Flanges Impact Testing Exemption Assessment

Over the last decade, multiple carbon steel flanges brittle fracture failures have led the industry to issue a global alert on standard ASTM A105 flanges toughness values at temperatures higher than −20°F (−29°C), the minimum temperature allowed by the current editions of ASME B16.5 and ASME B31.3. The ASME BPV VIII Subgroup Toughness penalized these components by assigning the material the UCS-66 Curve A and modified UCS-66(c) to limit the minimum temperature of standard A105 flanges to 0°F (−18°C), unless the flanges have been normalized and manufactured to fine grain practice, after which they can be used down to the temperature permitted by ASME B16.5. In order to determine whether these changes would provide acceptable toughness values, nineteen (19) flanges were purchased from local manufacturers in both as-forged and normalized conditions and were subjected to several tests including charpy testing at various temperatures, McQuaid-Ehn, hardness testing, metallography, grain sizing, and chemical analysis. The results suggest that complying with UCS-66(c) does not necessarily guarantee acceptable toughness results for flanges that were normalized and manufactured to fine grain practice, and this is attributed to low Mn:C ratios and possibly uncontrolled heat treatment procedure. On the other hand, a number of non-normalized standard flanges have been found to provide very low toughness values at temperatures as high as 32°F (0°C), despite the current state of UCS-66(c) allowing use down to a minimum temperature of 0°F (−18°C). In view of the above, this paper discusses and evaluates some of the possible additional technical requirements that users could specify to minimize the risk of brittle fracture on standard ASTM A105 flanges, as well as a number of methods to guarantee better toughness performance in standard flanges.