Available fracture toughness (FT) test methodologies are reviewed in this publication to compare their details.

Over the last five years there have been numerous reports of failures of carbon steel A105 flanges A234 fittings and some A106 seamless pipe. The failure primarily occurred in newly constructed material and the nature of the failures was Brittle Fracture with very low Charpy V-notch values (3 ft-lbs) at room temperatures when the expected notch toughness was higher than 40 ft-lbs. Typically these steels are exempted from impact testing for upto temperatures -20°F (-29°C) per ASME B31.3. It has been found that the cause of low toughness was a gradual change in the chemical composition of the steel during the steel making process primarily low Mn to C ratios (even though within specification limits) addition of alloying elements like boron vanadium kind of heat treatment applied grain size etc.This paper will identify and document how the different factors like low Mn high C addition of boron and resultant grain size affects the impact toughness of steels based on a review of currently available literature. A comparison with impact properties of other product forms of carbon steel like plates etc. will be presented. A review of the current industry best practices and recommendations to avoid brittle fracture due to metallurgical factors without affecting other mechanical properties during hydrostatic testing cold startups and other low temperature in service conditions will be documented and presented.

Electric Resistance Welded (ERW) pipes X60M / X65M API 5L PSL2, with resistance to ductile fracture propagation as per API 5L PSL2 Annex G [1] are achieved not only by setting the proper welding parameters and the steel cleanliness, but also by a combination of metallurgical processes affecting the final weld line and HAZ microstructure. The steel chemistry is the starting point to minimize the presence of inclusions, central segregation and the toughness impairment due to harmful elements, S, P, etc. on the pipe body, with a given casting and rolling technology. During the welding process, the right parameters combination is needed to avoid cold weld, penetrators, and other weld imperfections. At the last stage, the Seam Heat Treatment (SHT) has to be adjusted in a way that the steel response to the thermal cycles leads to the compliance of mechanical requirements at the weld line and Heat Affected Zone (HAZ). This heat treatment is performed through electromagnetic induction using several coils, which allows it to have a rapid and localized heating of the HAZ into the austenitic region, and that is followed by air cooling. The objective is to refine the structure and to eliminate brittle constituents around the weld line. As the SHT strongly affects the weld performance, the optimum processing conditions such as austenitization temperature and cooling rate may not be the same for all steel chemistry, and has to be carefully selected. The capability to model the thermal cycle after the ERW process and the understanding of the metallurgical behavior of different steel chemistries and dimensional configuration becomes the main target of any ERW pipe manufacturer aiming supply reliable Line Pipes as per API 5L PSL2 Annex G. In this work, a numerical thermal model of the SHT is presented along with validation and simulation results. A summary of metallurgical thermal cycle simulations by means of a Gleeble® 3500, applied on different steels is also included.