NEW PREHARDENED STEEL GRADE FOR DRILL-THROUGH EQUIPMENTS

摘要

Drill-through equipments such as blow-out preventer (BOP) require high level of reliability and safety. These components are manufactured from big blocks, made typically of AISI 4130 or F22, 75 ksi minimum yield strength with NACE service requirements. These equipments should be in accordance with API 16A~1 and NACE MR0175/ISO 15156-2.~2 In order to achieve the required properties the forged blocks are generally delivered as raw material in the normalized state. The final heat treatment is then performed after raw machining to obtain the final mechanical properties. A new prehardened steel grade has been especially developed for such applications. The final properties can be reached through the thickness of blocks up to 950 mm (37 inch) thick. This means that no further heat treatment is necessary after raw machining. The chemical analysis of this new grade, which is a combination of low carbon and slight additions of molybdenum, chromium and boron, has been defined in order to ensure a very good hardenability even for big thicknesses. The paper will describe the way used to manufacture big blocks (3000×2000×thickness, in mm), which is a combination of forging and rolling. Full mechanical testing was then performed confirming a good homogeneity of properties whatever the sampling in the block. Comparison is made between properties obtained on the block itself and on Qualification Testing Coupons (QTC). As NACE service requirements can be asked for such applications, tests according to NACE TM0177-2005 were carried out.~3 The results will be given and discussed.