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Factors Affecting Impact Toughness in Carbon Steels

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.

Product Number: 51319-13361-SG
Author: Sangeetha Cathapuram
Publication Date: 2019
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