Page 404 - Handbook of Materials Failure Analysis

402 CHAPTER 15 Welding-associated failures in power boilers

A failure investigation on secondary super-heater tubes in a power boiler indicated
that SCC failure started at a crack originating from a highly stressed area and pro-
gressed outwards, with presence of branched cracks and pits, following an intergranu-
lar microstructural path associated with other characteristics of an IGSCC mechanism
[30]. The macroscopic examination of the external and internal surfaces of in-service
failed 304H tubes of a boiler (of the composition shown in Table 15.6) that exhibited
SCC during service in a boiler has revealed that the tubes have experienced the occur-
rence of thin cracking originating at the internal surface of the tube and progressing
outward circumferentially, as shown in Figure 15.7, showing the progression of the

Table 15.6 Chemical Composition of Studied Material (wt.%)
C Cr Ni Mn Si S P Al Ti Fe

0.089 18.05 9.48 1.66 0.455 0.005 0.025 0.00359 0.00402 Bal

FIGURE 15.7
Full section crack [30].