Abstract
Experience of Accidents at petroleum-refining plants strongly demand improvements in the safety of facility operations. Brittle fracture at relatively low temperature is the most catastorophic type of accident of pressure vessel that can occur in use. To prevent it, various approaches of reliability evaluation have been taken. The most important factor in reliability evaluation is the toughness of the construction material. There are more than a few cases in which a fracture originated in lower toughness than expected.
Pressure vessels of 1/2 Mo steel are the most widely used in such petroleum-refining facilities as naphtha, kerosene, and light oil hydrotreating reactors. The significance of their toughness has become highlighted resently.
22 samples of 1/2 Mo steels, which had been in long-term service for pressure vessels, were investigated for the purpose of prediction of the vTrs of 1/2 Mo steel. It was found that the vTrs of 1/2 Mo steel can be estimated nondestructively by using the following parameter.
vTrs(°C)= 22.6 X-32.59
X= 100 (P+B)/ HV·N
where P+B: Pearlite plus bainite fractions in the microstructure, HV: Vickers hardness, N: ASTM ferrite grain size No.
