubed lane across the middle of the steam generator (16,17). The steam carries entrained droplets of water through the open lane to the upper tubesheet region where the droplets dry out and concentrate the chemicals. Long tube inserts have been used to sleeve tubes in this region where wall defects have been detected. 

FIGURE 35 Situations in which defects interact. Cases of interaction through direct contact are shown in (a) and (b), where wall defects are in direct contact with other wall defects or line defects, respectively. Cases of indirect interaction are shown in (c) and (d). Here, the distortion field emanating from line defects result in a mutual energy with a wall defect. 

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