Determinação da tenacidade à fratura da região da solda de um tubo de aço ferrítico ASTM A 335 Gr.P22 através do Deslocamento da Abertura da Ponta da Trinca (CTOD)

Abstract

Ferritic alloy steels with chromium and molybdenum, as ASTM A335 P22, are widely used in steam generators in power plants around the world and may have broken fatigue during operation. The assembly of the components of the steam generators in the field is performed by manual welding techniques and has been identified as a critical factor for the quality of these devices when some parameter is ignored during the welding process. The welded region of an alloy is influenced thermal cycle during welding, alloying elements present in the steel and weld metal increases hardenability, and thus favors the formation of bainíticas or martensitic microstructures in the welded region. In this study, a weld made according to the procedure qualified, pre-heating and post-weld relief of stress was compared with a weld treatments performed without preheating and relieving stress, and was further compared with a solder heat treatments performed without preheating and stress relief heat input and determined by the above procedure. For this, the performance of each weld was analyzed for performance in tensile tests, lateral bending (qualification requirements of ASME IX by procedure code), and testing of Charpy impact resistance and toughness of each major region of the fracture weld (base material, HAZ and weld metal). The fracture toughness of each region was determined by fracture mechanics technique of elastic-plastic fracture Crack Tip Open Displacement (CTOD) applied to ductile materials. The result of this comparative study shows that even neglecting the parameters limits of the welding procedure specified for ASTM A335 P22 with thickness of 21mm and diameter of 304.8 mm, the procedure would have passed in qualification tests established by ASME IX (tensile and lateral bending). However, the results of Charpy impact and the CTOD tests performed in weld regions showed that the weld metal had a very low tenacity than was observed in the HAZ and the base material. Thus the realization of pre-heating and postweld treatment relief produced microstructures with lower hardness but that was not reflected in an increase in the toughness of weld metal.

Qualification of welded joints used in the sugar and alcohol sector of ASTM A335 P22 steel pipes welded by GTAW and SMAW processes

“…The microstructure of the HAZ of joints 1 and 2 is mixed up of tempered bainite and polygonal ferrite, which is a typical microstructure of this steel when subjected to PWHT. Similar results were observed by Júnior (2014). Polygonal ferrite grew during cooling from the grain contours as alotriomorphs, which subsequently advanced into the interior of the austenitic grains.…”

“…On the other hand, the weld metal showed completely brittle behavior with average values of impact toughness ranging between 2 and 4 J. This severe drop in impact toughness in the weld metal was also observed by Júnior (2014), where BM absorbed about 180 J, HAZ absorbed about 140 J and WM absorbed between 12 and 16 J of energy in the Charpy impact test. According to Jia et.…”

A Influência Da Temperatura De Pré-Aquecimento Em Junta Soldada Pelo Processo Tig Em Aço Astm A335 P11

“…O aço-liga ASTM A-335 P11 apresenta em sua composição 1,0% de cromo e 0,5% de molibdênio. É um material empregado em tubulações de indústrias químicas, estações de geração de energia, tubos superaquecidos, caldeiras, trocadores de calor e vasos de pressão devido desempenho à elevadas temperaturas (FONSECA, 2004;ZAMPIERI JÚNIOR, 2014).…”