While recently developed platform steels have excellent low temperature toughness properties they may be nevertheless, susceptible to cleavage fracture initiation at focally brittle zones (LBZ" s) developed in coarse grain heat affected zones (CGHAZ" s) of welds. Current offshore material specifications such as EEMUA and EPRCO require prequalification of plate in regard to LBZ such that a COD notchtip intersecting 15 percent or more of the CGHAZ in a weld sample meets lower bound toughness values. In the present work the significance of the 15 percent intersection requirement has been assessed using a roll bonded sandwich technique with a 0.45 percent carbon steel plate bonded between outer plates of offshore steel. It was observed that at this percentage intersection cleavage fracture, initiated as microvoid cleavage, readily propagated into the off shore plate resulting in crack opening displacement toughness values of less than O.lmm at -30°C. The significance of the pre-qualification requirement and the roll bonding technique are discussed.
Owing to section size, offshore platforms are fabricated using multi-pass welds, with the heat affected zone (HAZ) adjacent to the welds comprising a complex array of individual zones where the HAZ of one weld is influenced by the heat of subsequent passes. Multi-pass weldments as a whole have improved toughness as compared with single run welds due to the refining and tempering effect subsequent weld runs have on previous deposits. However" there are small, zones generated in multi-pass welds that suffer poor toughness, properties, similar to those experienced in single weld HAZ" s. Of particular importance are coarse grained heat affected zones (CGHAZ) from a previous run that constitute tile inter critical- heat affected zone (ICHAZ) or CGHAZ as shown in Figure: I. The ICHAZ is that region exposed to temperatures between AC3 and AC3 of approximately 850°C.
