Evaluation of Microstructure and Mechanical Properties of Seamless Steel Pipes API 5L Type Obtained by Different Processes of Heat Treatments

Abstract

This research presents the influence of manufacturing processes and heat treatments on the resulting microstructures and mechanical properties of an API 5L PSL2 seamless steel pipe. Three different conditions are considered -as rolled, normalized and quenched and tempered -to obtain the grades X42R, X42N and X70Q, respectively. Scanning electron microscopy techniques was used to characterize the resultant microstructures. Tensile, hardness, impact, fracture toughness (J integral) and fatigue crack growth tests (da/dN x ΔK) were used to study the materials mechanical behavior. The results show the possibility of achieving API grades for a seamless pipeline steel, through suitable heat treatments. The microstructural modifications and mechanical properties changes observed showed a remarkable structure-properties relationship of the steel, and attempt to a proper selection as required by the structural design. The quenching and tempering process increased tensile mechanical properties and fracture toughness, but combined to a significant decrease in fatigue crack growth resistance.

Effect of the Chemical Homogeneity of a Quenched and Tempered C-Mn Steel Pipe on the Mechanical Properties and Phase Transformations

“…However, the steel in position 2 exhibited a mixture of rupture mechanisms, presenting dimples, characteristic of ductile fracture, and cleavage facets and river marks, characteristic of brittle fracture (Figure 9(b)). This result is consistent with the results presented in Table 4, since the SEM fractography exhibits dominant brittle fracture morphology, indicating low values of absorbed energy by the samples 9 .…”

“…Figure 8(d) shows the microstructure of the tempered sample (CMn-QT) that exhibited a microstructure consisting of ferrite, bainite and tempering sorbite (ferrite and cementite particles). Different authors obtained similar results in their works, analyzing the microstructures after quenching and tempering of steels with similar chemical compositions to the one studied 9,47 .…”

“…are added to increase the mechanical strength and toughness of low carbon steels. Previous studies have shown that Mn is the main alloying element responsible for the development of banding in microalloyed steels 9,[42][43][44][45][46] . In fact, it can be observed in Table 1 that there is a higher concentration of Mn in the innermost part of the pipe wall.…”

“…The occurrence of this phenomenon has become relevant in the seamless pipe manufacturing process because, recently, there are applications that require pipes with higher diameters and thicker walls 5,6 . These demands stem from the need to improve the efficiency of the oil and natural gas transportation in deeper waters for longer distances, subjecting pipelines to high-pressure conditions [5][6][7][8][9] .…”

CINÉTICA DE TRANSFORMAÇÃO DE FASES DE UM AÇO C-Mn UTILIZADO NA FABRICAÇÃO DE TUBO SEM COSTURA

“…Nas últimas décadas, os aços para tubos têm sido submetidos a um extensivo desenvolvimento devido ao constante aumento da demanda por aços com boa combinação de elevada resistência mecânica e boa tenacidade. Esta exigência está relacionada ao crescente consumo de energia produzida a partir do petróleo e do gás natural no mundo, levando à exploração de poços cada vez mais profundos e o transporte de seus produtos por distâncias cada vez maiores [1][2][3][4]. Para alcançar essa demanda é necessário que o tubo tenha grandes diâmetros, espessura de parede relativamente grande e trabalhe sob elevadas pressões internas a fim de melhorar a eficiência no transporte [3][4][5][6].…”