New Prehardened Steel Grade for Drill-Through Equipments

Drill-trough equipments such as Blowout Preventer (BOP) require high level of reliability and safety. These components are manufactured from big blocks, made typically of AISI 4130 or F22, 75ksi minimum Yield Strength, with NACE service requirements. 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 in order to achieve the final mechanical properties.

A new pre-hardened steel grade has been specially developed by Industeel for such applications. The final properties can be achieved through the thickness of blocks up to 1000 mm (39”) thick. This means that no further heat treatment is necessary after raw machining.

The chemical analysis, combination of low C and slight additions of Mo, Cr, and B, of this new grade has been defined in order to achieve a very good hardenability even for big thicknesses.

The paper will describe the way used to manufacture big blocks (3000x2000x thickness), which is a combination of forging and rolling. Full mechanical characterizations have been done confirming a good homogeneity of properties whatever the sampling in the block.

NACE service requirements can be asked for such applications. Tests according to NACE TM01-77 have been performed. The results will be given and discussed.

Key words: blow-out preventer - mechanical properties - prehardened -  homogeneity