DEVELOPMENT OF PRESSURE VESSEL STEEL SERIES FOR WET H_2S REFINERY SERVICE

摘要

Cracking in refinery service due to uptake of hydrogen has led to specific requirements for pressure vessel steels used for wet H_2S refinery service. The generally qualification test to cover this aspect is the HIC test as defined by the NACE Standard TM0284. The usual restrictions in steel chemistry such as limitation of sulfur content to extreme low values (< 10 ppm) only help to improve but do not optimize the resistance against H_2S related cracking. Therefore a special production route that includes each by itself as well as a combination of one subsequent to the other optimized steps of steel making and plate manufacturing was developed. The main production steps are explained. As a result of this optimization a new family of unalloyed and low alloyed steels is presented. These steels meet the HIC test demands of modern specifications, i.e. they can be ordered at 3 different levels of HIC test acceptance criteria. On principle these steels are available according to all main pressure vessel steel standards. Above all the steel grades according to ASTM/ASME A/SA516 Gr60, Gr65 and Gr70 and P275... and P355... according to EN 10028 part 3 are delivered as sour service steels even in case of low tonnage per ordered lot. During fabrication of vessels PWHT is generally recognized and used to improve resistance against H_2S related cracking. But special attention must be focussed on temperature and time for PWHT in order to avoid impairment of mechanical properties. The different effects of PWHT are pointed out.