Bolts in a flanged joint between an air reheater and a converter in an ammonia plant failed by stress corrosion cracking after short service. They were submerged in a water jacket as shown in Figure 1. Type 321 stainless steel bolts (chrome 1.68, nickel 9.79) originally installed failed after 18 months. Four Type 410 specially heat treated bolts (after lasting 21 days) snapped off in succession when being tightened for a second run.
Examination of the Type 321 bolts showed many branched and transcrystalline cracks as illustrated in Figure 2.
The Type 410 bolts, made of 1-inch bar stock, were 8 inches long and threaded on one end for about 2¼ inches. The fractured surfaces (carbon 0.14, chromium 11.70) are shown in Figure 3. Dark areas in the fracture indicate partial cracking occurred before failure as shown in Figure 4. Mechanical properties are given in Table...
